Extensive & Intensive

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Many fluid properties are defined with respect to intensive properties.  This graph shows the pressure of water as a function of specific volume and temperature isotherms.  Liquid and vapor phases are shown.

By Emok (Own work) [CC-BY-SA-3.0 or GFDL], via Wikimedia Commons

Physical properties of matter can be classified as either extensive or intensive.


Extensive properties depend on the amount of matter presentExamples of extensive properties are mass, weight and volume.  If the amount of matter present changes, then the extensive properties also change.

Intensive properties do not depend on the amount of matter present.  Examples of intensive properties are density, color, temperature, and hardness.

Intensive properties can be obtained by dividing an extensive property by another extensive property.  Density is obtained by dividing mass (extensive property) by volume (extensive property) to obtain the mass per unit volume (intensive property). 

Specific energy is another example.  The internal energy, U, of an object depends on the amount of matter present.  Increasing the amount of matter increases the internal energy.  Dividing the internal energy (extensive property) by the mass (extensive property) gives the specific energy, u, that has units of energy per unit mass.  There are many “specific” properties used in fluid dynamics.  All of these “specific” properties are per unit mass.

 

Learning Objectives:

Describe the difference between extensive and intensive properties.