# Extensive

 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, extensive, as contrasted with "intensive", is a quantity, property, variable or parameter, sometimes referred to as extensity, is a quantity proportional to the dimension of the system. [1]

The dimension may be, generally, of: a length, l, a surface, A, or a volume, V, amount of electricity, of substance, an entropy S, the functions internal energy U, enthalpy H, or free energy, F or G, as well as momentum and kinetic energy. [2]

Heat and inertia, according to Norman Dolloff (1975), supposedly, also are extensive properties. [3]

An extensive variable or property, defined another way, is one that depends on the mass of the system. If two systems are brought together the extensive properties of the new system is the sum of the extensive properties of the original two systems. [2]

Specific properties
If an extensive variable is divided by the mass, symbol m, what is called a “specific property” results, an example being the specific volume: [2]

As is sometimes customary, although not necessarily uniform (see: characteristic function notation table), uppercase letters are used to represent an extensive property [exception: m for mass] and lower case letters are used to denote the associated intensive property. [2]

References
1. Perrot, Pierre. (1998). A to Z of Thermodynamics. Oxford: Oxford University Press.
2. Potter, Merle C. and Somerton, Craig W. (2009). Schaum's Outlines: Thermodynamics for Engineers (pg. 4). McGraw-Hill.
3. Dolloff, Norman H. (1975). Heat Death and the Phoenix: Entropy, Order, and the Future of Man (pg. 4). Exposition Press.