Stability is sensitive to frequency characteristics of the system
This is a dramatic example of the significance of the two interpretation types: here the interpretation expressed in terms of time and route conceals the potentially extreme danger of marching in stride close the bridge’s frequency of vibration.
The amplitude–frequency curve of the bridge’s mechanical model shows that the bridge substantially amplifies sinusoidal input signals at a given frequency. If the frequency of the soldiers’ marching feet matches this range, the bridge can collapse.