In physics, energy () is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems. Since work is defined as a force acting through a distance (a length of space), energy is always equivalent to the ability to exert pulls or pushes against the basic forces of nature, along a path of a certain length.

The total energy contained in an object is identified with its mass, and energy (like mass), cannot be created or destroyed. When matter (ordinary material particles) is changed into energy (such as energy of motion, or into radiation), the mass of the system does not change through the transformation process. However, there may be mechanistic limits as to how much of the matter in an object may be changed into other types of energy and thus into work, on other systems. Energy, like mass, is a scalar physical quantity. In the International System of Units (SI), energy is measured in joules, but in many fields other units, such as kilowatt-hours and kilocalories, are customary. All of these units translate to units of work, which is always defined in terms of forces and the distances that the forces act through.

A system can transfer energy to another system by simply transferring matter to it (since matter is equivalent to energy, in accordance with its mass). However, when energy is transferred by means other than matter-transfer, the transfer produces changes in the second system, as a result of work done on it. This work manifests itself as the effect of force(s) applied through distances within the target system. For example, a system can emit energy to another by transferring (radiating) electromagnetic energy, but this creates forces upon the particles that absorb the radiation. Similarly, a system may transfer energy to another by physically impacting it, but that case the energy of motion in an object, called kinetic energy, results in forces acting over distances (new energy) to appear in another object that is struck. Transfer of thermal energy by heat occurs by both of these mechanisms: heat can be transferred by electromagnetic radiation, or by physical contact in which direct particle-particle impacts transfer kinetic energy.

Energy may be stored in systems without being present as matter, or as kinetic or electromagnetic energy. Stored energy is created whenever a particle has been moved through a field it interacts with (requiring a force to do so), but the energy to accomplish this is stored as a new position of the particles in the field—a configuration that must be "held" or fixed by a different type of force (otherwise, the new configuration would resolve itself by the field pushing or pulling the particle back toward its previous position). This type of energy "stored" by force-fields and particles that have been forced into a new physical configuration in the field by doing work on them by another system, is referred to as potential energy. A simple example of potential energy is the work needed to lift an object in a gravity field, up to a support. Each of the basic forces of nature is associated with a different type of potential energy, and all types of potential energy (like all other types of energy) appears as system mass, whenever present. For example, a compressed spring will be slightly more massive than before it was compressed. Likewise, whenever energy is transferred between systems by any mechanism, an associated mass is transferred with it.

Any form of energy may be transformed into another form. For example, all types of potential energy are converted into kinetic energy when the objects are given freedom to move to different position (as for example, when an object falls off a support). When energy is in a form other than thermal energy, it may be transformed with good or even perfect efficiency, to any other type of energy, including electricity or production of new particles of matter. With thermal energy, however, there are often limits to the efficiency of the conversion to other forms of energy, as described by the second law of thermodynamics.

In all such energy transformation processes, the total energy remains the same, and a transfer of energy from one system to another, results in a loss to compensate for any gain. This principle, the conservation of energy, was first postulated in the early 19th century, and applies to any isolated system. 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.

Although the total energy of a system does not change with time, its value may depend on the frame of reference. For example, a seated passenger in a moving airplane has zero kinetic energy relative to the airplane, but non-zero kinetic energy (and higher total energy) relative to the Earth.

History

The word ''energy'' derives from the Greek '''', which possibly appears for the first time in the work of Aristotle in the 4th century BC.

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

William Thomson (Lord Kelvin) amalgamated all of these laws into the laws of thermodynamics, which aided in the rapid development of explanations of chemical processes by Rudolf Clausius, Josiah Willard Gibbs, and Walther Nernst. It also led to a mathematical formulation of the concept of entropy by Clausius and to the introduction of laws of radiant energy by Jožef Stefan.

During a 1961 lecture 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:

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. That is, energy is conserved because the laws of physics do not distinguish between different instants of time (see Noether's theorem).

Energy in various contexts

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, as 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.

The concept of energy is widespread in all sciences. In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structure, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light; thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The ''speed'' of a chemical reaction (at given temperature ''T'') is related to the activation energy ''E'', by the Boltzmann's population factor e^{−''E''/''kT''}that is the probability of molecule to have energy greater than or equal to ''E'' at the given temperature ''T''. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation.The activation energy necessary for a chemical reaction can be in the form of thermal energy. In biology, energy is an attribute of all biological systems from the biosphere to the smallest living organism. Within an organism it is responsible for growth and development of a biological cell or an organelle of a biological organism. Energy is thus often said to be stored by cells in the structures of molecules of substances such as carbohydrates (including sugars), lipids, and proteins, which release energy when reacted with oxygen in respiration. In human terms, the human equivalent (H-e) (Human energy conversion) indicates, for a given amount of energy expenditure, the relative quantity of energy needed for human metabolism, assuming an average human energy expenditure of 12,500kJ per day and a basal metabolic rate of 80 watts. For example, if our bodies run (on average) at 80 watts, then a light bulb running at 100 watts is running at 1.25 human equivalents (100 ÷ 80) i.e. 1.25 H-e. For a difficult task of only a few seconds' duration, a person can put out thousands of watts, many times the 746 watts in one official horsepower. For tasks lasting a few minutes, a fit human can generate perhaps 1,000 watts. For an activity that must be sustained for an hour, output drops to around 300; for an activity kept up all day, 150 watts is about the maximum. The human equivalent assists understanding of energy flows in physical and biological systems by expressing energy units in human terms: it provides a “feel” for the use of a given amount of energy In geology, continental drift, mountain ranges, volcanoes, and earthquakes are phenomena that can be explained in terms of energy transformations in the Earth's interior., 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 atmosphere of the planet Earth.

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. 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 that 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.

Familiar examples of such processes include nuclear decay, in which energy is released that was originally "stored" in heavy isotopes (such as uranium and thorium), by nucleosynthesis, a process ultimately using 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. This energy is triggered and released in nuclear fission bombs. In a slower process, radioactive decay of these atoms in the core of the Earth releases heat. This thermal energy drives plate tectonics and may lift mountains, via orogenesis. This slow lifting represents a kind of gravitational potential energy storage of the thermal energy, which may be later released to active kinetic energy in landslides, after a triggering event. Earthquakes also release stored elastic potential energy in rocks, a store that has been produced ultimately from the same radioactive heat sources. Thus, according to present understanding, familiar events such as landslides and earthquakes release energy that has been stored as potential energy in the Earth's gravitational field or elastic strain (mechanical potential energy) in rocks. Prior to this, they represent release of energy that has been stored in heavy atoms since the collapse of long-destroyed supernova stars created these atoms.

In another similar chain of transformations beginning at the dawn of the universe, nuclear fusion of hydrogen in the Sun also releases another store of potential energy which was created at the time of the Big Bang. 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 that can be released by fusion. 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 turbines or 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 captured by plants as ''chemical potential energy'' in photosynthesis, when carbon dioxide and water (two low-energy compounds) are converted into the high-energy compounds carbohydrates, lipids, and proteins. Plants also release oxygen during photosynthesis, which is utilized by living organisms as an electron acceptor, to release the energy of carbohydrates, lipids, and proteins. Release of the energy stored during photosynthesis as heat or light may be triggered suddenly by a spark, in a forest fire, or it may be made available more slowly for animal or human metabolism, when these molecules are ingested, and catabolism is triggered by enzyme action.

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.

Distinction between energy and power

Although in everyday usage the terms ''energy'' and ''power'' are essentially synonyms, scientists and engineers distinguish between them. In its technical sense, power is not at all the same as energy, but is the rate at which energy is converted (or, equivalently, at which work is performed). Thus a hydroelectric plant, by allowing the water above the dam to pass through turbines, converts the water's potential energy into kinetic energy and ultimately into electric energy, whereas the amount of electric energy that is generated per unit of time is the electric power generated.

Conservation of energy

Energy is subject to the law of conservation of energy. According to this law, energy can neither be created (produced) nor destroyed by itself. It can only be transformed.

Most kinds of energy (with gravitational energy being a notable exception) are 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. Conservation of energy is the mathematical consequence of translational symmetry of time (that is, the indistinguishability of time intervals taken at different time) - see Noether's theorem.

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.

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. Put differently, yesterday, today, and tomorrow are physically indistinguishable.

This is because energy is the quantity which is canonical conjugate to time. 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. On any time scales, the uncertainty in the energy is by

: $\backslash Delta\; E\; \backslash Delta\; t\; \backslash ge\; \backslash frac\; \{\; \backslash hbar\; \}\; \{2\; \}$

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 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). 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.

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.

The total energy of a system can be subdivided and classified in various ways. 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). 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, while energy is always conserved (in the sense that the total energy does not change despite energy transformations), energy can be converted into a form, e.g., thermal energy, that cannot be utilized to perform work. When one talks about "conserving energy by driving less," one talks about conserving fossil fuels and preventing useful energy from being lost as heat. This usage of "conserve" differs from that of the law of conservation of energy.

In classical physics energy is considered a scalar quantity, the canonical conjugate to time. In special relativity energy is also a scalar (although not a Lorentz scalar but a time component of the energy-momentum 4-vector). In other words, energy is invariant with respect to rotations of space, but not invariant with respect to rotations of space-time (= boosts).

Energy transfer

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

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if there are no other energy-transfer processes involved. Here $E$ 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:

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where $Q$ represents the heat flow into the system.

There are other ways in which an open system can gain or lose energy. 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).

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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 ($E\_p$) to kinetic energy ($E\_k$) and then back to potential energy constantly. This is referred to as conservation of energy. In this closed system, energy cannot be created or destroyed; therefore, the initial energy and the final energy will be equal to each other. This can be demonstrated by the following:

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

Energy and the laws of motion

In classical mechanics, energy is a conceptually and mathematically useful property, as it is a conserved quantity. Several formulations of mechanics have been developed using energy as a core concept.

The Hamiltonian

The total energy of a system is sometimes called the Hamiltonian, after William Rowan Hamilton. 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.

The Lagrangian

Another energy-related concept is called the Lagrangian, after Joseph Louis Lagrange. This is even more fundamental than the Hamiltonian, and can be used to derive the equations of motion. It was invented in the context of classical mechanics, but is generally useful in modern physics. The Lagrangian is defined as the kinetic energy ''minus'' the potential energy.

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

Energy and thermodynamics

Internal energy

Internal energy is the sum of all microscopic forms of energy of a system. It is the energy needed to create the system. It is related to the potential energy, e.g., molecular structure, crystal structure, and other geometric aspects, as well as the motion of the particles, in form of kinetic energy. Thermodynamics is chiefly concerned with changes in internal energy and not its absolute value, which is impossible to determine with thermodynamics alone.

The laws of thermodynamics

According to the second law of thermodynamics, work can be totally converted into heat, but not vice versa. This is a mathematical consequence of statistical mechanics. The first law of thermodynamics simply asserts that energy is conserved, and that heat is included as a form of energy transfer. A commonly used corollary of the first law is that for a "system" subject only to pressure forces and heat transfer (e.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 as the following equation:

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

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 d''S'' 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, d''V'', is negative when work is done on the system). Although this equation is the standard textbook 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. 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 the following equation:

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

which is unsatisfactory 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. 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.

This principle is vitally important to understanding the behavior of a quantity closely related to energy, called entropy. Entropy is a measure of evenness of a distribution of energy between parts of a system. When an isolated system is given more degrees of freedom (i.e., given new available energy states that are the same as existing states), then total energy spreads over all available degrees equally without distinction between "new" and "old" degrees. This mathematical result is called the second law of thermodynamics.

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. 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 whether the electric energy is 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. This model is useful, for example, when the electromagnetic Lagrangian is of primary interest and is interpreted in terms of potential and kinetic energy.

2. On the other hand, in the key equation $m^2\; c^4\; =\; E^2\; -\; p^2\; c^2$, the contribution $mc^2$ 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 $0.5\; p^2/m$ at speeds much smaller than ''c'', as can be proved by writing $E\; =\; mc^2$ √$(1\; +\; p^2\; m^\{-2\}c^\{-2\})$ 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, a form of energy, is force times distance.

: $W\; =\; \backslash int\_C\; \backslash mathbf\{F\}\; \backslash cdot\; \backslash mathrm\{d\}\; \backslash mathbf\{s\}$

This says that the work ($W$) is equal to the line integral of the force F along a path ''C''; for details see the mechanical work article.

Work and thus energy is frame dependent. 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. The Schrödinger equation equates the energy operator to the full energy of a particle or a system. In results 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. 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. In the solution of the Schrödinger equation for any oscillator (vibrator) and for electromagnetic waves in a vacuum, the resulting energy states are related to the frequency by the Planck equation $E\; =\; h\backslash nu$ (where $h$ is the Planck's constant and $\backslash nu$ the frequency). In the case of electromagnetic wave these energy states are called quanta of light or photons.

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 an unexpected by-product of these calculations to be an energy term which does not vanish at zero speed. He called it rest mass energy - energy which every mass must possess even when being at rest. The amount of energy is directly proportional to the mass of body:

:$E\; =\; m\; c^2$, 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. 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. In this system the matter (electrons and positrons) is destroyed and changed to non-matter energy (the photons). However, the total system mass and energy do not change during this interaction.

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.

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

Energy and life

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. 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. The food molecules are oxidised to carbon dioxide and water in the mitochondria ::C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O ::C₅₇H₁₁₀O₆ + 81.5O₂ → 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). Only a tiny fraction of the original chemical energy is used for work: :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. 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"). 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. 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 124.7 Pg/a of carbon that is fixed by photosynthesis, 64.3 Pg/a (52%) are used for the metabolism of green plants, i.e. reconverted into carbon dioxide and heat.

Measurement

Because energy is defined as the ability to do work on objects, there is no absolute measure of energy. Only the transition of a system from one state into another can be defined and thus energy is measured in relative terms. The choice of a baseline or zero point is often arbitrary and can be made in whatever way is most convenient for a problem.

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.

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.

Units

Throughout the history of science, energy has been expressed in several different units such as ergs and calories. At present, the accepted unit of measurement for energy is the SI unit of energy, the joule. In addition to the joule, other units of energy include the kilowatt hour (kWh) and the British thermal unit (Btu). These are both larger units of energy. One kWh is equivalent to exactly 3.6 million joules, and one Btu is equivalent to about 1055 joules.

Energy density

Energy density is a term used for the amount of useful energy stored in a given system or region of space per unit volume.

For fuels, the energy per unit volume is sometimes a useful parameter. In a few applications, comparing, for example, the effectiveness of hydrogen fuel to gasoline it turns out that hydrogen has a higher specific energy than does gasoline, but, even in liquid form, a much lower energy ''density''.

Forms of energy

In the context of physical sciences, several forms of energy have been defined. These include: {| |

Thermal energy, thermal energy in transit is called heat

Chemical energy

Electrical energy

Radiant energy, the energy of electromagnetic radiation

Nuclear energy

|

Magnetic energy

Elastic energy

Sound energy

Mechanical energy

Luminous energy

| |}

These forms of energy may be divided into two main groups; kinetic energy and potential energy. Other familiar types of energy are a varying mix of both potential and kinetic energy.

Energy may be transformed between these forms, some with 100% energy conversion efficiency and others with less. Items that transform between these forms are called transducers.

The above list of the known possible forms of energy is not necessarily complete. Whenever physical scientists discover that a certain phenomenon appears to violate the law of energy conservation, new forms may be added, as is the case with dark energy, a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe.

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. 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. It has been attempted to categorize ''all'' forms of energy as either kinetic or potential: this is not incorrect, but neither is it clear that it is a real simplification, as Feynman points out:

Transformations of energy

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. Similarly, in the case of a chemical explosion, chemical potential energy is transformed to kinetic energy and thermal energy in a very short time. Yet another example is that of a pendulum. At its highest points the kinetic energy is zero and the gravitational potential energy is at maximum. At its lowest point the kinetic energy is at maximum and is equal to the decrease of potential energy. 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.

Energy gives rise to weight when it is trapped in a system with zero momentum, where it can be weighed. It is also equivalent to mass, and this mass is always associated with it. Mass is also equivalent to a certain amount of energy, and likewise always appears associated with it, as described in mass-energy equivalence. The formula ''E'' = ''mc''², derived by Albert Einstein (1905) quantifies the relationship between rest-mass and rest-energy within the concept of special relativity. In different theoretical frameworks, similar formulas were derived by J. J. Thomson (1881), Henri Poincaré (1900), Friedrich Hasenöhrl (1904) and others (see Mass-energy equivalence#History for further information).

Matter may be destroyed and converted to energy (and vice versa), but mass cannot ever be destroyed; rather, mass remains a constant for both the matter and the energy, during any process when they are converted into each other. However, since $c^2$ is extremely large relative to ordinary human scales, the conversion of ordinary amount of matter (for example, 1 kg) to other forms of energy (such as heat, light, and other radiation) can liberate tremendous amounts of energy (~$9x10^\{16\}$ joules = 21 megatons of TNT), 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 (loss of mass) from most systems is difficult to measure by weight, unless the energy loss is very large. Examples of energy transformation into matter (i.e., kinetic energy into particles with rest mass) are found in high-energy nuclear physics.

Transformation of energy into useful work is a core topic of thermodynamics. In nature, transformations of energy can be fundamentally classed into two kinds: those that are thermodynamically reversible, and those that are thermodynamically 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. 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, quantum states of lower energy, present as possible excitations 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. In this heat death the energy of the universe does not change, but the fraction of energy which is available to do produce work through a heat engine, or be transformed to other usable forms of energy (through the use of generators attached to heat engines), grows less and less.

See also

Index of energy articles

Outline of energy

Notes and references

Further reading

External links

Category:Fundamental physics concepts Category:Greek loanwords Category:Introductory physics Category:Physical quantities Category:State functions

af:Energie am:አቅም ar:طاقة an:Enerchía arc:ܐܢܪܓܝ ast:Enerxía (física) az:Enerji bn:শক্তি zh-min-nan:Lêng-liōng be:Энергія be-x-old:Энэргія bs:Energija br:Energiezh bg:Енергия ca:Energia cs:Energie cy:Egni (gwyddonol) da:Energi de:Energie et:Energia el:Ενέργεια es:Energía eo:Energio eu:Energia fa:انرژی hif:Shakti fr:Énergie gv:Bree gl:Enerxía ko:에너지 hy:Էներգիա hi:ऊर्जा hr:Energija io:Energio id:Energi ia:Energia is:Orka it:Energia he:אנרגיה kn:ಶಕ್ತಿ ka:ენერგია kk:Энергия sw:Nishati ht:Enèji ku:Wize la:Energia lv:Enerģija lb:Energie lt:Energija li:Energie ln:Molungé lmo:Energia hu:Energia mk:Енергија mg:Angôvo ml:ഊർജ്ജം mr:ऊर्जा arz:طاقه mzn:انرژی ms:Tenaga mwl:Einergie mn:Энерги my:စွမ်းအင် nl:Energie new:ऊर्जा ja:エネルギー no:Energi nn:Energi nov:Energie oc:Energia pnb:جان nds:Energie pl:Energia (fizyka) pt:Energia kaa:Energiya ro:Energie qu:Micha rue:Енерґія ru:Энергия sah:Энергия sq:Energjia scn:Enirgìa si:ශක්තිය (‍භෞතිකවේදය) simple:Energy sk:Energia sl:Energija so:Awood ckb:وزە sr:Енергија sh:Energija su:Énergi fi:Energia sv:Energi tl:Enerhiya ta:ஆற்றல் tt:Энергия th:พลังงาน tg:Энергия tr:Enerji uk:Енергія ur:توانائی ug:ئېنېرگىيە vec:Energia vi:Năng lượng war:Enerhiya wo:Kàttan yi:ענערגיע zh-yue:能量 bat-smg:Energėjė zh:能量 sn:Simba

Coordinates	28°36′36″N77°13′48″N
name	Keri Hilson
background	solo_singer
birth name	Keri Lynn Hilson
birth date	December 05, 1982
birth place	Decatur, Georgia,
genre	R&B;, pop, hip hop
occupation	Singer–songwriter
years relevant	2008
label	Zone 4, Mosley Music, Interscope
associated acts	The Clutch, Timbaland, Polow da Don, Kanye West, Chris Brown, Akon
website	}}

Keri Lynn Hilson (born December 5, 1982) is an American R&B; recording artist, and songwriter. Born and raised in Decatur, Georgia, Hilson made herself a name as a songwriter, penning tracks for several artists in the mid-2000s as part of the five-person production/songwriting team known as The Clutch. In 2006, she signed a recording contract with Timbaland's label, Mosley Music. Critics have credited Hilson for her amazing songwriting skills and her vocal performances.

Hilson released her debut studio album, ''In a Perfect World...'' in March 2009, which peaked within the top five of the ''Billboard'' 200 albums chart and featured the hit singles "Knock You Down" and "Turnin Me On". The album reached number one on the US Top R&B;/Hip-Hop Albums chart and was eventually certified gold. Hilson earned two Grammy Award nominations for the album including Best Rap/Sung Collaboration for "Knock You Down", which features Kanye West and Ne-Yo. A reissue of the album, included previously unreleased songs such as "I Like". The song became Hilson's first number one hit in Germany and certified platinum there. Unfortunately for Hilson, however, saw no success in receiving a Grammy. As a prominent guest vocalist in both the contemporary R&B; and hip hop genres, Hilson has been featured on over a dozen singles by other artists, including the number-one hit single "The Way I Are" with Timbaland.

Life and career

1982–2000: Early life and career beginnings

Hilson was born in Decatur, Georgia. She attended Tucker High School in Tucker, Georgia. At the age of 12, Hilson began piano and singing lessons. During her mid to late teens, Hilson began her career as a songwriter and background vocalist, working under producer Anthony Dent. After trying and failing with two girl groups, Pretty Toni and D'Sign, Hilson enrolled at Oxford College of Emory University in Oxford, Georgia while still pursing a music career. Hilson cites Janet Jackson as a major influence in her career.

2001–2007: Songwriting with The Clutch and solo ventures

When the pennies from performances at Magic City in Atlanta Georgia were not making ends meet, Hilson began writing music for other artists in 2001 as part of the five-person production/songwriting team known as The Clutch. She also made a name for herself as a song arranger and sung background vocals on many of the songs she had written for artists such as Usher, Ludacris, Kelly Rowland, and Ciara. Hilson's songwriting was responsible for numerous hit singles, including Mary J. Blige's "Take Me as I Am", Omarion's "Ice Box", the Pussycat Dolls' "Wait a Minute", Britney Spears' "Gimme More", Nas's "Hero",and also Ciara's "Like a Boy".

She remained mostly behind the scenes until 2004, when she was featured on the single "Hey Now (Mean Muggin)" by the rapper Xzibit. Hilson made her performing debut at the 2004 MTV Europe Music Awards in which she performed the song live with Xzibit. In 2006 she signed as an artist to Timbaland's record label, Mosley Music. In 2007 Hilson made several appearances on Timbaland's solo effort ''Shock Value'', including the singles "Scream" and "The Way I Are" which reached number three on the US ''Billboard'' Hot 100. Furthermore, she was featured on the track "Lost Girls" on Zone 4-labelmate Rich Boy's debut album and its second single "Good Things". Hilson was credited as a writer and backing vocalist on Britney Spears's album ''Blackout''. She made several appearances in music videos for singles such as "Love in This Club" by Usher and also in the music video for Ne-Yo's single, "Miss Independent".

2008–2009: The Year of Relevance: ''In a Perfect World...''

After several pushbacks, Hilson's debut album ''In a Perfect World...'' was released in March 2009. According to the singer, the title of the album is her way of "saying nothing in the world is perfect and no person in it is, either. None of us are exempt from certain hardships and heartbreaks and we all have something about our lives that we'd change if only we could - be it body image, financial status, love life... It was really important for me to write songs that women can relate to from real situations. I didn’t want to do an album that painted myself as perfect because no matter how things look, no one is. I called it that with the ellipses - dot dot dot - because it's an incomplete statement. I wanted to talk about how nobody's exempted from the realities of life and all those things." It was executively produced by Timbaland and Polow da Don. ''In a Perfect World...'' debuted at number four on the US ''Billboard'' 200 and at number one on the US Top R&B;/Hip-Hop Albums chart with first week sales of approximately 94,000 copies, and earned generally favorable reviews from music critics who noted it a "seductive debut CD full of slick, radio-friendly cuts." and was eventually certified gold by the RIAA.

"Energy" was released as the album's lead single on May 20, 2008. It reached a peak of number seventy-eight on the US ''Billboard'' Hot 100, number twenty-one on the Hot R&B;/Hip-Hop Songs chart, and achieved minor success in the UK. The song became a success in New Zealand, where it reached a peak of number two and gained a gold accreditation there. In October 2008 Hilson collaborated with fellow singer Chris Brown on a song titled "Superhuman", which reached the top twenty in Ireland and New Zealand. "Return the Favor" which features Timbaland was released as the album's second single. It peaked within the top twenty in the UK, Ireland, and Belgium. "Turnin Me On" which featured Lil Wayne became Hilson's first top twenty hit as a solo artist on the ''Billboard'' Hot 100, where it reached number fifteen on the chart. The song reached number two on the Hot R&B;/Hip-Hop Songs chart, becoming Hilson's first top five hit on the chart.

"Knock You Down", a collaboration with Kanye West and Ne-Yo, was released as the album's fourth single. The song has proven to be Hilson's most successful worldwide single to date. It peaked at number three on the ''Billboard'' Hot 100 for three non-consecutive weeks and topped the Hot R&B;/Hip-Hop Songs chart. It additionally appeared the in top ten of five other countries and certified platinum in New Zealand and gold in Australia. The song received a nomination for Best Rap/Sung Collaboration at the 52nd Grammy Awards. A reissue of the album, included previously unreleased songs such as "I Like". The song was used for the German film ''Zweiohrküken'' and became Hilson's first number one hit in Germany which certified platinum there. Meanwhile Hilson continued appearing on single releases by several artists throughout 2009 including Plies' single "Medicine", Fabolous' "Everything, Everyday, Everywhere," Nas' "Hero" and Sean Paul's "Hold My Hand".

2010–present: ''No Boys Allowed''

In January 2010 Hilson guest featured on Akon's charity single "Oh Africa". She was also part of the extended A-list of musical artists during the recording session of "We Are the World 25 for Haiti." Hilson also made guest features on other singles including "Million Dollar Girl" by Trina and T.I's "Got Your Back". In April 2010 it was revealed she was the new face of Avon, replacing singer Jennifer Hudson.

Her second studio album, ''No Boys Allowed,'' was released on December 21, 2010. Hilson explained that "''No Boys Allowed'' is a deeply personal project designed to bring women to their feet. The provocative title, is not what you may think. It's not about excluding men. It's more about women understanding that there comes a time in your life when you want a man. A real man. A grown up. Not a boy. And that's not a bad thing. I write from a female perspective, but I'm also telling men what women are really thinking and feeling about them." The album debuted at number 11 on the ''Billboard'' 200 with 102,000  copies sold. Though it sold 8,000  copies more than her debut album, ''In a Perfect World...'', it failed to match that album's debut chart position of number four.

"Breaking Point," produced by Timbaland was released as the album's lead single in the United States on September 7, 2010. It reached a peak of number forty-four on the US Hot R&B;/Hip-Hop Songs chart. "Pretty Girl Rock" was released as the second single on October 12, 2010. It has reached a current peak of number ten on the US Hot R&B;/Hip-Hop Songs chart and peaked at number twenty four on the US ''Billboard'' Hot 100. The music video for the song has received critical acclaim and praise for its homage to musical icons of the past such as Josephine Baker, Dorothy Dandridge, The Andrews Sisters, Diana Ross, Donna Summer, Janet Jackson and TLC. Hilson appears as each singer in a well-known scene from the era depicted. As of early 2011 she is preparing for a spring tour and is opening for TLC's 20th Anniversary celebration concert and beginning work on a third album featuring TLC, Blaque and more girl groups.

"One Night Stand " featuring Chris Brown, is the album's third single. In February 2011, Hilson told ''Rap-Up'' magazine that she was considering choosing "One Night Stand" as the next single from ''No Boys Allowed'', after an outpouring of fan support. She said, "My fans are really liking "One Night Stand" with Chris Brown ... I have a lot of favorites, but the fans are wanting "One Night Stand." It’s going to be my urban single. Not going to be, but if we go with it, we'll go with that." The song has appeared on the US Hot R&B;/Hip-Hop Songs chart at number sixty-eight. It has been announced that "Lose Control" featuring Nelly, will serve as the album's next single.

Discography

''In a Perfect World...'' (2009)

''No Boys Allowed'' (2010)

Awards and nominations

! Year	! Type	! Nominated work	! Award	! Result
2007		"The Way I Are" with Timbaland and D.O.E.	Monster Single of the Year
			Favorite Female R&B;/Soul Artist
Breakthrough Artist
	Best New Artist
Best Female R&B; Artist
	Viewer's Choice
Best Collaboration
rowspan="2"	''In a Perfect World...''	Best Album
	Best Female Act
	Best International Act
Best R&B;/Soul Act
	Best New Artist
"Turnin Me On"	Song of the Year
	Best Collaboration
Record of the Year
		Best Rap/Sung Collaboration
	Best New Artist
NAACP Image Awards	Outstanding New Artist
		Best Female R&B; Artist
"Pretty Girl Rock"	Video of the Year

References

External links

Category:1982 births Category:African American singers Category:American dance musicians Category:American female singers Category:American rhythm and blues singers Category:Emory University alumni Category:Interscope Records artists Category:Living people Category:Musicians from Georgia (U.S. state) Category:People from Atlanta, Georgia

ar:كيري هيلسون cs:Keri Hilson da:Keri Hilson de:Keri Hilson es:Keri Hilson eo:Keri Hilson fa:کری هیلسون fr:Keri Hilson ko:케리 힐슨 hsb:Keri Hilson hr:Keri Hilson it:Keri Hilson he:קרי הילסון sw:Keri Hilson lv:Keri Hilsone mk:Кери Хилсон nl:Keri Hilson ja:ケリー・ヒルソン no:Keri Hilson pl:Keri Hilson pt:Keri Hilson ksh:Keri Lynn Hilson ro:Keri Hilson ru:Хилсон, Кери simple:Keri Hilson sr:Keri Hilson fi:Keri Hilson sv:Keri Hilson th:เคอรี ฮิลสัน tr:Keri Hilson zh:凯莉·希尔森

Coordinates	28°36′36″N77°13′48″N
name	Alexandra Stan
alt	Alexandra Stan
nickname	Stanny, ALE(a-lee)
years active	2009–present
background	solo_singer
birth name	Alexandra Stan
birth date	June 10, 1989
origin	Constanța, Romania
label	Maan Music, Media Pro Music, Ultra Records
instrument	Vocals
genre	House, pop, dance, R&B;
occupation	Singer-songwriter, musician, entertainer, model, dancer
associated acts	Carlprit
website	}}

Alexandra Stan (born June 10, 1989 in Constanța, Romania) is a Romanian singer-songwriter.

Biography

Alexandra Stan was born on June 10, 1989 in Constanța, Romania. She studied at the "Traian" Lyceum in Constanța and as of 2011 she is enrolled in her second year as a student at the Faculty of Management Andrei Saguna. In the past she has participated in various music-related contests with a notable appearance at the Mamaia Festival section interpretation.

In 2009, she released her debut promotional single, "Lollipop (Param Pam Pam)" The following year her first official single was released, "Mr. Saxobeat", which reached number one on the Romanian Airplay Chart in November 2010. The song also reached the top spot on the Romanian Top 100. From then on it slowly began to climb the charts in Europe, becoming an international hit, peaking within the top 10 in over 20 countries. "Lollipop (Param Pam Pam)" served as her second single in US and Canada, released in May 2011. Her second single worldwide is "Get Back (ASAP)", which is currently climbing the charts and peaked at number four Romania.

Discography

Albums

! Album Title	! Album details
''Saxobeats''		* Release: September 9, 2011	* Label: Columbia Records	* Format: [[Compact Disc

Singles

{|class="wikitable plainrowheaders" style="text-align:center;" border="1" ! scope="col" rowspan="2"| Year ! scope="col" rowspan="2"| Song ! scope="col" colspan="11"| Peak chart positions ! scope="col" rowspan="2"| Certifications ! scope="col" rowspan="2"| Album |- ! scope="col" style="width:3em;font-size:85%;"|ROM !style="width:3em;font-size:85%"|AUT !style="width:3em;font-size:85%"|CAN ! scope="col" style="width:3em;font-size:85%;"|FRA ! scope="col" style="width:3em;font-size:85%;"|GER ! scope="col" style="width:3em;font-size:85%;"|IRE ! scope="col" style="width:3em;font-size:90%;" | ITA ! scope="col" style="width:3em;font-size:85%;"|SPA ! scope="col" style="width:3em;font-size:90%;" | SWI ! scope="col" style="width:3em;font-size:85%;"|UK ! scope="col" style="width:3em;font-size:85%;"|US |- | 2009 ! scope="row"| "Lollipop (Param Pam Pam)" | — || — || — || — || — || — || — || — || — || — || — | |rowspan="5"| ''Saxobeats'' |- | rowspan="1"|2010 ! scope="row"| "Mr. Saxobeat" | 1 || 1 || 25 || 6 || 1 || 6 || 1 || 3 || 1 || 3 || 38 | ITA: 2× Platinum SWE: Platinum DEN: Gold SPA: Gold |- | rowspan="3"|2011 ! scope="row"| "Get Back (ASAP)" | 4 || — || — || 18 || — || — || 37 || — || — || — || — | |- ! scope="row"| "One Million" (featuring Carlprit) | — || — || — || — || — || — || — || — || — || — || — | |}

Music videos

Year	Song	Album
	"Lollipop (Param Pam Pam)"
	"Mr. Saxobeat"
	"Get Back (ASAP)"

References

External links

Alexandra Stan at Music-covers

Fans Website

German Fan Website

Category:Articles created via the Article Wizard Category:1989 births Category:Living people Category:People from Constanţa Category:Romanian dance musicians Category:Romanian female singers

cs:Alexandra Stan da:Alexandra Stan de:Alexandra Stan es:Alexandra Stan fr:Alexandra Stan hy:Ալեքսանդրա Ստան he:אלכסנדרה סטן hr:Alexandra Stan it:Alexandra Stan hu:Alexandra Stan nl:Alexandra Stan ja:アレクサンドラ・スタン no:Alexandra Stan pl:Alexandra Stan pt:Alexandra Stan ro:Alexandra Stan ru:Стан, Александра fi:Alexandra Stan sv:Alexandra Stan tr:Alexandra Stan uk:Александра Стан

Coordinates	28°36′36″N77°13′48″N
sport	baseball
current title	Head coach
current team	Oregon State
birth date	1959
birth place	McMinnville, Oregon
overall record	611-384-5
championships	NCAA champions 2006, 2007
awards	Baseball America Coach of the Year 2006Pac-10 Coach of the Year 2005, 2006
player	*
player years	1980
player teams	University of Portland
player positions	outfielder
coach years	1988-19941995-present
coach teams	George Fox UniversityOregon State }}

Pat Casey (born 1959 in McMinnville, Oregon) is the head coach for the Oregon State Beavers baseball team. He is best known for winning the 2006 College World Series for the Beavers' first-ever baseball National Championship. Despite losing all but two starters on the team and being selected last in the NCAA College World Series bracket, he led the Beavers to a repeat championship in the 2007 College World Series, the first unranked team in history to accomplish this feat.

Playing career

A three-sport athlete at Newberg High School, Casey attended the University of Portland where he played baseball as well as basketball. In baseball, he was named to the All-Pac-10 Conference Northern Division first team in 1979 and 1980, and was drafted in the 10th round by the San Diego Padres in the 1980 Major League Baseball Draft. He played seven seasons in the minor leagues, including the Beaumont Golden Gators, the Calgary Cannons and the Portland Beavers.

Coaching career

After his playing career ended, Casey became head baseball coach at George Fox University, where he earned his undergraduate degree in 1990, also playing basketball for the school while coaching baseball. In seven seasons at George Fox, his baseball team compiled a 171-113-1 record.

In 1995, he was named head coach at Oregon State, where through the 2009 season, he had compiled at 505-314-4 record. He has guided the Beavers to three straight 45+ win seasons, including back-to-back Pac-10 championships, three trips to the College World Series, and two national championships. He is the only coach in NCAA history to lead a team to the National Championship after playing in six elimination games. After winning the 2006 national championship, the program received its first ever number 1 ranking by all four college baseball polls. He was named the Pac-10 Coach of the year in both 2005 and 2006, and was named Baseball America Coach of the Year in 2006.

Personal

Casey and his wife Susan have three sons and one daughter.

References

Category:1959 births Category:Living people Category:Oregon State Beavers baseball coaches Category:People from McMinnville, Oregon Category:Portland Pilots men's basketball players Category:George Fox University faculty Category:George Fox University alumni

: ''For other uses of the title The Grid, see Grid (disambiguation).''

Coordinates	28°36′36″N77°13′48″N
name	The Grid
background	group_or_band
origin	England
genre	HouseTechnoAmbient house
years active	1988–19962003–present
label	East West, Virgin, Deconstruction, Some Bizzare
associated acts	Soft Cell, Chris Braide
current members	Richard NorrisDavid Ball
notable instruments	}}

The Grid are an English electronic dance group, consisting of Richard Norris and David Ball (formerly of Soft Cell), The lead single from this album, "Swamp Thing", featuring elaborate banjo lines played by Roger Dinsdale. "Swamp Thing" proved to be a commercial success in the UK, Europe and Australia, reaching #3 in the UK || align="center"| 14 || Deconstruction Records |- | 1995 || ''Music for Dancing'' || align="center"| 67 || Deconstruction Records |- | 2008 || ''Doppelgänger'' || align="center"| - || Some Bizzare Records |}

Singles

"Floatation (song) "Swamp Thing (The Grid song)

Year !! Single !! UK Singles Chart
1989	"On the Grid" (promo only)	-
1989	Intergalactica" (promo only) >
1990	Floatation" |	60
1990	A Beat Called Love" >
1990
1991
1992
1992
1993
1993
1993	Swamp Thing" |	3
1994
1994
1995
2006
2007

References

External links

Grid Central - An Unofficial Page for The Grid

Death of Roger Dinsdale.

[ The Grid on allmusic.com]

The Grid MySpace page

Category:English dance music groups Category:English electronic music groups Category:English house music groups Category:British techno music groups Category:Remixers Category:Electronic music duos

de:The Grid pl:The Grid ru:The Grid sv:The Grid