NOTE 1 For a continuous body in a domain D, momentum is equal to the integral $p={\displaystyle {\int }_{\text{D}}\rho }vdV={\displaystyle {\int }_{\text{D}}vdm}$, where ρ is the mass density in a domain having quasi-infinitesimal volume dV and mass dm, and velocity v. For a system of bodies, it is equal to the sum of their momentums.

NOTE 2 If the sum of external forces is equal to zero, momentum of a body follows a law of conservation.

NOTE 3 If the theory of relativity is applied, m is relativistic mass.

NOTE 4 The coherent SI unit of momentum is kilogram metre per second, kg·m·s⁻¹.