Wikipedia:Reference desk/Archives/Science/2015 November 6

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November 6

Is it possible to say that one dimensional is one axis?

Is it possible to say that one dimensional is one axis? (doesn't matter if it's X,Y,Z). if it's right, how can it be, here is also there are length and width. I don't understand it and I would like to get explanation about it.78.111.187.209 (talk) 01:35, 6 November 2015 (UTC)

Yes, you can say that. One Dimension, is One Axis. When you have two dimensions, you also have two axes. They go together. Explain more about what you don't understand. Ariel. (talk) 02:09, 6 November 2015 (UTC)

You can say anything you want, but if you have an axis, you must have a rotation. You need at least two dimensions for a rotation to work... In two dimensions, an axis would be a point. In three it's a line. In one it's... impossible. --Jayron32 02:53, 6 November 2015 (UTC)

I think Jayron32 is using the word "axis" to mean "an axis of rotation," while Ariel is using it to mean a geometric representation of a basis vector. There are many usages of the word "axis" in mathematics and other disciplines; it is not clear to which the original question is referring. Nimur (talk) 03:13, 6 November 2015 (UTC)

Sorry yes. Brain no makee the smart thots. I go sleepy now. be better tomorrow. --Jayron32 03:39, 6 November 2015 (UTC)

Ariel, I simply want to ask this question, and you answered me about. Thank you! 78.111.186.226 (talk) 02:43, 7 November 2015 (UTC)

Neutrino blackbody radiation

Suppose I have an immense number of slow neutrinos is a huge ball in space, so many neutrinos in one place that interactions are frequent, but not energetic enough to escape the gravity of this neutrino [not neutron] star. Does that star have a temperature? Is so, what happens to blackbody radiation? If I drop some matter into this star it seems to me it would transfer some heat energy between itself and the neutrinos. Is this star opaque or transparent to light? Are W bosons able to interact with photons? Would that be enough to give it blackbody radiation? Ariel. (talk) 02:04, 6 November 2015 (UTC)

You present an interesting scenario. Neutrinos are not believed to interact electromagnetically, so they do not emit or absorb light. So the "star" would be transparent. Light is the electromagnetic interaction. And this is easy to demonstrate: Look Around You! Trillions of neutrinos are blasting through you every second, but you don't see them. They're constantly being produced by the fusion reactions in the Sun. And the neutrino flux doesn't change with time of day, since neutrinos just go right through the Earth. As for the W and Z bosons, if I'm understanding the article correctly, the W bosons interact electromagnetically but the Z doesn't. But, these bosons' half-lives are so incredibly short that I'm pretty sure you'd never notice any macroscopic effect. They're more massive than iron atoms! Now I'd like to think about your scenario a little more. Neutrinos have such a tiny mass that I'm not sure they'd have any appreciable gravitational interaction. If I'm right, they wouldn't be in a bound state, so it wouldn't really be a star, just a big unbound cloud. But I'm not a physicist so I could certainly be wrong about this. And I'm not sure if taking general relativity into account changes anything. --71.119.131.184 (talk) 03:22, 6 November 2015 (UTC)

A gravitationally bound cloud of neutrinos is possible in principle. It would be similar to an ideal gas or a photon gas (photons also barely interact with each other), and it would likewise have a temperature. Neutrinos do interact with photons (via charged virtual particles) but extremely weakly. I don't know if it would be possible to pack neutrinos densely enough to be opaque without their collapsing into a black hole. A blackbody by definition absorbs all incoming radiation. An opaque neutrino cloud (if such a thing is possible) would be a blackbody and would radiate according to the Stefan–Boltzmann law, but an almost transparent neutrino cloud would emit almost no light. -- BenRG (talk) 06:02, 6 November 2015 (UTC)

Cosmic neutrino background and Neutrino decoupling may be of interest. --Wrongfilter (talk) 07:30, 6 November 2015 (UTC)

Interesting thought experiment though not sure that neutrinos could be bound by their own gravitational force. To wit, the supermassive black hole at the center of the Milky Way seems to be emitting neutrinos. It's not unreasonable to speculate a consequence of gravity is neutrino/anti-neutrino production. That kind of makes it look like neutrinos would work like anti-gravity which is another weird thought experiment. It would be kind of satisfying if dark matter were neutrinos trying to spread out gravity. --DHeyward (talk) 15:43, 6 November 2015 (UTC)

I found this one but it describes production during shock waves, high energy events ... not antigravity :) Wnt (talk) 16:49, 6 November 2015 (UTC)

That's the what makes it weird. A condensing cloud of low energy neutrinos due to gravity creates black hole and starts emitting high energy neutrinos. That's kind of a backlash against gravity. "anti-gravity" if you will as it evaporates. Probably a whole slew of laws would need rewriting. --DHeyward (talk) 21:59, 6 November 2015 (UTC)

@DHeyward: It doesn't seem any more counterintuitive than solar wind or supernova, or (especially) those crazy stellar jets that shoot away from stars. Wnt (talk) 13:03, 7 November 2015 (UTC)

Black holes are perfect blackbodies, absorbing all incoming matter, and they likewise emit all types of matter as blackbody radiation, including neutrinos. It has nothing to do with "anti-gravity" or "neutrinos trying to spread out gravity". -- BenRG (talk) 00:24, 7 November 2015 (UTC)

Ben, a gravitationally confined set of low energy neutrinos that condenses under it's own gravity is nothing observed. Neutrino radiation from blackholes is also not well understand nor predicted. Surely you see the paradox of condensing neutrinos beyond the black hole event horizon. --DHeyward (talk) 06:49, 7 November 2015 (UTC)

You're talking about something that has occasionally been studied as a "neutrino star" -- just a big ball of neutrinos bound under their own gravity. (Be careful, though; "neutrino star" can have other meanings.) This type of object actually cannot be very dense at all because of degeneracy pressure, which creates a kind of hydrodynamics even though the neutrinos are almost completely non-interacting. The problem is that the neutrino mass is so small, the neutrinos have to have an extremely tiny energy to stay gravitationally bound. This means there are only a few states for them to occupy within a finite volume, and because the neutrinos are fermions, there can only be one of them per state. It just isn't possible to pack any more in without giving them a higher energy, in which case they would free stream away. Such a neutrino star would therefore be an enormous, very diffuse object. Not only would it be transparent to light, you wouldn't notice at all if you were in the middle of one. --Amble (talk) 08:41, 7 November 2015 (UTC)

Hmmm, here's a ref. Wnt (talk) 12:43, 7 November 2015 (UTC)

Yes, that's one example, but note that they're not talking about neutrinos as we know them. Instead, they're talking about a star made from a hypothetical and unknown additional neutrino species with much greater mass than the standard model neutrinos. This sort of thing was very interesting back in the 1990's when people thought there might be a 17 keV neutrino (although that turned out to be wrong). Since then, it requires a sterile neutrino or some other new neutrino-like particle with a large enough mass that you can build a compact object; that's what makes it a "heavy neutrino" star. With the very light neutrinos we know about, the density ends up being ridiculously tiny. --Amble (talk) 17:24, 7 November 2015 (UTC)

Here's another paper assuming a 3 eV neutrino [1]. This was on the heavy end of possible standard model neutrino masses, but it's ruled out now. They were talking about galaxy-sized neutrino "stars" in the center of galaxy clusters. --Amble

brain vs computer damage

I understand that depriving someone of oxygen will cause unconsciousness, but why does it cause permanent brain damage?

After all, if you unplug a computer, its battery will run out, but it won't suffer permanent damage. 203.45.134.227 (talk) 04:25, 6 November 2015 (UTC)

The brain starts to die, because without oxygen your brain cells can't produce enough energy to stay alive. See hypoxia (medical) and cerebral hypoxia. The brain is very energy-hungry (an adult human's brain accounts for about 25% of the body's energy demands), so the brain is very sensitive to oxygen deprivation. To examine your analogy, our brains don't have any permanent storage akin to a hard drive or flash memory, that stays as-is without using energy. Living cells constantly need to expend energy. In the vein of your computer analogy, you could say the brain is all CPU and RAM. And to be a little pedantic, computers can suffer damage from loss of power. If nothing else you lose any data that hasn't been written to permanent storage. This can be especially bad if it leaves the file system in an inconsistent state. Ever seen a message telling you not to shut off your computer, like while installing operating system updates? Modern file systems use techniques like journaling and copy-on-write to make catastrophic file system corruption less likely. And, hard drives these days tend to be more fault-tolerant, but in years past it wasn't unheard of for hard drives to be physically damaged or destroyed from a head crash after a sudden power loss. --71.119.131.184 (talk) 04:46, 6 November 2015 (UTC)

Good description. I would add that most machines are designed to be able to be shut completely off, but complex animals can't do this and survive. The closest complex animals come is hibernation and hypothermia. Plants and some simple animals seem more able to go dormant for long periods. There's seeds and bulbs in the case of plants, and some insects and spiders may be able to do something similar. StuRat (talk) 05:27, 6 November 2015 (UTC)

It isn't only simple animals; some mammals can survive long periods of hibernation at very cold temperatures: The Arctic ground squirrel can survive conditions where its internal body temperature is below the freezing point of water (the body itself doesn't freeze solid because the body isn't pure water, it's pretty salty, see Freezing-point depression) --Jayron32 13:26, 6 November 2015 (UTC)

Hibernation isn't the same as a machine being shut off, as metabolic activity continues, just at a slower rate. It's more akin to an idling machine. StuRat (talk) 20:51, 8 November 2015 (UTC)

Apoptosis is a frequent contributor to brain injury, and often it seems like the death really doesn't "need" to happen. See [2] for information, including various ways in which some of the damage can be prevented. As I recall xenon stood out - even if given after the injury. But necrosis is a feature of some of the damage, so it's not like there's a magic bullet in that regard. Wnt (talk) 10:10, 6 November 2015 (UTC)

Weak points in/of a human body

I wish to learn about all the weak point(s) in/of a human body; from head to toe. Does anybody know? Illustrations with summaries would be helpful. -- Space Ghost (talk) 10:11, 6 November 2015 (UTC)

I think we'd need a better pointer as to what you want to know. For instance hair is fairly strong when pulled but pretty weak if you push two ends towards each other or if you bend it. And I believe it is stronger when pulled than a fiber of nylon but weaker than a thin wire of good steel. I think my brain would be pretty weak if taken out and poked too. Dmcq (talk) 10:39, 6 November 2015 (UTC)

(edit conflict) Assuming that you mean "weak points" in respect of physical assault rather than infection, in Japanese martial arts (particularly Ju-jutsu and Judo), attacking these points is called atemi waza ("striking techniques"). See Atemi-Waza - Vital Point Striking for details. Alansplodge (talk) 10:42, 6 November 2015 (UTC)

Saw the pictures . Thank you! -- Space Ghost (talk) 18:46, 6 November 2015 (UTC)

Where can you find whole grains?

Commercial bread contains carcinogenic preservatives or is very expensive and not very tasty. Rice is full of arsenic. You can eat only so much whole-grain pasta. 69.22.242.15 (talk) 11:49, 6 November 2015 (UTC)

Grow your own wheat, rice, and pasta? 140.254.136.179 (talk) 13:16, 6 November 2015 (UTC)

Here are a few articles on choosing good whole grain products: [3] [4]. --Jayron32 13:22, 6 November 2015 (UTC)

Not sure you will escape periodic table. It's true that industry can concentrate certain bad things in areas where they weren't concentrated before but many places have natural background variations of carcinogens that simply exist. "Natural spring water" for example can exceed EPA safe limits for many elements without ever being touched by humans. Lead, arsenic, mercury, uranium etc, etc, all exist naturally and often near water sources necessary for agriculture. But why "Whole grains?" Humans don't seem particularly suited to eat whole grains without processing of some type and became dietary for economic reasons. We seem more naturally suited to eat fruits, vegetables and vertebrates. --DHeyward (talk) 16:01, 6 November 2015 (UTC)

Whole grains contain higher amount of dietary fiber; its indigestibility IS its main positive trait. Also, whole grains contain bran, which besides the dietary fiber contains other nutrients not available in more processed grains; the processing can remove these nutrients, and lower the amount of dietary fiber. --Jayron32 16:09, 6 November 2015 (UTC)

I agree with Dheyward, that humans have only recently started eating grains, on an evolutionary scale, and thus haven't fully evolved to digest grains. Whole grains, for example, can be indigestible. While this provides fiber, so do many vegetables, and with better nutrients. Cracking whole grains make them a bit more digestible, as does rolling oats. As for avoiding preservatives, then you need to eat the whole grains quickly. Also, the fat in the grains will go rancid. An alternative is to make "breads" from nut flours, such as almond flour, which are more nutritious, but also need to be eaten quickly. StuRat (talk) 21:02, 8 November 2015 (UTC)

Humans have been eating grains for at least tens of thousands of years. And grains are just seeds, which are widely consumed by many animals. --71.119.131.184 (talk) 03:31, 9 November 2015 (UTC)

Yes, and tens of thousands of years isn't much time on an evolutionary scale, at least for a species with some 20-30 years between generations. Other animals that eat seeds or grains have major adaptations, such as gizzards. StuRat (talk) 05:45, 9 November 2015 (UTC)

Many things are carcinogenic, including oxygen and ethanol. Just saying something is carcinogenic is effectively meaningless. I am not aware of any scientific evidence that the preservatives used in most foods are a health concern at the levels used. --71.119.131.184 (talk) 06:44, 7 November 2015 (UTC)

STD Transmission

Why do health educators say that abstinence provides 100% protection and at the same time they say that, even if a person does not engage in sexual activities, has never had sexual contact or a kiss on the lips, has never had organ transplant or blood transfusion, has not shared needles with others, has no congenital STDs, has never shared clothing, etc., as having a very low risk of STD? "A very low risk of STD" is not 100%, which implies that even if a person is abstinent all his life, he may still have an STD out of the blue or some kind of occupational needle-stick injury? I notice that if pathogens can be transmitted by aerosol or water or food, then somehow it is not considered an STD? If those are not considered STDs, what is the reason behind the "very low risk" as opposed to saying "no risk at all unless you have a freak accident or an occupational needlestick injury"? 140.254.136.179 (talk) 13:45, 6 November 2015 (UTC)

Could you provide a source where a medical professional or professional body or health educator has stated that there is a low risk of an STD for a non-sexually active person?--Phil Holmes (talk) 14:00, 6 November 2015 (UTC)

Few babies are sexually active, but may get an STD from their mother either in utero or during the birth process. See vertically transmitted infection and HIV and pregnancy. So, obviously, you can get STDs through non-sexual means. Abstinence is only considered 100% effective if you're only considering STDs that are literally being transmitted during sex - sexual abstinence would not stop you from getting HIV from a dirty needle either. 64.235.97.146 (talk) 14:33, 6 November 2015 (UTC)

For one thing, you can kiss even if you are abstinent. Kissing carries a non-zero risk of transmitting disease. Second, STDs are "infections that are commonly spread by sex" (italics by me) as our article Sexually transmitted infection says. It's still called that even if it's transmitted in a non-sexual way, much like the common cold doesn't become an STD if somebody gets it through sexual contact.

Phil, CDC says that abstinence protects against STDs. I don't think anyone questions that the risk generally is low for non-sexually active adults (with exceptions, such as IV drug users). Sjö (talk) 14:40, 6 November 2015 (UTC)

I think this is one of those self evident things that gets blown out of proportion. If you never commit any activity which could ever bring you into contact with those infectious agents, you never get the infectious agents. Of course, the discussion over passing STIs via non-sexual contact is a different discussion, but lets put that aside for a second. If (I know this is never true, but pretend it is true for the discussion), If a specific disease is ONLY passed on through sexual relations, then if a person never has sexual relations, the NEVER get the disease. That's how concepts like "ONLY" and "NEVER" work. In logic, this is called the Logical conjunction: A person can become infected only if a) they have sexual contact with b) a person who is themselves infected. Since a person only has complete knowledge of option (a) (whether or not they have sexual contact), that's the only thing they have control over. The actual discussion over whether or not that is true as to whether STIs can be passed by non-sexual contact is not relevant to the message being delievered for the purpose being delivered. From a public health standpoint, reducing preventable infections is a basic goal. If the message "If you don't have sex, you don't get infected" reduces infections by stopping people from having risky sex, that's why its stated that way; it's also accurate enough, at least within significant figures when comparing the infection rates of people who get STIs from non-sexual sources, that is while the numbers are not zero, the numbers are both a) low enough that they don't much affect the overall percentage of total STIs and 2) not readily preventable by behavioral modification. This article mentions non-sexual transmission methods, but does not go into statistical details. It does, however, contain links to articles which do. This article notes that the risk of catching HPV infections outside of sexual intercourse is about 11.6%, much higher than most STIs, but that still means eliminating sexual activity reduces your risk of catching it by an order of magnitude. this rather long article also has some information on infection rates and infection pathways for various STIs. --Jayron32 14:57, 6 November 2015 (UTC)

(EC) I'm not sure Phil is questioning the risk is low. I think Phil is querying whether health authorities say the risk is low instead of saying there is no risk. But as you said, the risk is low is the correct assessment. I would also note that I don't think many health authorities refer to someone who "has never shared clothing, etc" anyway. Probably even the kissing on lips doesn't generally come up. Nil Einne (talk) 15:01, 6 November 2015 (UTC)

Indeed, as I mentioned (and just to clarify the thesis, just because it may get lost) the issue is "Where is the message coming from and for what purpose." Since the message is coming from public health officials, the purpose is to reduce rates of infections. Public health officials have identified sexual behavior as a major vector for these diseases, and are making statements to alter behavior so as to lower transmission rates. There's a difference here between statements made by public health officials who are trying to get people to change behavior, and research scientists who are trying to find verifiable statistics. While the latter certainly informs the former, the actual statements they make have different purposes. --Jayron32 15:08, 6 November 2015 (UTC)

There's always something. Dentists who don't clean their equipment. Tattoo parlors. Getting shot and the bullet goes through someone with HIV on its way to you. (Well, honestly, I don't know if that one works :) ) Sharp edge on a railing. There's always something... you have to be creative to come up with a whole list of ideas, but nature is more creative than that. Wnt (talk) 16:54, 6 November 2015 (UTC)

You may have been thinking of Legrand G. Capers' claim that a woman had become pregnant during the american civil war by a bullet that passed through the body of a man and into her, however, that turns out to have been untrue. SteveBaker (talk) 15:22, 7 November 2015 (UTC)

I hadn't heard that one. But transfer of intact sperm cells is clearly going to be more difficult than transfer of viral particles. (There's no guarantee you can do either, though - my main concern would actually be the immense heat and air exposure of the bullet, which might well sterilize any adherent fluid) Wnt (talk) 01:42, 8 November 2015 (UTC)

There's a factor that nobody has mentioned yet. Health authorities do not know a person's sexual activity history, and are obliged to record what the person tells them about it. If the person lies and says they have never had any form of sexual relations, nobody can challenge that, so 'low risk' gets ticked in the Total Abstinence column when there's really a distortion of data taking place. Akld guy (talk) 05:30, 7 November 2015 (UTC)

Adoption of abstinence as a method of preventing transmission of sexually transmitted diseases fails when sexual activity takes place. Therefore, the adoption of abstinence has a failure rate, and there is a non-zero risk for sexually transmitted diseases if you adopt abstinence. It's the same principle that failures of comdom use as method of contraception gets counted against condom use even if the reason for the failure was "forgot my condom". - Nunh-huh 02:06, 9 November 2015 (UTC)

Abstinence is 100 percent safe. If sexual activity takes place, it is no longer abstinence. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:00, 9 November 2015 (UTC)

You forgot to put your joke in small text. At least I suppose that it is a joke as even skimming the section will tell you that abstinence isn't a 100 % protection against STDs. Sjö (talk) 12:17, 9 November 2015 (UTC)

Actual abstinence (as opposed to claiming abstinence) is 100 percent safe. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:57, 9 November 2015 (UTC)

But advocating abstinence as a method means that you are suggesting that people adopt it. And that adoption has a failure rate. That failure rate is part of the reason why "abstinence-only sex education" has such an abysmal track record. - Nunh-huh 20:05, 9 November 2015 (UTC)

"Pledging" abstinence from sexual conduct is likely to have a failure rate, because pledges tend to be broken. Actually being abstinent is a 100 percent safe guarantee of no STD's through sexual contact. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:33, 10 November 2015 (UTC)

Yeah, what I said. People lie when being admitted to hospital with STD symptoms, so you can't trust the 'low risk' statistic for those who claim total abstinence. What those people probably mean is that they have been abstinent since the symptoms first came to their attention. Might have been a ten-partners-a-week hero before that. Prostitutes have a pecuniary interest in minimizing their activity level; admitting to a high number of clients might render them liable for more income tax than they were previously declaring. Akld guy (talk) 03:06, 10 November 2015 (UTC)

List of tallest elevators?

Hello Wikipedia Reference Desk:

I am looking for a list of the world's tallest elevators. I have only been able to find our list of tallest buildings in the world; but most of these buildings have complex elevator systems; it is not generally true that the taller buildings have taller individual elevator shafts. Furthermore, there are a handful of sophisticated elevators in the mining industry, freight transport, and other more esoteric applications that dwarf the elevators of many modern skyscrapers.

Is this eclectic information organized anywhere on Wikipedia, or should I start engaging with the folks at Talk:Elevator?

(I am aware that Shanghai Tower reputedly contains the tallest - rather, the furthest-travel - at some 580 meters... I'm looking to qualify and compare that factoid in context).

Nimur (talk) 15:32, 6 November 2015 (UTC)

This looks like it has some promising leads. It led me to This which claims to have information on the tallest elevators on Earth. --Jayron32 15:40, 6 November 2015 (UTC)

wow. I was surprised modern elevators still use cables. --DHeyward (talk) 22:10, 6 November 2015 (UTC)

What did you think they used? --71.119.131.184 (talk) 06:37, 7 November 2015 (UTC)

There are hydraulic elevators - which are common in buildings about 4 stories and less, others that use gear wheels to climb a toothed 'rack'...check out Elevator#Types_of_hoist_mechanisms for several alternatives to cables. SteveBaker (talk) 15:15, 7 November 2015 (UTC)

Do chemists tend to memorize solubility guidelines?

The textbook I have says "Unfortunately, there are no rules based on simple physical properties such as ionic charge to guide us in predicting whether a particular ionic compound will be soluble or not." and there is a table of soluble ionic compounds with lines such as "chlorides, bromides, and iodides are soluble except in compounds with Ag+, Hg2+, and Pb2+" and "sulfates are soluble except in compounds with Sr2+, Ba2+, Hg2+, and Pb2+". There is another table of insoluble compounds with a list of exceptions, but you get the point. Is this information generally memorized by most people whose job title includes the word "chemist"? 20.137.7.64 (talk) 18:19, 6 November 2015 (UTC)

I don't think they have to pass an exam about it, but compounds like silver chloride, mercury iodide and strontium sulfate are entities that people who are even not officially chemists start to become familiar with. Wnt (talk) 20:33, 6 November 2015 (UTC)

Yes, chemists know those general guidelines. Every chemist I know knows the basic solubility rules. Of course, if chemists really want to know solubility in a quantitative way (that is, the exact solubility of a substance at a given set of conditions) they look it up somewhere. The solubility rules are really a heuristic taught to high school and first-year college chemistry students to remember which ionic compounds tend to be soluble, and which tend to not be, based on general patterns and trends. As soon as someone is on the path towards being a professional chemist, they learn the more detailed aspects of solubility (such as the role of Coulomb's law, the details of solute-solvent interactions, solubility product, etc. etc.) Just like you can still sing the "ABC song" even though you probably were taught it as a child, Chemists would still all pretty much know and understand that all halide salts except silver, mercury, or lead are fairly water soluble, and similar guidelines. The main utility of those rules, for what it's worth, is not in actually making solutions from first principles, like dumping solids into water and stirring them until they dissolve. The purpose of learning those guidelines is to be able to predict the results of precipitation reactions. In simplest terms, YES every chemist knows those rules, because they all learned them as a step along the way of their education. Many chemists would use more quantitative calculations and principles (like solubility product) on their actual jobs, but they don't undergo some elaborate "memory erasing" technique to forget their high school chemistry classes. --Jayron32 21:23, 6 November 2015 (UTC)

Thanks. (OP, different IP) I was pretty much wondering if this table's worth of information was worth expending the effort to hard commit to memory. 75.75.42.89 (talk) 22:26, 6 November 2015 (UTC)

Has anyone ever installed a swimming pool on an aircraft?

Has there ever been a plane with a swimming pool on board? I mean a working plane that can still fly, and a pool big enough to actually swim a little before you hit the other end. I've heard of jacuzzis on private jets, and the Evergreen Museum Waterpark in Oregon that has water slides built through a retired 747, but not an actual airborne pool. 94.12.76.44 (talk) 20:30, 6 November 2015 (UTC)

I'm thinking [5] which gets " the U.S. Forest Service will get 22 military aircraft — seven HC-130H Hercules air tankers and 15 C-23B Sherpa cargo planes ". Whether a tank is a swimming pool is kind of subjective... because airlines change attitude, the notion of one surrounded by a nice flat tile area to sunbathe on is problematic! Looks like Lockheed HC-130 and Short C-23 Sherpa are the articles for those. The former holds 45,000 kg = 45,000 liters; the latter is only a tenth that according to the articles. So think 20 dm x 20 dm x 115 dm = 2 m x 2 m x 11.5 m, I think, assuming nothing else on board? That's a fair swim lane, I suppose... Wnt (talk) 20:42, 6 November 2015 (UTC)

Thanks! Hadn't thought of firefighting planes, but now that you mentioned them it reminds me of the old story about the scuba diver caught in a water scoop[6]... luckily not true! 94.12.76.44 (talk) 20:50, 6 November 2015 (UTC)

It would be difficult to do this safely (for an actually swimmable pool), because the water would be subject to the free surface effect. The normal mitigations to this (breaking the volume up into multiple compartments, or having baffles or honeycombing inside the tanks) wouldn't be viable for a pool (I guess one could have a pool where the baffles were removed when the aircraft was on the ground - but that seems like even more work). I can't find much info about the tankage of firefighting airtankers, but this patent for the Bombardier 415 talks about baffling for its tanks (i.e. it's not one big volume of free water). -- Finlay McWalterᚠTalk 21:04, 6 November 2015 (UTC)

• I don't believe it has been done yet. This article notes that a Saudi Prince once asked Airbus to install one on his airplane, and they flatly refused. Several other sources note that it's never happened before; there's been rumors, but no one has ever actually built a full-fledged swimming pool on any airplane. The closest I could find was this article which notes that the Airbus Beluga is big enough to house one, but not that anyone actually ever installed one. --Jayron32 21:13, 6 November 2015 (UTC)

Thanks both. If someone basically richer than God asked Airbus directly and they said it can't be done, I guess that answers my question. But does it take a certain minimum volume of water for the free surface effect to be significant, or could it build to a dangerous level even in a large jacuzzi? If jacuzzis deal with it by really fast drainage controlled from the flight deck, presumably that could work for a bigger pool too if it had enough pumps. 94.12.76.44 (talk) 21:51, 6 November 2015 (UTC)

The problem is oscillation of a relative mass. Even fire trucks and milk trucks and fuel trucks have baffles. Multiple, small jacuzzis is fine. A pool with jets to simulate a lap pool is fine. But even the fuel tanks in large aircraft are baffled so that sloshing doesn't alter the center of gravity in any way that makes it close to observable (let alone unstable). I believe Jet A is about 7 lbs per gallon while water is 8 lbs per gallon. They can deal with the weight but likely not such a large, unbaffled structure as a pool. A Swim spa is fine. --DHeyward (talk) 07:50, 7 November 2015 (UTC)

For greater clarity: by "gallon", D. means a gallon, not a gallon, which would weigh 10 pounds. --70.49.170.168 (talk) 09:05, 7 November 2015 (UTC)