This Demonstration shows the transversal oscillations of a four-spring, three-mass system. The bodies (red dots) are constrained to move only in the vertical direction.
A periodic force acts on the right end of the fourth spring, so at certain frequencies (displayed on the plot) resonance occurs with different oscillation modes. You can see free vibrations by setting the frequency of the periodic force to 0 Hz. As a bonus you can see the influence of the gravitational field on the system.
