How to understand Feynman's Lectures on Physics

[leo.]

I study Physics at college and I'm on the third year. Currently, I'm facing a very complicated problem: I can learn advanced math, do complicated proofs, but I simply can't read Feynman's Lectures on Physics. Until now, I just had classes about physics for engineers (Halliday's book), so no teacher taught real physics, their classes was basically just pass formulas for people to remember and apply without understanding the phenomena, or the reasoning that a theoretical physicist need.

On the other hand, I also had advanced math classes, like analysis over R^n, analysis on manifolds, linear and multilinear algebra, done both with vector spaces and modules. All of that kind of math I can understand, and I can do well with any book of these topics.

Since there were no classes about real theory of physics, I asked a teacher from the university that I know, and he told me to read Feynman's books.

The problem is that I'm trying for months and I simply can't understand his reasoning. I've read multiple times his way to derive the gravitational potential energy expression, but I simply couldn't understand all of that reasoning with perpetual motion and so on.

Then I've moved to the next chapter about measurements of time, and I also simply cannot graps all of those experimental methods.

I really don't like the idea of understanding math without understand physics. I really want to be a physicist, not a mathematician. And despite all of that, I would really like to understand Feynman's book, since it seems to be very interesting.

Does anyone has a suggestion so that I can understand Feynman's reasonings and move on? I've googled about video lectures, but there are no lectures on classical Physics on the lines of those books. All the videos I found are again aimed at engineers, and this really isn't what I'm looking for.

I don't know if any other person also faced this kind of situation, but if someone did, I would really like to know how to deal with Feynman's books. Any help or suggestion is welcome. Thanks very much in advance.

 

[MisterX]

I think some of his explanations can be hit-or-miss. Maybe some of of them can be pretty confusing or just plain not very good. I don't recommend the Feynman Lectures for initial learning of a subject. That being said they can be a valuable resource once you have some familiarity with the subject.

You may want to try a classical mechanics text like Taylor and an E&M text like Griffiths.

 

[leo.]

Thanks for the suggestion MisterX. My main worry is that I wasn't able to get much understanding and intuition about the concepts on those basic physics courses. So I feel I don't quite have a good intuition about energy, momentum and things like that.

Altough many people in those courses manage to grasp those ideas quickly seeing practical applications to engineering and so on, I really ain't able to get it this way. I think that may be due to the fact I'm more used to abstract math texts rather than practical examples.

Do you think that given that starting with something like Taylor's book is a good choice? Or do you think it would be better to start somewhere else?

Thanks again.

 

[guitarphysics]

Hey, thought I'd chime in. I don't know nearly as much math as you, but I seem to know a bit more physics if you've only learned from Halliday's book, so maybe my opinion would be useful. From what you've said, you think you can "plug n chug" formulas but don't actually understand the conceptual side very deeply. If that's so, there's two books I highly recommend (as well as a few others I want to mention).

For classical mechanics, check out Kleppner and Kolenkow. If you can read and understand that text, and actually do the problems on there, there's no doubt you have a good understanding of classical (only Newtonian, by the way) mechanics. Momentum, energy, angular momentum, etc. will all be very intuitive afterwards. For electricity and magnetism, PURCELL, PURCELL, PURCELL. I can't recommend that book enough. It's really hard, but you get a lot out of it. The author is amazing, and he really helps you understand the physical side of things. A lot of his proofs/arguments are largely constructed from physical reasoning, which is great for understanding how everything's connected and the actual underlying concepts of the theory. After reading those two books, you could probably comfortably read a lot of Feynman's first volume (I don't know about the optics or thermodynamics bits, for those you would have to learn the material from somewhere else), and probably all of the second one (and gain a lot of valuable insight, as well as entertainment, from both).

As for Taylor and Griffiths: Taylor is good for me, probably not necessary for someone with your math background. It's like a book that would go in between Kleppner and Kolenkow, and an analytical mechanics book like Goldstein or Landau (1st volume). Basically, if you're comfortable with calculus of variations, go on straight to Goldstein/Landau after Kleppner. Griffiths: I really like this book, and recommend you check it out (after Purcell, or at the same time).

As for the parts of Feynman that you mentioned you had trouble with: do you mean the reversible machine example in the gravitational potential energy section (in chapter 4)? I had trouble with that too; like MisterX said, some of his explanations are hit-or-miss, so don't worry too much if you don't get some of them (although the section before that, on conservation of energy, is a $\textit{classic}$ :D).

Hopefully this was some help, good luck.

 

[homeomorphic]

Other books are definitely a good option to try, but I'm a fan of Feynman. What you might have to do is focus on one sentence at a time and think about it for 15 minutes or something until it makes sense, trying to visualize it, if that's what's called for. If it makes sense on its face, you don't need to spend too much time on it. It may take practice before you can hold the whole argument in your mind and be able to put it all together. You could try summarizing things in your own words, and writing it down as if you were explaining it to someone else, which was one of Feynman's own techniques. Practice remembering without looking. That's how to get it planted in your mind.

Here are some notes about elementary mechanics for mathematicians.

http://www.math.uga.edu/~shifrin/Spivak_physics.pdf

It's possible that the "mathematician's" style of Spivak would help, although I'm not sure, since you can't get away from the physical reasoning. Spivak's book does appeal to the stereotypical idea that mathematicians like to understand things for themselves, so that may be the sense in which it is a book for mathematicians. Good physicists should be that way, too, though, to my mind.

 

[mpresic]

First I laud you effort to repair what you consider your inadequate physics background.

Feynman's books are addressed multiple times in these forums. The overwhelming consensus is:

1. The books are instructive, informative, and entertaining.
2. These are not the introductory texts prospective physicists should start with.

I whole-heartedly agree. I do not know anyone who learned their introductory physics effectively using only Feynman's texts. I also believe (I know in my case) Freshman physics used textbooks for (some) problems, and reading and as a supplement. I suspect Cal Tech in 1960 (where Feynman taught) supplemented Feynman's texts with problems. Feynman's texts were not the only material.

I think the draw of these books by some students and teacher's is they feel they can use the texts to glimpse what is in the mind of a great physicist. It may be they think if it is good enough for honors students at Cal Tech in 1960, it is good enough for me. This is misguided.

However in the interest of full disclosure, I taught physics in the 80's where Resnick taught at RPI, and I was taught introductory in the mid-70's, using Resnick and Halliday, (for some reading and problems), and professor's notes.

I know from experience, that you can learn physics and develop intuition from RH which you probably already own. Halliday should not be mischaracterized as physics for "engineers". Resnick taught (honors) physics to pre-selected students at RPI. (The rest of us TA's had the luck of the draw).

While RPI in the 70's-80's is not Cal Tech in the 50-60's; (they were slide-rule jockies and I was teaching pocket calculator jockies), Resnick and Halliday has strongly influenced several generations of successful physicists. Resnick has written other good textbooks on relativity and modern physics as well. These are strongly physical and not just for engineers.

I emphasize I know this from experience.

It is unfortunate the teacher taught your class as "plug and chug", but a careful reading, reflection, and judicious problem solving will develop your intuition. In point of fact, I believe after about a year of RH you will examine Feynman at a quicker rate, and express, "so that is what he means.". I have seen it happen .

You have a strong math background. I (half-facetiously) offer if you want to read a book by Feynman, his book Feynman and Hibbs on Path Integrals, may be the way to go. (Not yet though, repair your physics first and complete your undergrad first). Good Luck on your study.

 

[f95toli]

Just to add to the above.
The Feynman lectures are oftern referred to as "Physics for physicists".
They are definately not suitable as introductory texts; but are really good to read once you've already learned about a subject: they give you a good overview and make connections between different areas within a subject; I guess you could say that they teach you how to "think" about a subject.
I personally read them when I was a first year graduate student (having already done all my graduate courses); and I think that was just about the right time for me.

I still use them as reference texts sometimes