Wikipedia:Reference desk/Archives/Science/2014 December 22

= December 22 =

What is the difference between tap water to the physiology solution?
I know the tap water is hypotonic, but what are the values of the tap water compared to physiology solution? 5.28.180.110 (talk) 04:04, 22 December 2014 (UTC)


 * I assume you are talking about blood? See isotonicity which gives you (grams of NaCl/L water) and human serum albumin. μηδείς (talk) 04:35, 22 December 2014 (UTC)

When I take a shower does I lose my body water?
I don't understand if it depends on the temperature? (I mean if it's always true that you lose your body water when you take a shower, even when the temperatures are high or the same of the body temperature). 5.28.180.110 (talk) 04:12, 22 December 2014 (UTC) Same question by Tel Aviv IP, see prior answer: https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2014_December_15#When_taking_a_shower.2C_does_the_body_loses_liquids_.28.2Fwater.29.3F μηδείς (talk) 04:21, 22 December 2014 (UTC)

Why weren't compound bows invented much sooner?
Leonardo's crossbow was a very simple design scaled up massively, but it still looks like a crossbow. Yet in the 1960s there was a sudden profusion of many different designs for compound bows with pulleys/eccentric pulleys/cams, extra limbs, and many other creative features. Reading it sounds like "modern glues and fibreglass" was a key advance, but..... was it really necessary for the invention? Aluminum alloys are used, but wouldn't steel or even bronze have worked in ancient times? Ultra-high-molecular-weight polyethylene is used for the cables, but is there no classical sort of ultra-strong "thong from the hide of the yellow ox" that might have done the job? And Leonardo didn't merely fail to make a compound bow... he failed to try. I just don't get how people missed such innovations for so long only to end the drought so abruptly; can it be explained scientifically?

I'll admit that I haven't used a compound bow and there are many aspects of the eccentric/cam design that aren't obvious to me, so more general explanations (or preferably better clarification in the article itself!) would be very welcome also. Wnt (talk) 04:49, 22 December 2014 (UTC)


 * This is an old design infact. See Laminated bow or Yumi. Such products seem much more result of an artisan tradition than result of one ingeniouse inventor. --Kharon (talk) 13:21, 22 December 2014 (UTC)
 * The main purposes of the compound bow are to reduce the accelerated mass of the limbs, and to get a better force/draw curve. I don't think the theory the first idea was obvious before Isaac Newton. You can get a lot of the second advantage with less hassle and less complex engineering with a composite bow. --Stephan Schulz (talk) 14:46, 22 December 2014 (UTC)


 * I think there's a couple of things at play here. At the article notes, compound bows are complicated to make and consist of some rather specialized kinds of materials including rubbers, plastics, aluminum, carbon fibers, and other goodies. By the time these were in regular use, the problems of making easier to use bows had already been solved with guns. It wasn't until relatively recently that guns became deadlier than bows for an expert to use, but they've long had advantages in being simpler to use. The original point and click program! The end result being that the iron mongers that might have spent their time and expertise making bows easier to use (i.e. making them into compound bows) instead put their skills into developing rifling and tweaking the cross-section of bullets. Matt Deres (talk) 14:51, 22 December 2014 (UTC)


 * Hmmm, I'm getting the feeling from this that the compound bow is an emergent property of modern technology. With the accompanying skepticism of whether emergent properties are really real and meaningful... but nonetheless, an interesting representative. Wnt (talk) 00:27, 23 December 2014 (UTC)
 * I see the compound bow as a very sophisticated hobbyist development. Guns long ago rendered bows obsolete for military and subsistence hunting purposes. Use of bows continued for aesthetic reasons, for target shooting and in a subset of hunting for pleasure as a hobby or a sport. As leisure time and the money available for hobby and sport activities increased in the 20th century, the equipment used in hobbies and sports became ever more sophisticated, incorporating cutting edge technologies. A modern America's Cup yacht is perhaps the ultimate example, with the compound bow representing a more economical but still very sophisticated example. Cullen328  Let's discuss it  01:47, 23 December 2014 (UTC)
 * It think there are other reasons to want a bow rather than a gun. For starters, you don't have to buy ammunition - for another, they are virtually silent (which could have MANY advantages) - for yet another, there are many places in the world where private possession of guns is illegal, but bows are OK.  SteveBaker (talk) 17:49, 23 December 2014 (UTC)
 * I think the "hobbyist" aspect is a bit of a side-track, because what I was really wondering is why Leonardo da Vinci or one of the earlier Chinese inventors didn't come up with a similar design, at a time when one might have made a hobby of killing people with them. Unlike racing yachts, compound bows aren't tremendously expensive, nor are they specialized for only one purpose; hunters in general actually tend to like them for routine tasks, whereas you don't see a racing yacht put to use as a water taxi or passenger ferry. Wnt (talk) 18:27, 23 December 2014 (UTC)
 * It's hard to guess why someone DIDN'T think of something clever. Even if all of the necessary underpinnings of an idea are present - sometimes nobody puts two and two together for many, many generations.  Why didn't DaVinci think of negative numbers?  Why didn't anyone in Georgian England come up with the idea of Evolution?  Why wasn't sliced bread invented until 1912?  Why weren't retro-reflective Cat's eye (road) used in road construction before 1933?  Who knows why some people come up with bright ideas and others don't?   It's not something you need a reason for.  Some ideas are just not obvious, and even with millions of human brains contemplating how to make a better bow, it's perfectly possible that nobody ever thought of using pulleys to help pull it...until the day that somebody did.  SteveBaker (talk) 21:25, 23 December 2014 (UTC)
 * Actually, they were indeed created much sooner than they were. Originally, they weren't scheduled until the Fall of 2041. μηδείς (talk) 02:29, 24 December 2014 (UTC)
 * I don't want to discount your points, which are entirely valid (why didn't New World civilizations invent the wheel, why didn't Europeans invent paper), but I think there's a very real issue of availability in this case. At the risk of over-generalizing, by the time the materials and craftsmanship that are needed to go into compound bow production became available, the bow had largely been superseded. To respond to your earlier point above, while bows have some obvious advantages, history seems to show that the negatives outweigh them. The chief problem comes down to skill and ability; it takes a lot of training to use a bow well; not just to work on your aim, but also to develop the large shoulder and back muscles you need. Even the skeleton was noticeably warped by the intensity. Compare that with pulling your trigger finger! Matt Deres (talk) 04:02, 24 December 2014 (UTC)

many versions forms of the arm veins
In the past, someone gave me here (in our page) a link for site or book that shows how many versions there are in the forms of the arms veins. I looked for it and I couldn't find it. I would like to get help. 5.28.180.110 (talk) 07:43, 22 December 2014 (UTC)
 * Well, we have the illustration File:Sobo 1909 597.png, which may be of some help. This page discusses some of the observed variations. Are these of any use to you? Deor (talk) 19:07, 22 December 2014 (UTC)
 * Yes. these are. Thank you! But I looked for the information that was given here before :) I remember that there are more than three versions (I think even 50 or something like that) 5.28.180.110 (talk) 23:22, 22 December 2014 (UTC)
 * Was this your previous question? Deor (talk) 23:53, 22 December 2014 (UTC)
 * Yes, it is! Thank you deeply :) (How could you do that?!...)5.28.180.110 (talk) 04:24, 23 December 2014 (UTC)
 * I don't like to destroy my reputation as a man of mystery. ... However, in this case I just entered arm veins in the reference-desk search box at the top of this page, and that thread came up third in the list of results. Deor (talk) 04:57, 23 December 2014 (UTC)
 * If so, I don't have a good answer for that :/ I looked for this and I saw a lot of results. 5.28.180.110 (talk) 12:18, 23 December 2014 (UTC)

Given a perfectly sealed airship, could it remain in the air for years?
Would an airship, or a kind of balloon, made with a tough material, with the same density as air at 10,000 m, ever fall back to Earth? --Noopolo (talk) 18:46, 22 December 2014 (UTC)


 * There's be some diffusion across the material of the gas-bag in the long term. So even "perfectly sealed" it would slowly lose lifting gas.
 * But the reality is that most airships that don't crash or get shot down, are eventually lost to storms. List_of_airship_accidents APL (talk) 19:41, 22 December 2014 (UTC)


 * Are you presuming the balloon contains lighter-than-air gas such as hydrogen or helium? ←Baseball Bugs What's up, Doc? carrots→ 20:05, 22 December 2014 (UTC)


 * Yes, and the balloon is made of something really tough, like a thin sheet of titanium. Noopolo (talk) 20:09, 22 December 2014 (UTC)


 * First, let's just suppose it were possible to create a perfectly sealed container that's lightweight and durable. Did you want the balloon to maintain a certain usable altitude? Or just to rise until it reaches some kind of equilibrium and "hangs" there? ←Baseball Bugs What's up, Doc? carrots→ 20:51, 22 December 2014 (UTC)


 * In theory yes, in reality, no. Lightning, UV light, hurricanes, tornadoes, etc., would get it eventually. StuRat (talk) 02:01, 23 December 2014 (UTC)


 * Obviously a calamity could occur. The question seems to be what happens if there is no calamity. Would it rise clear out into space and drift away? Or would it reach some sort of equilibrium and hang there? Of course, any sort of wind would move it around. But would it stay at a more-or-less fixed altitude? ←Baseball Bugs What's up, Doc? carrots→ 02:51, 23 December 2014 (UTC)


 * Even hydrogen has mass, so obviously it would reach equilibrium even with the lightest of containers. The greatest equilibrium height that has been achieved in practice seems to be around 25 miles.    D b f i r s   08:57, 23 December 2014 (UTC)


 * OK, so at some point, it would become as heavy as the air around it, and would rise no further. So, barring calamity, it would float around in the upper atmosphere indefinitely, right? ←Baseball Bugs What's up, Doc? carrots→ 14:58, 23 December 2014 (UTC)


 * In a universe with no UV light where materials last forever, yes. In the real world, no. StuRat (talk) 16:22, 23 December 2014 (UTC)


 * The start of the question, "Given a perfectly sealed airship..." presumes an ideal situation rather than real-world. Even forgetting that, the questions asks both "for years" and whether it would "ever fall back to Earth." So in the real world, a sufficiently sealed balloon could stay aloft for a lengthy time, but just how long would depend on many factors. ←Baseball Bugs What's up, Doc? carrots→ 16:33, 23 December 2014 (UTC)


 * I take "a perfectly sealed airship" to mean that it was initially perfectly sealed, not that it would remain so forever, which would require changing the nature of the universe. StuRat (talk) 17:04, 23 December 2014 (UTC)


 * The practical problem is that the available lighter-than-air gasses all have very small molecules (especially hydrogen and helium) - and they'll leak through any reasonable material - especially because the pressure inside the balloon is likely to be higher than outside. A hot-air balloon wouldn't have that problem - but keeping it hot would likely be impossible.  So as a practical matter, the answer is definitely "No!".  But as a thought-experiment, then with a material that was somehow magically impervious to hydrogen or helium would be able to stay aloft indefinitely.
 * If we're getting picky about "indefinitely" and "exactly the same density of air at 10,000 meters" then there might be other issues. List of birds by flight heights indicates that there are a couple of bird species that can fly that high - and if one of them decided to land on the perfectly set up craft, then it would start to slowly fall back to earth and find a new equilibrium at a lower altitude where other birds could reach it and push it down further...unlikely to happen...but "indefinitely" is a very long time!  At least at 10,000 meters, you're above obvious obstructions like mountains and man-made structures.  SteveBaker (talk) 17:43, 23 December 2014 (UTC)
 * The OP contradicts himself, between "for years" and "would it ever", the latter implying "forever". However, it looks like he's got ample information from various responders. ←Baseball Bugs What's up, Doc? carrots→ 21:36, 23 December 2014 (UTC)
 * While it's possible that wind phenomena could "bring it to Earth" at high mountains like the Himalayas, the real answer is probably that xeric plants like lichens would grow on it, accumulate dust, get some moss or grass growing, until it was so encrusted that it came to rest. Weary travellers would doubtless decamp on this raised soft and verdant spot in the otherwise barren Tibetan plain, until this modern-day sinking island, without warning, would pitch off some of its burden and bear its hapless passengers away to the depths of the sky, never to return. Wnt (talk) 22:29, 23 December 2014 (UTC)
 * Maybe. I was imagining a balloon the size of a beach ball. ←Baseball Bugs What's up, Doc? carrots→ 23:15, 23 December 2014 (UTC)


 * You get a better buoyancy/weight ratio with a larger balloon, see surface-area-to-volume ratio. You need one that will pass over the highest mountains (The Andes and the Himalayas) over which the jet streams pass.  You can calculate this from the air pressure at the top of Mount Everest.  You'll get the best results from a high-entropy alloy like AlLiMgTiSc which is as light as aluminum and as strong as titanium.  You should be able to fill this with H2 at a partial pressure less than the air at the same altitude at which it will fly. μηδείς (talk) 01:37, 24 December 2014 (UTC)

Baumgartner's video
Why in this particular Red Bull's video the altimeter shows something like 4,469 ft (1,363 m) when Felix had already landed (although the airspeed looks correct)? Aren't they live-streamed parameters? Brandmeistertalk  21:10, 22 December 2014 (UTC)


 * Because that's the altitude of the place, 40 miles east of Roswell, where he landed. Google Earth gives an altitude of 4462 ft at the landing location given in the Red Bull Stratos article. -- Finlay McWalterᚠTalk 21:41, 22 December 2014 (UTC)
 * QNH is the technical term. Tevildo (talk) 22:23, 22 December 2014 (UTC)
 * ....Although, I have never heard of "QNH" in common use as an aviator in the United States. I think you would get a lot of blank stares if you used that terminology at an airfield in New Mexico.  Here, we use "flight level," and only when appropriate (generally, for Class A airspace, above 18,000 feet MSL).  Perhaps the Q code terminology is more common in Europe or elsewhere.  Nimur (talk) 15:08, 23 December 2014 (UTC)

The longest half life medication is known?
5.28.180.110 (talk) 23:23, 22 December 2014 (UTC)


 * See answers to a similar question at Reference desk/Archives/Science/2014 December 16. Plasmic Physics (talk) 02:15, 23 December 2014 (UTC)


 * This Tel Aviv IP is repeatedly asking the same questions multiple times, over and over again, redundantly. μηδείς (talk) 02:48, 23 December 2014 (UTC)