I could not find an answer by web search. From Why is rolling friction less than the maximum static friction? I understand static balls "experience" static friction, not rolling one.
I'm trying to build a tetrahedron from tennis balls, like here https://en.wikipedia.org/wiki/Tetrahedral_number.
I noted large pyramids are unstable, of about 10 balls edge is very easily breaking/falling/rolling apart during construction (8 balls are ok, 9 is doable but difficult).
My floor is rather smooth, so the structure can be approximated by placing ideal balls with some friction due to the rough surface on a no-friction floor.
The weight of the pyramid grows by the power of 3 whereas the surface of the basement by the power of 2, but static friction is proportional to weight, so still I do not immediately see why larger tetrahedrons should be more unstable. But building real ones shows they are. Why? can some formula be derived for maximum height with friction coefficients, size and weight of the balls?