Dual Axis Sand Pendulum

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Dual Axis Sand Pendulum: the kinetic energy trades back and forth between swinging toward the support arm and then swinging perpendicular to that path tracing Lissajous figures in the sand. The sand slowly dissipates the energy and the traced figures get smaller so the next one fits inside the last. Coupled oscillations like this can occur when multiple modes of motion (degrees of freedom) are available to the system.