  We show that the natural resonant frequency of a suspended flexible string is
significantly modified (by one order of magnitude) by adding a freely pivoting
attached mass at its lower end. This articulated system then exhibits complex
nonlinear dynamics such as bending oscillations, similar to those of a swing
becoming slack, thereby strongly modifying the system resonance that is found
to be controlled by the length of the pivoting mass. The dynamics is
experimentally studied using a remote and noninvasive magnetic parametric
forcing. To do so, a permanent magnet is suspended by a flexible string above a
vertically oscillating conductive plate. Harmonic and period-doubling
instabilities are experimentally reported and are modeled using the Hill
equation, leading to analytical solutions that accurately describe the
experimentally observed tonguelike instability curves.
