Bulk Modulus

The bulk modulus is a constant for describing the resistance of the substance to the compression. It is defined as the ratio between the increase in the pressure and the resulting decrease in the volume of the material. Together with the shear modulus, Young’s modulus, and Hooke’s law, this modulus describes the response of the material to the strain or stress.

The formula of Bulk Modulus of Elasticity

Bulk modulus is the ratio between the applied pressure, to the corresponding relative decrease in the material’s volume. The formula for this modulus is given below.

B = ΔP /(ΔV/V)

Here B is used for representing the bulk modulus. ΔP is the change of pressure or applied force per unit area on the material. ΔV refers to the change in the volume of the material, which is resulting due to the compression. Whereas, the V indicates the initial volume of the material in the English units, and can also be exhibited in the metric units.

Importance of Bulk Modulus

Usually, in the equations and tables, this modulus is indicated by the B or K. While this modulus is applied to the uniform compression of the substances, it is often used for describing the behavior of the fluids. It can also be used for predicting the compression, calculation of density and indirectly indicating the types of chemical bonding in the substances. This modulus is regarded as a descriptor of the elastic properties, as the compressed materials are returned to their original volume, after removal of the pressure. For bulk modulus, the units of Pascal (Pa), Newtons per square meter (N/M2), in the metric system are used. However, in the English system, the units of Pounds Per Square Inch (PSI) are used. As the denominator, the strain is a ratio that does not has any dimensions, so the dimensions of the bulk modulus are the same as that of the pressure.

Explaining Concept By Diagram


Uses of Bulk Modulus

The bulk modulus is just a numerical constant, that is used for measuring and describing the properties of the fluids or solids when there is the application of the pressure on all the surfaces. The bulk modulus of elasticity is used for the measurement of the mechanical properties of the solid substances. In any case, the specific bulk elastic properties of the materials are used for a determination that how much the material will be compressed under the given amount of the externally applied pressure.


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