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 1.
(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 lesser than static friction.
Question 2. Four children were asked to arrange forces due to rolling, static and sliding frictions in 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
Solution 2.
(c) static, sliding, rolling
Question 3. Alida runs her toy car on the dry marble floor, wet marble floor, and 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
Solution 3.
(a) wet marble floor, dry marble floor, newspaper and towel.
Question 4. Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of the frictional force acting on it.
Solution 4. If the writing desk is tilted a little. A book kept on it starts sliding down and the frictional force will act against the sliding motion 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 5. If we spill a bucket of soapy water on a marble floor accidentally then It would be very difficult to walk on the floor because there will be no friction force between the ground and our feet. The frictional force allows us to walk on any ground acting against the direction of our feet and pushing us forward. Hence, if there will be no friction force it will become very difficult to walk on the soapy floor.
Question 6. Explain why sportsmen use shoes with spikes.
Solution 6. Shoes with spikes give the sportsman a better grip while running because of the friction force that acts between the ground and the shoes. That is why sportsmen use shoes with spikes.
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 7. Seema has to apply a larger force than Iqbal because the surface of the heavier box is strongly interlocked with the surface of the table. Hence, more force is required to overcome the interlocking of the heavier box.
Question 8. Explain why sliding friction is less than static friction.
Solution 8. The interlocking between the two surfaces creates the friction force stronger the interlocking more will be the frictional force. The time when this interlocking is very small, sliding friction comes into play. That is why sliding friction is less than static friction.
Question 9. Give examples to show that friction is both a friend and a foe.
Solution 9.
Advantages of friction
a) We are able to walk because of friction.
b) We are able to write because of friction.
Disadvantages of friction
a) The tires and soles of shoes wear out because of friction.
b) Machines get damaged because the heat produced by the friction produces heat between different parts of the machines.
Question 10. Explain why objects moving in fluids must have special shapes.
Solution 10. An object moving in fluids must have special shapes to minimize the force of friction. The opposing force or the drag force acts upon the moving body in the fluid and hence the objects are given special shapes so that it can become easier to move through the fluid.