Centrifugal separation velocity is governed by modified Stokes' law: $v_c = \frac{d_p^2 (\rho_s - \rho_f) r \omega^2}{18 \eta}$, where $d_p$ is fat globule diameter, $(\rho_s - \rho_f)$ is density difference, $r$ is effective radial distance from rotational axis, $\omega$ is angular velocity, and $\eta$ is dynamic viscosity of continuous serum phase. Thus, velocity is directly proportional to centrifuge radius ($r$) and inversely proportional to skim milk viscosity ($\eta$).