is the frictional force overcome in sliding one "layer"
of fluid along another, as in any fluid flow. The shear stress of a
petroleum oil or other
Newtonian fluid at a given temperature
varies directly with shear rate (velocity).
The ratio between shear stress and shear rate is constant; this ratio is
termed viscosity. The higher the viscosity of a
Newtonian fluid, the greater the shear stress as a function of rate of
shear. In a non-Newtonian fluid —
such as a grease or a
polymer-containing oil (e.g.,
multi-grade oil) — shear stress is not proportional to the rate of
shear. A non-Newtonian fluid may be said to have an
apparent viscosity, a viscosity that
holds only for the shear rate (and temperature) at which the viscosity is
determined.
Also see Brookfield
viscosity.
Application
Notes:
