Impulse is the average net external force multiplied by the time this force acts, and impulse equals the change in momentum, Δ p = F net Δ t Newton’s second law of motion in terms of momentum states that the net external force equals the change in momentum of a system divided by the time over which it changes, F net = Δ p Δ t

The law of conservation of momentum is written p tot = constant or p tot = p ′ tot (isolated system), where p tot is the initial total momentum and p ′ tot is the total momentum some time later In an isolated system, the net external force is zero

law of conservation of momentum — when the net external force is zero, the total momentum of the system is conserved or constant. isolated system — system in which the net external force is zero. change in momentum — the difference between the final and initial values of momentum; the mass times the change in velocity. impulse — average net external force multiplied by the time the force acts; equal to the change in momentum.