2D Domino Chain Reaction: Toppling Physics

A domino chain reaction looks simple, but whether it actually reaches the far end depends on one ratio: the gap between dominoes versus how tall they are. This 2D side-view simulator models each domino as a rigid rod pivoting about its base, driven by the real falling-rod torque equation α = (3g)/(2H)·sinθ, and only knocks over the next domino once the toppling one's top edge — reaching forward a horizontal distance H·sinθ — physically closes the spacing gap between them. Drag the spacing slider past a domino's own height and the chain reaction breaks partway through, no matter how many times you push it, because sinθ can never exceed 1. The size slider changes both the toppling speed (taller dominoes fall more slowly per unit angle, since angular acceleration scales as 1/H) and the energy each one releases (mass and potential-energy drop both scale with domino size), so the propagation-speed and energy readouts genuinely respond to the physics rather than just to a cosmetic animation setting.