Time
Start
Energy
drift 0%
Split apart at
gap 0 mm
How to play
- Drag a bob to where you want it to start. Let go.
- Watch: at first all the pendulums move as one.
- Wait for the moment they split apart.
| Do this | Phone | Keyboard |
|---|---|---|
| Set the start | Drag a bob | ← → top rod, ↑ ↓ bottom rod (on the stage) |
| Play / Pause | Pause button | P |
| Start again | Reset | R |
| Random start | New start | N |
What's happening?
- Every pendulum starts just 0.001° further round than the last. That's far too small to see.
- The computer uses the exact same rules for all of them. No randomness at all.
- But a double pendulum is chaotic: tiny differences grow, doubling again and again.
- Watch the gap readout. It grows from a hair's width to a whole swing.
- The energy stays the same the whole time. That shows the maths is honest, not making things up.
- This is why weather can't be forecast weeks ahead: we can never measure the start perfectly.
Try this: start both rods hanging only a little way out (drag a bob just off the bottom). Do they ever split? Now try a big swing.