Question

Frictional force in a ceiling fan is reduced by using
(A) Reduced air resistance
(B) Ball bearings
(C) Both (A) and (B)
(D) None of the above

Answer 1

Hint
Here we should first understand that frictional forces are contact forces and using that concept we deduce that to minimize the frictional force we should minimize the contact area. This deduction helps us easily reach the answer from the given options.

Complete step by step answer:
Frictional forces are contact forces. Thus, the less the contact surface, the lesser the frictional force produced. Since ball bearings are spherical in nature and provide a lesser surface of contact, hence, the frictional force can be reduced by using ball bearings. However, reduced air resistance can reduce drag force on the ceiling fan but not the frictional force, as air resistance does not affect the frictional force.
$\therefore $ Option (B) is the correct option out of the given options.

Note
Friction can also be minimized by applying oil or paint or varnish as these fluids come in between the contact surface and thus reduce friction. Polishing the surface can also reduce friction but over polishing increases friction as it exposes the molecules to the surface and they stick with molecules of other surfaces thereby increasing the friction. It is worth noting that air resistance plays no role in increasing or decreasing frictional forces, but it does play a role in increasing the Drag forces on the blades of the ceiling fans. To minimize the drag forces in the blades, the ceiling fans are made in streamlined fashion or given an aerodynamic shape.