Proper velocity the traveling object. It equals the object's momentum p divided by its rest mass "m", and is made up of the space-like components of the object's four-vector velocity. William Shurcliff's monograph mentioned its early use in the Sears and Brehme text. Fraundorf has explored its pedagogical value while Ungar, Baylis and Hestenes have examined its relevance from group theory and geometric algebra perspectives. Proper velocity is sometimes referred to as celerity. Unlike the more familiar coordinate velocity v, proper velocity is synchrony-free (does not require synchronized clocks) and is useful for describing both super-relativistic and sub-relativistic motion. Like coordinate velocity
Mass flow rate ejecting spent fuel. Often, descriptions of such objects erroneously invoke Newton's second law F =d("m"v)/d"t" by treating both the mass "m" and the velocity v as time-dependent and then applying the derivative product rule. A correct description of such an object requires the application of Newton's second law to the entire, constant-mass system consisting of both the object and its ejected mass. In hydrodynamics, mass flow rate is the rate of flow of mass. In electricity, the rate of flow of charge is electric current. Mass flow rate In physics and engineering, mass flow rate is the mass of a