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The ''bulk modulus'' ( or ) of a substance measures the substance's resistance to uniform compression. It is defined as the ratio of the infinitesimal pressure increase to the resulting ''relative'' decrease of the volume. Its SI unit is the pascal, and its dimensional form is M1L−1T−2.〔(【引用サイトリンク】title= Bulk Elastic Properties )〕 ==Definition== The bulk modulus can be formally defined by the equation : where is pressure, is volume, and denotes the derivative of pressure with respect to volume. Equivalently : where ''ρ'' is density and d''P''/d''ρ'' denotes the derivative of pressure with respect to density. The inverse of the bulk modulus gives a substance's compressibility. Other moduli describe the material's response (strain) to other kinds of stress: the shear modulus describes the response to shear, and Young's modulus describes the response to linear stress. For a fluid, only the bulk modulus is meaningful. For an anisotropic solid such as wood or paper, these three moduli do not contain enough information to describe its behaviour, and one must use the full generalized Hooke's law. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「bulk modulus」の詳細全文を読む スポンサード リンク
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