A standing wave in a tube is produced by interference with the wave traveling down the tube and its reflection from the end. The standing waves in a tube are represented by a graph line shown in green. This indicated the amount of vibration, but it can be misleading. It seems to show the molecules vibrating across the tube, but the do not. Sound is a longitudinal wave, the molecules vibrate back and forth along the tube.

The green line is a graphical indication of the amount of vibration of the air molecules along the tube. This resulting in rapid pressure changes at the antinodes from compression to rarefaction. 

  back and forth in a direction along the tube. To make the individual molecules vibrate an energy input has to be made. This could be 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.