Since MECHANICS is so intimately concerned with the relationships between mass, time and distance, the weird properties of the time and space revealed by the may be expected to be accompanied by some equally weird MECHANICS at relativistic velocities. This is indeed the case. On the other hand, we can rely upon Einstein's first postulate of the STR, namely that the "Laws of Physics" are the same in one reference frame as in another. Thus most of our precious paradigms of MECHANICS (such as CONSERVATION LAWS) will still be reliable.