Five polished steel spheres hang from a frame, and this simulation numerically integrates each one as a simple pendulum under gravity. Newton's cradle is a classic demonstration of the conservation of momentum and kinetic energy in near-elastic collisions: when one ball strikes the row, the impact travels through the middle balls (which barely move) and launches an equal number of balls from the far end at matching speed. This is only possible because momentum (mv) and energy (½mv²) must both be conserved simultaneously - if two balls swung out instead of one, energy would not balance. Real steel spheres lose a little energy each swing to air resistance and inelastic deformation at contact, which is why real cradles slowly wind down; here a damping factor and periodic re-injection of energy keep it swinging.