= Radial drift of solids in a gas disk
{title2=$v_{pr}=-2\eta v_K\mathrm{St}/(1+\mathrm{St}^2)$}
For test particles with linear <drag>, negligible radial gas flow and negligible dust feedback, <Sub-Keplerian rotation> removes solid-particle <angular momentum>. The displayed inward <velocity> uses <Stokes number> $\mathrm{St}=\Omega_Kt_s$ and the <pressure-gradient parameter of a protoplanetary disk>. Drift is fastest at $\mathrm{St}=1$; the physical particle size at that point depends on the local gas and drag law.
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