Why and how is oil used to reduce the effects of friction in large machines

By reducing friction

Explanation:

A big machine is composed of several moving and stationary parts. Some of these parts are in a state of constant motion hence they periodically rub against each other. The friction between the body parts causes the body part to wear out and heat up in the process. This heat is symbolic of waste of energy.

The lubricating agents are a saviour in such conditions. Lubricating oils with high viscosities reduces friction. If we go deep into the working of the lubrication we find that the interacting parts of machines are quite rough when viewed under microscope. These rough surfaces when interact produce bumpy motion, wear and tear, heat etc.

Oil fills these microscopic voids and thus provides temporary relief. When these lubricated body parts interact, they encounter plain surface with decreased friction (due to high viscosity of the oils) and thus glide over each other freely thereby producing smooth movements, noiseless working.

it may be wrong but i think its a

it is called kinetic energy