What exactly counts as "homework"?

[Warp]

Please excuse the backstory below, but I think it's important to explain the context, the background, of how I came to write a recent post which was quickly removed as "misplaced homework", which it was not. Please allow me to explain this background for full context. I'll mark the "backstory" section for clarity. I'll elaborate on my complaint after it.

Backstory begins:

I presented this (classical, although reworded to be less ambiguous) problem on a particular discord server: "It takes Mark 3 hours to walk from town A to town B. It takes Julia 5 hours to walk from town B to town A. If they start walking at the same time, and assuming they walk at a constant speed, how long does it take for them to meet?" (This is classically presented as people painting a house, but I think this is much more unambiguous and easier to understand.)

After the discussion on that problem, and correct answers given, I noted that the generic solution (x*y)/(x+y) holds for any pair of times. Somebody noted that that's in fact the same formula as for calculating the total resistance of two resistors in parallel. We wondered if that's pure coincidence, and came to the conclusion that it probably isn't. That the two problems are actually related.

I then started wondering that since there's a formula for any number of resistors in parallel, if that other problem could be posed in such a manner that you could have any amount of times, and thus the parallel-resistors formula could be used.

A different such wording then occurred to me. Particularly: "There's a water hose that can fill a container in 3 hours, and another water hose that can fill it in 5 hours. How long does it take to fill the container if both hoses are used at the same time?" This version of the problem can easily be generalized to any amount of times, by simply increasing the number of simultaneous water hoses. (It also probably is conceptually closer to the parallel resistors.)

I then started thinking how difficult the problem would be if there were an infinite amount of hoses, but their contribution does not diverge? If the problem with just two hoses is tricky enough for someone (who hasn't dealt with this particular problem before), how much more difficult would it be if there are infinitely many hoses?

So I devised a non-trivial pattern for the hoses: "It takes the first hose 1 hour to fill the container, the second hose 4 hours, the third 9 hours, and so on." In other words, the square numbers. So the question becomes "how long does it take to fill the container if all the hoses are used at the same time?"

I thought this could perhaps be an interesting brain twister to think about, as it may not be immediately obvious that this is actually solvable using the parallel-resistors formula. (The sum of the reciprocal of squares is also non-trivial, although the result is well known. This is the so-called Basel problem. However, seeing that this is a case of the sum of the reciprocals of the squares might not be trivial.)

Backstory ends.

So I posted that problem in the forums, thinking that it would be a nice little mathematical puzzle.

My post was quickly removed and marked as "misplaced homework", and I got a warning (with 0 points, but nevertheless). I find this dumbfounding. Mind you, I'm in my 40's, and I graduated from university over 15 years ago. This was most certainly not "homework". I was not asking for an answer because I don't know it. I presented it as a mathematical puzzle.

I don't really understand what exactly counts as "homework", or why this kind of math puzzle is not allowed. How could have I known that this is "homework"? (And yes, I did read the guidelines. They don't really explain why this particular post of mine is classified as "homework".)

 

[berkeman]

I didn't read your whole post (yet), but maybe this old thread will help to explain why we treat all schoolwork-type questions as homework...

https://www.physicsforums.com/threads/homework-coursework-questions.373889/

 

[Nugatory]

I don't really understand what exactly counts as "homework", or why this kind of math puzzle is not allowed. How could have I known that this is "homework"? (And yes, I did read the guidelines. They don't really explain why this particular post of mine is classified as "homework".)

Any post that would not be out of place in the "Exercises" section at the end of a textbook generally counts as homework, no matter where it actually came from.

If the post is asked in a way that suggests the poster has a basic conceptual misunderstanding, then we will often work on that misunderstanding (for example, in the discussion of third law pairs here) but if it's just a matter of a problem looking for an answer... chances are that the homework forum process will work better.

There is a gray area here, and we don't always get these judgment calls right. Any mentor's action can be appealed by reporting the message you receive about the warning.

 

[Borek]

Problem is - we have no way of knowing whether the question is not a homework, so when in doubt we apply https://en.wikipedia.org/wiki/Duck_test

 

[Warp]

Any post that would not be out of place in the "Exercises" section at the end of a textbook generally counts as homework, no matter where it actually came from.

One has to ask why. Why are questions that "look like exercises" (however that's defined) such a huge problem, even when they are, for example, mathematical puzzles and challenges? What exactly is the problem that this policy is trying to solve?

For example, I once asked the question of why the oceans look blue from orbit. Apparently this wasn't deemed "misplaced homework". But if I ask "what's the sum of the reciprocal of squares?" that is deemed as homework? What's the essential difference between those two questions, making one problematic and the other not? And, once again, what exactly is the problem, the issue, that the classification, the distinction between those two things, is trying to solve?

 

[Vanadium 50]

What exactly is the problem that this policy is trying to solve?

People posting homework in the non-homework forums where they

• Don't have to follow the template
• Don't have to tell us what they have tried
• Don't have to show any work

 

[berkeman]

What exactly is the problem that this policy is trying to solve?

Did you read the old thread that I linked to? We frequently have posters who try to post homework problems and disguise them as non-school questions. Those often get deleted instead of moved, depending on how much effort the OP has shown.

And you will usually get good responses in the HH forums anyway, even if the question seems like a puzzle to you or is for self-study. As long as you show good effort, we can provide lots of advice and help.

 

[berkeman]

And to add a couple more points in case they help...

Sometimes posts *are* about textbook problems, but are obviously not homework because the OP has already solved the problem and is asking a thematic or procedural question about the solution. Those threads can go either in HH or in the appropriate technical thread in general. Here's a recent example:

https://www.physicsforums.com/threa...-changing-magnetic-field.977597/#post-6235769
And part of the PF rules is that very advanced homework/schoowork problems can actually be posted in the technical forums, if they are advanced enough and the OP shows lots of their work. That does happen occasionally, and the questions are usually very interesting to work through. I'll do a search when I have time to try to post an example of that type of thread.

 

[Nugatory]

One has to ask why. Why are questions that "look like exercises" (however that's defined) such a huge problem...

They aren't a problem, but they are most effectively handled through the homework forum process. Do remember that we are not here to provide answers - that's what stackexchange.com is for - but to "provide a community for people (whether students, professional scientists, or hobbyists) to learn and discuss science as it is currently generally understood and practiced by the professional scientific community." Exercises, puzzles, and challenges contribute to this objective only to the extent that they support discussions of the underlying scientific principles.

Another concern with puzzle/challenge threads is that someone has to moderate them (Do not dismiss this concern! You are not seeing the stuff that the mentors have taken care of before it ever hits the forum!). These days @fresh_42 runs the monthly "Math Challenge" threads; that's proven to be an effective way of supporting puzzle-style problems.

 

[fresh_42]

For example, I once asked the question of why the oceans look blue from orbit. Apparently this wasn't deemed "misplaced homework". But if I ask "what's the sum of the reciprocal of squares?" that is deemed as homework? What's the essential difference between those two questions, making one problematic and the other not?

The problem here is that you consider homework questions obviously as problematic

(however that's defined)

which they are not. Why should they? It is quite easy:
1.

Any post that would not be out of place in the "Exercises" section at the end of a textbook generally counts as homework, no matter where it actually came from.

2.

Problem is - we have no way of knowing whether the question is not a homework

3.
Others cannot know either, so we cannot establish two different rules. We would soon discuss rules instead of exercises.
4.
Not all members read all threads. Some prefer to answer in the homework sections, others the technical forums, and not few of them wouldn't even consider to answer a question on homework level.
5.
To post a problem in the homework forums does not demean anybody. I got the impression that you feel it would, but there is no reason to assume this.

 

[Warp]

Exercises, puzzles, and challenges contribute to this objective only to the extent that they support discussions of the underlying scientific principles.

I honestly believe that the puzzle I posed offers some interesting insight into how resistors in parallel work, as once one realizes that the same formula works for both cases, it gives a very nice and intuitive analogue to the resistors-in-parallel scenario: They work with the same principle is water hoses with different flow speeds filling a container at the same time.

I think it's a shame that such a marvelous insight into an aspect of physics is lost because of some odd principle about "misplaced homework", which is quickly removed and lost.

 

[fresh_42]

I honestly believe that the puzzle I posed offers some interesting insight into how resistors in parallel work

If so, why did you phrase it like an ordinary homework question:

How long does it take to fill the container if all of them are used at the same time to fill it?

If the intention was to demonstrate a general principle and you wanted to open a DYK thread, then I see no reason to make it an exercise.

 

[bhobba]

I usually do not answer homework questions. But I did one about solving a differential equation. With my background in math I gave the detailed answer at the level a mathematician would do it. But guess what - they only wanted to take the Laplace Transform, solve it, then do the inverse transform. Although often used by engineers etc, mathematician's also are taught that one, but tend to fall back on things like integrating factors, or the auxiliary polynomial, which is how I explained the answer. They were fascinated by my reply, but it was not what they wanted. The message I took away from it was find out first exactly what they want.

Thanks
Bill

 

[Warp]

I think this rule is problematic in that it seems to be based on a very ill-defined and arbitrary concept that's completely up to each individual moderator to judge based on their personal subjective opinion. This means that a visitor to these forums has pretty much no way of knowing if a question will be deemed by some moderator as "looks like homework to me" or not, because it's completely up to that subjective opinion of whoever happens to be moderating.

Someone may well be asking something in all earnestness, because they are passionate about it and have been thinking about it, and want to discuss it... only to get their post classified as "homework" and removed, and receive a warning. That's quite discouraging. It makes people wary to ask anything, lest they get yet another warning and have the post removed. It doesn't feel like a very warm and welcoming environment to ask simple things. On the contrary, it discourages people from asking and getting more information about something they may be passionate about.

Is that really what you want?

 

[mfb]

I didn't see infractions handed out if it is not obviously homework in the wrong forum and of the style "solve this for me, go!". Questions that are somewhere in between are often moved between forums. The thread stays, the user can get answers, but now in a forum where they will get better answers.
Someone passionate about a topic asking about a homework question will include their thoughts about that problem.

 

[Warp]

Well, when I go to my "your threads" page, I cannot find the thread in question (that elicited this complaint). Either it has been removed, or moving a thread removes it from that list. Either way, I can't find it.

 

[fresh_42]

Well, when I go to my "your threads" page, I cannot find the thread in question (that elicited this complaint). Either it has been removed, or moving a thread removes it from that list. Either way, I can't find it.

You can go to "Your content" under the "MY PF" label.

The decision homework or not is up to a few cases far less arbitrary and left to the moderators than you think it is. The golden rule "if it has figures it's homework" works in 95% of all cases. It is described in more detail in the rules. The split into technical forums and homework is due to two different goals of ours: helping students solving their problems on one hand, and discussing scientific developments and principles on the other hand. These are two very different goals, i.e. some separation has to take place for otherwise people would be annoyed by the mixture. I still think the problem you want to create is the unwarranted assumption that "homework" is a belittering. That's not the case. And if you were interested in the answer to your question rather than where it is placed, you wouldn't bother anyway.