Mechanically isolated system

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In thermodynamics, a mechanically isolated system is a system that is mechanically constrained to disallow deformations, so that it cannot perform any work on its environment. It may however, exchange heat across the system boundary.

For a simple system, mechanical isolation is equivalent to a state of constant volume and any process which occurs in such a simple system is said to be isochoric. {{cite book |last=Guha |first=Evelyn |title=Basic Thermodynamics |url=https://books.google.com/books?id=oEfVJJC4mpsC |accessdate=2012-12-11 |year=2000 |publisher=Alpha Science Int'l Ltd. |isbn=9781842650004 |page=150}}

The opposite of a mechanically isolated system is a mechanically open system,{{cn|date=April 2013}} which allows the transfer of mechanical energy. For a simple system, a mechanically open boundary is one that is allowed to move under pressure differences between the two sides of the boundary. At mechanical equilibrium, the pressures on both sides of a mechanically open boundary are equal, but only a mechanically isolating boundary can support pressure differences.