The change in linear momentum, $\Delta \vec{p}$, represents the difference between the final momentum $\vec{p}_f$ and the initial momentum $\vec{p}_i$ of an object over some time interval.

A change in momentum occurs whenever an object experiences a change in speed, a change in direction, or a change in mass.

For a single object with constant mass $m$, the change in momentum is directly related to the change in velocity $\Delta \vec{v}$.

Consider an object of mass $m$ initially moving with speed $v_i$ that accelerates to a final speed $v_f$ in the same direction. The magnitude of the change in momentum is:

However, if the object changes directions, the subtraction from a negative final velocity will yield a larger momentum change than just stopping.

Stopping