When two steel balls are glued together and spun on a flat surface, one ball inevitably rises above the other and the pair spins like a top with a fixed center of mass. Popularly known as hurricane balls, a spinning double sphere can easily be driven to rotation rates of more than 5000 rpm. Moreover, because it rolls without slipping, there is very little friction, so the system will remain whizzing around for several minutes. The resulting motion is quite captivating. (For the dynamics of another intriguing spinning system, see the Quick Study on page 70.)

As the double-sphere system spins about its axis of symmetry, it also precesses about the vertical axis. Interestingly, due to the system geometry, the spin and precession rates perfectly match, as demonstrated in the time-lapse sequence shown here. A team of researchers at Dickinson College spun up this double sphere to 2449...

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