Shear Stress

Stress is given by force divided by the area of the surface on which it acts. When the direction of the applied force is tangential to the surface (shearing force), you have a shear stress. In Rheology, shear stress is related to melt pressure (apparent shear stress is directly proportional to the measured pressure), and shear stress divided by shear rate gives shear viscosity. Stress is expressed (SI units) in pascal (Pa) or newton per square meter.