Click green flag. Touch background or hit spacebar to see a new background (my wife Kathy painted both). The particles start at random positions up high and move down until they touch a stationary particle. Coral like patterns appear. Just for effect, we add a pen mark to each stationary particle. The color of new pen marks change over time. My wife drew the backgrounds so this is a husband-wife project. A few months ago we shared a variant of this one.
A similar pattern is seen in crystal formation, coral, fungi growth, liquid seeping through soil, lightning, or what you see when you drop dye into glue, which is called viscous fingering. A process called diffusion-limited aggregation (DLA) happens to create the same patterns as seen in viscous fingering, in which a less viscous liquid presses through a more viscous liquid. The finger-like projections result from pressure being somewhat greater at the tips. We added a pen mark for color effect. Note that the pen size is smaller than the surrounding blue-green clone. My wife Kathy did the background painting (part of our box on sea life ecology and coding). We shared one with a different color scheme last year. In NetLogo, we were able to give more control: https://lifepatternsemerging.com/wp-content/uploads/2020/11/DLA-additive-stickiness.html
