energy, \(E\)
In mechanics the sum of @P04778@ and @K03402@. In thermodynamics the @I03103@ or @I03103@ increase, \(\Delta U\), is the sum of @H02752@ and @W06684@ brought to the system. Only changes in energy are measurable. For photons \[E=h\ \nu \] where \(h\) is the @P04685@ 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]