Editing Energy (section)

=== Equipartition of energy ===
The energy of a mechanical [[harmonic oscillator]] (a mass on a spring) is alternately [[kinetic energy|kinetic]] and [[potential energy]]. At two points in the oscillation [[Frequency|cycle]] it is entirely kinetic, and at two points it is entirely potential. Over a whole cycle, or over many cycles, average energy is equally split between kinetic and potential. This is an example of the [[equipartition principle]]: the total energy of a system with many degrees of freedom is equally split among all available degrees of freedom, on average.

This principle is vitally important to understanding the behavior of a quantity closely related to energy, called [[entropy]]. Entropy is a measure of evenness of a [[distribution (mathematics)|distribution]] of energy between parts of a system. When an isolated system is given more degrees of freedom (i.e., given new available [[energy state]]s that are the same as existing states), then total energy spreads over all available degrees equally without distinction between "new" and "old" degrees. This mathematical result is part of the [[second law of thermodynamics]]. The second law of thermodynamics is simple only for systems which are near or in a physical [[equilibrium state]]. For non-equilibrium systems, the laws governing the systems' behavior are still debatable. One of the guiding principles for these systems is the principle of [[principle of maximum entropy|maximum entropy production]].<ref>{{cite journal|last1=Onsager|first1=L.|title=Reciprocal relations in irreversible processes.|journal=Phys. Rev. |volume=37|issue=4|date=1931|pages=405–26|bibcode=1931PhRv...37..405O|doi=10.1103/PhysRev.37.405|doi-access=free}}</ref><ref>{{cite journal |last1=Martyushev |first1=L. M. |last2=Seleznev |first2=V. D. |date=2006 |title=Maximum entropy production principle in physics, chemistry and biology |journal=Physics Reports |volume=426 |issue=1 |pages=1–45 |bibcode=2006PhR...426....1M |doi=10.1016/j.physrep.2005.12.001}}</ref> It states that nonequilibrium systems behave in such a way as to maximize their entropy production.<ref>{{cite journal|last1=Belkin|first1=A.|last2=et.|first2=al.|title=Self-Assembled Wiggling Nano-Structures and the Principle of Maximum Entropy Production|journal=Sci. Rep. |volume=5|pages=8323|date=2015|issue=1 |doi=10.1038/srep08323|pmid=25662746|pmc=4321171|bibcode=2015NatSR...5.8323B}}</ref>