JohnDenker
commented
9 years ago The chapter 7 summary on page 175 adds yet another layer of inconsistency. The summary definitions of "thermal energy" and "source energy" are wildly inconsistent with the definitions given in the body of the chapter.
For one thing, "source energy" on page 156 explicitly includes wind, which is surely not "configuration".
On the other side of the same coin, the discussion of "thermal energy" on page 155 doesn't explicitly say so, but any physically reasonable definition would have to include random PE, not just KE. The heat capacity of an ordinary solid is half PE and half KE. Insofar as page 155 intended to say this, it's very unclear; insofar as it didn't intend to say this, it's wrong physics. Either way, the summary definition on page 175 is wrong physics. It is probably fixable within the narrow context of chapter 7, but the whole idea of "thermal energy" aka heat aka caloric is not viable in the long run.
Thirdly, insofar as the summary definition of "thermal energy" needs to be changed, the summary definition of "source energy" also needs to be changed. It probably isn't fixable, not in the short run or otherwise.
The Pearson web site http://www.pearsonhighered.com/mazur1einfo/detail/features/index.html says:
Statistical treatment of thermodynamics. The traditional, 19th-century approach to thermodynamics is intensely confusing to students. This text builds thermodynamics on a more logical and coherent foundation, starting with an accessible treatment of the statistical basis for entropy.
It's true that chapter 19 uses a modern statistical approach, but the discussion _starts_ in chapter 7, which uses a 19th- or 18th-century approach, not mentioning entropy at all, but rather classifying and re-classifying the energy.
Suggestion: The laws of physics mostly deal with energy, just plain energy. The more ways you invent of sub-classifying the energy, the more likely you are to make a mistake.
Constructive suggestion: In the name of consistency and plain old correctness, rewrite chapter 7 to match chapter 19. Dissipation and irreversibility have precious little to do with energy; they are understandable in terms of _entropy_ and not otherwise.
I am not happy with section 7.4. It looks like trouble at the conceptual physics level, at the detailed physics level, and at the pedagogical level.
For starters, the fact is there exist two major definitions of energy. -- There is the physics energy, and -- There is the Department of Energy «energy», which involves some notion of "useful" or "available" energy.
Section 7.4 from end to end, starting with the section-title itself, mercilessly tramples on this distinction. If you're talking about DoE «energy», then yes we need a "source" of «energy». However, the idea that there is some quantifiable thing called «source energy» is a Bad Idea. In particular, if you're talking about the physics energy, the conservation law tells us quite emphatically that there are no sources and there are no sinks.
There is such a thing as "dissipation" ... but it has more to do with entropy than energy. See item #155 for a catalog of entropy-related issues.
The idea that we need a "source" of energy to keep the car moving is an example of Aristotelian physics, which most physics teachers consider the bane of their existence.
The term "incoherent" is used. Since it is not defined in the book, I assume the usual vernacular definition applies. In particular, I assume it is a euphemism for "disorder" ... which in turn is a discredited euphemism for entropy. Please let's not go there. Let's not go anywhere near there. Constructive suggestion: Stick to the sensible approach as set forth in chapter 19, where entropy is defined in terms of probability.
The so-called «source energy» is defined to be incoherent. However, the given examples of «source energy» are not incoherent in any way that I can see. I reckon this is not just a problem with the definition, but also an incurable problem with the whole concept. Consider for example a car that uses solar energy stored in a flywheel or a supercapacitor. According to the book, that counts as «source energy». But is a flywheel or supercapacitor incoherent? I don't see how it could be, if the word means anything at all.
Furthermore, the whole idea of dividing energy into «thermal energy» and «source energy» et cetera is a Bad Idea. Generally the laws of physics involve the energy, period. The more ways of dividing it up, the more ways of making a mistake. Sure, sometimes it is possible to define a notion of «thermal energy» distinct from the «mechanical energy», for example in the infamous Slinktato™ ... but only if you are sufficiently lucky, selective, and/or industrious. There is nothing in the laws of physics that makes it certain -- or even likely -- that such a distinction makes sense. For details on this, see https://www.av8n.com/physics/thermo/cramped.html
Specific constructive suggestions: