Question

Which of the following is not used to reduce friction?

• A. Using oil between contact surfaces
• B. Using grease between contact surfaces
• C. Using ball-bearing
• D. Making scratches on the contact surfaces

Answer 1

The correct option is D

Making scratches on the contact surfaces

Explanation for the correct option: (D) Making scratches on the contact surfaces

1. Friction is the resistance offered by the surfaces that are in contact when they slide or roll over each other.
2. The causes of this resistive force are molecular adhesion, surface roughness and deformations.
3. When we make scratches on the contact surfaces, then the roughness of the surface increases. So, resistance offered during sliding or rolling increases and hence friction also increases.
4. So, making scratches on the contact surfaces is not used to reduce friction.

Explanation for the incorrect options:

(A) Using oil between contact surfaces

Using oil on contact surfaces makes the surfaces slippery. So, they slide over each other more easily and hence, friction is reduced.

(B) Using grease between contact surfaces

Using grease between contact surfaces makes the surfaces slippery and smooth. So, they slide over each other more easily and hence, friction is reduced.

(C) Using ball-bearing

When we use ball bearing, the contact surfaces roll rather than slide. In rolling, friction is lesser than the sliding. Thus, the ball bearing reduces the friction.

Thus the option (D) making scratches on the contact surfaces will not reduce the friction is correct