Hourglass Sand Timer (2D) | mysimulator.uk

Hourglass Setup

Neck width 3 cells

Fill level 100%

Sand cells stacking through the neck…

Live Readout

Flow rate

0 cells/s

Elapsed

0.0 s

Remaining (top)

Settled (bottom)

How it works

This is a discrete falling-sand cellular automaton — the same family of rule used in classic "falling sand" games — rather than a continuous particle simulation. The hourglass is a grid of cells; each occupied cell tries to move straight down every step, and if that cell is blocked it tries diagonally down-left or down-right at random. A cell that can do neither has settled.

That simple local rule is enough to reproduce two real granular effects without any explicit formula: grains pile up at a stable angle of repose (diagonal moves stop once both neighbors below are occupied, so the surface self-limits its own slope), and the narrow neck throttles throughput because only the columns within its width ever have an open path from the top bulb to the bottom one — widen it and more columns can carry sand simultaneously; narrow it to a single cell and grains must queue one at a time.

The flow-rate readout counts how many cells actually cross the neck row per second — a measured quantity, not a plugged-in equation — so you can watch it respond live as you drag the neck slider or as the top bulb empties and the driving column of sand above the neck gets shorter.