VIVA VOICE- ENGINEERING MECHANICS

EXPERIMENT NO.-1Exp no 1.-To verify the law of force polygon

Q1) what is parallelogram law of forces?

ANS- If two vectors acting simultaneously on a particle are represented in magnitude and direction by the two adjacent sides of a parallelogram drawn from a point, then their resultant is completely represented in magnitude and direction by the diagonal of that parallelogram drawn from that point.

Q2) Explain triangle law of forces?

ANS-Triangle law of forces states that, If two forces acting at a point are represented in magnitude and direction by the two adjacent sides of a triangle taken in order, then the closing side of the triangle taken in the reversed order represents the resultant of the forces in magnitude and direction.

Q3) what are the condition for equilibrium of a body under variousconcurrent and non concurrent forces ?

ANS- Condition for equilibrium of a body under various concurrent and non-concurrent forces :-

Q4) what do you mean by concurrent forces?

ANS- In physics, concurrent forces are defined as forces that pass through a common point. In other words, a concurrent force system is a set of two or more forces whose lines of action intersect at a point.

EXPERIMENT N0.-2

Exp no. 2- To verify the law of moments using parallel force apparatus.

Q1) What are the reasons for the deviation in theotretical value and experimental value?

ANS- Zero error of the compression balances must be check.

Weights should not be put on the beam with a jerk which may cause error in the readings

Q2) why in general beam is supported by one hinge and one roller supports?

ANS-This beam representation covers both the above disadvantages i.e.it provides room for thermal expansion as well as it constraints the beam in horizontal direction at one side to handle the inclined load.

Q3) Define various types of supports and which type of support is used in this experiment?

ANS-Various types of supports and reactions developed are listed below: Simple Support: If the beam rests simply on a support it is

called a simple support. In such case the reaction at the support is at right angles to the support and the beam is free to move in the direction of its axis and also it is free to rotate about the support .

Roller Support: In this case, beam end is supported on rollers. In such cases, reaction is normal to the support since rollers can be treated as frictionless. Many mechanical components are having roller supports which roll between guides. In such cases, reaction will be normal to the guides, in both the direction . At roller support beam is free to move along the support. It can rotate about the support also.

Hinged Support: At a hinged end, a beam cannot move in any direction. However, it can rotate about the support . Hence the support will not develop any resisting moment, but it can develop reaction in any direction to keep the end stationary. The reaction R can be split into itshorizontal and vertical components for the purpose of analysis.

Fixed Support: At such supports, the beam end is not free to translate or rotate. Translation is prevented by developing support reaction in any required direction.

Q4) Sketch various types of beams sections.

ANS-Simply Supported Beam: When both end of a beam aresimply supported it is called simply supported beam . Such a beam cansupport load in the direction normal to its axis.

Beam with One End Hinged and the Other onRollers: If one end of a beam is hinged and other end is onrollers, the beam can resist load in any direction (see Fig.9.6).

Over-hanging Beam: If a beam is projecting beyondthe support. It is called an over-hanging beam (Fig. 9.7). The overhang may be only on one side as in Fig. 9.7(a) or maybe on both sides as in Fig. 9.7(b).

Cantilever Beam: If a beam is fixed at one end andis free at the other end, it is called cantilever beam (Fig. 9.8).

Propped Cantilever: It is a beam with one end fixed and the other end simply supported (Fig. 9.9).

Both Ends Hinged: In these beams both ends will be having hinged supports (Fig. 9.10).

Continuous Beam: A beam is said to be continuous, if

it is supported at more than two points (Fig. 9.11).

EXPERIMNET NO.-3

Exp no. 3- . To determine the co-efficient of friction between wood and various surface (like Leather, Wood, Aluminum) on an inclined plane.

Q1) what is limiting friction?

ANS- The maximum value of frictional force, which comes into play when the motion is impending is known as Limiting Friction.

Q2) Define angle of repose, angle of friction and laws of friction?

ANS- AN G L E O F R EPOS E -

The angle of repose is the maximum angle that a surface can be tilted from the horizontal, such that an object on it is just able to stay on the surface without it sliding down.

EXPRESSION FOR ANGLE OF REPOSE:-

AN G L E O F FRI C T ION-

Angle of friction is defined as the angle made between the normal reaction force and the resultant force of normal reaction force and friction. Let us first explore this definition and attempt to express the angle of friction in terms of a formula. Angle of repose has same value as angle of friction.

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LAWS OF FRICTI ON-

(i) The frictional force always acts in a direction opposite to that in which the body tends to move.

(ii) Till the limiting value is reached, the magnitude of frictional force is exactly equal to the tangential force which tends to move the body.

(iii) The magnitude of the limiting friction bears a constant ratio to the normal reaction between the two contacting surfaces.

(iv) The force of friction depends upon the roughness/smoothness of the surfaces.

(v) The force of friction is independent of the area of contact between the two surfaces.

(vi) After the body starts moving, the dynamic friction comes into play, the magnitude of which is less than that of limiting friction and it bears a constant ratio to the normal force. This ratio is called coefficient of dynamic friction.

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Q3) define cone of friction.

ANS- This inverted cone with semicentral angle, equal to limiting frictional angle , is called cone of friction.

Q4) Differentiate between static and dyanamic friction.

ANS- when the applied tangential force is less than the limiting friction, the body remains at rest and such friction is called Static Friction, which will have any value between zero and limiting friction. If the value of applied tangential force exceeds the limiting friction, the body starts moving over another body and the frictional resistance experienced while

(iii) The magnitude of the limiting friction bears a constant ratio tothe normal reaction between the two contacting surfaces.

(iv) The force of friction depends upon the roughness/smoothness of the surfaces.

(v) The force of friction is independent of the area of contactbetween the two surfaces.

(vi) After the body starts moving, the dynamic friction comes into play, the magnitude of which is less than that of limiting friction and it bears a constant ratio to the normal force. This ratio is called coefficient of dynamic friction.

Q6)does force of friction depends on area of contact surfaces?

ANS- The force of friction is independent of the area of contact between the two surfaces.

EXPERIMNET NO.-4

AIM- To find the forces in the members of Jib Crane.

Q1) Define the principle on which this experiment is based.

ANS- The principle on which this experiment is based is triangle law of forces.

Q2) Explain the practical use of this experiment.

ANS- the practical use of this experiment is in JIB crane which are used in construction.

Q3)define triangle law of forces.

ANS) Triangle law of forces states that, If two forces acting at a point are represented in magnitude and direction by the two adjacent sidesof a triangle taken in order, then the closing side of the triangle taken in the reversed order represents the resultant of the forces in magnitude and direction.

Q4)If three co planar, collinear and like forces act on a body will it bestable.

ANS- NO, it will depend upon the resulting vector,

EXPERIMENT NO. -5

AIM- To determine the mechanical advantage, Velocity ratio

and efficiency of a screw jack.

Q1)List the practical application of this experiment?

ANS- A jackscrew is a type of jack that is operated by turning a leadscrew. In the form of a screw jack it is commonly used to lift moderately heavy weights, such as vehicles. More commonly it is used as an adjustable support for heavy loads, such as the foundations of houses, or large vehicles.

Q2)Define machine, mechanical advantage, velocity ratio and efficiency?

ANS- M A C HIN E -

A machine is a thing that is created by human to make work easier. Some machines have many parts that move. Examplesare bicycles and clocks.Some machines do not have parts that move. Examples are computers and telephones.Often a machine will change one form of energy to another form of energy. Simple machines increase or change the direction of a force.M E C H A NI C A L A D V A N T A G E - Mechanical advantage is defined as the ratio of load lifted to the effort applied to lift the weight.V E L O C I TY R A TI O - Velocity ratio is the ratio of distance moved by the effort and distance moved by the load.EFFCIE N C Y - The efficiency of a machine defined as the ratio of useful work done by the machine to the actual work put into the machine.

Q3)What is self locking and state its mathematical condition.

ANS- An advantage of jackscrews over some other types of jack is that they are self-locking, which means when the rotational force on the screw is removed, it will remain motionless where it was left and will

not rotate backwards, regardless of how much load it is supporting. Thismakes them inherently safer than hydraulic jacks, for example, which will move backwards under load if the force on the hydraulic actuator is accidentally released.

Mathematical condition-

Where, P= effort applied

D= distance moved by effort

d= distance moved by load

w=load lifted

EXP 6

To determine the mechanical advantage, Velocity ratio and Mechanical e ciency of the Wheel and Axle

1) Where is the ywheel most commonly used? And what areits primary uses?

Ans- Common uses of a ywheel include:• Providing continuous energy when the energy source is discontinuous. For example, flywheels are used in reciprocating enginesbecause the energy source, torque from the engine, is intermittent.

• Delivering energy at rates beyond the ability of a continuous energy source. This is achieved by collecting energy in the flywheel over time and then releasing the energy quickly, at rates that exceed the abilities of the energy source.

• Controlling the orientation of a mechanical system. In suchapplications, the angular momentum of a flywheel is purposely transferred as a torque to the attaching mechanical system when energy is transferred to or from the flywheel, therebycausing the attaching system to rotate into some desired positio Primary use of a flywheel releases stored energy by applying torque to a mechanical load, thereby decreasing the flywheel's rotational speed.

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EXP 6

To determine the mechanical advantage, Velocity ratio and Mechanical e ciency of the Wheel and Axle

2) De ne moment of inertia?

Ans- A quantity expressing a body's tendency to resist angular acceleration, which is the sum of the products of the mass of each particle in the body with the square of its distance from the axis of rotation.

3) Whatis the formula for moment of inertia for hollow circular lamina about its centroidal axis?

Ans- I= ½ m(r12+r 2)

EXP 7 To determine the MA, VR, n of Worm Wheel

1) De ne mechanical advantage and velocity ratio?

Ans- The ratio of the force produced by a machine to the force applied to it, used in assessing the performance of a machine is called mechanical advantage.

Velocity ratio is also de ned as the ratio of a distance through which any part of a machine moves, to that which the driving part moves during the same time. An object has a mechanical advantage if it exerts a force higher than the velocity ratio.

2) For what purpose worm and worm wheel is used? Ans. Worm Gears – Applications & Uses. A worm gear(orworm drive) is a speci c gear composition in which a screw (worm) meshes with a gear/wheel similar to a spur gear. The set-up allows the user to determine rotational speed and also allows for higher torque to be transmitted.

EXP 7 To determine the MA, VR, n of Worm Wheel

Applications of Worm GearsTuning Instruments Elevators/Lifts Torsen Di erentialsGates and Conveyor Belts

3) On what principle worm and worm wheel apparatus works?

Ans- An electric motor or engine applies rotational power via tothe worm. The worm rotates against the wheel, and the screw face pushes on the teeth of the wheel. The wheel is pushed against the load.

EXP 8 Veri cation of force transmitted by members ofgiven truss.

1) What is the condition for perfect frame?

Ans- Necessary and su cient condition of a perfect frame is thatit should retain its shape when load is applied at any joint in any direction

2) What is a framed structure ?Ans- Frame structures are the structures having the combination of beam, column and slab to resist the lateral and gravity loads.

3)What is a truss?

Ans- A framework, typically consisting of rafters, posts, and struts, supporting a roof, bridge, or other structure.

3) Di erentiate between perfect and imperfect truss?

Ans- Perfect truss=structure made of su cient members just to keep it in equilibrium position when loaded without any change of shape.

EXP 8 Veri cation of force transmitted by members ofgiven truss.

N=2j-3 n= no. of members , j= no. of jointsImperfect truss= structure made of members more or lesserthan the minimum no. necessary to keep it in equilibrium, when loaded.

n≠2j-3n>2j-3 redundant n<2j-3 de cient

4) What do you understand by space truss and plane truss?Ans- A space truss is a combination of prefabricated tetrahedral, octahedral or skeleton pyramids or inverted pyramids having triangular, square or hexagonal basis with top and bottom members normally not lying in the same vertical plane.

Planar trusses: A Truss is a structure composed of slender members (two-force members) joined together at their end points.Joints are modeled by smooth pin connections.

Members are either under tension or compression.

EXP 9 To verify the law of moments using Bell cranklever

1) De ne moment of force?

Ans- MOMENT OF A FORCE1. of a point : the product of the distance from the point tothe point of application of the force and the component of the force perpendicular to the line of the distance2. of a line : the product of the perpendicular distance from the axis to the point of application of the force and the component of the force perpendicular to the line of the distance and in a plane perpendicular to the axis

2) Discuss varignon’s theorem?Ans- The theorem states that the moment of a resultant of two concurrent forces about any point is equal to the algebraic sum of the moments of its components about the same point. In other words, "If many coplanar forces are acting on a body, then the algebraic sum of moments of all the forces about a point in the plane of the forces is equal to the moment of their resultant about the same point.

EXP 9 To verify the law of moments using Bell cranklever

3) What do you mean by principle of moment?

Ans- The principle of moments states that when in equilibrium the total sum of the anti clockwise momentis equal to the total sum of the clockwise moment. When a system is stable or balance it is said to be in equilibrium as all the forces acting on the system cancel each other out.