Timeline for Why was my question put on-hold?
Current License: CC BY-SA 4.0
22 events
| when toggle format | what | by | license | comment | |
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| May 13, 2018 at 13:54 | comment | added | knzhou | @AccidentalFourierTransform That's a shame, I'm really glad we didn't lose you because of it! | |
| May 13, 2018 at 13:23 | comment | added | AccidentalFourierTransform | @knzhou for the record, my first question was closed :-P | |
| May 13, 2018 at 9:26 | comment | added | knzhou | @AccidentalFourierTransform When I classify questions as physics or math I'm taking the perspective of an intro physics teacher. Usually, the questions will contain both physics and math errors, but you need to put some effort in to figure out which of the two, the physics or the math, is the real issue. Teaching requires you to put yourself in the shoes of the OP, not just sit back in an armchair and say "that is blatantly mathematically invalid". | |
| May 13, 2018 at 9:24 | history | edited | knzhou | CC BY-SA 4.0 | added 26 characters in body |
| May 13, 2018 at 9:21 | comment | added | knzhou | @AccidentalFourierTransform I think we're going in circles here. What is "blatantly false" depends on how much you know. I am sure some of this site's experts could have closed your first questions for being "blatantly" wrong. Are they any introductory physics questions involving a problem the OP gets wrong that you wouldn't close under these grounds? | |
| May 13, 2018 at 9:14 | history | edited | knzhou | CC BY-SA 4.0 | added 484 characters in body |
| May 13, 2018 at 9:10 | comment | added | knzhou | @ZeroTheHero It seems completely clear to me. The problem statement says "X", where X is something we agree is true. The OP says "but I thought not-X". Then they OP shows their work, which also concludes "not-X". Then they ask what is going on. | |
| May 13, 2018 at 2:22 | comment | added | ZeroTheHero | I simply do not understand the question. Never mind the “And clearly the solution to those equations can't depend on initial conditions.” part. Instead I’m trying to reconcile “The basic thing that doesn't make sense is that the frequency of the current somehow depends on the initial conditions of the circuit” but the OP finds $\omega=1/\sqrt{3LC}$ that does NOT depend on the initial conditions. Maybe it’s old age or I’m getting tired... | |
| May 12, 2018 at 23:30 | comment | added | AccidentalFourierTransform | Well, if the question contains "clearly $A^2=A$ for any operator" or "obviously the metric is always its own inverse" or a blatantly false statement like those, then yes: I will vote to close. If the confusion is based on a very basic mathematical misunderstanding, I don't think the question is on-topic. The answer is just "you got the maths wrong", which is not useful to anyone but OP (and one could argue that it lacks research effort, and that the question is unclear, etc.). | |
| May 12, 2018 at 23:26 | comment | added | knzhou | The better you know introductory physics, the more it looks like “just” differential equations. But it doesn’t look like that at all for someone just learning it! There is a stark difference between the physics and the math for beginners, they don’t have them properly linked together yet. Anyone who wishes to retain the ability to communicate with beginners must remember this. | |
| May 12, 2018 at 23:26 | comment | added | knzhou | @AccidentalFourierTransform Where do you draw the line here? Would you close half of all QM questions as ‘not understanding (infinite-dimensional) vector spaces and distributions’? How about most basic GR questions as ‘not understanding Riemannian geometry’? | |
| May 12, 2018 at 23:20 | comment | added | AccidentalFourierTransform | We agree that "The basic thing that doesn't make sense is that the frequency of the current somehow depends on the initial conditions of the circuit." is the key sentence. OP is confused as to why the frequency depends on the initial conditions. So far so good. But you read this as OP not understanding the physics, while I read it as OP not understanding the mathematics of ODE's. I would say both interpretations are correct, and it's up to OP to make the question clear. If they were to edit it, I will be happy to reopen it. As of now, it's still unclear to me. | |
| May 12, 2018 at 23:16 | comment | added | knzhou | Beginners will often make missteps describing their reasoning, they’ll use words wrong, because they are beginners. The job of a teacher is to figure out what they are actually confused about, not hone in on the most inaccurate statement they said in their confusion. One misplaced word (i.e. not saying “frequency” in the third sentence) should not flip their question from on-topic to off-topic. | |
| May 12, 2018 at 23:14 | comment | added | knzhou | See the first sentence I quoted. The OP probably slipped up in the third sentence (that you quoted). From the rest of their work, it is clear that they aren’t so naive as to think initial conditions never matter; with that kind of misunderstanding they wouldn’t be in this course in the first place. They mean it’s confusing that initial conditions affect the frequency, a phenomenon they have not seen before. | |
| May 12, 2018 at 23:12 | comment | added | AccidentalFourierTransform | (2/2) The question is not that OP doesn't understand the physics of the problem, but that the solution to the ODE's didn't match their expectations about what a linear system does. | |
| May 12, 2018 at 23:10 | comment | added | AccidentalFourierTransform | Again, what you say is true if your interpretation of the question is correct. But not according to how I understood the question. For one thing, OP says "And clearly the solution to those equations can't depend on initial conditions.". In other words, for some reason OP thinks that the solution to a linear equation doesn't depend on the initial conditions (which is a purely mathematical statement, and a false one). So, to me, the question is not about a physically counter-intuitive situation, but a wrong mathematical preconception. (1/2) | |
| May 12, 2018 at 23:08 | comment | added | knzhou | It is important to be able to step back and imagine a time when you didn’t know something already. Sure, the question sounds to you like, “I got 1+1=3, but apparently this is wrong, why?”, but with less math background and a beginning student’s undeveloped physical intuition it is a perfectly reasonable thing to ask. For a beginner, the question asked is definitely a more puzzling thing than just “the solution depends on the ICs”, even though it is obvious to us it is just a special case of that statement. | |
| May 12, 2018 at 23:05 | comment | added | knzhou | Sure, it’s true that the answer is “obvious” once you know the full, proper mathematical setup. But that’s true for almost any question. For particle physics? “That’s just how representations work.” For formal QFT? “That’s just how C* algebras work.” Every piece of physics is “just” math, that doesn’t make physics questions math questions. | |
| May 12, 2018 at 23:03 | comment | added | AccidentalFourierTransform | 1) If that is the question, then I mostly agree it should be open. But that's definitely not how I read the question initially, and I'm still unsure that's what OP was trying to transmit. If your interpretation is indeed correct, and OP were to edit the post to make it clear that that is the question, I will be happy to vote to reopen. 2) I didn't mean to say that "obvious answer = must be closed". What I meant is that there is no physics (and, arguably, no maths) in the question (at least in my interpretation of the question, which may wrong anyway). | |
| May 12, 2018 at 22:58 | comment | added | knzhou | @AccidentalFourierTransform The OP is confused because the behavior of this physical system is in conflict with their physical intuition, because, e.g. a pendulum swings with the same frequency no matter how you start it. I can think of many physical systems which demonstrate that this intuition is false. This opens the door to a nice discussion of normal modes. | |
| May 12, 2018 at 22:48 | comment | added | AccidentalFourierTransform | I am probably missing something, but if the question is "how can the solution of a linear system of ODE's depend on the initial conditions?", then the answer is quite obviously "the solution of a differential equation always depends on the initial conditions". How is this a physics question? And what meaningful answer is there beyond "that's how differential equations work"? | |
| May 12, 2018 at 20:14 | history | answered | knzhou | CC BY-SA 4.0 |