In physics, the product of an object's mass and velocity is called momentum. It is written as p = mv, where p is momentum, m is mass, and v is velocity. Because velocity includes direction, momentum is a vector: a moving object can have the same momentum magnitude as another but point in a different direction.
Momentum helps explain collisions, recoil, and why heavier or faster objects are harder to stop. Its SI unit is the kilogram metre per second (kg·m/s), which is equivalent to a newton-second. Newton's second law can be expressed as force equals the rate of change of momentum.
A common mix-up is impulse. Impulse is not momentum itself; it is the change in momentum produced by a force acting over time. Torque, meanwhile, describes the turning effect of a force, while inertia is an object's resistance to changes in motion. In a closed system, total momentum is conserved, making the concept central to collision analysis and rocket propulsion.