Rarefaction

Rarefaction

Rarefaction is the reduction of a medium's density, or the opposite of compression.

A natural example of this is as a phase in a sound wave or phonon. Half of a sound wave is made up of the compression of the medium, and the other half is the decompression or "rarefaction" of the medium.

Another natural example of rarefaction is in the layers of our atmosphere. Because what constitutes our atmosphere has mass, it is definite that most of the atmospheric matter will be nearer to the Earth. Therefore, air at higher layers of the atmosphere is considered to have less pressure, or is "rarefied" in relation to air at lower layers.

Rarefaction can be easily observed by compressing a spring and releasing it.

Rarefaction waves expand with time; for most gases the rarefaction wave keeps the same overall profile at all times (it is a 'self-similar expansion'). Each part of the wave travels at the local speed of sound, in the local medium. This expansion behaviour is in contrast to the behaviour of pressure increases, which get narrower with time, until they steepen into shock waves.

Rarefaction can refer to an area of low relative pressure following a shockwave.

See also

* Prandtl-Meyer expansion fan

External links


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Look at other dictionaries:

  • raréfaction — [ rarefaksjɔ̃ ] n. f. • 1370; lat. médiév. rarefactio 1 ♦ Fait de se raréfier; diminution de la densité d un gaz et augmentation de son volume. Raréfaction de l air en haute montagne. Pathol. Raréfaction du tissu osseux : ostéoporose. 2 ♦ (1872)… …   Encyclopédie Universelle

  • rarefaction — Rarefaction. s. f. v. Terme dogmatique. Action de rarefier, & estat de ce qui est rarefié. Il est opposé à condensation. La rarefaction de l air. cela se fait par la rarefaction …   Dictionnaire de l'Académie française

  • Rarefaction — Rar e*fac tion (r[a^]r [ e]*f[a^]k sh[u^]n), n. [Cf. F. rar[ e]faction. See {Rarefy}.] The act or process of rarefying; the state of being rarefied; opposed to condensation; as, the rarefaction of air. [1913 Webster] …   The Collaborative International Dictionary of English

  • Rarefaction — (v. lat.), 1) Ausdehnung einer diffusibeln in einem begrenzten Raume eingeschlossenen Materie, so daß auf ein gegebenes Raumtheilchen von der darin enthaltenen Materie weniger Atome, als vorher, gehen, die Atome also darin seltener geworden sind; …   Pierer's Universal-Lexikon

  • Rarefaction — Rarefaction, lat. deutsch, Erweiterung der Schweißlöcher; Verdünnung der Luft durch Wärme …   Herders Conversations-Lexikon

  • rarefaction — c.1600, noun of action from L. rarefacere (see RAREFY (Cf. rarefy)) …   Etymology dictionary

  • raréfaction — (ra ré fa ksion) s. f. Terme de physique. Action de raréfier ; état de ce qui est raréfié. •   C est cette seule raréfaction du sang qui est cause du mouvement du coeur, DESC. Foetus, 2. •   À une très forte chaleur, la raréfaction de l air est… …   Dictionnaire de la Langue Française d'Émile Littré

  • rarefaction — noun Etymology: French or Medieval Latin; French raréfaction, from Medieval Latin rarefaction , rarefactio, from Latin rarefacere to rarefy Date: 1572 1. the action or process of rarefying 2. the quality or state of being rarefied 3. a state or… …   New Collegiate Dictionary

  • RARÉFACTION — s. f. T. didactique. Action de raréfier ; État de ce qui est raréfié. Il est opposé à Condensation. Cela se fait par la raréfaction. La raréfaction de l air …   Dictionnaire de l'Academie Francaise, 7eme edition (1835)

  • rarefaction — rarefactional, adj. rarefactive /rair euh fak tiv/, adj. /rair euh fak sheuhn/, n. 1. the act or process of rarefying. 2. the state of being rarefied. [1595 1605; < ML rarefaction (s. of rarefactio), equiv. to L rarefact(us) (ptp. of rarefacere;… …   Universalium

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