Ink Drop in Water Simulator (2D)

This 2D simulator drops colored ink into a glass of still water and lets thousands of particles spread out by real Brownian-motion diffusion rather than a simple fade effect: each particle takes its own random step every frame, sized by the Stokes–Einstein diffusion coefficient D = k_BT / (6πηr). Raise the water temperature or lower its viscosity to watch the ink spread faster, or drop in a bigger cloud of ink and see how long it takes to fill the glass. The live readouts track the diffusion coefficient and the cloud's spreading radius in real time, showing the classic √t growth law of diffusion.