# Newtonian fluid

A Newtonian fluid is one which has a linear relationship between stress and strain rate: the ratio of stress to strain rate represents the viscosity of the fluid.

**Figure**: Stress and strain rate of a Newtonian fluid.

A Newtonian fluid is one which has a linear relationship between stress and strain rate: the ratio of stress to strain rate represents the viscosity of the fluid.

**Figure**: Stress and strain rate of a Newtonian fluid.