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This question asked by me has been put on hold

they say that this question belongs to engineering and not physics.

where should i ask this question ?

edit : how can i modify the question so that my post is back from [ON HOLD] ?

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    $\begingroup$ It's unnecessary to copy the question in its entirety here, the link you put in is sufficient. $\endgroup$ – Kyle Kanos Feb 20 '14 at 3:16
  • $\begingroup$ let me fix this $\endgroup$ – Mukul Kumar Feb 20 '14 at 3:17
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Quite honestly, I think it is a perfectly legitimate question for this site since the answer will be based on fluid mechanics. It doesn't take that many votes to close a question however, and we have a lot of theorists/purists around here. If your approach showed a little more personal effort to understand the effect of the bottle's neck on the exhaust, then it likely would have received an answer and/or not have been closed. Also, it wouldn't hurt to cast the question in the language of fluid mechanics.

We are trying to build a repository of quality questions, and questions which can be typed out in 30 seconds will often be closed; the reason for doing so is somewhat arbitrary.

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    $\begingroup$ If the question were phrased more like "How does the curve of a bottle affect the escape of air?" rather than "How do I build a bottle rocket?" I would agree with you. The former is physics, the latter is (what we call) engineering. $\endgroup$ – David Z Feb 22 '14 at 22:53
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Currently, there is no place to ask this question. However, there is an Engineering site proposed in Area 51 that you might want to support. They will not answer any questions at this point (still in the "Definition" stage), but this seems like it'd be on-topic on that site (if it goes live).

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You did ask a engineering question, although it could have probably been a reasonable physics question if asked properly.

This site seems to be largely about theoretical physics. There is a gray area between engineering and applied physics, but I have noticed that questions that aren't about advanced theoretical physics are treated a lot less well than more advanced questions.

However, I would have probably voted to close your question too, not because of the level of physics or the fact that is about applied physics (I personally enjoy those), but because:

  1. The title (Which kind of exhaust should I use?) makes no sense. I can see asking about the type of bottle or the type of proplellent, but the "kind of exhaust"? Huh?

  2. The disrespect shown with the very first letter is not a good start. The first letters of English sentences are capitalized. It's a arbitrary but well known and basic rule. Regardless of how unfamiliar you are with English, that is so basic a rule that there is no excuse. You are saying "I don't care about your silly language conventions and how annoying it may be for you if others don't follow them. I'm more important than you are, so you'll just have to put up with it".

  3. The whole question is just a homework problem dumped on us without any effort on your part. "Here, solve this for me while I go off and do more important things. And no, I'm not interested in the physics, I just need the answer to hand in to get my grade."

  4. "Which kind of bottle exhaust" Huh? The pictures imply you are asking about the bottle, but then what is "bottle exhaust" supposed to mean?

  5. You can't imagine any practical difference between the bottles shown yourself at all? Really!!? It never even occurred to you that size, pressure capability, and weight might have some bearing on the problem? Frankly if you haven't even thought about those issues as possibly being relevant, then you really are at too low a level to ask a question here. How are you going to understand any of the possible answers, other than "Use that one."?

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    $\begingroup$ <your point-1> there is a physics(i meant to ask about the curve just before the exhaust) <your point-2> I'll fix that <your point - 3> this question is not a homework question but it came from my mind while building one <your point-5> I'll try my best $\endgroup$ – Mukul Kumar Feb 21 '14 at 16:11
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    $\begingroup$ I made some changes to my question please reconsider my question $\endgroup$ – Mukul Kumar Feb 21 '14 at 17:36
  • $\begingroup$ For the record: this site is about experimental and theoretical physics, but it is not about how to build things using physics. The difference is roughly that when someone comes asking about a physical principle that affects the thing they are trying to build, that's okay, but when they ask us to do the physics analysis so they can just carry on with building the thing, that's not okay. $\endgroup$ – David Z Feb 22 '14 at 22:55
  • $\begingroup$ @David Z I just want to ask for the theoretical physics(if any) behind the type of bottle chosen and I think that the shapes will make difference in flight time......after that building part is mine. $\endgroup$ – Mukul Kumar Feb 23 '14 at 3:46

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