Question

When two surface are coated with lubricant, the they will:
(A) Slide upon each other
(B) Stick to each other
(C) Roll upon each other
(D) Jump on each other

Answer 1

In order to answer this question, we need to analyse the role of lubricants in day-to-day life. Lubrication is used to reduce friction. It is generally used for moving machine parts. A lubricant or a lube is a substance that helps to reduce the friction between two bodies in contact. It usually exists in a liquid form and it is applied between the two surfaces where friction occurs.

Complete answer:
The lubricants are the substances which are used to reduce the friction which acts between two surfaces in contact, between which relative motion can occur. As the friction acts along the interface between two surfaces, the lubricants are applied there only. Hence, they help to keep the parts smoothly moving. By reducing the friction, they basically reduce the loss of energy in the form of heat. As the energy losses are prevented, the overall efficiency of a machine is increased.
The lubricants are classified, on the basis of their molecular structure, as the solid and the liquid lubricants.
The solid lubricants are in the powdered form. They are also known as dry lubricants. An example of the solid lubricants is Graphite.
The liquid lubricants are composed of different kinds of base oil and some additives. An example of the liquid lubricants is mineral oil.
Hence, we can conclude by saying that if two surfaces are coated with lubricant then friction will be reduced. Hence, they slide over each other if one is pushed on the other. It is friction which prevents relative motion between two surfaces.
So, the correct option is (A).

Note:
It should be remembered that the solid lubricants are inserted between the bearing surfaces. They are used in very extreme conditions. They are used in the anti-friction linings, metallic films, in suspensions etc. The example of graphite given above is used in air compressors, ball bearings, track joints etc.