Time
Bodies
Paused
Total energy
drift 0%
Momentum
0 crashes
Start
Throw a
Drag to
How to play
- Pick a size, then drag in space to throw it. Longer drag = faster.
- The dotted line shows where it will go. Let go to throw.
- Too slow and it falls in. Too fast and it escapes. Just right and it orbits.
| Do this | Phone | Keyboard |
|---|---|---|
| Throw a body | Drag in space | Enter = into orbit at the centre |
| Zoom | Pinch | + - (or scroll) |
| Pan | Two fingers, or Move view | Arrow keys (on space) |
| Follow centre of mass | Follow centre | F |
| Play / Pause | Pause | P |
| Start again | Reset | R |
| Size | Moon / Planet / Star | 1 2 3 |
What's happening?
- Everything pulls on everything else. Heavier pulls harder. Twice as far away pulls 4 times weaker. That's Newton's law of gravity.
- An orbit is falling and missing: the planet falls towards the star, but it's going sideways so fast it keeps missing.
- When two bodies crash they merge. The new body keeps their total momentum (mass × velocity), so the momentum number doesn't change.
- The energy number stays almost fixed too. A crash turns some into heat, so it drops a little then.
- The Figure-8 is a real solution found in 2000: three equal stars chasing each other along one loop. Nudge it and it falls apart.
Try this: on Sun + planets, throw a moon so it swings close past a planet and gets flung away much faster. That's a slingshot, the trick space probes use to reach the outer planets.