4 ms·
Nitpick in the article conclusion: >Heat flows from hot to cold because the number of ways in which the system can be non-uniform in temperature is much lower
by anon84873628 2y ago
Nitpick in the article conclusion:
>Heat flows from hot to cold because the number of ways in which the system can be non-uniform in temperature is much lower than the number of ways it can be uniform in temperature ...
Should probably say "thermal energy" instead of "temperature" if we want to be really precise with our thermodynamics terms. Temperature is not a direct measure of energy, rather it is an extensive property describing the relationship between change in energy to change in entropy.
- johan_felisaz 2y agoNitpick of the nitpick... Temperature is actually an intensive quantity, i.e. combining two subsystems with the same temperature yields a bigger system with the same temperature, not twice bigger.
- timewizard 2y agoThis is why the "thermodynamic beta" is really useful. https://en.wikipedia.org/wiki/Thermodynamic_beta https://en.wikipedia.org/wiki/Thermodynamic_beta
- deleted 2y ago[deleted]
- anon84873628 2y agoD'oh! Thanks for the correction
- kgwgk 2y agoI think you used “extensive” in the sense of “defined for the whole system and not locally”. It’s true that thermodynamics is about systems at equilibrium.
- anon84873628 2y agoI meant to say "intensive" in the physics sense but just brain farted while typing.
- kgwgk 2y agoAh, then I don’t see what’s wrong with “the number of ways in which the system can be non-uniform in temperature is much lower than the number of ways it can be uniform in temperature”. In equilibrium one doesn’t have a gradient of temperature because “…” indeed.
- anon84873628 2y agoIf you take "temperature" to mean "average kinetic energy of molecules" then it's fine. But that's sort of the same class of simplification as saying "entropy is the amount of disorder".
- kgwgk 2y agoI don't follow you. Whatever you take temperature to mean, for an isolated system in equilibrium that intensive thermodynamic property will have the same value everywhere and the entropy of the system will thus be maximized given the constraints. If you put two subsystems at different temperatures in thermal contact the combined system will be in equilibrium only when the cold one warms up and the hot one cools down. The increase in the entropy of the first is larger than the decrease in the entropy of the second (because ΔQ/T1 > ΔQ/T2 when T1<T2) and the total entropy increases. No kinetic energies of molecules are involved in that phenomenological description of heat flowing from hot to cold.