Énergie
Définition(s)
Définitions générales
| L'énergie est définie en physique comme la capacité d'un système à produire un travail, entraînant un mouvement ou produisant par exemple de la lumière, de la chaleur ou de l’électricité. C'est une grandeur physique qui caractérise l'état d'un système et qui est d'une manière globale conservée au cours des transformations. L'énergie s'exprime en joules (dans le système international d'unités) ou souvent en kilowatt-heure (kW·h ou kWh).Outre l'énergie au sens de la science physique, le terme « énergie » est aussi utilisé dans les domaines technologique, économique et écologique, pour évoquer les ressources énergétiques, leur consommation, leur développement, leur épuisement, leur impact écologique. Les principales ressources énergétiques sont les énergies fossiles (le gaz naturel, le charbon, le pétrole), l’énergie hydroélectrique, l’énergie éolienne, l’énergie nucléaire, l’énergie solaire, l'énergie géothermique.Les activités économiques telles que les productions industrielles, le transport, le chauffage des bâtiments, l'utilisation d'appareils électriques divers, sont consommatrices de beaucoup d'énergie ; l'efficacité énergétique, la dépendance énergétique, la sécurité énergétique et le prix de l’énergie y sont des préoccupations majeures.Une sensibilisation accrue aux effets du réchauffement climatique a conduit ces dernières années à un débat mondial sur la maîtrise des émissions de gaz à effet de serre et à des actions pour leur réduction. Cela conduit à envisager des transformations des modes de consommation énergétique (transition énergétique), pas seulement en raison des contraintes liées à l'épuisement de l'offre, mais aussi à cause des problèmes posés par les déchets, l'extraction des énergies fossiles, ou certains scénarios géopolitiques. |
Termes associés (Wikipedia)
| In physics, energy is a property of objects which can be transferred to other objects or converted into different forms. The "ability of a system to perform work" is a common description, but it is misleading because energy is not necessarily available to do work. For instance, in SI units, energy is measured in joules, and one joule is defined "mechanically", being the energy transferred to an object by the mechanical work of moving it a distance of 1 metre against a force of 1 newton. However, there are many other definitions of energy, depending on the context, such as thermal energy, radiant energy, electromagnetic, nuclear, etc., where definitions are derived that are the most convenient. Common energy forms include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature. All of the many forms of energy are convertible to other kinds of energy. In Newtonian physics, there is a universal law of conservation of energy which says that energy can be neither created nor be destroyed; however, it can change from one form to another. For "closed systems" with no external source or sink of energy, the first law of thermodynamics states that a system's energy is constant unless energy is transferred in or out by mechanical work or heat, and that no energy is lost in transfer. This means that it is impossible to create or destroy energy. While heat can always be fully converted into work in a reversible isothermal expansion of an ideal gas, for cyclic processes of practical interest in heat engines the second law of thermodynamics states that the system doing work always loses some energy as waste heat. This creates a limit to the amount of heat energy that can do work in a cyclic process, a limit called the available energy. Mechanical and other forms of energy can be transformed in the other direction into thermal energy without such limitations. The total energy of a system can be calculated by adding up all forms of energy in the system. Examples of energy transformation include generating electric energy from heat energy via a steam turbine, or lifting an object against gravity using electrical energy driving a crane motor. Lifting against gravity performs mechanical work on the object and stores gravitational potential energy in the object. If the object falls to the ground, gravity does mechanical work on the object which transforms the potential energy in the gravitational field to the kinetic energy released as heat on impact with the ground. Our Sun transforms nuclear potential energy to other forms of energy; its total mass does not decrease due to that in itself (since it still contains the same total energy even if in different forms), but its mass does decrease when the energy escapes out to its surroundings, largely as radiant energy. Mass and energy are closely related. According to the theory of mass–energy equivalence, any object that has mass when stationary in a frame of reference (called rest mass) also has an equivalent amount of energy whose form is called rest energy in that frame, and any additional energy acquired by the object above that rest energy will increase an object's mass. For example, with a sensitive enough scale, one could measure an increase in mass after heating an object. Living organisms require available energy to stay alive, such as the energy humans get from food. Civilisation gets the energy it needs from energy resources such as fossil fuels, nuclear fuel, or renewable energy. The processes of Earth's climate and ecosystem are driven by the radiant energy Earth receives from the sun and the geothermal energy contained within the earth.In biology, energy can be thought of as what's needed to keep entropy low. |
Source : http://dbpedia.org/resource/Energy
External references (Wikipedia)
| Reference |
|---|
| http://www.biocab.org/Heat.html |
| http://www.lightandmatter.com/html_books/lm/ch11/ch11.html |
Médias référencés
Objet de commun (4)
- Construisons ensemble - Auto construction d'éoliennes (France, 00:05:35)
- Energy as a Common Good (Belgique,, 00:02:41)
- Interview with Cecile Blanchet, Commons Network (Belgique,, 00:04:36)
- Public Trust (USA, 01:38:01)
Enjeu (1)
- MétamorphOsons! (Suisse)
Sources
Wikidata : Q16024197
DBpedia FR : Énergie
DBpedia EN : Energy
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