Scene
Shrinking circle
The arena shrinks until the ball no longer fits. The climax is guaranteed: space runs out, and the video ends in the final squeeze.
Open Shrinking circle in the editor
Parameters
The same controls as the editor, with the same range. The default is what the example page uses.
| Parameter | Range | Default |
|---|---|---|
| Shrink rate | 0 – 2u/s | 0.22 |
| Balls | 1 – 12 | 3 |
| Gravity | 0 – 40 | 12 |
| Bounciness | 0 – 1 | 0.96 |
| Minimum radius | 0.2 – 10 | 1 |
| Initial speed | 0 – 30 | 4.5 |
| Growth per collision | 0 – 0.2 | 0 |
How it usually ends
Measured by the engine with the default configuration over a fixed sample of seeds. No number here is an estimate.
- Seeds in the sample
- 40
- Escapes
- 0%
- Settles
- 100%
- Times out
- 0%
- Collisions (median)
- 146.5
- Duration (median)
- 13.9 s
- Climax (median position)
- 97%
- The fraction of the video where event density peaks. Close to 100% means the best moment is at the end.
Seeds that end well
The five best in the sample by the same heuristic the editor's search uses. Each link opens exactly this variation.
- seed3887318score 92 out of 100124 collisions13.9 ssettledOpen seed 3887318 in the editor
- seed2002196score 91 out of 100117 collisions13.9 ssettledOpen seed 2002196 in the editor
- seed3363673score 91 out of 100124 collisions13.9 ssettledOpen seed 3363673 in the editor
- seed326532score 90 out of 100134 collisions13.9 ssettledOpen seed 326532 in the editor
- seed850177score 90 out of 100130 collisions13.9 ssettledOpen seed 850177 in the editor
Watch
Videos of this scene published by the channel, each with the recipe that produced it.
Two Balls, One Shrinking Arena, 163 Hits — Simbounce
Shrinking circle · Sep 11, 2026
Two balls grow bigger with every hit while the arena keeps closing in. It takes 163 collisions before there's no space left to move. Physics simulation, no cuts, no scripting.
scene163 collisionsView the video and the recipeFour Balls, No Room Left — Simbounce
Shrinking circle · Sep 9, 2026
The arena never stopped shrinking on these four balls, colliding harder and harder, until there was nowhere left to bounce. 166 hits total. Physics sim, no cuts, no scripting.
scene166 collisionsView the video and the recipeThree Balls, One Shrinking Arena — Simbounce
Shrinking circle · Sep 8, 2026
Three balls kept colliding as the arena closed in around them — 86 hits before there was nowhere left to bounce. Physics sim, no cuts, no scripting.
scene86 collisionsView the video and the recipe
Frequently asked questions
How do I make a Shrinking circle video?
Open the scene in the editor, adjust the parameters, try a few seeds and export to MP4. Rendering happens in your browser and costs nothing.
Why does the same seed always give the same video?
The simulation is deterministic: fixed-step physics and seeded random numbers. The same seed with the same parameters reproduces the same video on any machine.
How long is a Shrinking circle video?
The video ends when the scene ends. The median duration measured in the sample is in the outcomes section, and the seed search shows each candidate's duration before rendering.
Can I use the video on TikTok, YouTube and Instagram?
Yes. The export is a vertical video with audio, ready for Shorts, Reels and TikTok. On the free plan it carries a discreet watermark.
How do I pick a seed that ends well?
Use the editor's seed search: it simulates dozens of variations without drawing and ranks the ones with a late climax. The seeds on this page came from the same heuristic.
Make your own variation
Open the scene in the editor with one of the seeds above, or let the search find another.
Open Shrinking circle in the editor