Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

February 15

Lists of textbooks

The MAA has "a list of books recommended by the Association for purchase by college and university libraries". Where are the lists for topics other than math? I know many universities have lists of their course books online, but those aren't that comprehensive. --83.84.137.22 (talk) 00:43, 15 February 2013 (UTC)

Perthes disease

perthis diseases — Preceding unsigned comment added by 115.249.81.251 (talk) 01:41, 15 February 2013 (UTC)

See Perthes disease. Ariel. (talk) 02:09, 15 February 2013 (UTC)

Research access to data in the New England Journal of Medicine

I am not familiar with the usages that prevail in medical journals. When an article published in the New England Journal of Medicine reports conclusions of a statistical analysis of data, without explicitly giving the data itself, does the journal provide access, via the web or otherwise, to the actual data? Michael Hardy (talk) 12:10, 15 February 2013 (UTC)

Different journals have different standards and requirements. Within a particular journal, the specific requirements may depend on the type of data and type of analysis. NEJM makes specific demands for accessibility to raw clinical trial data and raw microarray data: NEJM manuscript submission requirements. Many medical journals, NEJM included, follow the ICMJE's Uniform Requirements for Manuscripts Submitted to Biomedical Journals. TenOfAllTrades(talk) 13:47, 15 February 2013 (UTC)

Interesting, but it only applies to studies with human subjects and to microarray data, and not necessarily to public health data, which is closer to what I'm looking for. Michael Hardy (talk) 02:02, 16 February 2013 (UTC)

Depending on the nature of the data that you're looking for, and the degree of 'raw'-ness, there may be issues with converting the data into a properly anonymized form that would be suitable for release (and permitted by ethics committee of the institution or organization that generated the data in the first place). TenOfAllTrades(talk) 15:55, 16 February 2013 (UTC)

It would be impossible for a journal to provide raw data -- the variability in formats would be impossible to handle in a reasonable way. Even if the journal requires the data to be available, you would have to contact the corresponding author of the paper to get it. Looie496 (talk) 22:04, 15 February 2013 (UTC)

Experimenters often spend years accumulating a dataset (and tons of grant money) and can be pretty reluctant to lend the data to somebody else who is essentially in competition with them for grant money, and can get points for publising some analysis without spending the time/money to put the data together. Outside from Congressmen who are hostile to the conclusions of the researchers, most folks don't expect them to hand over the data until they've finished wringing any possible publications out of it. So, basically, if you want access to it, you contact the researcher and make your case; if they figure you're not in competition or something you'll probably get it. On the other hand are people who analyze public datasets put together by the government; public health, meteorology, etc., so anybody can access the same data. Gzuckier (talk) 07:37, 18 February 2013 (UTC)

Fluorine Swallowing

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

TenOfAllTrades(talk) 13:29, 15 February 2013 (UTC)

Air pressure

Hi,
I would like to know why in different heights only the ears feel the pressure, and not some other organs.
Exx8 (talk) 12:19, 15 February 2013 (UTC)

The thin tympanic membrane bulges inward or outward. The eustacian tube is supposed to equalize pressure, but is easily blocked. The nerves in the area are quite sensitive, in order to protect the ear from damage (if you do something which would cause a hearing loss, you feel pain and hopefully stop). Most of the other organs aren't as sensitive to pressure, but the eyes might be the next most sensitive. However, people with rheumatism often report their pain varies with atmospheric pressure. StuRat (talk) 13:07, 15 February 2013 (UTC)

The bends can cause pain and injury elsewhere, but the pressure change involved is much greater. Ears are designed to sense pressure changes (sound), even vibrations on the scale of a single atomic diameter. Wnt (talk) 16:32, 15 February 2013 (UTC)

The difference between Fjord and Gulf?

Hi,
I would like to know what is the difference between a Fjord and a Gulf? Exx8 (talk) 12:23, 15 February 2013 (UTC)

A fjord is an inlet carved by a glacier. A gulf is just a general term for a large inlet. Dauto (talk) 14:32, 15 February 2013 (UTC)

To quote our own article, a fjord is "a long, narrow inlet with steep sides or cliffs, created in a valley carved by glacial activity". It isn't just any small inlet. Gulfs are arms or bays of oceans or seas. In fact the Gulf of Mexico is larger than most seas. (Aside, why can't I find a list of water bodies by size on Wikipedia?) Rmhermen (talk) 18:45, 15 February 2013 (UTC)

Wnt please go away from my sections. You are right buy you annoy me.I had a mistake okay, English IS NOT my mother tongue such as modesty is not your main attribute. Thanks for the rest who resisted their desire of making fun of spelling mistakes and for answering my answer.Exx8 (talk) 21:03, 15 February 2013 (UTC)

Hey man, don't let it get to you. Humor is a good thing. I though the jokes were OK. What's not OK is for you (or whoever did it) to erase other people's posts (even if they were just jokes.) Dauto (talk) 21:56, 15 February 2013 (UTC)

Here's a link to the deleted posts since none of this makes any sense otherwise: diff. μηδείς (talk) 02:41, 16 February 2013 (UTC)

It sounds like Exx8 got my statement backwards here - I was not making fun of him and indeed do not even regard saying "a Golf" as a mistake when you are speaking of a map of Sweden. Wnt (talk) 21:23, 16 February 2013 (UTC)

Note that the tern "fjord" is a technical term used by geographers, but in general speech specifically refers to these features in Scandinavia. In Scotland, they are generally called "sea lochs", an example is Loch Goil, and in the rest of the English speaking world (someone will correct me if I'm wrong about this) "inlet" is used, an example is Burrard Inlet in Canada. However, because these are general terms, they are sometimes applied to features that are not technically fjords. Alansplodge (talk) 11:42, 16 February 2013 (UTC)

The region of New Zealand where the inlets are very similar in both look and geology to those of Norway is "correctly" called Fiordland. However, the fjords themselves have names containing the word sound, e.g. Milford Sound./Coffeeshivers (talk) 15:12, 17 February 2013 (UTC)

The role of splitter plates in jet engine inlet geometry

I started the article Splitter plate (aircraft) thinking I knew I how they worked, otherwise I wouldn't have started the article, but looking for citations on the net has led me to doubt my understanding of the topic. I had thought that what the splitter plate did in supersonic flight was that in breaking up the boundary layer air, it tipped turbulent air into the stream of air entering the intakes creating an air dam that slowed the ingested air sufficiently that a simple pitot intake, without the need for intake ramps or inlet cones, was sufficient to insure air entering the engine was within its operational range. Am I very mistaken? One source I found stated that the purpose of the splitter plates was to prevent slow boundary layer air entering the intakes since the engine would work at their most efficient by maximising the intake of fast travellin free air. I know that these things are compromises and trade offs, are different effects at play at different speeds/altitudes --KTo288 (talk) 14:42, 15 February 2013 (UTC)

I don't fly jets, so I'm not very familiar with supersonic technology; but fast piston-powered aircraft use cowl flaps to control airflow for cooling and air-intake, at the expense of extra drag. Complex aircraft can open and close the cowl flaps as needed. Nimur (talk) 15:33, 15 February 2013 (UTC)

• I don't design or fly jets either. I did carry out a quick Google search, however, using the term "boundary air control above mach 1" which resulted in this: Hughes, Donald L; Holztman, Jon K; Johnson, Harold J (1972). "Flight-Determined Characteristics of an Air Intake System of an F-111A Airplane" (PDF). Technical Note. D–6679. NASA. Retrieved 15 February 2013. It may be of help --Senra (talk) 19:55, 15 February 2013 (UTC)
• Also Hünecke, Klaus (1997). Jet Engines. England: Airlife. pp. 76–79. ISBN 1853108340. ... the thickening of the boundary layer that develops at high angles-of-attack along the lower side of the fuselage forebody [in the F-16]. In order to prevent low-energy flow from entering the engine, the intake had to be offset from the fuselage to free it from the boundary layer, which uninterruptedly passes along the fuselage. The intake cowl [of the F-16] features a moderately blunt lower lip that transitions into a sharp leading-edge extension or splitter plate on the upper side (close to the fuselage). My bold-italic emphasis --Senra (talk) 20:32, 15 February 2013 (UTC)

Perhaps this will help: Diverterless supersonic inlet talks about diverting the boundary layer with some sexy grooves and bumps, and the photo in that article contrasts it with the F16's conventional intake. More explicitly, that article cites as a reference this Lockheed Martin article, which talks about different ways of dealing with boundary layer effects in supersonic jet intakes. That seems to be differentiating between a "diverter" and a "splitter plate". This says "Splitter plate not required with proper diverter design". So I'm not sure that what Splitter plate (aircraft) is talking about isn't really a diverter, of which a splitter plate is an optional element (rather than a synonym). But anyway, all of that differs from your "breaking up the boundary layer" idea, but rather at preventing the boundary layer air from entering the intake at all. -- Finlay McWalterჷTalk 21:27, 15 February 2013 (UTC)

Entropy

Is the following the correct equation to use to find the entropy generation when iron is quenched?

S(water)= mclnT/T S(iron) = mclnT/T Total S generated = S(water) + S(Iron)

Thanks Clover345 (talk) 17:59, 15 February 2013 (UTC)

Entropy production

I know that dS=(Q/T)out - (Q/T)in + S(produced in the system). But how do you find dS so that you can find S(produced in system). For some reason my calculation works if I set dS to 0 but I don't know why. My system is a building wall and I calculated the entropy generated by it given the temps outside and inside, it's conductivity & convection heat transfer coefficients from wall to environment and wall to inside. Why is dS 0? Clover345 (talk) 19:04, 15 February 2013 (UTC)

Because no entropy is produced in the wall except for one related to heat transfer through the wall. Ruslik_Zero 19:21, 15 February 2013 (UTC)

isn't that contradictory? If entropy is produced by heat transfer through the wall, shouldn't dS be over 0? Clover345 (talk) 19:47, 15 February 2013 (UTC)

$\Delta S=0$ for the wall over any period during which the temperatures on the two sides are (taken to be) constant, because entropy is a state function and the wall's state is constant. The entropy changes from the heat transfer occur on the two sides: a negative change on the warm side and a (larger) positive side on the cold side. --Tardis (talk) 03:58, 16 February 2013 (UTC)

thanks but this confuses me. If dS=0, why is the entropy produced by the wall higher than 0. Clover345 (talk) 19:43, 16 February 2013 (UTC)

The entropy produced "by" the wall (that is, because the wall isn't a perfect insulator and heat is flowing through it) can be non-zero even though the entropy produced in the wall (that is, because of any change in the wall's state) is zero.

We can associate with any heat flux an entropy flux: ${\vec {s}}:={\frac {1}{T}}{\vec {q}}$ (recall that we usually do not define division (as in $\Delta S={\frac {Q}{T}}$) for vectors), and in direct analogy to the first law, we may write ${\frac {\partial \rho _{S}}{\partial t}}=\rho _{\dot {S}}-{\vec {\nabla }}\cdot {\vec {s}}$ (the change of entropy density is equal to the entropy (density) generation rate minus the divergence of the entropy flux). (The difference between the first and second laws is that $\rho _{\dot {Q}}$ must be balanced by some change in the internal energy of the system, whereas $\rho _{\dot {S}}\geq 0$ but is otherwise unrestricted.) For every point in the wall, ${\frac {\partial \rho _{S}}{\partial t}}=0$, so $\rho _{\dot {S}}={\vec {\nabla }}\cdot {\vec {s}}$. The only kind of process occurring is heat flow (no chemistry, work, compression, etc.), so this entropy production is entirely due to the heat flow.

Assuming a linear temperature profile in (say) x, as for a wall of uniform material and small temperature changes, this rate is ${\frac {\partial s_{x}}{\partial x}}={\frac {d}{dx}}{\frac {q}{T}}=q{\frac {-1}{T^{2}}}{\frac {dT}{dx}}={\frac {k}{T^{2}}}\left({\frac {dT}{dx}}\right)^{2}$ (the thermal conductivity times the square of the logarithmic derivative of temperature over space). Letting the wall extend from 0 (where the temperature is $T_{1}$) to X (where the temperature is $T_{2}$), this is ${\frac {k}{(T_{1}/m+x)^{2}}}$, where $m={\frac {T_{2}-T_{1}}{X}}$ is the thermal gradient. So the entropy is produced throughout the wall, most intensely at the colder side ($x=0$ for $m>0$), but it is all emitted at that side and none is retained in the wall. (I won't claim to have proven this point, since I derived $\rho _{\dot {S}}$ from the statement that ${\frac {\partial \rho _{S}}{\partial t}}=0$, but I hope that it's easier to accept given this context and explanation.) --Tardis (talk) 19:25, 17 February 2013 (UTC)

February 16

One Kidney Giving Out

If one of someone's kidneys gives out but the person's other kidney is still working, would the person need to remove the failed kidney from his body in order to continue to survive or how would that work? Also, one kidney can fail while another would continue to function properly, correct? Thank you very much and sorry if this is a stupid question. Futurist110 (talk) 00:11, 16 February 2013 (UTC)

It all depends on why one kidney failed; if it's cancer, then it should be removed (or irradiated or otherwise dealt with). If not, it may just atrophy without causing any further problems. And yes, one kidney can continue to function alone, although a diet and habits that take it easy on the remaining kidney would be a good idea. StuRat (talk) 00:30, 16 February 2013 (UTC)

StuRat's answer is, unfortunately, a typical StuRat off-the-cuff answer. He's right of course about a cancerous kidney - as cancer can spread. However, as with muscles and most other things in the body, kidneys grow to a size able to take the load. If you lose one kidney, the other one increases in size and there is more or less no permanent impact. There is no need for a special diet or habits. See http://www.kidney.org/atoz/content/onekidney.cfm. The main impact is that a urinary tract infection that impacts on the kidney will have a more serious impact, but such infections are fairly rare, especially in men. Sulpha antibiotics, which tend to cause scaring in the urinary tract, have a higher impact in people with only one kidney. No doubt StuRat will come back, he usually does, with some abuse and/or some website that almost but not quite supports that a special diet is indicated. Wickwack 58.164.228.62 (talk) 03:48, 16 February 2013 (UTC)

Yea, like this source: "You simply need to make healthy choices, including fruits, vegetables, grains, and low-fat dairy foods. Limit your daily salt (sodium) intake to 2,000 milligrams or less if you already have high blood pressure. Reading nutrition labels on packaged foods to learn how much sodium is in one serving and keeping a sodium diary can help. Limit alcohol and caffeine intake as well. Avoid high-protein diets. Protein breaks down into the waste materials that the kidneys must remove, so excessive protein puts an extra burden on the kidneys. Eating moderate amounts of protein is still important for proper nutrition. A dietitian can help you find the right amount of protein in your diet." [1]. Now for your abuse: You're the one who doesn't know what he's talking about, as usual. StuRat (talk) 04:18, 16 February 2013 (UTC)

You left out the first sentence in that section (Eating sensibly): "Having a single kidney does not mean you have to follow a special diet". And you didn't mention that the 2 grams of salt and the rest of it is just about standard advice given to every one these days, regardless of number of kidneys. Wickwack 124.182.162.210 (talk) 05:00, 16 February 2013 (UTC)

The moderating protein intake isn't a normal recommendation. Also, I didn't say a special diet was required, that was you. I just said "a diet and habits that take it easy on the remaining kidney would be a good idea". This is using "diet" to mean "what you eat", not "a crash weight loss plan" or any other meaning. StuRat (talk) 05:45, 16 February 2013 (UTC)

Consuming an excessive fraction of protein is not a particularly good idea for anyone, two kidneys or not, and is standard advice ever since the Swedish Govt devised the well-known "food pyramid" in 1974 (which advises protein consumption between 10 and 15% measured by calorific content), and was inherent dietry advice for the general population well before 1974 - I remember being taught at school 60 years ago to eat from a balance of 5 food groups (Most govts now advise on the basis of 7 groups). The essense of the advice from the various websites provided here by myself, yourself, and others can be summed up as follows: No special diet is needed, however a bad diet may carry greater risk for a person with only one kidney. If that's what you meant, why didn't you say so? You said "a diet and habits that take it easy on the the remaining kidney would be a good idea." Which means a special diet. Why didn't you say no special diet needed? Because you posted off-the-cuff without thinking or checking, as usual. Wickwack 121.221.31.66 (talk) 09:48, 17 February 2013 (UTC)

It does not mean that, you just look for any possible way to attack me, even if it means intentionally misinterpreting whatever I say. StuRat (talk) 03:35, 18 February 2013 (UTC)

As our article Kidney transplantation says, when someone receives a new kidney his or her own kidneys are not removed. There seems to be no drawback to keeping the non-functional kidneys, and an increased risk by removing them. Also, as I understand it, sometimes their own kidneys still have some function and you want to keep that if possible. Sjö (talk) 08:21, 16 February 2013 (UTC)

---

Information about High protein, high fat, low carbohydrate (Atkins) diets and normal (dual) kidneys:

http://abcnews.go.com/blogs/health/2012/06/01/high-protein-low-carb-diet-safe-for-kidneys/

http://news.yahoo.com/atkins-type-diets-look-kidney-friendly-study-210610591.html

http://health.usnews.com/health-news/news/articles/2012/05/31/atkins-type-diets-look-kidney-friendly-study

We know that some sorts of kidney disease require a low protein diet, so the person with one kidney should ask his/her physician if whatever was wrong with the first one is also wrong with the second one.

We also know that obesity is bad for your kidneys, so if the diet helps you to lose weight that is a plus.

I cannot find any studies on high-protein diets and single kidneys. Some doctors advise avoiding a high-protein diets with a single kidney, but the question is whether this is backed up by studies or just being cautious. --Guy Macon (talk) 09:00, 16 February 2013 (UTC)

This is all pure OR. My father received a kick to one of his kidneys while playing rugby, which resulted in him missing 18 months schooling and the kidney itself failing completely. That was not known until 40 years later, when he was hospitalised for severe hypertension. His kidney function was assessed as 20% in the one remaining functional kidney. He didn't need any special diet, he was advised to moderate his salt intake (which he ignored) and was put on medication which he took for the remaining 30 years of his life. So the answer to the OP's questions are no, you don't need to have a non-functional kidney removed: in fact, you can live for many years without even knowing you have a non-functional kidney. I'll have a trawl of a website to confirm with references for you. --TammyMoet (talk) 13:17, 16 February 2013 (UTC) Here's a webpage that answers your questions. --TammyMoet (talk) 13:22, 16 February 2013 (UTC)

What do these terms mean?

On the Doctor Who Restoration Team website, there are repeated references to "tramline damage", "off-lock"s, and "phosphor hole"s. What do these terms mean? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:20, 16 February 2013 (UTC)

• Tramline damage is simply long scrapes down the film or tape caused by something scratching the tape is it moves past. [2]
• Video tape, and analog video signals in general, contains synchronisation information about the end of a line and the end of the whole screen (it's much more complicated than that, but that's the idea). A player uses that information to keep its own clock in line with the tape. If the tape is damaged or degraded, that synchronisation information can be corrupted. This causes the player to lose an accurate idea of where the video has got to; it has lost "lock". When this happens the picture rolls up or down or breaks up entirely. See Analog television#Synchronization
• This posting (the bottom one) explains a phosphor hole.

-- Finlay McWalterჷTalk 01:04, 16 February 2013 (UTC)

So when it loses lock, the player simply scribbles lines across the screen in all the wrong places? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 02:28, 16 February 2013 (UTC)

Assuming you are familiar with that site, are they bringing back any lost episodes, or just restoring known ones? μηδείς (talk) 02:37, 16 February 2013 (UTC)

See Doctor Who missing episodes and Doctor Who Restoration Team. -- Finlay McWalterჷTalk 02:48, 16 February 2013 (UTC)

Thanks. I was familiar with the first article. It would be interesting to see one of the improved episodes. μηδείς (talk) 03:50, 16 February 2013 (UTC)

If you've watched any dvds of the first seven doctors' adventures, then you already have. 86.163.209.18 (talk) 09:33, 16 February 2013 (UTC)

If it loses vertical lock, the picture rolls up (or down) (with stuff that goes off one margin coming on at the other) - usually there's a wide blanking gap (a black strip) which sometimes contains flashing garbage. If you ever had to tune an old TV with a bad antenna you'd recognise this. Losing horizontal lock is worse; depending on the system, and the kind of degradation, the picture might slide sideways, go all sideways-diagonal-ish, or just turn into a horrible cascade of little horizontal slices of picture that jerk about on the screen. -- Finlay McWalterჷTalk 02:46, 16 February 2013 (UTC)

How many isomers does 1024-ane have(both including and excluding stereoisomers)?

Already checked the OEIS record, but that is still too complicated for me to understand. I just want to add this information to a humor page.--Inspector (talk) 01:37, 16 February 2013 (UTC)

It is too long ago, but I think I remember that only if you exlude ring systems which you obviously not do a solution with a relative easy algorythm is possible with ring systems they said it is very complicated.--Stone (talk) 10:24, 17 February 2013 (UTC)

Let's s say there is no ring system. What does the formula expanded look like?--Inspector (talk) 12:12, 17 February 2013 (UTC)

If a closed formula were known, I'd expect OEIS to show it. —Tamfang (talk) 07:02, 19 December 2013 (UTC)

Conservation of energy

Consider a workman using a heavy implement such as an axe or sledgehammer to do irreversible work such as splitting a block of wood, breaking a rock or flattening an empty beverage can. The workman gives the implement a large amount of potential energy by raising it above his head. He then lets it fall and the potential energy is converted to kinetic energy. After the implement has struck the wood, rock or beverage can, all mechanical energy has disappeared. It is not possible to recover the lost mechanical energy by re-joining the block of wood, re-assembling the rock or stretching the flattened beverage can. Has energy been conserved? If so, to what form of energy has the mechanical energy been converted? How do we explain the validity of the law of conservation of energy in this situation? Dolphin (t) 03:17, 16 February 2013 (UTC)

Is this a homework question? Someguy1221 (talk) 03:27, 16 February 2013 (UTC)

No, it isn't a homework question. I know the answer ("Yes, energy is conserved") but I am asking it here to see how different Users go about explaining it. Our article Conservation of energy doesn't address the situation. Dolphin (t) 03:32, 16 February 2013 (UTC)

Wait a sec, you claim on your userpage to have a college degree in engineering...Someguy1221 (talk) 03:28, 16 February 2013 (UTC)

I would like to think that only someone with a college degree in physics or engineering would be able to formulate this question. I think it would be a good question in a physics exam. Dolphin (t) 03:41, 16 February 2013 (UTC)

Of course I can tell you where the energy is going, but I do not have the competence in physics to really explain why the energy cannot be got back without waving my hands rather furiously. I was hoping to build an explanation around conservative vs. non-conservative forces, but our article seems to go into no detail on the practical implications of a force being one or the other. Someguy1221 (talk) 03:49, 16 February 2013 (UTC)

Most literature, including Conservation of energy, focusses all attention on converting energy from one form to another. A small amount of literature also talks about doing reversible work such as dropping an object onto a spring so that the object rebounds to its original height. All the literature (that I am aware of) is silent on the subject of doing irreversible work. Dolphin (t) 03:54, 16 February 2013 (UTC)

(ec) Ignore the energy lost because a human is an inefficient chemically-driven thermodynamic machine. (That is easy to understand in a hand-waving way, but it's harder to explain specifically unless we want to dive into the depths of biochemistry and metabolism). Consider only the irreversible energy-transfer related to the cutting of a material. Plastic deformation is the opposite of elastic deformation, in that it is irreversible. In the microscopic case, if we really really really zoom in on the act of cutting a material, we see that the act of cutting performs work on the material, in the form of both elastic- and plastic- deformation. Both types of work on a material can result in temperature change; temperature change can mean that additional heat energy will be lost via conduction and radiation, and will not be recoverable (for the usual reasons). Now - why are some materials subject to plastic (irreversible) deformation; and others are not? Because the molecules are arranged differently. This is a game of statistics calculated among ensembles of particles. For some materials, there are lots and lots and lots of local minima in the energy for lots of arrangements of molecules, so by proverbially "shaking up the lattice" you might find a different mechanical layout that is stable. For other molecule arrangements, there is one clearly-lowest-energy arrangement, and if you deviate from that arrangement, the material's constituent particles all try to go back towards its optimal arrangement. The exact nature of these materials is well-studied; we can elaborate on different metallurgies and ductile deformations and brittle failures and so forth; but, you're an aeronautical engineer! This should have been covered ad nauseum in a materials engineering class! Nimur (talk) 03:58, 16 February 2013 (UTC)

(ec) Just about any undergrad uni physics textbook has this question or something just like it in the student exercises section (Mine has the workman driving a nail into wood), so I am a bit skeptical about the clained college degree too. The answer of course, it that the potential energy given to the hammer by the workman when he lifts it is conveted to kinetic energy, which, when the can is flattened / nail driven in / wood split or whatever, is converted via plastic deformation / friction / whatever, as respectively applicable, into heat. With a bit of "spherical cow" simplification and a value for specific heat of the can / nail /wood you can calculate the temperature rise in the can / nail/ wood. Wickwack 121.221.89.248 (talk) 04:00, 16 February 2013 (UTC)

A lot of the energy goes into producing sound and heat. The sound pretty soon turns into heat too. The heat can't be collected together again and put back into moving the axe because of the nature of entropy. SteveBaker (talk)

Not much will go into sound though. Almost all will go directly into heat. I can show why with some calcs, but doing so will reveal too much. I think this is a homework question (because in undergrad physics it is a common homework question), so I won't show the math, unless the OP comes back and shows he's made an honest go at it, and got stuck. You don't need to understand the concept of entropy to do this one. Wickwack 121.215.77.163 (talk) 09:58, 16 February 2013 (UTC)

I like SteveBaker's explanation, particularly his reminder that entropy is relevant in this situation. I agree with Wickwack that an understanding of conservation of energy comes before an understanding of entropy, but despite that, I think I will find some of the concepts from thermodynamics to be helpful. For example, when flattening an empty beverage can the work done on the beverage can will equal the increase in internal energy of the material comprising the can. It may all go to an increase in temperature of the material, or alternatively work hardening of the deformed metal may also represent an increase in internal energy, leading to less of an increase in temperature. I will think about it overnight.Dolphin (t) 12:10, 16 February 2013 (UTC)

Agreed; the reference to the second law makes the whole thing make more sense. Thanks Steve! Rutebega (talk) 03:43, 20 February 2013 (UTC)

I am proposing some initial changes to Conservation of energy. See the Talk page - diff and please join in the discussion. I have also made some changes to Mechanical energy – diff 1 and diff 2. Dolphin (t) 02:09, 19 February 2013 (UTC)

About orbits of planets, electrons and other objects in dimensions higher than 3

Is is true that there can be no stable orbits for dimensions higher than 3, because the strength of gravitational and electrical field decreases more rapidly than in 3 dimensions, (e.g in 4 dimensional space the gravitational force is inversely proportional to the cube of distance)?--Inspector (talk) 14:56, 16 February 2013 (UTC)

The article Newton's theorem of revolving orbits has a short discussion of other central force laws like the inverse cubic. Actually magnets at some distance apart attract with an overall inverse cubic force so one could try this in space with a couple of magnets. Well actually they'd have to keep the same orientation, if one is rotating it goes down quite a bit faster. Dmcq (talk) 01:23, 17 February 2013 (UTC)

Next glacial period and survival of civilization

The earth is currently in an interglacial period (Holocene interglacial) since the last 12000 years. The next glacial period will start 50000 years later. I'm interested in knowing whether the global climate in a glacial period suitable for normal functioning of civilization (agriculture, public health, industry, transport etc). Will the next glacial period affect human activities in certain regions or all over the world (to the extent that human populations from one region have to migrate to other or die out)? --PlanetEditor (talk) 15:24, 16 February 2013 (UTC)

If what we've been told so far is true, natural cooling and warming cycles like this happen so slowly that we could "migrate" the necessary distance by each generation being born in a hospital ten miles further north or south (as necessary). My mathematics may be a little off, but you get the idea - if a climate change takes thousands of years, it's really not quick enough for human civilisation to really care.

Or, of course, we might be experts on anthropogenic climate change by then, and be able to stave off ice ages by increasing our CO2 output by some amount. --Demiurge1000 (talk) 15:33, 16 February 2013 (UTC)

Agreed. Our technology then will be so far advanced, that we shouldn't worry about it. For example, we may also have fusion reactors working then, providing the cheap energy needed for hydroponics. StuRat (talk) 17:29, 16 February 2013 (UTC)

• First, there's no prediction that the next glacial period will begin in 50,000 years--the record is chaotic and there have been interglacials that have lasted less time than the one were'in. Second, there's evidence the change may be rather abrupt, on the order of a decade, not centuries. Migration on that scale would be rather traumatic. Third, there's absolutely no guarantee of progress, Rome fell and something like a luddite caliphate is always possible. But lastly, there's no reason to believe humanity wouldn't survive in the lower latitudes no matter what. μηδείς (talk) 20:17, 16 February 2013 (UTC)

• There have been short-term, localized regions where technological progress stopped, or even reversed, but not worldwide, over a period of 50,000 years, during the era of modern humans. StuRat (talk) 20:43, 16 February 2013 (UTC)

Well, once again, there is no reliable source for the 50,000 year number--this could happen within the century--and global civilization could easily fall due to nuclear war or a plague, etc. The bottom line is, assuming there are people alive they will not go extinct because of an ice age itself. μηδείς (talk) 20:13, 17 February 2013 (UTC)

Unusually long interglacial, happens every 400,000 years I think. And also, due to anthropogenic greenhouse gasses, we are guaranteed at least 50,000 years of no glacial. Sagittarian Milky Way (talk) 21:12, 17 February 2013 (UTC)

There are several reliable sources positing that the present interglacial will last roughly 50,000 years based on climate modeling and drawing analogies with Marine Isotopic Stage 11, which was the last time an interglacial happened near a minimum in orbital eccentricity. See for example, Loutre and Berger, Climatic Change, 2000. There is far from a scientific consensus on how long the present interglacial will last (or would last without anthropogenic interference), but 50,000 years is a value that is commonly discussed. Saying that no such prediction exists is simply wrong. Secondly, all of the glacial transitions appear to have taken thousands of years to develop. Within the glaciations, there were abrupt regional changes, e.g. European climate swings occurring over a decade, but the global-scale changes took longer and were likely tied to the growth of ice sheets over thousands of years. A multi-kilometer ice sheet over northern North America simply can't appear overnight no matter what climate scenario one imagines. If an ice age starts to occur (which seems unlikely given the present tendency toward man-made global warming), then most of humanity will have generations to respond to it. As suggested though, tropical communities will see relatively little impact. During the last glacial, the tropics only cooled by about 1 C, while most of the cooling was at higher latitudes. Dragons flight (talk) 00:35, 19 February 2013 (UTC)

I remember a decade or so ago there was this speculation in Nature (I think) about how the Arctic Ocean thaws out entirely due to global warming, its upper layers become fresh water, plants flourish in it, sink to the bottom, consuming all the carbon dioxide and causing an Ice Age. Sounded kinda crazy to me at the time... what happened to the idea? Wnt (talk) 05:26, 20 February 2013 (UTC)

I've never heard that theory, and I agree it sounds rather crazy the way you describe. Perhaps you have some of the details wrong? Melting in Greenland can cause perturbations in the North Atlantic currents that lead to localized cooling (or less rapid warming) in Europe, but I'm not aware of any work discussing Arctic ocean plants sucking out all the carbon dioxide. Dragons flight (talk) 19:52, 20 February 2013 (UTC)

was robert boyle an idiot.? or only had a partial understanding of the world.

i would like to ask if robert boyls was an idiot - or he had only a partial understanding of the world.

because he 'invented' the perpetual-motion machine, the "self-flowing flask" (visible in his wikipedia page if you search for 'self-flowing flask'). In fact, if he had actually built it, he would have seen that it does not work.

so was he an idiot? today every school child knows "boyle's law." So, while he was naive and wrong, still, did he advanced the state of understanding in the world which shows he was not idiot?

similar with a perpetual-motion machine: especially when there is a readily available source of energy, such as a heat differential (at different water depths), a current moving against the bottom of a river, wind moving against a surface, large amounts of light that can be harnessed via the photovoltaic effect, natural motions of the earth or moon, negative acceleration that is already in use to bring vehicles to a stand-still in traffic, and so forth. All of these are an actual source of energy input - ulike boyle's contraption.

so, if he was not idiot surely same devices with actual source of energy input is not worthy of calling idiot? or should i abandon exploration of such systems? 86.101.32.82 (talk) 15:32, 16 February 2013 (UTC)

Boyle died in 1691. The law of conservation of energy (which essentially forbids perpetual motion machines) wasn't truly formulated and accepted until 140 years later. So it was far from obvious to Boyle that perpetual motion is impossible. Like many perpetual motion machine inventors - the problem that they state is always that some small optimisation in performance will make this theoretical machine work - even though their current practical implementation doesn't quite work. For a classic example of this kind of failed reasoning, check out the "SMOT" (Simple Magnetic Overunity Toy) - which was "invented" three hundred years after Boyle and doesn't work (of course)...despite endless numbers of faked videos on YouTube. The web is full of people who think they could make this perpetual motion machine work, if only they could just reduce the friction a tiny bit more - or get a tiny bit stronger magnet - or if they could just adjust that ramp to exactly the right shape. Those people are indeed idiots because there is rock-solid science that says that they are all wasting their time.

In the case of the self-filling flask, you can easily be lead to believe that it might work because surface tension will indeed make the height of the liquid in the thin tube be a little higher than in the main bowl of the goblet. Surface tension was not studied methodically until Benjamin Franklin in the 1740's, so Boyle had no science available to him to allow him to understand that effect. His reasoning behind the failure of the practical machine might have been that he imagined that the precise taper of the glass tube (required for this idea to work) might have been incorrect or that the material that it was made of caused a problem...something like that. The state of science in the 1680's (when several people reported this idea) was actually rather primitive. Alchemy was still widely practiced. Isaac Newton (who was definitely not an idiot!) was still practicing alchemy some 40 years after Boyle died. At the time Boyle was working, calculus had not been invented and even the concept of negative numbers had not yet entered European mathematics!

You, on the other hand, have the benefit of three hundred years of solid scientific experimentation and theory. "The Scientific Method" is well-established now. You have access to all of the great ideas of science at your literal fingertips here at Wikipedia and elsewhere. Mathematics has advanced beyond recognition and even children at the age of 8 years old understand the usefulness of negative numbers and teenagers are taught calculus. So, if still you think you have a perpetual motion machine, then you will most likely (and justifiably) be called "an idiot". But a machine that operates with a bonafide source of energy and which doesn't violate any of the laws of thermodynamics is perhaps not impossible.

SteveBaker (talk) 16:20, 16 February 2013 (UTC)

Justified? Hardly, and not by anyone who knows the difference between scientific knowledge and the scientific method. -Modocc (talk) 17:13, 16 February 2013 (UTC)

(ec) Robert Boyle was certainly smarter than your average guy (not an idiot) and he had a partial understanding of the world (who doesn't?). He understood energy, but not the current paradigm of thermodynamics, in which perpetual-motion machines of any kind are considered impossible, came later. In addition, our science is supposed to fit reality, thus its important to keep a critical eye on the models because sometimes theorists unintentionally build sandcastles and strawmen instead. In other words, their models do not entirely accord with reality and therefore get knocked down. As to what you should do, that is entirely your decision. -Modocc (talk) 16:48, 16 February 2013 (UTC)

These links are fascinating, thanks to everyone. It's amazing that these obviously impossible devices (due to thermodynamics, as there is no source external power) gets so many youtube view. Check this: http://www.youtube.com/watch?v=zz-Lupbn7mc 86.101.32.82 (talk) 20:04, 16 February 2013 (UTC)

Since paradigms have changed since Boyle's day and can change again, you may also be interested in the article on Paradigm shift. Modocc (talk) 21:43, 16 February 2013 (UTC)

And you might be interested in Maxwells demon to see that all the business abot perpetual motion machines is not at all obvious. Dmcq (talk) 01:12, 17 February 2013 (UTC)

Russian meteor

Meteor/asteroid coincidence

According to 2013_Russian_meteor_event#Coinciding_asteroid_approach, those two events happening 16 hours apart are just a coincidence. I'm not convinced:

1) What are the odds of such major events happening within 16 hours, if independent ? (Use whatever assumptions you like.) Here are my thoughts:

The meteor appears to be the biggest since the 1908 Tunguska event, so we could use 1/((2013-1908)*365) or 1/38325 chance of it happening on a given day. If we allow for the events to happen in either order, that's a 32 hour window, so let's multiply by 32/24 to get a 1/28744 chance of it happening within 16 hours of this particular asteroid. However, there must have been other asteroids as significant as this one. Here I'm less sure of the numbers.

2) Have scientists considered all ways in which the two events might be related ? For example, could a piece have broken off the asteroid on the last pass by the Earth, traveled roughly parallel to the main piece, but slowly diverged, then have gone around the far side of the Moon, quite close to it, and been wildly deflected this time ? StuRat (talk) 16:54, 16 February 2013 (UTC)

Well it isn't a coincidence. It is a secret, but as I know you can keep it, I will tell you. The Proxies, the space aliens from Proxima Centauri will not tolerate any space-faring races in their proximity, so they decided to eliminate our spaceports. 2012 DA14 was sent to destroy Cape Canaveral Air Force Station. Being the Proxies first try, they sent a heavy asteroid that would work disaster even when it didn't hit the target exactly. Lucky for us, it missed completely. With advances in their technology, they again sent now a cheaper, smaller, but faster and more well aimed object to destroy Baikonur. It was orchestrated as a double blow, so we wouldn't have the time to take defensive measures. As our radio transmissions need some time to reach them, they don't know of other launch sites yet.

The two orbits were not related. If something were broken off and then widely altered in orbit - it also wouldn't arrive at the same time . Rmhermen (talk) 19:29, 16 February 2013 (UTC)

Wouldn't they, under the scenario I gave ? They only diverge slightly until one goes behind the Moon, just hours before hitting/passing. StuRat (talk) 19:31, 16 February 2013 (UTC)

They came from opposite directions. If you look up any specific meteor shower you will see that all the meteors from one shower will move in the same direction from one origin in the sky, the constellation out of which they come giving the name of the shower; e.g., the Perseids. If these tow bodies had been associated they'd have come from the same area of the sky and been moving in the same direction. μηδείς (talk) 19:58, 16 February 2013 (UTC)

Not if one had gone around the far side of the Moon and had it's direction changed by 180°, as I suggested. Can someone tell me if the Moon was in the proper position for this ? StuRat (talk) 20:01, 16 February 2013 (UTC)

My first thought was that it could be some satellite orbiting 2012 DA14. As I am plain lazy, and besides, it would violate wikipedia rule WP:OR, I did not look at celestial mechanics to calculate the hypothetical orbit of the object that hit the earth around 2012 DA14 by myself. From imagination, it could well be some moonlet on its way back (back relative to the trajectory of the main object). 95.112.182.106 (talk) 20:30, 16 February 2013 (UTC)

Nope. This isn't biology, so some things really are impossible. :) And one of those things is a satellite orbiting a really, really weak gravity source, but doing so with such speed that when the primary nearly strikes the earth at that tremendous speed, the satellite strikes us at something near a right angle to it.

I'll go with the theory that friendly aliens moved the 150-foot meteoroid just enough so that it wouldn't hit us, but sent the other one at us to remind us that we ought to learn to do this for ourself. :) Wnt (talk) 21:16, 16 February 2013 (UTC)

Yes, the supposition is impossible. You are suggesting that two bodies travelling together with the same speed and trajectory and then closely passing by the moon (which was not predicted for DA14) were deflected so that one simply kept going (albeit much more slowly to explain the 16 hor time gap--although it arrived exactly when it had been predicted to do so for weeks), while the other one swang around the earth, but, instead of staying in orbit, then dropped down into the atmosphere from the entirely opposite direction. μηδείς (talk) 20:08, 17 February 2013 (UTC)

You don't seem to be understanding me at all. Here's a diagram:

          _                <-  . Little asteroid
         / \ Moon
         \_/  
               __
              /  \
             |    | Earth
              \__/
                                                                   <-  ∘ Big asteroid

      <-  .
         / \ Moon
         \_/  
               __
              /  \
             |    | Earth
              \__/
                                              <-  ∘

          _
        ./ \ Moon
         \_/  
               __
              /  \
             |    | Earth
              \__/
                                            <-  ∘

          _
         / \ Moon
        .\_/  
               __
              /  \
             |    | Earth
              \__/
                                           <-  ∘

          _
         / \ Moon
         \_/   
           .   __
              /  \
             |    | Earth
              \__/
                                          <-  ∘

          _
         / \ Moon
         \_/   __
            . /  \
             |    | Earth
              \__/
                                         <-  ∘

          _
         / \ Moon
         \_/   __
              /  \
              )   | Earth
              \__/
                                       <-  ∘

16 hours later:
          _
         / \ Moon
         \_/   __
              /  \
              )   | Earth
              \__/
        <-  ∘

You see, they already would have broken apart years before approaching Earth (this time), and would have separated in space and/or time since then. StuRat (talk) 00:02, 18 February 2013 (UTC)

Well, once again, impressive diagramming. But yes, I did actually expect that was what you meant. The problem is one of scale. The big and little asteroid were supposedly 50 and 150 ft across. At the sizes you show, the Moon and Earth would be much further apart, more like a ball bearing and a non-pareil at arms length from each other, with the nonpareil orbitting the bb once a month. The asteroids would be invisible dust grains on this scale. If they were associated, i.e., following the same path, each would then be affected by the moon's gravity if one was, but there was no such affect noted for the larger asteroid. Also, both dust grains would still have to travel the length of the arm in the same direction to get to the earth. The smaller asteroid would have to then do a very sharp half orbit around the earth (any less tight of a path and it would never strike the earth, just orbit or be deflected) but it was estimated to be travelling well over Earth's escape velocity when it hit, not under it, so some sort of "spiralling in" would have been quite impossible. μηδείς (talk) 01:18, 18 February 2013 (UTC)

They wouldn't be equally affected by the Moon, since one is extremely close to the Moon and the other is far away. I don't see why it would have to spiral into the Earth, if the deflection of the Moon shot it straight towards Earth. I do realize that the chances of such a deflection aiming it right at the Earth are low, but this relates to my first question. That is, are the odds of such a scenario lower or higher than this just being a random coincidence ? StuRat (talk) 03:30, 18 February 2013 (UTC)

No matter what you spot it and throw at it: 2 x 1km/s lunar orbit speed, the full Earth's escape velocity, whatever amount of the lunar escape velocity remains at 100 moon diameters, I'm not sure there's enough there. Sagittarian Milky Way (talk) 06:04, 18 February 2013 (UTC)

not to scale

StuRat, you are making ad hoc and contradictory assumptions which don't match the known facts. If the two rocks were associated, as is your primary assumption, they would be travelling in the same orbit around the sun in a "train" like the "string of pearls" fragments of Comet Shoemaker-Levy 9 which was disrupted by jupiter on its first pass and impacted jupiter on its second. If they were in the same orbit both rocks would have to pass by the moon relatively closely. But look at this diagram from our 2012 DA14 article. The sort of deflection you show would be impossible. A wide deflection would fling a rock off into space or put it in a wide orbit around the earth. A narrow deflection would leave the rock still coming from the same direction, which is not what happened. μηδείς (talk) 15:57, 18 February 2013 (UTC)

The Shoemaker-Levy 9 comet broke up just 2 years before it hit, versus many years, in my example. Over that time, the fragments would diverge far more. Looking at the "string of pearls" you can see that they're not all in a perfect line, even after only 2 years. Also, you talked about minor and major deflections, but how about moderate deflections ? StuRat (talk) 16:43, 18 February 2013 (UTC)

OK, now that you fixed the diagram, I think I finally see what you were saying. The Moon was not in the proper position, at the time. Of course, this would be over 16 hours earlier, so the Moon would have been in a slightly different position, but not on the other side of the Earth. StuRat (talk) 17:39, 18 February 2013 (UTC)

Comparison of the orbits of the Chelyabinsk meteor (larger elliptical blue orbit) and asteroid 2012 DA₁₄ (smaller circular blue orbit), showing they are completely dissimilar

I suggest you click on the image to the left and read its description at its file page (not the caption here) for a good brief explanation of why thyet are not considered related. μηδείς (talk) 17:45, 18 February 2013 (UTC)

Too bad they didn't put direction arrows on those two orbits or show them from the side view. If the two approached the Earth from the opposite sides, this might imply they were orbiting the Sun in opposite directions. If the orbits are both in the same plane, and going in the same direction, then they are somewhat similar, and having been deflected on a previous pass would still be possible. If they are headed in opposite directions, then probably not. Also note that we can only have a very approximate orbit for the meteor/comet which hit Russia, unless they've been able to find it in old photographs. StuRat (talk) 18:12, 18 February 2013 (UTC)

Yes, I had the same frustration. μηδείς (talk) 17:15, 19 February 2013 (UTC)

I see a new conspiration theory here. Honestly, wondering about coincidences after the facts is a waste of time at least. — Preceding unsigned comment added by 88.8.74.141 (talk) 20:29, 16 February 2013 (UTC)

A conspiracy requires conspirators. Or are you imagining a scenario where humans somehow caused this ? I believe looking at apparent coincidences after the fact has led to many scientific discoveries. StuRat (talk) 20:38, 16 February 2013 (UTC)

Well, moving a 10-ton rock is far from impossible, with even a small rocket. One might even explain the coincidence of dates as being because the nefarious party stupidly expected people to think it was a chunk of the famous meteor everyone was looking at. I imagine that the Russians will be looking over the wreckage of the meteor very carefully for signs of terrestrial rocket motors being attached, but then again ... a smart villain would have programmed his rocket to take off into space after it finished doing its job and long before impact. Wnt (talk) 22:18, 16 February 2013 (UTC)

To be clear the one that hit Earth was 10,000 tons, not 10 tons. Rmhermen (talk) 17:43, 17 February 2013 (UTC)

Ah; but how about the coincidence of the asteroid flyby, the meteorite strike, the pope retiring, lightning hitting the vatican, and North Korea testing a nuke? I tell you, something is definitely up. I'd advise checking out the CDC zombie apocalypse survival pages again. Gzuckier (talk) 07:54, 18 February 2013 (UTC)

Impact crater

Something else which confuses me is that the meteor appeared to be going through the atmosphere at a shallow angle, yet the impact crater in a frozen-over lake is circular, not elliptical, as I would have thought: 2013_Russian_meteor_event#Impact. Why is this ? StuRat (talk) 17:00, 16 February 2013 (UTC)

That's quite a common question and [3] hopefully will answer it for you. Dmcq (talk) 18:22, 16 February 2013 (UTC)

Thanks. StuRat (talk) 20:46, 16 February 2013 (UTC)

Window glass

Excuse me for hijacking the original questions. On some pictures it looks like the windows were "old fashioned" double glass windows, the kind easily broken by a mislead ball by some playing kids, not the kind of glass that is used nowadays with high thermal insulation and nearly indestructible even when deliberately using a hammer. So I wonder if the extent of destruction also has to do with cheap, or old, buildings.

I also wonder if buildings specially designed to withstand earthquakes, as Japan, would have had less damage or it protection against on does not give protection against the other.

95.112.182.106 (talk) 18:56, 16 February 2013 (UTC)

Much of the construction under communism was quite shoddy, yes. And, even since then, there are pockets of poverty where new construction, if any, is likely to be just as bad. StuRat (talk) 19:13, 16 February 2013 (UTC)

What this super glass you're referring to with for example 'high thermal insulation' which allegedly is used 'nowadays'? NZ is notorious for having poorly insulated homes with laws requiring decent insulation only very recent. Notably in many places window insulation is poor as double glazing is rare. The requirements for new homes since 2008 do make double glazing likely since it's difficult to achieve the requirements without it but obviously this is a very new requirement [4] [5]. Safety glass has been required since 1993 and is also required for replacements [6] but only where human impact is likely, in other words, not for many windows [7] [8] [9]. Nil Einne (talk) 02:48, 18 February 2013 (UTC)

If it really made that much of a difference, many homeowners who could afford it in NZ would do so to save their own money. Much of the population's winters are not quite as bad as most of the continental US I believe there might even be at least South Carolina-looking flowers in the equatorward of their two majorest cities (the one on the isthmus). Sagittarian Milky Way (talk) 03:03, 18 February 2013 (UTC)

Causes of raised pcp levels in the body

I would like to confirm what the causes for raised (Natural) PCP levels in the body are. I know that Pcp is a halucinogenic drug, I know there are natural levels of pcp in the body, I would like to identify what causes the natural levels to become elevated. & if Hyperthyroid could cause this. — Preceding unsigned comment added by 96.243.19.132 (talk) 17:41, 16 February 2013 (UTC)

Are you sure you mean PCP itself ? Piperidine is found in black pepper and also used in the production of PCP. StuRat (talk) 18:14, 16 February 2013 (UTC)

Did you confuse PCP with PTP (Protein tyrosine phosphatase)? PTPs are a class of hormones. I don't know what their connection to hyperthyroidism may be... --Jayron32 20:49, 16 February 2013 (UTC)

Hunting for endogenous phencyclidine I find a probably non-reliable source [10] which briefly describes a 1986 NIDA research monograph [11] (does anyone actually have access to these?) which postulated a PCP-like compound in schizophrenics. But so far as I know the mainstream thought runs toward PCP having a mix and match of effects on certain dopamine and glutamate receptors [12] which is dependent on the qualities of this exact chemical, which does not occur naturally in the body. As such, I would surmise that PCP-like states of mind might be assembled if these pathways are affected strangely enough in just the same proportion by natural or pathogenic physiological conditions, but there would be no particular mechanism to cause a mentally ill person to have that exact set of changes in these pathways as opposed to some other set that causes weird behavior but different weird behavior. But ... no promises that is true; this sort of biology is notorious for major do-overs. Wnt (talk) 21:12, 16 February 2013 (UTC)

It sounds like the OP has had a blood test and been told that they have elevated "PCP", which almost certainly won't be referring to phencyclidine (unless it was a drugs test). Maybe they misheard PCV. Either way, this is bordering on medical advice so until the OP asks a more specific question we can't answer it. Markr4 (talk) 13:33, 17 February 2013 (UTC)

Or maybe in this case, PCP actually stands for pentachlorophenol? 24.23.196.85 (talk) 07:28, 20 February 2013 (UTC)

what does it mean that relativity and qm are incompatible?

what does it mean that relativity and qm are incompatible? I've put this query into the google and read the first answer. it is from 2009 however and says : "Quantum Mechanics (QM) and relativity are both 100% accurate, so far as we have been able to measure (and our measurements are really, really good). The incompatibility shows up when both QM effects and relativistic effects are large enough to be detected and then disagree. This condition is strictly theoretical today, but in the next few years our observations of Sagittarius A*, and at CERN should bring the problems between QM and relativity into sharp focus."

since it is 2009 + 4 = 2013 can you elaborate thank you. 86.101.32.82 (talk) 22:07, 16 February 2013 (UTC)

General relativity is not incompatible with quantum mechanics, it is just that the theory is non-renormalizable, which means that the results of computations depend on exactly how you define the theory down to the smallest lengths scales. In case of renormalizable theories, what happens at some fixed lenght or energy scale in some experiment can be expressed in terms of a few other measuarable quantities to any accuracy that is desired. So, you can then eliminate the unknown physics at the very smallest length scales (or equivalently, the highest energy scales). Count Iblis (talk) 23:06, 16 February 2013 (UTC)

For the benefit of other readers, the answer you're talking about is here.

The extremely successful standard model of particle physics combines special relativity and quantum mechanics. Combining general relativity and quantum mechanics (into quantum gravity) has turned out to be amazingly difficult, but they are obviously not incompatible since they coexist in the real world.

There is a philosophical/foundational problem with combining even special relativity with quantum mechanics, which is that both special and general relativity treat time and space in essentially the same way, while in quantum mechanics they are totally different: This is called the problem of time, and Wikipedia should have an article on it but currently doesn't. It probably has something to do with the difficulty of making quantum gravity work, and it's surprising (to me, anyway) that it doesn't cause more trouble in the Standard Model as well.

I don't know why "The Physicist" thought that observations of Sagittarius A* (a black hole) or experiments at CERN (presumably meaning the LHC) would cast any light on quantum gravity. Sagittarius A* is very far away and we can only vaguely measure its properties. The LHC has a maximum design collision energy of 14 TeV, while quantum gravitational effects are expected to become significant at around 10,000,000,000,000,000 TeV (the Planck energy). Many particle physicists did hope that the LHC would find something new that would tell us something about quantum gravity, but it hasn't happened yet. -- BenRG (talk) 19:14, 17 February 2013 (UTC)

Regarding the article Homogenized Milk and Atherosclerosis

I have removed this discussion because we are not allowed to give medical advice. All a wikipedia article can give you is general information. For specific situations, you need to see a doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:54, 17 February 2013 (UTC)

February 17

KEF-2013

This is being reported as the name of the Russian meteor, but the name doesn't seem to follow the patterns discussed in our Astronomical naming conventions article. What system are the Russians using here (and do we need to expand our article)? Rmhermen (talk) 00:40, 17 February 2013 (UTC)

If any astronomy convention applies, it would be Provisional designation in astronomy, not Astronomical naming conventions. That being said, I don't think that either of those apply to objects within the earth's atmosphere. The Meteoritical Society has some guidelines,[13] but if it is within Russian airspace, I am pretty sure that the Russian Federal Space Agency gets to name it. --Guy Macon (talk) 08:25, 17 February 2013 (UTC)

Our Astronomical naming conventions article covers provisional naming. But that would yield a name like 2013 C[x]_[x] and meteorite naming will involve the name Chelyabinsk probably. Our articles don't seem to mention national bodies making up their own naming system. Do we know any details? Rmhermen (talk) 14:00, 17 February 2013 (UTC)

The question is whether astronomical naming conventions apply to non-astronomical phenomena such as meteors and meteorites. What is the IAU designation for the Canyon Diablo meteorite? The Sutter's Mill meteorite? The Sikhote-Alin meteorite? The only meteor or meteorite that I know of that has an IAU designation is 2008 TC3, and that is because it was observed, tracked, and named prior to reaching Earth. --Guy Macon (talk) 14:55, 17 February 2013 (UTC)

Non-astronomical? Not really. But my question is what system yields a name KEF-2013 and why doesn't Wikipedia seem to know about this system? 17:35, 17 February 2013 (UTC)

I'm very sceptical that anyone really does call this KEF-2013. Our use of that name seem to come from this report, which says Speaking at the Krasnoyarsk Economic Forum, Mr Medvedev called the fallen meteorite in Chelyabinsk "KEF-2013," according to a translation obtained by Newsroom America. I'm suspicious if that site has mistaken the name for the meeting at which Medvedev was speaking - Krasnoyarsk Economic Forum (KEF-2013 / КЭФ-2013) [14] - for a name for the meteor. I note that the Russian Wikipedia article about the meteor does not call it KEF or КЭФ (except for where it parrots that questionable, unsure newsroomamerica ref, as we do). So TL;DR: I don't believe it is called KEF-2013, as I can find no reliable source that it is. -- Finlay McWalterჷTalk 18:49, 17 February 2013 (UTC)

I should say that I don't think there is anywhere in Russia called "Кзф" (except what I think is a North African restaurant in Yekaterinburg). There's a really minor geoname Кеф in northern Sakhalin, which is nowhere near the meteor's area. -- Finlay McWalterჷTalk 18:58, 17 February 2013 (UTC)

• I have been editting the article, and when I had added the KEF name to the lead I went to look for better reliable science sources, of which there are apparently none in English or Russian. μηδείς (talk) 19:59, 17 February 2013 (UTC)

Turns out this is a myth with a rather funny explanation after all, see here for what I discovered about the supposed designation. μηδείς (talk) 16:57, 18 February 2013 (UTC)

Response to the above claim. --Guy Macon (talk) 20:51, 18 February 2013 (UTC)

Quantum tunneling

What's the probability that Andy Roddick's fastest serve (155 mph) would tunnel through the net? Also, how fast must he serve in order for the ball to have a non-negligible tunneling probability? (Also, for the sake of the argument, how fast must he serve in order to physically make a hole in the net?) 24.23.196.85 (talk) 06:46, 17 February 2013 (UTC)

what makes you think there is a speed at which there is non-negligible tunnelling probability at such huge, macro scales? you do know there's a univeral speed limit.... 86.101.32.82 (talk) 08:53, 17 February 2013 (UTC)

What would happen as that speed limit was approached by a baseball or tennis ball is analyzed here. --Guy Macon (talk) 15:00, 17 February 2013 (UTC)

In that case, assume that he's playing tennis on the Moon.  ;-) (That should also get rid of the quantum zeno effect that Iblis mentioned.) 24.23.196.85 (talk) 04:14, 18 February 2013 (UTC)

Interesting question! Answering the first question is a bit tricky, as the standard textbook estimates based on particles tunelling through a barrier will greatly overestimate the probability. What happens with the ball is that the constant interactions with the air molecules effectively leads to the state of the ball being measured very frequently, which greatly suppresses the tunneling probability. This is called the quantum zeno effect. Count Iblis (talk) 15:45, 17 February 2013 (UTC)

Reminds me of an exercise in my physics class where we had to calculate the probability of Santa Claus tunneling into a house. As far as I remember assuming a rectangular potential barrier was considered sufficient then (it was Christmas time so the examiners were kind...). bamse (talk) 20:56, 17 February 2013 (UTC)

If we can find a RS with a numeric answer for Tunneling Santa it might make a good example of a number that exceeds the range of the Quadruple-precision floating-point format. --Guy Macon (talk) 20:59, 18 February 2013 (UTC)

(un-indent) OK, another related question: Suppose A-rod makes a "normal" 140-150 mph serve over the net, but Roger Federer returns it with so much top spin that the ball's angular velocity around its own axis reaches a relativistic value. (In real life, of course, the ball would disintegrate long before that point, but assume that for some reason this doesn't happen.) What kinds of weird non-Newtonian effects (if any) can be expected in this sci-fi scenario? 24.23.196.85 (talk) 04:48, 19 February 2013 (UTC)

Relevance of physics to microbiology.

What are the relevance of physics to biology? — Preceding unsigned comment added by 196.46.246.49 (talk) 12:31, 17 February 2013 (UTC)

You might want to start with gravity, acoustics, optics, thermodynamics, motion, aerodynamics, sound, sun, tides, and energy.--Shantavira|^{feed me} 13:55, 17 February 2013 (UTC)

Also you should know that you, your body is nothing but a combination of chemical elements held together by laws of physics. Your mind is nothing but a manifestation of chemical activities. Simply put, you are nothing but a complex combination of natural elements. There is no difference between you and a rock except that you have signaling and self-sustaining processes known as life. A rock lacks signaling and self-sustaining process. And this very thing called life would have never originated without the laws of physics. The laws of physics enabled you to write this question in the reference desk. --PlanetEditor (talk) 15:55, 17 February 2013 (UTC)

There's a whole discipline called biophysics. -- 67.40.213.4 (talk) 21:46, 17 February 2013 (UTC)

3d effect when watching TV while you look through a small hole with one eye

A long time ago when I got interested in 3D pictures I noticed you get a strange 3 D effect watching a normal t.v. program if one of the eyes is looking through a small hole. The effect is clearly visible when looking at moving objects on the screen. I guess what is going on is that by looing at the screen this way, you mess up the information about the parallax (which should be amost exactly the same for all objects on the screen) slightly, and then the brain uses other information like motion to "correct" the information about the parallax, usually leading to natural 3d effect. I'm not sure about this explanation, though. Count Iblis (talk) 15:39, 17 February 2013 (UTC)

This sounds like one of a few strange effects that depend on the fact that the response time of the retinal cells is dependent on light intensity. I assume you mean a hole small compared to your iris, in a card or something held close to the eye, thus "stopping down" the light entering the eye. Stronger light produces a faster response. You get an effect similar to what you describe if, if lighting conditions are right, you look at a TV with a sunglass lens (not polaroid type) in front of only one eye. A more surprising (to most people) is trying this with an analog TV tuned to a vacant channel, so that what's on the screen is just snow. The effect of reducing the light intensity to only one eye is a rotating barrel effect - some of the the snow seems to move to the right in front of or behind some of the snow moving in the opposite direction. If (say) your are looking at a scene with objects moveing to the right, and you stop down the right eye, then the right eye image is effectively delayed slightly, which means the object is displaced to the left, giving a false 3D effect. There was a university chap who researched this about 20 years ago. No promises, but if I can remember his name, I'll post some details. Wickwack 121.221.31.66 (talk) 16:08, 17 February 2013 (UTC)

Is this related to the Pinhole camera effect? Alansplodge (talk) 17:36, 17 February 2013 (UTC)

That was my thought. Perhaps his vision just needs correction, and a pinhole lens corrects it to the point where his brain can assign depths more accurately than it can with blurry objects. StuRat (talk) 23:36, 17 February 2013 (UTC)

Certainly technically possible, but not very likely, as he should have noticed poor vision and gone to an optometrist or doctor - what about it Count Iblis? The boffin who investigated the visual effects of stopping down the light to only one eye had the familay name Sala, but I have not tracked down his paper yet. Wickwack 120.145.59.43 (talk) 00:23, 18 February 2013 (UTC)

The thing is, with gradual visual acuity loss, you don't notice it. Blurry is your normal. This happened to me, and I didn't realize I needed contacts until years later. I was amazed how much clearer things looked. StuRat (talk) 00:30, 18 February 2013 (UTC)

I remember hearing on a radio programme, years ago, a caller whose teenaged sister was too vain to wear glasses and took to watching television through one of the holes in a Rich tea biscuit. Perhaps she could see it in 3D too - who knows? Alansplodge (talk) 01:17, 18 February 2013 (UTC)

I've found just closing one eye means any photo or video looks much more 3D, I presume because there only depth information is the same between these and a real scene. How much are you actually seeing with the eye through pinhole here? It wouldn't surprise me if you're having a similar problem. Nil Einne (talk) 02:54, 18 February 2013 (UTC)

Hmmm... it seems like looking through a pinhole while using a contact lens (-5) produces a distortion effect - letters on the monitor are noticeably displaced toward the edges of the pinhole. I'm not immediately sure why that is. The overall effect is subtle - it doesn't seem like there's a net magnification when superimposing with the other eye, rather, the words in some lines in between don't quite line up, and move very noticeably if it is wiggled. Wnt (talk) 20:11, 18 February 2013 (UTC)

velocity of meteor

NASA gives the aphelion of the Russian meteor at about 2.5 AU. Suppose you want to calculate the speed of it when it crosses the Earth's orbit, assuming that the Earth is not there. Can you calculate the difference in potential energy between 1 AU and 2.5 AUs and assume that is converted into kinetic energy? Bubba73 ^{You talkin' to me?} 20:53, 17 February 2013 (UTC)

Yes, you can, but this gives only a lower bound, since you'd have to add the kinetic energy at aphelion to this to get the total kinetic energy. --Roentgenium111 (talk) 21:24, 17 February 2013 (UTC)

At aphelion, the kinetic energy would approach zero, right? Bubba73 ^{You talkin' to me?} 00:41, 18 February 2013 (UTC)

Well, kinetic energy towards or away from the object it's orbiting would be zero, yes. However, it would still have kinetic energy in a direction normal to that, in the orbital plane. StuRat (talk) 01:20, 18 February 2013 (UTC)

StuRat, energy is a scalar. It doesn't have a direction. Dauto (talk) 19:26, 19 February 2013 (UTC)

Yes, you are right. But assuming that it had no kinetic energy at aphelion, I get that its velocity should be 32,700 m/s when it reached Earth's orbit, but NASA said that its speed was 18,000 m/s. Bubba73 ^{You talkin' to me?} 01:59, 18 February 2013 (UTC)

Whoops, that would be the speed relative to the Sun - not the moving Earth. Bubba73 ^{You talkin' to me?} 02:19, 18 February 2013 (UTC)

Well, this website gives an approximate semi-major axis of 1.66AU and eccentricity of 0.52. That is enough for a better calculation, with a little more work. Bubba73 ^{You talkin' to me?} 02:15, 18 February 2013 (UTC)

I heard back from the NASA meteor expert, and he says that about 14 of the 18 km/sec speed of the Russian meteor was from its orbit around the Sun - the rest from gravitational attraction from the Earth. Bubba73 ^{You talkin' to me?} 00:08, 19 February 2013 (UTC)

Underground bunker effects of the Russian meteoroid?

Would a underground survivalist type of bunker 2 - 4 meters down with 10 cm concrete walls be affected from the 2013 Russian meteor event in any significant manner ..? Missile bunkers are protected from shock waves by having most interior equipment mounted on springs. Perhaps a meteor ground impact would be different and blast the walls located underground with shock waves much in the same manner that sea waves become larger closer to the beach. I find the behaviour of underground shock waves hard to predict and their behavior when they encounter a sharp density change that perhaps results in a superposition reflection that result in an force from the surrounding ground that cracks the walls. Electron9 (talk) 22:41, 17 February 2013 (UTC)

An underground bunker is going way too far. Any modern building in a first-world country could have survived the meteor with minimal damage, provided it was built to code. Most of the damage the meteor caused was broken glass, but most glass windows nowadays are shatter-proof. See this discussion above. --140.180.243.51 (talk) 23:17, 17 February 2013 (UTC)

Do they really use tempered glass in modern windows now? Which is not shatter-proof anyway. I think if you bang it with a hammer really hard, it'll still break. Maybe it might take multiple hits but it's not shatter-proof. I know you didn't mean blast-resistant bulletproof glass, and even a big enough asteroid's shock wave would shatter that. My windows (among others in this part of the first-world) bend and sound like plastic. Is that really glass? Sagittarian Milky Way (talk) 01:40, 18 February 2013 (UTC)

Glass bends if it's thin enough. It also may be coated with plastic to hold it together, if it does shatter (I think they normally put the plastic layer between the glass panes, though, so it doesn't get scratched up). And you're right that being resistant to point impacts, like bullets, is quite different from being resistant to pressure changes over the entire surface, which you get in blasts. 01:46, 18 February 2013 (UTC)

I dunno, almost everywhere I've lived sounds really plasticky when tapped, like a dull thud. I thought flexible Gorilla Glasses were shelved though for lack of need until the advent of demand for 0.7mm smartphone screens? I found out that my uncle's cheap landlord didn't fix all of the windows (or the bell) by giving one a love tap that shouldn't have been anything close to breaking it, and I made the Fall-Winter 2011 hole. Yay impact resistance! It was an umbrella, so no Cheylabinsk-esque injuries Sagittarian Milky Way (talk) 02:29, 18 February 2013 (UTC)

It probably sounds "plasticky" because its laminated glass. There's a layer of plastic between both panes of glass, which would certainly alter the sound from plain glass. — The Hand That Feeds You:^Bite 23:01, 19 February 2013 (UTC)

As I remarked in reply to the original thread, I'm not convinced the OP is correct nor 140. Perhaps it's a requirement where they live, but while I'm unclear precisely what they're referring to, I'm not sure it's a requirement here in New Zealand. Nil Einne (talk) 02:57, 18 February 2013 (UTC)

February 18

Why didn't Earth's gravity capture the asteroid 2012 DA14?

What I'm really asking is in what approach, distance, and speed should the asteroid that passed a little bit over 17,000 miles above the earth have approached earth in order for the earth's gravity to have captured it in such a way that the asteroid would have become earth's second moon? I ask because many of the planets' moons in the solar system, like the moons of Mars and many of the small moons of the Gas Giants, are actually asteroids that were captured by the planets' gravity in the distant past. 71.98.163.183 (talk) 00:06, 18 February 2013 (UTC)

I don't think it's as simple as coming in on the right velocity vector. Some complex gravitational interaction involving the Moon and Earth would need to slow it down, otherwise the speed it gains "falling" towards the Earth would be enough to make it too fast to achieve orbit. Another option is that it could skim Earth's atmosphere, and this could slow it just enough. And captured moons seem to be relatively rare, with most moons forming in place. Our Moon might be stranger, still, resulting from ejected material from Earth after an early giant impact on Earth. StuRat (talk) 00:24, 18 February 2013 (UTC)

Mars and Jupiter have greater densities of asteroids near them then out here, in the relative outskirts of asteroid-ville, and the giant planets have a Huge! capture radius and numerous moons (Ganymede is as big and massive as Mercury) to make the necessary slowdowns. Sagittarian Milky Way (talk) 01:49, 18 February 2013 (UTC)

The earth didn't capture the asteroid, but it had enough impact to change its orbital period around the sun. And keep in mind that for every Deimos or Phobos there could be thousands of asteroids that came near Mars and were not captured into an orbit. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:39, 18 February 2013 (UTC)

And it is not surprising that it was not captured into an orbit. If you just consider the two body problem of earth + asteroid, you get Kepler orbits, i.e. if the asteroid is not in an (elliptic) orbit at the start, its path will merely get disturbed by the earth, but it will not end up in an orbit around earth. For this to happen you'd need additional forces, e.g. from the moon, sun, other planets, Asteroid impact avoidance or perhaps crashing into satellites. bamse (talk) 13:08, 18 February 2013 (UTC)

So, in the case of Comet Shoemaker–Levy 9, did it kind of had all the right forces when it was captured by Jupiter in the 1960s and kept orbiting around the planet until one day the comet got so close to Jupiter and its Roche limit that the comet collided with the planet in July 1994? Would Comet Shoemaker–Levy 9 have been considered to be a moon, or at least almost a moon, of Jupiter for about 30 years? It seems that Comet Shoemaker–Levy 9 was the latest known case of a large celestial body (Jupiter) capturing a smaller celestial body. 71.98.163.183 (talk) 15:35, 18 February 2013 (UTC)

I guess you can kind of look at that comet as a model of how a planet can capture something and turn it into a satellite, but I think that the problem was that it took 2 years to revolve around Jupiter. 131.247.244.23 (talk) 15:25, 19 February 2013 (UTC)

The blue path is a hyperbolic trajectory.

• Several of the responses above are correct, but perhaps aren't making the point quite clearly enough. The default, when a body approaches a much larger body, is a hyperbolic trajectory, as illustrated in the figure -- the smaller body exits moving in a different direction, but just as fast as it came in. Very special and very unusual things have to happen in order for capture to occur. Looie496 (talk) 17:51, 18 February 2013 (UTC)
  • The OP asked why the earth didn't capture it, so maybe flip that around: What would have to happen in order for an approaching asteroid to be captured by earth's gravity and become a second "moon"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:54, 18 February 2013 (UTC)

• • • But wouldn't the earth's gravitational pull be stronger than that of the sun's gravitational pull where asteroid 2012 DA14 was at its closest point to earth? Or was the gravitational pull too weak for the asteroid to be captured by earth for orbit, and why? And what was the case with comet Shoemaker–Levy orbiting Jupiter for about 20 or 30 years? P.S: There were 2 edit conflicts in a row. 71.98.163.183 (talk) 23:29, 19 February 2013 (UTC)

"Cannon fire" following meteorite impacts

Looking through reports of the 2013 Russian meteor event (we really need a better title), I've come across reports of sounds said to resemble "artillery bombardment" following the explosion. This seems to match up with similar reports from the Tunguska event, including:

After 1.5–2 minutes ... six more thumps were heard, like cannon firing, but individual, loud and accompanied by tremors.

and

After that such noise came, as if rocks were falling or cannons were firing, the earth shook, and when I was on the ground, I pressed my head down, fearing rocks would smash it.

The first thought that comes to my mind is that the sounds could have been caused by larger fragments of the meteorite impacting the ground, but this seems unlikely since no fragments of the Tunguska object have ever been found, and so far no large pieces of KEF-2013 have been found either (at least as far as I know). Does anyone have a good guess as to what might cause this effect? Evanh2008 ^{(talk|contribs)} 01:15, 18 February 2013 (UTC)

The process of it breaking up can be quite explosive. StuRat (talk) 01:18, 18 February 2013 (UTC)

Yes, but this is noise following the main explosion, by at least several minutes. Evanh2008 ^{(talk|contribs)} 01:25, 18 February 2013 (UTC)

Watch the video of the shuttle breaking up. It happened in several stages. StuRat (talk) 01:47, 18 February 2013 (UTC)

The flashes from exploding meteors always travel at the speed of light while the radiated heat from the explosions travel at similar speeds. The reason why the noise is heard several minutes later is due to the fact that noise travels at the speed of sound. Therefore a noticeable delay occurs before the sound reaches the observer. 1.178.33.170 (talk) 01:54, 18 February 2013 (UTC)

I think you're still failing to understand that the sound I am describing is not the primary explosion of the object. I am well aware of the difference between the speed of light and the speed of sound. These are noises following the fireball and the associated sound. They may be reflections of that sound, but it is not simply a matter of delay. Evanh2008 ^{(talk|contribs)} 02:03, 18 February 2013 (UTC)

The 'primary explosion' of the object was never accompanied by a fireball. In some videos you can clearly make out two meteors traveling side by side, one slightly overtaking the other long before the fireball erupted. Even the smoke trail itself shows two very distinct paths that lay side by side in almost perfect symmetry. This indicates that the meteor impacted the upper atmosphere first and exploded (broke apart) before it started heating up during re-entry. Therefore it seems likely that this initial 'boom' we hear was never actually accompanied by an explosion. There are also two distinct groups of sonic booms that seem to correspond closely to the initial eruption of the fireball followed by a final, very loud sonic boom that seems to correspond to the second, smaller eruption as the meteor breaks apart into several smaller pieces. The hundreds of smaller pops and crackles could very well have been caused by the hundreds (some say 'thousands') of tiny pieces still traveling along at supersonic speeds peppering the ground. Much of this lingering noise would have been accompanied by acoustic reflections bouncing off the Ural Mountains directly underneath the path of the meteor. The mountains themselves would have acted as a natural sounding board. 1.178.161.116 (talk) 05:26, 19 February 2013 (UTC)

I heard what you are talking about on the video. One animation that I saw had it breaking into one big piece followed by five smaller ones, but I don't know if that is accurate. The smaller booms could have been from the smaller pieces. Just my guess. Bubba73 ^{You talkin' to me?} 02:13, 18 February 2013 (UTC)

It could have been explosions of bits separated by the main explosion, but more likely the subsequent bangs were sound reflections. I have a book describing a test nuclear explosion in the South Australian desert. At distances of 200 - 300 km or or so, three bangs were heard - the primary shockwave travelling outward at ground level first, then a boom that was due to reflection of sound from the upper atmosphere (ie longer path), then a rumble from reflections off prominent ground features. A high altitude explosion could be expected to produce a degree of reverberation from reflection from the ground and high altitude velocity of propagation changes. Air temperature, and thus velocity of sound, reduces with increasing altitude until a certain height, whereupon temperature increases again. Wickwack 124.182.151.79 (talk) 01:56, 18 February 2013 (UTC)

Ah, that's very interesting. I find the sound reflection idea much more plausible than my idea of fragment impacts. Thanks! Evanh2008 ^{(talk|contribs)} 02:03, 18 February 2013 (UTC)

And the 30,000,000 tons TNT of the Tunguska event is alot of boom, even spread out. That is the size of 15,000 atomic bombs or millions of Oklahoma Cities. Sagittarian Milky Way (talk) 02:01, 18 February 2013 (UTC)

Every time I have tried to type here got an edit conflict :) so here is a short Q: Why do all the meteor videos start with a bang? ie there is no lead up sound, no build up to the bang, just silence then boom, then diminishing fireworks for a minute or so. Possibly because it broke apart almost immediately - two trails appear almost right from the start. Interested in any thoughts. Zeb253 (talk) 02:04, 18 February 2013 (UTC)

Because the film editor thought it had more impoect if it started with a good bang? Wickwack120.145.150.250 (talk) 02:14, 18 February 2013 (UTC)

Here is one video of the sound I am talking about - 30 seconds of near silence followed by the big bang and fireworks - no lead up to the big bang. http://www.youtube.com/watch?feature=player_embedded&v=MKx97csfPy0# - possibly part is the mics adjusting the sound level but still it does start suddenly but not end suddenly. Zeb253 (talk) 02:20, 18 February 2013 (UTC)

Evanh2008 - There is certainly a big bang at the start of the audio - my guess for the canon fire and fireworks after the bang is a combo - the meteor broke up in explosive stages (perhaps one big one and many more subsequent ones as the pieces got smaller and smaller), and of course it happened at such a speed that sonicboom/shockwave add to the noise, plus there will be some echo too. Zeb253 (talk) 02:10, 18 February 2013 (UTC)

Our Russian meteor article tells us that it was "[m]oving at a speed of 15 km/s to 18 km/s (34,000 mph to 40,000 mph)". If this speed is correct, it is about Mach 44 (assuming speed of sound at sea-level and 20°C and thus 761 mph). Our sonic boom article explains that "[s]everal smaller shock waves can, and usually do, form at other points on the [aircraft meteor]". Hence the multiple sounds heard. In addition, that article also says "[as] those who have witnessed landings of space shuttles have heard, when the aircraft is nearby the sonic boom is a sharper 'bang' or 'crack'. The sound is much like the 'aerial bombs' used at firework displays" --Senra (talk) 14:10, 18 February 2013 (UTC)

• Don't forget, it was traveling at about Mach 45, whereas the sounds that it was making traveled at Mach 1. So, all of the noise that it made along it's path would take a while to "catch up" and reach observers who were near the main explosion later in the path. North8000 (talk) 17:45, 18 February 2013 (UTC)

• According to NASA:Russia Meteor Not Linked to Asteroid Flyby 02.15.13: "The meteor entered the atmosphere at about 40,000 mph (18 kilometers per second)", "its estimated mass [is] 10,000 tons", "... the event, from atmospheric entry to the meteor's airborne disintegration took 32.5 seconds" and "Based on the duration of the event, it was a very shallow entry". I cannot calculate its terminal velocity but it would be considerably less that Mach 44 --Senra (talk) 21:08, 18 February 2013 (UTC)

I wouldn't want to original-research this one without having at least five tapes with GPS coordinates for the location each one was taken and accompanying video so that they can be precisely timed based on the point where the trail turns from very wide to quite narrow. But maybe somebody will post that. :) Wnt (talk) 20:01, 18 February 2013 (UTC)

Historical accounts of past meteor events report the same phenomenon. A good example is the meteorite fall that occurred near Hatford, Bedfordshire, in England on 9 April 1628. Accounts of that are given here and here. The first link is a contemporary account as later published in Chambers's Papers for the People (1850) - not sure when it was first published. The second link (a pdf from an Oxfordshire museum) gives what it says are the only two known contemporary accounts of the Hatford meteorite fall. What I'm quoting here is from the museum's quote from that anonymous 1628 account (the wording in the Chambers's Papers for the People version is different and includes other details):

"In an instant was heard first a hideous rumbling in the air, and presently after followed a strange and fearful peal of thunder; it maintained the fashion of a fought battle. It began thus: first, for an onset, went off one great cannon as it were of thunder alone, like a warning-piece to the rest that were to follow. Then, a little while after, was heard a second; until the number of 20 were discharged, or thereabout. In some little distance of time after this, was audibly heard the sound of a drum, beating a retreat. Amongst all these angry peals shot off from heaven, at the end of the report of every crack, a hissing noise made way through the air, not unlike the flying of bullets from the mouth of great ordnance, and by judgement were thunderbolts; for one of them was seen by many people to fall at a place called Bawlkin Green..." - anonymous leaflet on the Hatford meteorite fall of 1628

That all sounds very much like what was observed and heard for this meteorite fall in 2013. Carcharoth (talk) 20:26, 18 February 2013 (UTC)

Very interesting indeed, thank you. I note that on this video you can hear the multiple explosions persisting for at least 90 seconds after the initial detonation. The physics of the sound are probably going to keep some researcher busy for a long time... Prioryman (talk) 20:46, 18 February 2013 (UTC)

tempature of LED

On the wikipedia page for Light-emitting diode (LED) it states as one of the advantages, "Cool light: In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED." My question is what does very little heat mean? How hot does the inside get? — Preceding unsigned comment added by 69.115.221.5 (talk) 03:27, 18 February 2013 (UTC)

While the total heat generated is low, each LED is tiny, so the heat inside it might be more than you'd think. StuRat (talk) 05:19, 18 February 2013 (UTC)

An incandescent globe operates essentailly as a black body radiator. The filament is heated by the electric current to a white heat temperature - 3800 deg C or higher. In consequence, most of the energy is emitted as infra red i.e., heat, and only a small fraction of the energy is emitted as visible light. In contrast, LED's operate completely differently, emitting visible light photons as electron- hole pairs collapse. Heat in a LED is only generatted by the current floowing through the electrical resistance and is not an essential part of the light emitting process. Hence the fraction of total energy emitted as light in a LED is very high compared to incandescents.

LEDs must be operated at an internal temperature less than the limit imposed by the chemically doped crystal structure - usually taken as 200 deg C. However, the reliability of LEDs, as with any semiconductor device roughly doubles for each 10 C drop in temperature. For this reason, LEDS should generally be opereted at an internal temperature of around 55 C or less.

Keit 120.145.52.14 (talk) —Preceding undated comment added 11:25, 18 February 2013 (UTC)

While I don't disagree with the majority of Keit's post, I'd note that given the demands of lighting systems, particularly replacement bulbs for existing fixture, many LED manufacturers seem to be coming round to a higher limit usually 85 degrees C maximum for the internal junction temperature under normal operating conditions. Cree bins or rates most of their LEDs at this temperature[15], as does Philips/Lumileds [16] (which they call real world operating conditions) and actually I believe most reliable manufacturers now do so, rather then the ridiculous 25 degrees C they used to use. You can also see this Osram document which also recommends a similar thing [17] and interesting enough the Indian Railways seems to have specific requirements at 85 degrees C [18]. This does have negative effects on lumen maintenance and lifespan in general, as well as in performance but as I said, thermal management is not always easy, particularly when used in replacement style bulb. (And of course once it's binned at that temperature, if it meets your requirements the fact it could be better if cooler is not necessarily a big concern. Of course since the colour tends to change and the changing performance means the brightness changes, you do want to have a good idea of what the junction temperature is likely to be.) The absolute maximum BTW tends to be in the 120 - 150 degrees C range. You may also be interested in Thermal management of high-power LEDs. Nil Einne (talk) 12:28, 18 February 2013 (UTC)

Water heater producing hydrogen

From the instruction manual of my washing machine:

“ WARNING: Under certain conditions, hydrogen gas may be produced in a hot water system that has not been used for 2 weeks or more. HYDROGEN GAS IS EXPLOSIVE. If the hot water system has not been used for such a period, before using the washer, turn on all hot water faucets and let the water flow from each for several minutes. This will release any accumulated hydrogen gas. Hydrogen gas is flammable; do not smoke or use an open flame during this time. ”

How would an unused "hot water system" produce hydrogen gas, and is this a real hazard, or is it something that happened to somebody once so the lawyers now insist on a warning? --Carnildo (talk) 04:23, 18 February 2013 (UTC)

When two different metals are connected by a conductor, an electrochemical reaction occurs which will corrode one of the metals. In the case of a steel water heater tank and copper pipes, it is the steel that corrodes. To slow this process down, water heaters have a replaceable sacrificial anode rod that corrodes instead of the steel. High end water heaters often have two rods.

The most common rod material is magnesium. Magnesium sacrificial anodes have the advantages of not dropping debris into the tank and not expanding when they corrode. However, they can release hydrogen gas as they corrode. How much depends a lot of the chemistry of your water. Of course the warnings are for the worst case. When the water contains sulfur, bacteria can grow that produces hydrogen sulfide gas (that's the one with the "rotten egg" odor).

Aluminum anodes also prevent corrosion and do not produce hydrogen gas, but they expand as they corrode, often becoming larger than the opening they were inserted through. Also, debris from the aluminum anode drops into the bottom of the tank and can clog the hot water system. Also, decide for yourself whether you buy the stories about aluminum in the diet and Alzheimer's.

Zinc rods are really aluminum rods with a section of zinc The zinc lessens the odor of sulfur within the water. Otherwise they act kike any other aluminum rod.

If you have a bacteria problem, the first step is to set the temperature on your water heater to high for three days. Be careful not to scald yourself when using the faucet or shower. Another effective way to fight the bacteria is to oxygenate the water with hydrogen peroxide. Anaerobic bacteria thrive where there is little or no oxygen, and the hydrogen peroxide creates an oxygenated environment. One pint of hydrogen peroxide per forty gallons of tank capacity should be enough. Keep open flames away just in case there is some oxygen buildup. Run all the hot water taps until they run hot and then turn them off Let the water stand for two to four hours then run each hot water tap for about five minutes to flush the peroxide. Sometimes you have to repeat this several times until you kill all the bacteria. --Guy Macon (talk) 05:22, 18 February 2013 (UTC)

(ec) Galvanic action between different metals can set up a slight electric field, which might decompose water, by electrolysis, into hydrogen and oxygen. I would expect a microscopic amount, but, if it accumulates, it might add up to something substantial. StuRat (talk) 05:25, 18 February 2013 (UTC)

It's not electrolysis, which turns water into hydrogen and oxygen. It is anaerobic galvanic corrosion, which turns water and magnesium into hydrogen and magnesium oxide. This process is used in industry to create bulk hydrogen without the high electricity costs of electrolysis. Basically, you put magnesium in a 100% steam atmosphere and set it on fire as the steam flows past. As it burns it creates magnesium oxide and hydrogen gas. (Steam works better than water, because it avoids magnesium hydroxide forming). --Guy Macon (talk) 07:19, 18 February 2013 (UTC)

Why not use same metal in the whole hot water system? Electron9 (talk) 08:51, 18 February 2013 (UTC)

Most water heaters are steel to keep the price down, but there are copper water heaters that would match copper pipes. The problem is that a household water system needs to connect with the rest of the world, and re-plumbing your entire city with copper is impractical, so you would still have galvanic corrosion where your copper pipes connect to the water main. The answer to that would be a sacrificial anode somewhere in the system.

Plastic pipes are an interesting variant; you would still get an electric current between, say, a copper faucet and a steel water tank connected by a long plastic pipe, but the long column of water would have significant resistance, thus lowering the current and the corrosion. --Guy Macon (talk) 14:15, 18 February 2013 (UTC)

The girl with an IQ of 161

I've never understood what an IQ actually means. Using this girl as an example, is she able to read this entire reference desk page and understand everything everyone is discussing? I'm assuming she still has to "learn", but maybe her capacity for retaining and recalling information is advantageously high? Why is a high IQ usually equated with science and math, anyway? Can someone have a (technically) high IQ, but have no interest or even comprehension of higher and complex sciences and mathematics on paper, but be brilliant at something else? Mozart probably had a high IQ, I'm guessing? He could absorb music and spit it back out, but if he were alive today, would he have also been designing rockets on the side? Do polymaths have high IQs? What about people who were extremely good at one thing and one thing only, like someone who has an uncanny ability to learn and speak languages fluently, but more or less isn't good at anything else? – Kerαunoςcopia^◁_galaxies 08:34, 18 February 2013 (UTC)

Oh, and how much of IQ do you think is affected by impatience? – Kerαunoςcopia^◁_galaxies 08:34, 18 February 2013 (UTC)

See g factor (psychometrics) for the hypothesized quantity that IQ is supposed to measure. The extent to which such a thing exists is hotly debated (you'll probably get a lot of responses that say there's no such thing, because, apparently, that's what the "good" people are supposed to think </snarky aside> ). Even if there is such a quantity, of course, IQ, like any test, is an imperfect measure of it. --Trovatore (talk) 08:38, 18 February 2013 (UTC)

I happen to believe IQ tests are laughable metrics, but it has less to do with any moral judgement on equality and more to do with coming from a background in the cognitive sciences and knowing the difficulties involved in quantifying mental phenomena (though in the case of IQ tests I daresay anyone with common sense ought to be perplexed out how subjective weighting of different mental tasks is supposed to yield an absolute) and in knowing the well-documented origin of such tests in pseudo-science and general quackery (usually of the highly racist variety). This is one subject I typically can't help weighing in on -- the disconnect between the actual empirical study of the mind by those in a field of relevance and the perception amongst people who are not (even those who are undoubtedly are extremely gifted) can be pretty profound and fascinating -- but my time is limited just now, so it will have to wait until tomorrow. In the meantime, to anyone interested in the subject, an excellent primer is Stephen Jay Gould's The Mismeasure of Man, which looks in detail at the methodology of the early IQ tests in the context of the broader trend towards ridiculous psychometrics of the time, including craniology and so-forth. Of course, IQ tests have come a long way in trying to eliminate biasing elements with regard to social factors, but they haven't made much progress in terms of improving upon the general subjectivity in their basic assumptions and priorities between mental tasks, which is why they are of little interest to anyone doing genuinely empirical work in exploring the brain's (or the mind's) capabilities. Snow (talk) 10:17, 18 February 2013 (UTC)

Gould is exactly one of the ones I had in mind with my "good people" comment. I got a very strong impression, when reading Mismeasure, that while he certainly made valid criticisms of the scientific objectivity of the ones he criticized, his own was equally suspect. --Trovatore (talk) 10:21, 18 February 2013 (UTC)

It's an interesting book for him; most of his other supposedly broad-audience works I've found to be pretty dry. He obviously felt impassioned about this subject. But for all of that, I don't know that I ever felt his objectivity was flawed in that particular work. He certainly busts some balls, but it's hard to find fault with his arguments, as well documented as he makes them. Snow (talk) 10:26, 18 February 2013 (UTC)

To me it comes across as a straight polemic. I cannot claim to have studied the topic in any depth, but I find it very difficult to trust the objectivity of a worker who writes polemics on the subject he studies. His argument that g is nothing but principal component analysis is particularly facile in my view. --Trovatore (talk) 10:30, 18 February 2013 (UTC)

Hold that thought, back to discuss this in greater detail tomorrow. (All in the interest of more fully answering the OP's inquiry, of course! :) Snow (talk) 10:36, 18 February 2013 (UTC)

(Trovatore, you just committed the unspeakable crime of having an unmatched tag.) The g factor, which IQ tests are designed to measure, is the "average" of a wide variety of abilities that make up intelligence. As an analogy, suppose a company wanted to evaluate how good a potential employee is. It might consider a wide variety of factors that affect "goodness". How much experience does he have? How patient is he? How logical is he? Does he have good people skills? Motivation? Passion? Flexibility with work hours? All of these factors are part of his goodness, but someone with very high goodness doesn't necessarily score highly in every aspect, and someone with very low goodness could score highly on a few aspects. The same is true with IQ tests. Getting a high score is far easier if you're good at everything, but you could be absolutely hopeless at a few things and still score highly if you're a genius at everything else. --140.180.243.51 (talk) 09:19, 18 February 2013 (UTC)

IQ is the attribute measured by IQ tests. HiLo48 (talk) 10:23, 18 February 2013 (UTC)

In much the same way ghosts are the things pursued by ghost hunters. ;) Snow (talk) 10:28, 18 February 2013 (UTC)

Yes, an excellent analogy. HiLo48 (talk) 10:35, 18 February 2013 (UTC)

Except, IQ strongly correlates to performance on a wide range of other skill-tests, from rifle marksmanship to average salary over the person's entire career. In this August 2010 discussion, I attempted to refute the point that IQ is meaningless. I will concede that IQ is not the only factor in human cognitive performance, but it is a reliable and repeatably-measurable metric. The accuracy and precision and repeatability of modern tests are all surprisingly high. And when judging people in the statistical aggregate, which is often necessary for large organizations, it can efficiently summarize other performance metrics. If misused or misinterpreted, the data-point can lead to very invalid conclusions. But it's not fair to say that IQ is pseudoscience. On the whole, it is a measurable, quantifiable, repeatable metric. Any conclusions drawn from this metric are falsifiable and can be substantiated by experiment. Nimur (talk) 13:25, 18 February 2013 (UTC)

Nimur, do you have citation for the IQ-marksmanship correlation? I'd like to read more about it. It's not too surprising, since IQ is correlated with height.Dncsky (talk) 14:39, 18 February 2013 (UTC)

Yes, in the discussion I linked above, or directly linked here: Whole and Part Methods in Learning a Perceptual Motor Skill (1954). The study compared some three hundred infantrymen at Fort Knox; trained some in marksmanship using Method A and others using Method B; and analyzed the results. A secondary analysis of the same data treated the the training method a a null factor, and instead compared the marksmanship results against each man's previously-measured intellectual aptitude. And finally, they analyze whether higher-intelligence riflemen learn better using Method A or B. There is no reason to slander the intellectual aptitude of "army guys." Completion of an ASVAB (part of which is essentially an IQ test) is mandatory for most recruits to most branches of the armed services in the United States; and the intellectual entrance requirements for many career military tracks are as stringent as those for some universities. At the very least, the armed forces have standardized empirical data, which can be used to objectively analyze their recruits: many universities do not even have such data, or rely on a third-party corporation to provide it. Nimur (talk) 15:01, 18 February 2013 (UTC)

What a jolly good read, thanks. I have retracted the joke; it was made in poor taste and inappropriate for the RD. A certain Australian must be rubbing off on me. For the record, I will soon be one of the "army guys" and the joke was intended as self-deprecating humor.Dncsky (talk) 15:10, 18 February 2013 (UTC)

Yeah, but consider an anologous Athletic Quotient, which is measured by a test which inncludes things like a 100 yard dash, a bench press, ability to catch a fastball, triathlon, etc. I think the average person would see that there is some validity in such an overall measurement, but would realize that it's really looking at a wide variety of individual skills, which are only slightly related; if you have some sort of neuromuscular disorder, for instance, you'd do badly overall, but marathon running and weight lifting skills probably aren't that tightly correlated. Same for IQ; if you brain is defective, you do badly overall, but there's no real evidence that there is a specific function used in visualizing what the object in a picture would look like if rotated and also used in reading comprehension. Gzuckier (talk) 14:57, 18 February 2013 (UTC)

As I mentioned above, IQ is measurable and tests can be designed that stand up to scientific scrutiny. That does not equate to "any conclusion about IQ is immediately true." There are many hypotheses about IQ that can be tested and proven false. If your hypothesis is that IQ correlates (or does not correlate) to performance on spatial reasoning tasks, then I am not sure about the answer; but I am sure there are experiments that have tested that hypothesis and published their findings. Nimur (talk) 15:01, 18 February 2013 (UTC)

• The issue with IQ tests is that they are statistically valid without necessarily being individually deterministic. That is, IQ tests are valid when averaged across wide swaths of population: for enough people, they seem to be roughly useful predictors of certain aptitudes and skills they may have. If you average out IQ results over many millions of people, then the outliers get averaged out. That is, there are going to be some people for whom the IQ test is woefully wrong in terms of acting as a predictor of anything. These people are common enough that, anecdotally, enough people will know someone like this, to make it seem like the IQ test is worthless. And for that person, it is. However, when that person's results are averaged into "all of humanity", it doesn't make much of a difference at all. So, are IQ tests useful? Yes, except when they aren't. --Jayron32 16:24, 18 February 2013 (UTC)

As a random comment, not an answer, I would suggest that the layman's terms of "dull" and "bright" are about as useful. IQ measures something, but just what is hard to say. If you do a chemical reaction and the mixture turns some color, sometimes you can surmise something, but it doesn't really tell you much for sure, and that is about what IQ tells you. It is a single scalar measurement of a very complex matrix of many kinds of data. Wnt (talk) 19:57, 18 February 2013 (UTC)

Wnt just neatly and concisely said what may very well have taken me (is about to take me?) several paragraphs to voice. It's a bit of a case of not seeing the forest (the concepts in this case) for the tress (the raw mathematical data and various trends found therein). Nimur makes some decent arguments above as to why the field cannot be said to be completely without structure, but statistical self-consistency is not the only measure by which the extraordinary claims of this field must be analyzed. That people or sample populations can repeat similar testing scores under similar conditions is not in itself surprising. What said results actually say about the nature of intelligence and where people rank in some abstract spectrum is another matter entirely. Though the specific claims that are made may vary some between tests, they mostly share in common an assumption that "this is a reasonable measure of some form of general and/or practical intellect." -- an assumption that is just not established by any line of reasoning that doesn't rely heavily on subjective assesments. Oh, look at that, managed to keep it to one. :) Snow (talk) 00:42, 19 February 2013 (UTC)

In 1967 I applied for a job with the Australian Government Public Service. At that time, entry was by sitting a 3-part exam. When I sat it, there were about 1500 applicants for 120 jobs. The exam results were ranked 1 thru to 1500, 1 = highest score, 1500 = lowest score, and they sent job offer letters to the folk with rankings 1 thru 140, knowing from experience that about 20 would not take up the job offer. No interviews were conducted. The three parts to the exams were a) Mathematics, pitched at about 1st year high school level, b) General knowledge: multi-choice - typical questions were things like From what direction does the sun rise in the morning? East, West, North, South; Is the differential in a motor vehicle connected to - engine, radiator, gearbox, prop-shaft; c) A raven's style IQ test. I should think that every one would have done well in Part A and B, so the IQ test was probably the decider. I was ranked 37, so I got a job. They sent a list of all 140 successful applicants, with their ranking, to each succesful applicant. I still have my copy, and I now have known most of the succesful applicants for 46 years. Some turned out a dead loss. Some are now top leaders in major businesses. So how does the ranking correlate with the career success? Answer - no correlation AT ALL! And nothing I have experienced in my career ever since has indicated to me that IQ and aptitude testing has any value at all. Ratbone 124.178.182.45 (talk) 00:21, 19 February 2013 (UTC)

I don't know how you compared the success of those selected against that of the ones not selected. For quite a few jobs doing an interview after selecting candidates that way actually reduces the number of good outcomes compared to not doing any interviews so I wouldn't dismiss it so quickly. There's no 100% successful way to select people to employ - and in fact even selecting only the most suitable is often a wrong thing to do as one wants a mix with some people willing to do the nitpicky stuff and others to have grand ideas and others who just hold a team together properly. Dmcq (talk) 13:06, 19 February 2013 (UTC)

As to IQ it is designed as a measure of mostly problem solving ability and as people said above doesn't measure a number of important factors like being able to get on with others. Intelligence tends to be a bit more integrated than athletic ability, but even so whilst it is true that a top class runner won't shine against a top class weightlifter but compared to your average man on the street they probably still would wipe the floor with them at most things athletic. IQ can be thought of as an equivalent of measuring general fitness by seeing how people get on with a range of athletic tasks. Dmcq (talk) 13:06, 19 February 2013 (UTC)

Disease transmission from sharing a cup?

What is the likelihood of contracting a disease, illness or infection from the sip of a shared cup at a social gathering in church? 140.254.226.238 (talk) 15:20, 18 February 2013 (UTC)

Yes, I recognize that some churches individualize cups. 140.254.226.238 (talk) 15:24, 18 February 2013 (UTC)

I'm curious about this too, always seemed instinctively to be a really bad idea - perhaps some sort of alcohol content helps kill the germs, hopefully someone can find us a study --_nonsense ferret 17:01, 18 February 2013 (UTC)

I don't think the alcohol in church wine is sufficient for sterilization, you'd need something more like vodka. Also, as I note below, the rim may carry the microorganisms, and not have any wine on it. StuRat (talk) 17:09, 18 February 2013 (UTC)

Do you think churches should use something like vodka or individualize cups instead? 140.254.226.238 (talk) 17:12, 18 February 2013 (UTC)

Individual cups, yes. Straight vodka, no. That would burn people's throats. (Enough alcohol to kill bacteria cells also kills the cells lining your throat.) StuRat (talk) 17:19, 18 February 2013 (UTC)

Well, if you can distill wine and count it as valid for sacramental use when it condenses, perhaps one could merely boil the alcohol and the congregation could take inspiration from the ... :) Wnt (talk) 19:50, 18 February 2013 (UTC)

Well, quite a few diseases can be transmitted by saliva, especially if the recipient has a cold sore or chapped lips, allowing the bacteria to enter thru a crack in the skin. The previous person to use the cup might have had similar lip problems, and have bled on the cup rim. Exposure to air quickly kills many microorganisms, but the time between sips may not be long enough. Inside the mouth and throat, there may be other breaks in the skin. Once the sip makes it to the stomach, disease transmission is unlikely, as stomach acid is sufficient to kill the small bacteria load. StuRat (talk) 17:04, 18 February 2013 (UTC)

This is actually much closer to "medical advice" than many of the redacted topics - however, public health seems to be something traditionally left to guesswork (and the will of God). I would think of meningitis (e.g. Neisseria meningitidis, Streptococcus pneumoniae) and (if cleanliness lags behind godliness) hepatitis A transmission, among other things. Wnt (talk) 19:48, 18 February 2013 (UTC)

• If anyone is interested in references that address this question (I see Wnt has supplied some nice wikilinks for diseases during my EC), please see the study entitled "Survival of bacteria on the silver communion cup", here [19]. The article is on Jstor, and should be freely available to the public. I found this reference by searching google scholar for /disease transmit cup/, and this came up as the third hit. Granted, the work is old, and there are probably much more recent studies. These can be found by perusing the list of works that cite this one, etc. SemanticMantis (talk) 20:12, 18 February 2013 (UTC)

Should be, alas is not. But you're right I should have looked more carefully. Even so... I imagine every species of bacteria is potentially its own experiment. Anyway, respected sites [20][21] support cup sharing for meningitis. Wnt (talk) 22:17, 18 February 2013 (UTC)

Ok, my link assumes institutional access, which we obviously don't all have. However, I believe anyone can get to it if they register (for free) at Jstor's "register and read" program, here [22]. From there, the title quoted above should get you to the paper. (and the "no refs" comment was not directed at anyone individually, and you at least did give some relevant wikilinks). SemanticMantis (talk) 22:26, 18 February 2013 (UTC)

And to save time for the only mildly curious, the study concludes "Evidence is presented which indicates that bacteria swabbed on the polished surface of the silver chalice die off rapidly. Experiments on the transmission of test organisms from one person to another by common use of the chalice showed that approximately 0.001 % of the organisms are transferred even under the most favorable conditions; when conditions approximated those of actual use, no transmission could be detected. Only small numbers of bacteria from the normal mouth could be recovered from the chalice immediately after its use by 4 persons. It is concluded that in practice the silver communion cup is not an important vector of infectious disease" -- But I'm not sure how this conclusion would hold up under modern scrutiny. SemanticMantis (talk) 21:44, 18 February 2013 (UTC)

Yea, the main thing missing from that statement is how long they waited afterwards to do the test. Since there may only be seconds between uses of the cup, the test would need to be done within seconds to be valid. StuRat (talk) 21:51, 18 February 2013 (UTC)

They figured out that 5 minutes was too long to wait. So they had person A drink, then immediately person B, then took samples within a minute. (I'm not quoting directly because of formatting issues, the quote above took me several annoying minutes. If you don't trust my paraphrasing, please register and read the paper ;) SemanticMantis (talk) 22:31, 18 February 2013 (UTC)

I also should note that their conclusions are based on the treatment wherein the cup was wiped with a cloth between drinkers (which I think is common practice in USA christian churches that have a communal communion cup) -- so that this claim of "not a big risk" is specific to communion cups which are wiped, not drink sharing in general. As Wnt points out above, several diseases are known to propagate via casual drink sharing. SemanticMantis (talk) 23:47, 18 February 2013 (UTC)

Water jet that pops up after somethings drops in water

When something is dropped in water, a thin jet rises up (like this). What is the technical name for it? I cannot recall. It was something like williamson jet. Does anyone here know the right name? —  Hamza  ^{[ talk ]} 15:32, 18 February 2013 (UTC)

According to Wikipedia's page on Drop (liquid), it looks like it's called a "backjet". 140.254.226.238 (talk) 15:37, 18 February 2013 (UTC)

Resolved

Thankus Maximus. —  Hamza  ^{[ talk ]} 16:08, 18 February 2013 (UTC)

Sulfuric acid and nitric acid for cleaning glassware

In Introduction to Organic Laboratory Techniques [23] two solvents are suggested for cleaning glassware:

1. Acetone

2. A mixture of concentrated sulfuric acid and concentrated nitric acid

Isn't #2 kinda dangerous since it could lead to nitration and thus explosive compounds like RDX and TNT?

Googling "cleaning glassware sulfuric acid nitric acid" gets me plenty of other textbooks suggesting the exact same formula [24][25], albeit as an alternative for the standard chromic acid. Dncsky (talk) 16:50, 18 February 2013 (UTC)

Geez, if you need to use dangerous chemicals like that the clean your glassware, maybe you'd best just replace it. I sure wouldn't want to inhale those fumes, either. StuRat (talk) 16:57, 18 February 2013 (UTC)

The glassware under question typically isn't a set of Ikea bowls. Depending on the reaction vessel under consideration, you're talking $50 or more each - sometimes much more if it's a specialized piece of apparatus. "Toss and replace" is impractical if there is a simple and inexpensive way of cleaning them. Sulfuric & nitric acid aren't all that hazardous if handled properly, and "wouldn't want to inhale those fumes" isn't an issue if you have a exhausting fume cabinet, as would most who are doing such procedures. - Regarding nitration, yes, that can lead to explosive compounds, but generally you would remove most of the organic material by soap&water/solvent washes prior to the acid bath. The acid bath is primarily to get rid of residual contamination. Only a small amount of nitrated compounds will be made, they'll be dissolved in an excess of solution, and there's enough excess nitric acid that they'll likely be completely oxidized. Care must be exercised, though. Consult with an experienced organic chemist (most love to talk shop, especially if you're paying for the beer) before attempting. - That said, using concentrated sulfuric and nitric acid isn't all that common in my (limited) experience. Perhaps if you have some persistent contamination and nothing else works. Most organic labware gets cleaned with soap&water and an acetone rinse. If that doesn't work, a soak overnight in dilute acid is usually done. Dilute sodium hydroxide baths are sometimes also used, although that can etch glass and ruin ground glass joints, so base baths are typically used sparingly. As Pavia says, the sulfuric/nitric mix would only be for "troublesome stains and residues that adhere to the glass despite your best efforts". -- 67.40.213.4 (talk) 17:56, 18 February 2013 (UTC)

OK, but basic test tubes and flasks can be replaced cheaply. StuRat (talk) 18:02, 18 February 2013 (UTC)

Test tubes are nearly always designed to be disposable.. especially the smaller ones that you fit into fraction collectors. Flasks on the other hand can be quite a bit more expensive, especially precisely calibrated volumetric flasks. Back to the original question, as 67 pointed out you'd really only be using this sort of acid rinse in a functional hood so the fumes aren't much of an issue. Not to mention, we do keep both dilute sulfuric acid and dilute nitric acid in the teaching labs here, it can't be too hazardous if they let freshman/undergrads use it in genchem. For really persistent contaminants you can use concentrated nitric acid; I've certainly cleaned cuvettes that way on occasion. It's certainly more cost effective than replacing a quartz cuvette! And yes, base baths will etch glass rather quickly, so as already stated above you wouldn't want to use them on anything with joints or fittings. (+)H₃N-Protein\Chemist-CO₂(-) 19:12, 18 February 2013 (UTC)

Cleaning classware with nitric is on par with lighting a barbecue with liquid oxygen [26]. Spectacular but dangerous. Don't try it at home folks – in your neighbors garage yes – it invokes a lot of 'wows' etc (followed by the sound of sirens from the emergency services ) but not in your own house please.--Aspro (talk) 22:55, 18 February 2013 (UTC)

Note, "concentrated" is of course a relative term. Nowhere did I say that I was cleaning cuvettes with fuming nitric acid. I think it's a little silly to make such a big deal about nitric acid without even factoring in concentration. Yes, you probably don't want to pour even moderately concentrated nitric on exposed skin or bad things would happen.. but I doubt many solvents would pass the "I can pour it on my arm without adverse affects" test, so that's an odd safety requirement. (+)H₃N-Protein\Chemist-CO₂(-) 02:11, 19 February 2013 (UTC)

I'd compare it with things normally used to clean glassware, like detergent and water (distilled water in this case). In that context, these cleaning methods seem quite extreme. I suppose they have their place, on expensive items which can't be cleaned in any other way, but their use should certainly be limited. StuRat (talk) 02:17, 19 February 2013 (UTC)

Not limited. No reason it should be either. We used to keep a garbage pail of dilute acid for the first day's soak and a garbage pail of sodium hydroxide for the second day's soak then a day in the oven to dry. For every single piece of glassware. Chemists work with far more dangerous chemicals all the time. Which is why we have lab coats - and gloves, safety glasses, fume hoods, eye washes, emergency showers, acid spill kits, mercury vacuums, gieger counters, lead aprons, inert atmospheres, etc. Rmhermen (talk) 15:52, 19 February 2013 (UTC)

Small clarification, my statement "we do keep both dilute sulfuric acid and dilute nitric acid in the teaching labs here" in no way implied that it's used for cleaning glassware or that we let the undergrads just randomly play with strong acid. (+)H₃N-Protein\Chemist-CO₂(-) 02:19, 19 February 2013 (UTC)

But there are some professionals who specifically specify fuming nitric acid though[27], hence my question. In any case, thanks for all the responses, guys. It's been a real eye opener. Dncsky (talk) 04:44, 19 February 2013 (UTC)

Resolved

If 'you' know what effect that RFNA has on baked-on encrusted carbonated glassware then fine. I'm just saying that for those folks that can obtain access to these chemicals – they should not try it at home – especially, if they live next door to me and if they don't know the A to W to archive the right dilution. De-rusting the gas tank on your classic car with nitric.... forget it … a little knowledge can be a dangerous thing. “Hi Aspro, can you be right neighbourly and lend me some of you battery top up acid? My son's following this recipe where he boils up some cotton wool in nitric and now he need a little sulphuric... I'll tell you this, that 'ol tree stump in the back yard will be out the ground tomorrow – just you wait and see.” So just saying.--Aspro (talk) 15:31, 19 February 2013 (UTC)

Arthur C Clarke Space Elevator

Hi, I read the quote from Arthur C Clarke again today about the space elevator being built "50 years after everyone stops laughing". What did he mean by this? Did he just mean 50 years after everyone starts taking the idea seriously, or is there something more I'm missing? I'm sure its really obvious but my brain is slow today... 80.254.147.164 (talk) 16:55, 18 February 2013 (UTC)

I think your 1st instinct was right. That is, it will take some 50 years of development to make it work, and that can't start until the idea is taken seriously. StuRat (talk) 16:58, 18 February 2013 (UTC)

NASA started spending money on space elevators in 1995. So we can be fairly sure that at least those people had stopped laughing. So we're about 40% of the way into Arthur Clarke's 50 years. That would put the space elevator completion date around 2045. I don't think any of the developers believe that's possible. However, Clarke left himself a loophole - he said "50 years after everyone stops laughing" - I'm pretty sure there will still be laughing right up the the first day it actually works!

Sadly though - it's looking like he may not be correct. I think enough people have taken the idea seriously - and between the tremendous difficulties with making a sufficiently light/strong tether - and the much more problematic issues of stability - he may have been wrong about whether it'll ever be built. However, there are lots of people working on various aspects of the problem - and a good amount of research money is going into solving these problems - so nothing is certain.

SteveBaker (talk) 20:32, 18 February 2013 (UTC)

Well, even if the version he had in mind, only supported at the top and bottom, doesn't work, you could always have one which is powered and has upward propulsion at various points along it. StuRat (talk) 21:57, 18 February 2013 (UTC)

No-one questions that (given sufficiently strong materials) it would work once erected: the difficulties lie in the erection and the dangers of failures during that process. {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 13:57, 19 February 2013 (UTC)

No, no, no. That is absolutely not the case! There are severe concerns about the stability of the cable due to things like Coriolis effect forces on the elevators. These things start the cable swaying - and damping out that motion is difficult with the vast majority of the system being above the atmosphere and extremely flexible. As StuRat points out, you might be able to put rocket motors at intervals along the cable to counter this motion - but then the system needs power and fuel and all sorts of other things that make the whole concept much more difficult. There have been suggestions that you could cancel out these forces by running the elevator very slowly (like 2 months to get from bottom to top) - or by having multiple elevators climbing the cable at the same time (which makes the strength requirements of the cable vastly bigger - and means that you can't bring the elevators back down again once they're up there).

Then there are issues of how to handle wear on the cable and small breakages due to flaws in the materials. Those are exceedingly hard to repair on-the-fly.

With our present level of knowledge, the space elevator is far from a "do-able" problem - even if the cable strength issues can be resolved using something exotic like carbon nanotubes.

SteveBaker (talk) 14:29, 19 February 2013 (UTC)

For a single robot crawler, a single cable should suffice, but as loads increase, its really just a matter of designing a larger structure to handle these. --Modocc (talk) 17:06, 19 February 2013 (UTC)

But that's just not true. The technology doesn't scale at all well. SteveBaker (talk) 20:50, 19 February 2013 (UTC)

I would hate to be on such an elevator when an asteroid or meteor came along and severed it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:36, 19 February 2013 (UTC)

If that catastrophe were to happen, I'd make sure one could fly away! :) I imagine too that a large spiraling suspension bridge type construction would work, because each counter-weighted (the weights are in orbit, which can be bundled with a large structure, like with marionette control bars) cable would need to support only a very small portion of the road (or tracks). The structure can have lanes for both directions of travel and the suspension cables would be isolated from the vehicles. The vehicles which are capable of traversing this bridge could also be wheeled like when one climbs up and down a mountain with an auto. With a large enough structure, the incline can be gradual, but with a shorter near vertical incline, a coilgun type system should get you to orbit and back. At some point, if we ever are able to manufacture cables that are strong enough, it could become commonplace to be taking out one's favorite retrofitted computer driven auto to an upscale establishment. Modocc (talk) 16:12, 19 February 2013 (UTC)

That at least isn't a problem! These machines are unlikely to ever carry people. The elevator would travel through the atmosphere quite slowly and that would expose people to huge amounts of dangerous radiation as it passes through the Van Allen belt. Astronauts only survive this right now because the spacecraft are moving really fast and don't hang around in the dangerous areas for very long. The power requirements for the elevator and the nature of a friction grip on a valuable, highly stressed cable means that the elevator will rise very slowly. They'd spend hours to days of travel through Van-Allen belts - and that would fry the astronaut without many tons of lead shielding - which kills the performance of the machine and makes for impossibly strong cables. The space elevator would have to be a cargo-carrier only. But the probability of an meteor/asteroid/comet hitting the cable is utterly negligable - there are much larger concerns here. For example, an earthquake or tsunami (for example) would induce dangerous waves along the cable. Lightning strikes on a wet cable in the rain would be a serious risk also - so it's likely that the base station will have to be mounted on a ship and moved around to avoid storms...which brings a whole other cluster of issues. SteveBaker (talk) 20:50, 19 February 2013 (UTC)

"...friction grip on a valuable, highly stressed cable..."???? You apparently didn't comprehend my design method. The bridge spans put a static downward load on the many cables which are numerous (essentially as many as are needed). The vehicles have no contact with the cables and there for no friction. There are reaction forces, but their effects will depend on the bridge's resistance to these and other environmental loads due to its inertial mass which, as a mass, will be considerable. The bridge is suspended and anchors need not be inelastic, thus probably earthquake resistant. Storms might be a factor... again it depends on the mass and plenty of bridges weather storms (and floods), but the whole thing doesn't have to (although it probably will) extend all the way to the ground and/or it could have a few light-weight tethers to the ground to give it lateral stability. Depending on the orbit one wants to achieve it could take hours perhaps, and far less if a rail system is used, thus shielding (we will need some substantial shielding anyway, something the astronauts could not afford much of due to mass restrictions) may or may not be much of a factor. -Modocc (talk) 21:46, 19 February 2013 (UTC)

Respondents here have clearly read the PR blurb and missed the math. Read this: http://www.sciencedirect.com/science/article/pii/S009457650800338X - it's not saying that the elevator is impossible, but very likely so inefficient that it won't ever be economically viable.

SteveBaker (talk) 20:50, 19 February 2013 (UTC)

Very first sentence: "The space elevator offers an alternate and efficient method for space travel." Its unstated conclusions are behind a paywall, but why bother? -Modocc (talk) 21:46, 19 February 2013 (UTC)

Completely fictional, but Kim Stanley Robinson described the fate of a space elevator that was severed at anchor point (in space) in Red Mars as mentioned above by Baseball Bugs. I've never liked the idea in the first place, but Robinson's description of the thing crashing down was enough to convince me that—feasibility and other subjects touched upon above aside—this is one of the most frightening ideas we've ever come up with as a race. Which means it'll probably happen several centuries from now, at some point in the far future when celebrities own their own moons. – Kerαunoςcopia^◁_galaxies 22:45, 19 February 2013 (UTC)

Personally, I found the concept in SimCity 2000 of a microwave energy satellite going off-track far more disturbing. Entertaining in a game, though. — The Hand That Feeds You:^Bite

Salticid eyes

Hello,

what colors do the retina layers of salticids recognize? Is it blue, red or green or how is it constructed?

Greetings HeliosX (talk) 19:35, 18 February 2013 (UTC)

From the Wikipedia article on Jumping spider, it says that those types of spiders have tetrachromatic vision and are sensitive to UV light. Their retina presumably can detect up to four colors. See Tetrachromacy. 140.254.121.36 (talk) 19:52, 18 February 2013 (UTC)

Also enjoy this nice book article "How jumping spiders see the world", here on google books [28]. Of note is that they have a "staircase" retina, which they move to focus, rather than their lenses! SemanticMantis (talk) 20:17, 18 February 2013 (UTC)

They also have one of the most robust visual cognition systems of all invertebrates; with certain species like the domestic jumping spider in particular, you can note that they will track the movement of a large entity like a human (and even individual body parts thereof) with much finer attention than the overwhelming number of critters their size. To the OP, this article describes the specific frequencies of light which the photoreceptors of the retinas are sensitive to, with regard to two specific species. Snow (talk) 07:34, 19 February 2013 (UTC)

Identify guinea fowl-like bird with white cheeks and orange wattles

My nephews and I went out to feed the geese in the US North East this weekend in freezing weather. We found instead what I think of a standard guinea fowl with coal-colored feathers with small white spots. But they had bright white cheeks, yellow beaks, and a small bright orange wattle along what would be the jawline on a human on each side. Can anyone suggest what species these might be or what variety of what species? Google image searches get me things that look like the same genus but not identical. Thanks. μηδείς (talk) 20:37, 18 February 2013 (UTC)

Could it be Helmeted Guineafowl? 140.254.121.36 (talk) 20:55, 18 February 2013 (UTC)

(EC) There is a a lot of variety in guinea fowl. Some of them have white cheeks, yellow beaks, and orange wattles. I think there must be some plasticity in the color of the cheeks and wattles, even within species (think overall health and diet). Anyway, check out the helmeted guineafowl. Our article shows one with bluish cheeks, but this zoo page shows [29] theirs with white cheeks. Is that close at all? SemanticMantis (talk) 20:58, 18 February 2013 (UTC)

Related: does anyone have refs of feral GF flocks in the NE USA? I had not heard of that before... SemanticMantis (talk) 21:00, 18 February 2013 (UTC)

Common Birds of the New England Area — Preceding unsigned comment added by 140.254.121.36 (talk) 21:09, 18 February 2013 (UTC)

First, I am absolutely certain they are Guinea Fowl, which aren't native to the US. Second, while they do look like helmeted guinea fowl from the neck down, they have bright yellow beaks, no wattles at the nares or above the "jawline", and bright orange ones at that, and bright white cheeks--they could be Crayola Crayon standard colors or the focal colors of Berlin and Kay. Third, they have absolutely no helmet or crest whatsoever--even though in body shape and the color and pattern of the plumage they are identical to standard helmeted guineas, and their beaks seemed a bit less robust. There were six individuals, and they were identical, no apparent sexual or age variation, so I am wondering if perhaps they were hens or juveniles or juvenile hens. Their white heads were closer to the Pearl variety, but still no crests and their wattles were smaller than and less forward pointing, basically only the size of the white are of the wattles on this Pearl specimen, as if the white part were orange and the red part snipped off. Pearl. μηδείς (talk) 01:57, 19 February 2013 (UTC)

Standard components in Edison, Tesla, and Marconi's day

Where'd they go to get, say, a resistor of X ohms, a capacitor of Y microfarads, or an inductor of Z henries when implementing one of their designs? Not Radio Shack or Mouser, I presume :) 67.163.109.173 (talk) 22:48, 18 February 2013 (UTC)

Edison had his own staff, and I imagine the others did, too, or made the items themselves. StuRat (talk) 23:01, 18 February 2013 (UTC)

I wold like to know (for knowledge's sake, not that I would expect to be able to do it in my garage) if records/documentation for their "recipes" and construction methods/procedures to construct components with specified component values have been preserved. 67.163.109.173 (talk) 23:06, 18 February 2013 (UTC)

Michael Faraday's Experimental Researches... contains many experimental descriptions that are very cook-book-recipe-like. By the era of Edison and Marconi, electrical components were already commercially available. For example, Federal Telegraph Company is famous in these parts; they used to sell great big ferrite cores and integrated radio systems, dating back to the very early era of radio. Telegraph and telephone companies, like Western Union and Bell and AT&T (the original corporation) were already building large scale telecommunications systems, and they manufactured support electronics on industrial scales. Nimur (talk) 23:48, 18 February 2013 (UTC)

Thanks. Related to first precision components, I always wondered; the first calibration measurement devices to be able to measure to a given precision, how were they calibrated, given that prior to them, one could not know that their components were accurate to that given precision. For example, the first capacitors asserted to be accurate to within 10 microfarads, the tester used on them would need to be able to measure within 10 microfarads to know what value they were. So the device to test the first capacitor with a value within 10 microfarads of its nominal value needs to be able to do whatever it does to indicate "yes" within 10 microfarads of that value. Doesn't that device need such level precision capacitors in it? But prior to this moment, no such precision capacitor has been made (knowably with any degree of confidence). This questioning could go for resistors or inductors, I suppose, not just capacitors, which I used as an example. 67.163.109.173 (talk) 00:29, 19 February 2013 (UTC)

Well, for simpler measurements, like length, they just carved a line in stone somewhere, declared that to be a foot, and measured everything else against that. I suppose a similar method could have been used with more complex measurement devices. StuRat (talk) 01:50, 19 February 2013 (UTC)

I am an electrical engineer by occupation, and electronic engineer by qualifications and hobby, and have been involved in a bit of chemistry. The great thing about electrics and electronics is that it is quite simple and easy, if a pretty bit tedious, to home-make basic components because they are calculable, and you can build up from there. For instance, given the physical dimensions, the capacitance of an air-spaced capacitor can be calculated with a high degree of precision (> 4 place accuracy is not at all difficult with a modicum of enginuity). The inductance of a toroidally wound air core inductance can also be calculated from its physical dimensions with a high degree of precision. I wish chemistry was like this!

In a home electronics lab, all you really need is an accurate DC voltmeter, and accurate frequency meter (both easy to get without much expense: 5-digit digital voltmeter ~ $200, 6-digit frequency meter about the same), and an accurate capacitor (home-made), and you can construct apparatus to relate all measurements back to these, for calibration purposes. 100 years ago, labs used the Weston Cell as an accurate voltage for calibration purposes. Oscillators were compared with others by counting beats and ultimately referred back to a mechanical clock, whose accuracy was assured by comparison with observations at astronomical observatories.

Ratbone 60.230.235.171 (talk) 02:39, 19 February 2013 (UTC)

Standards might be determined in world-class physics labs, such as the work of Maxwell and Thompson in the 1860's [30] with standard cells and carefully managed galvanometers, or Lord Rayleigh and (his faithful companion Mrs. Sidgwick) to define a column of mercury of some length of some cross section at some temperature as having a specified resistance. See [31]. They followed on the heels of Davy, Faraday and others. The telegraph industry made use of standards and measuring instruments by the 1850's, to achieve commercial success. A useful and practical lab standard resistance could be made with a certain length of resistance wire, such that it has a desired resistance with a stated precision at a stated temperature, and correction factors could be applied for other temperatures. Lab supply houses could make and sell to experimenters such standards. Bridge circuits could be used with standard voltage cells, standard resistances, inductances or capacitances to measure or adjust other secondary standards. An early 20th century or late 19th century electrical lab had big, expensive and delicate instruments for precision measurements, museum pieces today, just to achieve similar precision to a digital meter today costing a few hundred dollars.Edison by the 1870's could buy or have whatever measurement devices he needed. Tesla in the 1890's could just write Westinghouse and have motors or generators built for his lab, or could have his workmen build new devices. Experimenters did not always need state of the art accuracy in measurements, compared to the physics labs developing standards with many digits of accuracy. Edison (talk) 16:58, 19 February 2013 (UTC)

freezing point of water

Would a solution with 250 ml of rock salt and 25 ml water 125 ml ice have a much lower freezing point than a solution with 175 ml of rock salt, and 25 ml water 200 ml ice? At the beginning of my experiment, the 400 ml beaker was half full with ice, and the rest was rock salt (with a tiny bit of rock salt). Alot of rock salt was added to the beaker, over the course of the experiment. — Preceding unsigned comment added by 99.146.124.35 (talk) 23:29, 18 February 2013 (UTC)

Does our freezing-point depression article help? Mikenorton (talk) 23:37, 18 February 2013 (UTC)

If the extra rock salt dramatically lowers the freezing point of the ice in the 400 ml beaker, how would that impact the freezing point depression constant of the fluid inside the vial that is positioned inside the 400 ml beaker? All of the freezing point depression constant Kf values of the water that was mixed with citric acid inside the vial were much lower than what they should be (0.5 and 0.65 is what they came out to be. — Preceding unsigned comment added by 99.146.124.35 (talk) 23:41, 18 February 2013 (UTC)

Citric acid ? As for the effect of more rock salt, there's only so much salt that can be dissolved in the (liquid) water. Beyond that, more won't change it's properties, it will just sit on the bottom. However, rock salt has lots of other junk in it, some of which might be dissolved by water and affect it's properties. In a chemistry experiment, I expect you'd want to use pure table salt (non-iodized sodium chloride). StuRat (talk) 02:35, 19 February 2013 (UTC)

If you want to REALLY lower the freezing point of water, you can make a saturated solution of calcium chloride and see how cold you can get it without freezing it.  :-) 24.23.196.85 (talk) 05:01, 19 February 2013 (UTC)

Rock salt will lower the freezing point of water by maximum −21.12 °C for saturated solution with 23.31 wt% of NaCl. See also [32]. Ruslik_Zero 07:54, 19 February 2013 (UTC)

February 19

contracting rabies

I have looked extensively for information that would tell me if deer or elk can contract rabies. I have never heard of these animals becoming infected and would like to know if it is possible and/or how common.98.22.220.148 (talk) 01:40, 19 February 2013 (UTC)

Yes deer can get rabies, e.g. [33][34], though rabies is rather rare for deer. Based on the first link, of the 7000 rabid animals found in the United States each year, about 5 will be deer in the typical year. Dragons flight (talk) 02:04, 19 February 2013 (UTC)

Thank you!98.22.220.148 (talk) 02:47, 19 February 2013 (UTC)

All mammals can get rabies, apparently birds also but I don't know if that's ever been found in the wild. A factor which limits finding rabid animals is their survival of the infective event; for instance, small mammals like mice and rabbits aren't found infected, apparently because they rarely or never survive the attack by an infected animal. In a similar vein, deer or elk are unlikely to survive an attack by an infected large carnivore like a cougar, wolf, or even a large dog; but also are unlikely to be successfully attacked by something small like a rabid fox or raccoon so wouldn't get infected in an attack they could survive. Just my opinion. Gzuckier (talk) 19:53, 19 February 2013 (UTC)

Double-slit experiment and scale

When performed on subatomic "particles", like electrons and photons, I understand that the resulting interference pattern associated with waves is produced. When performed with much larger objects, like bullets, no interference pattern is observed. So, my question is, at what scale does the transition from wave behavior to particle behavior occur, and how does it occur ? Is there a gradual change from one to the other, or an instant change ? We could try larger subatomic "particles", like protons and neutrons, small atoms, large atoms, small molecules, large molecules, etc., until we get to the size of a bullet. StuRat (talk) 04:00, 19 February 2013 (UTC)

By theory, ALL well-defined objects should be subject to wave-like properties, per the de Broglie relations; it's really an engineering problem and not a science problem; that is, even for bullets, there should be an associated wavelength which could be calculated given the mass and velocity of the bullet; knowing that wavelength would give you the way to construct a set of slits through which the double-slit experiment should be valid, the issue is in the actual construction of them, which may be a physical impossibility due to the restraints imposed by using real materials in the experiment, but again this is an engineering issue, not one in the theory. In actual experimentation (according to information at the Matter wave article), the largest particles shown to diffract experimentally (and thus display real wave-like characteristics) have a mass just shy of 7,000 atomic mass units, which would be about the size of a smallish protein molecule (for comparison, hemoglobin has a mass of about 64,000 amu.) --Jayron32 04:56, 19 February 2013 (UTC)

And, at that scale, do we get a pure interference pattern, like a wave ? StuRat (talk) 05:01, 19 February 2013 (UTC)

Again, there are no theoretical limits here, just engineering limits. You can calculate all the parameters; the size and distance between the slits, the parameters of the interference pattern you get, for any arbitrary object, from an electron up to, say, a star. The parameters work to infinity in all directions; there is no hard limit where any well defined object stops following quantum behavior. Instead, there's a limit where the difference between quantum behavior and classical behavior becomes smaller than tolerances of our measuring devices, or where the actual means to construct, say, two slits to diffract bullets becomes a physical impossibility. But the math should work, and we have no reason to suspect that it would be wrong per se, just that the actual construction of an apparatus to test it would be impossible. --Jayron32 05:25, 19 February 2013 (UTC)

(edit conflict) Someone should check my math, but I just did the calculation of a 20 gram bullet (0.020 kg) fired at a speed of 1000 m/s, and came up with a de Broglie wavelength of 1.91 x 10^-40 m. For comparison, the charge radius of a proton is 8.75 x 10^-16m, which means that you could fit about 200,000,000,000,000,000,000,000 or so de Broglie wavelengths of the bullet within the radius of a proton. If you can create slits small enough and close enough to run a double-slit experiment on something like that, you're a better man that I. --Jayron32 05:43, 19 February 2013 (UTC)

Clearly a bullet wouldn't fit through those slits. Does that mean there's a hard limit where the particle is larger than the required slit ? StuRat (talk) 05:49, 19 February 2013 (UTC)

It also depends on velocity; I believe (and I may be wrong on this assumption) that objects moving closer to the speed of light could fit through smaller slits, due to relativistic effects on their dimensions. So, depending on how fast you can get your bullet moving, you could get it to squeeze through any arbitrarily sized slit. Practically, of course, you are correct, eventually, your object size and your slit size are moving in opposite directions, and you reach a limit where the slits become too small to fit the object in question through, at which point the experiment becomes impossible. See below, where I found the results of an experiment where the slits were only about 500 times larger than the diameter of the object, which is still pretty close in size. --Jayron32 06:12, 19 February 2013 (UTC)

I don't think so. Relativistic length contraction will only apply to the axis along which the object is moving. Your relativistic bullet would be just as wide as before, but shorter. You'd also run into the issue of higher speeds producing ever shorter wavelengths. Someguy1221 (talk) 06:21, 19 February 2013 (UTC)

Like I said, I wasn't too confident on that part. So, there would be a real physical limit, which is where the shrinking slit size and the growing object size pass. --Jayron32 06:31, 19 February 2013 (UTC)

There are ways to "cheat". The simplest demonstration is to have slits that are much narrower than the object's wavelength, but weaker effects can allow one to demonstrate interference and other quantum effects even if that isn't the case. However, in that scenario one needs to do the analysis of the situation more carefully and the measurements are generally harder. In the C₆₀ molecule interference demonstration, the C₆₀ have a diameter of about 1 nm and passed through slits ~50 nm wide with a 100 nm separation. However, in this case, the de Broglie wavelength is only about 2.5 pm (i.e. 0.0025 nm). In other words the slits were already orders of magnitude larger than the de Broglie wavelength, so the waves would only be very weakly diffracted, but the quantum effect was still large enough to measure. (In this case "large enough to measure" meant diffraction peaks separated by about 20 microns.) Dragons flight (talk) 06:33, 19 February 2013 (UTC)

There are theoretical limits. First, the wavelength you calculated is smaller than the Planck length, so it probably doesn't make sense to talk about it without a theory of quantum gravity. Second, unless they're cooled to near absolute zero, bullets emit blackbody radiation which leads to environmental decoherence within a much shorter time than you'd need for the experiment. Third, even if you do this at very low temperature, bullets have a lot of internal state (they're malleable, for example), which would likely record which-path (welcher-Weg) information, which destroys the interference pattern. Any one of these alone makes the experiment impossible. -- BenRG (talk) 08:26, 19 February 2013 (UTC)

And I'm also interested in the reverse Q: What's the smallest object which can be fired thru the double slits, without a detector to show which slit, that still doesn't exhibit an interference pattern ? StuRat (talk) 05:37, 19 February 2013 (UTC)

I'm not really good with the optics calculations, but roughly speaking the more massive the object, the smaller its de Broglie wavelength is, so the smaller and closer you'd have to make the slits in a viable double-slit experiment. So, what you would need to do is calculate the relationship between slit size and wavelength, and then figure out what the smallest slits you can make are, and then use the de Broglie wavelength equation to calculate what mass corresponds to whatever wavelength you can diffract with the smallest slits possible to make. That would be the practical upper limit for an object you could successfully run a double slit experiment on. --Jayron32 05:47, 19 February 2013 (UTC)

Just for an example of a good double-slit experiment using massive particles, here is the results of such an experiment run on Buckminsterfullerene molecules (C₆₀, mass = 720.64 amu) which showed interference patterns consistent with theoretical predictions based on calculated de Broglie wavelengths. The slit sizes here are really freaking small: it required 50 nanometer slits spaced 100 nm apart. The diameter of one of these molecules is about 10.18 Å (according to https://sesres.com/PhysicalProperties.asp), which means that the slits are about 500 times larger than the molecules themselves. At some point, you'd reach the point where the slits become smaller than the diameter of the particles; this may (or may not) represent some sort of physical limit. I think you can count on relativistic effects to allow for an object larger than the slit to pass through it (that is, by firing the object at some speed very close to the speed of light, you can still get it to pass through a slit which is smaller than it is, when the slit and the object are at rest relative to each other), but we're getting out of the realm where I'm capable of doing such calculations, or even discussing it confidently in broad terms. --Jayron32 06:06, 19 February 2013 (UTC)

I don't see how you could use length contraction to get an object through a narrow slit, given that only lengths in the direction of motion are contracted. -- BenRG (talk) 08:26, 19 February 2013 (UTC)

Yeah, like I had already said above, I was wrong about that. I'm still wrong about that. --Jayron32 13:32, 19 February 2013 (UTC)

Small correction: 10 Angstrom = 1 nm, so it's 50 times larger, rather than 500 times larger. -- 205.175.124.30 (talk) 22:19, 19 February 2013 (UTC)

Imaging C60 in double-slit experiment

This post has reminded me of something I meant to ask.

Given that buckminsterfullerene has a diameter of 1 nm, each molecule can be imaged with e/m radiation of over 300PHz, which is soft x-rays and up. Is it possible to use a hard X-ray camera pointed in the same direction as the slits, (normal to the direction of the C60), and then fire individual C60 molecules in the experiment, to track each molecule? Or does this violate wave/particle duality? CS Miller (talk) 20:49, 19 February 2013 (UTC)

Presumably, just like other attempts to tell which slit they use, if successful, this would destroy the interference pattern, and you'd see the simple sum of particles passing through both slits, at the detectors, instead. As for how it can do this, we have to imagine that the x-rays in some way disturb the particles. StuRat (talk) 22:00, 19 February 2013 (UTC)

For the second part of your answer, you are probably right StuRat, a 3,000PHz photon has 2 fJ of energy, enough to accelerate a 60*12 amu object to 57.7 km/s; unless the molecule can complete the experiment in a few microseconds, it will probably be forced onto the far end of the container.

For the first part, if the camera was far enough away for the photos to reach it, after the molecules hit their detector, then the observation can't affect the interference pattern. (I think, I'm not strong on quantum mechanics). CS Miller (talk) 23:18, 19 February 2013 (UTC)

wireless electricity transmission

please give me the details that how it possible to transmit electricity without wires(wireless)? what are the recent researches in this field? as well as what is the future of this?? — Preceding unsigned comment added by 49.50.96.200 (talk) 08:11, 19 February 2013 (UTC)

The wireless power article would be a good place to start. -- BenRG (talk) 08:15, 19 February 2013 (UTC)

Transmitting small amount of electricity wirelessly over small distances is easy, you can use things like electromagnetic fields to convey power a few inches. Transmitting large amounts of electricity wirelessly a long distance is more problematic. Tesla wanted to do it with radio waves, but this is quite dangerous, inefficient, and it's difficult to do billing (current radio and broadcast/satellite TV does transmit a tiny amount of electricity wirelessly, but needs electricity from wires to amplify the signal (with the exception of a crystal radio). You could also point a laser at a distant solar cell, and transmit electricity that way, but this would be inefficient and require a clear line-of-sight. StuRat (talk) 09:39, 19 February 2013 (UTC)

Talking of fields, this video shows transmission in a field.[35] Unfortunately, the camera used is not sensitive enough to actually convey how amazing this is when demonstrating it to the doubting Thomas's and grandchildren. When your eyes become light adapted to the darkness the tubes are bright enough to read by. If a factory or office near you is replacing its tubes, the old ones can be picked up for a few cents each. I'm surprised that this demo didn’t use balancing coils to enhance the power -(as the tube are only four to six feet long).--Aspro (talk) 15:55, 19 February 2013 (UTC)

Back in the dawn of time when I used to subscribe to Popular Electronics, they had a project that was a crystal radio with a one transistor amplifier stage, which was powered by another crystal radio which was tuned to a powerful local station. Never built one, but how cool is that? Gzuckier (talk) 19:58, 19 February 2013 (UTC)

Nice way to make the big guys to support the little guys. Now if we can just get Microsoft to support Linux. :-) StuRat (talk) 20:05, 19 February 2013 (UTC)

See Space-based solar power as one possibility. Note that this isn't directly "electricity" being transmitted, rather solar power being transmitted as a microwave signal to the ground, which then converts to usable electricity. — The Hand That Feeds You:^Bite 23:24, 19 February 2013 (UTC)

Classification of animals

In here (page 95) the classification of animals is shown. I'm having trouble understanding how animals with tissue level of organisation are further divided. Can anybody please explain? Thanks. --Yashowardhani (talk) 10:30, 19 February 2013 (UTC)

Our body cavity article explains this pretty clearly -- see the section called Grouping. If you need more information, please follow up. Looie496 (talk) 16:21, 19 February 2013 (UTC)

Is it possible to discharge electricity by alternating current (AC)?

In discharge tube, electric discharge takes place when we supply direct current (DC). If we supply AC instead of DC, will the electric discharge take place in the same way as in case of DC? 27.62.227.241 (talk) 11:17, 19 February 2013 (UTC)

Yes, however there is an important difference. With DC, there must be sufficient voltage to start the discharge, ytermed the striing voltage. Once the arc has started, a gnenerally very much lower voltage is required to kepp it going. With AC, unless the arc is quite large, as in arc welding, the will stop each time the voltage goes to zero, 100 times a second (120 times in USA and certain other countries). Hence with AC the peak voltage must be kept continuously above the strike voltage in order to keep the arc going. Keit 60.230.216.137 (talk) 12:28, 19 February 2013 (UTC)

Electric discharge in gases and arc lamp are two relevant articles. DMacks (talk) 16:30, 19 February 2013 (UTC)

One thing you should notice that, in discharge tube (DC) cathode and anode never exchange their position, on the other hand, AC is fluctuating. 27.62.227.241 (talk) 16:54, 19 February 2013 (UTC)

Biochemistry

is that right that Glucose and Phosphat (or phosphorous) are the main ATP sources (and thus, sources for short-time energy), while, Creatine and Fat are the main "long term energy" sources ?.

thanks.

All (or almost all) of the biological energy sources go through ATP. The question is how the body regulates the conversion. The process of glycolysis is the main energy generating pathway in heterotrophs, so typically glucose is thought of as a primary energy source. It's certainly the case that blood glucose, when available, is typically used as the preferred external energy source. In contrast, energy generation from fat (acetyl-CoA production by fatty acid degradation, which ultimately leads to ATP production through the citric acid cycle and oxidative phosphorylation) is more complex, so it typically reserved for long-term energy storage. Even then, a portion of the fat isn't used directly, but instead is used for gluconeogenesis to produce blood glucose. Fat, being more energy dense than carbohydrates, tends also to be better for long-term storage of energy, although things like glycogen are used for medium-term energy reserves. As to the other compounds, phosphate/phosphorus by itself is not an energy source. It's role in energy metabolism is to serve as a building block of things like ATP. Creatine per se isn't an energy source, at least anymore so than standard amino acids are. The reason it's mentioned is because of creatine phosphate, which, like ATP, is a high-energy phosphoester that can serve as a store of energy. It's not used as an energy donor itself, though, instead functioning as a "buffer" for ATP in places like muscles, regenerating ATP when ADP levels are high, and being created itself from ATP when ATP levels are high. But that's more of a short/medium-term storage rather than long-term storage. -- 205.175.124.30 (talk) 22:13, 19 February 2013 (UTC)

Maybe the OP means polyphosphate (a universal acidocalcisome component, not just in polyphosphate-accumulating organisms) which holds energy-rich bonds comparable to those in ATP. For review see [36] [37]. I'm actually not quite sure what overall percent of the cell energy budget it represents in typical organisms. Wnt (talk) 23:25, 19 February 2013 (UTC)

Pantoon?

what is pantoon — Preceding unsigned comment added by 210.212.95.98 (talk) 12:57, 19 February 2013 (UTC)

Do you mean pontoon? StuRat (talk) 15:58, 19 February 2013 (UTC)

Or pantaloon or Pantone or platoon?--Shantavira|^{feed me} 16:12, 19 February 2013 (UTC)

Or Panton, pantun, Penton or Panettone? Red Act (talk) 16:16, 19 February 2013 (UTC)

Is there some reason to omit poontang?

Can you please give this word as used in a sentence. Pantoon could refer to a boat which as StuRat points out is an alternative spelling. We need the context to take this further.--Aspro (talk) 16:10, 19 February 2013 (UTC)

• Could also be Pantone (a system for color management)? Looie496 (talk) 16:13, 19 February 2013 (UTC)

How do you polish a copied key to make it work better?

I've noticed that duplicate keys made by automated machines have groove marks on the cut surfaces, transverse to the length of the key. I think the groove marks make a duplicate key difficult to insert into and pull out of the lock. Is there an easy way to polish way the groove marks without affecting the function of the key? --108.2.210.178 (talk) 13:29, 19 February 2013 (UTC)

I've always used 400-600 grit "flatting paper" (carborundum type sandpaper that is normally used wet esp. in the automotive bodywork industry.) It's hard enough to remove any superficial burrs but fine enough that it will take some hard work to actually alter the shape of the key. An emery board (used for manicures) also works well for the same reasons. 196.214.78.114 (talk) 14:03, 19 February 2013 (UTC)

Common "Pin tumbler locks" only depend on the height of the high spots and the depth of the low spots on the key. What makes the key harder to insert and remove is the grooves on the sloping parts. As you insert the key, the pins inside the lock have to slide up and down those slopes - so if they are rough, you'll find the key hard to insert and remove...AND you'll wear out the lock prematurely too.

Hence, so long as you don't reduce the height of the 'hills' or the depth of the 'valleys' of the key - you should be able to gently smooth off the slopes between them using a very fine emery paper or a polishing stone on a Dremel (or something similar) without affecting the ability of the key to open the lock. I would only do this on a duplicate key for which you still have the original!

SteveBaker (talk) 14:12, 19 February 2013 (UTC)

Rope walking

I have seen people walking on ropes taking a long stick in their hands. I know they use the stick to balance their body. How can we explain this in scientific terms? 27.62.227.241 (talk) 15:03, 19 February 2013 (UTC)

Our article on tightrope walking explains the basic mechanics -- the increased weight, coupled with the increased distance from center of mass, increases the moment of inertia which reduces the angular acceleration of the person. This slows the tipping process and gives the person time to correct. — Lomn 15:12, 19 February 2013 (UTC)

There's a similar counter-intuitive experiment you can do. Try balancing a ruler and then a yardstick (or meter stick) on your fingertips, vertically. You'd think the smaller one would be easier to balance, right ? Nope, you need to make much faster adjustments to keep it steady than the longer stick. StuRat (talk) 16:02, 19 February 2013 (UTC)

similarly, weight one ennd of a yard/meter stick and you'll find it's easier to balance vertically on a finget with the heavy end up in the air, than with the heavy end down at the finger end. Hey, that would be one heck of a field blood-alcohol test for cops to use, no? "Your honor, we could only slide the weight 6 inches down the meter stick before the defendant could no longer balance it, he was clearly inebriated?" Gzuckier (talk) 20:03, 19 February 2013 (UTC)

Phone signal disconnecting a mouse

Hi, this may seem like a question for the computing desk, but I am not interested in how to fix the problem, just the scientific reason behind what is happening - I don't even intend to fix it, it fascinates me so much I kind of like it...

My PC at home has a standard wired mouse connected via USB to the back off the PC. Every time I have my mobile phone on my desk, and recieve a call/text on it, the mouse "disconnects", the cursors won't move and the Windows "hardware disconnected" sound plays. I have observed this happening too many times for it to be a coincidence, and I actually have to sit far back from my PC if I want to use the mouse whilst on the phone. My question is why is this happening? Is it the phone signal inducing a current in the wire? The signal interfering with the infared sensor on the bottom?

To reiterate: nothing is particuarly special aboout the set up; it is a plastic cheap-ish mouse with a plastic coated wire connecting it via USB to the motherboard at the back. Again, nothing is special about my phone, and I have observed it happening with multiple phones (I am not sure about mice). Thanks! 80.254.147.164 (talk) 15:24, 19 February 2013 (UTC)

I have observed a "galloping sound" on my PC speakers when the cell phone is near the wires. So, I do believe it's picking up interference on the wires, in your case, too. I would hope that it would "reconnect" once the text is finished. Does it ? StuRat (talk) 16:08, 19 February 2013 (UTC)

Yes it does, I thought the "galooping" sound was due to the signal interfering with the magenets in the speakers? 80.254.147.164 (talk) 16:27, 19 February 2013 (UTC)

I did an experiment where I wrapped the speaker wires around the cell phone, then sent a text, and the galloping sound was much louder, despite the distance to the actual speakers being the same. StuRat (talk) 16:37, 19 February 2013 (UTC)

Clever, I might do the same with the wire on my mouse - see if I can get to happen away from the actual mouse but wrapped in its wire. I will report on my findings tommorow. YEAHH SCIENCE!!!! 80.254.147.164 (talk) 16:41, 19 February 2013 (UTC)

Cool, please let us know how it goes. StuRat (talk) 16:43, 19 February 2013 (UTC)

Sounds like Electromagnetic interference to me. The interesting question is whether it is the microcontroller inside the mouse or the USB host on the motherboard that is getting confused. Cand you try another mouse on that computer and/or another computer with that mouse? --Guy Macon (talk) 19:48, 19 February 2013 (UTC)

Yeah - it definitely sounds like electrical interference. I would suggest adding a ferrite bead to the mouse cord - but to be honest, it would be probably be both cheaper and easier to replace the mouse instead. You might also try changing the length of the cord - if it's acting as an antenna, that might fix it...but again, it's not an easy thing to do.

What's happening (probably) is that the mouse cord is acting like a radio antenna. The abrupt emission of radio waves from the phone to the cell tower acknowledging that it's there is evidently just the right frequency to be picked up by the USB cord and that's evidently enough to cause either the mouse or the PC to decide that something went horribly wrong. When you halve the distance between the antenna and the transmitter, you quadruple the amount of energy produced in the antenna. So when you consider that the phone signal has to be picked up by a cell tower several miles away - and when the mouse cable is just inches away, the power is going to be millions of times more than the cell tower sees. Moving the phone further from the USB cord would obviously be a good idea.

SteveBaker (talk) 20:26, 19 February 2013 (UTC)

determination of pesticides by QuEChERS method using LC-MS/MS

HI I WOULD LIKE TO KNOW WHETHER IT IS POSSIBLE TO USE CLOPYRALID AS THE INTERNAL STANDARD IN THE DETERMINATION OF TRYCLOPYR IN WHEAT GRAIN COMMODITY.WILL IT NOT ELUTE AT THE SAME TIME AS THE COMPOUND OF INTEREST OR COURSE ANY INTERFERENCES OF SOME SORT? — Preceding unsigned comment added by Tsbu (talk • contribs) 15:29, 19 February 2013 (UTC)

For reference, we have clopyralid, Triclopyr, Quechers and Elution. Rojomoke (talk) 18:56, 19 February 2013 (UTC)

Polarized lens sunglasses

1) Is it true that, if you have two polarized lenses, arranged in series, so each photon passes thru both, and each lens blocks 50% of the light, that by varying the angle of rotation of one lens, so it's either in the same orientation as the stationary lens (both horizontally polarized or both vertically, for example), or at a 90° angle (so one is horizontal, and one is vertical, for example), you can vary the total blocking of light from 50% to 100% ? StuRat (talk) 16:16, 19 February 2013 (UTC)

Yes, or nearly a 100%. If the light is bright enough some light leaks through.--Aspro (talk) 16:18, 19 February 2013 (UTC)

Why is that ? Is it some flaw in the polarized lenses, or does light have the ability to change it's polarization from one lens to the other, or is it just that you can never quite get exactly 90° ? StuRat (talk) 16:23, 19 February 2013 (UTC)

Because attenuation is not a "binary," "completely on" or "completely off" effect. Polarized light incident on a differently-polarized medium is attenuated. If we analyze one single photon, we can say "one single photon has a probabilty P% of passing through the medium." And if we analyze a large ensemble of photons as a continuous incident light source, then we say "the polarizer attenuates the light to P% of its incident value." Nimur (talk) 16:28, 19 February 2013 (UTC)

OK, so if it's not 100% blockage, what percent can be achieved ? StuRat (talk) 16:35, 19 February 2013 (UTC)

That depends on the thickness of the glass and the sensitivity of your experiment. At some point, increasing the attenuation of "wrongly-polarized" light will also increase the attenuation of "correctly-polarized" light, and soon we have an opaque material. Are you asking for the optical properties of many common glass? My go-to reference, Applied Photographic Optics, has a full chapter on polarization, and another on attenuation, and has lots of details about commonly-used glass. We can easily build polarizers that attenuate 50% of all light and 95% of oppositely-polarized light. Sunglasses are probably in that ballpark. Nimur (talk) 16:43, 19 February 2013 (UTC)

So, then, my set-up would vary from 50% to 95% blockage, as well, depending on the angle of rotation ? StuRat (talk) 17:08, 19 February 2013 (UTC)

2) Does anyone make such a pair of sunglasses ? StuRat (talk) 16:16, 19 February 2013 (UTC)

Doubt it. We are talking rays not photons (which are packets of light energy). The medium used to filter light of one orientation only (were talking around 500 nano meters) have an angle of error and internal refraction. Hold two of the best polarization filters up to the sun and I reckon you will still see it. No 100%.--Aspro (talk) 16:36, 19 February 2013 (UTC)

P.S. Why are you asking? If you want to block out light competently why not use a thick bit of cardboard? Cornflake packets are cheap and readily available. A really low tech and practical solution. --Aspro (talk) 16:47, 19 February 2013 (UTC)

I'd like a pair which I can adjust. I'm aware of the ones which darken automatically in bright sunlight, but that fails in four respects:

A) They lag the light change, so, when driving under a bridge, everything can go black. I'd rather adjust my sunglasses going into a dark space, than have to take them off and put them back on. (Less chance of me poking myself in the eye this way.)

B) They don't adequately account for a single bright point of light ahead, like the old Airstream trailers (which should have been banned as a road hazard).

C) They don't account for my preference for light levels. Sometimes my eyes are bothering me and particularly photo-sensitive, so I'd like darker lenses. (Alcohol may be involved here.) :-)

D) At times I want to block more light to one eye than the other, right up to 100%. If I just had an eye drop in one eye, for example, which causes photosensitivity. (Yes, I could use an eye patch for this, but then I'd feel the need for a hook arm, peg leg, and parrot on my shoulder.) :-) StuRat (talk) 16:54, 19 February 2013 (UTC)

You don't strictly need any property of polarization, then; except to fine-tune the darkness. You can stack extra neutral density filters until the glass is as dark as you like, and use one rotatable crossed polarizer for fine adjustment. Nimur (talk) 17:08, 19 February 2013 (UTC)

Yes, but keep in mind that I don't want the minimum to go too high, either. For example, I wouldn't want sunglasses that can be adjusted to block between 90-99% of the light, as 90% might well be too much, in some cases. Of course, I could take them off, but then it might be too bright. Ideally they would be fully adjustable from 0% to 100%, but I don't think that's possible in something light enough for sunglasses, at present. Perhaps sunglasses with very tiny LCDs could do that, but this would increase the complexity and weight. StuRat (talk) 17:17, 19 February 2013 (UTC)

If it's any help, one can (or could) buy a similar arrangement for SLR cameras with one polarized filter rotating on another which is screwed to the front of the camera lens. A competent handyman could build a pair of these double adjustable filters into a spectacles frame. {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 18:07, 19 February 2013 (UTC)

Cool, have any links ? StuRat (talk) 18:48, 19 February 2013 (UTC)

could probably cobble something together from a couple pairs of the polarized variety of 3D glasses filched from the local showing of whatever is being foisted upon the public. Gzuckier (talk) 20:10, 19 February 2013 (UTC)

A couple of "products" (I don't see any actual ordering information) that claim to do this with two different technologies:

http://www.allproducts.com/optical/hurricane/as01_print.html

http://www.photonics.com/Article.aspx?AID=29481

--Guy Macon (talk) 21:05, 19 February 2013 (UTC)

The first one claims to use my concept, but I'm confused, since they aren't circular. How could you rotate non-circular lenses relative to each other without having bits sticking out ? StuRat (talk) 21:55, 19 February 2013 (UTC)

Displacement vs. Distance

Suppose a person marks two points along the circumference of a piece of pizza. The person may measure the border of the pizza and calculate the distance from Point A to Point B along the perimeter of the pizza. That will be the distance. The displacement from Point A to Point B, if they are across from each other, would be the diameter of the pizza, while the distance, if measuring the border, is only the half-circumference of the pizza. In this example, the displacement is the shortest distance. I wonder how you apply it to the universe, which astronomers describe as being linear, parabolic or hyperbolic-shaped. The distance will probably mean how far one travels from Point A to Point B in the universe, but the displacement is presumably the shortest distance, even though this distance may be difficult to actually to calculate, because one may need to know how curvy is the curve of the universe. Is displacement really practical in the latter case? 140.254.226.230 (talk) 17:29, 19 February 2013 (UTC)

This concept of displacement requires that it be possible to embed the space in question in a higher-dimensional Euclidean space, and that there be essentially only one way to do this. In your example, the one-dimensional pizza border is embedded in our three-dimensional Euclidean space. However, there are many non-Euclidean geometries that cannot be embedded in a finite-dimensional Euclidean space, and even for those that can, the embedding is often not unique. So basically the answer is that unless an embedding space exists and we have some way of observing it, this concept of displacement is not practical. Looie496 (talk) 18:08, 19 February 2013 (UTC)

I suppose there are similar concepts in space flight. For example, the distance a space ship must travel between Earth and Pluto is not simply the minimum distance between the two, since you can't go that way. For one, the target is always moving, and, also, the spaceship will be rotating about the Sun with the velocity of Earth, more or less, once launched, not travelling straight out radially. If you add in detours around other planets on the way, the distance traveled becomes even longer.

Similarly, travel on Earth usually means along the surface, not through the crust. A great circle route is the shortest route on the surface, but detours are frequently needed, so total distance traveled from point A to B can be far more than the straight distance from A to B. StuRat (talk) 18:40, 19 February 2013 (UTC)

A great circle route is actually a good example of a geodesic. A great circle route is a geodesic within the 2-dimensional manifold of Earth's surface. Red Act (talk) 19:43, 19 February 2013 (UTC)

Although the concept of a displacement vector only really works in a Euclidean space, there's a related concept of a geodesic, which works in both Euclidean space and in a curved spacetime. Geodesics do not require any assumption that spacetime is embedded in a higher-dimensional space. Of all the spacelike curves between two events that are spacelike separated, the shortest such curve is a geodesic between the two events. In a Euclidean space, the length of the displacement vector between two points is the same as the length of the geodesic between the two points. Red Act (talk) 19:07, 19 February 2013 (UTC)

Really simple question about boiling water

I'm learning to use a wood stove that works simply by heating up and letting the warmth spread through the house, rather than through a central heating system; as such, its surface is quite hot. Upon advice from friends who have experience with these things, I've placed a small pan (one of these with the rolls removed) on top and filled it with water, so that the house will be humidified; I typically fill it by filling a cup at the sink and pouring it into the pan. The surface of the furnace is hot enough that it boils water that drips off the cup (even though it's cold water), but to my confusion, the water in the pan doesn't boil: tiny bubbles form at the bottom and the water gradually becomes steam, but despite sitting on top for hours it never boils. Why not? The Leidenfrost effect doesn't seem to apply here, since I filled the pan before starting the fire; the water has warmed gradually as the fire's gotten hotter. However, I witness the effect when little bits of water drip off the cup. Nyttend (talk) 17:48, 19 February 2013 (UTC)

Is it a cast iron stove? [[38]] spells out the basics of how this works, but cast iron heats up slowly and dissipates heat slowly - it is not a very fast conductor of heat. — Preceding unsigned comment added by 207.189.106.4 (talk) 17:57, 19 February 2013 (UTC)

It's cast iron, but I'm not sure how that's relevant. The iron under the pan (which is aluminium) is the same temperature as the iron on which little bits of water drip, so it's conducting just as much heat into the water. Nyttend (talk) 18:05, 19 February 2013 (UTC)

Aluminum foil (which this pan basically is) is a sucky heat conductor, especially given that its direct contact area with the stove is probably pretty small. I bet that you could place that pan on the stove without any water and press your finger against the bottom for a second or two without burning yourself (but if you want to try it, try a brief touch first to make sure). If you used a proper saucepan and the stove was hot enough, the water would certainly boil -- people cooked on stoves like that for ages. Looie496 (talk) 18:16, 19 February 2013 (UTC)

Aluminum isn't the best conductor, I agree. A copper pot would conduct heat better. Also, make sure that the pan is touching the stove continuously. (You sometimes get a warped pan that only touches at a few points, greatly reducing the conduction.) Ensuring that both the stove and pan are free of cruft like carbonized food is also important, as that's a good insulator, too. StuRat (talk) 18:25, 19 February 2013 (UTC)

I don't recommend this method of humidification, unless you have a freakin' big pot. The problem is that the water evaporates too rapidly, and burns the pan up when it runs dry. Also, scale accumulates on the pan as the water evaporates, leaving only it's minerals (unless you used distilled water, but that's expensive). I do actually use this method, with a huge junk stock pot at a low flame, so it takes about 2 days to evaporate. I'm unlikely to neglect it for that long. Also, note that this method of humidifying a home only makes a slight difference, as water vapor escapes through the wall cracks, chimney, etc., almost as fast as this method can add it, and, if you do manage to get the humidity up much, in winter, it may condense on nearby windows, possibly causing mold on the sills. StuRat (talk) 18:25, 19 February 2013 (UTC)

• You simply don't have enough heat capacity, meaning the temperature is high enough but the quantity of heat is not. Imagine trying to boil that water with a candle which also burns at above boiling temperature but provides only "heat quantity" for a real tiny tiny cup.TMCk (talk) 18:38, 19 February 2013 (UTC)

• I'd expect that the total heat capacity of the wood stove is more than enough to boil the water, it's just not being effectively conducted into the pan. StuRat (talk) 18:46, 19 February 2013 (UTC)

• Yes, but you don't get the whole heat capacity of the stove to the pot. (And heat is disapearing quickly once it reached the pot.)TMCk (talk) 18:57, 19 February 2013 (UTC)

Aluminium (regardless of spelling) is a very good heat conductor indeed - worse than copper, but much much better than stainless steel. See List of thermal conductivities. And that may indeed be the problem here. Heat is conducted into the pot via a relatively ineffective interface (the uneven surface of the foil on the uneven surface of the stove), and distributed very evenly through the pan. So all of the surface of the pan serves as a cooling surface, which probably keeps it slightly below 100 °C. --Stephan Schulz (talk) 20:23, 19 February 2013 (UTC)

Gun safety

A lot of firearms accidents seem to involve people not realizing a gun was loaded. Why is it not possible / why hasn't it become normal for guns to be designed in such as way as to make it really obvious whether there is a round in the chamber? — Preceding unsigned comment added by 207.189.106.4 (talk) 17:55, 19 February 2013 (UTC)

It's nowhere near safe to make the round visible from the outside, since breech-loading weapons can only work if their chambers are sealed — otherwise the gases escape in wrong directions. Cartridges don't normally (in my experience) do anything to the rest of the gun when they're just sitting in the chamber, so I can't imagine a way that the presence of the cartridge could be used to change the way something else looks or feels. Nyttend (talk) 18:09, 19 February 2013 (UTC)

A few people have been in the news lately because of accidentally firing a loaded weapon that was in their breeches Gzuckier (talk) 20:19, 19 February 2013 (UTC)

Hmmm, bullets should change the ability of a magnetic field to be transmitted from one side of the chamber to the other, slightly, so you could possibly devise such a device using this principle. The added complexity of the gun might not be welcomed, though. StuRat (talk) 18:45, 19 February 2013 (UTC)

Clearly it's possible to do this. Mechanical, magnetic, electrical, optical - you can come up with a dozen ways to measure whether there is a bullet in the chamber or not. Why it hasn't become a standard feature is because there isn't a market for such weapons - people who buy weapons are clearly more concerned about cost than safety - and the legal/fiscal framework to compel such things hasn't been put in place in the target markets for gun manufacturers. A more subtle (but just as lethal) problem is that guns with magazines will typically leave one round in the chamber when you remove the magazine - and will fire it if the trigger is pulled. This fools a lot of people who think that removing the magazine unloads the weapon and many, many people have died as a direct result of this. There is a very simple, cheap fix for it that locks out the trigger when the magazine is removed - yet many weapons don't implement it. Why? It saves lives - but it's not always done. If we can't get something as simple as that fixed - then there is no chance for more difficult improvements such as you suggest. SteveBaker (talk) 20:07, 19 February 2013 (UTC)

Indeed. Even something as simple as allowing the hammer to rest a fraction of an inch further in when there is no bullet in the chamber to impede it, which would then actuate some sort of indicator. Gzuckier (talk) 20:14, 19 February 2013 (UTC)

Which brings up something else I've wondered about; why do some manufacturers of semiautomatic handguns (maybe other varieties, I don't know) not have a safety? Because they're designed for use somewhere where instant use is a requirement and a safety would get you shot? All I can think of.Gzuckier (talk) 20:16, 19 February 2013 (UTC)

Vacuum metastability event implosion?

All the sources I've seen state that freeing ourselves from the current horrid false vacuum where we slog along hindered by the heavy shackles of the Higgs mechanism will cause a zero mass vacuum state. Is there any chance it will do the reverse and unmask the "true weight" of all the virtual particles causing a sudden Big Rip? Hcobb (talk) 18:52, 19 February 2013 (UTC)

If you have a good internet source for what your talking about could you do me the favor of linking to it? I'd like to read it. μηδείς (talk) 19:15, 19 February 2013 (UTC)

applications

what are the applications of the ultra thin capacitors? — Preceding unsigned comment added by 115.240.6.7 (talk) 19:20, 19 February 2013 (UTC)

Film_capacitor#Applications. SteveBaker (talk) 19:57, 19 February 2013 (UTC)

Speakers & moisture/humidity

Can you tell whether audio speakers have been damaged from humidity? Are there any specific kind of noises or loss of sound quality it might have? Thanks. Clover345 (talk) 21:06, 19 February 2013 (UTC)

Paper cone woofer? Polymer dome tweeter? Horn?

The basic tests you want to do are a complete visual inspection, then run some very low frequency tones (not too loud!) and listen for anything rubbing or rattling. Something like this: http://www.youtube.com/watch?v=BdQbQa-rIbw or this: http://www.youtube.com/watch?v=lfXXQfG1T3g --Guy Macon (talk) 23:06, 19 February 2013 (UTC)

How long was it humid for? This might allow mould to grow on the cone (is there antifungal agents doped onto the it?). CS Miller (talk) 23:22, 19 February 2013 (UTC)

Unless you plan to buy them, sell them, or make an insurance claim, wouldn't it just be easier to continue using them, and, if unsatisfactory, replace them ? That is, if they are damaged, but you can't tell by normal listening, does it matter ? StuRat (talk) 23:26, 19 February 2013 (UTC)