Show that, when a rigid body rotates about a fixed axis through $O$ perpendicular to the body, the system of the momenta of its particles is equivalent to a single vector of magnitude $m \bar{r} \omega,$ perpendicular to the line $O G,$ and applied to a point $P$ on this line, called the center of percussion, at a distance $G P=\bar{k}^{2} / \bar{r}$ from the mass center of the body.
