The branch of physics that deals with the motion of bodies whose relative velocities approach the speed of light or whose kinetic energies are comparable with the product of their masses and the square of the velocity of light is referred to as Relativistic Physics. Relativistic Physics provides a non-quantum mechanical description of a system. The system may be of particles, or a fluid, in cases where the velocities of moving objects are comparable to the speed of light. Relativistic mechanics implies the mechanics compatible with special relativity and general relativity. The merging of special relativity with quantum mechanics is relativistic quantum physics, and for that of general relativity is quantum gravity.