This experiment explores the behavior of a pair of loosely coupled compass needles in air with weak damping. The needles are far enough apart that the magnetic interaction between their magnetic dipoles is much weaker than their interaction with the Earth's magnetic field. The resulting motion displays beats--when one compass is momentarily at rest, the other oscillates with maximum amplitude.

A trz file is a zip file that contains additional information for Tracker.  It can also be opened with standard zip tools to extract the video clips.

Please note that this resource requires at least version 1.6 of Java (JRE).