View source for Law of conservation of energy

[[Category:Done 2020-02-29]]
[[Category:Translated to French]]
[[fr:Conservation d'énergie]]
<onlyinclude>The '''law of conservation of energy''' states that [[energy]] can neither be created nor destroyed - only converted from one form of energy to another.</onlyinclude> This means that a [[system]] always has the same amount of [[energy]], unless it's added from the outside. This is particularly confusing in the case of [[non-conservative force]]s, where energy is converted from [[mechanical energy]] into [[thermal energy]], but the overall energy does remain the same. The only way to use energy is to [[energy transformations|transform energy]] from one form to another.

The amount of energy in any system, then, is determined by the following equation:

<math>U_{T} = U_{i} + W + Q</math>
:*<math>U_T</math> is the total [[internal energy]] of a [[system]].
:*<math>U_i</math> is the initial internal energy of a system.
:*<math>W</math> is the [[work]] done by or on the system.
:*<math>Q</math> is the [[heat]] added to, or removed from, the system. 

It is also possible to determine the change in internal energy of the system using the equation: 
<math>\Delta U = W + Q</math>

This is also a statement of the [[first law of thermodynamics]].

While these equations are extremely powerful, they can make it hard to see the power of the statement. The takeaway message is that energy cannot be created from nothing. [[High energy society|Society]] has to get energy from somewhere, although there are many sneaky places to get it from (some sources are [[primary fuel]]s and some sources are [[primary energy flow]]s). 

Early in the 20<sup>th</sup> century, [http://www.nobelprize.org/nobel_prizes/physics/laureates/1921/ Einstein] figured out that even [[mass]] is a form of energy (this is called [[mass-energy equivalence]]). The amount of mass directly relates to the amount of energy, as determined by the most famous formula in physics:

<math>E = mc^{2}</math>
:*<math>E</math> is the amount of energy in an object or system.
:*<math>m</math> is the mass of the object or system.
:*<math>c</math> is the [[speed of light]], roughly <math>3\times10^8 m/s</math>.

==For Further Reading==
*[[First law of thermodynamics]]
*[[Internal energy]]
*[[Work]]
*[[Heat]]
*[[Carnot efficiency]]
*Or explore a [[http://energyeducation.ca/encyclopedia/Special:Random| random page]]

To learn more about the physics of the law of conservation of energy, please see [http://hyperphysics.phy-astr.gsu.edu/hbase/conser.html#coneng hyperphysics] or for how this relates to chemistry please see UC Davis's [http://chemwiki.ucdavis.edu/Physical_Chemistry/Thermodynamics/Laws_of_Thermodynamics/First_Law_of_Thermodynamics/Conservation_of_Energy chem wiki].
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