Conservation of Momentum
F = m a
in looking at the cause and effect of motion.
Now we turn our attention to Newton's Third Law,
F12 = - F21
From Newton's Third Law, we already know that these two forces are always equal in magnitude and opposite in direction, F12 = - F21,
This means the total momentum is a constant; we call this Conservation of Momentum.
Impulse Inelastic Collisions Return to ToC, Momentum (c) 2005, Doug Davis; all rights reserved