Bulk Modulus

The bulk modulus of a gas is a measure of its compressibility (elastic property).
K = bulk modulus [Nm-2]
P = pressure [Nm-2]
V = volume [m3]

The difference in pressure for a fractional change in volume, a volume increase with a fall in pressure giving the negative sign. The value of B depends on whether the changes in the gas arising from wave motion are adiabatic or isothermal. They must be thermodynamically irreversible in order to avoid the energy loss mechanisms of diffusion, viscosity and thermal conductivity. The complete absence of these random, entropy generating processes defines an adiabatic process - a thermodynamic cycle with a 100% efficiency in the sense that none of the energy in the wave, potential or kinetic, is lost. In a sound wave sound such thermodynamic concepts restrict the excess pressure amplitude; too great an amplitude raises the local temperature in the gas at the amplitude peaks and thermal conductivity removes energy from the wave system. Local particle velocity gradients will also develop, leading to diffusion and viscosity.

Ratio of stress to change in volume of a material subjected to axial loading. For isotropic solids it is related to Young's modulus E and to the shear modulus G by

ν = Poisson's ratio
E = Young's modulus [Nm-2]
G = Shear modulus [Nm-2]

When ν = 1/3, E = K, and K = (8/3)G.
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Acetic Acid 2490000000 Nm-2Clip Acetone 800000000 Nm-2Clip Aluminium 75500000000 Nm-2Clip
Antimony 42000000000 Nm-2Clip Arsenic 22000000000 Nm-2Clip Benzene 1100000000 Nm-2Clip
Bismuth 31300000000 Nm-2Clip Bromine 1580000000 Nm-2Clip Cadmium 41600000000 Nm-2Clip
Caesium 1600000000 Nm-2Clip Calcium 17200000000 Nm-2Clip Carbon 542e9 (diamond) 33e9 (graphite) Nm-2Clip
Carbon Disulphide 1160000000 Nm-2Clip Carbon Tetrachloride 1120000000 Nm-2Clip Chlorine 1100000000 Nm-2Clip
Chloroform 1100000000 Nm-2Clip Chromium 160100000000 Nm-2Clip Copper 137800000000 Nm-2Clip
Fused Silica 36700000000 Nm-2Clip Glycerol 4030000000 Nm-2Clip Gold 217000000000 Nm-2Clip
Iodine 7700000000 Nm-2Clip Iron 169800000000 Nm-2Clip Lead 45800000000 Nm-2Clip
Lithium 11100000000 Nm-2Clip Magnesium 44700000000 Nm-2Clip Manganese 118000000000 Nm-2Clip
Mercury Hg 26200000000 Nm-2Clip Methyl Alcohol 970000000 Nm-2Clip Molybdenum 231000000000 Nm-2Clip
Nickel 177.3e9 (soft) 187.6e9 (hard) Nm-2Clip Nitrobenzene 2200000000 Nm-2Clip Olive Oil 1600000000 Nm-2Clip
Palladium 182000000000 Nm-2Clip Paraffin Oil 1620000000 Nm-2Clip Phosphorus 10.9e9 (red) 4.9e9 (white) Nm-2Clip
Platinum 228000000000 Nm-2Clip Polymethyl Methacrylate Resin 6600000000 Nm-2Clip Potassium 3100000000 Nm-2Clip
Pyrex Glass 40000000000 Nm-2Clip Rubidium 2500000000 Nm-2Clip Selenium 8300000000 Nm-2Clip
Silicon 100000000000 Nm-2Clip Silver 103600000000 Nm-2Clip Silver Bromide 44030000000 Nm-2Clip
Sodium 6300000000 Nm-2Clip Sodium Chloride 24420000000 Nm-2Clip Sulphur 7700000000 Nm-2Clip
Thallium 43000000000 Nm-2Clip Tin 58200000000 Nm-2Clip Toluene 1090000000 Nm-2Clip
Turpentine 1280000000 Nm-2Clip Water 2050000000 Nm-2Clip Zinc 72000000000 Nm-2Clip
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See also: Compressibility, Ideal Gas Law.

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Subjects: Mechanical Engineering Noise & Vibration Physics