Setups other learners found interesting in Pi From Collisions. Try one, then tweak it.
Two blocks slide on a frictionless floor with a wall on one side. When the left block is heavier than the right by a factor of 100ᴺ, the total number of collisions equals the first N+1 digits of π. It is a startling link between elastic-collision conservation laws and geometry — the collisions trace out an angle on a circle in velocity space.
Read the full theory: How Two Sliding Blocks Compute π — The Most Surprising Result in Physics →