Sand

pour. watch it find its angle.

a falling-sand world — pour with your finger

Loose grains poured into a pile don't stack straight up — each one slides and settles until the whole pile reaches an angle it can hold, and pouring more from above just extends that same slope instead of building a taller wall. The angle belongs to the material, not to how much of it there is.

Concepts: physics, granular-flow.

An interactive you play with one thumb, on Wundr.