The following outline is provided as an overview of and topical guide to energy: Energy – in physics, this is an indirectly observed quantity often understood as the ability of a physical system 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 force (a pull or a push) against an object that is moving along a definite path of certain length.
Forms of energy Chemical energy – Energy released from chemical substances Electrical energy – Energy related to forces on, and movement of, charged particles Free energy – State function whose change relates to the system's maximal work output Geothermal energy – Thermal energy generated and stored in the Earth Gravitational energy – energy from gravitational fields Ionization energy – energy that binds an electron to its atom or molecule Kinetic energy – (≥0), energy of the motion of a body Magnetic energy – energy from magnetic fields Mechanical energy – The sum of (usually macroscopic) kinetic and potential energies Mechanical wave – (≥0), a form of mechanical energy propagated by a material's oscillations Nuclear binding energy – energy that binds nucleons to form the atomic nucleus Potential energy – energy possessed by a body by virtue of its position relative to others, stresses within itself, electric charge, and other factors. Elastic energy – energy of deformation of a material (or its container) exhibiting a restorative force Gravitational energy – potential energy associated with a gravitational field. Nuclear potential energy Radiant energy – (≥0), energy of electromagnetic radiation including light and of gravitational radiation Renewable energy – energy from renewable natural resources that are replenished on a human timescale Rest energy – (≥0) given by E = mc2, where m is an object's rest mass Solar energy Surface energy Sustainable energy Thermal energy – a microscopic, disordered equivalent of mechanical energy Heat – an amount of thermal energy being transferred (in a given process) in the direction of decreasing temperature Work (physics) – an amount of energy being energy transferred in a given process due to displacement in the direction of an applied force Electric power Electricity
Measurement
Units
List of common units for energy. Official or common symbol in brackets after name and exact or approximate value of unit in joule in brackets after description.
SI unit Joule (J) – the SI-unit for energy. Also called newton meter, watt second, or coulomb volt.
Other metric units Kilowatt-hour (kW·h) – corresponds to one kilowatt of power being used over a period of one hour (3.6 MJ). Calorie (cal) – equal to the energy need to raise the temperature of one gram of water by one degree Celsius (~4.184 J). Erg (erg) – unit of energy and mechanical work in the centimetre-gram-second (CGS) system of units (10−7 J).
Imperial or US Customary units British thermal unit (BTU) – equal to the energy need to raise the temperature of one pound of water by one degree Fahrenheit (~1055 J). Therm (thm) – unit of heat energy. In the US gas industry it is defined as exactly 100,000 BTU59 °F. It is approximately the heat equivalent of burning 100 cubic feet (2.8 m3) of natural gas (~105.5 MJ). Quad – unit of energy equal to 1015 (a short-scale quadrillion) BTU. Foot-pound (ft·lbf or ft·lbf) – unit of mechanical work, or energy, although in scientific fields one commonly uses joule (~1.356 J).
Other units Electronvolt (eV) – the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt (~1.60 × 10−19 J). Planck energy (EP) – natural unit of energy common in particle physics (~1.96×109 J). Barrel of oil equivalent (BOE) – energy unit equal to the energy released when burning one barrel (159 litres) of oil (~6.12 GJ). Tonne of oil equivalent (toe) – energy unit equal to the energy released when burning one tonne of oil (~42 GJ).
Related units and concepts Volt Ampere Coulomb Efficient energy use Energy recovery Energy recycling Enthalpy EU energy label Fill factor – 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. 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) – (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 Mass–energy equivalence – where mass has an energy equivalence, and energy has a mass equivalence Megawatt Net energy gain Power factor – of an AC electric power system is defined as the ratio of the real power to the apparent power. Waste-to-energy Waste-to-energy plant Watt Voltage Zero-energy building
Energy industry Energy industry
Worldwide energy supply, outline by country/region World energy resources and consumption List of energy resources, substances like fuels, petroleum products and electricity Energy crisis, the need to conserve energy resources Energy development, development of energy resources — ongoing effort to provide abundant and accessible energy, through knowledge, skills and construction Embodied energy, the sum total of energy expended to deliver a good or service as it travels through the economy Energy conservation, tips for conserving energy resources Energy economics, as the foundation of other relationships Energy policy, government policies and plans for energy supply Energy storage, methods commonly used to store energy resources for later use Energy system, an interpretation the energy sector in system terms Ecological energetics Energy balance Energy speculation Free energy suppression conspiracy theory Future energy development – Provides a general overview of future energy development. History of perpetual motion machines Hubbert peak theory, also known as peak oil – 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 Power harvesting Renewable energy development
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