Through numerical investigations, we study examples of the forced quadratic spring equation [image omitted]. By performing trial-and-error numerical experiments, we demonstrate the existence of stability boundaries in the phase plane indicating initial conditions yielding bounded solutions, investigate the resonance boundary in the [omega] "F"-plane for fixed [epsilon], examine harmonic and subharmonic trajectories and van der Pol plane analysis. All these invite further numerical and analytic investigations suitable for student or small group computer laboratory research problems. (Contains 11 figures.)