Wikipedia:Reference desk/Archives/Science/2014 July 8

= July 8 =

Simple change to laws of Physics to reverse cup anemometer
Is there some simple change to the laws or constants of Physics, that will cause cup anemometers to rotate in the reverse direction?

That is, I want clockwise-rotating anemometers to rotate anticlockwise, and vice versa.

Thanks in advance --RM — Preceding unsigned comment added by 121.247.86.28 (talk) 12:10, 8 July 2014 (UTC)


 * Probably not without changing the universe in dramatic ways. StuRat (talk) 14:07, 8 July 2014 (UTC)


 * Turn the anemometer upsidedown? CBHA (talk) 14:53, 8 July 2014 (UTC)


 * Or the OP could stand on his head while observing it. ←Baseball Bugs What's up, Doc? carrots→ 15:40, 8 July 2014 (UTC)


 * We're discussing changing the universe so presumably the solution would be to turn the universe upside-down, not the anemometer. F=-ma would be interesting but I have a feeling the rest of the universe wouldn't work well enough for your anemometer and wind to continue existing. K ati e R  (talk) 16:35, 8 July 2014 (UTC)


 * The most obvious solution is to turn the time vector 180 degrees. To accomplish that, the OP would need to leave a message in God's suggestion box. ←Baseball Bugs What's up, Doc? carrots→ 17:11, 8 July 2014 (UTC)
 * In the mean time, just put the battery in your analog clock in backwards. Bonus, your sense of "clockwise" also reverses, so the anemometer now is already going backwards in that sense. DMacks (talk) 17:22, 8 July 2014 (UTC)


 * What we would need to do is arrange things so that the drag coefficient of a concave hemisphere is greater than that of a convex hemisphere. Without attempting to think about the maths, possibly if air were rheopectic, so that the slower air associated with the concave vane would have a lower viscocity than the faster air at the convex vane, and therefore generate less of a drag force? Tevildo (talk) 20:30, 8 July 2014 (UTC)

Thanks Tevildo.

I read up about drag. Pressure drag is the strongest component of drag here, am I right? Assuming that the other components of drag are negligible, is there a simple explanation as to why pressure drag of a concave hemisphere is less than that of a convex hemisphere? And what are the laws/constants that can be altered to invert this? --RM


 * From what I infer from Anemometer, the actual wind speed is calculated from a combination of the "captured" air in the cups and the partially offsetting drag the wind hitting the back of the cups. That calculation is going to vary depending on the shape of the cups, and the article mentions an optimal construction of the cups. I'm at a loss to comprehend what laws of physics would have to change to make the flow of gasses and liquids behave differently than they do. ←Baseball Bugs What's up, Doc? carrots→ 22:45, 8 July 2014 (UTC)


 * The answer to 'what are the laws/constants that can be altered to invert this?' is 'None.'
 * I'm not just being flippant. Not only are the laws of the universe fixed, they're also a matched set. All the laws we see in action are the product of the comsic and quantum scale laws that we have come to regard as fundamental. The behaviour of a human-scale device like an anemometer depends on the laws for the fundamental particles, in ways that are difficult to comprehend. AlexTiefling (talk) 22:55, 8 July 2014 (UTC)


 * It's certainly possible to imagine a universe with different laws of physics - but the likelyhood of there being anemometers in such places seems exceedingly remote. Even the smallest changes to the laws seems to result in there being no stars, no planets, no atmospheres and no people...which pretty much precludes anemometers. SteveBaker (talk) 03:34, 9 July 2014 (UTC)


 * If the anemometer had negative mass, it would go the other way.
 * If F is fixed, F = m a implies that if the mass changes sign, so does acceleration. Negative mass comes with its own weirdness; a negative-mass planet could orbit the sun, but it could not have a moon, neither of positive nor negative mass. A negative-mass planet itself wouldn't be stable, either. - ¡Ouch! (hurt me / more pain) 06:03, 9 July 2014 (UTC)
 * ¡No! Nor would a zero-mass anemometer stand still in the wind. Air molecules striking the concave sides are decelerated more than molecules striking the convex sides because the latter can form streamlines around the cup. It is the mass of the air molecules that would have to be negative to allow less force to cause greater deceleration, and that's impossible. 84.209.89.214 (talk) 17:34, 10 July 2014 (UTC)

Astigmatism
Are small astigmatisms of -0.25 or less normally corrected? 82.132.216.31 (talk) 13:48, 8 July 2014 (UTC)


 * With glasses, it's easy to correct astigmatism, so they might as well. However, since contact lenses are normally free to rotate, it's more of a challenge to correct for astigmatism there. StuRat (talk) 14:04, 8 July 2014 (UTC)


 * My personal experience is that optometrists only measure and specify prescriptions (for e.g. astigmatism, myopia) in multiplies of 0.25 dioptre, but this might be outdated. Without the need for other associated correction (e.g. myopia), most people would not bother with glasses for such limited astigmatism.  If glasses are being prescribed anyway, 0.25 dioptre might be corrected, but not say half of that. With contact lenses, I would expect this not to be corrected – basically exactly what StuRat is saying. —Quondum 18:56, 8 July 2014 (UTC)
 * I have 0.50/0.75 astigmatism correction on my contact lenses. AFAIK it's not a big deal to fix it in contacts, it's just an engineering problem that has been solved. 88.112.50.121 (talk) 19:08, 8 July 2014 (UTC)
 * My wife was astigmatic and wore contacts (before she had her eyes lasered!) - and the weighted/rotating contact lenses were a continual pain. The problem is that they get rotated out of position for one reason or another and actually make your vision worse until they move back to the correct position.   She'd find that blinking kinda helped - but the ones that rely on gravity to do the job suck when you're driving because every time you take a corner, centrifugal force messes up their position.   So I strongly disagree that it's "been solved" - the "solution" is only partially effective. SteveBaker (talk) 20:09, 8 July 2014 (UTC)
 * AFAIK the gravity-driven solution is old fashioned, first generation kind of stuff. It's now driven by micro serrations on the lens, and as the wearer blinks, the eyelid vs. serration action will orient the lens, gravity has nothing to do with it. Works fine for me, sorry it didn't work for your wife. 88.112.50.121 (talk) 20:32, 8 July 2014 (UTC)

SLEEP STUDY
Can anyone help me find out when (what year) the United States Air Force conducted it's first sleep study for Sleep Apnea? Thank You! B~u~g~g~e~d — Preceding unsigned comment added by 173.171.120.204 (talk) 21:01, 8 July 2014 (UTC)
 * You can contact the Sleep Lab at the US Air Force Academy here. Perhaps someone there may be able to answer your question.  -- Jayron  32  05:27, 9 July 2014 (UTC)

Biological taxonomy (history of)
Which taxa have not been revised since Carolus Linnaeus introduced his system of biological taxonomy? —Wavelength (talk) 23:52, 8 July 2014 (UTC) I have mentioned this discussion at Wikipedia talk:WikiProject Tree of Life. —Wavelength (talk) 23:57, 8 July 2014 (UTC)
 * Species like Canis lupus are normally mentioned for the first time in a text or paper with their original identifier. Are you asking us to list all species attributed like this to Linnaeus, or some other question? μηδείς (talk) 00:45, 9 July 2014 (UTC)
 * I have read of some taxa being split, and other taxa being combined, on the basis of things like genotypes and phenotypes. Which taxa have never been revised?
 * —Wavelength (talk) 00:49, 9 July 2014 (UTC)
 * I don't know that there's a specific list anywhere, but many of the articles in, , and remain at the same name Linnaeus gave them. Linnaeus' Species Plantarum (1753) was the beginning of binomial nomenclature for plants and fungi; the 10th edition of Systema Naturae (1758-1759) was the beginning of binomial nomenclature for animals. Rkitko (talk) 02:11, 9 July 2014 (UTC)
 * Linnaeus named many thousands of taxa of all levels of hierarchy; many (probably most) still exist as names today (though some may be modified in terms of their membership), it would be beyond the scope of anyone here to list all of them in a reasonable amount of time. It is possible (but unlikely) that you'll find such a list existing.  You'd have to go through every taxon Linnaeus himself named and then compare it to the modern list, which has millions upon millions of names on it.  Good luck.  -- Jayron  32  05:24, 9 July 2014 (UTC)


 * Well, an obvious example that hasn't been revised if one looks synchronically is Homo sapiens. We simply don't have any close enough relatives for there to be any confusion, and racial epithets like Homo sapiens mongolensis were never a matter of settled consensus--and the species level, although as mentioned above as suffering borderline cases really is the only objectively definable taxonomic level.  Everything else is a judgment call. μηδείς (talk) 19:41, 9 July 2014 (UTC)
 * Carl Woese would beg to differ. See Five-kingdom_system and Three-domain_system. The modern systematists almost universally use cladistics these days, and the old school of morphological taxonomy is literally dying off. The modern perspective can be summed up as "the most natural divisions of life are between domains, and between species, everything else is artifice born of convenience." SemanticMantis (talk) 19:55, 9 July 2014 (UTC)
 * Woese would beg to differ, but as I said, his view is neither established consensus, not objectively definable in the way species is. To quote Nicholas Wade's recent book on race, if races were clearly definable they wouldn't be races, they'd be species.  It remains that as a species, there has been no scientific splitting or combining of two existing populations of Homo as species.
 * There isn't really established consensus on definition of species either, as you likely know. Woese' view is supported in systematics about as much as climate change is supported by climate scientists (i.e. widely). But we're far off topic here, and I have not other references of use to add. SemanticMantis (talk) 20:18, 9 July 2014 (UTC)
 * Yes, indeed, there is almost total consensus on the definition of a species as it applies to sexual species. What there often isn't consensus upon is how it applies in certain borderline cases. μηδείς (talk) 18:16, 10 July 2014 (UTC)
 * I was tempted to ignore this, but I don't want any readers to be misinformed. Your link provides ample evidence that there is not total consensus on the definition of species, and how they are to be identified. In case anyone's curious, it says: About two dozen species concepts have been identified or proposed since Mayr's 1942 book, and many articles and several books have been written on the species problem. At some point, it became common for articles to profess to "solve" or "dissolve" the species problem.

Some have argued that the species problem is too multidimensional to be "solved" by one definition of species or one species concept. Since the 1990s, articles have appeared that make the case that species concepts, particularly those that specify how species should be identified, have not been very helpful in resolving the species problem.
 * (bolding by me, citations removed for clarity) You also mention sexual species, and this is another reason why the domain split is often more objective and natural than species distinctions, because definitions based on sexual reproduction cannot be used for huge chunk of organisms. For example, the archaea/bacteria split is much less arbitrary than the distinction between e.g. Escherichia_coli and Escherichia_fergusonii. Since you asked for it, there it is. This is not to say that species is a useless concept. It is in fact very useful, and the problems are mostly of interest to small subfields of biology. I'm really done here now, but feel free to grab the last word if you like ;) SemanticMantis (talk) 19:57, 10 July 2014 (UTC)