The viscous force present between two layers of a liquid is expressed as F A = - dv dz . The quantity F/A can be referred to as

Step-by-step solution

The viscous force F acts parallel to the layers of the liquid to oppose their relative motion. Since the force is applied tangentially to the surface area A of the layers, the quantity F/A represents the tangential force per unit area. The tangential force per unit area is defined as tangential stress or shear stress.