Talk:Second law of thermodynamics
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Strangely constructed first sentence
The first sentences is poorly constructed. The first phrase up to the "that is" makes sense but the second clause is incomprehensible as it stands. A simple correction would be to insert an "it is" before the "a system" and stylistically, "in other words" sounds better to me than "that is"
..."the total entropy of an isolated system of particles can never decrease over time, that is, a system in which neither energy nor matter can enter nor leave. — Preceding unsigned comment added by 2A02:C7F:C409:DA00:A91E:3E6A:6C23:3615 (talk) 17:58, 14 March 2018 (UTC)
Not sure why this doesn't break the Second Law
I'll assume it doesn't, but I can't see why. Advice welcome, I've been scratching my head for a decade.
The molecules of a gas, have most of their energy as translation. As they move about, they are subject to gravity, losing speed as they rise, and gaining speed as they fall. Particle speed equates to temperature, so a column of gas, in a gravitational field, will be colder with height, as is observed in the atmosphere. There may well be adiabatic cooling as a pocket of gas rises and expands, caused by stirring ; but the principle suggests that cooling with altitude would occur, even if there were no other effects. That means an atmosphere of gas, around a planet, will maintain a permanent variation of temperature.
Power could be extracted continuously in many ways :
A very long thermo-couple would connect large metal plates at different altitudes
A vapour-filled balloon is bigger when hotter, so it has more net buoyancy ; and any thermal insulation would give a time lag. The balloon would rise until it chilled, then fall until it heated, cyclically.
A reservoir at one altitude, is hotter than one at a higher altitude. A U-tube which is fed from the top reservoir, and is insulated except where it dips in the lower reservoir would, once flow was started, have cold water in one arm, and hot water in the other. The water in the cold falling arm being denser, would support a taller rising column of water in the hot arm ; the excess of which would be ejected as a fountain. GeoffAvogadro (talk) 21:35, 6 July 2018 (UTC)
Imagine the Earth were so far from the Sun, that there was no solar heating, and it had no internal radioactive decay ; would the atmosphere ( probably needing to be only Helium, to be a gas at 6 Kelvin ) be the same temperature on the surface, as at say 10 kilometres altitude ? If so, how would a molecule of air moving vertically, in the Earth's gravitational field, keep the same kinetic energy ( and hence velocity and hence temperature ), as it gained or lost the gravitational potential energy, of that 10 km of height ? Air molecules may well interact, sharing and equalising their kinetic energy ; but over any finite change of height, there must be an equal and opposite change of kinetic energy. If this were not true, a molecule of air which was moving upwards, would continue at the same speed, indefinitely, until it escaped to space ; and that would seem to break the even-more unbreakable First Law.GeoffAvogadro (talk) 19:42, 24 July 2018 (UTC)
@GeoffAvogadro: Ask such questions at Wikipedia:Reference_desk/Science. The talk page of articles is intended to discuss how to edit articles, not the topics they cover. TigraanClick here to contact me 07:13, 25 July 2018 (UTC)