I made these videos using my cell phone and a magnetic ball-and-stick polyhedron building system which my wife bought for me. It’s the sticks that have magnets in them, not the steel balls. First, a triangular dipyramid (n = 3). This is the simplest of the dipyramids.
Next, a square dipyramid, also known as an octahedron (n = 4).
Next, for n = 5, the pentagonal dipyramid.
If you limit yourself to dipyramids that have equilateral triangles for faces, that’s the complete set. Here’s what happens when you try n = 6 — the dipyramid has zero height, and collapses into a pair of isosceles trapezoids when lifted.
To get this to work, you’d need to use isosceles triangles, not equilateral ones. The same is true for n = 7 and greater numbers.
I’ve made those same spinners in the top two videos. They’re so cool and so satisfying, aren’t they. Thanks for making them into videos, and inspiring some further exploration!
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It’s amazing how long it takes friction to slow down and stop one of these.