compressibly

Compressibly is the adverb form of the adjective compressible. It is used to describe actions, processes, or media in which compression and density changes are relevant, especially in scientific and technical contexts. In general English, compressibly can modify verbs or phrases to indicate that something can be or is being compressed, but its most common and precise uses appear in physics and engineering.

In fluid dynamics and thermodynamics, compressibly refers to media whose density varies with pressure and temperature. This contrasts with incompressible flows, where density is treated as constant. Gases are typically modeled as compressible, especially at high speeds or under large pressure changes, while many liquids are treated as nearly incompressible under ordinary conditions. The study of compressible flow requires the full set of compressible Navier–Stokes equations together with an equation of state that links pressure, density, and temperature. The Mach number, the ratio of flow speed to the speed of sound, is a central indicator of compressibility effects; high Mach numbers generally entail significant density variations and phenomena such as shocks and strong acoustic waves.

In solid mechanics, the term can describe materials or responses that involve volume change under load, as opposed to perfectly incompressible behavior. However, in common usage, compressibly is more often encountered in technical discussions of fluids than in everyday language.

Examples: Air behaves compressibly at high speeds. The gas is treated as compressible in the shock-tube experiment. The material deforms compressibly under increased loading.