Intensive variable
An intensive variable of a substance is such that its value does not depend on the amount of the substance.It is the counterpart of an extensive variable.
Let there be one piece of substance whose quantity is n and another piece of substance whose quantity is m. Let V be an intensive variable. The value of variable V corresponding to the first substance is V(n) and the value of V corresponding to the second substance is V(m). Then put the two pieces together forming a substance with quantity n+m, then the value of their intensive variable should be
Examples of intensive variables are: density, temperature, pressure, specific heat, voltage (electric potential), speed.
Table of contents 
2 Proof 3 Corollary 4 Products of Variables 5 Example 
Theorem
where V_{2} and V_{3} are extensive variables, then V_{1} is an intensive variable.Proof

 (extensivity of V_{2} and V_{3})

 (hypothesis)

 (extensivity of V_{3})

Corollary
If an intensive variable V_{1} is a ratio of two extensive variables, as in equation (2), then
Products of Variables
IfBut if V_{2} and V_{3} are both intensive, then
 ,
Example
Pressure is force divided by area. But neither force nor area are either extensive or intensive. However, force multiplied by length is work, which is extensive, and area multiplied by length is volume, which is extensive. Therefore pressure actually is a ratio of two extensive variables  work/volume  and so it is intensive.The following variables are neither extensive nor intensive: length, time, area, force, angular momentum.