Momentum and impulse
p = mv. Impulse I = Ft = Δp. Conservation of momentum in collisions.
Y13 Mechanics. Momentum is mass × velocity (vector). Impulse is the change of momentum, equal to force × time. Conservation: total momentum before = total after for a closed system.
Worked examples
2 kg ball at 5 m/s hits stationary 3 kg ball; balls coalesce: combined velocity = (2×5)/5 = 2 m/s.
Force 50 N for 0.2 s: impulse = 10 N·s = change in momentum.
Coefficient of restitution e: speed of separation = e × speed of approach.
Frequently asked questions
Conservation always?
Only for a closed system: no external forces during the collision.
Coalesce vs bounce?
Coalesce (e = 0): same final velocity. Bounce (e > 0): separate.