Talk:Second law of thermodynamics
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My ha'penny worth
"...natural processes have a preferred direction of progress..." should be re-phrased without using the concept of preference. It is absurd to suggest that natural processes 'prefer' anything. Please try to work out exactly what you mean, and express it clearly. Perhaps 'spontaneous' might be what you have in mind ?
"This also means that it is impossible to build solar panels that generate electricity solely from the infrared band of the electromagnetic spectrum without consideration of the temperature on the other side of the panel (as is the case with conventional solar panels that operate in the visible spectrum)." It is not impossible in principle that photovoltaic cells working on the energy-gap principle could be made to work in the infra-red region. In fact, given the properties of silicon as a semiconductor one can predict that conventional photocells do in fact operate in the infrared. The point which should be made here is not the difference in wavelength involved, but alternative thermodynamic principles, namely the random nature of heat, and the 'ordered' nature of e-m radiation as energy forms. Replacing "the infrared band of the electromagnetic spectrum" by "heat" would be a gesture in the right direction. Conversion of e-m radiant energy to other forms is theoretically possible with 100% efficiency just as the conversion of mechanical energy is; this happens in wireless aerials. But the conversion of thermal energy to other forms is subject to the implications of the 2nd law, Carnot's law, etc; it is in fact the basic problem of thermodynamics. Perhaps rather than obscuring this important basic idea it might be worth elaborating it, and trying to say what it is about thermal energy which distinguishes it from other forms in this respect. This, it seems to me, is the key concept involved in the 2nd law, and in fact is what it is all about; it should at least be mentioned, preferably at the top of the page.
Style of article
The entire article is written in a style that only a scientist or a science major can fully grasp. It assumes that the ordinary layman can understand all this, which is not the case. It should be rewritten in a style that is intelligible to people who are not scientists. AlbertSM (talk) 16:54, 13 February 2014 (UTC)
In particular, note the interpretation of dq.... as an "infinitesimal" is at odds with the universal teaching of calculus that dq is a real number. To most non specialists this is nonsense - it conveys no useful information. Pondhockey (talk) 04:10, 22 July 2015 (UTC)
The Second Law does not say
The Second Law does NOT say "The second law of thermodynamics states that in a natural thermodynamic process, there is an increase in the sum of the entropies of the participating systems." If that were the case, then it could be used to "prove" that water could flow uphill to a lake provided it flows further downhill in another creek. — Preceding unsigned comment added by 126.96.36.199 (talk) 08:58, 11 October 2014 (UTC)
- Isn't that what they call a siphon? 188.8.131.52 (talk) — Preceding undated comment added 06:28, 9 July 2015 (UTC)
You have no valid grounds for changing this version referring to every process ....
Processes in which the entropy of an isolated system would decrease do not occur, or, in every process taking place in an isolated system, the entropy of the system either increases or remains constant
That version of the 2nd law comes from the textbook An Introduction to Thermodynamics, the Kinetic Theory of Gases, and Statistical Mechanics (2nd edition), by Francis Weston Sears, Addison-Wesley, 1950, 1953, page 111 (Chapter 7, "the Second Law of Thermodynamics").
- Thank you for these comments.
- There are very many statements of the second law. None of them is unreservedly perfect. It may not be easy for us to reach agreement about how it should be stated in the lead of this article. You object to the new version. You cite here another version.
- Perhaps I may suggest that you might look more widely than at the version you have cited here.
- There are reasons for the new version in the lead.
- It should be brief and readily readable.
- It should make the point that it refers to thermodynamic processes, not to physical processes in general.
- It should be positive, not merely a negation.
- It should be based on the best sources.
- It should refer explicitly to real thermodynamic processes as opposed to fictive ones.
- Very likely it should be stated in terms of entropy.
- It should not be phrased so as to suggest that it is more widely applicable than is proper.
- The new version to which you object was constructed with those reasons in mind. Perhaps that is enough comment from me for the moment.Chjoaygame (talk) 10:58, 11 October 2014 (UTC)
The 2nd law applies only to isolated systems?
That “The 2nd law applies only to isolated systems” is a premise used to explain evolution. Objections to evolution ( Violation of the second law of thermodynamics) This interesting understanding of the law should be addressed.LEBOLTZMANN2 (talk) 20:14, 12 November 2014 (UTC)
- I don't think this particular article needs to accommodate or address cranks. Rklawton (talk) 21:51, 12 November 2014 (UTC)
The processes must be dependent: they are "participating" (sub-)systems within the isolated system being considered. The law cannot apply to a sum of the entropy of two or more independent processes like water flowing uphill just because it "knows" it will flow further down the other side. That only happens when the up and down processes are dependent in a siphon. Cut the hose at the top and they are independent, each then gaining entropy. The Second Law applies to all forms of energy, not just thermal (kinetic) energy. For example, it also applies to potential energy in a force field like gravity. In such a case we have thermodynamic equilibrium when (PE+KE)=constant in a vertical plane and there are thus no unbalanced energy potentials, this meaning we have maximum entropy with a density gradient and a temperature gradient, each resulting from the Second Law. The pressure gradient is a corollary. See http://climateblogcritique.homestead.com — Preceding unsigned comment added by 184.108.40.206 (talk) 10:45, 9 January 2015 (UTC)
- The immediately foregoing unsigned IP comment is conflict of interest promotion by an easily recognised recidivist and is an improper comment here.Chjoaygame (talk) 13:44, 9 January 2015 (UTC)
No it's not a "conflict of interest" as the author had no significant pecuniary interest in presenting such valid physics which cannot be refuted because it is a direct corollary of the Second Law of Thermodynamics.— Preceding unsigned comment added by 220.127.116.11 (talk) 23:48, 15 February 2015 (UTC)