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.
Ans:
(a) motion
(b) nature
(c) heat.
(d) reduces .
(e) lesser
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
Ans:
The correct answer is (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:
The correct answer is (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:
When the book slides down on the desk, the frictional force acts between the book and the surface of the desk. The direction of the frictional force is opposite to the direction of the motion of the book and acts upward along the surface of the desk.
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?
Ans:
It would become difficult to walk on the floor because the friction between your feet and the ground decreases when soapy water is spilt. Friction provides the grip necessary for walking by resisting the backward push of your feet on the ground. With soapy water, the reduced friction makes it hard to maintain balance and walk properly.
6. Explain why sportsmen use shoes with spikes.
Ans:
Sportsmen use shoes with spikes to increase friction between the shoes and the ground, providing a better grip. This enhanced grip prevents slipping and helps in running and stopping quickly, making their movements more efficient during sports activities.
7. Iqbal has to push aighter 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 will have to apply a larger force because the heavier box presses the floor with greater force, making the interlocking of surface irregularities stronger. As a result, the friction between the box and the floor increases, requiring more force to overcome it compared to the lighter box pushed by Iqbal.
8. Explain why sliding friction is less than static friction.
Ans:
Sliding friction is less than static friction because, during sliding, the irregularities between the two surfaces in contact do not have enough time to interlock completely. In contrast, in static friction, the irregularities are tightly interlocked, requiring more force to overcome.
9. Give examples to show that friction is both a friend and a foe.
Ans:
Advantages of friction (Friend):
a) Friction allows us to walk without slipping.
b) Friction helps us write by providing grip between the pen/pencil and paper.
Disadvantages of friction (Foe):
a) Friction causes wear and tear in tires and shoe soles.
b) Friction generates heat in machine parts, which can lead to damage over time.
10. Explain why objects moving in fluids must have special shapes.
Ans:
Objects moving in fluids experience an opposing force called drag force, which resists their motion. The shape of an object affects the amount of drag force acting on it. By giving the object a streamlined shape, the frictional resistance is reduced, allowing it to move more easily and efficiently through the fluid. This is why airplanes, ships, and fish have streamlined shapes.