Slip length
= Slip length
{title2=$\ell_s$}
The slip length is the distance obtained by extrapolating a locally linear tangential velocity profile back to zero velocity beneath a wall. A <Navier slip boundary condition> has $u_b=\ell_s\partial_nu$. Zero <slip length> gives a <no-slip boundary condition>; large slip permits approximately plug-like motion when the surrounding geometry and forces allow it.