The unexpectedly hard windmill question (2011 IMO, Q2)

The famous (infamous?) “windmill“ problem on the 2011 IMO Help fund future projects: An equally valuable form of support is to simply share some of the videos. Special thanks to these supporters: Home page: The author of this problem was Geoff Smith. You can find the full list of problems considered for the IMO that year, together with their solutions, here: You can find data for past IMO results here: Viewer-created interactive about this problem: And another: I made a quick reference to “proper time“ as an example of an invariant. Take a look at this minutephysics video if you want to learn more. ------------------ These animations are largely made using mani