Newton's second law of motion
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:
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 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 to is , the momentum at time is , and the momentum at time is , then:
- Physclips by University of New South Wales -- choose and play Section 5.2