What does rarefaction mean?
Rarefaction is the noun for the process or condition of something becoming less dense or less pressurized. It most often describes a gas or another medium in which pressure decreases, causing the material to expand. The word is also important in acoustics: a sound wave contains alternating regions of compression, where pressure is higher, and rarefaction, where pressure is lower. These changing pressure regions travel through the surrounding air and are perceived as sound. In engineering and physics, rarefaction can refer to a wave or region produced when a fluid moves away from a particular area. The related verb is 'rarefy,' meaning to make less dense or to cause to expand. Although 'rarefaction' is precise and technical, familiar alternatives such as 'expansion' and 'decompression' are often preferable in general contexts.
nounA decrease in the density or pressure of a medium, especially a gas, often caused by the lowering of pressure. In acoustics, it refers to a region where sound-wave pressure falls below the surrounding level.
- A decrease in the pressure or density of a medium, especially a gas.
- An acoustical region in which the pressure of a sound wave is lower than the surrounding pressure.
"The rarefaction of the air around the vibrating surface helped produce the low-frequency sound."
"The rarefaction of the gas allowed it to expand and fill the chamber."
"As the sound wave traveled through the room, its rarefaction moved toward the listener."
Plural rarefactions are used for separate regions or instances of reduced pressure or density.
"The rarefactions in the sound wave alternated with regions of compression."
A rarefaction is what makes a sound wave's quietest moment: pressure drops as the wave passes, just as it rises at a compression.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does rarefaction come from?
Rarefaction comes from Latin rarefactio, a noun meaning 'the process of making rare or thin,' formed from rarefacere, 'to make rare or thin.' The English word entered scientific usage in the seventeenth century, initially in relation to the treatment or separation of substances and later in the study of gases and sound. Its close English relative is 'rarefy,' while Latin-derived words such as 'rarity' share the underlying idea of being uncommon or thinly distributed.
Related word forms
How rarefaction is actually used
The term is most common in physics, acoustics, engineering, and technical descriptions of waves and gases. In general writing, 'decompression' or 'expansion' may be more accessible.
Easily confused with rarefaction
Rarefaction is a reduction in pressure or density, whereas refraction is the bending of a wave as it passes from one medium into another.