komprimerbare

Komprimerbare is a term used in Scandinavian languages to denote something that can be compressed. In physics and engineering, the related concept is compressibility, a property that describes how a material’s volume responds to pressure.

Compressibility is quantified by isothermal and adiabatic forms. The isothermal compressibility κ_T is defined as κ_T = - (1/V) (∂V/∂P)_T, showing how volume changes at constant temperature when pressure is varied. The adiabatic compressibility κ_S is similarly defined at constant entropy: κ_S = - (1/V) (∂V/∂P)_S. The bulk modulus B, the measure of a material’s resistance to compression, is the reciprocal of compressibility: B = 1/κ_T. For practical use, κ_T has units of inverse pressure (Pa⁻¹).

Special cases and general trends. For an ideal gas, κ_T = 1/P, and κ_S = 1/(γP), where γ = Cp/Cv. Gases are typically highly compressible, while liquids show much lower compressibility, and solids are often the least compressible. In real materials, compressibility depends on temperature, pressure, and molecular structure, and is related to the bulk modulus, phonon spectra, and phase transitions.

Applications and contexts. Compressibility is central in thermodynamics, materials science, geophysics, and fluid dynamics. In compressible flow, density and pressure vary significantly, described by the Mach number and related equations. Methods to determine compressibility include P–V–T measurements, ultrasonic testing, and fitting to equations of state, with real gases often expressed through a compressibility factor Z that deviates from unity.