Double Pendulum

Chaos you can drag. A ghost twin shows how fast prediction breaks.

0/2challenges

Ghost twin

t = 0.0 s

Upper angle°

Lower angle°

Upper masskg

Lower masskg

Upper lengthm

Lower lengthm

Gravitym/s²

Upper angle now: 0°
Lower angle now: 0°
Twin divergence: 0.0000°
Energy drift: 0.0e+0%

The model

Two point masses on rigid, massless rods, with no friction. The equations of motion come from the Lagrangian and are integrated with fourth-order Runge-Kutta, twenty steps per frame.

The system is chaotic: tiny differences in the start grow exponentially. The cyan twin starts just one millionth of a radian away from the orange one. For a while you cannot tell them apart. Then you can.

Try this

Drag either bob to set the start. The Gentle preset stays predictable; Chaotic splits within seconds. Watch the energy readout: the integrator keeps it nearly constant, which is how you know the chaos is real and not numerical noise.

Assumes rigid massless rods, point masses, a frictionless pivot and no air resistance. Educational model, not an engineering design or validation tool.

Achievements0/2

Butterfly effect +30Watch two almost identical pendulums drift apart.
Flip +20Drag the arms into a start that loops the lower arm over the top.

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