The thickness of any fluid is known as viscosity. For example, honey has higher viscosity as compared to water. There are fluids with different densities, and things can change on considering this factor. The outcome of the interaction between the different molecules in a fluid can also be termed as viscosity as the molecular level. It is also known as friction between the molecules in the fluid. It is the energy needed for the fluid flow.

This is an important parameter as it affects heat generation in cylinders, bearings and gear sets. In the case of oils, viscosity determines the resistance flow.

BY Best Interview Question ON 21 Apr 2019