This is a CDF file and requires Wolfram's free CDF Player plugin for your browser. It shows the solution to an undamped second order linear differential equation with a square wave input fixed at the natural frequency. This results in resonance of course. There is a slider to extend the time scale, but no other values can be adjusted. The page includes a short text explaining the problem and the solution in terms of Laplace transforms, but the details of taking a Laplace transform of a square wave are omitted.