The quantity energy (E) is sometimes described as the ability to perform work or
to heat an object. The name is derived from the Greek word energeia (ἐνέργεια),
meaning "being at work". The corresponding unit is
joule (J).
Energy may manifest itself mechanically, electrically and thermally,
but also (classically) as
mass and (quantum mechanically) as
photon.
History
The concept of energy was introduced by the English scientist Thomas Young
(1773 - 1829), but the word itself goes back to the Greek philosopher Aristotle
(384 - 322 BC).