Compressibility

<p>In <a href="/facts/Thermodynamics/q4hIx3yP">thermodynamics</a> and <a href="/facts/Fluid_mechanics/NIy4tRfE">fluid mechanics</a>, the compressibility (also known as the coefficient of compressibility or, if the temperature is held constant, the isothermal compressibility) is a <a href="/facts/Measure_(mathematics)/yCq7zlI4">measure</a> of the instantaneous relative volume change of a <a href="/facts/Fluid/tMQ46Tmz">fluid</a> or <a href="/facts/Solid/hj5UsXno">solid</a> as a response to a <a href="/facts/Pressure/eyc37GRG">pressure</a> (or mean <a href="/facts/Stress_(physics)/ErAXDbbd">stress</a>) change. In its simple form, the compressibility 
  
    
      
        κ
      
    
    {\displaystyle \kappa }
  
 (denoted β in some fields) may be expressed as
</p>

β
        =
        −
        
          
            1
            V
          
        
        
          
            
              ∂
              V
            
            
              ∂
              p
            
          
        
      
    
    {\displaystyle \beta =-{\frac {1}{V}}{\frac {\partial V}{\partial p}}}
  
,
<p>where V is <a href="/facts/Volume_(thermodynamics)/dFxN6cz4">volume</a> and p is pressure. The choice to define compressibility as the <a href="/facts/Additive_inverse/n8gKUmCf">negative</a> of the fraction makes compressibility positive in the (usual) case that an increase in pressure induces a reduction in volume. The reciprocal of compressibility at fixed temperature is called the isothermal <a href="/facts/Bulk_modulus/yCRFQonn">bulk modulus</a>.
</p>

Compressibility open-in-new

Compressibility