Shear velocity
= Shear velocity
{title2=$u_*$}
= Friction velocity
{synonym}
The <shear velocity> is the <velocity> scale $u_*=\sqrt{|\tau|/\rho}$ associated with a <shear stress> $\tau$ in a fluid of <mass density> $\rho$. It is a stress scale, not automatically the actual local fluid <velocity> at a grain.