Planar Double Pendulum
RK4 · coupled equations of motion · no damping
| θ1 (upper arm) | – |
| θ2 (lower arm) | – |
| sim time | – |
| total energy | – |
| trail points | – |
upper bob
lower bob
trail
Space = pause/resume · R = reset
Trail fades from dim violet → bright cyan → warm gold along the path.