<P> In 1807, Thomas Young was possibly the first to use the term "energy" instead of vis viva, in its modern sense . Gustave - Gaspard Coriolis described "kinetic energy" in 1829 in its modern sense, and in 1853, William Rankine coined the term "potential energy". The law of conservation of energy was also first postulated in the early 19th century, and applies to any isolated system . It was argued for some years whether heat was a physical substance, dubbed the caloric, or merely a physical quantity, such as momentum . In 1845 James Prescott Joule discovered the link between mechanical work and the generation of heat . </P> <P> These developments led to the theory of conservation of energy, formalized largely by William Thomson (Lord Kelvin) as the field of thermodynamics . Thermodynamics aided the rapid development of explanations of chemical processes 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 . According to Noether's theorem, the conservation of energy is a consequence of the fact that the laws of physics do not change over time . Thus, since 1918, theorists have understood that the law of conservation of energy is the direct mathematical consequence of the translational symmetry of the quantity conjugate to energy, namely time . </P> <P> In 1843, James Prescott Joule independently discovered the mechanical equivalent in a series of experiments . The most famous of them used the "Joule apparatus": a descending weight, attached to a string, caused rotation of a paddle immersed in water, practically insulated from heat transfer . It showed that the gravitational potential energy lost by the weight in descending was equal to the internal energy gained by the water through friction with the paddle . </P> <P> In the International System of Units (SI), the unit of energy is the joule, named after James Prescott Joule . It is a derived unit . It is equal to the energy expended (or work done) in applying a force of one newton through a distance of one metre . However energy is also expressed in many other units not part of the SI, such as ergs, calories, British Thermal Units, kilowatt - hours and kilocalories, which require a conversion factor when expressed in SI units . </P>

What are the different types of energy in physics