Take a listen to the sound of a tuning fork struck by a hard mallet. The two panels of the graph show the time waveform of the sound. The displacement of the tongs is plotted on the y-axis and time is plotted on the x-axis. The time scale of the upper panel is in the order of seconds. The time scale of the lower panel is in the order of milliseconds. Note in the lower panel that the motion of the tongs is comprised of two visible oscillations. Superimposed on top of a large-amplitude, low-frequency oscillation is a low-amplitude, high-frequency oscillation. If you listen carefully you can here two separate pitches corresponding to the two frequencies of vibration.
