Concept of Viscosity

Abstract

However, when a //shear// stress latexτ (i.e. force applied per unit area tangential to the boundary of matter) acts, a solid responds with a finite angular (tangential) strain, whereas a fluid strains (deforms) continuously (in time) as long as the shear stress prevails. The stresses in an elastic solid are proportional to the finite deformation while in the fluid they are proportional to the rate of deformation.