The entropy may be expressed as a function of
* pressure and temperature
* temperature and volume
* heat and work

Bulk Modulus is a measure of the resistance of a fluid to compression. It is defined as the ratio of pressure stress to volumetric strain.
The value of bulk modulus of a fluid is required to determine Mach number. Mach number (M or Ma) is a dimensionless quantity. It represents the flow of velocity beyond the boundary when compared to the local speed of sound. It is used to determine the resistance of fluid or gas in its compressed state.

The term radiation is applied to the kinds of processes which transmit energy by means of electromagnetic waves. The amount of radiation mainly depends upon the nature of body, temperature of the body and type of surface of the body.

when the radiations are falling on a body, three things happen, i.e. a part of the radiations are absorbed by the body, a part of the radiations are reflected and the remaining radiations are transmitted through the body.