Question

which of the following materials lowers the friction when pushed between metal plates?
(a) water
(b) fine marble powder
(c) air
(d) oil.

Answer 1

Oil lowers the friction when pushed between metal plates.

Reason:

Friction is a dissipative force which tends to inhibit the relative displacement between two surfaces.

In between 2 metal plates , friction exists mainly due to the irregularities or micro-undulations on the metal surfaces

As a result, there is interlocking between the metal surfaces giving rise to a resistive force.

Application of oil in between the metal surface results in filling up of the irregularities for micro-undulations. This prevents any interlocking and hence lowers the friction.

This is indirectly known as lubrication between metal plates.