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Binding energy
A '''binding energy''' is the net negative [[potential energy]] (''i.e.'', the net energy debt) pulling a bound system together.<ref>Young, Hugh D.; Freedman, ‎Roger A. [https://www.google.co.uk/search?newwindow=1&tbm=bks&q=%22has+a+net+negative+potential+energy%22 University Physics]. Addison-Wesley, 2000, p. 736. "'''A crystal''' of table salt is made of ions of sodium (Na<sup>+</sup>) and chlori(contracted; show full)
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==Mass-energy relation==
{{main|Mass–energy equivalence}}
When a system becomes bound (''i.e.'', energetically indebted), the borrowed positive actual energy must be radiated away and subtracted from the [[rest mass]] of the unbound system, simply because this positive actual energy has a [[w:Mass in special relativity#Relativistic mass|relativistic mass]].<ref>
''HyperPhysics'' - "Nuclear Binding Energy". ''C.R. Nave'', Georgia State University. Accessed 7 September 2010. [http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html Nuclear Binding Energy]. ''HyperPhysics''</ref> Thus the bound system acquires a mass defect, or, which is the same (due to the [[mass–energy equivalence]]), a net negative [[potential energy]].<ref name="RestMass">Heighway, Jack. [https://books.google.co.uk/books?id=13vIAgAAQBAJ&pg=PA36 Einstein, the Aether and Variable Rest Mass]. HeighwayPubs, 2011, p. 36. "Understanding why rest masses are reduced in a gravitational field only requires a simple insight: '''''when an object is raised in a gravitational field, the gravitational potential energy increase is real, and exists as an increase, usually tiny, in the rest mass of the object.'''''"</ref>

From ''E''&nbsp;=&nbsp;''mc''<sup>2</sup>, it follows that '''''Binding energy'' = ''Mass change'' × ''c''<sup>2</sup>'''. Since the mass change is negative (a mass defect), the binding energy is negative too.

==See also==
*[[Minimum total potential energy principle]]
*[[Potential energy]]

==References==
{{Reflist}}

==External links==
*[http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html Nuclear Binding Energy]

{{DEFAULTSORT:Binding Energy}}
[[Category:Basic physics ideas]]
[[Category:Cosmology]]
[[Category:Energy]]