Question

If we apply oil on door hinges, the friction will:
A. Increase
B. Decrease
C. Disappear altogether
D. Will remain unchanged

Answer 1

Hint: As we all know that the motion of a body is obstructed by the motion resisted by the surface and this resistance is developed by the very small projections that are between the body and the surface.

Complete step by step answer:
We all know that after a certain period of time the doors start to stick up and we require very much effort to open or close the door. Since door portions are open and are interacting with the atmosphere, the chances of getting corroded are very high. As corrosion takes place, the surface becomes irregular, and factors for enhancing the friction increases. But as we put oil on the door and the oil can be any lubricant For example-Molybdenum sulfide and graphite. When we put the oil the rough interlocks between the surface and body are filled by the drops of oil and hence become smooth and then the friction decreases. So, here we can say that if we apply oil on door hinges, the friction will decrease.

$\therefore$ The correct option is (B).

Note:
We must keep in mind that while the motion of a body with respect to the surface, the friction taking place is the kinetic friction, and kinetic friction is less than the static friction. Because as the body comes into motion, the interlocks between the surface and the body breakdown, and the and body is set into motion and in that case, the coefficient of friction is called the coefficient of kinetic friction, and its value becomes less than the coefficient of static friction.