Originally shared by Eli Fennell
Sound Waves May Be Antigravitational
Sound waves are traditionally thought of as massless waves, and therefore not exactly governed by gravity, with any upward molecular motion countered by equal downward motion.
A new paper in the preprint journal arXiv argues that, in fact, sound waves (or, rather, the quasiparticles of sound vibration called phonons, which to be clear are not real particles but behave much like particles) have a slight positive mass. While you might expect this to mean they would fall under gravity (if perhaps very slowly), as other masses would do, in fact the opposite would be true: the sound waves would move slowly against gravity, in effect falling up instead of down.
This is because sound waves propagate more quickly through less dense media, and in an atmosphere under gravity like our own, this will be below the sound wave. This difference in speed above and below the wave causes it to gradually deflect upwards.
While this is of minimal interest for understanding sound waves here on Terra Firma, it has potential implications for exotic phenomenon such as near Speed of Light sound waves observed in neutron stars.
#BlindMeWithScience #Physics #Acoustics
https://www.livescience.com/63305-sound-waves-negative-gravity-mass.html
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