expresses the resistance of a
fluid to a decrease in volume
due to compression. A decrease
in volume would increase density.
Compressibility is the reciprocal
of bulk modulus or the tendency
to be compressed. Bulk modulus
varies with pressure, temperature,
molecular structure and gas content.
Generally, mineral oils are thought
to be incompressible. In high
pressure hydraulic systems a high
bulk modulus or low compressibility
is required to transmit power
efficiently and dynamically.