Marble Run — Rube Goldberg Machine — 2D Chain Reaction

This 2D companion draws the same chain-reaction idea as a flat side-view diagram with a genuinely different mechanism from the 3D version: instead of one marble rolling straight down a zigzag ramp into the dominoes, a first ball dropped from an adjustable height lands on a pivoted seesaw, and it is the seesaw's fling that launches the second ball onto the ramp. From there real incline acceleration, base-pivot domino toppling, a second lever (a spring-loaded catapult) and a final projectile arc into a target bucket carry the reaction to its payoff — each stage computed from real gravity, torque and momentum transfer, so an unbalanced setting anywhere along the chain can break it before the bell rings.