Often we get questions of the form

  • "How to build this particular device?" or
  • "Why was this design implemented in such-and-such product?"

Are these questions appropriate for Physics Stackexchange?

Note: this is an faq-style meta post, and it is a work in progress. We (you, the community) will be adding to it over the course of the next few days. If you have suggestions, leave comments so we can incorporate them, or (if not controversial) incorporate them yourself. –  Chris White Jul 9 '13 at 19:25
The goal is for this to be linked when we close questions as off-topic for being about engineering and not physics, similar to our homework policy. –  Chris White Jul 9 '13 at 19:26
Related: Can we ask applied Physics questions?. My answer contains some limits not mentioned here that I think should apply. –  dmckee Jul 9 '13 at 21:57
Not fully complete, but it's good enough to be FAQ-ified for now. –  Manishearth Jul 10 '13 at 1:22
Relevant query for finding such questions to example-ify –  Manishearth Nov 15 '13 at 8:14

5 Answers 5

up vote 11 down vote accepted

What exactly is the relation between physics and engineering?

Physics is a natural science. It seeks to study how and/or why nature works the way we observe. Engineering applies our understanding of nature to specific, real-world problems, creating new devices, products, or processes to solve those problems.

While both physics and engineering often work together, using similar toolsets from mathematics, they have different goals. Put one way, physics seeks to break down the world around us into more modular parts and more fundamental relations, while engineering seeks to reassemble those pieces into a new form.

So engineering is off-topic here?

Often, yes. When constructing a product for use in the world, there are many considerations that go into the decision-making process. The underlying physical principles are only a part of this. The physics community, while often tangentially knowledgeable in these areas, is not the place to seek guidance when ease-of-use, manufacturing costs, material availabilities, etc. are also primary considerations.

Are any engineering questions allowed?

Questions inspired by engineering considerations can be on-topic on this site. For instance, it would be valid to ask if there is a fundamental physical limit to

  • How well one could resolve an object with a telescope,
  • How energy-efficient a computer can be, or
  • How small a current can flow through a wire.

Similarly, questions like What really allows airplanes to fly? that ask how a man-made system works are also on topic, as long as they aren't too broad. Questions about the physical reasoning and analysis that lead to design decisions are on topic; questions seeking help designing or building something is off topic.

What about experimental physics and laboratory equipment?

Physics is not just theoretical, and experimental physics is on topic here. This includes questions about the usage of laboratory equipment.

If my question doesn't belong here, where can I ask it?

There are sites that allow certain types of engineering question on the Stackexchange Network. Your question may be suitable at one of the following:

Admittedly, that list does not cover all forms of engineering. You can always propose a new Stackexchange site or support a proposal over at Area 51. For a quicker response, users with at least 20 reputation can always bring up a question in our chat room. Note that there is no guarantee that anyone there has any input, and The h Bar is not a Q&A unto itself, but still we physics enthusiasts tend to like problem solving in general, as well as interesting questions.

I would remove Reverse Engineering from the list as it's not really "engineering" in the traditional sense. It's about disassembling software primarily. –  tpg2114 Jul 10 '13 at 2:45
@tpg2114 Done :) (though I really wish we had a site dedicated to physically breaking things...) –  Chris White Jul 10 '13 at 3:02
What about question about Mechanics. Like beam deflections, elasticity? What about rigid body mechanics and statics? Do they belong in PE? –  ja72 Jul 12 '13 at 13:23
Hopefully, if we can get Fabrication & Manufacturing into Beta there will be somewhere else that engineering questions which don't fit elsewhere can go. –  Mark Booth Jul 12 '13 at 14:06
@ja72 Those are all on topic here in my opinion –  tpg2114 Jul 12 '13 at 14:41
@MarkBooth If/when it (or any other engineering site) goes into beta, feel free to add it to the above post if no one else does. –  Chris White Jul 12 '13 at 15:11
Thanks @ChrisWhite - it's because it isn't in beta yet that I posted the link as a comment rather than editing it into the answer. If we keep up the current fairly steady rate of commits, it shouldn't take more than around 3 months. *8') –  Mark Booth Jul 12 '13 at 16:32

OK. I am an Engineering Physicist. And in my just-above-zero engineering experience, the application of Physics is of paramount importance. That being said, asking questions like "how to build this device? "should be off topic. However, questions related to engineering where questions pertain to a physical concept that has to be used, should be welcomed. After all, that is the goal of physics-making things that don't exist and improving things that exist for the good of mankind .

I'm an EP student, afaict most of the stuff that is done in EP is not considered off topic here. Of course, if you ask how to design a system that has certain properties, that would be both broad and off topic as engineering. If you read the policy draft above, you'll see that "questions pertaining to physics" has been covered, at least partially. –  Manishearth Jul 10 '13 at 8:00
"After all, that is the goal of physics-making things that don't exist and improving things that exist for the good of mankind." Actually that is not the goal of physics, it is the goal of engineering. Physics is about understanding the natural world. –  David Z Jul 19 '13 at 5:20
@DavidZ: I don't think you can claim that statement. We all do physics for different reasons. One might say the goal belongs to the agent, not the field. Certainly you may disagree on that but my point is that it's not obvious either way. –  DanielSank Dec 31 '14 at 5:51
@DanielSank well, yes, we can each have our own opinions, but I do unequivocally disagree with that. I think you can, in many cases (including this one), say that a given goal belongs or doesn't belong to a given field, and it need not be a goal shared or not shared by those who practice the field. One might certainly perform tasks that qualify as physics with the overarching goal of making and improving things that exist for the good of mankind, but that doesn't mean that is the goal of physics. –  David Z Dec 31 '14 at 6:21
@DavidZ: That is a somewhat Plantonic view (think of the "forms"). I guess I don't share it. –  DanielSank Dec 31 '14 at 11:45

Graduate physics students, and postdocs, often are in the position of having to design and build their own experimental apparatus. Questions about 'engineering' experimental apparatus for research seem on-topic to me. Questions about 'engineering' something intended for commercial use seems off-topic because there are people paid to do that.

Yes, but we don't cater to all needs of physicists/physics students. The aim here is to create a focussed site on physics concepts. –  Manishearth Jul 19 '13 at 9:01
Wow, that's incredible. You mean experimental physicists have no place raising questions here about experimental design? Testing hypotheses by experiment is still a part of physics. Seems like there are many examples of purely theoretical physics questions, might improve things by balancing that with a few more about experiments. IMHO cheers –  Mark Rovetta Jul 19 '13 at 16:04
No, experimental design and technology is explicitly allowed. I'm talking about a different type of question here. I agree that the line is a bit blurry, I'll work out a way to clarify it. –  Manishearth Jul 19 '13 at 19:48
I think this is important as many experimental tricks can be useful to physics students - for example, can I find a cheap reliable electrical vacuum leadthrough for under $10.... the answer is yes and may be valuable for a grad student building something –  tom Dec 1 '14 at 3:12
I don't see how the setting being commercial or not should matter at all. Grad students might want to ask the same questions for their work as someone interested in selling a technical product. –  DanielSank Dec 31 '14 at 5:52

From my own (not necessary unique) experience as a 'Backyard Physicist' (note - this is not the same as 'hobbyist'), I have to make my own tools a lot of the time.

The division between applied physics and engineering, to me at least, is:

  • asking about the specific physics principles involved with the specific aspect of the tool and questions about the measurement of a particular specific parameter are applied physics and ought to be on-topic as these questions seek to apply the theoretical physics principles to a practical situation.

  • asking how a tool could be made is engineering and ought to be off topic

Unless a question specifically asks for the 2nd case, it should not be assumed that they are asking for it.


As another answer mentioned Engineering is Physics (use same models, same domain, same principles). i would say engineering is practical physics (associated in some part to experimental physics as well).

So engineering as practical physics is certainly on-topic on this site.

Many times, real-world examples or analogies are used in physics (they are used in mathematics for crying out loud), to make concepts more intuitive or applicable.

Problem solving is not only for engineers. Physicists (and mathematicians and other domains) actually solve problems (and i mean practical problems as well).

R. Feynman and his diagrams were considered as less than physics (actually Schwinger considered them to be engineering "..all S and T lines and rays..", reference: "Genius, the life of R. Feynman").

i'm sure some people will disagree with providing intuition and real-world analogies.

Plus i would like to mention that some sites actually forbid (explicitly or implicitly) practical questions about physics. Personally i strongly disagree with this.

The whole point is not memorisation of given rules, but actual comprehension of the why and how to the point of actual application (and even beyond).

No, engineering is a lot more than practical physics. Yes, physics and other concepts from science need to be understood. But, engineering also includes tradeoffs with cost, manufacturability, market acceptance, speed of design, component availability, make versus buy, etc, etc. See Chris White's answer. He explained the difference between physics and engineering quite well. –  Olin Lathrop Nov 10 '14 at 14:48
@OlinLathrop, yes i know, but what i'm saying here is those practical physics questions which are closed as engineering. Not enginnering as a discipline and its potential relations to marketing. Practical physics to the point of actual application (i have personal examples as well of such closed questions or answers). This is the point i emphasize. –  Nikos M. Nov 10 '14 at 15:20

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