Editing Bulk modulus (section)

{{Short description|Resistance of a material to uniform pressure}}
{{Confusing|date=December 2023}}
[[Image:Isostatic pressure deformation.svg|thumb|300px|right|Illustration of uniform compression]]

The '''bulk modulus''' (<math>K</math> or <math>B</math> or <math>k</math>) of a substance is a measure of the resistance of a substance to bulk [[compression (physics)|compression]]. It is defined as the ratio of the [[infinitesimal]] [[pressure]] increase to the resulting ''relative'' decrease of the [[volume]].<ref>{{cite web| url= http://hyperphysics.phy-astr.gsu.edu/hbase/permot3.html|title= Bulk Elastic Properties|work=hyperphysics|publisher=Georgia State University}}</ref>

Other moduli describe the material's response ([[Strain (materials science)|strain]]) to other kinds of [[Stress (physics)|stress]]: the [[shear modulus]] describes the response to [[shear stress]], and [[Young's modulus]] describes the response to normal (lengthwise stretching) stress.  For a [[fluid]], only the bulk modulus is meaningful.  For a complex [[anisotropic]] solid such as [[wood]] or [[paper]], these three moduli do not contain enough information to describe its behaviour, and one must use the full generalized [[Hooke's law]]. The reciprocal of the bulk modulus at fixed temperature is called the isothermal [[compressibility]].