Ring Falling into a Chain: No Magic — Just Physics

Abstract

Magic tricks are very popular, and they can and should be used in teaching when the underlying principle is easily explained by physics. Such tricks often fall in the realm of hands-on experiments, which are considered to be potentially very effective in raising interest and motivating students.1 Unfortunately, many hands-on experiments are easy to do, but more difficult to explain. One of the reasons is that they often happen so fast that the underlying principle can only be guessed. Also, a magic trick can be disguised so that an observer cannot solve the puzzle with the naked eye. Quite often even regular camcorders do not provide the necessary time resolution. Fortunately, however, huge advances in microsystem technologies have recently led to the development of commercially available high-speed cameras that are relatively inexpensive. The low end of the price range is now at or below $300.2 Some models of the Casio Exilim series provide up to 1200 frames per second for reduced image size. The technology of such cameras has been extensively summarized elsewhere,3 and many nice examples of experiments recorded with high-speed imaging are under way.4 Here we present one example of a physics “magic trick” that is extremely easy to perform while giving stunning results. High-speed images (snapshots and movies) can nicely reveal the physics behind the trick.