Variable-mass system the momentum of the system varies for Therefore, by Newton's second law Noting that u - v is the velocity of d"m" relative to "m", symbolized as v, this final equation can be arranged as In a system where mass is being ejected or ablated from a main body, the derivation is slightly different. At time "t", let a mass "m" travel at a velocity v, meaning the initial momentum of the system is Since the main body will be losing mass, d"m" will be negative, meaning that at a time "t" + d"t" the momentum of the system becomes
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