Angle of repose
The angle of repose is the steepest slope at which a powder or granular material can be piled without slumping. Pile it steeper and the surface slides down until it returns to that angle.
| Material | Angle of repose (approx.) |
|---|---|
| Dry sand | 35° |
| Damp sand | 40° |
| Gravel | 40° |
| Dry ash | 33° |
Source: Engineering ToolBox, Angles of Repose (values vary with condition)
Damp sand
You cannot build a sandcastle from dry sand, but slightly damp sand works, because thin films of water between grains pull them together. That is why damp sand stands steeper. Add too much water, though, and the gaps fill completely, that pull disappears and the sand flows.
The hourglass secret
A water clock drips faster when full and slower when nearly empty. Dry sand drains through a hole at an almost constant rate no matter how much is left above it, which is why hourglasses use sand. Researchers have also reported that grains draining underwater surge faster near the end.
Source: Koivisto & Durian, Nature Communications 8, 15551 (2017)
How pixel sand does it
Falling-sand games do not calculate friction. Each cell repeats a simple rule: move down if the cell below is empty, otherwise try down-left or down-right. That alone makes sand pile into cones, but because grains slide one diagonal cell at a time, the slope ends up close to 45°, steeper than real sand at about 35°. That is why game sand piles look a little pointy.
Watch it in the app
Pour onto one spot
In Sandlab, pick Sand and hold your finger in one place: it keeps flowing like a faucet. The pile grows but the slope stays the same.
Hourglass preset
Open More → Wall presets → Hourglass and fill the top half with sand. It pours through the narrow neck and a cone grows in the bottom half, just like the real thing.
Tilt
Turn on Tilt gravity and tip your phone sideways: powders and liquids drift that way (an advanced tool, unlocked with one ad). For comparison, pour the same amount of water: instead of a cone it spreads flat.
FAQ
Do salt and snow pile into cones too?
In the game salt, snow, gunpowder, ash, concrete and seeds are all powders and pile the same way. Snow is set to fall a little more slowly.
Does damp sand stand steeper in the game?
No. The game has no damp sand state, and sand underwater sinks and piles by the same rule.
Sandlab - Falling Sand Physics
No sign-up, and the simulation runs fully offline. Your canvases stay on your device. Free on Android.