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.)

Other

Flanders and Swann produced a particularly insightful explanation of thermodynamics, which was popular in the 1950's and 1960's. Their work, entitled First and Second Law is unique in having been set to music.

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The Second Law is exhibited (coarsely) by a box of electrical cables. Cables added from time to time tangle, inside the 'closed system' (cables in a box) by adding and then removing cables. The best way to untangle them is to start by taking the cables out of the box and placing them stretched out. The cables in a closed system (the box) will never untangle, but giving them some extra space starts the process of untangling (by going outside the closed system).

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