is the velocity gradient and can also be represented as the strain rate. In general, when shear stress is applied on a fluid-volume, there are translation, deformation, dilation, rotation and distortion, mathematically expressed by strain rates. Analogous to the representation of shear stresses, strain rates are represented as the combination of the following velocity gradients:
The Newton’s extended law of viscosity relates . For example,
Again, it is obvious that if a fluid is stationary or inviscid
is the velocity gradient and can also be represented as the strain rate. In general, when shear stress is applied on a fluid-volume, there are translation, deformation, dilation, rotation and distortion, mathematically expressed by strain rates. Analogous to the representation of shear stresses, strain rates are represented as the combination of the following velocity gradients: 
. For example, 
