https://doi.org/10.1351/goldbook.S05676
An idealized treatment of a fluid between two large parallel plates (to permit ignoring edge effects) of area A, separated by a distance h. If one plate moves relative to the other with a constant velocity V, requiring a force F acting in the direction of movement, and the density, pressure, and
viscosity
throughout the fluid are constant, the Newtonian equation can be coupled with the equations of motion and of continuity to show that the velocity
gradient
in the fluid is constant (= Vh), and that FA=η Vh. This idealized case (simple shear) is sometimes used to define
shear viscosity
.
Source:
PAC, 1979, 51, 1213. (Terminology and Symbols in Colloid and Surface Chemistry Part 1.13. Definitions, Terminology and Symbols for Rheological Properties) on page 1216 [Terms] [Paper]