Coordinates locked in a circle

@Ignatz, thinking about it then there’s quite a lot of mathematics in there:

  1. Basic geometry: using and manipulating vectors to position the bowl and fish.
  2. Transformations: transforming the fish’s position to “bowl coordinates” and back again, and the formula for a reflection in a line.
  3. Newtonian Mechanics: working out the forces on the fish and F = m a to figure out the effect on the fish.
  4. Euler Step-by-step: numerical method for solving a differential equation.
  5. Calculus: how to figure out the normal vector for an ellipse.

I could probably get a whole text book out of that simple example …