Circular orbital speed from surface gravity
= Circular orbital speed from surface gravity
{title2=$v=\sqrt{g_sR^2/r}$}
For a spherical central body of radius $R$ with <surface gravity> $g_s=GM/R^2$, a circular test-particle orbit at radius $r$ has $v=\sqrt{g_sR^2/r}$. <surface gravity> is used to infer $GM$, not incorrectly kept constant at orbital height.