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When to Use this Tag

should be used if your question discusses the time-evolution of a mostly homogeneous, macroscopic system – for example a cold bottle of water in a warm bathtub. You can combine this tag with for a microscopic derivation of thermodynamical laws, and maybe with the other ‘macroscopic’ tags such as or , depending on your problem. Tagging a question as both and usually makes no sense, unless in the context of .

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