A simplified video (Ѻ) definition of extensive, as something that changes with amount (e.g. length, surface, V, S, U, H, F, G, momentum, or kinetic energy), vs intensive, as something that doesn’t change with amount (e.g. T, P, B, or μ).
In thermodynamics, intensive, as contrasted with "extensive", is a quantity, variable, property, or parameter, sometimes referred to as intensity, defined as a partial derivative of an extensive function with respect to an extensivestate variable. [1] Intensities are defined at one point of the space, and of degree zero with respect to amount of substance.
When the extensive function is internal energy, the corresponding intensive quantities are called "tensions". [1] A tension takes the same value on both sides of a boundary separating two systems at equilibrium, a character not shared by any other intensive quantity.
An intensive variable or property, defined another way, is one that does not depend on the mass of the system, and are the same for the entire system or for parts of the system. If two systems are brought together, intensive properties are not summed. [3]
References 1. Perrot, Pierre. (1998). A to Z of Thermodynamics, Oxford: Oxford University Press. 2. (a) Landau, David P. and Binder, Kurt. (2005). A Guide to Monte Carlo Simulations in Statistical Physics (pg. 174). Cambridge University Press. (b) Le Bellac, Michel, Mortessagne, Fabrice, and Batrouni, Ghassan G. (2004). Equilibrium and Non-equilibrium Statistical Thermodynamics (pg. 12). Cambridge University Press. 3. Potter, Merle C. and Somerton, Craig W. (2009). Schaum's Outlines: Thermodynamics for Engineers (pg. 3). McGraw-Hill.
