Mechanics of a point with spin and the general principle of inertia

The mechanics of a point with spin based on a general principle of inertia generalizing the Galileo-Newton principle is examined. This mechanics generalizes Einstein mechanics by taking into account the fundamental fact that an accelerated reference system, in general, behaves as a point with spin. In the three-dimensional case it has six degrees of freedom, while in the four-dimensional case it has ten degrees of freedom. Hence, the full four-dimensional description of the accelerated system must be specified by ten equations of motion, and not by four as in Einstein mechanics.