In physics

Physics

Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

, energy (from the Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

  – energeia, "activity, operation", from – energos, "active, working") is a scalar

Scalar (physics)

In physics, a scalar is a simple physical quantity that is not changed by coordinate system rotations or translations , or by Lorentz transformations or space-time translations . This is in contrast to a vector...

 physical quantity

Physical quantity

A physical quantity is a physical property of a phenomenon, body, or substance, that can be quantified by measurement.-Definition of a physical quantity:Formally, the International Vocabulary of Metrology, 3rd edition defines quantity as:...

 that describes the amount of work

Work (thermodynamics)

In thermodynamics, work performed by a system is the energy transferred to another system that is measured by the external generalized mechanical constraints on the system. As such, thermodynamic work is a generalization of the concept of mechanical work in mechanics. Thermodynamic work encompasses...

 that can be performed by a force

Force

In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

. Energy is an attribute of objects and systems that is subject to a conservation law

Conservation law

In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves....

. Several different forms of energy exist to explain all known natural phenomena. These forms include (but are not limited to) kinetic

Kinetic energy

The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

, potential

Potential energy

In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...

, thermal

Thermal energy

Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

, gravitational

Gravitational energy

Gravitational energy is the energy associated with the gravitational field. This phrase is found frequently in scientific writings about quasars and other active galaxies.-Newtonian mechanics:...

, sound, light

Light

Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

, elastic

Elastic energy

Elastic energy is the potential mechanical energy stored in the configuration of a material or physical system as work is performed to distort its volume or shape....

, and electromagnetic

Electromagnetic radiation

Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...

 energy. The forms of energy are often named after a related force.

Any form of energy can be transformed into another form, but the total energy always remains the same. This principle, the conservation of energy

Conservation of energy

The nineteenth century law of conservation of energy is a law of physics. It states that the total amount of energy in an isolated system remains constant over time. The total energy is said to be conserved over time...

, was first postulated in the early 19th century, and applies to any isolated system

Isolated system

In the natural sciences an isolated system, as contrasted with an open system, is a physical system without any external exchange. If it has any surroundings, it does not interact with them. It obeys in particular the first of the conservation laws: its total energy - mass stays constant...

. According to Noether's theorem

Noether's theorem

Noether's theorem states that any differentiable symmetry of the action of a physical system has a corresponding conservation law. The theorem was proved by German mathematician Emmy Noether in 1915 and published in 1918...

, 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

Frame of reference

A frame of reference in physics, may refer to a coordinate system or set of axes within which to measure the position, orientation, and other properties of objects in it, or it may refer to an observational reference frame tied to the state of motion of an observer.It may also refer to both an...

. 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

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

.

The following outline is provided as an overview of and topical guide to energy:

Essence of energy

Main article: Energy

Energy

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...

• Mass–energy equivalence (E=mc²)

Forms of energy

• Potential energy
  Potential energy
  In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...
  
  
  • Gravitational potential energy
  • Elastic potential energy
  • Nuclear potential energy
• Kinetic energy
  Kinetic energy
  The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
  
  
• Thermal energy
  Thermal energy
  Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....
  
  
• Electric energy
  • Magnetic energy
    Magnetic energy
    Magnetic energy and electric energy are related by Maxwell's equations. The potential energy of a magnet of magnetic moment m in a magnetic field B is defined as the work of magnetic force on re-alignment of the vector of the magnetic dipole moment, and is equal:while the energy stored in an...
    
    
  • Electromagnetic fields
• Chemical energy
  Chemical energy
  Chemical energy is the potential of a chemical substance to undergo a transformation through a chemical reaction or, to transform other chemical substances...
  
  
• Nuclear binding energy
  Nuclear binding energy
  Nuclear binding energy is the energy required to split a nucleus of an atom into its component parts. The component parts are neutrons and protons, which are collectively called nucleons...
  
  
• Surface energy
  Surface energy
  Surface energy quantifies the disruption of intermolecular bonds that occur when a surface is created. In the physics of solids, surfaces must be intrinsically less energetically favorable than the bulk of a material, otherwise there would be a driving force for surfaces to be created, removing...
  
  

Energy units (terms)

See Units of energy

Units of energy

Because energy is defined via work, the SI unit for energy is the same as the unit of work – the joule , named in honour of James Prescott Joule and his experiments on the mechanical equivalent of heat...

• Barrel of oil equivalent
  Barrel of oil equivalent
  The barrel of oil equivalent is a unit of energy based on the approximate energy released by burning one barrel of crude oil. The US Internal Revenue Service defines it as equal to 5.8 × 106 BTU...
  
  
• British thermal unit
  British thermal unit
  The British thermal unit is a traditional unit of energy equal to about 1055 joules. It is approximately the amount of energy needed to heat of water, which is exactly one tenth of a UK gallon or about 0.1198 US gallons, from 39°F to 40°F...
  
  
• Calorie
  Calorie
  The calorie is a pre-SI metric unit of energy. It was first defined by Nicolas Clément in 1824 as a unit of heat, entering French and English dictionaries between 1841 and 1867. In most fields its use is archaic, having been replaced by the SI unit of energy, the joule...
  
  
• Current solar income
  Current solar income
  The current solar income of the Earth, or an ecozone or ecoregion or any area, is the amount of solar energy that falls on it as sunlight. This is thought important in some branches of green economics, as the ultimate measure of renewable energy....
  
   – the amount of solar energy that falls as sunlight
• Electronvolt
  Electronvolt
  In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
  
   – (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt
• Planck energy, 1.22 × 10¹⁹ GeV (billion electron volts)
• Enthalpy
  Enthalpy
  Enthalpy is a measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.Enthalpy is a...
  
  
• Erg
  Erg
  An erg is the unit of energy and mechanical work in the centimetre-gram-second system of units, symbol "erg". Its name is derived from the Greek ergon, meaning "work"....
  
   – (symbol "erg") unit of energy and mechanical work in the centimetre-gram-second (CGS) system of units
• EU energy label
• Fill factor
  Fill factor
  Fill factor may refer to:*Fill factor , the ratio of maximum obtainable power to the product of the open-circuit voltage and short-circuit current*In vision science, the ratio of view areas to the object visible areas....
  
   – defined as the ratio of the maximum power (Vmp x Jmp) divided by the short-circuit current (Isc) and open-circuit voltage (Voc) in light current density – voltage (J-V) characteristics of solar cells.
• Foot-pound – (symbol ft·lbf or ft·lbf) is an Imperial and U.S. customary unit of mechanical work, or energy, although in scientific fields one commonly uses the equivalent metric unit of the joule (J). There are approximately 1.356 J/(ft·lbf).
• Gigaton – Metric Unit of mass, equal to 1,000,000,000 (1 billion) metric tons, 1,000,000,000,000 (1 trillion) kilograms
  • Any of various units of energy, such as gigatons of TNT equivalent, gigatons of coal equivalent, gigatons petroleum equivalent.
• Gray (unit)
  Gray (unit)
  The gray is the SI unit of absorbed radiation dose of ionizing radiation , and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter ....
  
   – (symbol: Gy), is the SI unit of energy for the absorbed dose of radiation. One gray is the absorption of one joule of radiation energy by one kilogram of matter. One gray equals 100 rad, an older unit.
• Heat
  Heat
  In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
  
  
• Joule
  Joule
  The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
  
   – (symbol J, also called newton meter, watt second, or coulomb volt)
• Kilowatt-hour – (symbol: kW·h) corresponds to one kilowatt (kW) of power being used over a period of one hour.
• Mass-energy equivalence
  Mass-energy equivalence
  In physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. In this concept, mass is a property of all energy, and energy is a property of all mass, and the two properties are connected by a constant...
  
   – where mass has an energy equivalence, and energy has a mass equivalence
• Megawatt
• Net energy gain
  Net energy gain
  Net Energy Gain is a concept used in energy economics that refers to the difference between the energy expended to harvest an energy source and the amount of energy gained from that harvest. The net energy gain, which can be expressed in joules, differs from the net financial gain that may result...
  
  
• Power factor
  Power factor
  The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load over the apparent power in the circuit, and is a dimensionless number between 0 and 1 . Real power is the capacity of the circuit for performing work in a particular time...
  
   – of an AC electric power system is defined as the ratio of the real power to the apparent power.
• Therm
  Therm
  The therm is a non-SI unit of heat energy equal to 100,000 British thermal units . It is approximately the energy equivalent of burning 100 cubic feet of natural gas....
  
   – (symbol thm) a non-SI unit of heat energy. It is approximately the heat equivalent of burning 100 cubic feet of natural gas. In the US gas industry it is defined as exactly 100,000 BTU_59°F or 105.4804 megajoules.
• Ton of oil equivalent
  Ton of oil equivalent
  The tonne of oil equivalent is a unit of energy: the amount of energy released by burning one tonne of crude oil, approximately 42 GJ .The toe is sometimes used for large...
  
  
• TPE – Ton Petroleum Equivalent, 45.217 GJ, see ton of oil equivalent
  Ton of oil equivalent
  The tonne of oil equivalent is a unit of energy: the amount of energy released by burning one tonne of crude oil, approximately 42 GJ .The toe is sometimes used for large...
  
  

Energy infrastructure

See especially :Category:Electric power and :Category:Fuels for a large number of conventional energy related topics.

• Energy storage
  Energy storage
  Energy storage is accomplished by devices or physical media that store some form of energy to perform some useful operation at a later time. A device that stores energy is sometimes called an accumulator....
  
  
• Electricity generation
  Electricity generation
  Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...
  
  
• Electricity retailing
  Electricity retailing
  Electricity retailing is the final process in the delivery of electricity from generation to the consumer. The other main processes are transmission and distribution.- Beginnings :...
  
  
• Grid energy storage
  Grid energy storage
  Grid energy storage refers to the methods used to store electricity on a large scale within an electrical power grid. Electrical energy is stored during times when production exceeds consumption and the stores are used at times when consumption exceeds production...
  
  
• Liquified natural gas
• Microwave power transmission
• Power plant
• Power supply
  Power supply
  A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
  
  
• Power transmission
  Power transmission
  Power transmission is the movement of energy from its place of generation to a location where it is applied to performing useful work.Power is defined formally as units of energy per unit time...
  
  
• Underground power station
  Underground power station
  An underground power station is a type of hydroelectric power station constructed by excavating the major components from rock, rather than the more common surface-based construction methods....
  
  

Energy applications

• Biofuel
  Biofuel
  Biofuel is a type of fuel whose energy is derived from biological carbon fixation. Biofuels include fuels derived from biomass conversion, as well as solid biomass, liquid fuels and various biogases...
  
  
• Distributed generation
  Distributed generation
  Distributed generation, also called on-site generation, dispersed generation, embedded generation, decentralized generation, decentralized energy or distributed energy, generates electricity from many small energy sources....
  
  
• Electric vehicle
  Electric vehicle
  An electric vehicle , also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion...
  
  
• Hybrid vehicle
  Hybrid vehicle
  A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles , which combine an internal combustion engine and one or more electric motors.-Power:...
  
  
• Hydrogen vehicle
  Hydrogen vehicle
  A hydrogen vehicle is a vehicle that uses hydrogen as its onboard fuel for motive power. Hydrogen vehicles include hydrogen fueled space rockets, as well as automobiles and other transportation vehicles...
  
  
• Passive solar building design
  Passive solar building design
  In passive solar building design, windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer...
  
  
• Steam engine
  Steam engine
  A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...
  
  

Physics of energy

• Energy
  Energy
  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...
  
  
• Activation energy
  Activation energy
  In chemistry, activation energy is a term introduced in 1889 by the Swedish scientist Svante Arrhenius that is defined as the energy that must be overcome in order for a chemical reaction to occur. Activation energy may also be defined as the minimum energy required to start a chemical reaction...
  
   explains the differences in the speeds of various chemical reactions
• Alternative Energy Index
• Bioenergetics
  Bioenergetics
  Bioenergetics is the subject of a field of biochemistry that concerns energy flow through living systems. This is an active area of biological research that includes the study of thousands of different cellular processes such as cellular respiration and the many other metabolic processes that can...
  
  
• Chemical energetics
• Energy in physical cosmology
• Energy in Earth science that is responsible for the macroscopic transformations on the planet Earth
• Electricity
  Electricity
  Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
  
  
• Exergy
  Exergy
  In thermodynamics, the exergy of a system is the maximum useful work possible during a process that brings the system into equilibrium with a heat reservoir. When the surroundings are the reservoir, exergy is the potential of a system to cause a change as it achieves equilibrium with its...
  
  
• Green energy
• Orders of magnitude (energy)
  Orders of magnitude (energy)
  This list compares various energies in joules , organized by order of magnitude.-SI multiples:-See also:*Conversion of units of energy*Energies per unit mass*List of energy topics*Metric system*TNT equivalent*Scientific notation-Notes:...
  
   – list describes various energy levels between 10⁻³¹ joule
  Joule
  The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
  
  s and 10⁷⁰ joules
• Thermodynamics
  Thermodynamics
  Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
  
  
• Perpetual motion
  Perpetual motion
  Perpetual motion describes hypothetical machines that operate or produce useful work indefinitely and, more generally, hypothetical machines that produce more work or energy than they consume, whether they might operate indefinitely or not....
  
  
• Heat
  Heat
  In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
  
  
• History of energy
  History of energy
  The word energy derives from Greek ἐνέργεια , which appears for the first time in the work Nicomachean Ethics of Aristotle in the 4th century BCE....
  
  
• Energy forms, the forms in which energy can be defined
• Energy transformation, relating to energy's changes from one form to another.
• Energy (signal processing), the inner product of a signal in the time domain
• Energy density spectrum
  Spectral density
  In statistical signal processing and physics, the spectral density, power spectral density , or energy spectral density , is a positive real function of a frequency variable associated with a stationary stochastic process, or a deterministic function of time, which has dimensions of power per hertz...
  
  , relating to the distribution of signal energy over frequencies.
• Potential energy
  Potential energy
  In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...
  
  , the form of energy that is due to position of an object
• Kinetic energy
  Kinetic energy
  The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
  
  , the form of energy as a consequence of the motion of an object or its constituents
• Mechanical energy
  Mechanical energy
  In physics, mechanical energy is the sum of potential energy and kinetic energy present in the components of a mechanical system. It is the energy associated with the motion and position of an object. The law of conservation of energy states that in an isolated system that is only subject to...
  
  , the potential energy and kinetic energy present in the components of a mechanical system.
• Binding energy
  Binding energy
  Binding energy is the mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower potential energy than its constituent parts; this is what keeps the system together—often this means that energy is released upon the creation of a bound state...
  
  , a concept explaining how the constituents of atoms or molecules are bound together
• Bond energy
  Bond energy
  In chemistry, bond energy is the measure of bond strength in a chemical bond. It is the heat required to break one Mole of molecules into their individual atoms. For example, the carbon-hydrogen bond energy in methane E is the enthalpy change involved with breaking up one molecule of methane into...
  
  , a measure of the strength of a chemical bond
• Nuclear energy, energy that is the consequence of decomposition or combination of atomic nuclei
• Osmotic power,or salinity gradient power and blue energy
  Blue energy
  Osmotic power or salinity gradient power is the energy available from the difference in the salt concentration between seawater and river water. Two practical methods for this are reverse electrodialysis and pressure-retarded osmosis.....
  
  , is the energy available from the difference in the salt concentration between seawater and river water
• Gibbs free energy
  Gibbs free energy
  In thermodynamics, the Gibbs free energy is a thermodynamic potential that measures the "useful" or process-initiating work obtainable from a thermodynamic system at a constant temperature and pressure...
  
  , a related concept in chemical thermodynamics that incorporates entropy considerations too
• Helmholtz free energy
  Helmholtz free energy
  In thermodynamics, the Helmholtz free energy is a thermodynamic potential that measures the “useful” work obtainable from a closed thermodynamic system at a constant temperature and volume...
  
  , a thermodynamic potential that measures the "useful" work obtainable from a closed thermodynamic system at a constant temperature, useful for studying explosive chemical reactions
• Elastic energy
  Elastic energy
  Elastic energy is the potential mechanical energy stored in the configuration of a material or physical system as work is performed to distort its volume or shape....
  
  , which causes or is released by the elastic distortion of a solid or a fluid
• Ionization energy
  Ionization energy
  The ionization energy of a chemical species, i.e. an atom or molecule, is the energy required to remove an electron from the species to a practically infinite distance. Large atoms or molecules have a low ionization energy, while small molecules tend to have higher ionization energies.The property...
  
   – the (IE) of an atom is the energy required to strip it of an electron.
• Interaction energy
  Interaction energy
  In physics, interaction energy is the contribution to the total energy that is caused by an interaction between the objects being considered.The interaction energy usually depends on the relative position of the objects...
  
  , the contribution to the total energy that is a result of interaction between the objects being considered
• Internal energy
  Internal energy
  In thermodynamics, the internal energy is the total energy contained by a thermodynamic system. It is the energy needed to create the system, but excludes the energy to displace the system's surroundings, any energy associated with a move as a whole, or due to external force fields. Internal...
  
   – (abbreviated E or U) the total kinetic energy due to the motion of molecules (translational, rotational, vibrational) and the total potential energy associated with the vibrational and electric energy of atoms within molecules.
• Negative energy
  Negative energy
  Negative energy is a concept used in energy , energy , and speculative fiction for a contrast with regular or positive energy.Negative energy may be used in:- Physics :* Particle physics** Exotic matter** Antiparticle...
  
  
• Energy conversion
  Energy conversion
  Transforming energy is when the energy changes into another form.In physics, the term energy describes the capacity to produce changes within a system, without regard to limitations in transformation imposed by entropy...
  
   – process of converting energy from one form to another
• Dark energy
  Dark energy
  In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...
  
  , used to explain some cosmological phenomena
• Energy quality
  Energy quality
  Energy quality is the contrast between different forms of energy, the different trophic levels in ecological systems and the propensity of energy to convert from one form to another. The concept refers to the empirical experience of the characteristics, or qualia, of different energy forms as they...
  
  , empirical experience of the characteristics of different energy forms as they flow and transform
• Energy density
  Energy density
  Energy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
  
  , amount of energy stored in a given system or region of space per unit volume, or per unit mass
• Energy flow
  Energy transfer
  Energy transfer is the transfer of energy from one body to another.There are a few main ways that energy transfer occurs:*Radiant energy *Heat conduction*Convection*Electrical power transmission*Mechanical work...
  
  , flow of energy in an ecosystem through food chains
• Energetics
  Energetics
  Energetics is the study of energy under transformation. Because energy flows at all scales, from the quantum level to the biosphere and cosmos, energetics is a very broad discipline, encompassing for example thermodynamics, chemistry, biological energetics, biochemistry and ecological energetics...
  
  , the scientific study of energy flows under transformation
• Stress-energy tensor
  Stress-energy tensor
  The stress–energy tensor is a tensor quantity in physics that describes the density and flux of energy and momentum in spacetime, generalizing the stress tensor of Newtonian physics. It is an attribute of matter, radiation, and non-gravitational force fields...
  
  , the density and flux of energy and momentum in space-time; the source of the gravitational field in general relativity
• Food energy
  Food energy
  Food energy is the amount of energy obtained from food that is available through cellular respiration.Food energy is expressed in food calories or kilojoules...
  
  , energy in food that is available
• Primary energy
  Primary energy
  Primary energy is an energy form found in nature that has not been subjected to any conversion or transformation process. It is energy contained in raw fuels, and other forms of energy received as input to a system...
  
   – Energy contained in raw fuels and any other forms of energy received by a system as input to the system.
• Radiant energy
  Radiant energy
  Radiant energy is the energy of electromagnetic waves. The quantity of radiant energy may be calculated by integrating radiant flux with respect to time and, like all forms of energy, its SI unit is the joule. The term is used particularly when radiation is emitted by a source into the...
  
   – energy that is transported by waves
• Rotational energy
  Rotational energy
  The rotational energy or angular kinetic energy is the kinetic energy due to the rotation of an object and is part of its total kinetic energy...
  
   – An object's rotational energy or angular kinetic energy is part of its total kinetic energy
• Solar radiation – radiant energy emitted by the sun, particularly electromagnetic energy
• Tidal power
  Tidal power
  Tidal power, also called tidal energy, is a form of hydropower that converts the energy of tides into useful forms of power - mainly electricity....
  
  , also called tidal energy, is a form of hydropower that converts the energy of tides into useful forms of power - mainly electricity, dynamic tidal power
  Dynamic tidal power
  Dynamic tidal power or DTP is a new and untested method of tidal power generation. It would involve creating large dam-like structure extending from the coast straight to the ocean, with a perpendicular barrier at the far end, forming a large 'T' shape....
  
  , tidal lagoons, Tidal barrage
  Tidal barrage
  A tidal barrage is a dam-like structure used to capture the energy from masses of water moving in and out of a bay or river due to tidal forces....
  
  
• Wave power
  Wave power
  Wave power is the transport of energy by ocean surface waves, and the capture of that energy to do useful work — for example, electricity generation, water desalination, or the pumping of water...
  
   is the transport of energy
  Energy
  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...
  
   by ocean surface waves, and the capture of that energy to do useful work — for example, electricity generation
  Electricity generation
  Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...
  
  , water desalination, or the pumping of water (into reservoirs). Machinery able to exploit wave power is generally known as a wave energy converter (WEC).
• Wind energy
  Wind energy
  Wind energy is the kinetic energy of air in motion; see also wind power.Total wind energy flowing through an imaginary area A during the time t is:E = ½ m v2 = ½ v 2...
  
   is the kinetic energy of air in motion;Wind power
  Wind power
  Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....
  
   is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships

Allegorical, esoteric, and pseudoscientific

• Energy (esotericism), invoked by spiritualists for alternative modes of healing the human body as well as a spirit that permeates all of reality.
• Orgone
  Orgone
  Orgone energy is a theory originally proposed in the 1930s by Wilhelm Reich. Reich, originally part of Sigmund Freud's Vienna circle, extrapolated the Freudian concept of libido first as a biophysical and later as a universal life force...
  
  , Wilhelm Reich
  Wilhelm Reich
  Wilhelm Reich was an Austrian-American psychiatrist and psychoanalyst, known as one of the most radical figures in the history of psychiatry...
  
   discovered this energy and tried to use it to cure various physical ailments and control the weather.
• Qi
  Qi
  In traditional Chinese culture, qì is an active principle forming part of any living thing. Qi is frequently translated as life energy, lifeforce, or energy flow. Qi is the central underlying principle in traditional Chinese medicine and martial arts...
  
   a concept from Oriental medicine
  Traditional Chinese medicine
  Traditional Chinese Medicine refers to a broad range of medicine practices sharing common theoretical concepts which have been developed in China and are based on a tradition of more than 2,000 years, including various forms of herbal medicine, acupuncture, massage , exercise , and dietary therapy...
  
   that is sometimes translated as "energy" in the West.
• Vitalism
  Vitalism
  Vitalism, as defined by the Merriam-Webster dictionary, is#a doctrine that the functions of a living organism are due to a vital principle distinct from biochemical reactions...
  
  , often referred to as "energy"
• Cold fusion
  Cold fusion
  Cold fusion, also called low-energy nuclear reaction , refers to the hypothesis that nuclear fusion might explain the results of a group of experiments conducted at ordinary temperatures . Both the experimental results and the hypothesis are disputed...
  
  , nuclear fusion at conditions close to room temperature.
• Bubble fusion
  Bubble fusion
  Bubble fusion, also known as sonofusion, is the non-technical name for a nuclear fusion reaction hypothesized to occur during a high-pressure version of sonoluminescence, an extreme form of acoustic cavitation...
  
  , also known as Sonofusion, energy from acoustic collapse of bubbles.
• Water-fuelled car, powering a car using water as fuel.

Energy industry

• World energy resources and consumption
  World energy resources and consumption
  ]World energy consumption in 2010: over 5% growthEnergy markets have combined crisis recovery and strong industry dynamism. Energy consumption in the G20 soared by more than 5% in 2010, after the slight decrease of 2009. This strong increase is the result of two converging trends...
  
  
• List of energy resources, substances like fuels, petroleum products and electricity
• Energy crisis
  Energy crisis
  An energy crisis is any great bottleneck in the supply of energy resources to an economy. In popular literature though, it often refers to one of the energy sources used at a certain time and place, particularly those that supply national electricity grids or serve as fuel for vehicles...
  
  , the need to conserve energy resources
• Energy development
  Energy development
  Energy development is the effort to provide sufficient primary energy sources and secondary energy forms for supply, cost, impact on air pollution and water pollution, mitigation of climate change with renewable energy....
  
  , development of energy resources
• Embodied energy
  Embodied energy
  Embodied energy is defined as the sum of energy inputs that was used in the work to make any product, from the point of extraction and refining materials, bringing it to market, and disposal / re-purposing of it...
  
  , the sum total of energy expended to deliver a good or service as it travels through the economy
• Energy conservation
  Energy conservation
  Energy conservation refers to efforts made to reduce energy consumption. Energy conservation can be achieved through increased efficient energy use, in conjunction with decreased energy consumption and/or reduced consumption from conventional energy sources...
  
  , tips for conserving energy resources
• Energy economics
  Energy economics
  Energy economics is a broad scientific subject area which includes topics related to supply and use of energy in societies. Due to diversity of issues and methods applied and shared with a number of academic disciplines, energy economics does not present itself as a self contained academic...
  
  , as the foundation of other relationships
• Energy policy
  Energy policy
  Energy policy is the manner in which a given entity has decided to address issues of energy development including energy production, distribution and consumption...
  
  , government policies and plans for energy supply
• Energy storage
  Energy storage
  Energy storage is accomplished by devices or physical media that store some form of energy to perform some useful operation at a later time. A device that stores energy is sometimes called an accumulator....
  
  , methods commonly used to store energy resources for later use
• Biosphere
  Biosphere
  The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed and self-regulating system...
  
  
• Ecological energetics
  Ecological energetics
  Ecological energetics is the quantitative study of the flow of energy through ecological systems. It aims to uncover the principles which describe the propensity of such energy flows through the trophic, or 'energy availing' levels of ecological networks. In systems ecology the principles of...
  
  
• Ecology
  Ecology
  Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
  
  
• Energy balance
  Energy economics
  Energy economics is a broad scientific subject area which includes topics related to supply and use of energy in societies. Due to diversity of issues and methods applied and shared with a number of academic disciplines, energy economics does not present itself as a self contained academic...
  
  
• Earth Day
  Earth Day
  Earth Day is a day that is intended to inspire awareness and appreciation for the Earth's natural environment. The name and concept of Earth Day was allegedly pioneered by John McConnell in 1969 at a UNESCO Conference in San Francisco. The first Proclamation of Earth Day was by San Francisco, the...
  
  
• U4energy, a pan European school challenge on energy education launched in September 2010. U4energy is an initiative funded under the IEE programme to improve energy consumption in schools and their local communities.
• Energy development
  Energy development
  Energy development is the effort to provide sufficient primary energy sources and secondary energy forms for supply, cost, impact on air pollution and water pollution, mitigation of climate change with renewable energy....
  
   – Ongoing effort to provide abundant and accessible energy, through knowledge, skills and constructions.
• Energy speculation
• Free energy suppression
  Free energy suppression
  Free energy suppression is a conspiracy theory claim that explains why advanced technology that would reshape current energy paradigms is being suppressed by certain special interest groups...
  
  
• Future energy development – Provides a general overview of future energy development.
• History of perpetual motion machines
  History of perpetual motion machines
  The history of perpetual motion machines dates back to the Middle Ages. For millennia, it was not clear whether perpetual motion devices were possible or not, but the development of modern theories of thermodynamics has indicated that they are impossible. Despite this, many attempts have been made...
  
  
• Hubbert peak theory
  Hubbert peak theory
  The Hubbert peak theory posits that for any given geographical area, from an individual oil-producing region to the planet as a whole, the rate of petroleum production tends to follow a bell-shaped curve...
  
  , also known as peak oil
  Peak oil
  Peak oil is the point in time when the maximum rate of global petroleum extraction is reached, after which the rate of production enters terminal decline. This concept is based on the observed production rates of individual oil wells, projected reserves and the combined production rate of a field...
  
  – the theory that world oil production will peak (or has peaked), and will then rapidly decline, with a corresponding rapid increase in prices.
• Primary production
  Primary production
  400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...
  
  
• Power harvesting
• Renewable energy development

Energy Issues

• 2000 Watt society
• Environmental concerns with electricity generation
  Environmental concerns with electricity generation
  The environmental impact of electricity generation is significant because modern society uses large amounts of electrical power. This power is normally generated at power plants that convert some other kind of energy into electrical power...
  
  
• Fuel poverty
  Fuel poverty
  A household is said to be in fuel poverty when they cannot afford to keep adequately warm at reasonable cost, given it's income. The term is mainly used in the UK, Ireland and New Zealand, although the concept also applies everywhere in the world where poverty may be present.As the term fuel...
  
  
• Greasestock
  Greasestock
  Greasestock is an American event held yearly in Yorktown Heights, New York. It is one of the largest alternative fuel, renewable energy, and low-energy green vehicle exhibitions in the United States. Exhibitors showcase a variety of alternative energy vehicles, as well as exhibits with a...
  
  , American showcase of vehicles and technologies powered by alternative energy
• Low-carbon economy
  Low-carbon economy
  A Low-Carbon Economy or Low-Fossil-Fuel Economy is an economy that has a minimal output of greenhouse gas emissions into the environment biosphere, but specifically refers to the greenhouse gas carbon dioxide...
  
  
• Peak Oil
  Peak oil
  Peak oil is the point in time when the maximum rate of global petroleum extraction is reached, after which the rate of production enters terminal decline. This concept is based on the observed production rates of individual oil wells, projected reserves and the combined production rate of a field...
  
  
• Soft energy path
  Soft energy path
  In 1976 energy policy analyst Amory Lovins coined the term soft energy path to describe an alternative future where energy efficiency and appropriate renewable energy sources steadily replace a centralized energy system based on fossil and nuclear fuels....
  
   – an energy use and development strategy delineated and promoted by some energy experts and activists
• Strategic Petroleum Reserve
  Strategic Petroleum Reserve
  The Strategic Petroleum Reserve is an emergency fuel storage of oil maintained by the United States Department of Energy.- United States :The US SPR is the largest emergency supply in the world with the current capacity to hold up to ....
  
  

International

• Energy policy
  Energy policy
  Energy policy is the manner in which a given entity has decided to address issues of energy development including energy production, distribution and consumption...
  
   – Introductory article
• Energy and Environmental Security Initiative (EESI)
  Energy and Environmental Security Initiative (EESI)
  Established in 2003, the Energy and Environmental Security Initiative is an interdisciplinary Research & Policy Institute located at the University of Colorado Law School. The fundamental mission of EESI is to serve as an interdisciplinary research and policy center concerning the development and...
  
  

Regional and national

• Energy law
  Energy law
  Energy laws govern the use and taxation of energy, both renewable and non-renewable. These laws are the primary authorities related to energy...
  
   – overview of many energy laws from various countries and states
  United States
  The United States of America is a federal constitutional republic comprising fifty states and a federal district...
  
  
  • New York energy law
    New York energy law
    New York energy law is the statutory and common law of the state of New York concerning the policy, conservation, and utilities involved in energy, along with its regulation and taxation.-Energy Law :...
    
    
• Energy Tax Act
  Energy Tax Act
  The Energy Tax Act is a law passed by the U.S. Congress as part of the National Energy Act. The objective of this law was shift from oil and gas supply toward energy conservation; thus, to promote fuel efficiency and renewable energy through taxes and tax credits.- Tax credits for conservation...
  
  – United States energy-related legislation. See also : :Category:United States federal energy legislation
• United Kingdom:
  • Energy policy of the United Kingdom
    Energy policy of the United Kingdom
    The current energy policy of the United Kingdom is set out in the Energy White Paper of May 2007 and Low Carbon Transition Plan of July 2009, building on previous work including the 2003 Energy White Paper and the Energy Review Report in 2006...
    
    
  • Energy use and conservation in the United Kingdom
    Energy use and conservation in the United Kingdom
    Energy use in the United Kingdom stood at 3,894.6 kilogrammes of oil equivalent per capita in 2005 compared to a world average of 1,778.0. In 2008, total energy consumed was 9.85 exajoules - around 2% of the estimated 474 EJ worldwide total...
    
    

Energy companies

• Exxon Mobil
• Enercon GmbH – Company based in Germany that operates in the wind turbine industry. One of the biggest producers in the world.
• Saudi Aramco
  Saudi Aramco
  Saudi Aramco , officially the Saudi Arabian Oil Company, is the national oil company of Saudi Arabia.Saudi Aramco is the world's largest and most valuable privately-held company, with estimates of its value in 2011 to be $7 trillion USD.Saudi Aramco has both the largest proven crude oil reserves,...
  
  
• Sasol
  Sasol
  Sasol Ltd. is a South African company involved in mining, energy, chemicals and synfuels. In particular, they produce petrol and diesel profitably from coal and natural gas using Fischer-Tropsch process...
  
  
• United States Enrichment Corporation
  United States Enrichment Corporation
  The United States Enrichment Corporation, a subsidiary of USEC Inc. , is a corporation that contracts with the United States Department of Energy to produce enriched uranium for use in nuclear power plants.-History:...
  
   – contracts with the United States Department of Energy to produce enriched uranium.

Industry associations

• OPEC
  OPEC
  OPEC is an intergovernmental organization of twelve developing countries made up of Algeria, Angola, Ecuador, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, the United Arab Emirates, and Venezuela. OPEC has maintained its headquarters in Vienna since 1965, and hosts regular meetings...
  
   – Organization of Petroleum-exporting Countries
• IEA
  International Energy Agency
  The International Energy Agency is a Paris-based autonomous intergovernmental organization established in the framework of the Organisation for Economic Co-operation and Development in 1974 in the wake of the 1973 oil crisis...
  
   – International Energy Agency
• CAPP
  Canadian Association of Petroleum Producers
  The Canadian Association of Petroleum Producers is the voice of the upstream Canadian oil and natural gas industry. The members of CAPP produce 90% of the petroleum production in Canada.-Background:...
  
   – Canadian Association of Petroleum Producers
• World LP Gas Association
  World LP Gas Association
  The World LP Gas Association is a worldwide industry association which represents the interests of the liquefied petroleum gas industry globally.The Association's mission is to:...
  
   – WLPGA

Energy technology inventors

• Alessandro Volta
  Alessandro Volta
  Count Alessandro Giuseppe Antonio Anastasio Gerolamo Umberto Volta was a Lombard physicist known especially for the invention of the battery in 1800.-Early life and works:...
  
  
• Charles Kettering
  Charles Kettering
  Charles Franklin Kettering was an American inventor, engineer, businessman, and the holder of 186 patents. He was a founder of Delco, and was head of research for General Motors for 27 years from 1920 to 1947. Among his most widely used automotive inventions were the electrical starting motor and...
  
  
• Farrington Daniels
  Farrington Daniels
  Farrington Daniels , was an American physical chemist, is considered one of the pioneers of the modern direct use of solar energy.- Biography :Daniels was born in Minneapolis, Minnesota on March 8, 1889...
  
   – solar energy
• Georges Leclanché
  Georges Leclanché
  Georges Leclanché was a French electrical engineer chiefly remembered for his invention of the Leclanché cell, one of the first modern electrical batteries and the forerunner of the modern dry cell battery.-Biography:...
  
   – battery
  Battery (electricity)
  An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
  
  
• John Frederic Daniell
  John Frederic Daniell
  John Frederic Daniell was an English chemist and physicist.Daniell was born in London, and in 1831 became the first professor of chemistry at the newly founded King's College London. His name is best known for his invention of the Daniell cell , an electric battery much better than voltaic cells...
  
   – Daniell cell
  Daniell cell
  The Daniell cell was invented in 1836 by John Frederic Daniell, a British chemist and meteorologist, and consisted of a copper pot filled with a copper sulfate solution, in which was immersed an unglazed earthenware container filled with sulfuric acid and a zinc electrode...
  
  
• Rudolf Diesel
  Rudolf Diesel
  Rudolf Christian Karl Diesel was a German inventor and mechanical engineer, famous for the invention of the diesel engine.-Early life:Diesel was born in Paris, France in 1858 the second of three children of Theodor and Elise Diesel. His parents were Bavarian immigrants living in Paris. Theodor...
  
   – compression ignition internal combustion engine
  Internal combustion engine
  The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
  
  
• Georges Imbert
  Georges Imbert
  Georges Christian Peter Imbert born March 25, 1884 in Niederstinzel, Lorraine died February 6, 1950 in Saar Union, Alsace. Around 1920 developed the wood gas generator for the automobile that was commonly used in Europe until petroleum fuel became more economical in the region. He studied chemical...
  
   – wood gas
  Wood gas
  Wood gas is a syngas fuel which can be used as a fuel for furnaces, stoves and vehicles in place of petrol, diesel or other fuels. During the production process biomass or other carbon-containing materials is gasified within the oxygen-limited environment of a wood gas generator to produce hydrogen...
  
  
• Leonardo da Vinci
  Leonardo da Vinci
  Leonardo di ser Piero da Vinci was an Italian Renaissance polymath: painter, sculptor, architect, musician, scientist, mathematician, engineer, inventor, anatomist, geologist, cartographer, botanist and writer whose genius, perhaps more than that of any other figure, epitomized the Renaissance...
  
  
• Moritz von Jacobi
• Nikolaus Otto – internal combustion engine
• Robert Stirling
  Robert Stirling
  The Reverend Dr Robert Stirling was a Scottish clergyman, and inventor of the stirling engine.- Biography :Stirling was born at Cloag Farm near Methven, Perthshire, the third of eight children...
  
   – Stirling engine
  Stirling engine
  A Stirling engine is a heat engine operating by cyclic compression and expansion of air or other gas, the working fluid, at different temperature levels such that there is a net conversion of heat energy to mechanical work....
  
   (external combustion)
• Nikola Tesla
  Nikola Tesla
  Nikola Tesla was a Serbian-American inventor, mechanical engineer, and electrical engineer...
  
  
• James Watt
  James Watt
  James Watt, FRS, FRSE was a Scottish inventor and mechanical engineer whose improvements to the Newcomen steam engine were fundamental to the changes brought by the Industrial Revolution in both his native Great Britain and the rest of the world.While working as an instrument maker at the...
  
   – steam engine
  Steam engine
  A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...
  
   with separate condensor

Energy-related lists

• List of books about energy issues
• List of energy abbreviations
• List of large wind farms
• List of notable renewable energy organizations
• List of photovoltaics companies
• List of renewable energy topics by country
• List of solar thermal power stations
• list of wave topics
• List of wind turbine manufacturers

External links