Standing Waves--Free/Open EndsStanding Waves--Free/Open Ends
This shows longitudinal standing waves, such as in sound waves in a pipe open at both ends. The spots are representative regions of air (not really molecules, whose high-speed random motion is not shown). The top wave is the fundamental (longest wavelength allowed), or first harmonic. It has displacement antinodes at each end, and a displacement node in the middle. When the displacement is large and to the right at one end, it is large and to the left at the other, and they're separated by one node. In other words, it is one-half wavelength from one end to the other. The next two waves show the next two harmonics, the second and the third. The pipe holds, respectively, two and three half-wavelengths, and shorter wavelengths correspond to higher frequencies--the frequencies are two and three times the fundamental.
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Standing Wave (open) |