Lightning is the electric breakdown of air by strong electric fields. Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or Heat and light from a lightning produces a plasma motion of air molecules.

In physics and other sciences, energy (from the Greek ἐνέργεια - energeia, "activity, operation", from ἐνεργός - energos, "active, working"[1]) is a scalar physical quantity that is a property of objects and systems which is conserved by nature. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. Science (from the Latin scientia, meaning " Knowledge " or "knowing" is the effort to discover, and increase human understanding Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Energeia (grc ἐνέργεια is an important Greek technical term in the works of Aristotle. In Physics, a scalar is a simple Physical quantity that is not changed by Coordinate system rotations or translations (in Newtonian mechanics or A physical Quantity is a physical property that can be quantified Energy is often defined as the ability to do work. In Thermodynamics, work is the quantity of Energy transferred from one system to another without an accompanying transfer of Entropy.

Several different forms of energy, including kinetic, potential, thermal, gravitational, sound energy, light energy, elastic, electromagnetic, chemical, nuclear, and mass have been defined to explain all known natural phenomena. The kinetic energy of an object is the extra Energy which it possesses due to its motion Potential energy can be thought of as Energy stored within a physical system Thermal energy is the sum of the sensible energy and latent energy. Gravitational energy is the energy associated with the gravitational field The elastic energy is the Energy which causes or is released by the elastic distortion of a solid or a fluid Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Nuclear Energy is released by the splitting (fission or merging together (fusion of the nuclei of Atom (s The rest energy E or rest mass-energy of a particle is its energy when it is at rest relative to a given Inertial reference frame.

Energy is converted from one form to another. In Physics and Engineering, energy transformation or energy conversion, is any process of transforming one form of Energy to another This principle, the conservation of energy, was first postulated in the early 19th century, and applies to any isolated system. In Physics, the law of conservation of energy states that the total amount of Energy in an isolated system remains constant and cannot be created although it may In the Natural sciences an isolated system, as contrasted with a open system, is a Physical system that does not interact with its Surroundings 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. Noether's theorem (also known as Noether's first theorem) states that any differentiable symmetry of the action of a physical system has [2]

Although the total energy of a system does not change with time, its value may depend on the frame of reference. See also Inertial frame A frame of reference in Physics, may refer to a Coordinate system or set of axes within which to For example, a seated passenger in a moving airplane has zero kinetic energy relative to the airplane, but non-zero kinetic energy relative to the earth.

## History

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. The word 'energy' derives from Greek ἐνέργεια ( energeia) which appears for the first time in the work Nicomachean Ethics of Aristotle A timeline of events related to Thermodynamics, Statistical mechanics, and Random processes Ancient times c In the history of Science, vis viva (from the Latin for living force) is an Obsolete scientific theory that served as an elementary 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. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements In 1807, Thomas Young was the first to use the term "energy", instead of vis viva, in its modern sense. Thomas Young (13 June 1773 &ndash 10 May 1829 was an English Polymath who contributed to the scientific understanding of vision, Light In the history of Science, vis viva (from the Latin for living force) is an Obsolete scientific theory that served as an elementary [3] Gustave-Gaspard Coriolis described "kinetic energy" in 1829 in its modern sense, and in 1853, William Rankine coined the term "potential energy. Gaspard-Gustave de Coriolis or Gustave Coriolis (21 May 1792 – 19 September 1843 was a French Mathematician, Mechanical engineer and The kinetic energy of an object is the extra Energy which it possesses due to its motion William John Macquorn Rankine FRS ( July 5, 1820 &ndash December 24, 1872) was a Scottish engineer and Potential energy can be thought of as Energy stored within a physical system " It was argued for some years whether energy was a substance (the caloric) or merely a physical quantity, such as momentum. In Classical mechanics, momentum ( pl momenta SI unit kg · m/s, or equivalently N · s) is the product

Energy has many different forms. Kinetic, Sound, Nuclear and Electrical are the main forms.

He 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. In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " Rudolf Julius Emanuel Clausius (Born Rudolf Gottlieb, January 2, 1822 &ndash August 24, 1888) was a German Physicist Josiah Willard Gibbs ( February 11, 1839 &ndash April 28, 1903) was an American theoretical Physicist, Chemist Walther Hermann Nernst ( June 25, 1864 &ndash November 18, 1941) was a German Physicist who is known for his theories 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. In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy Radiant energy is the Energy of Electromagnetic waves The quantity of radiant energy may be calculated by integrating Radiant flux (or power Joseph Stefan ( Jožef Stefan) ( March 24, 1835 &ndash January 7, 1893) was a Physicist, Mathematician and

During a 1961 lecture[4] for undergraduate students at the California Institute of Technology, Richard Feynman, a celebrated physics teacher and Nobel Laureate, said this about the concept of energy:

 “ There is a fact, or if you wish, a law, governing natural phenomena that are known to date. The California Institute of Technology (commonly referred to as Caltech) is a private, Coeducational research university located in Pasadena Richard Phillips Feynman (ˈfaɪnmən May 11 1918 – February 15 1988 was an American Physicist known for the Path integral formulation of quantum This is a list of Nobel Prize Laureates awarded for their outstanding contributions to Humanitarian causes for Peace, work in Literature 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. In Physics, the law of conservation of energy states that the total amount of Energy in an isolated system remains constant and cannot be created although it may 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[4]

Since 1918 it has been known that the law of conservation of energy is the direct mathematical consequence of the translational symmetry of the quantity conjugate to energy, namely time. In Physics, the law of conservation of energy states that the total amount of Energy in an isolated system remains constant and cannot be created although it may In Geometry, a translation "slides" an object by a vector a: T a (p = p + a In Physics, conjugate variables are pair of variables mathematically defined in such a way that they become Fourier transform duals of one-another For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of That is, energy is conserved because the laws of physics do not distinguish between different moments of time (see Noether's theorem). Noether's theorem (also known as Noether's first theorem) states that any differentiable symmetry of the action of a physical system has

## Energy in various contexts since the beginning of the universe

The concept of energy and its transformations is useful in explaining and predicting most natural phenomena. The direction of transformations in energy (what kind of energy is transformed to what other kind) is often described by entropy (equal energy spread among all available degrees of freedom) considerations, since in practice all energy transformations are permitted on a small scale, but certain larger transformations are not permitted because it is statistically unlikely that energy or matter will randomly move into more concentrated forms or smaller spaces. In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy For information on degrees of freedom in other sciences see Degrees of freedom.

The concept of energy is used often in all fields of science.

• In chemistry, the energy differences between substances determine whether, and to what extent, they can be converted into other substances or react with other substances. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties A chemical substance is a Material with a definite chemical composition.
• In biology, chemical bonds are broken and made during metabolic processes, and the associated changes in available energy are studied in the subfield of bioenergetics. Foundations of modern biology There are five unifying principles A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. Bioenergetics is the subject of a field of Biochemistry that concerns Energy flow through living systems Energy is often stored by cells in the form of substances such as carbohydrate molecules (including sugars) and lipids, which release energy when reacted with oxygen. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most Lipids are broadly defined as any fat- Soluble ( lipophilic) naturally-occurring Molecule, such as fats oils waxes cholesterol sterols fat-soluble Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the
• In geology and meteorology, continental drift, mountain ranges, volcanos, and earthquakes are phenomena that can be explained in terms of energy transformations in the Earth's interior. Earth science (also known as geoscience, the geosciences or the Earth Sciences) is an all-embracing term for the Sciences related to the planet Continental drift is the movement of the Earth 's Continents relative to each other A mountain is a Landform that extends above the surrounding Terrain in a limited area with a peak Plate tectonics and hotspots Divergent plate boundaries At the An earthquake is the result of a sudden release of energy in the Earth 's crust that creates Seismic waves Earthquakes are recorded with a Seismometer In Physics and Engineering, energy transformation or energy conversion, is any process of transforming one form of Energy to another [5] While meteorological phenomena like wind, rain, hail, snow, lightning, tornadoes and hurricanes, are all a result of energy transformations brought about by solar energy on the planet Earth. Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's) Rain is Liquid precipitation. On Earth it is the condensation of atmospheric Water vapor into drops heavy enough to fall often making it to Hail is a form of precipitation which consists of balls or irregular lumps of ice (hailstones "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation. Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or A tornado is a violent rotating column of air which is in contact with both the surface of the earth and a Cumulonimbus cloud or in rare cases the base of a Cumulus A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding Solar energy is the Light and radiant heat from the Sun that powers Earth 's Climate and Weather and sustains Life
• In cosmology and astronomy the phenomena of stars, nova, supernova, quasars and gamma ray bursts are the universe's highest-output energy transformations of matter. Physical cosmology, as a branch of Astronomy, is the study of the large-scale structure of the Universe and is concerned with fundamental questions about its A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth A nova (pl novae or novas) is a Cataclysmic nuclear explosion caused by the accretion of hydrogen onto the surface of a White A supernova (plural supernovae or supernovas) is a stellar Explosion. A quasar (contraction of QUASi-stellAR radio source) is an extremely powerful and distant Active galactic nucleus. Gamma-ray bursts ( GRB s are the most luminous electromagnetic events occurring in the Universe since the Big Bang. In Physics and Engineering, energy transformation or energy conversion, is any process of transforming one form of Energy to another All stellar phenomena (including solar activity) are driven by various kinds of energy transformations. Energy in such transformations is either from gravitational collapse of matter (usually molecular hydrogen) into various classes of astronomical objects (stars, black holes, etc. ), or from nuclear fusion (of lighter elements, primarily hydrogen).

Energy transformations in the universe over time are characterized by various kinds of potential energy which has been available since the Big Bang, later being "released" (transformed to more active types of energy such as kinetic or radiant energy), when a triggering mechanism is available. The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation.

Familiar examples of such processes include nuclear decay, in which energy is released which was originally "stored" in heavy isotopes (such as uranium and thorium), by nucleosynthesis, a process which ultimately uses the gravitational potential energy released from the gravitational collapse of supernovae, to store energy in the creation of these heavy elements before they were incorporated into the solar system and the Earth. Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the Thorium (ˈθɔːriəm is a Chemical element with the symbol Th and Atomic number 90 Nucleosynthesis is the process of creating new atomic nuclei from preexisting Nucleons (protons and neutrons This energy is triggered and released in nuclear fission bombs. Nuclear weapon designs are physical chemical and engineering arrangements that cause the physics package of a nuclear weapon to detonate In a slower process, heat from nuclear decay of these atoms in the core of the Earth releases heat, which in turn may lift mountains, via orogenesis. Orogeny (Greek for "mountain generating" is the process of natural Mountain building and may be studied as a tectonic structural event as a geographical event and This slow lifting represents a kind of gravitational potential energy storage of the heat energy, which may be released to active kinetic energy in landslides, after a triggering event. Earthquakes also release stored elastic potential energy in rocks, a store which has been produced ultimately from the same radioactive heat sources. Thus, according to present understanding, familiar events such as landslides and earthquakes release energy which has been stored as potential energy in the Earth's gravitational field or elastic strain (mechanical potential energy) in rocks; but prior to this, represents energy that has been stored in heavy atoms since the collapse of long-destroyed stars created these atoms.

In another similar chain of transformations beginning at the dawn of the universe, nuclear fusion of hydrogen in the Sun releases another store of potential energy which was created at the time of the Big Bang. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. At that time, according to theory, space expanded and the universe cooled too rapidly for hydrogen to completely fuse into heavier elements. This meant that hydrogen represents a store of potential energy which can be released by fusion. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus Such a fusion process is triggered by heat and pressure generated from gravitational collapse of hydrogen clouds when they produce stars, and some of the fusion energy is then transformed into sunlight. Such sunlight from our Sun may again be stored as gravitational potential energy after it strikes the Earth, as (for example) water evaporates from oceans and is deposited upon mountains (where, after being released at a hydroelectric dam, it can be used to drive turbine/generators to produce electricity). Sunlight also drives many weather phenomena, save those generated by volcanic events. An example of a solar-mediated weather event is a hurricane, which occurs when large unstable areas of warm ocean, heated over months, give up some of their thermal energy suddenly to power a few days of violent air movement. Sunlight is also is captured by plants as chemical potential energy, when carbon dioxide and water are converted into a combustible combination of carbohydrates, lipids, and oxygen. Release of this energy as heat and light may be triggered suddenly by a spark, in a forest fire; or it may be available more slowly for animal or human metabolism, when these molecules are ingested, and catabolism is triggered by enzyme action. For the related metabolic process see Anabolism. Catabolism is the set of Metabolic pathways which break down molecules into Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Through all of these transformation chains, potential energy stored at the time of the Big Bang is later released by intermediate events, sometimes being stored in a number of ways over time between releases, as more active energy. In all these events, one kind of energy is converted to other types of energy, including heat.

## Regarding applications of the concept of energy

Energy is subject to a strict global conservation law; that is, whenever one measures (or calculates) the total energy of a system of particles whose interactions do not depend explicitly on time, it is found that the total energy of the system always remains constant. In Physics, a conservation law states that a particular measurable property of an isolated Physical system does not change as the system evolves [6]

• The total energy of a system can be subdivided and classified in various ways. System (from Latin systēma, in turn from Greek systēma is a set of interacting or interdependent Entities, real or abstract For example, it is sometimes convenient to distinguish potential energy (which is a function of coordinates only) from kinetic energy (which is a function of coordinate time derivatives only). Potential energy can be thought of as Energy stored within a physical system The kinetic energy of an object is the extra Energy which it possesses due to its motion In Calculus, a branch of mathematics the derivative is a measurement of how a function changes when the values of its inputs change It may also be convenient to distinguish gravitational energy, electric energy, thermal energy, and other forms. These classifications overlap; for instance thermal energy usually consists partly of kinetic and partly of potential energy.
• The transfer of energy can take various forms; familiar examples include work, heat flow, and advection, as discussed below.
• The word "energy" is also used outside of physics in many ways, which can lead to ambiguity and inconsistency. The vernacular terminology is not consistent with technical terminology. For example, the important public-service announcement, "Please conserve energy" uses vernacular notions of "conservation" and "energy" which make sense in their own context but are utterly incompatible with the technical notions of "conservation" and "energy" (such as are used in the law of conservation of energy). [7]

In classical physics energy is considered a scalar quantity, the canonical conjugate to time. In Physics, conjugate variables are pair of variables mathematically defined in such a way that they become Fourier transform duals of one-another For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of In special relativity energy is also a scalar (although not a Lorentz scalar but a time component of the energy-momentum 4-vector). Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial In Physics a Lorentz scalar is a scalar which is invariant under a Lorentz transformation. In Special relativity, four-momentum is the generalization of the classical three-dimensional Momentum to four-dimensional Spacetime. In relativity, a four-vector is a vector in a four-dimensional real Vector space, called Minkowski space. [8] In other words, energy is invariant with respect to rotations of space, but not invariant with respect to rotations of space-time (= boosts). Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS In Physics, the Lorentz transformation converts between two different observers' measurements of space and time where one observer is in constant motion with respect to

### Energy transfer

Because energy is strictly conserved and is also locally conserved (wherever it can be defined), it is important to remember that by definition of energy the transfer of energy between the "system" and adjacent regions is work. A familiar example is mechanical work. In Physics, mechanical work is the amount of Energy transferred by a Force. In simple cases this is written as:

ΔE = W             (1)

if there are no other energy-transfer processes involved. Here ΔE  is the amount of energy transferred, and W  represents the work done on the system.

More generally, the energy transfer can be split into two categories:

ΔE = W + Q             (2)

where Q  represents the heat flow into the system.

There are other ways in which an open system can gain or lose energy. What Sir Issac Newton said was if mass is counted as energy (as in many relativistic problems) then E must contain a term for mass lost or gained. In chemical systems, energy can be added to a system by means of adding substances with different chemical potentials, which potentials are then extracted (both of these process are illustrated by fueling an auto, a system which gains in energy thereby, without addition of either work or heat). Winding a clock would be adding energy to a mechanical system. These terms may be added to the above equation, or they can generally be subsumed into a quantity called "energy addition term E" which refers to any type of energy carried over the surface of a control volume or system volume. Examples may be seen above, and many others can be imagined (for example, the kinetic energy of a stream of particles entering a system, or energy from a laser beam adds to system energy, without either being either work-done or heat-added, in the classic senses).

ΔE = W + Q + E             (3)

Where E in this general equation represents other additional advected energy terms not covered by work done on a system, or heat added to it.

Energy is also transferred from potential energy (Ep) to kinetic energy (Ek) and then back to potential energy constantly. This is referred to as conservation of energy. In this closed system, energy can not be created or destroyed, so the initial energy and the final energy will be equal to each other. This can be demonstrated by the following:

Epi + Eki = EpF + EkF'''

The equation can then be simplified further since Ep = mgh (mass times acceleration due to gravity times the height) and $E_k = \frac{1}{2} mv^2$ (half times mass times velocity squared). Then the total amount of energy can be found by adding Ep + Ek = Etotal.

### Energy and the laws of motion

Classical mechanics
$\vec{F} = \frac{\mathrm{d}}{\mathrm{d}t}(m \vec{v})$
Newton's Second Law
History of ...
Fundamental concepts
Space · Time · Mass · Force
Energy · Momentum
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In classical mechanics, energy is a conceptually and mathematically useful property since it is a conserved quantity. Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects Newton's laws of motion are three Physical laws which provide relationships between the Forces acting on a body and the motion of the Early Ideas on Motion The Greek philosophers, and Aristotle in particular were the first to propose that there are abstract principles governing nature Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object In Physics, a force is whatever can cause an object with Mass to Accelerate. In Classical mechanics, momentum ( pl momenta SI unit kg · m/s, or equivalently N · s) is the product Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects In Physics, the law of conservation of energy states that the total amount of Energy in an isolated system remains constant and cannot be created although it may

### The Hamiltonian

The total energy of a system is sometimes called the Hamiltonian, after William Rowan Hamilton. Hamiltonian mechanics is a re-formulation of Classical mechanics that was introduced in 1833 by Irish mathematician William Rowan Hamilton. Sir William Rowan Hamilton (4 August 1805 &ndash 2 September 1865 was an Irish Mathematician, Physicist, and Astronomer who The classical equations of motion can be written in terms of the Hamiltonian, even for highly complex or abstract systems. These classical equations have remarkably direct analogs in nonrelativistic quantum mechanics. [9]

### The Lagrangian

Another energy-related concept is called the Lagrangian, after Joseph Louis Lagrange. The Lagrangian, L of a Dynamical system is a function that summarizes the dynamics of the system This is even more fundamental than the Hamiltonian, and can be used to derive the equations of motion. In non-relativistic physics, the Lagrangian is the kinetic energy minus potential energy.

Usually, the Lagrange formalism is mathematically more convenient than the Hamiltonian for non-conservative systems (like systems with friction).

### Energy and thermodynamics

#### Internal energy

Internal energy – the sum of all microscopic forms of energy of a system. In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes  It is related to the molecular structure and the degree of molecular activity and may be viewed as the sum of kinetic and potential energies of the molecules; it comprises the following types of energy:[10]

TypeComposition of Internal Energy (U)
Sensible energythe portion of the internal energy of a system associated with kinetic energies (molecular translation, rotation, and vibration; electron translation and spin; and nuclear spin) of the molecules. In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes  Sensible heat is Potential energy in the form of thermal energy or Heat. In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes
Latent energythe internal energy associated with the phase of a system. In Thermochemistry, latent heat is the amount of Energy in the form of Heat released or absorbed by a substance during a change of phase In the Physical sciences a phase is a Set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties
Chemical energythe internal energy associated with the different kinds of aggregation of atoms in matter. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny Matter is commonly defined as being anything that has mass and that takes up space.
Nuclear energythe tremendous amount of energy associated with the strong bonds within the nucleus of the atom itself. Nuclear Energy is released by the splitting (fission or merging together (fusion of the nuclei of Atom (s Nuclear Energy is released by the splitting (fission or merging together (fusion of the nuclei of Atom (s
Energy interactionsthose types of energies not stored in the system (e. In Physics, a fundamental interaction or fundamental force is a mechanism by which particles interact with each other and which cannot be explained in terms g. heat transfer, mass transfer, and work), but which are recognized at the system boundary as they cross it, which represent gains or losses by a system during a process. In thermal physics, heat transfer is the passage of Thermal energy from a hot to a colder body Mass transfer is the phrase commonly used in engineering for physical processes that involve molecular and convective transport of Atoms and Molecules In Thermodynamics, work is the quantity of Energy transferred from one system to another without an accompanying transfer of Entropy. In Thermodynamics, a thermodynamic system, originally called a working substance, is defined as that part of the universe that is under consideration
Thermal energythe sum of sensible and latent forms of internal energy. Thermal energy is the sum of the sensible energy and latent energy.

#### The laws of thermodynamics

According to the second law of thermodynamics, work can be totally converted into heat, but not vice versa. The second law of Thermodynamics is an expression of the universal law of increasing Entropy, stating that the entropy of an Isolated system which In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature This is a mathematical consequence of statistical mechanics. Statistical mechanics is the application of Probability theory, which includes mathematical tools for dealing with large populations to the field of Mechanics The first law of thermodynamics simply asserts that energy is conserved,[11] and that heat is included as a form of energy transfer. In Thermodynamics, the first law of thermodynamics is an expression of the more universal physical law of the Conservation of energy. A commonly-used corollary of the first law is that for a "system" subject only to pressure forces and heat transfer (e. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface g. a cylinder-full of gas), the differential change in energy of the system (with a gain in energy signified by a positive quantity) is given by:

$\mathrm{d}E = T\mathrm{d}S - P\mathrm{d}V\,$,

where the first term on the right is the heat transfer into the system, defined in terms of temperature T and entropy S (in which entropy increases and the change dS is positive when the system is heated); and the last term on the right hand side is identified as "work" done on the system, where pressure is P and volume V (the negative sign results since compression of the system requires work to be done on it and so the volume change, dV, is negative when work is done on the system). Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy Although this equation is the standard text-book example of energy conservation in classical thermodynamics, it is highly specific, ignoring all chemical, electric, nuclear, and gravitational forces, effects such as advection of any form of energy other than heat, and because it contains a term that depends on temperature. Advection, in mechanical and chemical engineering is a transport mechanism of a substance or a conserved property with a moving Fluid. The most general statement of the first law (i. e. , conservation of energy) is valid even in situations in which temperature is undefinable.

Energy is sometimes expressed as:

$\mathrm{d}E=\delta Q+\delta W\,$,

which is unsatisfactory[7] because there cannot exist any thermodynamic state functions W or Q that are meaningful on the right hand side of this equation, except perhaps in trivial cases.

### Equipartition of energy

The energy of a mechanical harmonic oscillator (a mass on a spring) is alternatively kinetic and potential. This article is about the harmonic oscillator in classical mechanics The kinetic energy of an object is the extra Energy which it possesses due to its motion The Mathematical study of potentials is known as Potential theory; it is the study of Harmonic functions on Manifolds This mathematical At two points in the oscillation cycle it is entirely kinetic, and alternatively at two other points it is entirely potential. Over the whole cycle, or over many cycles net energy is thus equally split between kinetic and potential. This is called equipartition principle - total energy of a system with many degrees of freedom is equally split among all available degrees of freedom. In classical Statistical mechanics, the equipartition theorem is a general formula that relates the Temperature of a system with its average energies

This principle is vitally important to understanding the behavior of a quantity closely related to energy, called entropy. In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy Entropy is a measure of evenness of a distribution of energy between parts of a system. In Mathematical analysis, distributions (also known as generalized functions) are objects which generalize functions and Probability distributions When an isolated system is given more degrees of freedom (= is given new available energy states which are the same as existing states), then total energy spreads over all available degrees equally without distinction between "new" and "old" degrees. A quantum mechanical system or particle that is bound, confined spacially can only take on certain discrete values of energy as opposed to classical particles which This mathematical result is called the second law of thermodynamics. The second law of Thermodynamics is an expression of the universal law of increasing Entropy, stating that the entropy of an Isolated system which

### Oscillators, phonons, and photons

In an ensemble (connected collection) of unsynchronized oscillators, the average energy is spread equally between kinetic and potential types.

In a solid, thermal energy (often referred to loosely as heat content) can be accurately described by an ensemble of thermal phonons that act as mechanical oscillators. Thermal energy is the sum of the sensible energy and latent energy. In this model, thermal energy is equally kinetic and potential.

In an ideal gas, the interaction potential between particles is essentially the delta function which stores no energy: thus, all of the thermal energy is kinetic.

Because an electric oscillator (LC circuit) is analogous to a mechanical oscillator, its energy must be, on average, equally kinetic and potential. It is entirely arbitrary whether the magnetic energy is considered kinetic and the electric energy considered potential, or vice versa. That is, either the inductor is analogous to the mass while the capacitor is analogous to the spring, or vice versa.

1. By extension of the previous line of thought, in free space the electromagnetic field can be considered an ensemble of oscillators, meaning that radiation energy can be considered equally potential and kinetic. Radiant energy is the Energy of Electromagnetic waves The quantity of radiant energy may be calculated by integrating Radiant flux (or power This model is useful, for example, when the electromagnetic Lagrangian is of primary interest and is interpreted in terms of potential and kinetic energy.
1. On the other hand, in the key equation m2c4 = E2p2c2, the contribution mc2 is called the rest energy, and all other contributions to the energy are called kinetic energy. For a particle that has mass, this implies that the kinetic energy is 0. 5p2 / m at speeds much smaller than c, as can be proved by writing E = mc2 √(1 + p2m − 2c − 2) and expanding the square root to lowest order. By this line of reasoning, the energy of a photon is entirely kinetic, because the photon is massless and has no rest energy. This expression is useful, for example, when the energy-versus-momentum relationship is of primary interest.

The two analyses are entirely consistent. The electric and magnetic degrees of freedom in item 1 are transverse to the direction of motion, while the speed in item 2 is along the direction of motion. For non-relativistic particles these two notions of potential versus kinetic energy are numerically equal, so the ambiguity is harmless, but not so for relativistic particles.

### Work and virtual work

Work is roughly force times distance. Mechanics ( Greek) is the branch of Physics concerned with the behaviour of physical bodies when subjected to Forces or displacements In Physics, mechanical work is the amount of Energy transferred by a Force. In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons But more precisely, it is

$W = \int \mathbf{F} \cdot \mathrm{d}\mathbf{s}$

This says that the work (W) is equal to the integral (along a certain path) of the force; for details see the mechanical work article. In Physics, a force is whatever can cause an object with Mass to Accelerate. In Physics, mechanical work is the amount of Energy transferred by a Force.

Work and thus energy is frame dependent. See also Inertial frame A frame of reference in Physics, may refer to a Coordinate system or set of axes within which to For example, consider a ball being hit by a bat. In the center-of-mass reference frame, the bat does no work on the ball. But, in the reference frame of the person swinging the bat, considerable work is done on the ball.

### Quantum mechanics

In quantum mechanics energy is defined in terms of the energy operator as a time derivative of the wave function. In Quantum mechanics, the Hamiltonian H is the Observable corresponding to the Total energy of the system A wave function or wavefunction is a mathematical tool used in Quantum mechanics to describe any physical system The Schrödinger equation equates the energy operator to the full energy of a particle or a system. In Physics, especially Quantum mechanics, the Schrödinger equation is an equation that describes how the Quantum state of a Physical system It thus can be considered as a definition of measurement of energy in quantum mechanics. The Schrödinger equation describes the space- and time-dependence of slow changing (non-relativistic) wave function of quantum systems. A wave function or wavefunction is a mathematical tool used in Quantum mechanics to describe any physical system The solution of this equation for bound system is discrete (a set of permitted states, each characterized by an energy level) which results in the concept of quanta. A quantum mechanical system or particle that is bound, confined spacially can only take on certain discrete values of energy as opposed to classical particles which In the solution of the Schrödinger equation for any oscillator (vibrator) and for electromagnetic wave in vacuum, the resulting energy states are related to the frequency by the Planck equation E = hν (where h is the Planck's constant and ν the frequency). The Planck constant (denoted h\ is a Physical constant used to describe the sizes of quanta. In the case of electromagnetic wave these energy states are called quanta of light or photons. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena

### Relativity

When calculating kinetic energy (= work to accelerate a mass from zero speed to some finite speed) relativistically - using Lorentz transformations instead of Newtonian mechanics, Einstein discovered unexpected by-product of these calculations to be an energy term which does not vanish at zero speed. In Physics, mechanical work is the amount of Energy transferred by a Force. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Speed is the rate of motion, or equivalently the rate of change in position often expressed as Distance d traveled per unit of In Physics, the Lorentz transformation converts between two different observers' measurements of space and time where one observer is in constant motion with respect to Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects He called it rest mass energy - energy which every mass must possess even when being at rest. In Physics, mass–energy equivalence is the concept that for particles slower than light any Mass has an associated Energy and vice versa. The amount of energy is directly proportional to the mass of body:

E = mc2,

where

m is the mass,
c is the speed of light in vacuum,
E is the rest mass energy.

For example, consider electron-positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles (its invariant mass) remains (since all energy is associated with mass), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The positrons or antielectron is the Antiparticle or the Antimatter counterpart of the Electron. This is a reversible process - the inverse process is called pair creation - in which the rest mass of particles is created from energy of two (or more) annihilating photons. See also Electron-positron annihilation Meitner–Hupfeld effect Pair instability supernova

In general relativity, the stress-energy tensor serves as the source term for the gravitational field, in rough analogy to the way mass serves as the source term in the non-relativistic Newtonian approximation. [8]

It is not uncommon to hear that energy is "equivalent" to mass. It would be more accurate to state that every energy has inertia and gravity equivalent, and because mass is a form of energy, then mass too has inertia and gravity associated with it.

## Measurement

There is no absolute measure of energy, because energy is defined as the work that one system does (or can do) on another. Thus, only of the transition of a system from one state into another can be defined and thus measured.

### Methods

The methods for the measurement of energy often deploy methods for the measurement of still more fundamental concepts of science, namely mass, distance, radiation, temperature, time, electric charge and electric current. Measurement is the process of estimating the magnitude of some attribute of an object such as its length or weight relative to some standard ( unit of measurement) such as Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Distance is a numerical description of how far apart objects are Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere.

A Calorimeter - An instrument used by physicists to measure energy

Conventionally the technique most often employed is calorimetry, a thermodynamic technique that relies on the measurement of temperature using a thermometer or of intensity of radiation using a bolometer. A calorimeter is a device used for Calorimetry, the Science of measuring the heat of Chemical reactions or Physical changes as well as Heat Calorimetry is the Science of measuring the Heat of Chemical In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " The thermometer is a device that measures Temperature or Temperature gradient using a variety of different principles it comes from the Greek roots A bolometer is a device for measuring the energy of incident Electromagnetic radiation.

### Units

Main article: Units of energy

Throughout the history of science, energy has been expressed in several different units such as ergs and calories. Because Energy is defined via work, the SI unit for energy is the same as the unit of work &ndash the Joule (J named in honour of James An erg is the unit of Energy and Mechanical work in the centimetre-gram-second (CGS system of units symbol "erg" This article is about the unit of energy For its use in Nutrition and Food labelling regulations, see the article on Food energy. At present, the accepted unit of measurement for energy is the SI unit of energy, the joule. The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity

## Forms of energy

Heat, a form of energy, is partly potential energy and partly kinetic energy. In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature Potential energy can be thought of as Energy stored within a physical system The kinetic energy of an object is the extra Energy which it possesses due to its motion

Classical mechanics distinguishes between potential energy, which is a function of the position of an object, and kinetic energy, which is a function of its movement. Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects Potential energy can be thought of as Energy stored within a physical system The kinetic energy of an object is the extra Energy which it possesses due to its motion In Physics, motion means a constant change in the location of a body Both position and movement are relative to a frame of reference, which must be specified: this is often (and originally) an arbitrary fixed point on the surface of the Earth, the terrestrial frame of reference. See also Inertial frame A frame of reference in Physics, may refer to a Coordinate system or set of axes within which to Some introductory authors attempt to separate all forms of energy in either kinetic or potential: this is not incorrect, but neither is it clear that it is a real simplification, as Feynman points out:

These notions of potential and kinetic energy depend on a notion of length scale. For example, one can speak of macroscopic potential and kinetic energy, which do not include thermal potential and kinetic energy. Also what is called chemical potential energy (below) is a macroscopic notion, and closer examination shows that it is really the sum of the potential and kinetic energy on the atomic and subatomic scale. Similar remarks apply to nuclear "potential" energy and most other forms of energy. This dependence on length scale is non-problematic if the various length scales are decoupled, as is often the case . . . but confusion can arise when different length scales are coupled, for instance when friction converts macroscopic work into microscopic thermal energy.

Examples of the interconversion of energy
Mechanical energy is converted
intoby
Mechanical energyLever
Thermal energyBrakes
Electric energyDynamo
Chemical energyMatches
Nuclear energyParticle accelerator

### Potential energy

Main article: Potential energy

Potential energy, symbols Ep, V or Φ, is defined as the work done against a given force (= work of given force with minus sign) in changing the position of an object with respect to a reference position (often taken to be infinite separation). In Physics, mechanical energy describes the Potential energy and Kinetic energy present in the components of a mechanical system. Thermal energy is the sum of the sensible energy and latent energy. A brake is a device for slowing or stopping the motion of a Machine or Vehicle, or alternatively a device to restrain it from starting to move again Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where A dynamo, originally another name for an Electrical generator, now means a generator that produces Direct current with the use of a commutator. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. A synchrotron is a particular type of cyclic Particle accelerator in which the magnetic field (to turn the particles so they circulate and the electric field (to accelerate In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός A match is a consumable Tool for lighting a Fire under controlled circumstances on demand Nuclear Energy is released by the splitting (fission or merging together (fusion of the nuclei of Atom (s Potential energy can be thought of as Energy stored within a physical system If F is the force and s is the displacement,

$E_{\rm p} = -\int \mathbf{F}\cdot{\rm d}\mathbf{s}$

with the dot representing the scalar product of the two vectors. In Physics, a force is whatever can cause an object with Mass to Accelerate. In Mathematics, the dot product, also known as the scalar product, is an operation which takes two vectors over the Real numbers R

The name "potential" energy originally signified the idea that the energy could readily be transferred as work—at least in an idealized system (reversible process, see below). This is not completely true for any real system, but is often a reasonable first approximation in classical mechanics.

The general equation above can be simplified in a number of common cases, notably when dealing with gravity or with elastic forces. Gravitation is a natural Phenomenon by which objects with Mass attract one another

#### Gravitational potential energy

The gravitational force near the Earth's surface varies very little with the height, h, and is equal to the mass, m, multiplied by the gravitational acceleration, g = 9. Potential energy can be thought of as Energy stored within a physical system Newton 's law of universal Gravitation is a physical law describing the gravitational attraction between bodies with mass Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object In Physics, gravitational acceleration is the Acceleration of an object caused by the Force of gravity from another object 81 m/s². In these cases, the gravitational potential energy is given by

Ep,g = mgh

A more general expression for the potential energy due to Newtonian gravitation between two bodies of masses m1 and m2, useful in astronomy, is

$E_{\rm p,g} = -G{{m_1m_2}\over{r}}$,

where r is the separation between the two bodies and G is the gravitational constant, 6. Newton 's law of universal Gravitation is a physical law describing the gravitational attraction between bodies with mass Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study The gravitational constant, denoted G, is a Physical constant involved in the calculation of the gravitational attraction between objects with mass 6742(10)×10−11 m³kg−1s−2. [12] In this case, the reference point is the infinite separation of the two bodies.

#### Elastic potential energy

As a ball falls freely under the influence of gravity, it accelerates downward, its initial potential energy converting into kinetic energy. Gravitation is a natural Phenomenon by which objects with Mass attract one another Potential energy can be thought of as Energy stored within a physical system The kinetic energy of an object is the extra Energy which it possesses due to its motion On impact with a hard surface the ball deforms, converting the kinetic energy into elastic potential energy. The elastic Potential energy is defined as a work (force x distance needed to compress or expand an elastic body As the ball springs back, the energy converts back firstly to kinetic energy and then as the ball re-gains height into potential energy. Energy conversion to heat due to inelastic deformation and air resistance cause each successive bounce to be lower than the last. A material is said to be elastic if it deforms under stress (e In Materials science, deformation is a change in the shape or size of an object due to an applied force. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a

Elastic potential energy is defined as a work needed to compress (or expand) a spring. The elastic Potential energy is defined as a work (force x distance needed to compress or expand an elastic body The force, F, in a spring or any other system which obeys Hooke's law is proportional to the extension or compression, x,

F = − kx

where k is the force constant of the particular spring (or system). A spring is a flexible elastic object used to store mechanical Energy. In Mechanics, and Physics, Hooke's law of elasticity is an approximation that states that the amount by which a material body is deformed (the In Mechanics, and Physics, Hooke's law of elasticity is an approximation that states that the amount by which a material body is deformed (the In this case, the calculated work becomes

$E_{\rm p,e} = {1\over 2}kx^2$.

Hooke's law is a good approximation for behaviour of chemical bonds under normal conditions, i. A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic e. when they are not being broken or formed.

### Kinetic energy

Main article: Kinetic energy

Kinetic energy, symbols Ek, T or K, is the work required to accelerate an object to a given speed. The kinetic energy of an object is the extra Energy which it possesses due to its motion Indeed, calculating this work one easily obtains the following:

$E_{\rm k} = \int \mathbf{F} \cdot d \mathbf{x} = \int \mathbf{v} \cdot d \mathbf{p}= {1\over 2}mv^2$

At speeds approaching the speed of light, c, this work must be calculated using Lorentz transformations, which results in the following:

$E_{\rm k} = m c^2\left(\frac{1}{\sqrt{1 - (v/c)^2}} - 1\right)$

This equation reduces to the one above it, at small (compared to c) speed. In Physics, the Lorentz transformation converts between two different observers' measurements of space and time where one observer is in constant motion with respect to A mathematical by-product of this work (which is immediately seen in the last equation) is that even at rest a mass has the amount of energy equal to:

Erest = mc2

This energy is thus called rest mass energy. In Physics, mass–energy equivalence is the concept that for particles slower than light any Mass has an associated Energy and vice versa.

### Thermal energy

Examples of the interconversion of energy
Thermal energy is converted
intoby
Mechanical energySteam turbine
Thermal energyHeat exchanger
Electric energyThermocouple
Chemical energyBlast furnace
Nuclear energySupernova
Main article: Thermal energy

Thermal energy (of some media - gas, plasma, solid, etc) is the energy associated with the microscopical random motion of particles constituting the media. In Physics, mechanical energy describes the Potential energy and Kinetic energy present in the components of a mechanical system. A steam turbine is a mechanical device that extracts Thermal energy from pressurized Steam, and converts it into useful mechanical work Thermal energy is the sum of the sensible energy and latent energy. A heat exchanger is a device built for efficient Heat transfer from one medium to another whether the media are separated by a solid wall so that they never mix or the media Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where In Electrical engineering and industry thermocouples are a widely used type of temperature sensor and can also be used as a means to convert thermal Potential Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Physics, a black body is an object that absorbs all light that falls on it In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός A blast furnace is a type of metallurgical Furnace used for Smelting to produce metals generally Iron. Nuclear Energy is released by the splitting (fission or merging together (fusion of the nuclei of Atom (s A supernova (plural supernovae or supernovas) is a stellar Explosion. Thermal energy is the sum of the sensible energy and latent energy. For example, in case of monoatomic gas it is just a kinetic energy of motion of atoms of gas as measured in the reference frame of the center of mass of gas. In case of many-atomic gas rotational and vibrational energy is involved. In the case of liquids and solids there is also potential energy (of interaction of atoms) involved, and so on.

A heat is defined as a transfer (flow) of thermal energy across certain boundary (for example, from a hot body to cold via the area of their contact. A practical definition for small transfers of heat is

$\Delta q = \int C_{\rm v}{\rm d}T$

where Cv is the heat capacity of the system. Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity This definition will fail if the system undergoes a phase transition—e. In Thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another g. if ice is melting to water—as in these cases the system can absorb heat without increasing its temperature. In more complex systems, it is preferable to use the concept of internal energy rather than that of thermal energy (see Chemical energy below). In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes

Despite the theoretical problems, the above definition is useful in the experimental measurement of energy changes. In a wide variety of situations, it is possible to use the energy released by a system to raise the temperature of another object, e. g. a bath of water. It is also possible to measure the amount of electric energy required to raise the temperature of the object by the same amount. Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where The calorie was originally defined as the amount of energy required to raise the temperature of one gram of water by 1 °C (approximately 4. This article is about the unit of energy For its use in Nutrition and Food labelling regulations, see the article on Food energy. 1855 J, although the definition later changed), and the British thermal unit was defined as the energy required to heat one pound of water by 1 °F (later fixed as 1055. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 06 J).

### Electric energy

Main articles: Electromagnetism and Electricity
Examples of the interconversion of energy
Electric energy is converted
intoby
Mechanical energyElectric motor
Thermal energyResistor
Electric energyTransformer
Chemical energyElectrolysis
Nuclear energySynchrotron

The electric potential energy of given configuration of charges is defined as the work which must be done against the Coulomb force to rearrange charges from infinite separation to this configuration (or the work done by the Coulomb force separating the charges from this configuration to infinity). Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of In Physics, mechanical energy describes the Potential energy and Kinetic energy present in the components of a mechanical system. An electric motor uses Electrical energy to produce Mechanical energy. Thermal energy is the sum of the sensible energy and latent energy. |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός In chemistry and manufacturing electrolysis is a method of separating chemically bonded elements and compounds by passing an Electric current Nuclear Energy is released by the splitting (fission or merging together (fusion of the nuclei of Atom (s A synchrotron is a particular type of cyclic Particle accelerator in which the magnetic field (to turn the particles so they circulate and the electric field (to accelerate Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where In Thermodynamics, work is the quantity of Energy transferred from one system to another without an accompanying transfer of Entropy. ---- Bold text Coulomb's law', developed in the 1780s by French physicist Charles Augustin de Coulomb, may be stated in scalar form For two point-like charges Q1 and Q2 at a distance r this work, and hence electric potential energy is equal to:

$E_{\rm p,e} = {1\over {4\pi\epsilon_0}}{{Q_1Q_2}\over{r}}$

where ε0 is the electric constant of a vacuum, 107/4πc0² or 8. Vacuum permittivity, referred to by international standards organizations as the electric constant, and denoted by the symbol ε0 is a fundamental Physical 854188…×10−12 F/m. [12] If the charge is accumulated in a capacitor (of capacitance C), the reference configuration is usually selected not to be infinite separation of charges, but vice versa - charges at an extremely close proximity to each other (so there is zero net charge on each plate of a capacitor). A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors Capacitance is a measure of the amount of Electric charge stored (or separated for a given Electric potential. The justification for this choice is purely practical - it is easier to measure both voltage difference and magnitude of charges on a capacitor plates not versus infinite separation of charges but rather versus discharged capacitor where charges return to close proximity to each other (electrons and ions recombine making the plates neutral). In this case the work and thus the electric potential energy becomes

$E_{\rm p,e} = {{Q^2}\over{2C}}$

If an electric current passes through a resistor, electric energy is converted to heat; if the current passes through an electric appliance, some of the electric energy will be converted into other forms of energy (although some will always be lost as heat). Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | The amount of electric energy due to an electric current can be expressed in a number of different ways:

E = UQ = UIt = Pt = U2t / R

where U is the electric potential difference (in volts), Q is the charge (in coulombs), I is the current (in amperes), t is the time for which the current flows (in seconds), P is the power (in watts) and R is the electric resistance (in ohms). At a point in space the electric potential is the Potential energy per unit of charge that is associated with a static (time-invariant Electric field The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. The coulomb (symbol C) is the SI unit of Electric charge. It is named after Charles-Augustin de Coulomb. The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second In Physics, power (symbol P) is the rate at which work is performed or energy is transmitted or the amount of energy required or expended for The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is The ohm (symbol Ω) is the SI unit of Electrical impedance or in the Direct current case Electrical resistance, The last of these expressions is important in the practical measurement of energy, as potential difference, resistance and time can all be measured with considerable accuracy.

#### Magnetic energy

There is no fundamental difference between magnetic energy and electric energy: the two phenomena are related by Maxwell's equations. In Classical electromagnetism, Maxwell's equations are a set of four Partial differential equations that describe the properties of the electric The potential energy of a magnet of magnetic moment m in a magnetic field B is defined as the work of magnetic force (actually of magnetic torque) on re-alignment of the vector of the magnetic dipole moment, and is equal:

$E_{\rm p,m} = -m\cdot B$

while the energy stored in a inductor (of inductance L) when current I is passing via it is

$E_{\rm p,m} = {1\over 2}LI^2$. A magnet (from Greek grc μαγνήτης λίθος " Magnesian stone" is a material or object that produces a Magnetic field. In Physics, Astronomy, Chemistry, and Electrical engineering, the term magnetic moment of a system (such as a loop of Electric current In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges In Physics, mechanical work is the amount of Energy transferred by a Force. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about An inductor is a passive electrical component designed to provide Inductance in a circuit In Electrical circuits, any Electric current i produces a Magnetic field and hence generates a total Magnetic flux \Phi acting

This second expression forms the basis for superconducting magnetic energy storage. Superconducting Magnetic Energy Storage (SMES systems store energy in the Magnetic field created by the flow of Direct current in a superconducting coil

#### Electromagnetic fields

Examples of the interconversion of energy
intoby
Mechanical energySolar sail
Thermal energySolar collector
Electric energySolar cell
Chemical energyPhotosynthesis
Nuclear energyMössbauer spectroscopy

Calculating work needed to create an electric or magnetic field in unit volume (say, in a capacitor or an inductor) results in the electric and magnetic fields energy densities:

$u_e=\frac{\epsilon_0}{2} E^2$

and

$u_m=\frac{1}{2\mu_0} B^2$,

in SI units. In Physics, mechanical energy describes the Potential energy and Kinetic energy present in the components of a mechanical system. Solar sails (also called light sails or photon sails, especially when they use Light sources other than the Sun) are a proposed form of Thermal energy is the sum of the sensible energy and latent energy. A solar collector is a device for extracting the Energy of the Sun not indirectly into a more usable or storable form Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where A solar cell or photovoltaic cell is a device that converts Solar energy into Electricity by the photovoltaic effect. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Nonlinear optics (NLO is the branch of Optics that describes the behaviour of Light in nonlinear media, that is media in which the dielectric polarization In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Nuclear Energy is released by the splitting (fission or merging together (fusion of the nuclei of Atom (s Mössbauer spectroscopy (Mößbauer is a spectroscopic technique based on the Mössbauer effect. In Physics, mechanical work is the amount of Energy transferred by a Force. Energy density is the amount of Energy stored in a given system or region of space per unit Volume, or per unit Mass, depending on the context although

Electromagnetic radiation, such as microwaves, visible light or gamma rays, represents a flow of electromagnetic energy. Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions Applying the above expressions to magnetic and electric components of electromagnetic field both the volumetric density and the flow of energy in e/m field can be calculated. The resulting Poynting vector, which is expressed as

$\mathbf{S} = \frac{1}{\mu} \mathbf{E} \times \mathbf{B},$

in SI units, gives the density of the flow of energy and its direction. In Physics, the Poynting vector can be thought of as representing the Energy Flux (in W/m2 of an Electromagnetic field.

The energy of electromagnetic radiation is quantized (has discrete energy levels). A quantum mechanical system or particle that is bound, confined spacially can only take on certain discrete values of energy as opposed to classical particles which The spacing between these levels is equal to

E = hν

where h is the Planck constant, 6. The Planck constant (denoted h\ is a Physical constant used to describe the sizes of quanta. 6260693(11)×10−34 Js,[12] and ν is the frequency of the radiation. Frequency is a measure of the number of occurrences of a repeating event per unit Time. This quantity of electromagnetic energy is usually called a photon. The photons which make up visible light have energies of 270–520 yJ, equivalent to 160–310 kJ/mol, the strength of weaker chemical bonds. A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic

### Chemical energy

Examples of the interconversion of energy
Chemical energy is converted
intoby
Mechanical energyMuscle
Thermal energyFire
Electric energyFuel cell
Chemical energyChemical reaction

Chemical energy is the energy due to associations of atoms in molecules and various other kinds of aggregates of matter. In Thermodynamics, chemical thermodynamics is the mathematical study of the interrelation of Heat and work with Chemical reactions or with a In Physics, mechanical energy describes the Potential energy and Kinetic energy present in the components of a mechanical system. Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the Thermal energy is the sum of the sensible energy and latent energy. Fire is the heat and light energy released during a Chemical reaction, in particular a combustion reaction. Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where A fuel cell is an electrochemical conversion device It produces electricity from Fuel (on the Anode side and an oxidant (on the Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Glowworm (or glow-worm) is the common name for various different groups of insect Larva and adult Larviform females which glow through In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Matter is commonly defined as being anything that has mass and that takes up space. It may be defined as a work done by electric forces during re-arrangement of electric charges, electrons and protons, in the process of aggregation. If the chemical energy of a system decreases during a chemical reaction, the difference is transferred to the surroundings in some form (often heat or light); on the other hand if the chemical energy of a system increases as a result of a chemical reaction - the difference then is supplied by from the surroundings (usually again in form of heat or light). In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 For example,

when two hydrogen atoms react to form a dihydrogen molecule, the chemical energy decreases by 724 zJ (the bond energy of the H–H bond);
when the electron is completely removed from a hydrogen atom, forming a hydrogen ion (in the gas phase), the chemical energy increases by 2. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 In Chemistry, bond energy ( E) is a measure of Bond strength in a Chemical bond. 18 aJ (the ionization energy of hydrogen). The ionization potential, ionization energy or EI of an Atom or Molecule is the Energy required to remove an Electron

It is common to quote the changes in chemical energy for one mole of the substance in question: typical values for the change in molar chemical energy during a chemical reaction range from tens to hundreds of kJ/mol. The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this

The chemical energy as defined above is also referred to by chemists as the internal energy, U: technically, this is measured by keeping the volume of the system constant. A chemist is a Scientist trained in the Science of Chemistry. In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes  The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically However, most practical chemistry is performed at constant pressure and, if the volume changes during the reaction (e. g. a gas is given off), a correction must be applied to take account of the work done by or on the atmosphere to obtain the enthalpy, H:

ΔH = ΔU + pΔV

A second correction, for the change in entropy, S, must also be performed to determine whether a chemical reaction will take place or not, giving the Gibbs free energy, G:

ΔG = ΔHTΔS

These corrections are sometimes negligible, but often not (especially in reactions involving gases). In Thermodynamics and molecular chemistry, the enthalpy (denoted as H, h, or rarely as χ) is a quotient or description of In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy In Thermodynamics, the Gibbs free energy ( IUPAC recommended name Gibbs energy or Gibbs function) is a Thermodynamic potential which

Since the industrial revolution, the burning of coal, oil, natural gas or products derived from them has been a socially significant transformation of chemical energy into other forms of energy. The Industrial Revolution was a period in the late 18th and early 19th centuries when major changes in agriculture manufacturing and transportation had a profound effect on the Combustion or burning is a complex sequence of Exothermic chemical reactions between a Fuel and an Oxidant accompanied by the production of An oil is a substance that is in a viscous Liquid state ( "oily") at ambient temperatures or slightly warmer and is Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, the energy "consumption" (one should really speak of "energy transformation") of a society or country is often quoted in reference to the average energy released by the combustion of these fossil fuels:

1 tonne of coal equivalent (TCE) = 29 GJ
tonne of oil equivalent (TOE) = 41. Combustion or burning is a complex sequence of Exothermic chemical reactions between a Fuel and an Oxidant accompanied by the production of Fossil fuels or mineral fuels are fossil source Fuels that is Hydrocarbons found within the top layer of the Earth’s crust. The tonne of oil equivalent ( toe) is a unit of energy: the amount of energy released by burning one Tonne of Crude oil, approximately 42 87 GJ

On the same basis, a tank-full of gasoline (45 litres, 12 gallons) is equivalent to about 1. 6 GJ of chemical energy. Another chemically-based unit of measurement for energy is the "tonne of TNT", taken as 4. Trinitrotoluene ( TNT) is a Chemical compound with the formula C6H2(NO23CH3 184 GJ. Hence, burning a tonne of oil releases about ten times as much energy as the explosion of one tonne of TNT: fortunately, the energy is usually released in a slower, more controlled manner.

Simple examples of chemical energy are batteries and food. When you eat the food is digested and turned into chemical energy which can be transformed to kinetic energy.

### Nuclear energy

Examples of the interconversion of energy
Nuclear binding energy is converted
intoby
Thermal energySun
Nuclear energyNuclear isomerism

Nuclear potential energy, along with electric potential energy, provides the energy released from nuclear fission and nuclear fusion processes. Binding energy is the Mechanical energy required to disassemble a whole into separate parts In Physics, mechanical energy describes the Potential energy and Kinetic energy present in the components of a mechanical system. Alpha decay is a type of radioactive decay in which an Atomic nucleus emits an Alpha particle (two protons and two neutrons bound together into a particle Thermal energy is the sum of the sensible energy and latent energy. The Sun (Sol is the Star at the center of the Solar System. Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where Beta particles are high-energy high-speed Electrons or Positrons emitted by certain types of Radioactive nuclei such as Potassium -40 Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. Nuclear Energy is released by the splitting (fission or merging together (fusion of the nuclei of Atom (s A nuclear isomer is a Metastable state of an Atomic nucleus caused by the excitation of one or more of its Nucleons A nuclear isomer occupies Nuclear Energy is released by the splitting (fission or merging together (fusion of the nuclei of Atom (s Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing Free neutrons and other smaller nuclei which may In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus The result of both these processes are nuclei in which strong nuclear forces bind nuclear particles more strongly and closely. In particle physics the strong interaction, or strong force, or color force, holds Quarks and Gluons together to form Protons and Weak nuclear forces (different from strong forces) provide the potential energy for certain kinds of radioactive decay, such as beta decay. The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four Fundamental interactions of nature In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted The energy released in nuclear processes is so large that the relativistic change in mass (after the energy has been removed) can be as much as several parts per thousand.

Nuclear particles (nucleons) like protons and neutrons are not destroyed (law of conservation of baryon number) in fission and fusion processes. In Physics a nucleon is a collective name for two Baryons the Neutron and the Proton. In Particle physics, the baryon number is an approximate conserved Quantum number of a system A few lighter particles may be created or destroyed (example: beta minus and beta plus decay, or electron capture decay), but these minor processes are not important to the immediate energy release in fission and fusion. Rather, fission and fusion release energy when collections of baryons become more tightly bound, and it is the energy associated with a fraction of the mass of the nucleons (but not the whole particles) which appears as the heat and electromagnetic radiation generated by nuclear reactions. This heat and radiation retains the "missing" mass, but the mass is missing only because it escapes in the form of heat and light, which retain the mass and conduct it out of the system where it is not measured. The energy from the Sun, also called solar energy, is an example of this form of energy conversion. The Sun (Sol is the Star at the center of the Solar System. Solar energy is the Light and radiant heat from the Sun that powers Earth 's Climate and Weather and sustains Life In the Sun, the process of hydrogen fusion converts about 4 million metric tons of solar matter per second into light, which is radiated into space, but during this process, the number of total protons and neutrons in the sun does not change. The Sun (Sol is the Star at the center of the Solar System. In this system, the light itself retains the inertial equivalent of this mass, and indeed the mass itself (as a system), which represents 4 million tons per second of electromagnetic radiation, moving into space. Each of the helium nuclei which are formed in the process are less massive than the four protons from they were formed, but (to a good approximation), no particles or atoms are destroyed in the process of turning the sun's nuclear potential energy into light.

### Surface energy

If there is any kind of tension in a surface, such as a stretched sheet of rubber or material interfaces, it is possible to define surface energy. In particular, any meeting of dissimilar materials that don't mix will result in some kind of surface tension, if there is freedom for the surfaces to move then, as seen in capillary surfaces for example, the minimum energy will as usual be sought. For the work of fiction see Surface Tension (short story. Surface tension is a property of the surface of a Liquid that causes it to In Fluid mechanics and Mathematics, a capillary surface is a Surface that represents the interface between two different Fluids As a consequence

A minimal surface, for example, represents the smallest possible energy that a surface can have if its energy is proportional to the area of the surface. In Mathematics, a Minimal surface is a surface with a Mean curvature of zero For this reason, (open) soap films of small size are minimal surfaces (small size reduces gravity effects, and openness prevents pressure from building up. Note that a bubble is a minimum energy surface but not a minimal surface by definition). In Mathematics, a Minimal surface is a surface with a Mean curvature of zero

## Transformations of energy

Main article: Energy conversion

One form of energy can often be readily transformed into another with the help of a device- for instance, a battery, from chemical energy to electric energy; a dam: gravitational potential energy to kinetic energy of moving water (and the blades of a turbine) and ultimately to electric energy through an electric generator. In Physics and Engineering, energy transformation or energy conversion, is any process of transforming one form of Energy to another In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where A dam is a barrier that divides waters. Dams generally serve the primary purpose of retaining water while other structures such as Floodgates, Levees Potential energy can be thought of as Energy stored within a physical system The kinetic energy of an object is the extra Energy which it possesses due to its motion Water is a common Chemical substance that is essential for the survival of all known forms of Life. A turbine is a rotary Engine that extracts Energy from a Fluid flow Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where In Electricity generation, an electrical generator is a device that converts Mechanical energy to Electrical energy, generally using Electromagnetic Similarly, in the case of a chemical explosion, chemical potential energy is transformed to kinetic energy and thermal energy in a very short time. An explosive material is a material that either is chemically or otherwise Energetically unstable or produces a sudden expansion of the material usually accompanied In Thermodynamics and Chemistry, chemical potential, symbolized by μ, is a term introduced by the American engineer chemist and mathematical The kinetic energy of an object is the extra Energy which it possesses due to its motion Thermal energy is the sum of the sensible energy and latent energy. Yet another example is that of a pendulum. A pendulum is a mass that is attached to a pivot from which it can swing freely At its highest points the kinetic energy is zero and the gravitational potential energy is at maximum. The kinetic energy of an object is the extra Energy which it possesses due to its motion Potential energy can be thought of as Energy stored within a physical system At its lowest point the kinetic energy is at maximum and is equal to the decrease of potential energy. The kinetic energy of an object is the extra Energy which it possesses due to its motion Potential energy can be thought of as Energy stored within a physical system If one (unrealistically) assumes that there is no friction, the conversion of energy between these processes is perfect, and the pendulum will continue swinging forever. Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e A pendulum is a mass that is attached to a pivot from which it can swing freely

Energy can be converted into matter and vice versa. Matter is commonly defined as being anything that has mass and that takes up space. The mass-energy equivalence formula E = mc², derived independently by Albert Einstein and Henri Poincaré, quantifies the relationship between mass and rest energy. In Physics, mass–energy equivalence is the concept that for particles slower than light any Mass has an associated Energy and vice versa. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical Jules Henri Poincaré ( 29 April 1854 &ndash 17 July 1912) (ˈʒyl ɑ̃ˈʁi pwɛ̃kaˈʁe was a French Mathematician Since c2 is extremely large relative to ordinary human scales, the conversion of ordinary amount of mass (say, 1 kg) to other forms of energy can liberate tremendous amounts of energy (~9x1016 Joules), as can be seen in nuclear reactors and nuclear weapons. Conversely, the mass equivalent of a unit of energy is minuscule, which is why a loss of energy from most systems is difficult to measure by weight, unless the energy loss is very large. Examples of energy transformation into matter (particles) are found in high energy nuclear physics. Nuclear physics is the field of Physics that studies the building blocks and interactions of Atomic nuclei.

In nature, transformations of energy can be fundamentally classed into two kinds: those that are thermodynamically reversible, and those that are thermodynamically irreversible. For articles on other forms of reversibility including reversibility of microscopic dynamics see Reversibility (disambiguation. In science a Process that is not reversible is called irreversible. A reversible process in thermodynamics is one in which no energy is dissipated (spread) into empty energy states available in a volume, from which it cannot be recovered into more concentrated forms (fewer quantum states), without degradation of even more energy. For articles on other forms of reversibility including reversibility of microscopic dynamics see Reversibility (disambiguation. A reversible process is one in which this sort of dissipation does not happen. For example, conversion of energy from one type of potential field to another, is reversible, as in the pendulum system described above. In processes where heat is generated, however, quantum states of lower energy, present as possible exitations in fields between atoms, act as a reservoir for part of the energy, from which it cannot be recovered, in order to be converted with 100% efficiency into other forms of energy. In this case, the energy must partly stay as heat, and cannot be completely recovered as usable energy, except at the price of an increase in some other kind of heat-like increase in disorder in quantum states, in the universe (such as an expansion of matter, or a randomization in a crystal).

As the universe evolves in time, more and more of its energy becomes trapped in irreversible states (i. e. , as heat or other kinds of increases in disorder). This has been referred to as the inevitable thermodynamic heat death of the universe. The heat death is a possible final state of the universe, in which it has " run down " to a state of no Thermodynamic free energy to sustain In this heat death the energy of the universe does not change, but the fraction of energy which is available to do work, or be transformed to other usable forms of energy, grows less and less. The heat death is a possible final state of the universe, in which it has " run down " to a state of no Thermodynamic free energy to sustain

## Law of conservation of energy

Energy is subject to the law of conservation of energy. In Physics, the law of conservation of energy states that the total amount of Energy in an isolated system remains constant and cannot be created although it may According to this law, energy can neither be created (produced) nor destroyed itself. It can only be transformed.

Most kinds of energy (with gravitational energy being a notable exception)[1] are also subject to strict local conservation laws, as well. In this case, energy can only be exchanged between adjacent regions of space, and all observers agree as to the volumetric density of energy in any given space. There is also a global law of conservation of energy, stating that the total energy of the universe cannot change; this is a corollary of the local law, but not vice versa. [4][7] Conservation of energy is the mathematical consequence of translational symmetry of time (that is, the indistinguishability of time intervals taken at different time)[13] - see Noether's theorem. In Physics, the law of conservation of energy states that the total amount of Energy in an isolated system remains constant and cannot be created although it may In Geometry, a translation "slides" an object by a vector a: T a (p = p + a For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of Noether's theorem (also known as Noether's first theorem) states that any differentiable symmetry of the action of a physical system has

According to energy conservation law the total inflow of energy into a system must equal the total outflow of energy from the system, plus the change in the energy contained within the system. Energy conservation is the practice of decreasing the quantity of energy used

This law is a fundamental principle of physics. It follows from the translational symmetry of time, a property of most phenomena below the cosmic scale that makes them independent of their locations on the time coordinate. In Geometry, a translation "slides" an object by a vector a: T a (p = p + a For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of Put differently, yesterday, today, and tomorrow are physically indistinguishable.

Thus is because energy is the quantity which is canonical conjugate to time. In Physics, conjugate variables are pair of variables mathematically defined in such a way that they become Fourier transform duals of one-another This mathematical entanglement of energy and time also results in the uncertainty principle - it is impossible to define the exact amount of energy during any definite time interval. The uncertainty principle should not be confused with energy conservation - rather it provides mathematical limits to which energy can in principle be defined and measured.

In quantum mechanics energy is expressed using the Hamiltonian operator. Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons In Mathematics, an operator is a function which operates on (or modifies another function On any time scales, the uncertainty in the energy is by

$\Delta E \Delta t \ge \frac { \hbar } {2 }$

which is similar in form to the Heisenberg uncertainty principle (but not really mathematically equivalent thereto, since H and t are not dynamically conjugate variables, neither in classical nor in quantum mechanics). In Quantum physics, the Heisenberg uncertainty principle states that locating a particle in a small region of space makes the Momentum of the particle uncertain

In particle physics, this inequality permits a qualitative understanding of virtual particles which carry momentum, exchange by which and with real particles, is responsible for the creation of all known fundamental forces (more accurately known as fundamental interactions). Particle physics is a branch of Physics that studies the elementary constituents of Matter and Radiation, and the interactions between them In Physics, a virtual particle is a particle that exists for a limited time and space introducing uncertainty in their energy and momentum due to the Heisenberg Uncertainty In Classical mechanics, momentum ( pl momenta SI unit kg · m/s, or equivalently N · s) is the product In Physics, a fundamental interaction or fundamental force is a mechanism by which particles interact with each other and which cannot be explained in terms In Physics, a fundamental interaction or fundamental force is a mechanism by which particles interact with each other and which cannot be explained in terms Virtual photons (which are simply lowest quantum mechanical energy state of photons) are also responsible for electrostatic interaction between electric charges (which results in Coulomb law), for spontaneous radiative decay of exited atomic and nuclear states, for the Casimir force, for van der Waals bond forces and some other observable phenomena. In Physics, a virtual particle is a particle that exists for a limited time and space introducing uncertainty in their energy and momentum due to the Heisenberg Uncertainty A quantum mechanical system or particle that is bound, confined spacially can only take on certain discrete values of energy as opposed to classical particles which In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. ---- Bold text Coulomb's law', developed in the 1780s by French physicist Charles Augustin de Coulomb, may be stated in scalar form Spontaneous fission (SF is a form of Radioactive decay characteristic of very heavy Isotopes and is theoretically possible for any atomic nucleus whose mass is greater In Physics, the Casimir effect and the Casimir-Polder force are physical forces arising from a quantized field. The Van der Waals equation is an Equation of state that can be derived from a special form of the potential between a pair of molecules (hard-sphere repulsion

## Energy and life

Main article: Bioenergetics

Any living organism relies on an external source of energy—radiation from the Sun in the case of green plants; chemical energy in some form in the case of animals—to be able to grow and reproduce. Bioenergetics is the subject of a field of Biochemistry that concerns Energy flow through living systems The daily 1500–2000 Calories (6–8 MJ) recommended for a human adult are taken as a combination of oxygen and food molecules, the latter mostly carbohydrates and fats, of which glucose (C6H12O6) and stearin (C57H110O6) are convenient examples. This article is about the unit of energy For its use in Nutrition and Food labelling regulations, see the article on Food energy. Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Stearin (ˈstiəɹɪn or /ˈstɪɹɪn/ is a glyceryl Ester of Stearic acid, derived from animal Fats created as a byproduct of processing Beef The food molecules are oxidised to carbon dioxide and water in the mitochondria

C6H12O6 + 6O2 → 6CO2 + 6H2O
C57H110O6 + 81. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Water ( H2[[oxygen O]] H OH) is the most abundant Molecule on Earth 's surface composing of about 70% of the Earth's surface as In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. 5O2 → 57CO2 + 55H2O

and some of the energy is used to convert ADP into ATP

ADP + HPO42− → ATP + H2O

The rest of the chemical energy in the carbohydrate or fat is converted into heat: the ATP is used as a sort of "energy currency", and some of the chemical energy it contains when split and reacted with water, is used for other metabolism (at each stage of a metabolic pathway, some chemical energy is converted into heat). Adenosine diphosphate, abbreviated ADP, is a Nucleotide. It is an Ester of Pyrophosphoric acid with the Nucleoside Adenosine Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. In Biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell. Only a tiny fraction of the original chemical energy is used for work:[14]

gain in kinetic energy of a sprinter during a 100 m race: 4 kJ
gain in gravitational potential energy of a 150 kg weight lifted through 2 metres: 3kJ
Daily food intake of a normal adult: 6–8 MJ

It would appear that living organisms are remarkably inefficient (in the physical sense) in their use of the energy they receive (chemical energy or radiation), and it is true that most real machines manage higher efficiencies. A machine is any device that uses Energy to perform some activity However, in growing organisms the energy that is converted to heat serves a vital purpose, as it allows the organism tissue to be highly ordered with regard to the molecules it is built from. The second law of thermodynamics states that energy (and matter) tends to become more evenly spread out across the universe: to concentrate energy (or matter) in one specific place, it is necessary to spread out a greater amount of energy (as heat) across the remainder of the universe ("the surroundings"). The second law of Thermodynamics is an expression of the universal law of increasing Entropy, stating that the entropy of an Isolated system which [15] Simpler organisms can achieve higher energy efficiencies than more complex ones, but the complex organisms can occupy ecological niches that are not available to their simpler brethren. In Ecology, a niche (pronounced nich nēsh or nish A shorthand definition of niche is how an organism makes a living The conversion of a portion of the chemical energy to heat at each step in a metabolic pathway is the physical reason behind the pyramid of biomass observed in ecology: to take just the first step in the food chain, of the estimated 124. Ecology (from Greek grc οἶκος oikos, "house(hold" and grc -λογία -logia) is the scientific study of Food chains, also called food networks and/or trophic networks, describe the feeding relationships between species within an Ecosystem. 7 Pg/a of carbon that is fixed by photosynthesis, 64. Carbon fixation is a process found in Autotrophs (organisms that produce their own food usually driven by Photosynthesis, whereby Carbon dioxide is changed Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. 3 Pg/a (52%) are used for the metabolism of green plants,[16] i. e. reconverted into carbon dioxide and heat.

## Notes and references

1. ^ Harper, Douglas. In Chemistry, activation energy, also called midnight energy, is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined The American Museum of Science and Energy (AMSE is a Science museum in Oak Ridge Tennessee, designed to teach both children and adults about Energy In Thermodynamics and molecular chemistry, the enthalpy (denoted as H, h, or rarely as χ) is a quotient or description of Energy conservation is the practice of decreasing the quantity of energy used In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy In Physics, interaction energy is the contribution to the total Energy that is caused by an Interaction between the objects being considered In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by  U, or sometimes  This is a list of books about energy issues: See also List of books about nuclear issues List of books by Amory Lovins This is a list of energy topics which identifies articles and categories that relate to energy in general This list compares various energies in Joules (J organized by Order of magnitude. In Physics, power (symbol P) is the rate at which work is performed or energy is transmitted or the amount of energy required or expended for Renewable energy is Energy generated from Natural resources mdashsuch as Sunlight, Wind, Rain, tides and geothermal In Thermodynamics, the term thermodynamic free energy refers to the amount of work that can be extracted from a System, and is helpful in Engineering In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " Because Energy is defined via work, the SI unit for energy is the same as the unit of work &ndash the Joule (J named in honour of James Vacuum energy is an underlying background Energy that exists in Space even when devoid of Matter (known as Free space) Energy. Online Etymology Dictionary. Retrieved on May 1, 2007.
2. ^ Lofts, G; O'Keeffe D; et al (2004). "11 — Mechanical Interactions", Jacaranda Physics 1, 2, Milton, Queensland, Australia: John Willey & Sons Australia Ltd. , 286. ISBN 0 7016 3777 3.
3. ^ 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.
4. ^ a b c Feynman, Richard (1964). The Feynman Lectures on Physics; Volume 1. U. S. A: Addison Wesley. ISBN 0-201-02115-3.
5. ^ Earth's Energy Budget
6. ^ Berkeley Physics Course Volume 1. Charles Kittel, Walter D Knight and Malvin A Ruderman
7. ^ a b c The Laws of Thermodynamics including careful definitions of energy, free energy, et cetera.
8. ^ a b Misner, Thorne, Wheeler (1973). Gravitation. San Francisco: W. H. Freeman. ISBN 0716703440.
9. ^ The Hamiltonian MIT OpenCourseWare website 18. 013A Chapter 16. 3 Accessed February 2007
10. ^ Cengel, Yungus, A. ; Boles, Michael (2002). Thermodynamics - An Engineering Approach, 4th ed. . McGraw-Hill, 17-18. ISBN 0-07-238332-1.
11. ^ Kittel and Kroemer (1980). Thermal Physics. New York: W. H. Freeman. ISBN 0-7167-1088-9.
12. ^ a b c International Council of Science Committee on Data for Science and Technology (2007). The International Council for Science (ICSU formerly called the International Council of Scientific Unions, was founded in 1931 as an international non-governmental organization CODATA ( Committee on Data for Science and Technology) was established in 1966 as an interdisciplinary committee of the International Council of Science (ICSU formerly 2006 CODATA recommended values.
13. ^ Time Invariance
14. ^ These examples are solely for illustration, as it is not the energy available for work which limits the performance of the athlete but the power output of the sprinter and the force of the weightlifter. In Physics, power (symbol P) is the rate at which work is performed or energy is transmitted or the amount of energy required or expended for In Physics, a force is whatever can cause an object with Mass to Accelerate. A worker stacking shelves in a supermarket does more work (in the physical sense) than either of the athletes, but does it more slowly.
15. ^ Crystals are another example of highly ordered systems that exist in nature: in this case too, the order is associated with the transfer of a large amount of heat (known as the lattice energy) to the surroundings. In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating The lattice energy of an ionic solid is a measure of the strength of bonds in that ionic compound
16. ^ Ito, Akihito; Oikawa, Takehisa (2004). "Global Mapping of Terrestrial Primary Productivity and Light-Use Efficiency with a Process-Based Model." in Shiyomi, M. et al. (Eds. ) Global Environmental Change in the Ocean and on Land. pp.  343–58.