We have already learned that viscosity (also called absolute or dynamic viscosity) is the property of a liquid which offers resistance to the movement of one layer of liquid over another adjacent layer of liquid. In other words, viscosity is the property of a liquid which controls its rate of flow. The viscosity of a liquid is due to cohesion and interaction between particles.

In SI units, the unit of viscosity is Ns/m2 and in CGS units, it is expressed in poise, such that

1 poise = 0.1 Ns/m2

We have also discussed that the ratio of dynamic viscosity to the density of the liquid is called kinematic viscosity. In SI units, the unit of kinematic viscosity is m2/s and in CGS units, it is expressed in stoke, such that