According to relativistic theory, the mass which a body has when it is at absolute rest. Mass increases when the body is in motion according to: V 1 - v2/c2 where m is its mass in motion, mQ its rest mass, v the body's speed of motion, and c the speed of light. Newtonian physics, in contrast with relativistic physics, makes no distinction between rest mass and mass in general. N.B. Refer to source to verify equation(s)