Double Pendulum

Two rods and two masses, moving under gravity. The blue pendulum and the grey twin start about 0.001 radians apart (roughly 0.06°). They stay in step for a few seconds, and then their motions separate completely. Identical rules and nearly identical starting points still lead to totally different paths. The plot along the bottom shows how far apart the two tips are over time, and the moment they split happens at a different time on each run. Drag either bob to set a new starting pose.