@Thedadlab came up with this amazing demonstration using Polydron Sphera:

This relatively simple demonstration of the mechanical paradox is a great way to get young kids to think about physics principles. I used Polydron Sphera from Polydron to make a cylinder and a bicone (two cones joined together at their bases). The cylinder rolls downhill, but bicone rolls towards the upper end, apparently defying gravity. The “trick” here is that the track gets wider apart towards the upper end and because of its shape the bicone’s center of mass is actually traveling downhill!

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