energy, \(E\)
In mechanics the sum of @[email protected] and @[email protected] In thermodynamics the @[email protected] or @[email protected] increase, \(\Delta U\), is the sum of @[email protected] and @[email protected] brought to the system. Only changes in energy are measurable. For photons \[E=h\ \nu \]where \(h\) is the @[email protected] and \(\nu \) the frequency of radiation. In relativistic physics \[E=m\ c^{2}\] where \(c\) is the speed of light and \(m\) the mass.
Green Book, 2nd ed., p. 12 [Terms] [Book]