Wikipedia:Reference desk/Archives/Science/2014 March 7

= March 7 =

How do whales control their depth?
I cant seem to find any information that is informative on this and not just speculative.

Also how did avocado trees survive if the animals that transported their seeds died out?

70.210.72.203 (talk) 03:24, 7 March 2014 (UTC)
 * Lungs, according to this The compressability of the air in whale's lungs help keep them neutrally buoyant at any depth. As they dive, their lungs compress, and thus have a smaller volume, which makes the whale more "dense" and thus maintains buoyancy at the lower depth, where the water is also more dense.  In this way, the whale's lungs work akin to a swim bladder in fish, which is interesting because swim bladders are homologous to lungs in land animals.  Regarding the Avocado; the modern farm-raised avocado survives because of human cultivation.  It has been modified extensively from its wild ancestors.  Like maize, it is unlikely that cultivated avocado would survive without humans to keep them going.  Avocado have been cultivated for like 10,000 years, so there was time for humans to take over when the animals they coevolved with died out.  -- Jayron  32  03:34, 7 March 2014 (UTC)


 * Interesting. thank you, I came across this article Sink or Swim and it seemed really interesting but I couldn't figure out how to find the whole article and not just the abstract.
 * also how long must the avocado plant have survived without the animals that spread it's seeds being alive before human intervention?
 * 70.210.72.203 (talk) 03:43, 7 March 2014 (UTC)
 * It doesn't have to be any time at all. It's quite likely that the original seed-spreading animals which co-evolved with the wild avocado (as noted in the Wikipedia article avocado were still alive 10,000 years ago.  That same Wikipedia article notes that there's evidence of human cultivation of Avocado 10,000 years ago.  I'm just speculating, but it's clear that something like that happened... -- Jayron  32  03:46, 7 March 2014 (UTC)
 * You're right, I had assumed that the giant sloths that ate the seeds came well before human cultivation.70.210.72.203 (talk) 03:49, 7 March 2014 (UTC)
 * Although according to Avocado, the original, undomesticated variety still survives. Rojomoke (talk) 05:19, 7 March 2014 (UTC)


 * Passing an avocado stone may be difficult, but nothing beats the experience. Have you tried it? μηδείς (talk) 04:10, 7 March 2014 (UTC)


 * Regarding the whales: Jayron's answer is all bassackwards, because water is practically incompressible and does not become "more dense" as he said. The real answer is, whales control their depth with their fins, just like a submarine -- all that their lungs do is make their buoyancy approximately neutral so they don't sink (same thing as with a fish's swim bladder). 24.5.122.13 (talk) 07:39, 7 March 2014 (UTC)
 * Air is not water, dearie. —Tamfang (talk) 09:15, 7 March 2014 (UTC)
 * Here's Jayron's comment, for your reference: "As they dive, their lungs compress, and thus have a smaller volume, which makes the whale more "dense" and thus maintains buoyancy at the lower depth, where the water is also more dense." (emphasis mine) And don't you DARE call me "dearie"!!! 24.5.122.13 (talk) 10:20, 7 March 2014 (UTC)
 * It's a burden being right all the time. In case you don't wish to click that, Dearie,  "So, the density of ocean water increases and increases as you go to the bottom of the ocean. The deep ocean is layered with the densest water on bottom and the lightest water on top."  -- Jayron  32  10:47, 7 March 2014 (UTC)
 * Yeah right -- the increase in density from top to bottom is no more than 0.5% AT MOST, which is not nearly enough to matter, moron! 24.5.122.13 (talk) 11:25, 7 March 2014 (UTC)
 * IP 24.5: Don't insult other users, this is not Yahoo Answers.
 * On top of this, 0.5% doesn't look like much, but only the air inside the lungs is more compressible, so it could be enough. OTOH, since the blood and all the solid matter that make up the whale is slightly compressible, too, I can't say for sure. - ¡Ouch! (hurt me / more pain) 11:42, 7 March 2014 (UTC)


 * This article also discusses the role of lungs in maintaining neutral buoyancy in various sea animals. It should be noted that calling me a "moron" doesn't make that article disappear.  -- Jayron  32  12:15, 7 March 2014 (UTC)


 * If that graph in the link is right, that's only 3 parts in a thousand density difference, mostly near the top of the ocean (which is also where the air would be compressed, but even much faster). From  it looks like a bottlenose dolphin has a tidal volume of 10 liters (which is close to all of its lung capacity due to its adaptation) and from the article it weighs about 250 kg, so that is 1/25 of the animal's weight in buoyancy that is lost.  So it would seem that the lungs very much overcompensate for the density increase of seawater, which is essentially negligible.  Worse, the density change is in the "wrong direction", dragging the dolphin down when it is deep.  As a rule, swim bladders change in volume quite slowly to mediate a long-term change in neutral buoyancy - but whales, diving all the way down and back in a short time, need to move much faster than they would sink as dead weight. Wnt (talk) 15:22, 7 March 2014 (UTC)
 * The link to "This Article" that Jayron gives above answers the OP's question perfectly, and makes amazing reading!! It seems that Sperm Whales at least, control their buoyancy by heating or cooling (using hot blood or cool seawater) their spermaceti organ to alter the volume of the spermaceti oil. That's smart engineering. Thanks Jayron. 122.108.177.30 (talk) — Preceding undated comment added 08:17, 8 March 2014 (UTC)
 * "The compressability of the air in whale's lungs help keep them neutrally buoyant at any depth" is not supported by the linked article. Any scuba diver would be puzzled by such a claim, because the instability of buoyancy underwater with depth due to the relative compressibility of gasses (primarily the air in one's lungs) makes buoyancy control tricky nearer the surface.  Additional buoyancy control (energetic swimming, in the case of the whale) is needed precisely to combat this instability.  The article indicates that to dive, the whale has to expend considerable energy to overcome the initial positive buoyancy until the air in the lungs has compressed sufficiently.  The mechanism of oil density control is clearly to conserve energy during both the descent (with negative or not-so-positive buoyancy) and the ascent (with positive buoyancy), which may be a considerable distance (up to 3 km each way).  Once deep enough, the contribution to buoyancy due to the air in the lungs will be essentially negligible, and buoyancy will be comparatively stable.  So, the air in the lungs is far from a help: it is a hindrance to buoyancy control. —Quondum 18:09, 8 March 2014 (UTC)

The reaction between concentrated HNO3 and some metals
Can you give me the balanaced chemical equation of rection between concentrated HNO3 and Fe, Co, Al, Cr which should produce the metals' oxides. But I don't know what the other products are. Is it NO or NO2 like the reaction with copper? --G.Kiruthikan (talk) 14:32, 7 March 2014 (UTC)
 * You would not make the oxides. You make the nitrates.  In concentrated nitric acid, you make NO2, in dilute nitric acid, you make NO.  For copper, the basic reactions are:


 * Cu(s) +  4HNO3(aq)  ——>  Cu(NO3)2(aq)  +  2NO2(g)  +  2H2O(l)
 * 3Cu(s) +  8HNO3(aq)  ——>  3Cu(NO3)2(aq)  +  2NO(g)  +  4H2O(l)
 * For any other metal that reacts with nitric acid, you'll get similar reactions, excepting you'll make whatever is that metals most stable oxidation state. For Iron, for example, I'd expect Fe(NO3)3. -- Jayron  32  18:47, 7 March 2014 (UTC)

Teaching myself General Relativity
I am thinking about teaching meyself GR with the only the internet and maybe a few texts I can buy in an ebook format and no expert guidance. Is this a achivable goal? How much time should I set aside for it? And what resources (Ideally available online on a digital format) would you recomend for it?Diwakark86 (talk) 15:28, 7 March 2014 (UTC)


 * This depends heavily on your background. Are you familiar with linear algebra and calculus?  If so, you should be able to teach yourself basic GR, albeit with difficulty.  Check out Introduction to General Relativity by Lewis Ryder and Leonard Susskind's lecture series at Stanford University: .  --Bowlhover (talk) 16:03, 7 March 2014 (UTC)


 * The answer to that question is going to depend a lot on where you're starting from, and where you're hoping to get to. MIT offers an open courseware version of their course in general relativity 8.962, which I expect would give a reasonable working knowledge of the topic.  If you were to actually take the course, you'd be looking at three hours per week of lectures, times fifteen weeks, plus probably at least as much time spent on assignments and homework to try to apply what you had learnt&mdash;call it a hundred-plus hour commitment all told.
 * However, that presupposes that you are prepared to take a graduate-level course, and that you already have a reasonably firm grasp of the prerequisite material. From the syllabus,
 * The course catalog lists Differential Equations (18.03), Linear Algebra (18.06), and Electromagnetism II (8.07) as prerequisites. Students should also be familiar with Lagrangians and action principles, Green's functions, and numerical analysis (some homework assignments require the numerical solution of systems of differential equations).
 * There's some pretty heavy mathematical lifting involved in GR. (Note that the prerequisite courses specified each have their own list of prerequisites as well.)  There's a lot of foundational knowledge that you would be expected to have to build on.  You haven't specified what level of knowledge and experience you're coming in with, so it's hard to say how long it would take you to get up to speed.
 * The other side of the question is what you are hoping to do with it. General relativity is something that physicists can study and work with (and argue over) for entire careers; there's a very, very long road between knowing something about GR and knowing most of GR.  TenOfAllTrades(talk) 16:12, 7 March 2014 (UTC)
 * Here are: a simple introduction, a too-simple introduction and several videos about GR. 84.209.89.214 (talk) 16:58, 7 March 2014 (UTC)

Good free of charge comprehensive lectures. This is a good text, but it won't work for you if you don't have the rght attitude toward studying. 't Hooft already gves a hint of that in the introduction when he writes: "I see no reason to shield students against the phenomenon of changes of convention and notation. Such transitions are necessary whenever one switches from one field of research to another. They better get used to it.". The advantage of this text of just 72 pages over most other texts is that while you only need the same minimal knowledge to read other the introductory GR texts, if you complete these lecture notes, you will be able to do more advanced calculations, e.g. compute the amount of gravitational radiation emitted by a rotating object from first principles. Other lecture notes may also lead to the same end result but they typically comprise of hundreds of pages. Count Iblis (talk) 17:55, 7 March 2014 (UTC)

The PDF Count Iblis linked to looks good, but if you find it to be too condensed, you may need to buy a textbook to self-study. Unfortunately, the book I would recommend for that purpose doesn't appear to be available in a digital format.

I started off trying to self-study GR from Schutz, but I didn't get very far in that book because I found myself feeling like I wasn't really understanding the differential geometry being used. So I gave up on Schutz, and started over by self-studying MTW. Self-studying MTW worked much better, since MTW gives very thorough explanations of the needed differential geometry concepts. However, MTW's thoroughness made studying it take quite a while; it's huge. I'm not certain, but I'm under the impression that Wald is the most widely-used graduate-level GR textbook. I own a copy of Wald, and use it as a reference, but I think it would be similar to Schutz in that its coverage of differential geometry would be too dense if you haven't already had some exposure to the subject. I also have a copy of Hartle that I reference occasionally, and of the four books I own that give a broad coverage of the basics of GR, Hartle looks like it's easily the one that's the most accessible at an introductory level. It also has the plus of being considerably newer than any of the other three books. Hartle unfortunately didn't exist yet when I was self-studying GR, or I think I would have chosen that as my first book on the subject. In short, I would recommend Hartle as the book to initially learn the basics of GR from, and then follow that with Wald if you're feeling like you want a more rigorous understanding after finishing Hartle. Hartle's book is "Gravity: An Introduction to Einstein's General Relativity", and Wald's book is "General Relativity". Red Act (talk) 05:59, 8 March 2014 (UTC)


 * I personally think that one of the best books is General theory of relativity by Paul Dirac. It is very compact and contains all important concepts. Ruslik_ Zero 16:48, 8 March 2014 (UTC)

Is this cooking instruction correct?
I have a pack of Gnocchi that the packet says will cook in 2 minutes but for 500g it needs 5L of water. Simply south...... disorganising disorganisation for just 7 years 19:44, 7 March 2014 (UTC)
 * I'm inclined to believe the packet. To cook gnocchi you need a large pan of boiling water, and you need plenty of space around the gnocchi so (a) the water doesn't cool down too much when you put them in and (b) they don't stick together. If you don't have a pan big enough, just cook them 10 or so at a time. They sink when you first put them in, and when they are done they float to the surface. --TammyMoet (talk) 19:53, 7 March 2014 (UTC)
 * I don't get the concept of cooking them 10 at a time. For the gnocchi I'm familiar with, it would take an hour to cook a pound that way, and they'd be ruined by the time you finished.  If you don't have a pot that is quite large enough, I would say try it anyway, and very gently stir them once or twice to keep them from clumping together too much. Looie496 (talk) 20:08, 7 March 2014 (UTC)
 * Most of the time cooking pasta you ad little salt and oil to the water. The oil, especially, helps keep the pasta from sticking, it being necessary to lightly stir the gnochhi with a slatted spoon in the oil at the surface to distribute the oil on their surfaces.  Salt adds flavor, and salt will raise the boiling temperature of the water (although I'd expect no one wants to put five moles of salt in their pasta water).  Does the recipe not say to add oil to the water? μηδείς (talk) 22:22, 7 March 2014 (UTC)


 * The boiling point elevation provided by the addition of any amount of salt suitable for cooking is negligible &mdash; there will be significantly more variation in boiling point due to day-to-day changes in atmospheric pressure. From a culinary perspective, adding oil to the cooking water is strongly discouraged.  Coating the pasta with oil creates a barrier that prevents the pasta from absorbing any sauce; worse still, it encourages any sauce on the outside of the cooked pasta to just slide off.  TenOfAllTrades(talk) 23:28, 7 March 2014 (UTC)


 * Yes, that's what I said, who wants to add five moles of salt to 5L of water? (You do add about .1/mol/liter for hard boiled eggs--it makes peeling them a snap, although the yolks will green if you overcook them.)  As for the oil in the pasta water, it's been in every bible in every restaurant I have ever worked in, and on every container of pasta I can remember having bothered to read the instructions on.


 * Some recipes do call for very large amounts of added salt per volume of water, which can change the boiling temp by a small amount that does have some noticeable effect on cooking times. Also, the concentration of salt in the water is (roughly) hypertonic, leading to salt absorption by the pasta, which is often desired. As to oil, that's mostly personal taste. You are right about that tending to reduce absorption of sauce, but some people prefer pasta covered in sauce, as opposed to pasta saturated with sauce. This is also a matter of amount, surely a few cc of oil will prevent sticking without having much effect on permeability (my source on all this is memory of On_Food_and_Cooking; I have no idea what pages :) The main point relevant to the OP's question is that large volumes of water are often desirable, as the addition of pasta to boiling water then causes less temperature drop, as TammyMoet has already explained. SemanticMantis (talk) 00:22, 8 March 2014 (UTC)


 * Pasta needs to absorb a lot of water, that's why you need to boil it in a big pan of water. If you use less water than specified then the boiling time increases, if you add too little then it won't get boiled properly (if you add less water than the cooked pasta will have to absorb). Count Iblis (talk) 00:07, 8 March 2014 (UTC)


 * That's true, but the most important thing is noted by TammyMoet above. You need lots of water so the individual pasta pieces (whatever pasta you are cooking) have room to spread out, cook evenly, and avoid sticking.  You need space between all the noodles/dumplings/strands/whatever so that it cooks properly.  This site recommends 4-6 quarts of water per pound of dry pasta.  -- Jayron  32  01:54, 8 March 2014 (UTC)

Engineers in industry
Other than in engineering consulting, contracting/construction, and infrastructure maintenance and management, where do engineers work? Clover345 (talk) 23:27, 7 March 2014 (UTC)


 * What kind of engineers? Surely software engineers can work for startup companies, or google, or any number of other companies. We also have civil engineers, which are often employed by various levels of government. Or even sound engineers, who may work for e.g. a recording studio. My point is "engineer" is an incredibly broad description. To get better or more specific answers, please explain which types you are curious about. SemanticMantis (talk) 00:32, 8 March 2014 (UTC)


 * You could look at List of engineering branches or Category: Engineering for ideas to find articles to check out. 71.20.250.51 (talk) 01:31, 8 March 2014 (UTC)


 * Any technology-based company, in any industry, is likely to employ engineers. There are many different kinds of engineer.--Srleffler (talk) 16:15, 11 March 2014 (UTC)


 * Chemical engineering is a major employment field worldwide, as a result of the world's burgeoning energy, petrochemical and pharmaceutical markets. A decent chemical engineer will ALWAYS have work. Biomedical engineers can work in hospitals maintaining infrastructure and medical devices, or they can be hired by medical device manufacturers (although the rate at which income of medical device manufacturers is taxed under ObamaCare seems to assure these jobs will be outsourced from the United States in the future, and no sane startup in the medical device field will incorporate in the United States when Eire and the rest of the EU constitute comparative tax havens for that industry). loupgarous (talk) 23:59, 11 March 2014 (UTC)


 * As SemanticMantis mentioned above, government also employs many engineers. The US government employs a wide range of engineers in regulatory agencies (the Nuclear Regulatory Commission hires nuclear engineers, the Federal Communications Commission employs electrical and electronic engineers, The Environmental Protection Agency doubtless has its share of various engineering disciplines, etc.).


 * The Federal Government also does work that is not regulatory in nature, and engineers work in these roles, too. The Department of Energy hires a wide variety of engineers to maintain its various nuclear-related installations and perform research on new forms of energy production and distribution.  The US Army Corps of Engineers hires hydrologists and other civil engineers, and the US Department of Defense's other agencies hire just about every imaginable engineering specialty, because modern war isn't just about weapons (Eglin Air Force Base, among other things, hires a goodly number of engineers to design and test bombs; and the Natick Soldier Research, Development and Engineering Center hires engineers in various specializations to design and test just about anything a soldier might wear, use or aim), it's about combat and civil engineering in various areas of operations.  loupgarous (talk) 23:47, 11 March 2014 (UTC)