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Understanding the total energy in a AA battery

It's not a homework question, and seems very applicable to others. My question had very little to do with the math, and everything to do with the question, "could a single AA battery lift 10,000 pounds a whole foot?". I showed my logic, with a few simple calculations.

How could I rephrase the question?

Edit: I rephrased the question, in order to be less "yes/no" and less "check-my-work".

Can a question be reopened?

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    $\begingroup$ This is effectively a homework question in the check-my-work variety; please see these guidelines for how and when those are on-topic here. Note that the marking of a question as of homework-and-exercises type is independent of the origin of the question (i.e. self-study, formal homework, read it in a book, etc.). Regardless of where the question came from, it reads very much like a textbook set-piece. $\endgroup$ – Emilio Pisanty May 8 at 14:43
  • $\begingroup$ Your comment in no way sheds clarity to the problem or a potential solution. $\endgroup$ – Michael Lewis May 8 at 16:33
  • $\begingroup$ Which part of the linked discussion is applicable? Like I said, I don't care about checking-my-work... I just want to know if my logic is correct. $\endgroup$ – Michael Lewis May 8 at 16:36
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    $\begingroup$ There must be an appropriate way to ask this question... Or are you telling me that there's something inherently wrong or unacceptable about my question? $\endgroup$ – Michael Lewis May 8 at 16:37
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    $\begingroup$ @Michael Lewis: Doesn't the guidelines link answer it or cover it (not a rhetorical question)? $\endgroup$ – Peter Mortensen May 8 at 18:04
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    $\begingroup$ @EmilioPisanty I think your comment would make a pretty solid answer. $\endgroup$ – David Z May 8 at 19:19
  • $\begingroup$ David Z, I asked for help improving my question, not a huge set of guidelines which hardly makes it clear what's allowed and what's not. $\endgroup$ – Michael Lewis May 8 at 19:33
  • $\begingroup$ Every question on this site is of the variety, "here's what I'm thinking, what do you think?". How can you deem all "am I right?" questions as useless? And use the "homework" rule as the reason? $\endgroup$ – Michael Lewis May 8 at 19:35
  • $\begingroup$ It's extremely confusing and irritating... And after all this back and forth, you have nothing to add, except making it clear that you stand behind your decision, and refuse to offer any clarity. $\endgroup$ – Michael Lewis May 8 at 19:36
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    $\begingroup$ I posted a comment on your question containing the relevant equation in a form suitable for the Google Calculator, to show you how to verify your arithmetic, which kind of implied that your logic is correct. My comment got deleted, because we aren't supposed to answer off-topic questions, even in comments. And I guess including the result of the calculation in my comment made it even worse. Oops. $\endgroup$ – PM 2Ring May 8 at 23:54
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    $\begingroup$ Well, it isn’t hard to Google ‘energy in an aa battery’ and see the answer. Nor is it a conceptual physics question. So it got closed. $\endgroup$ – Jon Custer May 9 at 0:38
  • $\begingroup$ @JonCuster how is it not conceptual? Can x watt-hours really lift y pounds? In theory, yes, but in practice is that really possible? Seriously you guys, try empathizing with my perspective. This is completely ridiculous. Because "it reads very much like a textbook set-piece"? After poking around, it seems this community has had this problem for years. You try to close questions for unclear reasons, and get a lot of push back, surprise! $\endgroup$ – Michael Lewis May 9 at 15:24
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    $\begingroup$ And there are nearly 800,000 Joules in a Kristen Kreme glazed donut. Just think how high that lifts a truck! $\endgroup$ – Jon Custer May 9 at 21:55
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Honestly: your question is not very good for the site.

Ignoring losses, does that mean a AA battery could theoretically lift 10,620.9 pounds, 1 foot high?

YES. But of course, that’s not a very enlightening answer.

The next paragraph talks about efficiencies, but it’s not possible to answer “what’s the best efficiency you can hope for” as this would depend on the design of just about everything. Maybe engineers could answer that, in which case your question is still not well suited for the site.

I do not know how one can improve a question to which the answer is a simple yes/no and for which you have already answered YES. Maybe you could flesh out on what physical grounds you feel this is not right, but if you take out the engineering aspect (which to me is the most interesting aspect of your question: how to do it in practice) it’s basically an elementary calculation. I personally fail to find anything conceptual (in terms of physics) in the current formulation.

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Yes, an off-topic question can be reopened, if the author edits it so that it falls within the site guidelines, which are linked in the Closed notice, and in Emilio's first comment above.

Your question currently looks like a "check my work" question, which is why David closed it. That close reason doesn't just apply to checking arithmetic, it also applies to "am I using the correct equation" questions.

I think it's valid to ask about equations if you express it in a conceptual way. That is, you need to ask why $W = mgh$ is the correct equation to calculate the work $W$ in lifting a mass $m$ a height of $h$ in a constant gravitational field with gravitational acceleration $g$.

However, it appears from your question that you don't actually have a conceptual difficulty with that equation. You're just bewildered that a little AA cell can do so much work. ;) So maybe your real conceptual question is "how can an AA cell store 14400 joules?"

But in any case, you need to change your question so that it's asking a conceptual question, as discussed in How do I ask homework questions on Physics Stack Exchange?

I see that you have edited your question since it was closed. That edit automatically sent it to the Reopen review queue. But your question still isn't a conceptual physics question, so it doesn't yet qualify for reopening. And asking about efficiency is turning it into an engineering question, rather than a pure physics question. Note that future edits will not send the question to the Reopen queue, but they will bump it to the top of the Active view of the main question page, which means that people will see it and possibly vote to reopen it, if they think it deserves to be reopened.


(BTW, Google is "smart" enough to answer things like 4 watt-hours in foot-pounds).

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  • $\begingroup$ How is it not a conceptual physics question? The math part is not the question, we've all agreed that's simple and correct (and yes, I used Google). It's the logical conclusion that I'm having a hard time with. Also known as a "concept". You can't talk about these energy conversions without talking about (efficiency) losses. And you're right, it might be more of an engineering question, I'll try over there. $\endgroup$ – Michael Lewis May 9 at 14:03
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    $\begingroup$ @MichaelLewis It may be clear to you what your conceptual question is, but it's not necessarily apparent to readers of your question. By definition, 10620 foot-pounds of energy can lift 10620 pounds through 1 foot, ignoring losses. (Eg, the AA battery may be running a small water pump, slowly lifting 1272 US gallons of water from one tank to a tank a foot higher). So what is your conceptual question, exactly? $\endgroup$ – PM 2Ring May 9 at 14:13
  • $\begingroup$ @MichaelLewis Your question doesn't have a negative score, and if you do give your question a conceptual focus, the odds are high that it will be reopened. But I agree that it may be more suitable for Engineering.SE. $\endgroup$ – PM 2Ring May 9 at 14:23
  • $\begingroup$ Can a AA battery lift a pickup truck? Is that really the problem here? There are several concepts I was unsure of (the watt-hours to pound-feet conversion, the interpretation of pound-feet as a quantity of lift, and then the practical "could you actually do it"). We're splitting hairs. The reality is, your moderator didn't like my question, and nobody has been able to clearly articulate why. So don't blame me for not being clear. I think my conceptual question was 10x clearer than any of the reasons given for closing my question. $\endgroup$ – Michael Lewis May 9 at 15:08
  • $\begingroup$ By the way, it's still unclear to me exactly what the issue is, and I have no idea what sort of "fix" is in order. That's why I'm here, still waiting. It's unclear whether your reason (that it's not conceptual enough, or the conceptual question isn't clear enough) is the community consensus. It's unfortunate you're trying to fight their battle. Why doesn't David Z stand up for his decision? Or any of the other moderators? $\endgroup$ – Michael Lewis May 9 at 15:12
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    $\begingroup$ @MichaelLewis Nobody is blaming you for anything. But it's up to you to edit your question so that it asks a clear conceptual question. If you do that, I'm happy to cast a reopen vote on your question. $\endgroup$ – PM 2Ring May 9 at 16:16

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