I know as a general rule it's good to keep questions simple if possible. I also think they can differ from case to case.

Can someone please suggest whether to split this question into two? Or leave it together as question 1 may help provide context to question 2?

Thank you

  • $\begingroup$ There is some flexibility, particularly when questions are so closely related that it's sort of silly to separate. Can you clarify why you think this one might need to be split? It doesn't look like anybody commented that it should be and it's gotten some answers already. $\endgroup$ – tpg2114 Jun 18 '19 at 20:56
  • $\begingroup$ @tpg2114 - It has 3 votes to close and I don't know what the problem is. I thought it might be the 2 in 1 question. $\endgroup$ – Alex Doe Jun 18 '19 at 21:06
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    $\begingroup$ There are two votes that it is an engineering question and one that it's unclear. I wouldn't worry too much about it at the moment, it takes 5 to put it on hold. If it does get 5, then you'll see the majority reason selected and can try to edit it so it can be reopened. $\endgroup$ – tpg2114 Jun 18 '19 at 21:10

To answer the general question here -- it is, sometimes, okay to ask a couple questions at once if those questions are so tightly related that they can't really be separated. Your question is actually a decent example of that, because although you have written it as two questions, it's basically just one -- "Does the surface of a lens need to be a perfect sphere segment to operate as a concave lens" or something to that effect.

All the other details and questions are kind of ancillary to that. Once you understand what the shape needs to be for a lens to work as expected, you can answer for yourself whether the lens you proposed would work. Or, at the very least, you could ask a follow on question about what shape (or how to derive/determine the shape) a surface takes under suction or something to that effect.

From your comments, you are concerned because your question has (at this time) 3 close votes. Two of those votes are because the question appears to be about engineering. One is because somebody thought it was unclear.

It takes 5 votes to close something, and so until then it may not be something to worry about. You got some answers, it wasn't downvoted, so it could just be that a few people have an opinion but not enough to close it.

However, I can see why some feel it meets our definition of an engineering question. Particularly because you want to know if the approach you've chosen (vacuum pressure on plastic sheets) would work.

This can easily be modified so it is less about how you create the shape and more about A) what shapes are required, and B) a second question eventually about how to derive/determine/something the shape of an elastic surface under pressure forces.

Without knowing the final form of what B) might look like, I can't definitively say what would or wouldn't be on topic. But trying to determine the leading-order terms to balance external forces and internal stresses in a material could be on-topic if it is written correctly and doesn't run afoul of our policy on homework and exercise type questions.

  • $\begingroup$ If I write B) as "What shape will a plastic sheet take under pressure.." it would look a lot like a totally separate question with not much to do with the q. A) and then maybe a split in 2 question will be needed? $\endgroup$ – Alex Doe Jun 18 '19 at 22:01
  • $\begingroup$ @AlexDoe It's hard to say without seeing it written out. People in the chat room might be able to help you craft it correctly. But I think "What shape will a plastic sheet take under pressure" would probably end up closed as either homework-like or engineering. $\endgroup$ – tpg2114 Jun 18 '19 at 22:12
  • $\begingroup$ I don't think you need to split apart your current question -- in fact, it has answers already and so it would be poor form to radically change it. I wouldn't worry about it unless 5 people vote to close it and it gets put on hold. Then you can revise it, which will put it into the reopen queue and if you've addressed the flaws, then it will be reopened when 5 people vote to do so. $\endgroup$ – tpg2114 Jun 18 '19 at 22:13
  • $\begingroup$ My question eventually got put on hold as "off topic"/"engineering". I did a search in physics SE for "What shape" and found lots of questions asking what shape would x material take under x circumstances. Why is mine different? Just because this physics concept would be used in some engineering project later on? $\endgroup$ – Alex Doe Jun 19 '19 at 17:16

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