CBSE – 8th Standard Science

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Question Bank – Chapter 12 – Friction

CHAPTER 12 

FRICTION

 

Q1. What is friction?

Ans. Friction is caused by the irregularities on the two surfaces in contact. Friction opposes the relative motion between two surfaces in contact. It acts on both the surfaces

 

Q2. What is rolling friction?

Ans. When one body rolls over the surface of another, the resistance to motion is called the rolling friction.

 

Q3. Is it possible to make friction zero?

Ans. No it’s not possible to make friction zero because smoothest surface also have some irregularity which causes a little friction.

 

Q4. Explain why sportsmen use shoes with spikes.

Ans. Friction can be increased by making spikes on shoes it helps the sportsman to make grip on ground.

 

Q5. On what things Friction depends?

Ans. Friction depends upon speed, nature of material and pressure between the surfaces.

 

Q6. What are lubricants?

Ans. The substances which reduce friction are called lubricants. Example oil, grease, powder and graphite grease or graphite is applied between the moving part of a machine, a thin layer is formed there and moving surfaces do not directly rub against each other.

 

Q7. Explain why the sliding friction is less than the static friction.

Ans. The force required to move an object from rest is static friction this needs       more energy but rolling or sliding is easier thus it has less friction then static friction.

 

Q8. Give examples to show that friction is an evil?

Ans. Friction is sometimes undesirable it causes accidents, heat between machine and loss of energy which makes it evil.

 

Q9. Explain why objects moving in fluids must have special shapes.

Ans. When objects move through fluids, they have to overcome friction acting on them. In this process they lose energy. Efforts are, therefore, made to minimize friction. So, objects are given special shapes to minimize friction.

 

Q10. What is the use of ball bearings in machines?

Ans. Since the rolling friction is smaller than the sliding friction, sliding is

replaced in most machines by rolling by the use of ball bear

 

Try these :-

 

 Give reasons :-

  1. It is difficult to stop a moving boat
  2. Friction is necessary evil
  3. Meteors burn soon after entering earth’s surface
  4. A ball moving on horizontal surface stops moving after sometime

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