Wikipedia:Reference desk/Archives/Science/2024 February 5

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February 5

I have requested change

Recently, I have requested change in Talk:Potassium but no one replied. Hope someone jump in and let me know! 2405:4802:64C7:BF70:B50C:773B:1A40:16BA (talk) 02:56, 5 February 2024 (UTC)

Regardless of what the time was in Vietnam, you made your request on a Sunday morning in Europe, and in the early hours of Sunday in the USA, where the bulk of English-language Wikipedia editors live. Please remember that Wikipedia does not have a 24-hour duty roster of paid editors – we are all unpaid volunteers, who do everything in the spare time available from our everyday jobs and lives.

On the Help desks, you might reasonably expect a response in a few hours (less if you're lucky); on the Reference desks perhaps longer; on an article Talk page, you should allow at least several days. I'm sure an editor interested (and competent) in this type of correction (so not me) will evaluate your request within a week, and fulfil it or not according to what they think appropriate. {The poster formerly known as 87.81.230.195} 90.199.208.215 (talk) 03:09, 5 February 2024 (UTC)

I'm sorry, as far as I'm concerned, the Help desk is suitable only for questions involving editing and using Wikipedia, not demanded for questions about general knowledge and questions that need broad agreement. I'm afraid this doesn't fall into those categories, thus not count as a proper enquiry and may need consensus before performing the edit by my request. As a result, I seek for help in this page, reference page. 2405:4802:64C7:BF70:20BF:895B:4915:B58A (talk) 04:39, 5 February 2024 (UTC)

I wasn't advising you to ask on another Desk. I was advising you to be more patient, and wait longer for a response to your Talk page request. {The poster formerly known as 87.81.230.195} 90.199.208.215 (talk) 10:08, 5 February 2024 (UTC)

Is 9.8 meters per second squared really accurate?

Is the figure 9.8 m/s² really accurate for the gravitational acceleration on Earth? It seems overly simplistic to me. I figured that the actual value would be more variable based on an object’s mass and distance from the center of the Earth (as both are factors in calculating the force of gravity objects exert on each other). Primal Groudon (talk) 04:49, 5 February 2024 (UTC)

The article Gravity of Earth discusses the variation of g depending on various parameters. --Wrongfilter (talk) 04:55, 5 February 2024 (UTC)

Mass doesn't matter, but distance from center of the earth does. EvergreenFir (talk) 05:05, 5 February 2024 (UTC)

Yeah, now that I see it, the object’s mass cancels itself out, leaving us with just the UGC times the mass of the Earth divided by the square of the distance from the center of the Earth. Primal Groudon (talk) 06:56, 5 February 2024 (UTC)

It feels like we should include a brief review of accuracy and precision; "9.8" is accurate (with respect to the standardized gravity of Earth) to a few parts per thousand, and it's precise to two significant figures. Beyond those special adjectives, we might also say that one is engaging in a category mistake when they conflate "inaccuracy" of the standard parameter with well-understood variation in magnitude of the measured acceleration due gravity caused by location and realities of the shape and mass-distribution of Earth. This is also - yet again - categorically distinct from any theoretical question about whether such measurements ought to be sensitive to the object's mass (...it ought not be, based on pretty well-established physical relationships, but the effort to re-establish this certainty would be an interesting exploration of experimental and theoretical physics).

All of these ideas raise real and valid concerns; but these concerns are best described using words other than "accurate" or "inaccurate." Nimur (talk) 13:50, 5 February 2024 (UTC)

The section Gravity of Earth § Comparative values worldwide gives the reader a good idea of the variation one can expect while remaining earthbound. It may be assumed that the figures in the table are accurate within the precision with which they are presented.  --Lambiam 14:37, 5 February 2024 (UTC)

Exactly, and therein comes both the issue of accuracy vs precision and significant figures for the "9.8" value. According to that article, surface varies from 9.7639 m/s² to 9.8337 m/s². Of course, one shouldn't just assume that the average surface gravity is halfway between those two numbers, but we can say with a high degree of accuracy that the surface gravity is 9.8 m/s², which for most applications is going to be more than good enough. With far more measurements taken around the globe (which might already have been done), we could give that average with greater precision, but I imagine any application that would benefit from that higher precision would need to know the local surface gravity to a high precision and not the global average surface gravity. I would imagine that once you are out at a distance where a global, rather than local average of high precision is of use, you are also at a distance where you shouldn't be calculating gravity based on surface values anyways.

TLDR the needed precision depends upon the needs of the application, and the highly accurate 9.8 m/s² is precise enough for most everyday applications and, when it isn't precise enough, a highly precise global average would probably have a too low a local accuracy to be useful to said application. --OuroborosCobra (talk) 14:51, 5 February 2024 (UTC)

Naming of electromagnetism and optics standards

In Wikipedia and elsewhere we find different names like $I_{\nu (\nu ,T)},B_{\nu (\nu ,T)},B_{\nu T},M^{0}$,etc... for things that seem to be the same.
Is there a naming standard referenced somewhere?
Malypaet (talk) 09:30, 5 February 2024 (UTC)

I don't think there is, at least not among physicists (but there may be engineering regulations that I'm not aware of). Having said that, I believe that I've seen the convention that B refers specifically to a Planck spectrum, whereas I is the physical quantity "intensity" regardless of whether the spectrum is Planck or something else. --Wrongfilter (talk) 09:37, 5 February 2024 (UTC)

In the last link on wikipedia you gived me, one find:

$M^{\circ }=\sigma T^{4}$

I find also:

$P=\sigma T^{4}$

${\frac {P}{A}}=\sigma T^{4}$

$B_{\nu }(T)$ or $B_{\nu (\nu ,T)}$,etc,...

So, in fact there is no rule, it is like "Happy hour"...

I have just to give the naming convention at the beginning of my text!
Malypaet (talk) 13:39, 5 February 2024 (UTC)

Where do you see $B_{\nu (\nu ,T)}$? To me this notation looks confused. I think this ought to be $B_{\nu }(\nu ,T),$ in which $B_{\nu }$ is the name of a function and $(\nu ,T)$ is its argument. So the subscript $\nu$ is not a variable; the second $\nu$ is.  --Lambiam 14:25, 5 February 2024 (UTC)

What branch of physics discusses a given stationary system containing moving bodies?

Maybe Thermostatics? Maybe Hydrostatics? Maybe Aerostatics? I guess almost all branches of physics may discuss that, but I'm asking about the main branch. 2A06:C701:746A:1600:7422:E3A5:9217:C109 (talk) 09:31, 5 February 2024 (UTC)

Easy - physicists study stationary processes! Nimur (talk) 13:34, 5 February 2024 (UTC)

The adjective stationary means that something remains invariant as time progresses. What kind of system do you have in mind and which are the unchanging aspects that lead to its being characterized as "stationary"? Ergodicity with respect to its phase space? This is something studied in dynamical systems theory – not by itself a branch of physics, but applied in many different branches.  --Lambiam 14:15, 5 February 2024 (UTC)

If anything is moving inside the system, then "-statics" is not quite appropriate. Galaxies are stationary systems (approximately) even though all the stars in a galaxy are swarming around like crazy. In a way even the Solar System is stationary. Stationary systems appear in all many branches of physics; which branch is appropriate for describing any particular system depends on the characteristics of the system, for instance how many particles make up the system, which forces act between the particles, etc. --Wrongfilter (talk) 14:23, 5 February 2024 (UTC)

By "stationary" I mean "at rest". Actually, my aim is to solve a contradiction I'm coping with, regrading systems at rest, so I'd like to know where the whole issue may be dealt with. See below my new thread. 2A06:C701:746A:1600:7422:E3A5:9217:C109 (talk) 20:35, 7 February 2024 (UTC)