Molecular-vibration waves {sound, physics} can move through materials.
process
Molecules from outside material can collide with material, causing material molecules to move. Molecular movement causes collision with adjacent molecules. First molecules bounce backward, and second molecules move, causing collision with adjacent molecules, and so on. Collisions send longitudinal wave down motion line.
Sound compresses {compression, sound} material in front of it, leaving slight vacuum {rarefaction} behind compression. Compression pushes next material bit forward. Original bit bounces back to original position, so material does not move. Compression wave travels through material. Only wave and energy move.
speed
Medium determines sound-wave speed. Sound-wave speed increases with stronger interactions between molecules. Wave frequency and amplitude do not affect speed.
amplitude
Sound has kinetic energy {loudness, sound}. Kinetic-energy increase increases sound-wave amplitude, by moving molecules farther. Frequency, wavelength, and speed do not affect wave amplitude.
pitch
Sound has number {frequency, sound} of vibrations per second. People can hear sounds of 20 to 20,000 Hz.
Sound has frequencies at two, three, four, and so on, times fundamental frequency {harmonics, physics}. Higher harmonics have lower amplitude.
Outside-material vibration frequency determines sound-wave frequency. Materials can have resonance frequencies.
Sound waves travel in a medium, and the medium can be moving, making net sound-wave velocity faster or slower {Mach effect}.
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.
Rooms {whispering gallery} can have focal points, where sound focuses {echo}|. Canyons and buildings can echo sound. Echoes work best with low amplitude and high frequency.
High-frequency sound can locate objects by echo pattern {echolocation}| {sonar, location}.
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Date Modified: 2022.0225