Bulk modulus

The bulk modulus (
 
 
 
 K
 
 
 {\displaystyle K}
 
 or 
 
 
 
 B
 
 
 {\displaystyle B}
 
 or 
 
 
 
 k
 
 
 {\displaystyle k}
 
) of a substance is a measure of the resistance of a substance to bulk <a href="/facts/Compression_(physics)/2wwcVmM0">compression</a>. It is defined as the ratio of the <a href="/facts/Infinitesimal/JKcTMIgD">infinitesimal</a> <a href="/facts/Pressure/eyc37GRG">pressure</a> increase to the resulting relative decrease of the <a href="/facts/Volume/aeAXCBUd">volume</a>.
Other moduli describe the material's response (<a href="/facts/Strain_(materials_science)/xK7R59oI">strain</a>) to other kinds of <a href="/facts/Stress_(physics)/ErAXDbbd">stress</a>: the <a href="/facts/Shear_modulus/9e9IvJnz">shear modulus</a> describes the response to <a href="/facts/Shear_stress/aWWnzIhE">shear stress</a>, and <a href="/facts/Young%2527s_modulus/MV5JMCIM">Young's modulus</a> describes the response to normal (lengthwise stretching) stress. For a <a href="/facts/Fluid/tMQ46Tmz">fluid</a>, only the bulk modulus is meaningful. For a complex <a href="/facts/Anisotropic/YMqTQWVB">anisotropic</a> solid such as <a href="/facts/Wood/z13NpHPl">wood</a> or <a href="/facts/Paper/FUETwwKV">paper</a>, these three moduli do not contain enough information to describe its behaviour, and one must use the full generalized <a href="/facts/Hooke%2527s_law/7hTUcKUm">Hooke's law</a>. The reciprocal of the bulk modulus at fixed temperature is called the isothermal <a href="/facts/Compressibility/eePznleN">compressibility</a>.

Bulk modulus open-in-new

Bulk modulus