Vibration quanta {phonon}| are sound-wave packets. Crystal phonon vibrations cause temperature gradient sideways to phonon direction, analogous to Hall effect for electromagnetism.
Surfaces can have acoustic waves {Rayleigh wave}. Earthquakes and radio waves can put Rayleigh waves in Earth or ionosphere. Ultrasonic surface acoustic waves can store, recognize, filter, and channel electronic signals in semiconductors, at 10^9 Hz.
Moving objects make sound {sonic boom} as they push air aside {shock wave}|. If object speed becomes the same as sound speed, waves of pushed-aside air travel as fast as sound. Waves are in phase and grow to make large wave. If plane travels faster than sound speed, sound is behind pushed-aside air, waves do not build up, and no shock wave builds.
Objects can go through air faster than air sound speed. Sound from object contact with air cannot travel away faster than sound waves build up. Wave constructive interference creates shock wave, which carries extra energy away when object breaks sound barrier, causing sonic boom. After passing sound speed, acoustic waves at sound speed are slower than object speed, with no more constructive interference.
Speech sounds {speech sound} have frequency range from 250 Hz to 2000 Hz and loudness range from 63 to 95 decibels.
Sounds {ultrasonic sound}| can have frequency greater than 20,000 Hz. Ultrasonic sound can visualize body insides and clean dishware.
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Date Modified: 2022.0225