Collisions, explosions, and the quantity that stays conserved through all of it. Impulse links force and time the same way work links force and distance.
Episode Guide β Season 4
p = mv is a vector, not a number β same direction as velocity, always. It's the quantity that turns collisions and explosions into solvable problems.
Impulse is the integral of force over time β the area under an F-t graph. The impulseβmomentum theorem is Newton's second law in its most general form.
Choose an isolated system and total momentum never changes, no matter how violent the interaction inside it. The center of mass just keeps drifting at v_cm.
Momentum is conserved in every collision β kinetic energy only sticks around in elastic ones. Perfectly inelastic collisions are the extreme case where everything merges into one velocity.