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An '''Isolated system''', is a [[physical system]] that does not [[interaction|interact]] with its [[surroundings]]. It obeys a number of [[conservation law]]s: its total [[energy]] and [[mass]] stay constant. They cannot enter or exit, but can only move around inside. An example is in the study of [[spacetime]], where it is assumed that [[asymptotically flat spacetime]]s exist.
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A '''closed system''' or '''Isolated system''', is a [[system]] in the "state of being isolated from its surrounding environment."<ref>[[Bela H. Banathy]] (1992). ''A systems view of education: concepts and principles for effective practice‎''. p.184</ref> The term often refers to an idealized system in which closure is perfect. In reality no system can be completely closed; there are only varying degrees of closure.
   
Truly isolated physical systems do not exist in reality, but real systems may behave nearly this way for finite (possibly very long) times. The concept of an isolated system can serve as a useful [[scientific modeling|model]] approximating many real-world situations. It is an acceptable [[idealization]] used in constructing [[mathematical model]]s of certain natural [[phenomenon|phenomena]]; e.g., the [[Sun]] and [[planet]]s in our [[solar system]], and the [[proton]] and [[electron]] in a [[hydrogen atom]] are often treated as isolated systems. But from time to time, a hydrogen atom will [[absorption (optics)|interact]] with [[electromagnetic radiation]] and go to an [[excited state]].
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Truly isolated physical systems do not exist in reality, but real systems may behave nearly this way for finite (possibly very long) times. The concept of an isolated system can serve as a useful [[scientific modeling|model]] approximating many real-world situations. It is an acceptable [[idealization]] used in constructing [[mathematical model]]s of certain natural [[phenomenon|phenomena]].
 
Another reason no system can be truly isolated is that even in [[Interstellar medium|interstellar space]], there is the [[Kelvin|2.7&nbsp;K]] background [[black body|blackbody]] radiation left over from the [[Big Bang]]. This [[heat]] permeates every [[physical body]] in the [[Universe]].
 
 
In the attempt to justify the postulate of [[entropy]] increase in the [[second law of thermodynamics]], Boltzmann’s [[H-theorem]] used [[Ludwig Boltzmann#The Boltzmann equation|equations]] which assumed a system (e.g., a [[gas]]) was isolated: i.e., that all the mechanical [[Degrees of freedom (physics and chemistry)#Example: classical ideal diatomic gas|degrees of freedom]] could be specified, treating the walls simply as [[mirror]] [[boundary condition]]s. This inevitably lead to [[Loschmidt's paradox]]. However, if the [[stochastic]] behavior of the [[molecule]]s in actual walls is considered, along with the [[random]]izing effect of the ambient, background [[thermal radiation]], Boltzmann’s assumption of [[molecular chaos]] can be justified.
 
 
==Closed system==
 
 
By contrast, a '''closed (but not isolated) system''' can exchange [[heat]] and [[mechanical work|work]], but not [[matter]], with its surroundings. This is a basic concept in '''[[thermodynamics]]''', where it is assumed that a ''thermally'' isolated (insulated) system can be realized. It is a useful idealization, even if it can only be [[asymptote|asymptotically]] approximated.
 
   
 
==See also==
 
==See also==
 
 
* [[Dynamical system]]: Has components and/or flows that change over time.
 
* [[Dynamical system]]: Has components and/or flows that change over time.
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* [[Glossary of systems theory]]
 
* [[Open system]]: Can be influenced by events outside of the actual or conceptual boundaries.
 
* [[Open system]]: Can be influenced by events outside of the actual or conceptual boundaries.
   
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== References ==
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[[Category:Cybernetics]]
 
[[Category:Systems theory]]
 
[[Category:Systems theory]]
 
[[Category:Systems]]
 
[[Category:Systems]]
[[Category:Cybernetics]]
 
[[Category:Fundamental physics concepts]]
 
   
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{{enWP|Closed system}}
 
{{enWP|Closed system}}

Latest revision as of 16:32, March 25, 2010

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A closed system or Isolated system, is a system in the "state of being isolated from its surrounding environment."[1] The term often refers to an idealized system in which closure is perfect. In reality no system can be completely closed; there are only varying degrees of closure.

Truly isolated physical systems do not exist in reality, but real systems may behave nearly this way for finite (possibly very long) times. The concept of an isolated system can serve as a useful model approximating many real-world situations. It is an acceptable idealization used in constructing mathematical models of certain natural phenomena.

See alsoEdit

References Edit

  1. Bela H. Banathy (1992). A systems view of education: concepts and principles for effective practice‎. p.184


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