Torque the vector cross product, p is the particle's linear momentum, and r is the displacement vector from the origin (the origin is assumed to be a fixed location anywhere in space). The time-derivative of this is: This result can easily be proven by splitting the vectors into components and applying the product rule. Now using the definition of force formula_17 (whether or not mass is constant) and the definition of velocity formula_18 The cross product of momentum formula_20 with its associated velocity formula_21 is zero because velocity and momentum are parallel, so the second term vanishes. By definition, torque τ
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