Question 1. 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 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
Question 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
Question 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.
Answer- Frictional force will act upward i.e. direction opposite to that of sliding book.
Question 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?
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 6- 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 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?
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 8. 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 9. Give examples to show that friction is both a friend and a foe.
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 10- 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.
ONE MARK MCQs
1. Why is it difficult to walk on a smooth and wet floor?
A. Due to more friction
B. Due to very less friction (✓)
C. Due to gravity D. None
2. Frictional Force always acts in _________ direction?
B. Direction of motion of object
D. Direction opposite to the motion of the object (✓)
3. Spring Balance is used to measure________?
A. Direction of the force B. Density
C. Force of gravity acting on a body (✓)
4. Frictional Force Depends on ________.
A. Speed of the object
B. Smoothness of the surface
C. Roughness of the surface
D. B and C both (✓)
5. Frictional Force is produced because of _________?
A. Irregularities in two contacting surfaces. (✓)
B. To stop moving object
C. To make an object move easily
6. Why grooves are made in tyres?
A. To reduce friction
B. To increase friction. (✓)
C. To make the tyres look beautiful
D. To reduce consumption of fuel.
7. Why rolling friction is less than the sliding friction?
A. Direction of frictional force changes
B. Moving object becomes lighter
C. Because it is easier for a body to roll over another in comparison to slide (✓)
D. All of above.
8. Name the system which converts sliding friction to rolling friction?
A. Ball bearing (✓)
9. Friction produces ________
D. Heat (✓)
10. Why talcum powder is spread on the carrom board?
A. To reduce friction
B. To make the surface of carrom board smooth
C. To make the carrom coins (goti) move longer distance
D. All of the above. (✓)
11. What are factors responsible for friction?
A. Nature of surface in contact
B. Area of contact
C. The force with which both surfaces are pressed
D. All (✓)
12. Friction is not useful for us, why?
A. It causes wear and tear
B. Loss of energy
C. The heat produced during friction destroys the machine
D. All (✓)
13. Why the shapes of objects moving in fluids (air and water) are streamlined?
A. To reduce the friction (✓)
B. To increase the friction.
C. To make it look beautiful
14. _______ is used to reduce the friction in moving parts of the machines
A. Oil or grease (✓)
15. What are the factors on which the friction produced in fluids depends?
A. Nature of object
B. Shape of the object (✓)
16. Friction is useful for us, how?
A. It helps us in walking
B. To apply brakes
C. To run machines and motors
D. All (✓)
17. Four students were asked to arrange the forces due to static friction, rolling friction and sliding friction in decreasing order?
A. Rolling, sliding, static
B. Rolling, Static, sliding
C. Static, sliding, rolling (✓)
D. Sliding, static, rolling
18. It is difficult to walk on ice because of less _________?
A. Gravitational force
B. Frictional force (✓)
C. Weight of ice D. None
19. Why tyres are made circular?
A. Because rolling friction is less than sliding friction (✓)
B. To look beautiful
C. Because rolling friction is more than sliding friction
20. Soles of our shoes wear out because of ________?
B. Slow moving
C. Friction (✓)
Please refer to attached file for CBSE Class 8 Science Friction Worksheet Set B