NCERT Solutions for Class 8 Science Science - NCERT Solution Chapter 12

Friction Class 8

Exercise : Solutions of Questions on Page Number : 155

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.

(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.

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

(c) static, sliding, rolling

Friction comes into play when irregularities present in the surfaces of two objects in contact get interlocked with each other. Static friction comes into play when we try to move an object which is at rest. Sliding friction comes into play when an object slides over the surface of another object. In sliding friction, the time given for interlocking is very small. Hence, interlocking is not strong. Therefore, less force is required to overcome this interlocking. Because of this reason, sliding friction is less than static friction. Similarly, the area of contact in case of rolling friction is smallest as compared to static or sliding friction. This area of contact changes gradually because of rolling. Hence, rolling friction is lesser than both static and sliding friction. Thus, the correct sequence is - 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 orderwill 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

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.

Q5 :

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

Q6 :

Explain why sportsmen use shoes with spikes.

Q7 :

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?

Q8 :

Explain why sliding friction is less than static friction.

Q9 :

Give examples to show that friction is both a friend and a foe.