= Pedal equation for a central-force orbit
{title2=$p^{-2}=2m(E-V)/h^2$}
Let $p$ be the perpendicular distance from the force centre to the tangent of a regular planar <orbit>. Conserved physical <angular momentum> has magnitude $|h|=mpv$, while conserved <energy> is $E=mv^2/2+V(r)$. Eliminating speed gives the displayed equation when $h\ne0$. For a differentiable polar curve, $p=r^2/\sqrt{r^2+(dr/d\theta)^2}$, connecting the geometric tangent distance to the radial energy equation.
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