Question

Which among the following is the best lubricant?
A. Solids
B. Liquids
C. Gases
D. Both B and C

Answer 1

Hint: For questions related to lubricants , we must at the beginning use the conditions of being a good lubricant and all the properties that are needed to be a good lubricant. From our basic understanding of matter, we can surely say that a solid can never be a good lubricant.

Complete answer:
Let us list the basic characteristics which a good lubricant should generally possess :
-It should be able to prevent the material from corrosion.
-It should be thermally stable.
-It should have very high hydraulic stability.
-It should provide high resistance to oxidation.
-It should provide a slippery effect, thus it has to be in a liquid state for a wide range of temperature, thus it should have a high boiling point and low freezing point.
-It should have a high viscosity index.

Viscosity index: It is the measure of the fluid’s change in viscosity relative to the change in temperature. It is unit-less.
Hydraulic stability: Extreme low or extreme high temperature can damage the lubricant and alter its property, the property called hydraulic stability.
Studying all these above properties, we can surely say that the state which matches all of these above properties is only the liquid state.

Hence correct answer is option B.

Note: Lubricants range from use in machinery to usage in baking cakes, to skin ointment applications and many more. It helps in reducing friction between surfaces which are in mutual contact and thus ultimately helps in reducing the heat generated when the two surfaces are in motion. It helps to reduce the wear and tear suffered by the surfaces.