Learn Class 8 Science - Friction

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What is Friction? And what are the various factors which affect it? Are you curious to know more about things in detail?

About Friction

  • The friction force is also known as an external force.
  • It is the force that opposes relative motion.
  • LIKE: oppose between two surfaces.
  • Act only when it comes in touch with the bodies.

Types of Friction

Sliding Friction:

  • One which opposes the slide motion.
  • More minor as compared to static friction.

Static Friction:

  • The friction which is in 'rest.'
  • Force: 'Always equal & opposite to applied force.'

Rolling Friction:

  • Friction is present in two forces.
  • Smaller than sliding friction.

Effects of Friction

Friction:

  • It helps in the generation of heat.
  • It is always in motion.
  • Friction does wear and tear in tires.

Factors affecting Friction:

  • Nature of surface.
  • Polishing surfaces.
  • Normal reaction force.
  • Kinetic friction.
  • Spring balance.

These are factors that affect the frictional force. So make sure to keep all of the things in safe mode.

Pros:

  • The friction helps us to write on paper.
  • The friction helps to move on a road. I.e., friction between two surfaces.
  • Offer resistance to the actual motion.

Cons:

  • Wastage of energy.
  • The speed of the items becomes low.

Friction Sample Questions for Class 8

Question 1

In which of the following cases more friction is desirable?
A. movement of piston in a cylinder
B. braking of a vehicle
C. running on a track
D. all of these

Question 2

Smoother the surface,
A. Lesser is the friction it exerts on a given body in contact
B. More is the friction it exerts on a given body in contact
C. Sometimes less and sometimes more force depending on area of the body in contact
D. All of these

Question 3

A force of 5 N is required to move an object from rest. The value of static friction (f) is:
A. 5N
B. f >5N
C. f < 5N
D. 10 N

Question 4

Powder is used in carrom board for:
A. increasing friction
B. decreasing friction
C. Decoration
D. Fragrance

Question 5

A cube was placed on a ramp as shown in the picture. The box remains on the ramp and does not slide down. This is because ______.
A. The box is too heavy to slide down
B. The box does not have enough energy to slide down the ramp
C. The force of gravity cannot act on the box while it stands at the top of the ramp
D. The pull of gravity cannot overcome the force of friction acting between the box and the ramp.