Little physics simulations I built for fun. Laptop only.
That bright, heart-shaped curve of light at the bottom of a coffee mug — the caustic (a nephroid), traced out ray by ray.
Why two shadows seem to reach out and merge as they get close — the "magnetic shadow" effect, all down to the light source having width.
An interactive 1D & 2D Ising model — watch magnetic spins order and disorder as you cross the ferromagnetic phase transition.