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Answer :

When a body moves through a fluid, it experiences an opposing force which opposes the relative motion of the body through the fluid.

The opposing force is known as the drag force which is a result of friction between the surface of the body and the fluid.

This frictional force depends on the shape of the body. Objects with a special shape can minimize the effect of frictional force, thus making it more easier for movement of the body through the fluid.

- Q.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) The sprinkling of powder on the carrom board _______ friction. (e) Sliding friction is _______ than the static friction.
- Q.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
- Q.3 Alida runs her toy car on a 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.
- Q.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.
- Q.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?
- Q.6 Explain why sportsmen use shoes with spikes.
- Q.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?
- Q.8 Explain why sliding friction is less than static friction.
- Q.9 Give examples to show that friction is both a friend and a foe.

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