Il moto dell’altalena: un gioco antico studiato con tecnica moderna

See-saw motion is investigated using an on-line data acquisition system made of TI89, CBL, and a motion sensor (sonar). Two cases are considered: the twin-edges pivot and the round pivot. We discuss the different behaviours that lead either to strongly anharmonic or to nearly harmonic motions. Simple models are presented that predict the dependence of the oscillation period from the amplitude and from the geometric parameters. The relevance of the investigation of oscillatory motions in physics teaching is discussed.