Mass in special relativity (including the kinetic energy of the gas) only when it is measured in the center of momentum frame. Just as is the case for single particles, the calculated "rest mass" of such a container of gas does not change when it is in motion, although its "relativistic mass" does change. The container may even be subjected to a force which gives it an overall velocity, or else (equivalently) it may be viewed from an inertial frame in which it has an overall velocity (that is, technically, a frame in which its center of mass has a velocity). In this case,
Front velocity any medium tends to one as the frequency tends to infinity, that the wave discontinuity, called the "front", propagates at a speed less than or equal to the speed of light "c" in any medium. In fact, the earliest appearance of the front of an electromagnetic disturbance (the precursor) travels at the "front velocity", which is "c", "no matter what the medium". However, the process always starts from zero amplitude and builds up. Front velocity In physics, front velocity is the speed at which the first rise of a pulse above zero moves forward. In mathematics, it is used to