The crack of a pool break is an elastic collision announcing itself. In a perfectly elastic collision, two things survive the impact: total momentum and total kinetic energy. Real collisions always lose a little energy to heat and sound — that is the click you hear — but steel ball bearings, billiard balls, and the molecules in the air you breathe come remarkably close to the ideal.

The one-dimensional formulas look intimidating but say something simple: the lighter object bounces back faster, and equal masses trade velocities like relay batons. After a head-on elastic hit, the new velocities are v₁′ = ((m₁−m₂)v₁ + 2m₂v₂)/(m₁+m₂) and the mirror for v₂′. When a cue ball strikes a stationary eight ball dead center, the cue ball nearly stops and the eight ball inherits almost the full speed — mass traded for motion.

This calculator computes the momentum ingredient each formula needs. Type one ball's mass in the Variable A box and its velocity in the Variable B box; the Result box gives its momentum. Do it for both balls before and after — momentum conservation demands the totals match — then check that ½mv² totals match too. That double bookkeeping is what separates the elastic break from a fender bender.

With the pre-filled defaults — Variable A 10, Variable B 5 — the Elastic Collision Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.