2-2 The speed of sound

Formula - Bulk modulus

The bulk modulus of a medium is the property of the
medium that determines the fractional change in a volume of the medium when the pressure on
it changes.

A higher bulk modulus indicates a
less compressible medium. For example, steel has a bulk modulus of 160
x 10^{9} Pa while air has a bulk modulus of about 10^{5} Pa.

**The bulk modulus is always**
**
positive**. Increasing the pressure (Dp > 0)
causes a decrease in the volume (DV < 0) and decreasing the pressure
(Dp < 0) causes an increase in the volume (DV
> 0).

The SI unit of bulk modulus is the same as that of
pressure **N/m**^{2} or** Pascal (Pa)**.

DV/V is the fractional change in the volume
produced by a change in pressure by Dp.