Double Pendulum: Chaotic Motion Lab (2D)

This 2D canvas lab solves the genuine double-pendulum equations of motion — derived from the system's Lagrangian and advanced with a fourth-order Runge–Kutta integrator — with full control over both arm lengths, both bob masses and both release angles, plus a persistent fading trail that traces the lower bob's chaotic path. Flip on the sensitivity demo to run a second, near-identical pendulum in its own pane beside the first: released a fraction of a degree apart, the two panes look identical for a moment and then visibly diverge, making the sensitive dependence on initial conditions that defines chaos directly observable rather than merely asserted.