Magnetic Repulsion: An Introductory Experiment

To measure the repulsion between two bar magnets gives students direct experience of action at a distance and of an inverse square force. This can be done using a balance assembled from standard laboratory components. The results are analyzed by assuming an interaction between two fixed poles located near the ends of the magnets, the force between them varying inversely with the square of the distance. The theory can be extended to cover all the interactions of the two pairs of poles. Calculations from the extended theory show that within the useful range of the experiment there are no induction effects and the poles do remain fixed. Although these theories are inconsistent with the usual presentation of electromagnetic forces arising from the interactions of charges, the experiment is useful as an illustration of model-building in physics.