History of energy
The concept of energy emerged from the idea of vis viva (living force), 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.
Émilie marquise du Châtelet in her book Institutions de Physique (“Lessons in Physics”), published in 1740, incorporated the idea of Leibniz with practical observations of Gravesande to show that the "quantity of motion" of a moving object is proportional to its mass and the square of its velocity (not the velocity itself as Newton taught—what was later called momentum).
The product of the mass of a body into the square of its velocity may properly be termed its energy.
It was argued for some years whether energy was a substance (the caloric) or merely a physical quantity.
The development of steam engines required engineers to develop concepts and formulas that would allow them to describe the mechanical and thermal efficiencies of their systems. Engineers such as Sadi Carnot, physicists such as James Prescott Joule, mathematicians such as Émile Clapeyron and Hermann von Helmholtz, and amateurs such as Julius Robert von Mayer all contributed to the notion that the ability to perform certain tasks, called work, was somehow related to the amount of energy in the system. In the 1850s, Glasgow professor of natural philosophy William Thomson and his ally in the engineering science William Rankine began to replace the older language of mechanics with terms such as "actual energy", "kinetic energy", and "potential energy". William Thomson (Lord Kelvin) amalgamated all of these laws into the laws of thermodynamics, which aided in the rapid development of explanations of chemical processes using the concept of energy by Rudolf Clausius, Josiah Willard Gibbs and Walther Nernst. It also led to a mathematical formulation of the concept of entropy by Clausius, and to the introduction of laws of radiant energy by Jožef Stefan. Rankine, coined the term "potential energy". In 1881, William Thomson stated before an audience that:
The very name energy, though first used in its present sense by Dr Thomas Young about the beginning of this century, has only come into use practically after the doctrine which defines it had ... been raised from mere formula of mathematical dynamics to the position it now holds of a principle pervading all nature and guiding the investigator in the field of science.
Over the following thirty years or so this newly developing science went by various names, such as the dynamical theory of heat or energetics, but after the 1920s generally came to be known as thermodynamics, the science of energy transformations.
Stemming from the 1850s development of the first two laws of thermodynamics, the science of energy have since branched off into a number of various fields, such as biological thermodynamics and thermoeconomics, to name a couple; as well as related terms such as entropy, a measure of the loss of useful energy, or power, an energy flow per unit time, etc. In the past two centuries, the use of the word energy in various "non-scientific" vocations, e.g. social studies, spirituality and psychology has proliferated the popular literature.
Conservation of energy
In 1918 it was proved that the law of conservation of energy is the direct mathematical consequence of the translational symmetry of the quantity conjugate to energy, namely time. That is, energy is conserved because the laws of physics do not distinguish between different moments of time (see Noether's theorem).
There is a fact, or if you wish, a law, governing natural phenomena that are known to date. There is no known exception to this law—it is exact so far we know. The law is called conservation of energy; it states that there is a certain quantity, which we call energy that does not change in manifold changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity, which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number, and when we finish watching nature go through her tricks and calculate the number again, it is the same.—The Feynman Lectures on Physics
- Timeline of thermodynamics, statistical mechanics, and random processes
- History of physics
- History of the conservation of energy principle
- History of thermodynamics
- A Guide to the Scientific Knowledge of Things Familiar, a book by Ebenezer Cobham Brewer presenting explanations for common phenomena
- Caloric theory
- Aristotle, "Nicomachean Ethics", 1098b33, at Perseus
- Smith, Crosbie (1998). The Science of Energy - a Cultural History of Energy Physics in Victorian Britain. The University of Chicago Press. ISBN 0-226-76420-6.
- Thomas Young (1807). A Course of Lectures on Natural Philosophy and the Mechanical Arts, p. 52.
- Smith, Crosbie (1998). The Science of Energy - a Cultural History of Energy Physics in Victorian Britain. The University of Chicago Press. ISBN 0-226-76421-4.
- Thomson, William. (1881). "On the sources of energy available to man for the production of mechanical effect." BAAS Rep. 51: 513-18 (Quote: pg. 513); PL 2: 433-50.
- Feynman, Richard (1964). The Feynman Lectures on Physics; Volume 1. U.S.A: Addison Wesley. ISBN 0-201-02115-3.
- Smil, Vaclav (1994). Energy in World History. Westview Press. ISBN 0-8133-1902-1.
- Eugene Hecht, “An Historico-Critical Account of Potential Energy: Is PE Really Real?” The Physics Teacher 41 (Nov 2003): 486-93.
- Katalin Martinás, “Aristotelian Thermodynamics,” Thermodynamics: history and philosophy: facts, trends, debates (Veszprém, Hungary 23-28 July 1990), 285-303.