A flute and an organ produce sound from a resonating air column. The flutist’s lips direct a stream of air into the mouthpiece to set up the vibration of the air inside the instrument. The strength and direction of the air stream determine the harmonic content of the vibration and thereby the octave of the musical note. In the organ, compressed air is blown into each tube to create the resonance. Each pipe in the organ has a different length and produces a different note, with longer pipes producing lower notes. The flutist produces different notes by pressing keys to expose openings in the instrument that, in effect, change its length.