Editing Newtonian fluid (section)

=== Power law model ===
[[File:Dilatant-pseudoplastic.svg|thumb|In blue a Newtonian fluid compared to the dilatant and the pseudoplastic, angle depends on the viscosity.]]
The power law model is used to display the behavior of Newtonian and non-Newtonian fluids and measures shear stress as a function of strain rate.

The relationship between shear stress, strain rate and the velocity gradient for the power law model are:
<math display="block">\tau_{xy} = -m\left| \dot{\gamma} \right|^{n-1} \frac{dv_x}{dy},</math>
where
*<math>\left| \dot{\gamma} \right|^{n-1} </math> is the absolute value of the strain rate to the (''n''−1) power;
* <math display="inline">\frac{dv_x}{dy}</math> is the velocity gradient;
* ''n'' is the power law index.

If
* ''n'' < 1 then the fluid is a pseudoplastic.
* ''n'' = 1 then the fluid is a Newtonian fluid.
* ''n'' > 1 then the fluid is a dilatant.