bifilar and trifilar report
TRANSCRIPT
KUWAIT UNIVERSITYCOLLEGE OF ENGINEERING AND PETROLEUM
MECHANICAL AND ENGINEERING DEPARTMENTMechanical Engineering Fundamentals Lab
ME-373
Engineering Formal Laboratory ReportExperiment 5
Bifilar and Trifilar Suspensions(Mass Moment of Inertia Determination)
ByAhmad Abdullah Al-Kandri 206217099Hassan Hussain Saleem 206216926Nayef Nazih Ftouni 206216827
On our honor we pledge that this work of us does not violate the university provisions an academic misconduct By signing below we certify that we understand the university policies on academic misconduct and that when an act of academic misconduct is committed all parties involved in violation
1
Abstract
In this experiment a bifilar and trifilar suspension methods are applied to determine the mass momentum of inertia of a beam platform cylindrical mass and a body with an irregular mass
First with the bifilar method a body was suspended by two parallel cords with the same length and by displacing the system through a small angle and using few equations which will be given further in the report we get the time period and then calculating the mass moment of inertia
Moreover and for the trifilar method a platform was suspended by three cords having the same length and also by getting the time period and the moment of inertia of the platform we calculated the moment of inertia of a cylindrical mass and a body with an irregular mass
2
Table of contents
Abstract helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (3)Table of contents helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (4)List of figures and tableshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (5) Nomenclaturehelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (6)
Chapter 1
11 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip helliphelliphelliphellip(7)12 objectives helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip(8)
Chapter 2
Theoretical background helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (9)
Chapter 3
Experimental setup and procedure helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (15) 31 Equipments helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (15) 32 Procedurehelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (16)
Chapter 4
Results and discussionhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (18) 41 Sample calculationshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (19) 42 Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (39) 43 Uncertainty Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (40)
Chapter 5
Conclusionshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (42)
Referenceshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (43)
3
List of figures and tables
Figures
Figure (1) Bifilar suspensionhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (7)
Figure (2) (a) Bifilar suspension (b) Trifilar suspensionhelliphelliphelliphelliphelliphelliphelliphellip (10)
Figure (3) The relation between log L and log τhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (38)
4
List of tables
Table 1 Bifilar suspension with cord length equal to 04 (m)25Table 2 Bifilar suspension with cord length equal to 045 (m)26Table 3 Bifilar suspension with cord length equal to 048 (m)27Table 4 Trifilar suspension with cord length equal to 04 (m)35Table 5 Trifilar suspension with cord length equal to 044 (m)36Table 6 Trifilar suspension with cord length equal to 05 (m)38
5
Nomenclature
SymbolsScientific Name
dDistance between the cords (m)
FRestoring force (N)
gAcceleration of gravity (ms2)
IMass-Moment of inertia of the body (m4)
k Radius of gyration
L Length of the cords (m)
m
MR
T
θ
Mass (kg)
Restoring moment (Nm)
Tension in the cords (Nm)
Angle of twist (degrees)
umlθ(ω) Angular velocity (rads)
τ Time period (s)
Chapter 16
Introduction
In this chapter we will introduce to you two methods for determining the mass moment of inertia which are the bifilar and trifilar suspension
11 Bifilar suspension method
The bifilar suspension method is a way to determine the mass momentum of inertia (Fig a) shows a uniform rod of mass M and length L suspended horizontally by two vertical strings The length of each string is l and they are attached symmetrically about the center O a distance R apart If the bat is now twisted horizontally it will undergo SHM We wish to analyze this motion and in particular to find the period
And by calculating the time period we can calculate the mass moment of inertia by using some formulas we will provide later in the report
7
A B
Brsquo
O
R
l
L
Figure 1 Bifilar suspension
BA
Arsquo
φ
θ
12 Trifilar suspension method
The trifilar suspension method is a way to determine the mass moment of inertia for a bodies especially a body with an irregular mass as you can see in figure(c) a platform is suspended with three cords and three cords have the same length and they are spaces around the platform center now if we want to determine the mass of inertia we put the object or the body at the platform in the centroidal axis And by displacing the platform through a small angel we can calculate the mass time period and then using some formulas we will provide later we can determine the mass moment of inertia
13 Objectives
The objectives of this experiment are to introduce the bifilar and trifilar suspension methods as options for determining the mass moment of inertia of a rigid body or group of rigid bodies this should lead to the capability of designing experiments for determining moments of inertia of rigid bodies using either bifilar or trifilar pendulum systems
The other objective is to compare theoretical results obtained from pendulum modeling with experimental results and determining accuracy
8
Chapter 2
Theoretical Background
Inertia Determination
Mass- moment of inertia I about an axis of rotation is theoretically can be determined by
IiquestintM
r2 dm (1)
Where
r Distance between the location of mass element dm and the axis of rotation The integration is performed over the entire mass of the body if the axis of rotation coincides with the body centroidal axis the moment of inertia is given by Ī
The parallel axis theorem is given by
I= Ī + m d2 (2)
Where
I The inertia of the body about the axis of rotation
Ī the inertia of the body about its own centroidal axis
m Mass of the body
d the perpendicular distance from the centroidal axis of the body to the axis of rotation
9
Bifilar suspension
Figure 2 (a) Bifilar suspension (b) Trifilar suspension
In figure1 (a) shows the Bifilar suspension and the body is suspended by two parallel cords of length L at a distance R=d apart the tensions in the cords are respectively
T 1=mgd2
d and T 2=mg
d1
d (4)
d1+d2=d and T 1+T 2=mg(5)
If the system is displaced through a small angle θ about its central axis then angular displacement Φ1and Φ2 will result at the supporting chords If both angles are small then
10
Lϕ1=d1Ɵ and Lϕ2=d2
Ɵ (6)
ϕ1= d1
L Ɵ and ϕ2=
d2
L Ɵ (7)
The horizontal restoring forces at the points of attachment with the plate are
F1=iquest T1 sinΦ1iquest (8)
F2=iquest T2 sin Φ2iquest (9)
And using equation (7) to substitute into (8) and (9) and then get
MR= iquest (10)
Where the minus sign is related to the restoring effect
Using equation (4) the restoring moment is rewritten as
MR= -mg d1d2
L Ɵ (11)
Using Newtonrsquos second law and summing moment about the vertical centroidal axis give equation of motion of the body can be written as
Ī ϴ΄΄ = - mg d1d2
L Ɵ rarr ϴ΄΄+mg
d1d2
Ī LƟ=0 (12)
Where
Ī = Mass-moment of inertia of the body about the centroidal axis
The natural frequency of the system can be directly obtained from as
ω=radicmgd1 d2
Ī L (13)
The period that measured experimentally is related to the natural frequency by
11
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Abstract
In this experiment a bifilar and trifilar suspension methods are applied to determine the mass momentum of inertia of a beam platform cylindrical mass and a body with an irregular mass
First with the bifilar method a body was suspended by two parallel cords with the same length and by displacing the system through a small angle and using few equations which will be given further in the report we get the time period and then calculating the mass moment of inertia
Moreover and for the trifilar method a platform was suspended by three cords having the same length and also by getting the time period and the moment of inertia of the platform we calculated the moment of inertia of a cylindrical mass and a body with an irregular mass
2
Table of contents
Abstract helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (3)Table of contents helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (4)List of figures and tableshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (5) Nomenclaturehelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (6)
Chapter 1
11 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip helliphelliphelliphellip(7)12 objectives helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip(8)
Chapter 2
Theoretical background helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (9)
Chapter 3
Experimental setup and procedure helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (15) 31 Equipments helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (15) 32 Procedurehelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (16)
Chapter 4
Results and discussionhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (18) 41 Sample calculationshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (19) 42 Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (39) 43 Uncertainty Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (40)
Chapter 5
Conclusionshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (42)
Referenceshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (43)
3
List of figures and tables
Figures
Figure (1) Bifilar suspensionhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (7)
Figure (2) (a) Bifilar suspension (b) Trifilar suspensionhelliphelliphelliphelliphelliphelliphelliphellip (10)
Figure (3) The relation between log L and log τhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (38)
4
List of tables
Table 1 Bifilar suspension with cord length equal to 04 (m)25Table 2 Bifilar suspension with cord length equal to 045 (m)26Table 3 Bifilar suspension with cord length equal to 048 (m)27Table 4 Trifilar suspension with cord length equal to 04 (m)35Table 5 Trifilar suspension with cord length equal to 044 (m)36Table 6 Trifilar suspension with cord length equal to 05 (m)38
5
Nomenclature
SymbolsScientific Name
dDistance between the cords (m)
FRestoring force (N)
gAcceleration of gravity (ms2)
IMass-Moment of inertia of the body (m4)
k Radius of gyration
L Length of the cords (m)
m
MR
T
θ
Mass (kg)
Restoring moment (Nm)
Tension in the cords (Nm)
Angle of twist (degrees)
umlθ(ω) Angular velocity (rads)
τ Time period (s)
Chapter 16
Introduction
In this chapter we will introduce to you two methods for determining the mass moment of inertia which are the bifilar and trifilar suspension
11 Bifilar suspension method
The bifilar suspension method is a way to determine the mass momentum of inertia (Fig a) shows a uniform rod of mass M and length L suspended horizontally by two vertical strings The length of each string is l and they are attached symmetrically about the center O a distance R apart If the bat is now twisted horizontally it will undergo SHM We wish to analyze this motion and in particular to find the period
And by calculating the time period we can calculate the mass moment of inertia by using some formulas we will provide later in the report
7
A B
Brsquo
O
R
l
L
Figure 1 Bifilar suspension
BA
Arsquo
φ
θ
12 Trifilar suspension method
The trifilar suspension method is a way to determine the mass moment of inertia for a bodies especially a body with an irregular mass as you can see in figure(c) a platform is suspended with three cords and three cords have the same length and they are spaces around the platform center now if we want to determine the mass of inertia we put the object or the body at the platform in the centroidal axis And by displacing the platform through a small angel we can calculate the mass time period and then using some formulas we will provide later we can determine the mass moment of inertia
13 Objectives
The objectives of this experiment are to introduce the bifilar and trifilar suspension methods as options for determining the mass moment of inertia of a rigid body or group of rigid bodies this should lead to the capability of designing experiments for determining moments of inertia of rigid bodies using either bifilar or trifilar pendulum systems
The other objective is to compare theoretical results obtained from pendulum modeling with experimental results and determining accuracy
8
Chapter 2
Theoretical Background
Inertia Determination
Mass- moment of inertia I about an axis of rotation is theoretically can be determined by
IiquestintM
r2 dm (1)
Where
r Distance between the location of mass element dm and the axis of rotation The integration is performed over the entire mass of the body if the axis of rotation coincides with the body centroidal axis the moment of inertia is given by Ī
The parallel axis theorem is given by
I= Ī + m d2 (2)
Where
I The inertia of the body about the axis of rotation
Ī the inertia of the body about its own centroidal axis
m Mass of the body
d the perpendicular distance from the centroidal axis of the body to the axis of rotation
9
Bifilar suspension
Figure 2 (a) Bifilar suspension (b) Trifilar suspension
In figure1 (a) shows the Bifilar suspension and the body is suspended by two parallel cords of length L at a distance R=d apart the tensions in the cords are respectively
T 1=mgd2
d and T 2=mg
d1
d (4)
d1+d2=d and T 1+T 2=mg(5)
If the system is displaced through a small angle θ about its central axis then angular displacement Φ1and Φ2 will result at the supporting chords If both angles are small then
10
Lϕ1=d1Ɵ and Lϕ2=d2
Ɵ (6)
ϕ1= d1
L Ɵ and ϕ2=
d2
L Ɵ (7)
The horizontal restoring forces at the points of attachment with the plate are
F1=iquest T1 sinΦ1iquest (8)
F2=iquest T2 sin Φ2iquest (9)
And using equation (7) to substitute into (8) and (9) and then get
MR= iquest (10)
Where the minus sign is related to the restoring effect
Using equation (4) the restoring moment is rewritten as
MR= -mg d1d2
L Ɵ (11)
Using Newtonrsquos second law and summing moment about the vertical centroidal axis give equation of motion of the body can be written as
Ī ϴ΄΄ = - mg d1d2
L Ɵ rarr ϴ΄΄+mg
d1d2
Ī LƟ=0 (12)
Where
Ī = Mass-moment of inertia of the body about the centroidal axis
The natural frequency of the system can be directly obtained from as
ω=radicmgd1 d2
Ī L (13)
The period that measured experimentally is related to the natural frequency by
11
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Table of contents
Abstract helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (3)Table of contents helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (4)List of figures and tableshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (5) Nomenclaturehelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (6)
Chapter 1
11 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip helliphelliphelliphellip(7)12 objectives helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip(8)
Chapter 2
Theoretical background helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (9)
Chapter 3
Experimental setup and procedure helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (15) 31 Equipments helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (15) 32 Procedurehelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (16)
Chapter 4
Results and discussionhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (18) 41 Sample calculationshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (19) 42 Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (39) 43 Uncertainty Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (40)
Chapter 5
Conclusionshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (42)
Referenceshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (43)
3
List of figures and tables
Figures
Figure (1) Bifilar suspensionhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (7)
Figure (2) (a) Bifilar suspension (b) Trifilar suspensionhelliphelliphelliphelliphelliphelliphelliphellip (10)
Figure (3) The relation between log L and log τhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (38)
4
List of tables
Table 1 Bifilar suspension with cord length equal to 04 (m)25Table 2 Bifilar suspension with cord length equal to 045 (m)26Table 3 Bifilar suspension with cord length equal to 048 (m)27Table 4 Trifilar suspension with cord length equal to 04 (m)35Table 5 Trifilar suspension with cord length equal to 044 (m)36Table 6 Trifilar suspension with cord length equal to 05 (m)38
5
Nomenclature
SymbolsScientific Name
dDistance between the cords (m)
FRestoring force (N)
gAcceleration of gravity (ms2)
IMass-Moment of inertia of the body (m4)
k Radius of gyration
L Length of the cords (m)
m
MR
T
θ
Mass (kg)
Restoring moment (Nm)
Tension in the cords (Nm)
Angle of twist (degrees)
umlθ(ω) Angular velocity (rads)
τ Time period (s)
Chapter 16
Introduction
In this chapter we will introduce to you two methods for determining the mass moment of inertia which are the bifilar and trifilar suspension
11 Bifilar suspension method
The bifilar suspension method is a way to determine the mass momentum of inertia (Fig a) shows a uniform rod of mass M and length L suspended horizontally by two vertical strings The length of each string is l and they are attached symmetrically about the center O a distance R apart If the bat is now twisted horizontally it will undergo SHM We wish to analyze this motion and in particular to find the period
And by calculating the time period we can calculate the mass moment of inertia by using some formulas we will provide later in the report
7
A B
Brsquo
O
R
l
L
Figure 1 Bifilar suspension
BA
Arsquo
φ
θ
12 Trifilar suspension method
The trifilar suspension method is a way to determine the mass moment of inertia for a bodies especially a body with an irregular mass as you can see in figure(c) a platform is suspended with three cords and three cords have the same length and they are spaces around the platform center now if we want to determine the mass of inertia we put the object or the body at the platform in the centroidal axis And by displacing the platform through a small angel we can calculate the mass time period and then using some formulas we will provide later we can determine the mass moment of inertia
13 Objectives
The objectives of this experiment are to introduce the bifilar and trifilar suspension methods as options for determining the mass moment of inertia of a rigid body or group of rigid bodies this should lead to the capability of designing experiments for determining moments of inertia of rigid bodies using either bifilar or trifilar pendulum systems
The other objective is to compare theoretical results obtained from pendulum modeling with experimental results and determining accuracy
8
Chapter 2
Theoretical Background
Inertia Determination
Mass- moment of inertia I about an axis of rotation is theoretically can be determined by
IiquestintM
r2 dm (1)
Where
r Distance between the location of mass element dm and the axis of rotation The integration is performed over the entire mass of the body if the axis of rotation coincides with the body centroidal axis the moment of inertia is given by Ī
The parallel axis theorem is given by
I= Ī + m d2 (2)
Where
I The inertia of the body about the axis of rotation
Ī the inertia of the body about its own centroidal axis
m Mass of the body
d the perpendicular distance from the centroidal axis of the body to the axis of rotation
9
Bifilar suspension
Figure 2 (a) Bifilar suspension (b) Trifilar suspension
In figure1 (a) shows the Bifilar suspension and the body is suspended by two parallel cords of length L at a distance R=d apart the tensions in the cords are respectively
T 1=mgd2
d and T 2=mg
d1
d (4)
d1+d2=d and T 1+T 2=mg(5)
If the system is displaced through a small angle θ about its central axis then angular displacement Φ1and Φ2 will result at the supporting chords If both angles are small then
10
Lϕ1=d1Ɵ and Lϕ2=d2
Ɵ (6)
ϕ1= d1
L Ɵ and ϕ2=
d2
L Ɵ (7)
The horizontal restoring forces at the points of attachment with the plate are
F1=iquest T1 sinΦ1iquest (8)
F2=iquest T2 sin Φ2iquest (9)
And using equation (7) to substitute into (8) and (9) and then get
MR= iquest (10)
Where the minus sign is related to the restoring effect
Using equation (4) the restoring moment is rewritten as
MR= -mg d1d2
L Ɵ (11)
Using Newtonrsquos second law and summing moment about the vertical centroidal axis give equation of motion of the body can be written as
Ī ϴ΄΄ = - mg d1d2
L Ɵ rarr ϴ΄΄+mg
d1d2
Ī LƟ=0 (12)
Where
Ī = Mass-moment of inertia of the body about the centroidal axis
The natural frequency of the system can be directly obtained from as
ω=radicmgd1 d2
Ī L (13)
The period that measured experimentally is related to the natural frequency by
11
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
List of figures and tables
Figures
Figure (1) Bifilar suspensionhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (7)
Figure (2) (a) Bifilar suspension (b) Trifilar suspensionhelliphelliphelliphelliphelliphelliphelliphellip (10)
Figure (3) The relation between log L and log τhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip (38)
4
List of tables
Table 1 Bifilar suspension with cord length equal to 04 (m)25Table 2 Bifilar suspension with cord length equal to 045 (m)26Table 3 Bifilar suspension with cord length equal to 048 (m)27Table 4 Trifilar suspension with cord length equal to 04 (m)35Table 5 Trifilar suspension with cord length equal to 044 (m)36Table 6 Trifilar suspension with cord length equal to 05 (m)38
5
Nomenclature
SymbolsScientific Name
dDistance between the cords (m)
FRestoring force (N)
gAcceleration of gravity (ms2)
IMass-Moment of inertia of the body (m4)
k Radius of gyration
L Length of the cords (m)
m
MR
T
θ
Mass (kg)
Restoring moment (Nm)
Tension in the cords (Nm)
Angle of twist (degrees)
umlθ(ω) Angular velocity (rads)
τ Time period (s)
Chapter 16
Introduction
In this chapter we will introduce to you two methods for determining the mass moment of inertia which are the bifilar and trifilar suspension
11 Bifilar suspension method
The bifilar suspension method is a way to determine the mass momentum of inertia (Fig a) shows a uniform rod of mass M and length L suspended horizontally by two vertical strings The length of each string is l and they are attached symmetrically about the center O a distance R apart If the bat is now twisted horizontally it will undergo SHM We wish to analyze this motion and in particular to find the period
And by calculating the time period we can calculate the mass moment of inertia by using some formulas we will provide later in the report
7
A B
Brsquo
O
R
l
L
Figure 1 Bifilar suspension
BA
Arsquo
φ
θ
12 Trifilar suspension method
The trifilar suspension method is a way to determine the mass moment of inertia for a bodies especially a body with an irregular mass as you can see in figure(c) a platform is suspended with three cords and three cords have the same length and they are spaces around the platform center now if we want to determine the mass of inertia we put the object or the body at the platform in the centroidal axis And by displacing the platform through a small angel we can calculate the mass time period and then using some formulas we will provide later we can determine the mass moment of inertia
13 Objectives
The objectives of this experiment are to introduce the bifilar and trifilar suspension methods as options for determining the mass moment of inertia of a rigid body or group of rigid bodies this should lead to the capability of designing experiments for determining moments of inertia of rigid bodies using either bifilar or trifilar pendulum systems
The other objective is to compare theoretical results obtained from pendulum modeling with experimental results and determining accuracy
8
Chapter 2
Theoretical Background
Inertia Determination
Mass- moment of inertia I about an axis of rotation is theoretically can be determined by
IiquestintM
r2 dm (1)
Where
r Distance between the location of mass element dm and the axis of rotation The integration is performed over the entire mass of the body if the axis of rotation coincides with the body centroidal axis the moment of inertia is given by Ī
The parallel axis theorem is given by
I= Ī + m d2 (2)
Where
I The inertia of the body about the axis of rotation
Ī the inertia of the body about its own centroidal axis
m Mass of the body
d the perpendicular distance from the centroidal axis of the body to the axis of rotation
9
Bifilar suspension
Figure 2 (a) Bifilar suspension (b) Trifilar suspension
In figure1 (a) shows the Bifilar suspension and the body is suspended by two parallel cords of length L at a distance R=d apart the tensions in the cords are respectively
T 1=mgd2
d and T 2=mg
d1
d (4)
d1+d2=d and T 1+T 2=mg(5)
If the system is displaced through a small angle θ about its central axis then angular displacement Φ1and Φ2 will result at the supporting chords If both angles are small then
10
Lϕ1=d1Ɵ and Lϕ2=d2
Ɵ (6)
ϕ1= d1
L Ɵ and ϕ2=
d2
L Ɵ (7)
The horizontal restoring forces at the points of attachment with the plate are
F1=iquest T1 sinΦ1iquest (8)
F2=iquest T2 sin Φ2iquest (9)
And using equation (7) to substitute into (8) and (9) and then get
MR= iquest (10)
Where the minus sign is related to the restoring effect
Using equation (4) the restoring moment is rewritten as
MR= -mg d1d2
L Ɵ (11)
Using Newtonrsquos second law and summing moment about the vertical centroidal axis give equation of motion of the body can be written as
Ī ϴ΄΄ = - mg d1d2
L Ɵ rarr ϴ΄΄+mg
d1d2
Ī LƟ=0 (12)
Where
Ī = Mass-moment of inertia of the body about the centroidal axis
The natural frequency of the system can be directly obtained from as
ω=radicmgd1 d2
Ī L (13)
The period that measured experimentally is related to the natural frequency by
11
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
List of tables
Table 1 Bifilar suspension with cord length equal to 04 (m)25Table 2 Bifilar suspension with cord length equal to 045 (m)26Table 3 Bifilar suspension with cord length equal to 048 (m)27Table 4 Trifilar suspension with cord length equal to 04 (m)35Table 5 Trifilar suspension with cord length equal to 044 (m)36Table 6 Trifilar suspension with cord length equal to 05 (m)38
5
Nomenclature
SymbolsScientific Name
dDistance between the cords (m)
FRestoring force (N)
gAcceleration of gravity (ms2)
IMass-Moment of inertia of the body (m4)
k Radius of gyration
L Length of the cords (m)
m
MR
T
θ
Mass (kg)
Restoring moment (Nm)
Tension in the cords (Nm)
Angle of twist (degrees)
umlθ(ω) Angular velocity (rads)
τ Time period (s)
Chapter 16
Introduction
In this chapter we will introduce to you two methods for determining the mass moment of inertia which are the bifilar and trifilar suspension
11 Bifilar suspension method
The bifilar suspension method is a way to determine the mass momentum of inertia (Fig a) shows a uniform rod of mass M and length L suspended horizontally by two vertical strings The length of each string is l and they are attached symmetrically about the center O a distance R apart If the bat is now twisted horizontally it will undergo SHM We wish to analyze this motion and in particular to find the period
And by calculating the time period we can calculate the mass moment of inertia by using some formulas we will provide later in the report
7
A B
Brsquo
O
R
l
L
Figure 1 Bifilar suspension
BA
Arsquo
φ
θ
12 Trifilar suspension method
The trifilar suspension method is a way to determine the mass moment of inertia for a bodies especially a body with an irregular mass as you can see in figure(c) a platform is suspended with three cords and three cords have the same length and they are spaces around the platform center now if we want to determine the mass of inertia we put the object or the body at the platform in the centroidal axis And by displacing the platform through a small angel we can calculate the mass time period and then using some formulas we will provide later we can determine the mass moment of inertia
13 Objectives
The objectives of this experiment are to introduce the bifilar and trifilar suspension methods as options for determining the mass moment of inertia of a rigid body or group of rigid bodies this should lead to the capability of designing experiments for determining moments of inertia of rigid bodies using either bifilar or trifilar pendulum systems
The other objective is to compare theoretical results obtained from pendulum modeling with experimental results and determining accuracy
8
Chapter 2
Theoretical Background
Inertia Determination
Mass- moment of inertia I about an axis of rotation is theoretically can be determined by
IiquestintM
r2 dm (1)
Where
r Distance between the location of mass element dm and the axis of rotation The integration is performed over the entire mass of the body if the axis of rotation coincides with the body centroidal axis the moment of inertia is given by Ī
The parallel axis theorem is given by
I= Ī + m d2 (2)
Where
I The inertia of the body about the axis of rotation
Ī the inertia of the body about its own centroidal axis
m Mass of the body
d the perpendicular distance from the centroidal axis of the body to the axis of rotation
9
Bifilar suspension
Figure 2 (a) Bifilar suspension (b) Trifilar suspension
In figure1 (a) shows the Bifilar suspension and the body is suspended by two parallel cords of length L at a distance R=d apart the tensions in the cords are respectively
T 1=mgd2
d and T 2=mg
d1
d (4)
d1+d2=d and T 1+T 2=mg(5)
If the system is displaced through a small angle θ about its central axis then angular displacement Φ1and Φ2 will result at the supporting chords If both angles are small then
10
Lϕ1=d1Ɵ and Lϕ2=d2
Ɵ (6)
ϕ1= d1
L Ɵ and ϕ2=
d2
L Ɵ (7)
The horizontal restoring forces at the points of attachment with the plate are
F1=iquest T1 sinΦ1iquest (8)
F2=iquest T2 sin Φ2iquest (9)
And using equation (7) to substitute into (8) and (9) and then get
MR= iquest (10)
Where the minus sign is related to the restoring effect
Using equation (4) the restoring moment is rewritten as
MR= -mg d1d2
L Ɵ (11)
Using Newtonrsquos second law and summing moment about the vertical centroidal axis give equation of motion of the body can be written as
Ī ϴ΄΄ = - mg d1d2
L Ɵ rarr ϴ΄΄+mg
d1d2
Ī LƟ=0 (12)
Where
Ī = Mass-moment of inertia of the body about the centroidal axis
The natural frequency of the system can be directly obtained from as
ω=radicmgd1 d2
Ī L (13)
The period that measured experimentally is related to the natural frequency by
11
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Nomenclature
SymbolsScientific Name
dDistance between the cords (m)
FRestoring force (N)
gAcceleration of gravity (ms2)
IMass-Moment of inertia of the body (m4)
k Radius of gyration
L Length of the cords (m)
m
MR
T
θ
Mass (kg)
Restoring moment (Nm)
Tension in the cords (Nm)
Angle of twist (degrees)
umlθ(ω) Angular velocity (rads)
τ Time period (s)
Chapter 16
Introduction
In this chapter we will introduce to you two methods for determining the mass moment of inertia which are the bifilar and trifilar suspension
11 Bifilar suspension method
The bifilar suspension method is a way to determine the mass momentum of inertia (Fig a) shows a uniform rod of mass M and length L suspended horizontally by two vertical strings The length of each string is l and they are attached symmetrically about the center O a distance R apart If the bat is now twisted horizontally it will undergo SHM We wish to analyze this motion and in particular to find the period
And by calculating the time period we can calculate the mass moment of inertia by using some formulas we will provide later in the report
7
A B
Brsquo
O
R
l
L
Figure 1 Bifilar suspension
BA
Arsquo
φ
θ
12 Trifilar suspension method
The trifilar suspension method is a way to determine the mass moment of inertia for a bodies especially a body with an irregular mass as you can see in figure(c) a platform is suspended with three cords and three cords have the same length and they are spaces around the platform center now if we want to determine the mass of inertia we put the object or the body at the platform in the centroidal axis And by displacing the platform through a small angel we can calculate the mass time period and then using some formulas we will provide later we can determine the mass moment of inertia
13 Objectives
The objectives of this experiment are to introduce the bifilar and trifilar suspension methods as options for determining the mass moment of inertia of a rigid body or group of rigid bodies this should lead to the capability of designing experiments for determining moments of inertia of rigid bodies using either bifilar or trifilar pendulum systems
The other objective is to compare theoretical results obtained from pendulum modeling with experimental results and determining accuracy
8
Chapter 2
Theoretical Background
Inertia Determination
Mass- moment of inertia I about an axis of rotation is theoretically can be determined by
IiquestintM
r2 dm (1)
Where
r Distance between the location of mass element dm and the axis of rotation The integration is performed over the entire mass of the body if the axis of rotation coincides with the body centroidal axis the moment of inertia is given by Ī
The parallel axis theorem is given by
I= Ī + m d2 (2)
Where
I The inertia of the body about the axis of rotation
Ī the inertia of the body about its own centroidal axis
m Mass of the body
d the perpendicular distance from the centroidal axis of the body to the axis of rotation
9
Bifilar suspension
Figure 2 (a) Bifilar suspension (b) Trifilar suspension
In figure1 (a) shows the Bifilar suspension and the body is suspended by two parallel cords of length L at a distance R=d apart the tensions in the cords are respectively
T 1=mgd2
d and T 2=mg
d1
d (4)
d1+d2=d and T 1+T 2=mg(5)
If the system is displaced through a small angle θ about its central axis then angular displacement Φ1and Φ2 will result at the supporting chords If both angles are small then
10
Lϕ1=d1Ɵ and Lϕ2=d2
Ɵ (6)
ϕ1= d1
L Ɵ and ϕ2=
d2
L Ɵ (7)
The horizontal restoring forces at the points of attachment with the plate are
F1=iquest T1 sinΦ1iquest (8)
F2=iquest T2 sin Φ2iquest (9)
And using equation (7) to substitute into (8) and (9) and then get
MR= iquest (10)
Where the minus sign is related to the restoring effect
Using equation (4) the restoring moment is rewritten as
MR= -mg d1d2
L Ɵ (11)
Using Newtonrsquos second law and summing moment about the vertical centroidal axis give equation of motion of the body can be written as
Ī ϴ΄΄ = - mg d1d2
L Ɵ rarr ϴ΄΄+mg
d1d2
Ī LƟ=0 (12)
Where
Ī = Mass-moment of inertia of the body about the centroidal axis
The natural frequency of the system can be directly obtained from as
ω=radicmgd1 d2
Ī L (13)
The period that measured experimentally is related to the natural frequency by
11
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Introduction
In this chapter we will introduce to you two methods for determining the mass moment of inertia which are the bifilar and trifilar suspension
11 Bifilar suspension method
The bifilar suspension method is a way to determine the mass momentum of inertia (Fig a) shows a uniform rod of mass M and length L suspended horizontally by two vertical strings The length of each string is l and they are attached symmetrically about the center O a distance R apart If the bat is now twisted horizontally it will undergo SHM We wish to analyze this motion and in particular to find the period
And by calculating the time period we can calculate the mass moment of inertia by using some formulas we will provide later in the report
7
A B
Brsquo
O
R
l
L
Figure 1 Bifilar suspension
BA
Arsquo
φ
θ
12 Trifilar suspension method
The trifilar suspension method is a way to determine the mass moment of inertia for a bodies especially a body with an irregular mass as you can see in figure(c) a platform is suspended with three cords and three cords have the same length and they are spaces around the platform center now if we want to determine the mass of inertia we put the object or the body at the platform in the centroidal axis And by displacing the platform through a small angel we can calculate the mass time period and then using some formulas we will provide later we can determine the mass moment of inertia
13 Objectives
The objectives of this experiment are to introduce the bifilar and trifilar suspension methods as options for determining the mass moment of inertia of a rigid body or group of rigid bodies this should lead to the capability of designing experiments for determining moments of inertia of rigid bodies using either bifilar or trifilar pendulum systems
The other objective is to compare theoretical results obtained from pendulum modeling with experimental results and determining accuracy
8
Chapter 2
Theoretical Background
Inertia Determination
Mass- moment of inertia I about an axis of rotation is theoretically can be determined by
IiquestintM
r2 dm (1)
Where
r Distance between the location of mass element dm and the axis of rotation The integration is performed over the entire mass of the body if the axis of rotation coincides with the body centroidal axis the moment of inertia is given by Ī
The parallel axis theorem is given by
I= Ī + m d2 (2)
Where
I The inertia of the body about the axis of rotation
Ī the inertia of the body about its own centroidal axis
m Mass of the body
d the perpendicular distance from the centroidal axis of the body to the axis of rotation
9
Bifilar suspension
Figure 2 (a) Bifilar suspension (b) Trifilar suspension
In figure1 (a) shows the Bifilar suspension and the body is suspended by two parallel cords of length L at a distance R=d apart the tensions in the cords are respectively
T 1=mgd2
d and T 2=mg
d1
d (4)
d1+d2=d and T 1+T 2=mg(5)
If the system is displaced through a small angle θ about its central axis then angular displacement Φ1and Φ2 will result at the supporting chords If both angles are small then
10
Lϕ1=d1Ɵ and Lϕ2=d2
Ɵ (6)
ϕ1= d1
L Ɵ and ϕ2=
d2
L Ɵ (7)
The horizontal restoring forces at the points of attachment with the plate are
F1=iquest T1 sinΦ1iquest (8)
F2=iquest T2 sin Φ2iquest (9)
And using equation (7) to substitute into (8) and (9) and then get
MR= iquest (10)
Where the minus sign is related to the restoring effect
Using equation (4) the restoring moment is rewritten as
MR= -mg d1d2
L Ɵ (11)
Using Newtonrsquos second law and summing moment about the vertical centroidal axis give equation of motion of the body can be written as
Ī ϴ΄΄ = - mg d1d2
L Ɵ rarr ϴ΄΄+mg
d1d2
Ī LƟ=0 (12)
Where
Ī = Mass-moment of inertia of the body about the centroidal axis
The natural frequency of the system can be directly obtained from as
ω=radicmgd1 d2
Ī L (13)
The period that measured experimentally is related to the natural frequency by
11
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
12 Trifilar suspension method
The trifilar suspension method is a way to determine the mass moment of inertia for a bodies especially a body with an irregular mass as you can see in figure(c) a platform is suspended with three cords and three cords have the same length and they are spaces around the platform center now if we want to determine the mass of inertia we put the object or the body at the platform in the centroidal axis And by displacing the platform through a small angel we can calculate the mass time period and then using some formulas we will provide later we can determine the mass moment of inertia
13 Objectives
The objectives of this experiment are to introduce the bifilar and trifilar suspension methods as options for determining the mass moment of inertia of a rigid body or group of rigid bodies this should lead to the capability of designing experiments for determining moments of inertia of rigid bodies using either bifilar or trifilar pendulum systems
The other objective is to compare theoretical results obtained from pendulum modeling with experimental results and determining accuracy
8
Chapter 2
Theoretical Background
Inertia Determination
Mass- moment of inertia I about an axis of rotation is theoretically can be determined by
IiquestintM
r2 dm (1)
Where
r Distance between the location of mass element dm and the axis of rotation The integration is performed over the entire mass of the body if the axis of rotation coincides with the body centroidal axis the moment of inertia is given by Ī
The parallel axis theorem is given by
I= Ī + m d2 (2)
Where
I The inertia of the body about the axis of rotation
Ī the inertia of the body about its own centroidal axis
m Mass of the body
d the perpendicular distance from the centroidal axis of the body to the axis of rotation
9
Bifilar suspension
Figure 2 (a) Bifilar suspension (b) Trifilar suspension
In figure1 (a) shows the Bifilar suspension and the body is suspended by two parallel cords of length L at a distance R=d apart the tensions in the cords are respectively
T 1=mgd2
d and T 2=mg
d1
d (4)
d1+d2=d and T 1+T 2=mg(5)
If the system is displaced through a small angle θ about its central axis then angular displacement Φ1and Φ2 will result at the supporting chords If both angles are small then
10
Lϕ1=d1Ɵ and Lϕ2=d2
Ɵ (6)
ϕ1= d1
L Ɵ and ϕ2=
d2
L Ɵ (7)
The horizontal restoring forces at the points of attachment with the plate are
F1=iquest T1 sinΦ1iquest (8)
F2=iquest T2 sin Φ2iquest (9)
And using equation (7) to substitute into (8) and (9) and then get
MR= iquest (10)
Where the minus sign is related to the restoring effect
Using equation (4) the restoring moment is rewritten as
MR= -mg d1d2
L Ɵ (11)
Using Newtonrsquos second law and summing moment about the vertical centroidal axis give equation of motion of the body can be written as
Ī ϴ΄΄ = - mg d1d2
L Ɵ rarr ϴ΄΄+mg
d1d2
Ī LƟ=0 (12)
Where
Ī = Mass-moment of inertia of the body about the centroidal axis
The natural frequency of the system can be directly obtained from as
ω=radicmgd1 d2
Ī L (13)
The period that measured experimentally is related to the natural frequency by
11
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Chapter 2
Theoretical Background
Inertia Determination
Mass- moment of inertia I about an axis of rotation is theoretically can be determined by
IiquestintM
r2 dm (1)
Where
r Distance between the location of mass element dm and the axis of rotation The integration is performed over the entire mass of the body if the axis of rotation coincides with the body centroidal axis the moment of inertia is given by Ī
The parallel axis theorem is given by
I= Ī + m d2 (2)
Where
I The inertia of the body about the axis of rotation
Ī the inertia of the body about its own centroidal axis
m Mass of the body
d the perpendicular distance from the centroidal axis of the body to the axis of rotation
9
Bifilar suspension
Figure 2 (a) Bifilar suspension (b) Trifilar suspension
In figure1 (a) shows the Bifilar suspension and the body is suspended by two parallel cords of length L at a distance R=d apart the tensions in the cords are respectively
T 1=mgd2
d and T 2=mg
d1
d (4)
d1+d2=d and T 1+T 2=mg(5)
If the system is displaced through a small angle θ about its central axis then angular displacement Φ1and Φ2 will result at the supporting chords If both angles are small then
10
Lϕ1=d1Ɵ and Lϕ2=d2
Ɵ (6)
ϕ1= d1
L Ɵ and ϕ2=
d2
L Ɵ (7)
The horizontal restoring forces at the points of attachment with the plate are
F1=iquest T1 sinΦ1iquest (8)
F2=iquest T2 sin Φ2iquest (9)
And using equation (7) to substitute into (8) and (9) and then get
MR= iquest (10)
Where the minus sign is related to the restoring effect
Using equation (4) the restoring moment is rewritten as
MR= -mg d1d2
L Ɵ (11)
Using Newtonrsquos second law and summing moment about the vertical centroidal axis give equation of motion of the body can be written as
Ī ϴ΄΄ = - mg d1d2
L Ɵ rarr ϴ΄΄+mg
d1d2
Ī LƟ=0 (12)
Where
Ī = Mass-moment of inertia of the body about the centroidal axis
The natural frequency of the system can be directly obtained from as
ω=radicmgd1 d2
Ī L (13)
The period that measured experimentally is related to the natural frequency by
11
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Bifilar suspension
Figure 2 (a) Bifilar suspension (b) Trifilar suspension
In figure1 (a) shows the Bifilar suspension and the body is suspended by two parallel cords of length L at a distance R=d apart the tensions in the cords are respectively
T 1=mgd2
d and T 2=mg
d1
d (4)
d1+d2=d and T 1+T 2=mg(5)
If the system is displaced through a small angle θ about its central axis then angular displacement Φ1and Φ2 will result at the supporting chords If both angles are small then
10
Lϕ1=d1Ɵ and Lϕ2=d2
Ɵ (6)
ϕ1= d1
L Ɵ and ϕ2=
d2
L Ɵ (7)
The horizontal restoring forces at the points of attachment with the plate are
F1=iquest T1 sinΦ1iquest (8)
F2=iquest T2 sin Φ2iquest (9)
And using equation (7) to substitute into (8) and (9) and then get
MR= iquest (10)
Where the minus sign is related to the restoring effect
Using equation (4) the restoring moment is rewritten as
MR= -mg d1d2
L Ɵ (11)
Using Newtonrsquos second law and summing moment about the vertical centroidal axis give equation of motion of the body can be written as
Ī ϴ΄΄ = - mg d1d2
L Ɵ rarr ϴ΄΄+mg
d1d2
Ī LƟ=0 (12)
Where
Ī = Mass-moment of inertia of the body about the centroidal axis
The natural frequency of the system can be directly obtained from as
ω=radicmgd1 d2
Ī L (13)
The period that measured experimentally is related to the natural frequency by
11
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Lϕ1=d1Ɵ and Lϕ2=d2
Ɵ (6)
ϕ1= d1
L Ɵ and ϕ2=
d2
L Ɵ (7)
The horizontal restoring forces at the points of attachment with the plate are
F1=iquest T1 sinΦ1iquest (8)
F2=iquest T2 sin Φ2iquest (9)
And using equation (7) to substitute into (8) and (9) and then get
MR= iquest (10)
Where the minus sign is related to the restoring effect
Using equation (4) the restoring moment is rewritten as
MR= -mg d1d2
L Ɵ (11)
Using Newtonrsquos second law and summing moment about the vertical centroidal axis give equation of motion of the body can be written as
Ī ϴ΄΄ = - mg d1d2
L Ɵ rarr ϴ΄΄+mg
d1d2
Ī LƟ=0 (12)
Where
Ī = Mass-moment of inertia of the body about the centroidal axis
The natural frequency of the system can be directly obtained from as
ω=radicmgd1 d2
Ī L (13)
The period that measured experimentally is related to the natural frequency by
11
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
τ=2 πω = 2 π radic Ī L
mgd1d2 (14)
Using equation (14) the experimental mass-moment of inertia is given by
Ī =mgd1d2 τ
2
4 π2 L (15)
Equation (15) can be rewritten in terms of the radius of gyration
τ=2πk radic Lgd1 d2
(16)
Wherek = Radius of gyration defined by
Ī = m k 2 (17)
To reduce the error different readings at different cords length L should be taken and a relation between the cord length and the corresponding mass moment of inertia is to be obtained In this regard equation (15) can be written as
L = mgd1d2 τ
2
4 π2 Ī (18)
This can be rewritten as L = k τ 2 (19)
With k defined as
k = mgd1d2
4 π2 Ī (20)
12
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Trifilar suspension
The trifilar maybe more useful when the shape is highly irregular and a third suspension is required to give a more stable and consistent oscillation Figure1 (b) outlines the trifilar suspension in detail
Where the platform is suspended by three cords of equal length and is equally spaced about the platform centre And the round platform serves as triangular one The part whose moment of inertia is to be determined is carefully placed on the platform so that its centroidal axis coincides with that of platform
The platform is then made to oscillate and the number of oscillate is counted over a specific period of time
The sum of moment sumM about a vertical axis coinciding with the centroidal axis of the body is
ΣM=minusR (m+mp )g sinemptyminus( Ī+ I p )ϴ΄΄=0 (21)
Where
m mass of body whose moment of inertia is to be determinedm p Mass of platformĪ Moment of inertia of body about its centroidal axisI p Moment of inertia of platform about its centroidal axisR distance form platform center of mass to suspension point Ɵ platform displaced angle120601 cord displaced angleL cord length
Since dealing the small displacement angles the angles can be equated to the angles themselves (in radians) Therefore
120601 = RL
Ɵ
(22)
13
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
And equation (20) becomes
ϴ΄΄+(m+m p ) R2 g
L ( Ī+ I p )θ=0 (23)
Therefore the period is given by
τ=2π radic L ( Ī + I p )(m+mp ) R2 g
(24)
And the experimental mass moment of inertia is given as
Ī+ I p=(m+m p ) R2 g
L ( τ2π )
2
(25)
To reduce the error during the experiment more than one measurement is required Along this line a relation between the cord length L and the period τ is to be obtained
L = (m+m p )R2 g
4 π2 ( Ī + I p ) τ2 (26)
This can be rewritten as
L = C τ 2 (27)
With C defined as
C = (m+mp )R2 g
4 π2 ( Ī + I p ) (28)
14
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Chapter 3
Experimental setup and procedure
This chapter is divided into four parts and each part is illustrated briefly First of all the needed equipments for the Bifilar and Trifilar experiment will be illustrated with some figures for more details
While proceeding in this chapter the procedure involved in the Bifilar and Trifilar experiment will be explained briefly Beginning with adjusting the length of the cords until recording the needed data such as the oscillation time
Finally after the set of procedure is done for the both cases The study of the relationship between the mass-moment of inertia of the body and the time period is simply investigated
31 Equipments
In order to perform the bifilar and trifilar experiment a set of equipments is needed and is illustrated as follows
1 Stop watch2 Ruler3 Electronic scale for weighting parts
For the previous set of equipments some helpful notes should be considered such as being careful while recording the cord length and weighting parts
15
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
32 Procedure
This section of this chapter is divided into two parts First the procedure related to the bifilar apparatus is illustrated Secondly the procedure for the trifilar apparatus is discussed briefly
321 Bifilar apparatus procedure
In order to perform this case of this experiment sufficiently and achieve the needed results with a great possibility to eliminate the human errors as much as possible a specific set of procedures should be followed and is illustrated as follows
1 Measure the dimension and the mass of the beam
2 Suspend the beam by the cords and adjust their common length L
3 Displace the beam by small angle release it and determine the periodic time of free oscillations by timing 20 oscillations
4 Repeat step 3 for three different values of L
5 Measure the dimensions of the cylindrical masses
6 Place the cylindrical masses of known weight either side of the center of gravity of the beam maintaining a specified distance between the masses
7 Repeat the procedure with an irregularly shaped body that can be fixed on the beam
8 In each test record L time period and the mass of the beam Then use equation (13) and (14) to calculate the mass-moment of inertia and radius of gyration of the beam alone and of the beam with masses placed on it
16
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
322 Trifilar apparatus procedure
1 Measure the mass and radius of the plate Suspend the plate by the wires and adjust their common length L very accurately
2 Displace the plate with a small angle release it and determine the periodic time of free oscillations by timing 30 oscillations
3 Repeat step 2 for different values of L
4 Find the mass of the body then place it on the plate so heir centers of gravity coincide Repeat steps 2 and 3
5 Apply equation (22) to determine the mass-moment of inertia of the body and radius of gyration in each case Estimate the error involved
17
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Chapter 4
Results and discussion
In this chapter some sample calculations are obtained in order to achieve the desired results In the other hand these results which are obtained are discussed briefly
As a first step for both the bifilar and trifilar setups the time period theoretical and experimental mass-moment of inertia of different cases and the percentage error between them and the radius of gyration of the beam alone and of the beam with masses placed on it
18
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
41 Sample calculations
Bifilar Apparatus
1 Total mass of frame hanging with wires = 1444 kg2 Width of frame = 2525 mm3 Height of frame = 1275 mm4 Length of frame = 503 mm5 Distance between the wires = 15 mm6 Number of holes in hanging rectangular x-section bar = 157 Distance between each hole from center to center = 25 mm8 Diameter of each hole = 1042 mm9 Diameter of each cylinder fixed at the end of rectangular section = 20 mm10 Length of each cylinder fixed at the end of rectangular section = 50 mm11 Length of wires = 400mm 450mm 480mm12 Diameter of cylindrical mass 762513 Height of cylindrical mass = 509 mm14 Mass of each cylindrical mass = 179315 Distance between two masses 150mm 200mm 250mm16 Mass of the irregular shape = 2513 kg
19
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
For the Bifilar apparatus case the following three cases are to be investigated where the cord length was 400 (mm) as follows
(a) The beam only
Theoretical
I zz=I (beam )minusI ( holes )+ I (iquestcylinders)
I zz=(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))
= 045721497 (m4)
Experimental
20
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
For first trail when the length of the cord = 400 mm with having 20 oscillations the calculated mass-moment of inertia of the platform and the time period were found to be
τ = time
cycles = 1791
20 = 08955 (s)
And the mass-moment of inertia of the platform was calculated using equation (13) as follows
I p = (m )d1 d2 gτ 2
4π 2 L=
1444lowast02525lowast02525lowast076752lowast(981)4π 2(04)
= 045501 (m4)
Also the percentage error was found as shown
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=0482
(b) The beam with one cylindrical mass placed on it
21
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Theoretical
I=I ( plate )minusI (holes )+ I (iquestcylinders )+ I (cylinder placed)
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0152))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01752))))+(2lowast(05lowast01233lowast(0012)+01233lowast025252))+2lowast(05lowast1793lowast00381252)
= 0048327651 (m4)
Experimental
Using equation (13) the following experimental data of the mass-moment of inertia was found as follow
τ = timecycles =
121320
=06065(s)
I = (m )d1 d2 τ
2 g
4π 2 L
iquest (1444+1793 ) (052 )2(02525)(02525)(981)
4 π 2(04)
= 0045155684 (m4 iquest
Error = theoriticalminusexperimemtal
theoritical=65634
( c ) The beam with two cylindrical masses spaced 250 (mm)
Theoretical
22
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
I = I (plate) ndash I (holes) +I (fixed cylinders) + I (cylindrical masses placed)
=
iquest(((112)lowast1444lowast(05032+0025252))minus(2lowast(1444lowast(0005212)minus(000008528lowast(00252))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(0052))))minus(2lowast1444lowast(0005212))minus(000008528lowast(00752)))minus(2lowast(1444lowast(0005212)minus(000008528lowast(012))))minus(2lowast(1444lowast(0005212)minus(000008528lowast(01252))))minusiquest
= 0104358901 (m4 iquest
Experimental
In this case with the two cylindrical masses placed 250 (mm) the mass-moment of inertia was calculated using equation (13) as follows
τ = timecycles =
150920 = 07545 (s)
I = (m )d1 d2 gτ 2
4π 2 L
= (503 ) (05735 )2 (02525 ) (02525 ) ( 981 )
4 π2 (04 )
= 0104606813 (m4 iquest
Error = theoriticalminusexperimemtal
theoriticallowast100 = 0294
As the previous cases were discussed briefly on the theoretical and experimental basis the same previous steps were repeated for different cord length as illustrated in the next pages tables
23
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
24
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Table 1 Bifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cyclesrsquo)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam04 20 1785 08925
1782666667 0891333333 00457214970045196926 1147318216
04 20 1772 0886 0044540993 258194598404 20 1791 08955 0045501282 0481645472
Beam with one mass in the center
04 20 1206 06031209333333 0604666667 0048327651
0044636018 763875978504 20 1213 06065 0045155684 656346126304 20 1209 06045 0044858364 7178679599
Beam with two masses of distance
150 mm
04 20 1185 059251185666667 0592833333 0068498901
0064508686 582522521804 20 1178 0589 0063748809 693455239104 20 1194 0597 0065492285 4389290021
Beam with two masses of distance
200 mm
04 20 1328 06641324666667 0662333333 0084187651
0081017277 376584191504 20 1332 0666 0081506068 318524499304 20 1314 0657 0079318085 5784180162
Beam with two masses of distance
250 mm
04 20 1485 074251501 07505 0104358901
0101305821 362651766404 20 1509 07545 0104606813 029447598504 20 1509 07545 0104606813 0294475985
Irregular shape04 20 1635 08175
1634666667 0817333333 00487731420061356248 1494649851
04 20 1625 08125 0060608008 149464985104 20 1644 0822 0062033588 1494649851
25
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Table 2 Bifilar suspension with cord length equal to 045 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam045 20 1863 09315
1887666667 0943833333 00457214970043762855 4283854264
045 20 19 095 0045518416 04441707045 20 19 095 0045518416 04441707
Beam with one mass in the center
045 20 13 0651286666667 0643333333 0048327651
0046102556 4604185043045 20 1282 0641 0044834709 7227626401045 20 1278 0639 0044555366 7805646014
Beam with two masses of distance
150 mm
045 20 1268 06341264333333 0632166667 0068498901
006565495 4151819235045 20 1272 0636 0066069831 3546145034045 20 1253 06265 0064110788 6406107612
Beam with two masses of distance
200 mm
045 20 1503 075151504 0752 0084187651
009224587 9571735346045 20 1506 0753 0092614485 10009584045 20 1503 07515 009224587 9571735346
Beam with two masses of distance
250 mm
045 20 1575 078751580666667 0790333333 0104358901
0101295485 3638795325045 20 1585 07925 010258586 2106058254045 20 1582 0791 010219789 2566897967
Irregular shape045 20 1735 08675
1722333333 0861166667 00487731420061414329 1501548924
045 20 1716 0858 0060076597 1501548924045 20 1716 0858 0060076597 1501548924
26
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Table 3 Bifilar suspension with cord length equal to 048 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only beam048 20 1953 09765
1960333333 0980166667 00457214970045087453 1386753778
048 20 1956 0978 0045226077 1083561808048 20 1972 0986 0045968998 0541321699
Beam with one mass in the center
048 20 1344 06721337666667 0668833333 0048327651
0046196398 4410006579048 20 1328 0664 0045103031 6672411469048 20 1341 06705 0045990395 4836271348
Beam with two masses of distance
150 mm
048 20 1322 06611303333333 0651666667 0068498901
0066905706 2325869495048 20 1325 06625 0067209707 1882064854048 20 1263 06315 0061067051 1084959004
Beam with two masses of distance
200 mm
048 20 1463 073151458666667 0729333333 0084187651
0081938668 2671393071048 20 1466 0733 0082275056 2271823432048 20 1447 07235 0080156235 4788607411
Beam with two masses of distance
250 mm
048 20 1628 08141622 0811 0104358901
0101463315 3439442497048 20 1613 08065 0099602212 5650103475048 20 1625 08125 0101089716 3883211714
Irregular shape048 20 1766 0883
1751333333 0875666667 00487731420059651783 1292189689
048 20 1747 08735 0058375127 1292189689048 20 1741 08705 0057974842 1292189689
27
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
As investigated from the previous tables related to the bifilar suspension it is noticeable that the percentage error related to the theoretical and the experimental results is somehow small and acceptable
28
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Trifilar Apparatus
1 Total mass of round plate = 4365 kg2 Diameter of plate = 628mm3 Thickness of plate 334mm4 Length of wire 828mm5 Radius of circle at wire fixing position 272mm6 Inside diameter of hallow cylinder 8362mm7 Outside diameter of hallow cylinder = 200mm8 Height of hallow cylinder = 200mm9 Mass of hallow cylinder = 1386 kg10 Mass of irregular shape = 5656 kg
After recording the data obtained in the lab for this case and the theoretical equation for different shapes the values of (I) the Moment of inertia for different cases are calculated as follows
(a) The platform alone
Theoretical
I zz=25mr2
= 25
(4365 ) (0314 )2 = 048441024 m4
Experimental
Equations (23) (24) and (25) are used to get the theoretical data by substituting the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And average time for this case was calculated after three trails had been done and it was found to be t average=299 secsec
L = C τ 2
29
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
C = L τ 2
τ = timecycles
= 29930
= 099667 (sec)
C= 04
(099667)2=iquest0388 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I p = (mp )R2 g
4 π2 C=
4365(0272)2(981)4 π 2(0417)
= 0457430617 (m4)
Error = t h eoriticalminusexperimemtal
t heoriticallowast100 iquest5569
30
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
(b) The platform horizontal cylindrical mass placed on it at the centroid
Theoretical
I cy ondash I cy i=1
12m(3 riquestiquest2+h2)minus 1
12m(3 riquestiquest2+h2)iquestiquest
iquest((3 2)lowast4365lowast02722)+((112)lowast1386lowast((022)+3lowast012))minus((112)lowast1386lowast((022)+3lowast0041812))
= 0513003156 m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=16533sec
L = C τ 2
C = L τ 2
τ = timecycles =
1653330 = 05511 (sec)
C= 04
(0569)2=iquest1317 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (m p+m )R2 g
4π 2C=0563225526m2
31
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=9789875
And by performing the same procedure for each case for different cord lengths
( c ) The platform with vertical cylindrical mass placed on it at the centroid
Theoretical
I=32mr2+ 1
2mro
2minus12mr i
2
=((32)43650272^2)+((12)138601^2)-((12)138600418^2)
= 0541601867m4
Experimental
Equations (23) (24) and (25) were used to obtain the theoretical data by substitute using the data measured in the lab
For the first trail when the length of the cord = 400 mm and performing d 30 oscillations The average time involved in this case after three repetitions was found to be t average=163sec
L = C τ 2
C = L τ 2
τ = timecycles =
16330 = 054333 (sec)
32
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
C= 04
(05433)2=iquest13549 (m sec2)
C = (m+m p )R2 g
4 π2(I + Ip )
I+ I p = (mp+m )R2 g
4π 2C=0563225526m2
Error = theoriticalminusexperimemtal
theoriticallowast100=39925
( d ) The platform alone with irregular mass placed on it at the centroid
Experimental
Equations (23) (24) and (25) were used to get the theoretical data by substitute using the data measured in the lab
For first trail when the length of the cord = 400 mm and we had 30 oscillations And we did it three time to get the average time for this case To reduce the personality error and we got t average=2123sec
L = C τ 2
C = L τ 2
τ = timecycles
= 2123
30= 0676 sec
C= 04
(0676)2=iquest0707667 m sec2
C = (m+m p )R2 g
4 π2(I + Ip )
33
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
I+ I p = (m p+m )R2 g
4π 2C=052239m4
Note
For the irregular shape you canrsquot get the theoretical moment of inertia but you can approximate it for the irregular shape by treating it as group of homogenous solids
So the theoretical moment of inertia approximated to
I=(( 32 )lowast4365lowast02722)+( 2
5 )lowast5656lowast0152=0535314 m4
Error = t h eoriticalminusexperimemtal
t heoriticallowast100=2413
34
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Table 4 Trifilar suspension with cord length equal to 04 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate04 30 298 149
2993333333 1496666667 0484410240445393497 805448343
04 30 298 149 0445393497 80544834304 30 302 151 0457430617 5569581401
Plate with horizontal cylindrical mass placed
on it at the centroid
04 30 164 0821653333333 0826666667 0513003156
0563225526 978987534704 30 165 0825 0570115071 111328582804 30 167 0835 0584019806 1384331624
Plate with vertical cylindrical mass placed
on it at the centroid
04 30 157 0785163 0815 0541601867
05161714 469541704204 30 168 084 0591034996 912720797704 30 164 082 0563225526 399253776
Plate with irregular mass placed on it at
the centroid
04 30 213 10652123333333 1061666667 053531424
052239302 24137636304 30 212 106 0517499435 332791537304 30 212 106 0517499435 3327915373
35
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Table 5 Trifilar suspension with cord length equal to 044 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate044 30 314 157
3156666667 1578333333 0484410240449549951 7196439229
044 30 316 158 045529494 6010463261044 30 317 1585 0458181114 5414651525
Plate with horizontal cylindrical mass placed
on it at the centroid
044 30 162 0811626666667 0813333333 0513003156
0499610983 2610544028044 30 162 081 0499610983 2610544028044 30 164 082 0512023205 0191022412
Plate with vertical cylindrical mass placed
on it at the centroid
044 30 169 0845169 0845 0541601867
0543720061 0391098067044 30 167 0835 0530927096 1970962712044 30 171 0855 0556665324 2781278617
Plate with irregular mass placed on it at the
centroid
044 30 231 115523 115 053531424
0558559487 4342355492044 30 23 115 0553733942 344091388044 30 229 1145 0548929332 2543383077
36
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Table 6 Trifilar suspension with cord length equal to 05 (m)
SystemCord
Length L (m)
No of Oscillations
(cycles)
Time of Oscillations
(sec)
Period τ
Average time (s)
Average Period
Plate Moment of inertia Error
Theoretical Experimental
Only Plate05 30 343 1715
339 1695 0484410240472051706 2551253737
05 30 335 1675 0450288593 704395660505 30 339 1695 0461105951 4810857982
Plate with horizontal cylindrical mass placed
on it at the centroid
05 30 185 09251846666667 0923333333 051300315
6
0573360905 117655706105 30 187 0935 0585824908 141951859305 30 182 091 055491619 8170131796
Plate with vertical cylindrical mass placed
on it at the centroid
05 30 186 0931820666667 0910333333 054160186
7
0579576154 701147639405 30 1792 0896 0537973187 06699902505 30 181 0905 0548834963 1335500582
Plate with irregular mass placed on it at the
centroid
05 30 238 1192396666667 1198333333 053531424
0521773549 252948448605 30 239 1195 0526167412 170868376705 30 242 121 0539459539 0774367463
37
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Linear relation for case (a)
By drawing the relation between log τ and log l we obtained with the following linear graph and it is intersection with the ordinate is equal to the constant C and it slope is equal 2
-002-00100010020030040
005
01
015
02
025
03
035
04
045
log τ
log l
Figure (3) The relation between log L and log τ
The pervious graph indicates that the relation between log L and log τ is linear And it is intercept with y-axis at value equal to = 0388 which is the value of constant C that we had calculated in each case And the linear graph has a slope equal to 2 And thatrsquos what we expected in the theoretical equation
38
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
42 Discussion
When investigating the previous experimentally and theoretically results that were tabulated it is obvious that the theoretical and experimental results of the mass-moment of inertia for the bifilar and trifilar suspension are somehow close and the error involved is not large
In other words the human errors involved in this experiment such as while recording the length of the cords and weighting the parts are acceptable
In addition as noticed from the tabulated data for the bifilar and trifilar suspensions the relationship between the mass-moment of inertia of the body and the periodic time on log scale is linear
But it should be kept in mind that this linear relation involves some errors In other words this relation is very close to be perfectly linear due to the errors generated while performing this experiment
39
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
43 Uncertainty Analysis
In this part of this chapter it is important to evaluate the error involved in obtaining the mass-moment of inertia in order to ensure the accuracy related to it These errors occur due to the human errors such as measuring the lengths of the cords and the time of oscillations by the stop watch
This can be achieved by performing the uncertainty analysis as shown below for the first case of the bifilar suspension
I = md1 d2 gτ 2
4 π 2 L
uL=05480
=000104
ut=00051432
=000035
part Ipart L
=iquest (m )d1 d2 gτ 2
(4 π2 L)2
part Ipart t
=iquest (m )d1 d2 gτ
2π 2 L
u I= radic(LIpart Ipart L
uL)2
+( tIpart Ipart t
ut)2
minus iquest+iquestiquest iquest
40
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
As noticed from the uncertainty analysis the error involved is not large and is acceptable In other words and for an instance the values of the error involved in calculating the viscosities of the given oils indicate that the human error due to the usage of the stop watch was somehow acceptable
41
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
Chapter 5
Conclusion
The conclusion for this experiment is that the bifilar and trifilar suspension methods for determining the mass-moment of inertia can be considered as successful methods applied for that purpose
Moreover the errors involved in this experiment whether in the case of bifilar or trifilar suspensions are not large which can be considered as a good indicator of how successful this experiment was
Finally when this experiment was performed some recommendations and notices should be taken in mind for the purpose of improving the obtained results such as
Being careful while changing the length of the wires and make sure they are on the same level (exactly having the same length)
Using an electronic scale for weighting parts to increase the accuracy
Using the stop watch properly and carefully while recording the time of oscillation
42
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43
References
1 Mechanical Engineering Fundamentals Laboratory Sheet ldquoLab Ardquo Prepared by ProfAhmed H Elkholy
43