of these articles is concerned with physical dimension energy, for further meanings sees energy (term clarifying).

Energy is a physical variable of state.

The term became of the Scottish physicist William John Macquorn Rankine in the year 1852 in the today's senseintroduced to physics and is derived from the Greek one : εν = in, inside and εργον = work, working. Energy meant completely generally thus the objects inherent effectiveness regarded in physics. At the very front it becomes as somethingunderstood, which can be converted into work. Energy is figurativy spoken the ability of a body to perform work. 1852 ago for energy among other things the term Kraft, in Germany also “alive Kraft”, was used.

Usually becomes for thoseEnergy the symbol E uses. The energy E of a system cannot be measured, it is computed or over the work performed by it determined.

Table of contents

Forms of energy

with the physical procedures arise many different forms of energy, which are combined into 4 groups here. Since this organization is arbitrary, there are comprehensive terms for forms of energy, which combine special forms of energy from different groups. Energy is independent, of the form of energy,a characterizing size for the condition of a system, a variable of state in such a way specified. One finds a conceptually clean organization of the energy into memory and transmission forms in the physics of the dynamic systems.

Mechanical energy

the energy of a mechanical system can always as sum of kinetic and potenzieller energy to be represented. The two terms are used beyond the classical mechanics and quantum mechanics within nearly all fields of physics.

  • Kinetic energy is called also kinetic energy. It becomes by thoseMovement of a system opposite another system and by its mass determines and consists of Translationsenergie and Rotationsenergie.
  • Potential energy is called also Lageenergie. In the mechanics it is the energy of a system, it by itsSituation in a field possesses, for example in the gravitational field of the earth.
  • Oscillation energy: With the pendulum the potential energy alternates during maximum deflection with the equivalent large kinetic energy during the passage by the rest position. Beyond the mechanics are Oscillations generally by a periodic change between two forms of energy characterizes.
  • Flexible energy is the potential energy out their rest position of shifted atoms or molecules in a flexibly distorted body, for example a mechanical feather/spring. Generally one designates the energy, thosewith the flexible or plastic deformation in the body (or set free) becomes stored, as deformation energy.
  • Sound energy: With the sound the atoms in consequence of the elasticity of a solid body or the compression of a liquid or a gas in the clock that swingFrequency between the potenziellen energy of deflection from their rest position and the kinetic energy with the passage by this rest position. The term acoustic energy refers to all acoustic (partly not) oscillations perceptible of humans.
  • Wellenenergie is not a comprehensive term, thatonly to the acoustic waves applies, but to all spatially spread oscillation phenomena such as z. B. Water waves and electromagnetic waves.

Neither oscillation, nor sound still Wellen-Energie are own energies as variables of state, because oscillation, sound and wave describe in the timeprocedures running off, thus no conditions. In the explanations the energies (potential and kinetic) are called also correctly, which are substantial with these procedures as mechanical energies alone.

Flexible energy is the potential energy in the rest position. Becomes a bodyfrom the rest position shifted, then results an energy potential energy, which is caused by the shift and which belongs into the energy balance.

Such indistinct explanations concerning energies make their careful definitions more difficult.

Thermal and internal energy

thermal energy is the energy,in the unordered motion of the atoms or molecules of a material is stored. Thermal energy is colloquially often also falsely called heat energy, heat capacity or amount of heat. The manifestations of the thermal energy are described by thermodynamics. A descriptive examplefor complex dependence thereby of the physical phenomena which can be observed melting ice and developing water vapour from water are by supply of thermal energy.

One calls the sum of thermal energy, oscillation energy in the body and binding energy Internal energy. (Strictly the term is internal energy a Pleonasmus, as for instance a wet rain or a white mould. Philologically correctly would have to be spoken here of internal Ergie, see. the Etymologie in the introduction section).

Electrical and magnetic energy

  • electricityis among other things as potenzielle energy in the electrostatic field of electrical charges (e.g. in condensers) stored. In larger quantities it cannot be stored however. In power stations and batteries it e.g. becomes therefore. from heat energy and/or. produces for chemical energy, overStromleitungen to the consumers transport and with the consumers changed into other forms of energy (Kraft, Licht, Wärme).
  • Magnetic energy is contained in magnetic fields.
  • Electromagnetic oscillation energy: By induction electricity in the clock of the frequency with magnetic energy changes. This findsin electrical resonant circuits instead of, in addition, in the area, in which the electromagnetic field spreads. Then one speaks of electromagnetic radiation energy or photon energy and particularly for the visible frequency range of light energy.

Binding energy


after special relativity theory are mass and energy equivalent. That means that the proper mass of particles a certain energy quantity the so-called rest energy

<cdot> math E = m \c^2< /math>

corresponds. This can be converted with certain procedures into other forms of energy can and in reverse. So the reaction products of the nuclear fission and the nuclear fusion have measurably lower proper masses than the basic materials. In elementary particle physics in reverse also the production of particlesand thus of rest energy from other forms of energy observes.

Transformation of the forms of energy and energy use

energy can be produced nor destroyed neither, but be converted only into different forms of energy. In a closed system therefore the principle of conservation of energy applies, for the one most exactlyexperimentally secured sets of physics is. One calls energy preservation size. The energy conservation is over the Noether theorem a consequence of the independence of the physical laws from the time.

In open systems the energy inclination has, the standing area availableto fill out evenly. With it the arising and to observing physical regularities lead to the entropy, a thermodynamic variable of state with the same value as the energy.

By one at the system performed work is increased the energy of the system. Performs the systemWork, then becomes its energy smaller. The work causes here thus a change in status in form of a temperature, a form, a situation or a jerk load.

The term energy use refers to the transformation of a form of energy into another form of energy (→ work). One Energy production is not possible due to the principle of conservation of energy. The same applies to energy consumption, waste of energy, energy saving and loss of energy. In the colloquial language these words are often used with moral valuation for the energy conversion. Further it is not possible, the forms of energyto convert arbitrarily into one another. In particular it is impossible that a system delivers its heat energy completely as work.

Examples of the energy conversion are the production of light and warmth from electricity over an electrical resistance and the transformation of the electricitywith the help of electromagnetism over magnetic fields in an electric motor into kinetic energy.

Chemical energy of a fuel is transformed with the burn into heat energy or converted into combustion engines ( as fuel) into kinetic energy. On the efficiency of the engines becomes dependenta relatively large portion of the used up energy directly converted into waste heat.

Kinetic energy is converted with the movement against the gravity field of the earth, thus uphill, into potential energy or over friction into heat energy or acoustic energy.

In power stations becomes electric current produces. Either thereby existing potential energy (storage power station) becomes or kinetic energy (run power station, wind energy plant) over generators converted into electricity or it is selected the detour over a thermal engine, over from warmth energy toowin. Examples of it are thermal power stations, which are operated with coal , oil , gas , biomass , nuclear power or also garbage.

Radiation energy, also in the form of acoustic energy, mostly becomes with the impact an absorbing surface in heat energytransformed.

Examples of energy conversions
mechanical energy thermal energy radiation energy electricity chemical energy nuclear energy
mechanical energy transmission brakes synchrotron radiation generator Eischnee particle accelerator
thermal energy steam turbine heat-transfer agent glowing metal thermocouple blast furnace supernew facts
radiation energy radiometer solar heat collector nonlinear optics solar cell photosynthesis core photo effect
Electricity electric motor electric cooker lightning transformer accumulator
chemical energy muscle oil heating Glühwürmchen gas cell coal gasification Isomerieverschiebung
nuclear energy fast neutrons sun gamma-rays internal conversion radiolysis breeder reactor

power supply and - consumption

with power supply and - consumption (*) becomes the use of different energies in forHumans well usable forms designates. The forms of energy most frequently used by humans are heat energy and electricity. The human needs are directed particularly toward the ranges heating, food preparation and the enterprise from mechanisms and machines to the life easement. Herethe topic is progressive movement and consumption z. B. fossil source of energy in vehicles not insignificant.

The different sources of energy can reach the consumers over lines, like typically electricity, natural gas, long-distance heating and local heat supply, or they are to a large extent storable and arbitrarytransportable, like z. B.Hard coal and brown coals, fuel oils, fuels (gasolines, Diesel fuels), industrial gases,Nuclear fuels (uranium), biomasses (wood and. A.).

The energy consumption is world-wide very different and in the industrialized countries around a multiplemore highly than z. B. in the third world. In industrially highly developed countries 19 has themselves since that. Century enterprise with the production and supply of energy for general consumption employs. Here the central production of electrical standsEnergy as well as the transmission to the individual consumers in the foreground. Further are the procurement, the transport and the conversion from fuel material to heating purposes an important industry.

Approx. 40 per cent of the world-wide power requirement is covered by electricity. Front runner in consumptionthis portion are with approx. 20 per cent electric drives. Afterwards is the lighting with 19 per cent, which takes part air condition technology with 16 per cent and the information technology with 14 per cent in the world-wide electrical power requirement.

(*) Energy cannot in the actual sense used upwill, it can only from a form into another be converted. (Principle of conservation of energy)

source of energy

major item: Source of energy

exhaustible sources of energy

fossil sources of energy

(all chemical energy)

Nuclear fuels

(all nuclear energy)

renewable sources of energy

(see also renewable energy)


  • Potenzielle energy in a homogeneous gravitational field: <math> E_ {poet} \ approx m \ cdot g \ cdot h = F_G \ cdot h< /math> times height is equal to Gewichtskraft. For the gravity field of a heavenly body with radius <math> R_p< /math> it is only one approximationfor sufficiently small spaces. Is more exact: <math> E_ {poet} = mgh \ frac {R_p} {R_p+h}< /math>.
  • Potenzielle energy of a strained feather/spring (called therefore also clamping energy): <math> E_ {poet} = {1 \ more over 2} \ cdot D \ cdot s^2< /math>, whereby D is the spring rate and s the deflection of the feather/spring from the rest position.
  • Classical kinetic energy: <math> E_ {kin} = \ frac {1} {2} \ cdotm \ cdot v^2< /math>
  • Relativistic kinetic energy: <math> E_ {kin} = E - E_0 = \ frac {m_0 \ cdot c^2} {\ sqrt {1 \ frac {v^2} {c^2}}} - m_0 \ cdot c^2 = m_0 c^2 \ left (\ frac {1} {\ sqrt {1 - \ frac {v^2} {c^2}}} - 1 \ right)< /math>
  • Work (change of energy) <math> W = \ delta E = \ int P (t) dt </math>, whereby P is the achievement and t the time.


  1. The “formulas” specified here are the definitions of the different energies asVariables of state. Formulas, z. B. for the free case, is the mathematical representation for the procedure.
  2. For all energy definitions a large E for energy is used, although in some cases energies E, but referred energies e are not defined. Those“Feather/spring energy” is more =E/Feder the energy e referred to a feather/spring. Each form of energy Ej consists of a quantity size Mj and the referred energy ej: Ej = Mj ej. Only in such a way defined forms of energy Ej arise primarily in energy balances.
  3. Workis no energetic variable of state, like the other forms of energy defined here. Work is a procedure size, which can cause a change of energy in a system. Another usual definition is work is <math> W = \ int F dx< /math>


SI - unit of the energy is the joule.

1 J = 1 Nm = 1 WG = 10 7 suppl. = 0.2388 cal = 0.102 kpm = 0,2778·10 -6 KW/H

of orders of magnitude

the following list is to help to receive a feeling for the orders of magnitude from energy to.The major item is under order of magnitude (energy).

1 J = 1 WG = 1 Nm
potential energy, those with the raising of a Schokoladentafel (approx. 100 g) around 1 meter in this one stores.
3,6·10 6 J = 3600 kJ =a 3600 kWs = 1 KW/H
of Abrechungseinheit for river, gas etc.
2,9·KW/H = 1 kg SKE a hard coal unit corresponds to 10 7
J = 8.141 to the energy quantity, which is converted when burning 1 kg of hard coal. This is a usual measurethe indication of primary energy - quantities. (1998 amounted to the world-wide primary energy conversion 14.1 Gt SKE = 390·10 18 J)
1 eV = 1.602 176,462 (63) · 10,-19 J
the unit electron volt becomes among other things in the solid body, core and elementary particle physics used. A photon of violet light has an energy of approx. 3 eV, one of red approx. 1,75 eV.

See also

Wikiquote: Energy - quotations

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Wiktionary: Energy - word origin, synonyms and translations

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