Submission + - How To Build A Short Foucalt Pendulum (arxivblog.com)
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 Foucalt Pendulum, a bob atttached 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 behaviour 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 orginal 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 they've tested their motor on. That's just the start though. They say there is no limit to how short the new generation of Foucalt Pendulums can be and even talk about the possibility of tabletop devices."
