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How To Build a Short Foucault Pendulum
KentuckyFC writes "Set a pendulum in motion and you'll inevitably give it an ellipsoidal motion, which naturally tends to precess. That's bad news if you want to build a Foucault Pendulum, a bob attached to a long wire swinging in a vertical plane that appears to rotate as the Earth spins beneath it. The natural precession always tends to swamp the rotation due to the Earth's motion. There is a solution, however: the behavior of the ellipsoidal motion is inversely proportional to the pendulum's length. So the traditional answer has been to use a very long pendulum (Foucalt's original in Paris is 67 meters long). Now scientists at Carnegie Mellon University have another solution (abstract). They've created a motor that drives a pendulum in a way that always cancels out the precession. That means the effect of Earth's rotation can be seen on much shorter pendulums such as the 3-meter pendulum on which they've tested their motor. That's just the start though. They say there is no limit to how short the new generation of Foucault Pendulums can be, and even talk about the possibility of tabletop devices."
(maybe slightly OT)
As well as a physics experiment, Foucault's Pendulum is a fantastic book by Umberto Eco.
It's in the same subject area as the Da Vinci Code before that opportunist lightweight Dan Brown ever put pen to paper, and it has far more depth and erudition. There's even some code (BASIC) in it...
You don't, and as scientific proof of the Earth's rotation, this is obviously completely useless. But if you trust the motor, this is a fun way to see what a Foucault pendulum does, without the expense and inconvenience of needing a full-sized model.
True enough, but if you ever want to show it to others, there will be skeptics.
I once saw a full-size Foucault pendulum at a science museum. If you stood and watched it for a few minutes you could see the precession (there were markings on a ring around the pendulum, so it was easy to see where it swung before). I overheard some other patrons asking if it was powered, why it didn't come to a stop, etc. The museum guide explained that it was not powered and how it worked, and mentioned that because of air resistance they used an electromagnetic ring to give it a tiny "push" with each swing to keep it going. He also explained that because the magnet was circular, it would always push the pendulum directly back the way it came rather than from side to side.
Several onlookers remained convinced that it was a trick and the electromagnet was causing the precession. And remember, these are people standing in a science museum, looking at an exhibit so massive it required the entire building to be designed around it, whose entire point was to show this effect.
Now imagine if there had been a motor attached to it, designed to "compensate for ellipsoidal motion"....