Modeling mechanical, magnetic and thermal processes in high school lab activities: an experiment with a rotating disc

Abstract

In this paper we present the case study of a rotating disc stopped by a dissipative interaction arising from the relative motion between some magnets, fixed on top of the disc, and a copper plate kept at rest at a very short distance above them. We measure the time dependence of the angular velocity of the disc and the temperature change in the copper plate, during both the braking phase and the subsequent cooling process. The experiment is analysed and modelled step by step:• from the mechanical point of view, the dry friction (always present) and the magnetic braking interaction are separately modelled: indeed, comparing the model results with the collected data, from the measured angular velocity vs. time it is possible to determine the value of all the phenomenological coefficients;• from the thermal point of view, the model stresses the quantitative connection between the dissipative process (due to the eddy currents generated by the magnetic interaction), the thermal conduction with the surroundings, the temperature changes of the copper plate and that indicated by a thermometer placed inside it;• from the energy point of view, testing this way the coherence of the whole model.From a didactical perspective, each sub-model emerged step by step developing independently the various parts of the model can be considered as a quantitative conceptual map, and represents therefore a powerful tool for interaction with the thought schemes used by the students.