Second law of thermodynamics
From the Simple English Wikipedia, the free encyclopedia that anyone can change
 |
The English used in this article may not be easy for everybody to understand. You can help Wikipedia by making this page or section simpler. |
The second law of thermodynamics means that entropy increases. With other words: over time, differences in temperature, pressure, and density tend to even out.
This law is valid only in a physical system that is isolated from the outside world. Entropy is a measure of how far along this evening-out process has come.
The most common wording for the second law of thermodynamics is essentially due to Rudolf Clausius:
| “ | The entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium. | ” |
There are many statements of the second law which use different terms, but are all equivalent. Another statement by Clausius is:
Heat cannot of itself pass from a colder to a hotter body.
An equivalent statement by Lord Kelvin is:
A transformation whose only final result is to convert heat, extracted from a source at constant temperature, into work, is impossible.
The second law is only applicable to macroscopic systems. The second law is actually a statement about the probable behavior of an isolated system. As larger and larger systems are considered, the probability of the second law being practically true becomes more and more certain. For any isolated system with a mass of more than a few picograms, the second law is true to within a few parts in a million.[1]
Contents |
[change] Overview
In a general sense, the second law says that temperature differences between systems in contact with each other tend to even out and that work can be obtained from these non-equilibrium differences, but that loss of heat occurs, in the form of entropy, when work is done.[2] Pressure differences, density differences, and particularly temperature differences, all tend to equalize if given the opportunity. This means that an isolated system will eventually come to have a uniform temperature. A heat engine is a mechanical device that provides useful work from the difference in temperature of two bodies.
[change] Quotes
| “ | The law that entropy always increases, holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation. | ” |
-
-
-
-
-
-
-
-
- --Sir Arthur Stanley Eddington, The Nature of the Physical World (1927)
-
-
-
-
-
-
-
| “ | The tendency for entropy to increase in isolated systems is expressed in the second law of thermodynamics -- perhaps the most pessimistic and amoral formulation in all human thought. | ” |
-
-
-
-
-
-
-
-
-
-
-
-
- --Greg Hill and Kerry Thornley, Principia Discordia (1965)
-
-
-
-
-
-
-
-
-
-
-
| “ | There are almost as many formulations of the second law as there have been discussions of it. | ” |
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- --Philosopher / Physicist P.W. Bridgman, (1941)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
[change] Miscellany
- Flanders and Swann produced a setting of a statement of the Second Law of Thermodynamics to music, called "First and Second Law".
- The economist Nicholas Georgescu-Roegen showed the significance of the Entropy Law in the field of economics (see his work The Entropy Law and the Economic Process (1971), Harvard University Press).
[change] References
- ↑ Landau, L.D.; Lifshitz, E.M. (1996). Statistical Physics Part 1. Butterworth Heinemann. ISBN 0-7506-3372-7.
- ↑ Mendoza, E. (1988). Reflections on the Motive Power of Fire – and other Papers on the Second Law of Thermodynamics by E. Clapeyron and R. Clausius. New York: Dover Publications. ISBN 0-486-44641-7.
- Fermi, Enrico [1936] (1956). Thermodynamics. New York: Dover Publications, Inc. ISBN 0-486-60361-X.
[change] Further reading
- Goldstein, Martin, and Inge F., 1993. The Refrigerator and the Universe. Harvard Univ. Press. A gentle introduction, a bit less technical than this entry.
- Maxwell's demon 2 : entropy, classical and quantum information, computing. Edited by Harvey S. Leff and Andrew F. Rex. Bristol; Philadelphia : Institute of Physics, 2003
[change] Other websites
- Stanford Encyclopedia of Philosophy: "Philosophy of Statistical Mechanics." by Lawrence Sklar.
- The evolution of Carnot's principle, by E.T. Jaynes, in G. J. Erickson and C. R. Smith (eds.) Maximum-Entropy and Bayesian Methods in Science and Engineering vol. 1, p. 267 (1988).
- The Second Law of Thermodynamics.
