Double Pendulum Simulator (2D)

This 2D companion runs the exact same Lagrangian double-pendulum equations as the 3D scene — RK4-integrated, no small-angle shortcuts — but draws them as a plain flat side view built for reading the physics rather than orbiting a camera around it. Adjust both release angles, both arm lengths and both bob masses, watch the lower bob's fading trail trace out its path, and follow the live kinetic/potential energy split to see mechanical energy sloshing between the two forms as the pendulum swings, while the total stays flat — a direct check that the numerical integration is behaving.