Question

Friction can be reduced by

• A. the use of lubricants.
• B. polishing surfaces.
• C. by increasing the height.
• D. Both (A) and (B).

Answer 1

The correct option is D

Both (A) and (B).

Explanation for correct option

Option (D). Friction can be reduced by the use of lubricants and polishing surfaces.

Friction:

1. It is the force which opposes any tendency for relative motions between bodies in contact.
2. Friction is defined as the force which opposes any tendency for relative motion between bodies in contact.

Factors Affecting Frictional force:

1. Nature of the surfaces in contact . A rough surface offers greater friction than a smooth surface.
2. Normal force that acts on the body.
3. Nature of motion of the body (sliding or rolling).

Methods to reduce friction:

Friction can be reduced by the use of lubricants:

1. Lubricating the machine parts reduces friction.
2. By using lubricants the friction increases as the roughness of the surface increases.
3. Lubricants fill the fine pores and gaps between contact surfaces and reduces friction.

Friction can be reduced by polishing surfaces:

1. Polishing the surfaces make it smooth.
2. It makes the surfaces even and hence reduces friction.

Explanation for incorrect option

Option (C). By increasing the height:

1. We can not reduce the friction by increasing the height.
2. Thus, this option is incorrect.

Thus, friction can be reduced by the use of lubricants and polishing surfaces.

Hence, the option D is the correct answer.