Recent content by sponteous

I am trying to picture this setup but I don't quite follow. Are you saying that some of the work performed by the body is used to stir the surrounding medium with a paddle? At any rate, I haven't encountered that use of "reversible" before. I thought reversible meant everything, including...

Yeah, this is true if you seal the organism off in a box so that it is isolated from its surroundings. Or if you just wait until the heat death of the universe. But neither of these situations is of direct relevance to why living things get old and die. It can't be a consequence of the 2nd...

No problem, thanks for taking a look. I suspect the lack of clarity has to do with it being translated from Russian. Their little book on mechanics is extremely clear. Maybe it just has to do with the subject matter being more difficult to talk about precisely.

I've read something similar in a book written by an ecologist (I think it was). It is mumbo jumbo. Any macroscopic change at all is accompanied by a net increase in entropy, in accordance with the second law of thermodynamics. So there's no particular reason why ageing and dying are...

Okay I will. I'm pretty sure I see how to derive it already, but it can't hurt to see the official way. Thanks again! By the way, in Classical Physics someone posted a question: Maximum work done by a body in an external medium that hasn't been adequately answered yet. It has to do with a...

Thank you for the derivation. That's a good idea, using enthalpies in the first law statement. That way the accounting of the various expansion work contributions is automatically taken care of. I hadn't seen that version before, but that is definitely useful. Thanks.

Okay, that is pretty much the situation of the example, except in reverse. So if a gas is allowed to decompress from a high pressure tank into a low pressure tank isothermally, it can do some work along the way, like turning a shaft. I just don't get why it is the decrease in G = U-TS+pV...

I'm not a biologist, or even a scientist, but I would say yes, any living thing that metabolizes food gives off heat. Even "cold-blooded" animals. They just don't maintain their body temperature within as narrow a range as "warm-blooded" animals. As for why living things typically age and...

I agree, I found this section in Landau and Lifshitz very confusing for the same reasons as the OP when I read it a month or two ago. I just reread it to make sure, and I still find it confusing. It would certainly seem that for a reversible process the temperature of the body and the medium...

Good points. You are probably right that the author is looking for a simple example. It just seemed to me that they got the right answer for the wrong reason. But I'm still not certain of that, since the material is fairly new to me.

Does the entropy of a living organism ever decrease except for trivial reasons like losing weight or cooling off? My impression is that eating food does not decrease your entropy. It prevents you from reaching maximum entropy, provided that you are also excreting to balance the food intake...

If this belongs in classical physics, please move it there. But it seems like the kind of question chemistry people would know so I'm putting it here. I was reading a textbook on chemical thermodynamics, and it says to raise the partial molar Gibbs free energy of n moles a substance from...

What they're talking about here is the case where the wheel is not spinning. So it isn't spinning around the x-axis at all. The gyroscope is initially pointed along the x-axis. If you let go of it, it just falls over, staying in the x-z plane. Since the foot of the gyro is fixed at the...

That Archimedes proof was really something. Thanks for that. Amazing what the human mind can do. I also like these "low-tech" proofs that show off the power of careful reasoning and imagination. The Erlichson paper was very helpful, but it does not contain the "secret" argument of Carnot...

Thank you. I'll read that paper. Feynman made it sound like Carnot never really made an invalid argument based on caloric theory--that people had simply misread him. Maybe this paper will clear up the situation. Also, sorry for the duplicate thread. I was having connection issues and it...