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ericmazur / PnPbook

Tracking of typos, errors, and improvements for "The Principles and Practice of Physics"
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principle of virtual work #149

Open JohnDenker opened 8 years ago

JohnDenker commented 8 years ago

This is a missed opportunity (not an error).

In a book at this level, I would expect to see much more emphasis on the _principle of virtual work_. However, I can't find it in the index under P, under V, or under W ... even though other principles, other virtuals, and other works are indexed. (See #181 for a catalog of index-related issues.) I don't see it in the table of contents or in the text in the expected places. It might be hiding somewhere, but even so, it's safe to say it's not being emphasized as much as I would expect.

Given the emphasis on a principle approach to the subject, from the title of the book onwards, this seems quite strange.

This is a directory node; specific examples will be listed separately.

ericmazur commented 8 years ago

Interesting.... two thoughts coming to mind:

  1. Can I bring it down to the right level? Do you have an example of a simple discussion of it?
  2. What would be a logical place to put it?
JohnDenker commented 8 years ago

In reply:

  1. The canonical reference is Feynman. The idea is first mentioned in vol I section 4-2 : http://www.feynmanlectures.caltech.edu/I_04.html .... Then there are about a dozen places where the idea gets re-used : https://www.google.com/search?q=%22virtual+work%22+site%3Afeynmanlectures.caltech.edu .... Also, not coincidentally, the Leighton/Vogt book of exercises has some outstanding illustrations and applications of the idea. It is truly emblematic of the entire course. Recall that they put the epitaph of Stevinus on the cover of the paperback edition. The "bridge truss" problem is another favorite : https://www.av8n.com/physics/img48/bridge.png
  2. The discussion of the pressure associated with tension in the walls is certainly one place to put it. This includes surface tension in bubbles, surface tension in droplets (which is conceptually similar but not quite identical), transmural pressure in blood vessels (which is even more different) and cabin pressure in aircraft : #72. Meanwhile there are probably lots of other places, earlier as well as later in the book, where the principle can be applied. It would be somewhat laborious but probably worth it to scour both books from end to end, checking every occurrence of "work" and/or "force", to see if the idea could be applied.