Rarely do we manage to “see” the sound. We can sometimes notice digital ripples in voice recordings, but observing sounds, especially in real life, is a rarity. However, a classic physics experiment allows us to do just that. It's called a Rubens tube, or standing wave flame tube, and it shows the relationship between sound waves and sound pressure.
A viral post on Reddit demonstrates what this looks like in practice using a tube-operated Rubens tube. The fascinating result is a breathtaking demonstration of scientific principles.
The physical experiment was developed in 1905 by the German physicist Heinrich Rubens. The assembly is a length of pipe with holes drilled along its top and sealed at both ends. One end is a propane tank (or other flammable gas source) and the other is the sound source.
The chimney is then lit and a stagnant flame appears. When a sound is produced - in this case a trumpet is playing - the vibrational pressure of the sound waves allows the gas to escape and forms the sound curve.
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