CBSE Class 8 Science Friction VBQs

Question. 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
Answer : C

Question. 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
Answer : C

Fill in the blanks.

(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 the static friction.

Question. Give examples to show that friction is both a friend and a foe.
Answer : Advantages of the friction:
a) Due to friction, we are able to walk.
b) We are able to write because of the friction between the tip of the pen and paper.
Disadvantages of friction:
a) Because of friction, the tires and soles of shoes wear out.
b) Friction produces heat between different parts of the machines. This can damage the machines.

Question. 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.
Answer : Frictional force will act upward i.e. direction opposite to that of sliding book.

Question. Explain why sliding friction is less than static friction Answer- A bucket filled with water held above the ground experiences two types of forces:
Answer : When an object has already started moving (sliding), the irregularities on its surface do not get enough time to lock into the irregularities on the surface of the other object completely. Therefore, the sliding friction is less than the static friction.

Question- Explain why sportsmen use shoes with spikes.
Answer : Sportsmen use shoes with spikes because these shoes give them a better grip while running. This is because the force of friction between the shoes and the ground increases with the help of spikes.

Question. 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?
Answer : Seema will have to apply larger force, as heavy box interlock with ground to much extent. So heavy box have large force of friction.

Question. 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?
Answer : It is difficult to walk on a soapy floor because soapy floor applies very less friction and hence we can slip on such floor.

Question- Explain why objects moving in fluids must have special shapes.
Answer : This frictional force by fluid on a moving body in it, depends on the shape of the body. By giving the objects a special shape, the force of friction acting on it can be minimized. Hence, it becomes easier for a body to move through the fluid.