In quantum mechanics, position and momentum are canonical conjugate variables.

Mass is inversely related to density, which is the conjugate variable to pressure.

In the above description, the product of two conjugate variables yields an energy.

These forces and their associated displacements are called conjugate variables.

Here, pressure is the driving force, volume is the associated displacement, and the two form a pair of conjugate variables.

The temperature/entropy pair of conjugate variables is the only heat term; the other terms are essentially all various forms of work.

Volume is one of a pair of conjugate variables, the other being pressure.

Contrary to classical mechanics, one can never make simultaneous predictions of conjugate variables, such as position and momentum, with accuracy.

There are many types of conjugate variables, depending on the type of work a certain system is doing (or is being subjected to).

In classical physics, the derivatives of action are conjugate variables to the quantity with respect to which one is differentiating.