Can I make the sand disappear?

Only with the erase brush. The falling sand itself never loses grains — that is verified on every physics step.

Why does the sand not fall faster on a quicker phone?

Physics advances on a fixed time step, not once per screen refresh, so the speed is the same everywhere.

No. It is a sand box, not a game with a result.

No. It runs in the browser on a phone, tablet or computer and works offline after the first visit.

In Sand Sim you pour sand, build walls and watch it pile up and slide. No score, no losing — just a small sand box. Free, no install, no sign-up.

In Sand Sim you get a small box of falling sand. Drag to pour, build walls of stone, and watch the pile settle. There is no score and no way to lose.

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Works offline after the first visit. No install, no sign-up.

Sand falls and slides, nothing else
Each grain tries to move straight down. If that square is taken, it tries the square below-left or below-right. If all three are blocked, it stays where it is. That is the whole rule.
Grain count never changes by itself
The physics only ever swaps a grain with an empty square. It never overwrites one square with another. So the number of grains you poured is exactly the number still on the board — the simulation can rearrange sand, but it cannot create or destroy it. This is the one thing that is genuinely easy to get wrong, and it is checked directly.
Sand can never pass through stone
Stone does not move and cannot be swapped with. Grains pile up on top of it and slide around it.
Three brushes
The buttons at the top switch between sand, stone and erase. Use the arrow keys to change brush without touching the screen.
Drag to draw a line
The gap between two points is filled in as you drag, so a quick flick draws a continuous stream rather than a dotted line of blobs.
Physics runs on a fixed step
The simulation advances in fixed steps rather than once per drawn frame, so the sand falls at the same speed on a fast phone as on a slow one.
There is no objective
Nothing to beat and nothing to lose. Tip the whole board over and start again.

Stone first, then sand
Sand only ever falls or slides downward into empty cells and never displaces stone, so a stone shelf is the only way to build a floor that holds. Draw the shape you want with the stone brush, then pour sand into it. Building the container before the contents also stops sand spreading across the base you were not watching.
Slope decides where sand goes
A grain drops straight down when the cell below is free and only tries a diagonal when it is blocked. So a wide flat top sheds sand sideways much faster than a narrow one, and a steep pile spreads outward as it settles. Pour from a fixed point above a funnel rather than from several places, and the pile stays where you put it.
Nothing here is scored
There is no win condition and the score display never moves, so this is a sandbox rather than a test. That means the useful measure is the shape you end up with, not a number. Build a structure, then erase part of it and watch where the sand chooses to fall, which is the fastest way to learn how the sand behaves.

Can I make the sand disappear?
Only with the erase brush. The falling sand itself never loses grains — that is verified on every physics step.
Why does the sand not fall faster on a quicker phone?
Physics advances on a fixed time step, not once per screen refresh, so the speed is the same everywhere.
Is there a score?
No. It is a sand box, not a game with a result.
Does it need installing or an account?
No. It runs in the browser on a phone, tablet or computer and works offline after the first visit.