chapter  2
Non-Newtonian Fluid Behavior
Pages 40

Three distinct stages can be discerned in the evolution of fluid dynamics. The first stage of development deals with the study of imaginary perfect or ideal fluids, that is, those without viscosity or elasticity and incompressible in nature. Evidently, the shearing motion will not give rise to any shearing forces in such fluids and hence the flow is said to be frictionless. Exact analyses for a variety of physical situations involving ideal fluids have been developed over the years, some of which have proved to be useful approximations for the performance of real fluids under certain special conditions.