Rarefactions

Part of speech: noun

Definitions

1. The occurrences of a decrease in density within a medium, particularly in sound waves, indicating a region where particles are less concentrated
2. The phenomenon in physics describing regions where the pressure in a substance, such as air or water, is lower than its surrounding areas
3. Variations in mass or density occurring in a wave system, often associated with sound, where regions experience lowered pressure or density levels

Etymology: "Rarefactions" is the plural of "rarefaction," which came into English from Middle French "raréfaction." That French word was in turn built on the Latin verb "rarefacere," meaning "to make thin or loose," which combined "rarus" ("thin, sparse") with "facere" ("to make"). The English noun was formed on the pattern of "rarefy," and so "rarefaction" literally names the act of making something less dense. In physics, the word carries that same sense of thinning out. When a sound wave travels through air, the compressions and rarefactions alternate: a rarefaction is the stretch where air particles are spread farther apart, leaving pressure below its normal level. The term thus describes a region of lost density rather than an object or substance.

Synonyms: rarefaction, thinning, expansion, dilation, decompression