# Friction

### Question:

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, nterlocking 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 isâ€”static, sliding, rolling.

### Friction

#### Q 1.

static, sliding, rolling

#### Q 2.

wet marble floor, dry marble floor, newspaper and towel

#### Q 3.

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.

#### Q 4.

Explain why sliding friction is less than static friction.

#### Q 5.

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?

#### Q 6.

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

#### Q 7.

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?

#### Q 8.

Explain why objects moving in fluids must have special shapes.

#### Q 9.

Explain why sportsmen use shoes with spikes.