Momentum Integral Equation

An integrated form of the momentum equation across the boundary layer thickness

\delta

. It relates the drag force to the pressure gradient and the integral of the shear stress:

\frac{d}{dx} (\int_0^\delta u(x,y) \rho dy) = -\frac{d}{dx} (\frac{1}{2}\rho U^2) + \frac{d\tau_w}{dx}