## 10 April 2018

### Astronaut demonstrates rotational inertia

"The effect shown in this clip is true for any object that has three different moments of inertia, e.g. as shown here for a prism. If you try to spin the object along two of its axes, it will spin in a smooth stable way, as shown here. In particular, these axes are the ones that have the highest and lowest moment of inertia. On the other hand, if you try to spin it around the axis with the intermediate moment of inertia, things get a bit chaotic. The reason is that any small perturbation (e.g. if you didn't throw it perfectly or if a whiff of wind blows) in the motion will cause the object to try to rotate about another axis of rotation as well. The net result is that you get the tumbling you see in the GIF. This effect is called the intermediate axis theorem, or the tennis racket theorem. In case you are interested in a more technical explanation, I posted a longer write-up here a while back."
More discussion at the Wikipedia entry on the Tennis Racket Theorem and at the Educational GIFs subreddit source.