Introduction

Up to now, we have only analyzed the behaviour of dynamical systems which consist of single point masses (i.e., objects whose spatial extent is either negligible or plays no role in their motion) or arrangements of point masses which are constrained to move together because they are connected via inextensible cables. Let us now broaden our approach somewhat in order to take into account systems of point masses which exert forces on one another, but are not necessarily constrained to move together. The classic example of such a multi-component point mass system is one in which two (or more) freely moving masses collide with one another. The physical concept which plays the central role in the dynamics of multi-component point mass systems is the conservation of momentum.