We consider a point moving with respect to a rigid body. The system ma
de up of these two elements is deformable since the distance of the po
int and the body changes. This basic idea leads us to define strain ra
tes and interior forces. The latter are percussions related to collisi
ons and forces related to smooth evolutions. They are defined by their
virtual work. The equations of motion are derived from the principle
of virtual work. The constitutive laws for the interior percussions ar
e the other equations which describe the evolution of the system when
collisions occur between the point and the body. Examples illustrate t
he ability of the theory to analyse practical situations, for instance
multiple collisions.