Weighing a Magnet as it Falls with Terminal Velocity Through an Aluminum Pipe Available to Purchase

With the wide availability of strong neodymium magnets, the slow and stately fall of a magnet through a conducting pipe has become a favorite classroom demo for teaching electromagnetic induction, Newton’s third law, and Lenz’s law. Since Lenz’s law is conceptually difficult for some students, several authors have used this demo to explore in greater detail the role of eddy currents in braking the fall of the magnet through the conducting pipe. The demo also serves as an excellent application of Newton’s third law in a clear case of action-at-a-distance interaction. Other authors have focused attention on various aspects of this demo, from methods for measuring the terminal velocity to detailed analysis of electromagnetic damping. In this paper we explore the equilibrium condition of the magnet as it falls with constant velocity through a conducting pipe and present two simple methods for measuring the electromagnetic braking force directly during the magnet’s fall.