The study of the dynamics of a mechanical system starts with the description of its mechanical state (position and velocity of every point in the system). For the particular case of systems consisting of a finite number of rigid bodies, though the number of points is infinite, that description calls for a finite set of position variables – generalized coordinates (GC) – and speed variables – generalized speeds (GS). The vector space defined by the GC is called configuration space; that defined by the GC and the GS is known as phase space.