Double Pendulum
Hinge a second rod off a swinging pendulum's bob and release both from a large starting angle — watch a genuinely chaotic system where a fraction-of-a-degree difference in the start sends it on a completely different path.
Preview — sign up free to change the numbers yourself
What you can adjust
- Upper rod length
- 0.2 – 2 m
- Lower rod length
- 0.2 – 2 m
- Upper bob mass
- 0.1 – 8 kg
- Lower bob mass
- 0.1 – 8 kg
- Upper rod start angle
- -170 – 170 °
- Lower rod start angle
- -170 – 170 °
Large, uneven starting angles are what make the tumbling look chaotic from the very first swing.
Nudge this by a fraction of a degree and re-run — the two paths diverge completely within seconds. That sensitivity IS the chaos.
About this simulation
What it shows
A second rod is hinged to the bob of a swinging pendulum, and both are released together. The two bobs trace a tangled path.
The key idea
This system is chaotic: the equations are exact, but a tiny difference at the start grows rapidly, so the long-term motion cannot be predicted. Nothing random is involved.
Try this
Run it, then change Lower rod start angle by 1° and run again: the two paths start alike and then drift completely apart.