Bulk modulus equals change in external pressure divided by fractional volume compression.

Strain equals change in volume divided by original volume.

So the two terms in question have the same units... I guess that means it's different words for the same thing. Am I missing anything?


The one-word answer is "yes".

However bulk modulus on its own is not sufficient to describe the directional features of stress and strain in a material. Therefore it is mainly used for fluids rather than solids, where the material can not resist static shear forces and the only possible state of stress at a point is hydrostatic pressure.

For isotropic materials, there are well known formulas relating Young's modulus and Poisson's ratio (or any other pair of elastic moduli which completely describe the isotropic material behaviour) and the bulk modulus. See https://en.wikipedia.org/wiki/Bulk_modulus for a complete table.


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