Falling Sand Lab
A small material world on a 160 × 100 grid. Paint materials and press Play: sand falls and sinks through water, water spreads, steam rises and fades, fire boils water and burns plants, and plants spread where it is wet.
Paint materials into a tray and watch them fall, flow, rise, burn and grow.
FreeOn this device
A stylised material toy — not a chemistry or physics model.
| stone | 320 |
|---|---|
| sand | 1291 |
| water | 0 |
| steam | 0 |
| fire | 0 |
| plant | 0 |
Controls
- Choose a material, then press and drag on the tray to paint. The eraser removes material.
- Keyboard: focus the tray, move the brush with the arrow keys (Shift moves 5 cells), press Space to paint, hold Space while moving to paint a line, Escape ends the stroke.
- Play and Pause run the simulation at 30 steps a second; Step advances one step while paused; 2× doubles the speed; Replay from start returns the scene to how it was loaded.
The rules
- Stone never moves. The edge of the tray behaves like stone.
- Sand falls straight down or diagonally, and sinks through water by swapping places with it.
- Water falls, then spreads one cell sideways per step.
- Steam rises and disappears after 180 steps (six seconds).
- Fire stays where it is. Water next to fire becomes steam; a plant next to fire for 15 steps in a row burns and becomes fire.
- Every 30 steps each plant has a 15% chance (from the scene's seed) to grow into one empty neighbouring cell that touches water.
Scoring, saving and limits
There is no score: it is a sandbox. The same scene and seed always evolve the same way, so a scene can be replayed exactly.
Your scene is saved on this device when you pause, step, finish a brush stroke, load a scene, and every five seconds while it runs. Download a backup to keep or move it; Clear this game deletes only this scene.
A stylised toy, not a chemistry or physics model: there is no density, temperature, pressure or conservation of water when it boils. Only one step's worth of catch-up is allowed after a slow frame, so a busy device runs the simulation slower rather than freezing.
Questions
- Why does my water disappear?
- Water that touches fire turns to steam, and steam fades after six seconds. Nothing else removes water — sand only swaps places with it.
- Why are my plants not growing?
- A plant grows only into an empty cell that touches water, and only with a 15% chance every second. Put water beside or under the plants and give it a few seconds.
- Will the same scene do the same thing twice?
- Yes. Every random choice comes from the scene's seed and the step number, so Replay from start reproduces exactly the same evolution.