Density-weighted viscosity of a disk
= Density-weighted viscosity of a disk
{title2=$\bar\nu=\Sigma^{-1}\int\rho\nu\,dz$}
If angular <velocity> is independent of height, integrating the viscous stress $\rho\nu r\Omega'$ gives $\Sigma\bar\nu r\Omega'$. Thus the <surface density> weighted average, rather than an unweighted height average, enters <vertically averaged viscous disk equations>.