Physics 101Lecture 1

Units

Dr. Ali ÖVGÜN

EMU Physics Department

www.aovgun.com

Course Information: Instructor

q Instructor: Ali Övgünq Office: AS 245 ( Arts and Sciences Faculty)q Office hour: To be announced (check my

webpage). Other time by appointmentq Email: ali.ovgun@emu.edu.trq Website: www.aovgun.comq phys101.aovgun.com

Course Information:

q Midterm Exam (35%)q Quiz (10%)q Lab Experiments(5%)q Lab Exam (10%) q Final Exam (40%)q Participation to laboratory:q Attending at least 3 out of 5 experiments is a must,

otherwise the student will directly get NG from the lecture.

COURSE SCHEDULEq 1st Week Chapter 1 – Unitsq 2nd Week Chapter 3 – Vectorsq 3rd Week Chapter 2 – Motion Along Straight Lineq 4th Week Chapter 4 – Motion in 2D and 3Dq 5th Week Chapter 5,6 – Force and Motionq Midtermq 6th Week Chapter 7 – Kinetic Energy and Workq 7th Week Chapter 8 – Conservation of Energy q 8th Week Chapter 9 – Linear Momentumq Quizq 9th Week Chapter 10– Rotationq 10th Week Chapter 11– Torque,Angular Momentumq 11th Week Chapter 12 – Equilibriumq 12th Week Chapter 13 - Gravitationq 13th Week Reviewq 14th Week Finals

January 22-25, 2013

Physics and Mechanicsq Physics deals with the nature and properties of matter

and energy. Common language is mathematics. Physics is based on experimental observations and quantitative measurements.

q The study of physics can be divided into six main areas:n Classical mechanics – Physics I (Phys. 101)n Electromagnetism – Physics II (Phys. 102)n Optics –n Relativity –n Thermodynamics –Physics II (Phys. 102n Quantum mechanics –n Classical mechanics deals with the motion and

equilibrium of material bodies and the action of forces.

January 22-25, 2013

Classical Mechanicsq Classical mechanics deals with the motion of objectsq Classical Mechanics: Theory that predicts qualitatively &

quantitatively the results of experiments for objects that are NOTn Too small: atoms and subatomic particles – Quantum

Mechanicsn Too fast: objects close to the speed of light – Special Relativityn Too dense: black holes, the early Universe – General Relativity

q Classical mechanics concerns the motion of objects that are large relative to atoms and move at speeds much slower than the speed of light (i.e. nearly everything!)

January 22-25, 2013

Introductionq Physics 101 – Course Informationq Brief Introduction to Physicsq Chapter 1 – Measurements (sect. 1-6)

n Measuring thingsn Three basic units: Length, Mass, Timen SI unitsn Unit conversionn Dimension

January 22-25, 2013

Chapter 1 Measurementq To be quantitative in Physics requires measurementsq How tall is Ming Yao? How about

his weight?n Height: 2.29 m (7 ft 6 in)n Weight: 141 kg (310 lb)

q Number + Unit

n “thickness is 10.” has no physical meaningn Both numbers and units necessary for

any meaningful physical quantities

January 22-25, 2013

Type Quantitiesq Many things can be measured: distance, speed,

energy, time, force ……q These are related to one another: speed =

distance / timeq Choose three basic quantities (DIMENSIONS):

n LENGTHn MASSn TIME

q Define other units in terms of these.

January 22-25, 2013

SI Unit for 3 Basic Quantities

q Many possible choices for units of Length, Mass, Time (e.g. Yao is 2.29 m or 7 ft 6 in)

q In 1960, standards bodies control and defineSystème Internationale (SI) unit as,

n LENGTH: Metern MASS: Kilogramn TIME: Second

January 22-25, 2013

Fundamental Quantities and SI UnitsLength meter m

Mass kilogram kg

Time second s

Electric Current ampere A

Thermodynamic Temperature kelvin K

Luminous Intensity candela cd

Amount of Substance mole mol

January 22-25, 2013

Why should we care about units?

q Mars Climate Orbiter:http://mars.jpl.nasa.gov/msp98/orbiter

q SEPTEMBER 23, 1999: Mars Climate Orbiter Believed To Be Lost

q SEPTEMBER 24, 1999: Search For Orbiter Abandonedq SEPTEMBER 30, 1999:Likely Cause Of Orbiter Loss Found

The peer review preliminary findings indicate that one team used English units (e.g., inches, feet and pounds) while the other used metric units for a key spacecraft operation.

The Quick 6: Six Unit Conversion Disasters

qThink you had a bad day at work?

qForgetting to convert units can result in big-time disasters like these six examples.

1.Canyouimaginelosing$125millionthankstoalittlemetricsystemerror? That’sexactlywhathappened in

1999whenNASAlostaMarsorbiterbecauseoneteamusedmetricunitsforacalculationandtheother

teamdidn’t.2.In1983,anAirCanadaplaneranoutoffuelinthemiddleofaflight. Thecause?Notonebut twomistakesinfiguring howmuchfuelwasneeded.ItwasAirCanada’sfirstplanetousemetricmeasurementsandclearlynoteveryonehadthehangofityet.Luckily,noonewaskilledandonlytwopeople receivedminor injuries.That’s

amazingconsidering theflightcrewthought theyhaddouble thefuelthey

actuallyhad.

January 22-25, 2013

SI Length Unit: Meterq French Revolution Definition,

1792q 1 Meter = XY/10,000,000q 1 Meter = about 3.28 ftq 1 km = 1000 m, 1 cm = 1/100

m, 1 mm = 1/1000 mq Current Definition of 1 Meter:

the distance traveled by light in vacuum during a time of 1/299,792,458 second.

January 22-25, 2013

SI Time Unit: Second

q 1 Second is defined in terms of an “atomic clock”– time taken for 9,192,631,770 oscillations of the light emitted by a 133Cs atom.

q Defining units precisely is a science (important, for example, for GPS):n This clock will neither gain nor lose a second in 20 million years.

January 22-25, 2013

SI Mass Unit: Kilogramq 1 Kilogram – the mass of a

specific platinum-iridium alloy kept at International Bureau of Weights and Measures near Paris. (Seeking more accurate measure: http://www.economist.com/news/leaders/21569417-kilogram-it-seems-no-longer-kilogram-paris-worth-mass)

q Copies are kept in many other countries.q Yao Ming is 141 kg, equivalent to

weight of 141 pieces of the alloy cylinder.

January 22-25, 2013

Length, Mass, Time

January 22-25, 2013

Prefixes for SI Units10x Prefix Symbol

x=18 exa E15 peta P12 tera T9 giga G6 mega M3 kilo k2 hecto h1 deca da

q 3,000 m = 3 ´ 1,000 m= 3 ´ 103 m = 3 km

q 1,000,000,000 = 109 = 1Gq 1,000,000 = 106 = 1Mq 1,000 = 103 = 1k

q 141 kg = ? gq 1 GB = ? Byte = ? MB

If you are rusty with scientific notation,see appendix B.1 of the text

January 22-25, 2013

10x Prefix Symbolx=-1 deci d-2 centi c-3 milli m-6 micro µ-9 nano n-12 pico p-15 femto f-18 atto a

Prefixes for SI Unitsq 0.003 s = 3 ´ 0.001 s

= 3 ´ 10-3 s = 3 msq 0.01 = 10-2 = centiq 0.001 = 10-3 = milliq 0.000 001 = 10-6 = microq 0.000 000 001 = 10-9 = nanoq 0.000 000 000 001 = 10-12

= pico = pq 1 nm = ? m = ? cmq 3 cm = ? m = ? mm

January 22-25, 2013

January 22-25, 2013

Derived Quantities and Units

q Multiply and divide units just like numbersq Derived quantities: area, speed, volume, density ……

n Area = Length ´ Length SI unit for area = m2

n Volume = Length ´ Length ´ Length SI unit for volume = m3

n Speed = Length / time SI unit for speed = m/sn Density = Mass / Volume SI unit for density = kg/m3

q In 2008 Olympic Game, Usain Bolt sets world record at 9.69 s in Men’s 100 m Final. What is his average speed ?

m/s 10.32sm

9.69100

s 9.69m 100speed =⋅==

January 22-25, 2013

Other Unit Systemq U.S. customary system: foot, slug, secondq Cgs system: cm, gram, secondq We will use SI units in this course, but it is useful to

know conversions between systems.n 1 mile = 1609 m = 1.609 km 1 ft = 0.3048 m = 30.48 cmn 1 m = 39.37 in. = 3.281 ft 1 in. = 0.0254 m = 2.54 cmn 1 lb = 0.465 kg 1 oz = 28.35 g 1 slug = 14.59 kgn 1 day = 24 hours = 24 * 60 minutes = 24 * 60 * 60 seconds

n More can be found in Appendices A & D in your textbook.

Unit Conversionq Example: Is he speeding ?

n On the garden state parkway of New Jersey, a car is traveling at a speed of 38.0 m/s. Is the driver exceeding the speed limit of 75mi/h?

n Since the speed limit is in miles/hour (mph), we need to convert the units of m/s to mph. Take it in two steps.

n Step 1: Convert m to miles. Since 1 mile = 1609 m, we have two possible conversion factors, 1 mile/1609 m = 6.215x10−4 mile/m, or 1609 m/1 mile = 1609 m/mile. What are the units of these conversion factors?

n Since we want to convert m to mile, we want the m units to cancel => multiply by first factor:

n Step 2: Convert s to hours. Since 1 hr = 3600 s, again we could have 1 hr/3600 s = 2.778x10−4 hr/s, or 3600 s/hr.

n Since we want to convert s to hr, we want the s units to cancel =>2m 1mile 38.0 mile38.0 2.36 10 mile/s

s 1609m 1609 s−⎛ ⎞⎛ ⎞ ⋅ = ⋅ = ×⎜ ⎟⎜ ⎟⎝ ⎠ ⎝ ⎠

2 mile 3600 s38.0 m/s 2.36 10 85.0 mile/hr = 85.0 mphs hr

−= × ⋅ =

UsainBolt setanewworldrecordof9.58seconds inthemen's100matthe2009WorldChampionships inBerlin,aspeedof23.3mph(10.416m/s).

MarkWebber hadthehighestaveragespeedof119.61mphinhisRedBullatF1'sHungarianGrandPrixinJuly.

Mallard,aClassA4steamlocomotive,setthesteamlocomotionlandspeedrecord- 125.88mph- on3July1938.

FredMarriott hasheldthecurrentlandspeedrecordforsteam-poweredvehiclessince1906,whenhereached127.659mphinhisStanleycar.

The BritishSteamCarteam saytheircarhasreached137.14mphintesting,butthisisanunofficialfigure.Theyhopetoreachupto170mphintheirrecord

attempt(indicatedbyyellowbar).British-built ThrustSSC settheworldlandspeedrecordinOctober1997,

reaching763.035mphinadesertintheUSstateofNevada.The speedofsound changesaccordingtofactorsincludingtemperatureand

altitude,butastandardfiguregivenisroughly768mph.

1mph=0.44704m/s

6AnimalsFasterThanUsainBoltIt’swellknownthatJamaicansprinterand100mworldrecordholder, UsainBolt,isthefastesthumanonEarth.Buthowdoeshecomparetohisspeedyanimalcounterparts?Bolt’sworld

recordof9.58secondsforthe100mraceinBerlin2009placeshimatatopspeedof30mphwithanaveragespeed

of23.5mph.However, thesesixanimalslistedfromslowesttofastest,leavehiminthedust,reachingdoubleandeventriplethetopspeedsthatBoltwouldonlydreamofeverachieving.

Whenitcomestospeedefficiency,Boltcouldlearnathingortwofromhis

furry friends.

1. North African Ostrich40 mph

2.Greyhound43mph

3.ThoroughbredRacehorse55mph

4.Pronghorn Antelope55mph

5.Cheetah61mph

OnJune20,2012sheran100min5.95secondswithatopspeedof61mph.That’s

nearly4secondsfasterthanBolt’s100mworldrecordandmorethandoublehistopspeed.

6.PeregrineFalcon161mph

Fasterthanasportscar,thissmallpredatorcanreachuptoatopspeedof161mph.

That’sfivetimesfasterthanBolt’stopspeed.

January 22-25, 2013

q Quantities have dimensions:n Length – L, Mass – M, and Time - T

q Quantities have units: Length – m, Mass – kg, Time – s

q To refer to the dimension of a quantity, use square brackets, e.g. [F] means dimensions of force.

Dimensions, Units and Equations

Quantity Area Volume Speed AccelerationDimension [A] = L2 [V] = L3 [v] = L/T [a] = L/T2

SI Units m2 m3 m/s m/s2

January 22-25, 2013

Dimensional Analysisq Necessary either to derive a math expression, or equation

or to check its correctness.q Quantities can be added/subtracted only if they have the

same dimensions.q The terms of both sides of an equation must have the

same dimensions.

n a, b, and c have units of meters, s = a, what is [s] ?n a, b, and c have units of meters, s = a + b, what is [s] ? n a, b, and c have units of meters, s = (2a + b)b, what is [s] ?n a, b, and c have units of meters, s = (a + b)3/c, what is [s] ?n a, b, and c have units of meters, s = (3a + 4b)1/2/9c2, what is [s] ?

2.3 miles -> cm? 1 mile=5,280 ft , 1ft=12 in , 1 in=2.54

cm

1mile=1609m

January 22-25, 2013

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January 22-25, 2013

Summaryq The three fundamental physical dimensions of

mechanics are length, mass and time, which in the SI system have the units meter (m), kilogram (kg), and second (s), respectively

q The method of dimensional analysis is very powerful in solving physics problems.

q Units in physics equations must always be consistent. Converting units is a matter of multiplying the given quantity by a fraction, with one unit in the numerator and its equivalent in the other units in the denominator, arranged so the unwanted units in the given quantity are cancelled out in favor of the desired units.

Problem 1:

On an interstate highway in a rural region of Wyoming, car is travelling at a speed of 38 ! !. Is this car exceeding the speed limit of

75 !" ℎ? (1!" = 1609.344!)

Ans: (driving with 85 !" ℎ so exceeding)

Problem 2:

A worker is to paint the walls of a square room 8!" high and 12!" along each side. What surface area in square meters must she cover?

(1!" = 30.48!")

Ans: 35.58!!

Problem 3:

The volume of a wallet is 8.5!"!. convert this volume to !!. (1!" = 2.54!")

Ans: (1.39x10!!!!)

Problem 4:

A solid piece of lead has a mass of 23.94! and a volume of 2.1!"!. from these data, calculate the density of lead in SI units (!" !!).

Ans: 1.14x10! !" !!

Problem 5:

A pyramid has a height of 481!" and its base covers an area of 13!"#$%. ıf the volume of a pyramid is given by the expression ! = !!!ℎ, where

! is the area of the base and ℎ is the height, find the volume of this pyramid in cubic meters. (1!"#$ = 43560!"! !"# 1!" = 30!") Ans: 2.57x10!!!

January 22-25, 2013