The ballast metronome

We present an educational activity concerning the realization of a homemade ballast metronome and the experimental investigation of its oscillations that can be varied by changing the position of a movable weight along a vertical rod. The instrument is equipped with a mechanical escapement powered by an elastic rubber band. We analyze the mechanical system in terms of a compound pendulum. However, due to the presence of the escapement and friction, not taken into account in the model, the experimental data are only qualitatively accounted. The proposed experimental activity can be easily carried out in the classroom, at secondary and high school physics laboratory. The ballast metronome can be used for marking musical tempos, as a classical mechanical metronome. Furthermore, it gives the opportunity to teach/learn concepts at an elementary level concerning the elastic potential energy, the mechanism of the escapement, and the pendulum isochronism exploited for measuring time, contributing to increase student’s engagements in physics.