Torsion pendulum revisited

We present an analysis of the motion of a simple torsion pendulum and we describe how, with straightforward extensions to the usual basic dynamical model, we succeed in explaining some unexpected features we found in our data, like the modulation of the torsion mode at a higher frequency and the frequency splitting of the swinging motion. Comparison with observed values yields estimates for the misalignment angles and other parameters of the model. •We describe experimental results showing an unexpected libration of the oscillations.•Lagrangian model of an ideal torsion pendulum for small oscillations.•Lagrangian model for a torsion pendulum affected by small misalignments.•Comparison of this last model with the data achieved.