Question

Ball-bearings are used to reduce the friction by
(A) Applying lubricants to the balls used
(B) Increasing the area of contact with the use of metallic balls
(C) Reducing the area of contact with the use of metallic balls
(D) None of the above

Answer 1

Hint : To answer this question, we have to look into the design and the working of the purpose of the ball bearings. Then, relating these with their purpose of use, we can get the correct answer.

Complete step by step answer
The ball bearings are used in almost every device where the rotational motion is observed. They are fitted as a rolling element between the two bearing races to reduce the friction due to the rotational motion between these races.
We know that the friction between two surfaces in contact acts due to the relative motion between the two surfaces. It acts tangential to the area of contact in a uniform distribution. Thus the friction is proportional to the area of contact between the two surfaces. So if this area of contact is reduced, then the friction will get reduced.
As we know that any plane surface will have the least area of contact with a sphere. So, the spherical metallic ball bearings are employed in the rotating devices due to which the area of contact is minimised, and thereby the friction is reduced.
Thus, the ball bearings reduce the friction by reducing the area of contact with the use of the metallic balls.
Hence, the correct answer is option C.

Note
The ball bearings which are discussed in this question are used in many engineering applications. For example, in the centrifugal pumps, which are used for transporting fluids to minimise the losses of the energy dissipators in the form of heat. Also, they are used in computer fans, aircrafts, skateboards etc.