| scalar quantity which may be increased or decreased in a system when it receives or produces work, respectively
NOTE 1 Energy follows a law of conservation according to which the total energy of an isolated system remains constant.
NOTE 2 Energy can be manifested in different forms that are mutually transformable into each other, either totally or partially, depending on other laws such as conservation of momentum or 2nd law of thermodynamics.
NOTE 3 The energy in a system may be also increased or decreased when it receives or produces energy in other forms than work, e.g. heat.
NOTE 4 The coherent SI unit of energy is joule, J. A non-SI unit for use with the SI is electronvolt, eV.
NOTE 5 Specific energy, or energy per mass, is denoted e or w.