Lesson: Friction

# 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.

## Solution:

(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

c

# 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.

a

# 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.

## Solution:

The direction of frictional force will be upwards acting opposite to the movement of the book.

# Question: 5

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?

## Solution:

If a bucket of soapy water is spilled on a marble floor, then it would make it more difficult for us to walk on a soapy floor because the layer of soap will make the floor smooth. The coating of soapy water will reduce friction between the floor and our feet, and our feet will not be able to get a proper grip on the floor, thus increasing chances of slipping and falling.

# Question: 6

Explain why sportsmen use shoes with spikes.

## Solution:

Sportsmen use shoes with spikes to increase the friction. Due to spikes in shoes, sportsmen do not slip while they run or 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?

## Solution:

Seema will have to apply larger force because the heavy object will produce greater friction against the floor.

# Question: 8

Explain why sliding friction is less than static friction.

## Solution:

Sliding friction is always less than static friction. Friction comes into picture when irregularities on the surfaces of two objects get interlocked with each other. Two sliding objects find less time to get interlocked against each other’s surface irregularities. As a result, they experience less friction.

# Question: 9

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

## Solution:

Friction as friend:

·         Due to friction, we are able to walk on a surface.

·         Due to friction between a pencil’s tip and a paper, we are able to write.

Friction as foe:

·         Due to the friction, tyres wear out.

·         Engines of automobiles consume more fuel due to the friction between different parts of the engines.

# Question: 10

Explain why objects moving in fluids must have special shapes.

## Solution:

Any moving body in fluid experiences a force, which tries to oppose its motion that is known as drag or frictional force. This force depends on the shape of the body. Due to special shapes of objects, the force of friction can be minimised. Hence, it becomes easier for the body to move through fluids.