MOLECULES, WAVES, AND SOUNDS
Sounds occur wherever there are large numbers of molecules, or freely moving particles. Many sounds occur outside of the threshold of human hearing.
Sound waves occur in gas, liquids, organic and inorganic solids, and in plasmas and superconductors.Sound waves vibrate at frequencies which range from billions of cycles per second, to a single cycle within a period of several days, months, or years.
Sounds travel in a variety of media at different velocities ranging from subsonic speeds of several feet per second, to hypersonic speeds which approach the speed of light.
Sound waves range in scale from tiny microacoustic sounds produced by thermal fluctuations of the trapped particles in a normal sound wave, as well as infinitesimal sounds generated in plasmas and superconductors, to macroacoustic sounds including seismic waves, global waves, solar waves, and galactic waves.
At the human scale, various sounds are propagated in the Earth's atmosphere, hydrosphere, biosphere, and lithosphere, including normal sounds in air, weather patterns, ocean waves, and seismic waves.
Sounds are generated on or near other planetary bodies and satellites, in the stellar wind, on the surface of stars, in interstellar dust clouds, in spiral galaxies, and in intergalactic clouds which occur in the regions between galaxies and clusters of galaxies.
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