Newton's second law of motion

Statement

In terms of force and acceleration

The net external force on a system is the product of the total mass of the system and the acceleration of its center of mass (here, mass is a scalar quantity and both force and acceleration are vector quantities). In symbols:

${\overline {F}}=m{\overline {a}}$.

In particular, the direction of the net external force is the same as the direction of acceleration of the center of mass.

For a point mass or particle, we can talk of the acceleration of the whole body, and thus ${\overline {a}}$ in the above refers to the acceleration of the point mass.

In terms of momentum and impulse

The net external impulse exerted on a system over a time period equals the difference between the final and initial values of its linear momentum. In other words, if the impulse from time $t_{1}$ to $t_{2}$ is $I$, the momentum at time $t_{1}$ is $p_{1}$, and the momentum at time $t_{2}$ is $p_{2}$, then:

$I=p_{2}-p_{1}$.