Bouncing Bodies: Elastic Collisions & Energy Conservation (2D)

This 2D companion trades the 3D version's orbiting camera for a flat, readable box: bodies of different radius (and therefore different mass, since mass here scales with area) fall under an adjustable gravitational acceleration, lose a little speed each second to linear air drag, and bounce off the walls and each other with a tunable coefficient of restitution. Every collision — wall or body-to-body — resolves the way a real elastic impact does, using the standard restitution formula along the collision normal so momentum is exchanged correctly between unequal masses, and the live readouts (kinetic energy, total momentum magnitude, average speed and collision count) let you watch conservation laws hold, or watch them "leak" energy on purpose as you lower the restitution slider below 1.