compression, external stress applied to an object or substance, tending to cause a decrease in volume (see pressure). Gases can be compressed easily, solids and liquids to a very small degree if at all. Water, for example, is practically incompressible, thus making it especially useful for hydraulic machines. According to the kinetic-molecular theory of gases, when the molecules of a gas are brought close enough together by compression, the gas (under certain conditions of temperature) undergoes liquefaction. This principle is applied commercially to several gases, including liquid oxygen and the so-called bottled gas (a mixture of hydrocarbons) used as a fuel. Boyle's law deals with the decrease in the volume of a gas in relation to the increase of pressure upon it (see gas laws). The ability or the degree to which an internal-combustion engine reduces the volume of its fuel mixture preparatory to firing is called its compression. Also, a region of high pressure in a fluid is called a compression; thus sound waves are said to propagate at compressions and rarefactions (regions of low pressure) of their medium, such as air.

Compression may refer to:

In physical science:

  • Physical compression, the result of the subjection of a material to compressive stress (the opposite of tension)
    • Compression member, a class of structural elements, of which a column is the most common specific example
    • Compressibility, the reciprocal of the bulk modulus (typically for solids)
  • Gas compression, raising the pressure and reducing the volume of gases
    • Compression ratio, a number that predicts the performance of any internal-combustion engine
    • Compressibility, a measure of volume change resulting from pressure (typically for fluids)
  • Compression (geology), a system of forces that tend to decrease the volume of or shorten rocks

In information science:

In other sciences and technologies:

  • Compression, in zoology and paleontology, refers to when an animal, or part of an animal, is shorter or narrower compared with other animals in the same group; e.g. the body of a lizard may be compressed (flattened) so it can better fit into crevices under rocks
  • Compression (functional analysis), in mathematics
  • Compression bandage, designed to reduce the flow of blood

See also

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