Standing waves in a tube
A standing wave in a tube is produced by interference with the wave traveling down the tube and its reflection from the end.
The green line is a graphical indication of the amount of vibration of the air molecules along the tube, resulting in rapid pressure changes at the antinodes. The vibration is longitudinal, the molecules oscillate in a direction along the tube.
The individual molecules vibrate back and forth in a direction along the tube. To make them vibrate an energy input has to be made, for example by a speaker, a tuning fork or by blowing across the end of the tube. Most molecular motion occurs at the antinodes with changes between compression and rarefaction. The least (zero) molecular motion occurs at the nodes.
By blowing across a tube the fundamental note will be produced. The wavelength of the note will be 4 times the length of the tube.
Using a tuning fork or speaker we can induce harmonic notes.
A standing wave is possible in an open tube. There must be an antinode at each end. This is therefore a graphical representation of the fundamental note.
A PDF copy of notes which can be easily downloaded and printed is available here:Waves - standing waves in a tube (2 sheets)