Conservation of energy

:This article is about the physics principle. For information on using energy resources sustainably, see Energy Conservation.

Historical development

Although ancient philosophers as far back as Thales of Miletus had inklings of the first law, it was the German Gottfried Wilhelm Leibniz during 1676-1689 who first attempted a mathematical formulation. Leibniz noticed that in many mechanical systems (of several masses, mi each with velocity vi) the quantity:

Related Topics:
Ancient - Philosopher - Thales of Miletus - German - Gottfried Wilhelm Leibniz - 1676 - 1689 - Mass - Velocity

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:sum_{i} m_i v_i^2

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was conserved. He called this quantity the vis viva or living force of the system. The principle represents an accurate statement of the approximate conservation of kinetic energy in many situations. However, many physicists were influenced by the prestige of Sir Isaac Newton in England and of René Descartes in France, both of whom had set great store by the conservation of momentum as a guiding principle. Thus the momentum:

Related Topics:
Vis viva - Kinetic energy - Physicist - Isaac Newton - England - René Descartes - France - Conservation of momentum - Momentum

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:sum_{i} m_i v_i

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was held by the rival camp to be the conserved vis viva. It was largely engineers such as John Smeaton, Peter Ewart, Karl Hotzmann, Gustave-Adolphe Hirn and Marc Séguin who objected that conservation of momentum alone was not adequate for practical calculation and who made use of Leibniz's principle. The principle was also championed by some chemists such as William Hyde Wollaston.

Related Topics:
Engineer - John Smeaton - Peter Ewart - Karl Hotzmann - Gustave-Adolphe Hirn - Marc Séguin - Chemist - William Hyde Wollaston

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Members of the academic establishment such as John Playfair were quick to point out that kinetic energy is clearly not conserved. This is obvious to a modern analysis based on the second law of thermodynamics but in the 18th and 19th centuries, the fate of the lost energy was still unknown. Gradually it came to be suspected that the heat inevitably generated by motion was another form of vis viva. In 1783, Antoine Lavoisier and Pierre-Simon Laplace reviewed the two competing theories of vis viva and caloric{{ref|LL}}. Count Rumford's 1798 observations of heat generation during the boring of cannons added more weight to the view that mechanical motion could be converted into heat. Vis viva now started to be known as energy, after the term was first used in that sense by Thomas Young in 1807.

Related Topics:
John Playfair - Second law of thermodynamics - 18th - 19th centuries - Heat - 1783 - Antoine Lavoisier - Pierre-Simon Laplace - Count Rumford - 1798 - Boring - Cannon - Thomas Young - 1807

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The recalibration of vis visa to

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:rac {1} {2}sum_{i} m_i v_i^2

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was largely the result of the work of Gaspard-Gustave Coriolis and Jean-Victor Poncelet over the period 1819-1839. The former called the quantity quantité de travail and the latter, travail mécanique and both championed its use in engineering calculation.

Related Topics:
Gaspard-Gustave Coriolis - Jean-Victor Poncelet - 1819 - 1839

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In a paper Uber die Natur der Warme, published in the Zeitschrift für Physik in 1837, Karl Friedrich Mohr gave one of the earliest general statements of the doctrine of the conservation of energy in the words: "besides the 54 known chemical elements there is in the physical world one agent only, and this is called Kraft . It may appear, according to circumstances, as motion, chemical affinity, cohesion, electricity, light and magnetism; and from any one of these forms it can be transformed into any of the others."

Related Topics:
Zeitschrift für Physik - 1837 - Karl Friedrich Mohr

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A key stage in the development of the modern conservation principle was the demonstration of the mechanical equivalent of heat. The caloric theory maintained that heat could neither be created nor destroyed but conservation of energy entails the contrary principle that heat and mechanical work are interchangeable.

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The mechanical equivalence principle was first stated in its modern form by the German surgeon Julius Robert von Mayer.{{ref|JRvM}} Mayer reached his conclusion on a voyage to the Dutch East Indies, where he found that his patients' blood was a deeper red because they were consuming less oxygen, and therefore less energy, to maintain their body temperature in the hotter climate. He had discovered that heat and mechanical work were both forms of energy, and later, after improving his knowledge of physics, he calculated a quantitative relationship between them.

Related Topics:
Julius Robert von Mayer - Dutch East Indies - Blood - Red - Oxygen - Heat - Mechanical work

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Meanwhile, in 1843 James Prescott Joule independently discovered the mechanical equivalent in a series of experiments. In the most famous, now called the "Joule apparatus", a descending weight attached to a string caused a paddle immersed in water to rotate. He showed that the gravitational potential energy lost by the weight in descending was equal to the thermal energy (heat) gained by the water by friction with the paddle.

Related Topics:
1843 - James Prescott Joule - Potential energy - Heat - Friction

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Over the period 1840-1843, similar work was carried out by engineer Ludwig A. Colding though it was little-known outside his native Denmark.

Related Topics:
1840 - Ludwig A. Colding - Denmark

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Both Joule's and Mayer's work suffered from resistance and neglect but it was Joule's that, perhaps unjustly, eventually drew the wider recognition.

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:For the dispute between Joule and Mayer over priority, see

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Drawing on the earlier work of Joule, Sadi Carnot and Émile Clapeyron, in 1847, Hermann von Helmholtz postulated a relationship between mechanics, heat, light, electricity and magnetism by treating them all as manifestations of a single force (energy in modern terms). He published his theories in his book Über die Erhaltung der Kraft (On the Conservation of Force, 1847). The general modern acceptance of the principle stems from this publication.

Related Topics:
Sadi Carnot - Émile Clapeyron - 1847 - Hermann von Helmholtz - Light - Electricity - Magnetism

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In 1877, Peter Guthrie Tait claimed that the principle originated with Sir Isaac Newton, based on a creative reading of propositions 40 and 41 of the Philosophiae Naturalis Principia Mathematica. This is now generally regarded as nothing more than an example of Whig history.

Related Topics:
1877 - Peter Guthrie Tait - Philosophiae Naturalis Principia Mathematica - Whig history

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