Editing Closed system (section)

===In classical mechanics===
In [[Theory of relativity|nonrelativistic]] [[classical mechanics]], a closed system is a [[physical system]] that does not exchange any matter with its surroundings, and is not subject to any net [[force]] whose source is external to the system.<ref>{{cite book|last=Rana|first=N.C.|author2=P.S. Joag|title=Classical Mechanics|date=1991|page=78|publisher=McGraw-Hill Education (India) Pvt Limited |isbn=978-0-07-460315-4}}</ref><ref>{{cite book|last=Landau|first=L.D.|author-link=Lev Landau|author2=E.M. Lifshitz|title=Mechanics|edition=third|date=1976|page=8|publisher=Butterworth-Heinemann |isbn=978-0-7506-2896-9}}</ref> A closed system in classical mechanics would be equivalent to an [[isolated system]] in [[thermodynamics]]. Closed systems are often used to limit the factors that can affect the results of a specific problem or experiment.