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🎱 2D Ball Collisions — Canvas Momentum Lab

About this simulation

A plain Canvas2D companion to the WebGL version: a swarm of balls bounces and collides inside a box, each impact resolved with the same impulse-based collision response used in physics engines and games.

How it works

• Each ball moves by integrating its velocity, then bounces off the four walls.
• Every pair is tested for overlap; touching balls are pushed apart by their mass ratio.
• An impulse along the contact normal is computed from the relative velocity and e.
• The impulse updates both velocities, and the HUD recomputes total momentum and kinetic energy.

Key equations

j = -(1 + e)(v_rel . n) / (1/m1 + 1/m2) — j is the impulse magnitude, e the restitution, v_rel the relative velocity, n the unit contact normal, and m1, m2 the two masses. Velocities update as v1 += j*n/m1 and v2 -= j*n/m2.

Controls

• Ball count — number of balls in the box (2 to 20).
• Mass ratio (m2/m1) — relative mass of alternating balls.
• Restitution (e) — 1 is perfectly elastic, 0 is perfectly inelastic.
• Gravity — downward acceleration for pile-ups.
• Reset — respawn the balls; drag any ball to reposition it.