Non-Newtonian fluid

Summary

A non-Newtonian fluid is a fluid whose stress is not a fixed linear function of the rate of deformation. Its apparent viscosity may change with the shear rate, it may need a minimum stress before it flows, or it may remember its past deformation. Paints, blood, polymer solutions, ketchup and molten plastics are all non-Newtonian. Their study, part of rheology, explains effects that a Newtonian fluid can never show, such as rod climbing and die swell.