When two balls collide, the impulse-momentum theorem governs the exchange: the total momentum of the system is conserved regardless of the coefficient of restitution e. Setting e=1 gives a perfectly elastic collision (kinetic energy also conserved); e=0 gives a perfectly inelastic collision where the balls stick together and maximum kinetic energy is lost as heat.
Drag the Restitution (e) slider between 0 and 1 to switch between inelastic and elastic regimes. The Mass ratio slider changes the relative mass of alternating balls — unequal masses produce asymmetric velocity exchanges. Add Gravity for more complex multi-ball pile-ups. Drag any ball with the mouse to reposition it.
The coefficient of restitution was first studied by Newton and later formalised by Poisson. Real-world values: steel ball on steel plate ~0.9, rubber ball ~0.7, soft clay ~0.0. In snooker, the cue ball (e ≈ 0.97) transfers nearly all its momentum to the target ball when they hit head-on — a result that follows directly from equal masses and high e.