Eli5, Why does eulers disc spin for so long?
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It’s two very hard and smooth surfaces rolling (not sliding…that’s important) against each other. This means the friction is *very* low. Coupled with the disk being pretty heavy, there’s a lot of kinetic energy (from the initial spin) and gravitational energy (from the disc starting vertical) compared to the friction.
The system has almost no way to get rid of energy…there’s a *tiny* bit from rolling friction, but it’s small. There’s a tiny bit from air friction but it’s also small (the disc isn’t spinning so fast that air friction is huge compared to its mass). And that’s about it. The only way the disc can stop spinning is to get rid of all its energy but it has very few ways to do that and the few ways it does have are terrible at dissipating energy (on purpose).
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