How To Calculate A Change In Momentum

An object's momentum is the product of its velocity and mass. The quantity describes, for instance, the impact that a moving vehicle has on an object that it hits or the penetrative power of a speeding bullet. When the object travels at a constant speed, it neither gains nor loses momentum. When two objects collide, they again together gain and lose no momentum. The only way for a body to gain momentum is for an external force to act on it.

Step 1

Divide the magnitude of the external force on the object by the object's mass. For this example, imagine a force of 1,000 Newtons acting on a mass of 20 kg: 1,000 ÷ 20 = 50. This is the object's acceleration, measured in meters per second squared.

Step 2

Multiply the acceleration by the time for which the force acts. If the force acts, for instance, for 5 seconds: 50 × 5 = 250. This is the object's change in velocity, measured in m/s.

Step 3

Multiply the object's change in velocity by its mass: 250 × 20 = 5,000. This is the object's change in momentum, measured in kg m/s.