Second law of thermodynamics

The second law of thermodynamics is a law of thermodynamics that states that all work tends towards the production of greater entropy over time. Another way of saying this (known as the Clausius formulation) is that it is impossible to construct a perfect refrigerator. (This is why refrigerators always require an external power source.) An equivalent statement, known as the Kelvin-Planck formulation, is that "It is impossible for any cyclic process to occur whose sole effect is the extraction of heat from a reservoir and the perfromance of an equivalent amount of work." (If the reader is aware of the concept of heat engines, please understand that heat engines work by allowing two heat reservoirs of different temperatures to come in equilibrium with each other, and as such they do not violate the 2nd law.)

Related Topics:
Law of thermodynamics - Work - Entropy - Heat engines

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(Note: the second law of thermodynamics is not a result of the expansion of the universe - in fact it applies to any closed system.)

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In physics, the second law of thermodynamics, in its many forms, is a statement about the quality and direction of energy flow, and it is closely related to the concept of entropy. This law and its derivatives, such as the law of friction, define the arrow of time: most other physical laws are time-reversal invariant.

Related Topics:
Physics - Energy flow - Friction - Arrow of time - Physical law - Time-reversal

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