Avogadro constant of molecules in one gram-molecule of oxygen (exactly of oxygen, according to the definitions of the period), and this term is still widely used, especially in introductory works. The change in name to "Avogadro constant" ("N") came with the introduction of the mole as a base unit in the International System of Units (SI) in 1971, which regarded amount of substance as an independent dimension of measurement. With this recognition, the Avogadro constant was no longer a pure number, but had a unit of measurement, the reciprocal mole (mol). While it is rare to use units of amount of substance
Action (physics) in time and space. Action has the dimensions of [energy]⋅[time], and its SI unit is joule-second, which is identical to the unit of angular momentum. In classical physics, the term "action" has a number of meanings. Most commonly, the term is used for a functional formula_2 which takes a function of time and (for fields) space as input and returns a scalar. In classical mechanics, the input function is the evolution q("t") of the system between two times "t" and "t", where q represents the generalized coordinates. The action formula_3 is defined as the integral of the Lagrangian "L" for