Measuring and Modeling the Force between Permanent Magnets

In a 1993 book review, E. Pearlstein asks, “Why don’t textbook authors begin their discussion of magnetism by talking about magnets? That’s what students have experience with.” A similar question can be asked, “Why don’t professors have students measure the force between permanent magnets in introductory physics labs?” The answer to both questions may be the same. There is no simple equation describing the force between two permanent magnets. Yet, this familiar magnetic phenomenon deserves investigation. This article presents a novel apparatus using 3D-printed parts for measuring the force between two small cylindrical neodymium permanent magnets as a function of their separation. Data collected using this apparatus is compared to two models, namely an ideal dipole–dipole interaction, and the force between parallel coaxial loops of current.