Spinning Coin

The three things that cannot change

While the coin rolls without slipping, the contact force does no work. The energy is conserved — and so are two more quantities that come from the rolling disk being an integrable problem. Turn the friction off and watch all three stand still while the coin thrashes.

Drift is measured against the values at the moment you pressed Spin.

Which exponent is this?

Every published account of the speed-up predicts the same shape and a different number. The clean way to read it off needs no guess about when the motion stops: dOmega/dt grows as Omegaⁿ⁺¹, so the slope on these axes is all there is. The grey lines are what each published claim would look like.