Viscous drag coefficient (${\mathbf{F}}_{\mathrm{drag}}=-\gamma \mathbf{v}$)

The proportionality between drag force and relative velocity in a linear low-speed regime. Its translational units are $\mathrm{kg}{\mathrm{s}}^{-1}$; thermal equilibrium gives the Einstein diffusion relation $D=k_{B}T/\gamma$.