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4. First principle of thermodynamics
Thermodynamics, like the other so-called "exact" physical sciences (electromagnetism, mechanics...), is built on a number of postulates inspired by experimental observations. Some of these are characteristic of thermodynamics and are of particular importance: these are the "principles".
4.1 Conservative balances
The phenomenological approach to the physical sciences is based on a fundamental premise:
Extensive conservative state properties exist, i.e. they have constant values throughout the Universe.
(The Universe being defined as the whole (system)
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First principle of thermodynamics