Viscosity/Dynamic viscosity:
- Viscosity is the physical property that characterizes the flow resistance of simple fluids.
- Viscosity is the property of a fluid by virtue of its offers resistance to the movement of one layer of fluid over an adjacent layer.
Kinematic viscosity/ momentum diffusivity:
- It is defined as the ratio of dynamic viscosity to the density of the fluid.
Newton’s Law of Viscosity:
Newton’s viscosity law’s states that, the shear stress between adjacent fluid layers is proportional to the velocity gradients between the two layers.
The ratio of shear stress to shear rate is a constant, for a given temperature and pressure, and is defined as the viscosity or coefficient of viscosity.
Newtonian Fluid:
- A fluid, whose viscosity does not change with the rate of deformation or shear stain (V/Y), is called Newtonian fluid.
- A fluid which obeys Newton’s law of viscosity is termed as Newtonian fluid.
Non-Newtonian Fluid:
- A fluid, whose viscosity changes with the rate of deformation or shear stain (V/Y), is called Non-Newtonian fluid.
- A fluid which does not obey Newton’s law of viscosity is termed as Non-Newtonian fluid.
Mechanical Engineering 