Here's my second attempt at a groovy electromagnetic interaction demonstration. It's based on a setup I saw Don Walters use at The Naval Postgraduate School at an NCNAAPT meeting. He did a quick take, and I thought it was an improvement on The Exploratorium's Magnetic Pendulums.
As I often do, I milked this demo (and many tangents to it) for all I thought they were worth. To summarize, this demo shows electromagnetic interaction and slowly and carefully constructs observational evidence for Lenz's law.
Find the PDF here: Bobbing for Magnets PDF.
Find the answer key PDF here: Bobbing for Magnets Key PDF.
Find the preso here: Bobbing for Magnets QT. My presentations are rarely simple, linear expositions of the corresponding worksheet. You've been warned.
UPDATE: Fixed the link to the PDF. (Thanks Alby and Stephanie.) AND, I added a QuickTime Presentation for your enjoyment.