Editing Rarefaction (section)

==Physical examples==

A natural example of rarefaction occurs in the layers of [[Earth's atmosphere]]. Because the atmosphere has [[mass]], most atmospheric [[matter]] is nearer to the Earth due to the Earth's [[gravitation]]. Therefore, air at higher layers of the atmosphere is less dense, or ''rarefied'', relative to air at lower layers. Thus, rarefaction can refer either to a reduction in density over space at a single point of time, or a reduction of density over time for one particular area.

Rarefaction can be easily  observed by compressing a [[Spring (device)|spring]] and releasing it.