CBSE NCERT Solutions for Class 8 Science Chapter 12

If a student has trouble understanding a topic related to science, the student can go through questions and answers related to each topic covered in NCERT solutions of Class 8 science book.

CBSE NCERT Solutions for Class 8 Science Chapter 12:

Question-1:

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

Solution:

(c) static, sliding, rolling

Question-2:

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

Solution:

(a) wet marble floor, dry marble floor, newspaper and towel.

Question-3:

Give examples to show that friction is both a friend and a foe.

Solution:

Friction as friend:
→ We are able to walk because of friction.
→ Friction between the tip of the pen and a paper allows us to write.
Friction as foe:
→ Tyres and soles of shoes wear out because of friction.
→ Friction between the different parts of machines produces heat. This can damage the machines.

Question-4:

Explain why objects moving in fluids must have special shapes.

Solution:

When a body moves through a fluid, it experiences an opposing force which tries to
oppose its motion through the fluid. This opposing force is known as the drag force. This frictional force depends on the shape of the body. By giving objects a special shape, the force of friction acting on it can be minimized. Hence, it becomes easier for the body to move through the fluid.