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The tennis racket theorem, demonstrated in a Soviet space station. (Via Math Overflow.)

(The tennis racket theorem asserts that when rotating a rigid body with three distinct moments of inertia, the rotation around the axes with the largest or smallest moments of inertia is stable, but the rotation around the axis with the intermediate moment of inertia is unstable. Indeed, in the latter case the object will (when one looks just at the angular velocities) typically traverse periodically through the space of all states with the given angular momentum and energy, which is a closed curve known as a

(The tennis racket theorem asserts that when rotating a rigid body with three distinct moments of inertia, the rotation around the axes with the largest or smallest moments of inertia is stable, but the rotation around the axis with the intermediate moment of inertia is unstable. Indeed, in the latter case the object will (when one looks just at the angular velocities) typically traverse periodically through the space of all states with the given angular momentum and energy, which is a closed curve known as a

*herpolhode*that will pass close to both antipodes of the unstable equilibrium in an alternating fashion.)View 13 previous comments

- I also like the bit at 2:35 where the Earth has flipped chirality. The rest of the animations have the continents the right way out, which makes it extra funny.Nov 27, 2011
- I was under the impression that the Earth does exhibit true polar wander, but on a roughly 500Ma time scale rather than a 12Ka time scale - this is enough time for the mass distribution to shift due to plate tectonics and other geologic processes.Nov 27, 2011
- As Terry Tao already replied to Vladimir Nesov, the described phenomenon does not apply to the Earth. Totally different is the geomagnetic reversal whose possible dynamical model is the mechanics of the rattleback as proposed by Moffatt and Tokieda in their paper here: http://www.igf.fuw.edu.pl/KB/HKM/PDF/Moffatt_Tokieda_2008.pdf .Dec 1, 2011
- We used to do this exercise in my college physics class however the tennis racket was replaced with the textbook for the course and you just had to throw it up in the air hard enough that it would rotate enough times before it fell back down. It helped to put a rubber band around the book and also remember to subtract off the projectile motion of the center of mass (thus the same problem as on the space station).Dec 12, 2011
- I have made a machine,what you think the engineering department would do with it if I give it to them?.Dec 13, 2011
- +Andrea Bertozzi Indeed, a book with a rubber band around it is a good way to demonstrate the tennis rack theorem. When it is tossed up, if it is set spinning around the axis with the intermediate moment of inertia, it will tend to tumble, and be hard to catch.Dec 9, 2013