Question

V. Short answer type questions:-

1. On which factors the force of friction depends?

2. What is self adjusting force ?

3. On what factor does the frictional force of an object in a fluid depends?

4. Why are spaceships provided with heat shield?

VI. Long answer type questions -

1. How you can show that rolling friction is smaller than the sliding friction ?

2. What are the advantages of friction ?

3. What are the ways to reduce friction?
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Answer 1

Answer:

1..Friction depends partly on the smoothness of the contacting surfaces, a greater force being needed to move two surfaces past one another if they are rough than if they are smooth.

2...Static friction is recognised as a self-adjusting force because it wants the objects to remain at rest not move. Hence, if an external force is applied, the static friction force will be equal to the magnitude of the external force, until it surpasses the threshold of motion.

3...Frictional force on an object in a fluid depends on its speed with respect to fluid and on the shape of the object and nature of the fluid.

4..Spaceships are provided with heat shields to protect them during exist and reentry of the earth's atmosphere. If they didn't have these shields the ship would burn up.

long question answer..

1...The force of friction depends on the area of contact between the two surfaces. As the area of contact is less in the case of rolling than in the case of sliding, rolling friction is less than the sliding friction.

2..Advantages of friction:

.Friction enables us to walk freely.

.It helps to support ladder against wall.

.It becomes possible to transfer one form of energy to another.

.Objects can be piled up without slipping.

Breaks of vehicles work due to friction.

3..By polishing the surface, as polishing makes the surface smooth and friction can be reduced. Using lubricants such as oil or grease can reduce the friction between the surfaces. When objects are rolled over the surface, the friction between the rolled object and surface can be reduced by using ball bearings.

Explanation:

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