Measuring the speed of sound with a pan flute and a smartphone: a half-melodic and totally-didactic experiment

Abstract

Teaching wave-physics and related phenomena with musical instruments results in a very pleasant and didactic approach for undergraduate students. Music allows teaching concepts such as frequency, amplitude, harmonics, resonance, and so on. In addition, one may use some instruments to calculate other quantities such as the air density or the speed of sound in the air. In this work, we use a conventional bamboo-made panflute and a smartphone to obtain the speed of sound in the air. The method is simple. It consists of making the pipes sound and measuring the frequency of the fundamental harmonic. The frequency is approximately proportional to the inverse of the pipe length and this dependence allows us to obtain the speed of sound quite accurately from the slope of the curve. We compare it with the theoretical value and analyse three possible causes of discrepancy such as the end correction, the air composition, or the straightness of the tubes. The proposed experiment can be carried out completely by the students since it does not involve any danger. In addition, it could be appropriate for undergraduate students or even school students.