\frac{D {\bf u}}{Dt}  = \frac{1}{\rho} \nabla {\bf \sigma} + {\bf g}

where

	time and spatial variables
	velocity of Continuum Body
	density of Continuum Body
	stress tensor of Continuum Body
	sum of all body forces exerted on Continuum Body
	volumetric density of all contact forces exerted on Continuum Body
	Material derivative of the Continuum Body motion

In Fluid Mechanics it's known as Navier–Stokes equation and based on specific view of the stress tensor.

\sigma = - p  - \mu \cdot \left[  \Delta {\bf u} + \frac{1}{3} {\bf u} \nabla {\bf u}  \right]

See also