Class 8 Science Chapter 9 Practice Question Answers - Friction

Q1: What is the force of friction?
Ans: The force acting on a moving object equal and opposite to the direction of motion is called force of friction.

Q2: What is the cause of friction?
Ans: The irregularities on the two surfaces in contact is the cause of friction.

Q3: What is the force responsible for wearing out of bicycles tyres?
Ans: Frictional force

Q4: Is the friction same for all objects?
Ans: No

Q5: Why are wheels of vehicles made circular?
Ans: Rolling friction is less than sliding friction.

Q6: What is the direction of force of friction acting on a moving object?
Ans: Opposite to the direction of moving objects.

Q7: Why do pieces of luggage fitted with rollers?
Ans: To reduce friction and to pull them easily.

Q8: Why does a matchstick catch fire when rubbed on the rough surface of the box?
Ans: Due to friction between the stick and rough surface a matchstick catches fire.

Q9: Sliding friction is ___________ than static friction.
Ans: less

Q10: Friction can be reduced by using ___________.
Ans: oil or powder or grease

Q11: Friction can be increased by making surface ___________.
Ans: rough

Q12: Rolling friction is ___________ than sliding and static friction.
Ans: less

Q13: Friction due to fluid is also called ___________.
Ans: drag

Q14: Friction is a
(a) non-contact force
(b) contact force
(c) magnetic force
(d) electrostatic force
Ans: (b)
Explanation: Friction is a contact force that opposes the relative motion or attempted motion between two objects that are in contact with each other. It is caused by the irregularities on the surfaces of the objects coming into contact.

Q15: Which of the following produces least friction?
(a) Sliding friction
(b) Rolling friction
(c) Composite friction
(d) Static friction
Ans: (b)
Explanation: Rolling friction produces the least amount of friction among the options listed. This is because rolling motion involves less direct contact between surfaces compared to sliding friction, making it more efficient and resulting in lower friction.

Q16: Friction always
(a) opposes the motion
(b) helps the motion
(c) both (a) and (b)
(d) none of these
Ans: (a)
Explanation: Friction always opposes the motion or attempted motion between objects. It acts in the direction opposite to the direction of motion, which is why it often requires additional force to keep an object moving.

Q17: Friction can be reduced by using
(a) oil
(b) grease
(c) powder
(d) all of these
Ans: (d) 

Explanation: Friction can be reduced by using various methods, such as applying oil, grease, or powder between surfaces. These substances act as lubricants and help to reduce the direct contact between surfaces, thereby decreasing friction.

Q18: Static friction is less than
(a) sliding friction
(b) rolling friction
(c) both (a) and (b)
(d) none of these
Ans: (a)
Explanation: Static friction is typically greater than sliding friction. Static friction is the force that opposes the initiation of motion when an object is at rest. Once the object starts moving (sliding), the friction that opposes its motion is generally lower, resulting in sliding friction being less than static friction.

Value-Based Question

Q19: On Sunday Razak invited everybody to play carrom in his house. While playing, striker was not moving properly from one place to another. Everybody thought it is their bad luck. But Razia, one of the player, quickly got up and sprinkled some talcum powder on the board.

1. Why Razia sprinkled some talcum powder?
2. Can you give some other example which serve the same purpose?
3. What value of Razia is shown here?

Ans:

1. Razia sprinkled some talcum powder to make the surface of carrom board smooth and hence to reduce friction.
2. Friction can be reduced by using lubricants, ball bearings and painting the rough surface.
3. Razia is an intelligent girl with scientific aptitude.

Q20: Ram and Shyam while returning from school saw a labour pushing hard to move a heavy box. Ram immediately ran to him and started helping him in pushing the box whereas Shyam brought two iron bars and asked the labour to put them below the box and then to push the box.

1. What are the factors that affect friction?
2. Who will help the labour more-Ram or Shyam? How?
3. What values of Ram and Shyam are shown here?

Ans:

1. Nature of surfaces in contact, weight of the object, force of adhesion and deformation.
2. Shyam’s suggestion of keeping iron bar below the box will help the labour more. Putting the iron bar below the box will make it to roll over the bar. As rolling friction is less than sliding friction, it will help in moving the box with much easier.
3. Ram and Shyam are helping in nature. Shyam is intelligent with scientific aptitude.