19 March 2017

Difference between kinematic viscosity and dynamic viscosity

What is Dynamics viscosity?

It is a quantity measuring the force needed to overcome internal friction in a fluid.

What is Kinematic viscosity?

It is a quantity that represents the dynamic viscosity of a fluid per unit density. 

Let us have a deep insight into the difference between kinematic and dynamic viscosity. 

Difference :

  • Measure a fluid's resistance to flow when an external force is applied is called dynamic viscosity while measure it under the weight of gravity is kinematic viscosity.
  • Kinematic results are dependent on the density of the fluid and density is not a factor with dynamic viscosity.
The unit of measure for the dynamic viscosity is Centipoise (cP). 

The unit of measure for the kinematic viscosity is Centistokes (cSt).
  • For measuring dynamic viscosity rotational viscometers are used while for kinematic viscosity capillary tube is used.
  • In dynamic viscosity, the viscosity related to an external force applied to non-newtonian fluids while kinematic viscosity inherent viscosity of Newtonian fluids, that does not change with a change in applied force.
  • Dynamic viscosity is the quantitative expression of fluid’s resistance to flow whereas kinematic viscosity is the dynamic viscosity of a fluid divided by its density.
  • Dynamic viscosity is symbolized by either ยต or ‘n’ while kinematic viscosity is mathematically symbolized by v.
  • Dynamic viscosity is sometimes referred to as absolute viscosity, or just viscosity, whereas kinematic viscosity is sometimes referred to as momentum diffusivity.