Q1: Fill in the blanks:

(a) Friction opposes the ………. between the surfaces in contact with each other.

(b) Friction depends on the ………. of surfaces.

(c) Friction produces ………. .

(d) Sprinkling of powder on the carrom board ………. friction.

(e) Sliding friction is ………. than the static friction.

Ans.

(a) relative motion

(b) smoothness (or irregularities or nature)

(c) heat

(d) reduces

(e) smaller.

Q2: Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement.

(a) rolling, static, sliding

(b) rolling, sliding, static

(c) static, sliding, rolling

(d) sliding, static, rolling

Ans. (c) static, sliding, rolling.

Q3: Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be

(a) wet marble floor, dry marble floor, newspaper and towel.

(b) newspaper, towel, dry marble floor, wet marble floor.

(c) towel, newspaper, dry marble floor, wet marble floor.

(d) wet marble floor, dry marble floor, towel, newspaper.

Ans. (a) wet marble floor, dry marble floor, newspaper and towel.

Q4: Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.

Ans. Frictional force will act upward i.e., direction opposite to that of sliding book.

Q5: Explain why sportsmen use shoes with spikes.

Ans. It is done to provide the shoes better grip on the ground.

Q6: Name the force responsible for wearing out of bicycle tyres.

 Ans. Frictional force.

Q7: Answer the following

(a) A ball is rolling on a road towards the north. What will be the direction of the frictional force acting on it?

(b) If the direction of movement in the above case is changed to the south by applying force, then what will be the direction of the frictional force?

Ans.

(a) South

(b) North.

Q8: What is the cause of friction?

Ans. The cause of friction is the irregularities on the two surfaces in contact.

Q9: On which kind of surface the friction will be greater (i) smooth surface (ii) rough surface.

Ans. Friction will be greater in case of a rough surface.

Q10: Does the use of ball bearing reduce or increase friction?

Ans. Use of ball bearing reduces the friction.

Q11: Why do we sprinkle fine powder on the carrom board?

Ans. We want to reduce friction in order to increase efficiency.

Q12: What are lubricants?

Ans. The substances which reduce friction are called lubricants.

Q13: What is drag?

Ans. The frictional force exerted by fluids is also called drag.

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