(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 carom board ____ friction.
(e) Sliding friction is ______ than the static friction.
(a) Friction opposes the interlocking between the surfaces in contact with each other.
(b) Friction depends on the irregularities of surfaces.
(c) Friction produces force.
(d) Sprinkling of powder on the carom board reduces friction.
(e) Sliding friction is less than the static friction.
(2) Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below.
(a) rolling, static, sliding
(b) rolling, sliding, static
(c) static, sliding, rolling
(d) sliding, static, rolling
Ans-(c) static, sliding, rolling
(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.
Ans-(a) wet marble floor, dry marble floor, newspaper and towel.
(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.
Ans- The direction of frictional force on book is opposite to the direction of motion because force of friction opposes the motion.
(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?
Ans- If I spill a bucket of soapy water on a marble floor accidently it would be very difficult walk on the floor. Because interlocking between soapy water and my feet will be very less. Therefore, I have to put very little force to overcome interlocking.
(6) Explain why sportsmen use shoes with spikes.
Ans- Shoes with spike create strong interlocking between shoes and ground. Players needs more force of friction to overcome this interlocking. Therefore, players do not sleep on the ground with shoes with spikes.
(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?
Ans- Seema has to apply a larger force because the box which she is pushing is heavier. Therefore, interlocking of the box and floor will be very stronger than Iqbal’s box.
(8) Explain why sliding friction is less than static friction.
Ans- The contact points of both surfaces do not get time to lock in sliding friction. Therefore, less force of friction has to apply on the surface to overcome interlocking in sliding friction. While in static friction, the contact points of both surfaces get time to lock in static friction. Therefore, large force of friction has to apply on the surface to overcome interlocking in static friction. Thus, sliding friction is less than static friction.
(9) Give examples to show that friction is both a friend and foe.
Friction as a friend –
(i) Glass tumbler can be hold only because of friction.
(ii) An object can be stop from its moving stage because of friction.
(iii) Fixing a nail and tying a knot can be only possible only by friction.
(iv) Friction produces heat. Our palms feel warm when we rub them together.
Friction as a foe-
(i)Friction wears out the material.
Eg:- Ball bearings of wheels are wear out because of friction. Ball bearings have to move against friction which causes wear in ball bearings.
(ii) Friction opposes movement.
Eg:- It stops ball, bicycle or any other objects which is in motion.
(10) Explain why objects moving in fluids must have special shapes.
Ans- The transport mode of fluids designed to reduce friction between them and fluid which causes less energy consumption. Their design must have inspired by the natural things as birds and fishes. They have shapes which would make them lose less energy in overcoming friction.