# Newton's Law of Viscosity

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Newton's law of viscosity states that shear stress between adjacent fluid layers is porportional 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.

### Newton's Law of Viscosity Formula

$$\large{ \tau = \mu \frac {d \nu}{dy} }$$

Where:

$$\large{ \tau }$$  (Greek symbol tau) = shear stress

$$\large{ \mu }$$  (Greek symbol mu) = dynamic viscosity

$$\large{ \frac {d \nu}{dy} }$$ = rate of shear deformation