A fluid in which deformation is proportional to velocity gradients.
A fluid or dispersion whose rheological behavior is described by Newton's law of viscosity. Here shear stress is proportional to shear rate, with the proportionality constant being the viscosity.
a fluid in which the viscosity remains constant for all rates of shear if constant conditions of temperature and pressure are maintained. Most drilling fluids behave as non-Newtonian fluids, as their viscosity is not constant but varies with the rate of shear.