Mole (unit) measure the amount of substance (although in practice it is usual). There are many physical relationships between amount of substance and other physical quantities, the most notable one being the ideal gas law (where the relationship was first demonstrated in 1857). The term "mole" was first used in a textbook describing these colligative properties. Chemical engineers use the unit extensively, and decimal multiples may be more suitable for industrial use. For convenience in avoiding conversions in the imperial (or American customary units), some engineers adopted the "pound-mole" (notation "lb-mol" or "lbmol"), which is defined as the number of entities in
Action (physics) Action (physics) In physics, action is an attribute of the dynamics of a physical system from which the equations of motion of the system can be derived. It is a mathematical functional which takes the trajectory, also called "path" or "history", of the system as its argument and has a real number as its result. Generally, the action takes different values for different paths. Action has the dimensions of [energy]⋅[time] or [momentum]⋅[length], and its SI unit is joule-second. Hamilton's principle states that the differential equations of motion for "any" physical system can be re-formulated as an equivalent integral equation. Thus,