A force per unit area provided either by gravity or by the flow of viscous fluid.
In a viscous fluid, the normal stress is
where w is the vertical velocity, z is the vertical height, and is the dynamic viscosity.
Elasticity, Hooke's Law, Shear Stress, Strain, Stress Refringence, Stress Tensor
References
Turcotte, D. L. and Schubert, G. "Stress and Strain in Solids." Ch. 2 in Geodynamics: Applications of Continuum Physics to Geological Problems. New York: Wiley, pp. 74-103, 1982.
