Kinematic viscosity

Kinematic viscosity is dynamic viscosity divided by mass density: $\nu =\mu /\rho$.

If angular velocity is independent of height, integrating the viscous stress $\rho \nu r{\Omega }^{\prime }$ gives $\Sigma \bar{\nu }r{\Omega }^{\prime }$. Thus the surface density weighted average, rather than an unweighted height average, enters vertically averaged viscous disk equations.