# NCERT Solutions for Class 8 Science Chapter 12 Friction

## Exercises

Question:- 1. 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.

Answer:- (a) Friction opposes the motion between the surfaces in contact with each other.

(b) Friction depends on the nature of surfaces.

(c) Friction produces heat.

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

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

Question:- 2. 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

Answer:-  (c) Static, sliding, rolling

Question:- 3. 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

Answer:- (a) Wet marble floor, dry marble floor, newspaper and towel.

Question:- 4. 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.

Answer:-  The frictional force will act upward, means in the opposite direction of the sliding book.

Question:- 5. You spill a bucket of soapy water on a marble floor accidently. Would it make it easier or more difficult for you to walk on the floor? Why?

Answer:-  Friction will decrease because the soapy layer makes the floor smooth. As a result, the floor becomes slippery, and the foot struggles to maintain a proper grip. As a result, walking on a soapy floor is tough. It’s possible that we’ll slip or fall on the floor.

Question:- 6. Explain why sportsmen use shoes with spikes.

Answer:- Spikes Shoes are used by sportsmen to increase the friction between their shoes and the ground. So that  the spiked shoes do not slip while the sportsmen run and play.

Question:- 7. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?

Answer:-  A heavy box produces more friction as it is pressed hard against the opposite surface. So Seema will have to apply a larger force as compared to Iqbaal.

Question:- 8. Explain why the sliding friction is less than the static friction.

Answer:-  The sliding friction is less than static friction Because the sliding item has less time to interlock with the contact points on the floor. So it’s a little easier to move an item that’s already moving than it is to get it started.

Question:- 9. Give examples to show that friction is both a friend and a foe.

Answer:-  Some points are given below which show that friction is both a friend and a foe:

Friction as a friend:

It allows us to grip and catch anything.

It makes it easier for us to walk on the floor comfortably.

It helps with reducing the speed of any moving item or bringing it to stop.

It makes writing easier for us.

Friction as a foe:

It causes wear and tears in items.

It causes damage to the parts of machines and tools.

It slow down the speed of moving objects, so more force is required.

Question:- 10. Explain why objects moving in fluids must have special shapes.

Answer:- To overcome the fluid friction exerted on them, things moving through fluids must have an unique shape. As a result, efforts are made to reduce friction, and items are given unique shapes with sharp fronts and a somewhat larger centre region that tapers at the rear, known as streamlined.