Linear friction coefficient
= Linear friction coefficient
{title2=$\zeta$}
The dimensional linear friction coefficient relates <drag force> and <velocity>, $F_d=-\zeta v$, and has units of <force> divided by speed. It differs from the dimensionless aerodynamic <drag coefficient>. For an isolated sphere in <Stokes flow>, the <Stokes drag law> gives $\zeta=6\pi\eta a$.