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I'm in a classical mechanics class now. On our exams, most questions are quantitative. And in general, besides the theory part, all physics problems just require you to gather formulas, manipulate them a little bit by using other formulas, and come up with an appropriate value. In the question, you are given all the information you need. For our exams, they even give us a formula sheet, with every formula and equation we can possibly need. But even after all this, physics remains to be one of the most challenging subject for many students, including myself. I just dont get it. It seems like it should be so easy. Grab a formula or two, and manipulate it until all the given quantities can fit into these formulas. But yet, even after all this, its not easy to do, but it should be. Sorry if I'm not making any sense. I'm a student, and most of you already know this stuff, so try thinking as a newbie to physics.

Edit: Although this seems like a general study question, its actually a very specific question. I'm a really good student, but I think I've met my match with physics. It seems you just cant 'memorize' things in this class, like you can with any other class. You really just have to understand it. And lately, I've just been so discouraged to study since no matter how hard I study, I do really bad on the tricky exams. My study routine goes a little something like this:

  1. Watch pre-lecture video that explains the current chapter, and take notes on that.
  2. Do the weekly homework, which itself is pretty challenging.
  3. To study for the exams, I do a BUNCH of practice problems from previous semester exams that they supply us with. I literally go over and do 5 old exams, one question at a time, and I understand everything perfectly-atleast I think I do, until the REAL exam comes around, and I do absolutely terrible.

I dont know what else to do at this point :(

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closed as not constructive by David Z, Mark Eichenlaub, KennyTM, mbq, Michael Pryor Nov 29 '10 at 21:15

As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance.If this question can be reworded to fit the rules in the help center, please edit the question.

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I don't think this question belongs here. It's not really about physics, it's about the way people think and learn. (It is a good question given the right forum) I'm voting to close. –  David Z Nov 29 '10 at 1:40
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If you're good in computer science classes: Here it's the same. It's not enough to know what a for-loop is and how it works to become a good programmer. That requires lots of practice. –  Lagerbaer Nov 29 '10 at 2:10
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Anyone notice the irony between the title and the tag? –  Vortico Nov 29 '10 at 2:47
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@fprime: that doesn't make it about physics, though. You can't express this question using equations, it doesn't concern an experiment, it can't be answered by applying a physical theory. It's a question about learning, specifically about learning a particular subject, which just happens to be physics. You could ask the same question about any other subject, if that happened to be the one you were having trouble with. –  David Z Nov 29 '10 at 5:22
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professor had been providing to my deaf perception all the semester. I had the tools, because I had solved all the problems, but not the large picture. Probably this is your problem with physics, that you have the detail tools and are missing the forest for the trees. Try reading a physics book as if it is a novel, to see the large framework. This will help you when meeting new problems to assign them to the correct framework, in my opinion of course. –  anna v Sep 30 '11 at 12:12

10 Answers 10

up vote 17 down vote accepted

The problem is: There are so many formulas which you can combine, rearrange and manipulate in oh so many ways that just knowing the formulas doesn't get you that far. What you need is intuition and understanding as to which formulas relate to your problem and how you should relate them to get what you want. This intuition can only be built through experience, i.e. numerous hours of problem solving.

That's why it's so important you do all the problem sets you can find, because only then will you become really familiar with the formulas.

Think of it like learning to play chess: You can learn the rules in an afternoon, they aren't that hard. But this teaches you nothing about how to be a good chess player. That takes years of practice.

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Nice analogy :) –  maq Nov 29 '10 at 2:03
    
Feynman used the chess analogy a number of times, but not in this context. Nice! –  Vortico Nov 29 '10 at 2:57
    
Great analogy... for Physics AND programming. I will re-purpose it! :D –  Anonymous Type May 20 '13 at 1:08

Formulas are (merely) a means of describing relations between physical quantities. You should understand what a formula expresses, the physical concept (e.g. energy conservation) behind it. It's often useful if you can find an everyday analogy for it (e.g. 'money conservation': income equals expenses plus savings). Also, before applying a given formula you must check whether the assumptions made when deriving it are fulfilled in a given problem.

Unfortunately it's not clear why despite the learning effort you seem not to perform so well at the exams. Try studying together with other students (from whom you can learn). Or try asking questions here. And try to find out where your exam answers differ from the correct answers.

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The way I see it, there are two aspects to the practice of science, there is a constructive one and a destructive one. Let me try to expand on that.

The destructive one is the easiest to explain and usually the one on which a fair amount of time is spent. It is basically the skeptical part of science, the one where you test one idea against another. There are various tools at your disposition to do this: experiment, checking for mathematical/logical coherence of the ideas.

The constructive or creative aspect is the hardest part. We don't have a systematic approach to it, basically, all we do is just try. The reason some people are more successful than others at doing this is experience, they can immediately select the potentially successful ideas from a larger set of ideas, without going through all the steps of the destructive part. Or they just are willing to spend so much more time on working on the subject, giving up on many other activities, which of course forges experience.

To summarize: critique is always relatively easy, coming up with good ideas is the hard part.

Now, one might say that these two aspects are not necessarily exclusive to physics, which is true. An artist has to go through the same motions, but the criteria are different. Nature is a harsh mistress, and that's why physics is so difficult. We can come up with lots of ideas, but nature doesn't care about how creative we are, if the idea doesn't work it doesn't work.

I'd say sciences in general are difficult because of this. If you didn't encounter the problem in other sciences yet, it's because you are still at a more elementary study level in them as compared to physics.

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You can't just memorize it, you have to understand it

Suppose I tell you that an electron has been fired through an electric field towards an oscillating platform, and I want to know the time after which it will hit the platform, and what minimum initial energy I need. To answer that, you need to have a clear model in your head of what an electron is, how it interacts with electric fields, the idea that a particle follows a path defined by an equation of motion, the thought that the oscillation of the platform will change both the time taken and the minimum initial energy needed to reach the platform.

So:

  1. Learn the appropriate theory
  2. Form a mental model of that theory
  3. Using your mental model see, in your mind, what you think might happen in this specific circumstance
  4. Use the equations to construct some equations that reflect your intuition about what will happen.

You see the process of starting from the general (e.g. electromagnetism theory) to the specific (e.g. motion of an electron through an electric field). When doing research in Physics, you tend to do this to get an intuitive expectation, or prediction, of what will happen, and then you do an experiment to test it. Experimental Physics often works in the opposite direction, starting from some specific experimental results, and coming up with a general theory to tie them together.

If you haven't got the understanding, the intuitive mental model that captures all the rules (theory) that you know, then you will struggle to see your way to the solution.

So, you were right when you said "You really just have to understand it.".

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This is perhaps a bit besides the point and not really answering your question, but I'll mention it anyway. For me at least, the difference between "how can I possibly memorize all of this?" and true understanding often boils down to an interest and curiosity. I realize classes have a tendency to kill these things (even when done right, because you're now doing something because you have to), but I think it's worth the effort to try and rekindle your true interest.

Now, being told to "be more interested" is hardly help, and I'm sorry for that. I just know it tends to make the difference between being miserable cramming things into my head and working hard learning to understand something. When you learn something that explains a thing you've been wondering about, you no longer have to memorize. You feel in some sense immersed in your newfound knowledge, and you know it instead of just remembering it. I think this applies to most sciences (I've definitely experienced it in both physics, mathematics, computer science and electronics).

So my real advice is this: There will always be courses that don't interest you. For those you'll just have to cram it in. But at least the majority of courses can hopefully be viewed with from a different angle where they seem more like a way of answering a question or curiosity you have than a list of things you must know for the exam.

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There is an answer to your question in the form of a physics paper : Determining dynamical equations is hard by Toby Cubitt, Jens Eisert and Michael Wolf. Basically, of you define physics as determining dynamical equations —the laws of physics— from some observations —the experiments—, they prove that this problem is NP-complete.

In other words, physics is not only hard, it is NP-hard !

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The relevant concepts involved may not have been properly explained to you in sufficient detail for you to manipulate them easily.

Have you considered using a book with very clear definitions and many worked examples, like Schaum's outline series? See http://www.amazon.com/s/ref=nb_sb_ss_i_6_15?url=search-alias%3Dstripbooks&field-keywords=schaums+physics&sprefix=schaums+physics. They get surprisingly good reviews.

Can anyone recommend very good online lectures, preferably videos?

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Wow thanks for that link I wish I had seen these books earlier! –  maq Nov 30 '10 at 1:27

I dont know what else to do at this point :(

Party less? Just kidding. Well @fprime, the first thing to realize is that physics is really friggin' hard and it seems to me that once you're over that hump you might actually end up enjoying it. However, loving the subject does not imply that you will never have night terrors where you wake up screaming "Its a real job I tell you, its a real job".

So if you think you have what it takes then hold your nose and dive in. Six months and no social life later you might start finding physics a lot easier and also a lot more different than what you expect.

One good place for beginners seeking inspiration is the set of lectures by Feynman. Good luck !

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I do enjoy learning it, and I liked it a lot in the beginning. Then the exam scores came back and I hated it :( Where can I find these lectures? –  maq Nov 29 '10 at 6:11
    
@fprime: see this question if you want some nice books (Feynman's also). There also exist Feynman's video lectures -- very much recommended. –  Marek Nov 29 '10 at 11:48
    
@fprime: google "feynman djvu". That should do the trick! –  user346 Nov 29 '10 at 19:14

I don't know how helpful this group will be, we are probably a selfselected subgroup whose natural intuitions were such that physics was easy (at least up until some advanced level, when the math got challenging). A lot has to do with understanding the material, and being very good at problem solving. And I've always felt the statement about the worst teachers being those who didn't have to struggle to learn the material, has a lot of truth to it. I think being good at undrgrad level physics has a very high correlation with being good at math word problems, so if you don't get a satisfactory answer here (on how to make it much easier), I'd ask the math group the same question about word problems.

The best learning technique for me when I was learning it was to speedread the chapter in the text book, then take out lots of paper and derive all the formulas just taught -the speedreading was to get the gist of where you are trying to go to and a feeling for how to get there. Also you should have mentally noted any nonobvious tricks needed to get the math to work out. Once you can do that, your understanding should be high enough to enable you to work through problems that need the understanding of the theory, but for which a cookbook like approach (simply plug in equation XXX for problems of type YYY, almost never works). If you have a really good understanding of equation XXX, how it was arrived at etc., you have a good chance of being able to use it when it is appropriate, (at least if you are creative about problem solving).

I think the biggest thing about physics, is its mostly about a mode of thinking, and secondarily about the detailed material. Watch how those who are good at it descibe how they solve problems, hopefully some of their thinking style can be learned.

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Physics is about the ability to predict the outcome of scenarios. Either with formulas, simulation, or good old curve fitting. The underlying principles a few basic ones, but to use them you required to understand higher lever math, so to make it "easy", basic physics classes boil it down to a cookbook method. Add one of this, two of this, mix and voila here is the result. That is not how physics supposed to be, and it is a pitty you are stuck in such a situation. My suggestion is to bear with it, until you discover some of the commonalities by yourself and find your own way of making sense of the world.

Hang in there, it gets only beter from here!

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I'm going to disagree a little: the classroom gives you the cookbook, not because the instructor doesn't understand the limitation of that method, but because it is very hard to teach intuition. That's the whole point of PER: we've been working on "How to teach physics" for generation at we still have only a ad hoc collection of anecdotal advice. @fprime: that cookbook is only the beginning. Those are the tools, now you have to learn to use them. –  dmckee Nov 29 '10 at 1:56

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