Collisional-cascade relaxation time
= Collisional-cascade relaxation time
{title2=$t_c\sim1/R_{\rm cc}$}
A bin with mass $m$ loses mass at approximately $mR_{\rm cc}$, so changing an order-one fraction takes $m/(mR_{\rm cc})=1/R_{\rm cc}$. The <catastrophic planetesimal collision rate> must be evaluated using the contemporaneous projectile population. It supplies a relaxation scale, not an exact equilibration time for an arbitrary fragment kernel.