The equation of motion which applies to high Reynolds number regimes in which the viscous force is small compared to the inertia force, so it can be neglected in the Navier-Stokes equations. For nonsteady flow, this becomes

(1)

where is a substantive derivative, is the density, u is the fluid velocity, and P is the pressure. For steady flow, it simplifies to Fourier's law

(2)

Euler's Equations of Motion, Fourier's Law, Navier-Stokes Equations, Reynolds Number