(Once the box is selected/deselected you must reinitialize your choice.)
This physlet simulates a harmonic oscillator driven by a square wave. The natural frequency of the oscillator is 1.414 so oscillations grow quickly when the object is driven at this frequency. Find another drive frequency that is a multiple or fraction of the natural frequency and that also gives rise to growing oscillations. Explain why the new frequency is effective. What other frequencies would work? 

This Physlet was written by Tim Gfroerer and scripted by Mario Belloni.