Momentum
Momentum, (plural: Momenta or Momentums), in physics, the velocity of a body multiplied by its mass. A moving car, a running child, or a missile in flight has momentum. Like velocity, momentum has direction. Two bodies that have the same mass but different velocities have different momenta, as do two bodies that have the same velocity but different masses. The object with the larger mass or velocity has the greater momentum. Momentum is stated in units such as foot-pounds per second or kilogram-meters per second.
The law of the conservation of momentum states that unless an outside force acts on a body, its momentum will remain unchanged. The law also applies to the total momentum of two or more bodies that collide. The velocity of each of the bodies may be different after the collision, but the total momentum will not be changed.
The momentum of a body can be changed by an outside force. The change in momentum depends on the strength of the force and the length of time the force acts.