Q. What is viscosity?

Viscosity is resistance to flow of a liquid. It is a measure of the resistance of a fluid to deformation under shear stress. It is commonly perceived as "thickness", or resistance to pouring. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. Thus, water is "thin", having a Low viscosity, while vegetable oil is "thick" having a high viscosity. While studying about viscosity you will come across terms such as newtonian fluid and non-newtonian fluids. What do we mean by this? A Newtonian fluid is one in which the viscosity does not depend on the shear rate-no matter what shear is applied, the viscosity stays the same. Examples of newtonian liquids are mineral oil, water and molasses. In many applications, however, this is not the case and, as the fluid is sheared at greater rates, the viscosity will change. These types of liquids are known as non-newtonian and there are many classifications. Examples are toothpaste and whipped cream. Various methods for textural or rheological measurement are used.