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The question Why pouring milk from a height makes a chain shape? is marked as a duplicate of the question Wavy stream of liquid.

The first one is about the chain-shape of a stream of flowing milk and the second one about the helical shape of a stream of flowing wine.

The first question had an impressive answer that correctly explained the phenomena. This question was later marked as duplicate. But note that the questions are not similar, both the phenomena are fundamentally different. The helical shape is due to rotation of cross-sectional films, the chain shape is due to their 2-D oscillations.

Now here's where things get complex.

I happened to answer a similar question Why does water fall sort of helically from a cup? which was actually another duplicate of the Wavy stream of liquid question. For writing that answer, I had experimented and documented quite a bit on the flow patterns. Now it turns out that the pattern I observed was similar to the one mentioned in the chain shape question. So I thought the OP was referring to this rather than the helical shape. Hence my answer went on to explain the pattern which was not the one that OP meant.

By the time I got a clear picture of the real situation, my answer had gathered up-votes and was accepted by the OP.

I am confused. I want my answer to be posted in the right place, that is the chain shape question. The current answers to that question doesn't address the 'chain' shape at all, likely because of misinterpretation.

I tried putting links to my answer in the comments but it doesn't seem to be effective in gaining much attention.

So, should I post an exact copy of my answer to the 3rd question (helical flow from cup) as an answer to the 1st question (chain shape flow)? Is it right?

Please let me know if there's any other way. And yes, please do remove the duplicate badge from this question.

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Exact duplicate answers will be deleted; see Help Centre : Why and how are some answers deleted?

If you were to begin a new answer to the unanswered question with a link to the answer that you are thinking of duplicating, then went on to follow some of the same logic in your new answer as you wrote it off the top of your head, the new answer would almost certainly come out with substantive differences from the first one. Once it's written you can decide whether the new answer is different enough from the other to warrant posting. But if you post verbatim or nearly-verbatim copies of the same answer to multiple questions, they'll get flagged and probably deleted. Links are better than copy-paste.

As for your answer that is upvoted but whose relevance you have reconsidered: it might be appropriate to edit the answer to indicate why your thinking has changed, but it could be a mistake to erase, substantially replace, or otherwise vandalize an answer that's earned a lot of respect from the community --- proceed carefully. (This link is relevant : Should wrong answers be edited or replaced?.) If the situation as it stands is especially complex, the way to clarify would be with a follow-up question that links to all the relevant posts and is explicit about their shortcomings.

If you want to attract attention to an under-publicized question, place a bounty.

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  • $\begingroup$ Yes, I will post a new answer. But as of now, the question is closed. Please consider removing the duplicate badge for the question. physics.stackexchange.com/q/175635 $\endgroup$ – Krishnanand J Nov 9 '19 at 15:46
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    $\begingroup$ Oh, I see now. If this meta post doesn't prompt the community to re-open the question that you'd like to answer, then a clarifying follow-up question with appropriate links is the way to proceed. $\endgroup$ – rob Nov 9 '19 at 17:30
  • $\begingroup$ I agree about not deleting/replacing significant parts of an answer which has received substantial upvotes or comments. However I disagree that link-only answers are better than copy-paste answers. The community clearly disapproves of the former (see Are link-only answers acceptable?) whereas the latter are tolerated (see Is it OK to copy and paste part of own answer over and over, to answer new questions?) $\endgroup$ – sammy gerbil Jan 11 at 20:44
  • $\begingroup$ @rob When you state that exact duplicate answers will be deleted you mean answers to the same question, right? It's quite easy to inadvertently post a new answer while editing and overlook that you've created a duplicate. $\endgroup$ – sammy gerbil Jan 12 at 23:23
  • $\begingroup$ @sammygerbil Yes, and. The most common place where this arises from a diamond-moderator perspective is that a new user with a grand unified theory of basket-weaving (or whatever) will find all the questions in the basket-weaving tag and copy-paste some substantially-identical text that's nearly an answer into many of them. We delete those, but it only happensa few times a year. $\endgroup$ – rob Jan 13 at 5:06
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If I understand correctly you are asking about posting the same explanatory answer to two different questions.

I do not see anything wrong with this, even if the two answers are identical. It is possible for two different phenomena to have the same explanation, although you should try to tailor your answer to address the specific issues raised in each question.

As I think Rob is suggesting, you could post a brief answer on one question which refers readers to your detailed answer on another question. However the brief answer would need to be sufficiently self-contained to avoid being deleted as a link-only answer. If the link were to be broken then the link-only answer would become meaningless.

Possibly the two phenomena have different explanations, in which case at least one of your duplicate answers will be wrong and is likely to be down-voted. But a wrong answer would not be deleted by the community, only by the person posting it.

If the two phenomena are the same then one question is a duplicate of the other and would usually be closed. Site policy here seems to be that you should not post an answer if you are aware that the question is likely to be closed. For example if there are already 3 or 4 closed votes, and especially if you have yourself voted to close the question, for whatever reason.

It is acceptable for the same user to post two different answers to the same question, for example proposing two different explanations. But if these two answers gave the same explanation, even if they are not identical, then one of them might be flagged for deletion by a moderator. It seems to be acceptable also for the same user to post two or more different answers to the same question which address different aspects of the question.

Quite often different users post essentially the same answer to the same question. This is often unavoidable and neither answer would be deleted for this reason alone. Such a duplicate answer which was posted hours later might attract down-votes for failing to take note of the earlier answer or to acknowledge ideas borrowed from the earlier answer, but it would not be deleted. Conversely a better answer posted later would not trigger the deletion of an inferior earlier answer.


As to the issue of whether the 3rd question is a duplicate of the 1st, I think it is. I agree with voters that all 3 questions are duplicates of each other.

My reason is that all 3 questions are asking about an everyday-life phenomenon which could quite possibly contain several features which have slightly different - or possibly completely different - explanations.

The users who posted these questions have used different words to describe what puzzles them (chain shape, wavy stream, sort of helical) but they failed to make any distinction between subtly different features of the same phenomenon. I do not think they were intending to make any such distinction.

If the question were a purely abstract one then a particular feature could be singled out in the conditions imposed by the question-setter. Those different features with different explanations would distinguish them as separate questions asking about separate issues. However in this case the questioners do not seem to be interested in any particular feature other than the general waviness of the flow while liquid is poured from a container of some sort.

Consequently I think it is up to those who answer these questions to distinguish between the different features of the wavy flow and propose different explanations for them. As I have suggested above, different answers to the same question could legitimately address different features of the everyday-life phenomenon.

Therefore because I think these 3 questions are essentially the same I do not think your answer to helical flow from cup has been posted to the wrong question. It is not necessary to re-post it because you would be answering the same question not a different question. Your comment providing a link is good enough to re-direct users to a valuable answer. It will gain up-votes which will attract more attention. The link is also displayed more prominently to the right in the Linked column which serious users looking for good answers will be sure to check out.

Although the question where you posted your answer has been closed, so that further answers will be directed to the open question, your answer itself has not been deleted. The closed question and your answer will still appear in searches.

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  • $\begingroup$ Any reason for the down-vote? I am willing to learn from critical feedback. $\endgroup$ – sammy gerbil Jan 11 at 21:46
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    $\begingroup$ Probably someone doesn't agree with your thoughts here $\endgroup$ – BioPhysicist Jan 12 at 15:34
  • $\begingroup$ @AaronStevens Agreed. But which thought? I've included several. $\endgroup$ – sammy gerbil Jan 12 at 23:16
  • $\begingroup$ I'm not sure. I didn't down vote $\endgroup$ – BioPhysicist Jan 12 at 23:24

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