2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/116804We investigate a torsional pendulum containing a ferrofluid that is forced periodically to undergo small-amplitude oscillations. A homogeneous magnetic field is applied perpendicular to the pendulum axis. We give an analytical formula for the ferrofluid-induced ``selfenergy'' in the pendulum's dynamic response function for monodisperse as well as for polydisperse ferrofluids.7 pages, 6 figuresFluid Dynamicstext