A Few Questions Pertaining to Irodov's Problems in General Physics

[DemiGravija]

A Few Questions Pertaining to Irodov's "Problems in General Physics"

I've been informed that Irodov's "Problems in General Physics" is a renowned text in the realm of physics problem-solving, and I've downloaded it off the Net not too long ago. I've only skimmed cursorily through the "Kinematics" section though; there's always a different reading ambience when you're doing it off your the screen on your monitor as compared to doing it off a nicely propped book on your table.


1) How do Irodov's problems compare with that of the IPhO's in terms of relative levels of difficulty? As far as I'm concerned, the IPhO does not require any explicit use of calculus and differential equations.


2) I've downloaded an ad hoc solutions manual, and I'm solemnly deliberating upon its utility as a solid reference material after

a) I've attempted a problem and felt that it will be counter-productive to proceed any longer. To divagate from the objective of this post for a moment, I've been informed from many problem-solving references that vicariously experiencing the processes of problem-solving will strengthen one's problem solving skills. I acknowledge that extended periods of time expended on a problem will empower one's psychological capacities in the confrontation of a difficult problem, but I don't believe that this necessarily comprises the best way of acquiring problem-solving capabilities. An alternative example will be to learn and apply Polya's methods of heuristics.

b) I've completed a problem (or not) and wish to seek alternative routes to the answer.

Is this an effective method of learning, and if not, what modifications can any of you more experienced problem-solvers propose?

P.S. I'm using the solutions manual by Abhay Kumar Singh.

 

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Do you want to go to the IPhO?

1) That's a common misconception. IPhO has required some calculus and differential equations from its contestants. Take a look at the exams from 2000 onwards. Don't trust their syllabus that much. I remember they used some calculus in the IPhO in Spain, and some diff equations when solving a problem about the stability of the atmosphere.

Irodov's problems are shorter and demand a lot of creativity to solve. In the past few years, IPhO's questions were typically long, in multiple parts, and the questions tend to lead you into the physical thinking required to solve the problem. Personally, I think they rely too much on solving complicated algebraic expressions than on creativity (that rice question in Vietnam's IPhO is a good example of that). Their questions are (usually) designed so that most of the contestants can get at least a few points.

Overall, I'd say IPhO's problems are harder, although I wouldn't say they are creative. Take a look at Iran's IPhO (2007, I think). You'll find a question about dimensional analysis which is ridiculously easy from a Physics point of view, but which is somewhat time consuming because of the algebra.

If you plan to go to the IPhO, READ Irodov. Everybody does. It's good to know what your contestants know. And, if I'm not mistaken, a recent question has been criticized because it was too similar to a question from Irodov - even though according to the regulations, questions should be 100% fresh and original.


2) a) If time is running short (e.g. you have only three months before taking the exams that qualify for IPhO), you would be probably right. It's better to know how to solve the problems rather than spending your time trying to find your own solutions. BUT, I must say, I have a terrible time reading solutions written by someone else! I don't like Mr. Singh's solutions manual, but I guess he's the only option. What usually happens is that I come up with my own way of solving a problem - I think this is much, much easier than reading the solutions.

If I'm stuck in a problem, I prefer to read only the first lines of the solution, to get the guiding principle and try to solve the rest by myself. Reading the entire solution is usually both boring and confusing for me - but your mileage may vary.

An important aspect (and I hope not to contradict myself here) is that even if you come up with the correct solution, you should read the solutions manual or the resolution given by the IPhO committee. Sometimes, they have thought of really clever ways of simplifying the problem. I remember a particular time I've read about considering certain types of collisions inelastic, even though they weren't, in order to make complex systems easier to tackle. It's a wonderful idea, which I wouldn't have thought of myself, and which I've used a few times successfully. I usually have a hard time reading the solutions, but I still read them - you never know when they might give you an insight into the problem.

b) That sounds like a realistic idea. You should ALWAYS look into different ways of solving a problem.

 

[hikaru1221]

Aside from what Acut said, I would like to add one thing: if you have some time, read through the theory again, and derive whatever you can derive in the theory, and see if you can find any fundamental assumptions (and thus limitations) of the theory. Good understanding is a strong foundation before you can tackle any kind of problems. Though there are plenty of boring problems that seem not to require any creativity, you will see that the more you understand the theory by heart, the faster you jot your pen down, the more precise your equation would be the first time it is written down, and the more confident you are, especially when you face the kind of problems that have complex systems (e.g. triple pendulum - a classic one that is quite complex to high school students). And you will see that in fact, if you really understand the theory well, Irodov is no longer about creativity - it only tests how deep the theory is into your mind. You can try some problems in Kvant, a Russian physics journal, for real "creativity test."

 

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It's unfortunate, however, that the only online sources (at least the ones I know) for Kvant are in Russian.

 

[hikaru1221]

Perhaps Google Translate would help?
Anyway Kvant may not help boosting up problem-solving skills, if that is the kind of problem which requires formal analysis like the present IPhO. Kvant only helps you to look at things in different ways, and the best thing is it may help strengthening your intuition and you would get to the conclusion faster within fewer estimations, which is really good if you pursue engineering in college. The bad thing is it may lead you all the way to the tricky science and thus go away from what science really is.

 

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Perhaps Google Translate would help?

I've tried it and failed. Google did not want to translate it for me for free

 

[DemiGravija]

Hikaru, may you please demonstrate your case with a few specific examples? I don't fully understand what you're trying to convey; I only have a very general overview of what you're saying.

Anyhow, thanks for the replies to my first post on this forum. They've given me constructive insight into my problem.

P.S. I've seen a number of posts in the forum regarding books which are able to "develop physical intuition". Such a phrase seems both unintelligible and abstract to me, may someone kindly explain just what "physical intuition" means?

 

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P.S. I've seen a number of posts in the forum regarding books which are able to "develop physical intuition". Such a phrase seems both unintelligible and abstract to me, may someone kindly explain just what "physical intuition" means?

As any subjective concept, it is hard to define what physical intuition is. One way I can explain it is that a person with a developed physical intuition can guess what type of solution a particular problem will have. He or she usually knows what happens at limiting cases, and usually checks their final answer against those limiting cases. Some people can predict qualitatively what will happen to a complicated system without writing a single line of math. Also, if you develop physical intuition, you can tell if a solution is wrong almost immediately. Sometimes, while I'm solving a problem, I realize I've made a mistake somewhere because the solution doesn't "look" right.

There's another view of physical intuition: it is the ability of solving problems. To know which tools can be used in which problems. Be able to determine what's relevant to the problem and what is irrelevant.

 

[hikaru1221]

Well that gives me a really hard time to find some examples, since I've been away from physics for so long; it seems like I don't really remember at all the problems I solved I have to look up for my past posts; you may want to look at this problem:
https://www.physicsforums.com/showthread.php?t=481131
This problem addresses some understanding about the theory - it violates an assumption that most people may overlook, so I guess it's quite a good example, though I'm not sure if it shows any creativity or not (to me, it doesn't).

And if you can find me some problems in Irodov that need creativity to solve, I would not mid trying to persuade you to look at some of them from a more systematic and "physics" perspective. Sorry, I don't really remember anything

After solving the above problem, you may want to point out what the assumption I mentioned is. This is how intuition is developed - when you really grasp the concept. Intuition is more or less the trained instinct. It gives you a direction to solve a problem when you're in the dark.

Intuition can come from normal experience. For example, geometric optics theory says, if there is a line of sight from my eyes to your eyes, I and you should be able to see each other. Intuition says, if my room is so dark and your room is bright, I will see you but you won't see me. So what's wrong? Geometric optics can't explain. We then have to develop the viewpoint where light carries energy. Obviously you can't solve some relevant problems without writing down the energy equation for light.

Sometimes intuition may fail. Google for "A complete breakdown of intuition," a lecture video by Prof Lewin at MIT. The video may provide some insights on the assumption I mentioned earlier.

 

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And if you can find me some problems in Irodov that need creativity to solve, I would not mid trying to persuade you to look at some of them from a more systematic and "physics" perspective. Sorry, I don't really remember anything

I'm somewhat puzzled by your definition of creativity. Give us an example of what you consider to be a creative problem.

 

[hikaru1221]

For example, solving a traffic problem with a wave model. To me, creativity is more like you create something new / new perspective (in order to solve a problem), and the result is usually that it takes less time to solve it (and perhaps new insights). On the other hand, if the problem is solved using known principles, that should not be creative.
By right we should able to solve any problem without creating something, given that the problem is solvable within the known theory. So I would not say a problem is creative; the solution is the one that can be creative.
Perhaps we should define "new"? Creativity is subjective, I think, depending much on one's experience. (And so the wave model of traffic is not so new and creative to some people I guess).