Strike to hear the whole decay.
Equal masses on vertical rails, moving sideways only, shown in real time (displacements scaled to fit). Neighbours are joined by springs (tension k), and each mass resists bending (κ, on how far it sits off the line through its neighbours). The springs also stiffen as they stretch (k3): this is the nonlinearity. Strike gives one mass, or one normal mode, the energy on the slider.
The ends are clamped (fixed, and held level), pinned (fixed, free to turn), or a cantilever: clamped at the left and free at the right. Bending makes the overtones inharmonic, as in a bar or a cymbal. Weak strikes ring as independent normal modes; strong ones trade energy between them. The space bar pauses.
Mass, tension k, bending κ (either may be 0, not both), stretching k3, the rest spacing a (drawing only), and the decay time τ of the amplitude (drag on the masses; 0 for none). Apply restarts the beam at rest.
Stretching "local" stiffens each spring by its own stretch, as in the FPUT chain. "Kirchhoff" gives all springs one shared tension set by the total stretch, as for a beam whose ends are held apart. The two agree when every spring is stretched alike. The nonlinear scale below is the energy of mode 1 at which its stretching energy equals its linear energy.
A copy of the same strike, run fast enough to be heard: Pitch sets where the lowest normal mode lands, and the whole decay plays in a few seconds. While this panel is open each Strike plays a note; Replay plays the last one again with the current settings.
Save WAV saves the last note as heard (16-bit mono, normalized). Signal chooses what is heard. The spectrogram spans the whole note, with dashed lines at the normal-mode pitches; a warning shows when the top mode is above half the sample rate and would alias.