A
non-Newtonian fluid is a
fluid with properties that differ in any way from those of
Newtonian fluids. Most commonly, the
viscosity (the measure of a fluid's ability to resist gradual deformation by shear or tensile stresses) of non-Newtonian fluids is dependent on
shear rate or shear rate history. Some non-Newtonian fluids with shear-independent viscosity, however, still exhibit normal stress-differences or other non-Newtonian behavior. Many
salt solutions and molten polymers are non-Newtonian fluids, as are many commonly found substances such as
ketchup,
custard,
toothpaste,
starch suspensions,
paint,
blood, and
shampoo.