Recent content by pondhockey

On paying taxes (not that I don't sympathize!) http://www.wsj.com/articles/greece-struggles-to-get-citizens-to-pay-their-taxes-1424867495 “Greeks consider taxes as theft,” said Aristides Hatzis, an associate professor of law and economics at the University of Athens. “Normally taxes are...

Thank you for the article, Van. In the mean time I had searched for information on the pension system. My own sense is that the pension system is (or at least was) way out of balance, is a huge burden to the tax payer/ bailers out and needs to be dealt with. It appears to be part of what is...

Fascinating and informative discussion. Thanks to all and for the citations and links. In particular, the impression I have gotten from the media (or my faulty ingestion of the media) is that the Greeks are an entitled population with short work weeks and many benefits, such as early...

Mark writes: .. ..Thank you for the link. It makes me think that this info should be in an introduction to every physics and thermodynamics text. I've never seen it in an undergraduate math text. There's a culture, in physics, that I find regrettable: the prof used integrals and line...

I agree with this. And I think it begs the question of why mess with differentials in expositions of physics (and in particular thermodynamics.) To me it seems to cloud more issues than it simplifies. It certainly inspires a lot of threads just like this one!

Mark, thank you for the comment. Can you tell me, in what context d (i.e. the differential) is considered an operator? It is not defined that way in either calculus/advance calculus text that I just now referred back to. In those texts, dx is a real variable, referred to as an independent...

OK, here is an example of what I regard to be differential magic. I'm not going to attempt to provide the mathematically correct restatement because I'm still a thermodynamics grasshopper and I'll probably get it wrong. I think it conveys a "vague intuitive" understanding, but not a clear...

Christian, here is an answer to one of my questions in a thermodynamics thread; I'll provide the "differential algebra magic" example later. https://www.physicsforums.com/threads/manipulating-differentials-in-thermodynamics.791811/#post-5135710 I'm "LATEX challenged" so I'll have to talk...

Just a general note: doing "algebra" with dy/dx is only sometimes helpful, and other times is unsupported or unclear "magic" that substitutes a vague intuition for what is really intended. dy = f'(x) dx is an actual definition of dy. In this statement, dx and dy are both real numbers (not...

Thank you, Couchyam. After staring at the problem and the author's treatment for quite a while, I decided that in this simple case (move along an increasing T path, then along an increasing P path, then the opposite, to demonstrate lack of path independence) I could resolve the issue with the...

Here's another question from Thermodynamics: work, w, is accomplished when there is a volume change with a fixed pressure. In the text I am following (a geochem text) this is written as dw = P dV (the V actually has an overlying ~ to indicate molar volume). The author wishes dw to be thought...

Thanks to both of you, for your reply to Shawnstrausser. I would like to follow up: If I understand correctly, Couchyam affirms that (dE/dV)=(∂E/∂S)v (dS/dV)+(∂E/∂V)s not from the total differential that Shawnstrausser mentions, but directly from the multivariable chain rule.

Follow-up question: Thermodynamics texts routinely/commonly (maybe even universally) use expressions like: W = ∫P dV In the contexts that I see this same expression, it looks to me like P is often a function of V. One such expression continues like this: W = ∫P dV (lower limit...

I'd like to follow up on one point that Murphrid makes: "Typically, Δx (or any such quantity) is used to denote a real, finite quantity, whereas dx is used to mean a quantity that is infinitesimally small--i.e. that can be integrated." This still seems to be an issue for me. First of all, the...

For which I apologize. If it helps the cause, here is a location (as newbie I can't post a link yet) that explains differentials in action, in the context of thermodynamic equations. //www.physicsforums.com/showthread.php?t=525071&highlight=differential