bulk modulus

bulk modulus
a coefficient of elasticity of a substance, expressing the ratio between a pressure that acts to change the volume of the substance and the fractional change in volume produced.
[1905-10]

* * *

Numerical constant that describes the elastic properties of a solid or fluid under pressure from all sides.

It is the ratio of the tensile strength or compressive force per unit surface area to the change in volume per unit volume of the solid or fluid and thus is a measure of a substance's ability to resist deformation. Its units are newtons per square metre (N/m2). Matter that is difficult to compress has a large bulk modulus; for example, steel has a bulk modulus of 1.6 × 1011 N/m2, three times that of glass (i.e., glass is three times more compressible than steel).

* * *

      numerical constant that describes the elastic (elasticity) properties of a solid or fluid when it is under pressure on all surfaces. The applied pressure reduces the volume of a material, which returns to its original volume when the pressure is removed. Sometimes referred to as the incompressibility, the bulk modulus is a measure of the ability of a substance to withstand changes in volume when under compression on all sides. It is equal to the quotient of the applied pressure divided by the relative deformation.

      In this case, the relative deformation, commonly called strain, is the change in volume divided by the original volume. Thus, if the original volume Vo of a material is reduced by an applied pressure p to a new volume Vn, the strain may be expressed as the change in volume, VoVn, divided by the original volume, or (VoVn)/Vo. The bulk modulus itself, which, by definition, is the pressure divided by the strain, may be expressed mathematically as

      When the bulk modulus is constant (independent of pressure), this is a specific form of Hooke's law of elasticity.

      Because the denominator, strain, is a ratio without dimensions, the dimensions of the bulk modulus are those of pressure, force per unit area. In the English system the bulk modulus may be expressed in units of pounds per square inch (usually abbreviated to psi), and in the metric system, newtons per square metre (N/m2), or pascals.

      The value of the bulk modulus for steel is about 2.3 × 107 psi, or 1.6 × 1011 pascals, three times the value for glass. Thus, only one-third the pressure is needed to reduce a glass sphere the same amount as a steel sphere of the same initial size. Under equal pressure, the proportional decrease in volume of glass is three times that of steel. One may also say that glass is three times more compressible than steel. In fact, compressibility is defined as the reciprocal of the bulk modulus. A substance that is difficult to compress has a large bulk modulus but a small compressibility. A substance that is easy to compress has a high compressibility but a low bulk modulus.

* * *


Universalium. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • Bulk modulus — Incompressibility redirects here. For the topic in fluid dynamics, see Compressibility. Illustration of uniform compression The bulk modulus (K) of a substance measures the substance s resistance to uniform compression. It is defined as the… …   Wikipedia

  • bulk modulus — spūdos modulis statusas T sritis Standartizacija ir metrologija apibrėžtis Dydis, išreiškiamas kūną veikiančio slėgio ir santykinės jo tūrio deformacijos dalmeniu visapusio suslėgimo ar tempimo atveju, t. y. K = p/ϑ; čia p – slėgis, ϑ – santykinė …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • bulk modulus — spūdos modulis statusas T sritis fizika atitikmenys: angl. bulk modulus; compressibility modulus vok. Kompressionsmodul, m; Volumenelastizitätsmodul, m rus. модуль объёмного сжатия, m; модуль объёмной упругости, m pranc. module de compressibilité …   Fizikos terminų žodynas

  • Bulk modulus of elasticity (К) — Bulk modulus of elasticity (К). См. Объемный модуль упругости (К). (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

  • bulk modulus — noun the ratio of the change in pressure acting on a volume to the fractional change in volume • Hypernyms: ↑coefficient of elasticity, ↑modulus of elasticity, ↑elastic modulus * * * noun : the ratio of the intensity of stress to the volume… …   Useful english dictionary

  • bulk modulus — /bʌlk ˈmɒdʒələs/ (say bulk mojuhluhs) noun Physics the ratio of the volume of a body to the pressure distributed uniformly over the whole of its surface …  

  • bulk modulus — noun Physics the relative change in the volume of a body produced by a unit compressive or tensile stress acting uniformly over its surface …   English new terms dictionary

  • Bulk — can refer to:*Bulk mail *Bulk purchasing *Bulk liquids *Bulk modulus *Bulk material handling *Bulk British professional wrestler * Bulk and Skull, a pair of characters in the Power Rangers universe. * The bulk in brane cosmology is a hypothetical …   Wikipedia

  • modulus of elasticity — noun (physics) the ratio of the applied stress to the change in shape of an elastic body • Syn: ↑coefficient of elasticity, ↑elastic modulus • Topics: ↑physics, ↑natural philosophy • Hypernyms: ↑ …   Useful english dictionary

  • modulus of compression — spūdos modulis statusas T sritis Standartizacija ir metrologija apibrėžtis Dydis, išreiškiamas kūną veikiančio slėgio ir santykinės jo tūrio deformacijos dalmeniu visapusio suslėgimo ar tempimo atveju, t. y. K = p/ϑ; čia p – slėgis, ϑ – santykinė …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”