The product of mass and velocity — a conserved vector quantity describing motion.
conservation of momentum: total momentum in a closed system is constant
Newton's second law restated: force is the rate of change of momentum
central to mechanics, collisions, and orbital dynamics
relativistic momentum increases without bound as velocity approaches light speed — see relativity
in quantum mechanics, momentum is quantized and related to wavelength via de Broglie relation
angular momentum: rotational analog, conserved independently
transfer of momentum is the mechanism of force