Friction Interview Questions and Answers:

1. Define the term ‘Friction’.
Ans. If two bodies are in contact with one another. The force exerted between them at their point of contact to prevent one body from sliding on the other is called as friction.
2. What are the different types of friction?
Ans.
1. Static friction
2. Dynamic friction
  • Sliding friction
  • Rolling friction
3. Differentiate between static friction and dynamic friction.
Ans.
When two bodies in contact are at rest, then the force of friction between them is called static friction.
When one body moving over another, the force of friction between them is called as dynamic friction.
4. Differentiate between sliding friction and rolling friction.
Ans.
When one body is sliding over the other, the force of friction between them is called as sliding friction.
When one body is rolling over another body, the force of friction between them is called as rolling friction.
5. Distinguish between coefficient of static friction and coefficient of dynamic friction.
Ans.
According to law of friction F = μN
If F is force necessary to start sliding, then, μ is known as the coefficient of static friction.
If F is force necessary to maintain sliding once it has been started, then μ is called as the coefficient of dynamic friction.
6. Define Coefficient of friction.
Ans. It is defined as the ratio of the limiting friction to the normal reaction between the contact surfaces.
7. What do you mean by limiting friction?
Ans. The maximum amount of friction developed is known as the limiting friction.
8. Differentiate between angle of friction and cone of friction.
Ans.
The angle between the normal reaction and the resultant of the normal reaction and the limiting friction is known as angle of friction.
The cone of friction is the right circular cone formed by the resultant R with an apex angle 2θ.
9. Define angle of repose.
Ans. The maximum inclination of the plane at which the body remains in equilibrium under the action of frictional force is called angle of repose.
10. What are Wedges?
Ans. Wedges are small pieces of materials with two of its opposite surfaces not parallel.
11. Define dry friction (or) solid friction (or) Coulomb friction.
Ans. If no lubrication (oil or grease) is used between two surfaces then it is called solid friction.
12. What is impending motion?
Ans. The motion is said to be impending if the applied forces are such that the body is just about to slide.
13. What is fluid friction?
Ans. It is the friction between the adjacent layers of a fluid moving at different velocities.
14. Define ‘ladder’.
Ans. The ladder is defined as a device meant for climbing or scaling on the roofs or walls.
15. When will a block placed on an inclined plane will be in equilibrium?
Ans. The algebric sum of the resolved parts of the forces acting on the body along the supporting plane and perpendicular to the supporting plane is equal to zero. Then the block placed on an inclined plane will be in equilibrium.
16. List out the forces acting on a ladder.
Ans.
  • Self weight of the ladder
  • Normal reaction offered by the floor and wall
  • Friction force offered by the floor and wall.
17. What are the conditions for equilibrium of a ladder?
Ans. The algebric sum of the resolved parts of the forces along horizontal, vertical directions and moments of the forces about any point in their plane should be equal to zero.
18. What are the useful effects of friction?
Ans.
  • Friction is necessary for starting, moving and stopping of vehicles.
  • Motion and power will be transmitted from one pulley to other in belt drives due to friction only.
  • Walking of a man depends on the friction between the shoe and the ground.
19. What are the harmful effects of friction?
Ans.
  • Loss of energy due to friction in bearings.
  • Wear in parts of IC engines due to friction.
20. Mention some of the applications of friction in the engineering field.
Ans.
  • Ladder
  • Wedge
  • Belt drive
  • Power Screws
  • Clutches
  • Brakes
21. Why coefficient of dynamic friction is less than that of static friction?
Ans. The value of limiting friction in dynamic condition is less than that of in static condition, hence the coefficient of dynamic friction is less than that of static friction.