Skulls in the Stars

One of the challenges of doing physics outreach is that there are so many cool phenomena which simply can’t be demonstrated in an eye-catching way, because they are too small, too subtle, or too complicated.  So whenever I find a demo that really has a “WOW!” factor to it, I treasure it.

A perfect example of this is a demonstration of what are known as eddy currents, which can be done with a simple copper pipe and a neodymium magnet that fits easily inside it. I took the following video a few days back:

Isn’t this the coolest thing? The magnet seems to float down the tube, only occasionally touching the walls of the pipe, seeming to defy gravity.

The phenomenon is cool, and the way it was discovered is also fascinating: it was first observed by the Most Interesting Physicist in the World™, François Arago, using an ordinary compass!  It is one of those remarkable discoveries that is, however, largely unknown to most physicists, much less the general public — I only came across a chance mention of it recently that led me to explore further. In this post I want to look at both the physics and the history — and the arguments that followed.

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