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Energy (from the Greek ἐνέργεια}} - energeia, "activity, operation", from ἐνεργός - energos, "active, working" [1] is a scalar physical quantity that is an attribute of objects and systems that is conserved in nature. In physics textbooks, energy is often defined as the ability to do work or to cause change.



For lessons on the topic of Energy, follow this link.


The word energy derives from Greek ἐνέργεια (energeia), which appears for the first time in the work "Nicomachean Ethics" by Aristotle in the 4th century BC. In 1021 AD, the Arabian physicist, Alhazen, in the Book of Optics, held light rays to be streams of minute energy particles, stating that "the smallest parts of light" retain "only properties that can be treated by geometry and verified by experiment" and that "they lack all sensible qualities except energy." In 1121, Al-Khazini, in The Book of the Balance of Wisdom, proposed that the gravitational potential energy of a body varies depending on its distance from the centre of the Earth. (Encyclopedia of the History of Arabic Science ISBN 0415124107

The concept of energy emerged out of the idea of vis viva, which Leibniz defined as the product of the mass of an object and its velocity squared; he believed that total vis viva was conserved. To account for slowing due to friction, Leibniz claimed that heat consisted of the random motion of the constituent parts of matter — a view shared by Isaac Newton, although it would be more than a century until this was generally accepted. In 1807, Thomas Young was the first to use the term "energy" instead of vis viva, in its modern sense. (The Science of Energy - a Cultural History of Energy Physics in Victorian Britain ISBN 0-226-76420-6) Gustave-Gaspard Coriolis described "kinetic energy" in 1829 in its modern sense, and in 1853, William Rankine coined the term "potential energy." It was argued for some years whether energy was a substance (the caloric theory) or merely a physical quantity, such as momentum.


During a 1961 lecture California Institute of Technology, Richard Feynman, a celebrated physics teacher and Nobel Laureate, said this about the concept of energy:



See also