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Bulk modulus measures resistance of Continuum body to compression/decompression and to deformation and is inverse to Compressibility compressibility 

K = \frac{1}{c}

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Bulk modulus depends on the thermodynamic conditions at which it is measured and as such is not a material property.

The two major deformation medium compression/decompression processesprocesses of the medium are isothermal and isentropic which result in different values of Bulk modulus:

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In engineering practise, when the term Bulk modulus is used as material property it normally means Isothermal Compressibility: 

For isotropic materials it is related to Young modulus (E) and Poisson's ratio (ν) as:

K_T = \frac{E}{3 \, (1- 2\, \nu)}

See also

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Physics / Mechanics /  Continuum mechanics / Continuum Body / Deformation

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