## bulk modulusA physical constant of solids and fluids that indicates their elastic properties when they are under pressure over their entire surfaces. The bulk modulus ( K) is the inverse of the compressibility. It is also called the
incompressibility: if a solid or fluid (liquid or gas) has a high
bulk modulus, then it is difficult to compress. The bulk modulus is defined by K = -V (dP/dV)
where V is the volume, which is
decreased when a pressure P is
exerted uniformly in all directions. Usually, it is assumed that the temperature
is kept constant during the compression. K can be measured directly
by exerting a known pressure and measuring the change of volume –
and a whole technology has grown up for producing enormous pressures without
the substance leaking past the piston which compresses it. Usually the main
source of error is due to the non-uniformity of the forces acting in different
directions. Alternatively, the speed of propagation of sound waves through
a material can be found. This depends on the compressibility, though a number
of corrections have to be applied if exact values of K are required.
## Related entry• Hooke's law## Related category• PROPERTIES OF MATTER | |||||

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