Friction Basic | Theory of machine Interview Question and Answers

Friction Basic | Theory of machine Interview , viva ,oral Question and Answers

1 .What is meant by slope of a thread?

It is the inclination of the thread with horizontal.
Slope of thread = tan-1 [Lead screw/Circumference of screw]

2. What are the effects of limiting angle of friction?

1. If limiting angle of friction (φ) is equal to tan-1 µ,then the body will move over the plane
irrespective of the magnitude of the force (F) (Limiting force of friction).
2. If φ< tan-1 µ, then no motion of body on plane is possible irrespective of how large the magnitude of F may be.

3. Define co-efficient of friction (µ).

It is defined as the ratio of the limiting friction (F) to the normal reaction (RN) between the two bodies.
µ = Limiting force of friction/Normal reaction = F/RN

4. Differentiate coefficient of friction in square thread and V-thread.

(a) In square thread, µ = F/RN
(b) In V thread, µ1 = µ/cos β
Where F = Limiting force of friction,
RN = Normal reaction, and
2β = Angle of ‘V’ in a ‘V’ thread.

5. What is the efficiency of inclined plane?

The efficiency of an inclined plane is defined as the ratio between effort without friction (P0) and the effort with friction (P).

6. Why self- locking screws have lesser efficiency?

Self locking needs some friction on the thread surface of the screw and nut hence it needs higher effort to lift a body and hence automatically the efficiency decreases.

7. What are the functions of clutches?

1. It supplies power to the transmission system.
2. It stops the vehicle by disconnecting the engine from transmission system.
3. It is used to change the gear and idling the engine.
4. It gives gradual increment of speed to the wheels.

8. What is the difference between cone clutch and centrifugal clutch?

Cone clutch works on the principle of friction alone. But centrifugal clutch uses principle of centrifugal force in addition with it.

9. Why friction is called as ‘necessary evil’?

Friction is the important factor in engineering and physical applications such as belt and ropes, jibs, clutches and brakes, nut and bolts, so it is the necessary one. If the friction exceeds certain value it will cause heat, damage and wear when applied. So it is called ‘necessary evil’.

10. What are the belt materials?

1. Leather,
2. Cotton or fabric,
3. Rubber,
4. Balata, and
5. Nylon.

11. State the law of belting?

Law of belting states that the centre line of the belt as it approaches the pulley must lie in a plane perpendicular to the axis of the pulley or must lie in the plane of the pulley, otherwise the belt will runoff the pulley.

12. What you meant by ‘Crowing in pulley”?

The process of increasing the frictional resistance on the pulley surface is known as crowning. It is done in order to avoid slipping of the belt.

13. What is meant by initial tension in belts?

In order to increase the frictional grip between the belt and pulleys, the belts is tightened up. Due to this the belt gets subjected to some tension even when the pulleys are stationary. This tension in the belts is called initial tension (T0).

14. List out the commonly used breaks.

1. Hydraulic brakes: e.g., Pumps or hydrodynamic brake and fluid agitator.
2. Electric brakes: e.g., Eddy current brakes.
3. Mechanical brakes: e.g., Radial brakes and axial brakes

15. What do you mean by a brake?

Brake is a device by means of which motion of a body is retarded for slowing down (or) to bring it to rest which works on the principle of frictional force, it acts against the driving force.

16. Explain velocity ratio.

It is defined as the ratio between velocity of the driver and the follower (or) driven.

17. State the law of belting?

18. What is the centrifugal effect on belts?

During operation, as the belt passes over a pulley the centrifugal effect due to its weight tends to lift the belt from the pulley surface. This reduces the normal reaction and hence the frictional resistance. The centrifugal force produces additional tension in the belt.

19. Write down the disadvantage of V-belt drive over flat belt?

1. V belt cannot be used in large distance.
2. It is not as durable as flat belt.
3. Since the V belt subjected to certain amount of creep therefore it is not suitable for constant speed applications such as synchronous machines, and timing devices.
4. It is a costlier system.

20. When is the cross belt used instead of open belt?

1. Cross belt is used where the direction of rotation of driven pulley is opposite to driving pulley.
2. Where we need more power transmission there we can use cross belt drive.

21. Why lubrication reduces friction?

In practical all the manting surfaces are having roughness with it. It causes friction. If the surfaces are smooth then friction is very less. Lubrication smoothens the manting surface by introducing oil film between it. The fluids are having high smoothness then solids and thus lubrication reduces friction.

22. What you meant by ‘crowning in pulley’?

The process of increasing the frictional resistance on the pulley surface is known as crowning. It is done in order to avoid slipping of the belt.

23. What is meant by initial tension in belts?

In order to increase the frictional grip between the belt and pulleys, the belt is tightened up. Due to this belt gets subjected to some tension even when the pulleys are stationary. This tension in the belt is called initial tension (T0) .

24. Where does the P.I.V. drive system used?

P.I.V. (Positive Infinitely variable) drive is used in an infinitely varying speed system.

25. When the intensity of pressure acting brake shoe is is assumed to uniform?

The intensity of pressure is assumed to be constant when the break shoe has small angle of contact. For large angle of contact, it is assumed that the rate of wear of the shoe remains constant.