# Reopen request - Question about water splash on impact

This question was closed under the presumption of being off topic for being a homework-like question. Honestly, I cant see how this question is either off topic or a homework question since it ask a conceptual question about a nontrivial physics phenomenon and does not violate any of the rules specified on this set of guidelines.

And I'm not the only one wondering why was this question flagged:

How is this a homework question? – user7777777

As ZeroTheHero pointed out in this recent discussion:

One way to make a question more conceptual is to see if you can phrase it without numbers...if you can clearly write a question without resorting to numerical values, it will be conceptual rather than overly specific.

Which is exactly how the question is phrased. Moreover, OP is asking in the comments for guidance on how to make his question better (in case that was the issue).

So can you open it again? Also, why was it closed in first place?

• I would think it's not exactly homework, but it was closed as off-topic because it asks for a formula without supplying any thoughts or research efforts. Now whether that's justified... that's an appropriate question. I would cast a reopen vote if the question was something on the lines of "what factors is that splash dependent upon?". I'm upvoting this question because I really like the fact that you put a lot of background about related suggestions and you made a descriptive-ish title. – user191954 Oct 2 '18 at 15:32
• @Chair I dont think it is asking for a formula: "Is there a way to compute the height hwater that the water will reach after the object impacts on it?". I think that you are getting that idea form the fact that the author used symbols to describe his variables (volume V, and mass m, etc) which I dont think is enough to make that assumption. And even if that were the case, it should be clear to the author and the rest of the community, how can the author improve this or future questions if it is misleaded about why questions are closed? – user190081 Oct 2 '18 at 15:41
• Your question is a duplicate of Height of Water 'Splashing' – John Rennie Oct 2 '18 at 15:47
• @user190081 Now that I think of it, you may be right... formulae are just one way of answering it. Maybe the appropriate close reason is duplicate then. Oh well. – user191954 Oct 2 '18 at 15:49
• @JohnRennie I would be totally happy if that were the closing reason, I think it should be changed (with the link of the duplicate question, of course). This rises another issue, that guidelines are not applied equally, but that might be topic for a different discussion. – user190081 Oct 2 '18 at 15:53
• @Chair as John pointed out, it is indeed a duplicate, and the closing reason should reflect this. Marking it as a duplicate will also allow to provide a link the previous question which will help the author to resolve its doubts. – user190081 Oct 2 '18 at 15:57
• @user190081 Yep, linking the dupe would be much better. I don't think it's a good idea for the community to start a reopen vote and then close it again for a different reason. hopefully a mod'll come by and do both actions unilaterally; I think it's improbable that anybody'd disagree that the close reason should be changed. Interestingly, I don't fully understand why the new one was closed as homework while the old one wasn't; I don't see such a significant difference between them, beyond the tone. – user191954 Oct 2 '18 at 15:59
• @user190081: I agree that your question is not homework, and I suspect this is a mistake by DavidZ. In fairness to David, and all the mods, they have to check many such questions in their own time (and without any payment for it!) and mistakes do happen. Posting here in the Meta is exactly the right way to address such issues, and if the question weren't a duplicate it would be rapidly reopened. As it is, I imagine a moderator would be happy to change the close reason, though I suspect this won't be such a high priority. – John Rennie Oct 2 '18 at 16:00
• @Chair Oh, yes. That's what I had in mind. If a mod can directly make that change it should do it. – user190081 Oct 2 '18 at 16:01
• @JohnRennie kind of inconsequential point, but user190081 isn't the one who asked that question about water splashing. But it was nice that s/he took it up on meta on behalf of the OP since the a new user probably doesn't have a very good idea of how meta and stuff work. – user191954 Oct 2 '18 at 16:04
• Even if it's reopened, it's an abysmally poor question, because the tiniest amount of common-sense should have made the OP realize the answer depends more strongly on the shape of the object than on its mass and volume. The so-called duplicate question specifies a sphere. This question doesn't. – alephzero Oct 6 '18 at 17:03
• @alephzero Being honest, both questions are worded nearly identical, with the difference of the shape specification and the drawing. And if anything, specifying that the object must be a sphere makes the previous question even more homework-like than this one. I also disagree with the claim that the answer depends more on the shape, you can throw any object of any shape into water, but if the object has very little mass I assure you that you are not gong to have a big splash. – user190081 Oct 8 '18 at 13:08
• @user190081 I didn't say the splash size was independent of the mass. But compare the size of splash from a human diver doing (1) an Olympic-medal-standard high dive, (2) a belly-flop, from the same diving board. Same mass, same vertical speed - the only difference is the shape. – alephzero Oct 13 '18 at 13:20
• "both questions are worded nearly identical, with the difference of the shape specification" - So they are both identical, except one of them doesn't specify something which has a very big effect on the answer, and the other does specify it. Your point is what, exactly? – alephzero Oct 13 '18 at 13:22

I put that question on hold because it sounded like the type of question that could be a homework problem or educational exercise. Now, looking back at it, I'm not as sure as I was at the time I closed it, but I haven't changed to the opposite opinion either - that is, my thoughts on that question are conflicted but I still come down marginally closer to "should be on hold" than to "should not be on hold". Nevertheless, as people have pointed out in the comments, it's a duplicate of another question, so I'm happy to reopen it and mark it as a duplicate instead. (We could also discuss whether the duplicate target should have also been on hold as homework-like, but that should be a separate matter.)

A big part of the reason I put the question on hold was that it doesn't actually ask anything conceptual. Here is the core of the question for easy reference:

Suppose that there is a small object (e.g. hand sized) with volume $$V$$ and mass $$m$$ that falls into a water container from a height $$h_0$$ and with initial velocity $$v_0$$. Is there a way to compute the height $$h_{\text{water}}$$ that the water will reach after the object impacts on it?

This is just asking us to calculate something: given some input values, it seems that the question just wants a formula to produce an answer. That's not conceptual. There are a number of ways in which this question could be edited to ask something slightly different that would make it conceptual; for example, if the question had presented an argument for why it seems to not be possible to calculate the desired value from the given inputs and asked about that argument, then it would probably be a conceptual question. Or if the question had demonstrated a significant amount of prior work trying to tackle this problem and asked about a way to connect one specific piece of a calculation to another specific piece, that might also be conceptual.

I wonder if you might have been led astray about the meaning of "conceptual question" by this:

if you can clearly write a question without resorting to numerical values, it will be conceptual rather than overly specific.

I don't think that's true. At least, it's definitely not the case that any question that can be written without using numbers is conceptual. If this were the case, you could take almost any do-my-homework-for-me type problem and make it "conceptual" by just replacing the numbers with variables, but I'm sure I could point you to many examples of questions where you could make that replacement and yet we would all agree that it would still be off topic.

The inverse of that rule might be useful, in that a question which is written using specific numerical values is quite likely to not be conceptual. But it takes more than just removing the numbers to make the question conceptual. Off the top of my head, here are couple rules of thumb that I find useful:

• Conceptual questions are often "why"-type questions rather than "how"-type questions.
• Most conceptual questions require some amount of exposition (i.e. words, sentences, paragraphs) to answer; they're impossible to answer with only mathematical expressions or equations.