Wikipedia:Reference desk/Archives/Science/2008 October 22

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October 22

Temperature of Distillate during distillation

My chemistry teacher claims that during a salt water distillation, the temperature of the vapour should be equal to water's boiling point and not salt water's boiling point. He did not even give the name of this phenomenon, let alone an explanation. Can someone point me to a relevant article or external link? Thanks in advance. --99.237.96.81 (talk) 00:01, 22 October 2008 (UTC)

Distillation is interesting...you're "boiling" a mixture, but you're only monitoring the vapor coming out (the distillate, not the pot). During distillation of salt water, what is the vapor (mostly)...salt, water, or both? That tells you what (mostly) is "actually" boiling into the vapor. To think another way, what is the boiling point of salt, or water, and of salt-water? During distillation, you started at room temperature and heated until "distillation occurred", so you got to "the temperature of the lower of those answers" first, at which point you're distilling "whatever that is". Okay, I'm glossing over some details for the sake of what is mostly happening for this particular case. See our article about how distillation works for more technical info. DMacks (talk) 01:42, 22 October 2008 (UTC)

Sorry for not being clear. My class was divided into groups and each group conducted a distillation. The temperature was taken many minutes after the salt water started to boil. My group's thermometer indicated 102 degrees Celsius, which is near salt water's boiling point, but the teacher claimed it was broken and that it should read 100 degrees. I have no idea what the reason is.

Suppose the salt water is maintained at a temperature slightly below its boiling point. Since water is not yet escaping quickly, surely it's possible to wait for thermal equilibrium, make the solution a tad hotter, and have water vapour at least as hot as the water was? Or do all water molecules that reach 100 degrees escape? If the latter, why is it necessary to heat the solution a few degrees above 100 just because some ions are in the way? --99.237.96.81 (talk) 02:45, 22 October 2008 (UTC)

The question is good. Consider the salt solution, which has - ideally, assuming the activity is the same as the mole fraction - less water in it than pure water, so at the boiling point of pure water the vapor pressure will be less. You will have to heat it higher for its vapor pressure to reach atmospheric pressure and boil. The vapor is in your case pure water (because salt boils IIRC at 900 °C), but in the general case the composition depends on the requisite vepor pressures. Then consider your distillation apparatus. If done correctly, there ought to be a drop of condensate hanging from it. The temperature measured at the top of the apparatus is the boiling point of the condensate.

As usual, sadly, the teacher is a dunce. When you teach distillation you must introduce p-x diagrams, 'cause without them it won't make sense. 74.67.113.167 (talk) 05:25, 22 October 2008 (UTC)

Unfortunately, there is way to much variability that we don't know about to answer the question reliably. Any of the following could be what is going on. Measureing the temperature of the vapor is going to be tricky at best. There is LOTS going on. Lets look at some of these.

1. You are right in assuming that the temperature of the vapor immediately upon boiling will be the same as the boiling salt-water solution, however, this temperature quickly drops for several reasons, not the least of which is that this vapor is instantly hitting 25 degree air, and is condensing (which is an endothermic process, and thus removing heat energy from your thermometer as it does this) and all sorts of really complicated dynamic effects are going on. If you measure the vapor immediately above the boiling solution it will be warmer than even a few centimeters away.
2. Classroom analog thermometers are notoriously imprecise. Its not that the thermometer is "broken;" a 2 degree differenc on an alcohol thermometer of the type represents less than a 1% error (2 degrees out of 373 kelvin). This is pretty good, actually.
3. Barometric pressure will have an effect as well. Weather can vary the barometric pressure by +/- 30-40 torr or so and this could easily throw off boiling points by 1-2 degrees celsius. Also, a partially closed system, where the release of the steam is constricted in some way, will likely raise the local barometric pressure over the water, further raising the boiling point.

The upshot is that your teacher is probably expecting a level of precision that is unreasonable. The experiment could be done to precision, just not with the equipment you would likely have access to... --Jayron32.talk.contribs 11:41, 22 October 2008 (UTC)

20 minute chimes

I have acquired an antique spring-powered pendulum clock with a strange malady: instead of chiming N times at N:00 and once at N:30, it chimes N times at some time, then once a half hour later, then once again a half hour after that, and then $(N{\bmod {1}}2)+1$ times after a further half hour. (Obviously this quickly bears no relation to N:00 or any other time.) It gives the warning at N:22 and N:52 as one would expect, but somehow its internal notion of time is only advancing "20 minutes" per half hour. What could possibly be causing this, and how might I fix it?

As it is new to me, I unfortunately do not know what put it into this state, except that it may have been working properly before an attempt to set it that included moving its hands (forward) while it was preparing to chime or chiming. I suppose that it is possible that it is meant to chime at every quarter-hour and is missing one instead of every half-hour and gaining one, but the chiming mechanism starts very reliably every half-turn of the minute hand, so that seems unlikely. --Tardis (talk) 01:14, 22 October 2008 (UTC)

Sounds like the hands are no longer on the shaft in the same orientation as whatever tells the chimes what the time is (i.e. forcing the hands twisted them on the shaft; if so this is likely not the correct way of setting the time). If so then they need to be reset on the shaft. It would probably be fairly inexpensive to have someone who knows what they are doing fix this. If you can find a local clock repair facility you could call and ask for an estimate. RJFJR (talk) 21:10, 22 October 2008 (UTC)

How could any constant phase difference between the hands and the arbors (or any other object) explain that it performs the half-hour chime twice before doing the whole hour again? --Tardis (talk) 21:38, 22 October 2008 (UTC)

The Reference Desk volunteers should refrain from giving horological advice, and refer the questioner to a qualified clockmaker. Edison (talk) 21:48, 22 October 2008 (UTC)

Medical, legal, now horological. Where will it end? ;O) Wanderer57 (talk) 01:11, 23 October 2008 (UTC)

It seems hard to imagine how its striking interval could have gone from 30 minutes to 20 while the rest of the clock keeps good time - but I suppose we could hypothesise some missing teeth in the gearwheel that interfaces the hand-motion part of the mechanism to the chiming mechanism. Those clocks are generally pretty easy to take apart because they were made to last a long time and the mechanisms need occasional professional cleaning. I'd take a look inside and see if it's obvious from watching what happens when it chimes. I had a problem with my 30 day pendulum clock - it has two springs that have to be wound separately and one of them had somehow gotten jammed more than 50 years ago (before I was born aparrently) - it was the work of about 10 minutes to figure out what had jammed it (some fluff in one of the ratchets) - and since the second spring drives the chiming mechanism, we were able to get the clock to chime again for the first time in 50 years! It amazes me that nobody ever so much as peeked inside in all that time! SteveBaker (talk) 05:42, 23 October 2008 (UTC)

It turned out that the clock's count wheel was out of phase with the follower that reads it and determines how many times to strike (really, with the wheel that the follower stopped when it was time to stop striking); this was causing it to not make it out of the pits in the wheel on the second try and thus to strike only once (again). Unfortunately, rotating the count wheel independently of the follower's wheel involves disassembling the movement, but at least it's understood now. Thanks. --Tardis (talk) 02:38, 29 October 2008 (UTC)

Energy output of hydrogen using oxygen, fusion, and antimatter?

Hi all. I was wondering, given a fixed amount of hydrogen (let's say a gram), what it's energy output would be for:

1. chemically bonding it to oxygen.

2. nuclear fusion into helium.

3. energy discharge from antihydrogen.

Much help appreciated ! -=- Xhin -=- (talk) 03:18, 22 October 2008 (UTC)

1. Oxyhydrogen

2. Proton-proton chain reaction

3. e=mc²

All three give the answeres you want.--Stone (talk) 07:33, 22 October 2008 (UTC)

Wow. Answer 3 looks like about $250,000 worth of energy if it were in the form of electricity at 10 cents per kilowatt hour. Edison (talk) 14:22, 22 October 2008 (UTC)

Yeah, as long as you can find a way of making a gram of antihydrogen for less than $250,000. Confusing Manifestation(Say hi!) 22:23, 22 October 2008 (UTC)

According to Antimatter, a gram of antimatter costs $300 trillion. - Akamad (talk) 02:09, 23 October 2008 (UTC)

It's not just that it costs more - it takes more than $250,000 worth of electricity to do it. SteveBaker (talk) 05:33, 23 October 2008 (UTC)

Keep in mind, there are losses in energy in antimatter-matter annihilation due to neutrinos. 98.221.85.188 (talk) 23:04, 22 October 2008 (UTC)

Details, details. Edison (talk) 04:10, 23 October 2008 (UTC)

Bottom line is that IF you have a handy source of antihydrogen and some way to handle it (not so trivial!) then this would by far be the largest amount of energy you could make...but we don't have such sources so as a practical matter - it's not a way to make energy at all. Fusing to helium is the next best - but again, we don't really have the technology to do this on any kind of useful scale. Fusion power is probably out there in our future - but it's gonna take a while. So we're left with by far the least efficient of those three things - good old fashioned combustion in air. Sad - but true. SteveBaker (talk) 05:33, 23 October 2008 (UTC)

UK BODY FARM

I would be interested in donating my body to a Body Farm upon my death - does anybody have any idea who to contact in the United Kingdom - to be able to carry out my wish - all help appreciated - thank you ROEBUCK32 (talk) 06:50, 22 October 2008 (UTC)

I'm not sure that there are body farms in the UK. But you can donate your body to medical science (which is what I intend to do). Go to the Human Tissue Authority website http://www.hta.gov.uk/about_hta/faqs/body_donation_faqs.cfm you can donate to a specific medical school but usually they will only accept bodies of people who died locally. Local authorities impose a fee for transporting dead bodies across county borders, shocking but true. Jooler (talk) 08:04, 22 October 2008 (UTC)

According to Body farm, there is currently no body farms in the UK. Only 3 in the US. The complexity of an international donation may discourage any of the body farms from accepting your donation although they may be willing if you are responsible for the costs and arrangements. For example the University of Tennessee Anthropological Research Facility will only pay for transport if you are within a 200 mile range of them so you'd definitely need to make arrangments to fly the body out to them. This will probably be quite complicated since the body obviously can't be embalmed before being sent and there will be a bunch of regulations that would need to be take care. All in all, I personally don't think it'll be worth the effort but it's obviously up to you. There are a bunch of other things you could donate your body for. The most obvious one is for medical schools where it will be used in teaching (either anatomical or for to practice). I'm sure this has been discussed on the reference desk before and while some people seemed to disagree, those who have encountered the process and common sense suggests your body will be treated with a great deal of respect. Bodies can also be donated for various research. I also came across Body Worlds (although I'm not sure if they have any centres in the UK, they have them in Canada, US and of course Germany, however there is Bodies Revealed in the UK which does similar things). Obviously in most cases your body may only be accepted if it is local, or you pay for transport costs although at least if it's not international it's not going to be so complicated. You should also consider organ donation. While this is often mutually incompatible with body donation (although you may be able to donate organs or tissue) there's no guarantee you will be suitable for organ donation (and of course it is possible your body may not be suitable for donation either). Since there is definitely greater need for live organ donations then body donations, I would presume live organ donations always take precedence. These links should hopefully answer the specifics for the UK [1] & [2]. One key point... Whatever you do it is important that not only do you ensure the consent process is complete but you make your wishes clear to your family/next of kin. The death of a loved one can be a traumatic time and by making sure they know what you want, they hopefully won't have to worry whether they are making the right decision. For organ donation, and I suspect body donation, in most countries your next of kin can overide any prior consent you have given. Nil Einne (talk) 08:50, 22 October 2008 (UTC)

Thank you all for the information ~ most interesting! ~ I have already listed my body to be used for medical research ~ so I shall stay with that option ~ it is listed in my will and my next of kin is fully aware of my requests ~ again thank you all for your attention. ROEBUCK32 (talk) 20:02, 23 October 2008 (UTC)

Clipperton Island lagoon

Two questions concerning the lagoon on (inside?) Clipperton Island:

• The bottom of the lagoon is known to be highly acidic due to sulfuric acid. In one article I found on the web, it was mentioned that this acid is a product of the decay of vegetable matter in the absence of oxygen. What's the chemical mechanism behind that?
• It is also mentioned that the lagoon's water is "undrinkable". Being stagnant, I doubt it's healthy, but is it really totally undrinkable, i.e. will it not save you from death if you were stranded on the island during a dry spell? 24.160.175.196 (talk) 06:55, 22 October 2008 (UTC)

There is a two step process, first anaerobic decay produces hydrogen sulfide and iron sulfides. This is then oxidized by oxygen from the air to make sulfuric acid or iron sulfate. The water probably tastes foul. You may ask why does not normal organic matter decay produce the acid directly? I assume that the alkalies are left in the mud at the bottom, such as potassium or calcium trapped in clay. Graeme Bartlett (talk) 02:05, 23 October 2008 (UTC)

Mutation in mitosis

On average how often does a mutation occur during mitosis? Only a rough estimate is required. But a sourced answer is preferred. Jooler (talk) 08:05, 22 October 2008 (UTC)

Our article on Mutation has some references that may lead to the right answer. Mutation is a rather vague term, there errors that can occur at ANY point in the transcription or translation process, and many different mechanisms by which this occur. --Jayron32.talk.contribs 10:39, 22 October 2008 (UTC)

Try this article, which estimates the somatic (i.e. mitotic) mutation rate for one particular gene at 10.6 x 10(-7) mutations per cell division. Assuming that all stretches of DNA have the same mutation rate (a big assumption) one could then estimate the number of mutations per genome per cell division, which is (I think) what you are really asking. However, there are some BIG caveats to this estimate.

• First, they are basing their estimate on the detection of alterations in post-translational modifications of cell-surface molecules caused by mutations that change the functional properties of a particular enzyme that catalyzes those post-translational modifications. It is definitely a clever and elegant assay, but I'm almost certain that this assay would be "blind" to either mutations that do not cause an amino acid substitution or mutations that cause only a slight decrease in enzyme function (hypomorphic alleles). So perhaps what they are really estimating is the rate of pathologic mutations at a given gene per cell division.
• Second, the assay uses an immortalized cell line derived largely from B-lymphocytes, which are already known to have different characteristics in terms of somatic hypermutation duing immunoglobulin formation. Therefore, the mutation rate estimate may be true only for this cell line and not necessarily generalizable to all other tissues of the body.
• Third, there are other types of DNA mutations (amply described in the Mutation article) that involve larger genome-scale changes such as deletions, duplications, inversions, translocations, loss of heterozygosity, aneuploidy, etc. which are not necessarily considered in the typical "mutation rate" question (i.e. changes at the level of the DNA nucleotide) but are just as important (perhaps more-so, depending on your point of view) in terms of human disease.

I hope this helps. It turns out that by asking a simple question you have discovered that it's actually a VERY complicated question (which, in my experience with biology, is almost always the case). Medical geneticist (talk) 14:36, 22 October 2008 (UTC)

Biting your lip

Why, when you bite your lip, does the small cut in your lip expand so much that you can readily feel it with your tongue? And why does feeling it with your tongue sting so much? Attn: Over zealous editors, I'm not asking for medical advice! Dismas|^(talk) 09:40, 22 October 2008 (UTC)

Aphthous ulcer is what this is called, and the article is pretty detailed. Cheers! --Jayron32.talk.contribs 10:35, 22 October 2008 (UTC)

Didn't know they had a name! Thanks! Dismas|^(talk) 12:20, 22 October 2008 (UTC)

Most commonly, they are called "canker sores". I typed "canker sore" into the search box, and it redirected there... --Jayron32.talk.contribs 12:23, 22 October 2008 (UTC)

I didn't know what a canker sore was but I thought it was something different. I've learned a few things today... Dismas|^(talk) 12:26, 22 October 2008 (UTC)

You're conflating sense-organ size and sensitivity, when they're not related at all: what's important is nerve-density. Relative to the area of the tongue populated by somatic (touch sensitive) nerves, the cortical map of the tongue in the somatosensory cortex (area of the brain that receives touch info) is huge. I've always found that when I bite my lip, it always feels much bigger when I inspect it with my tongue than it actually appears when I look in the mirror. Your tongue is a pretty sensitive insturment to detail, don't let it trick you into thinking those ulcers are exploding. Your tongue can identify even the tiniest scrathes in your mouth, probably better than your fingertips! --Shaggorama (talk) 09:03, 23 October 2008 (UTC)

jet flow

what are researching centers aboat "jet flow". —Preceding unsigned comment added by 78.39.192.29 (talk) 09:43, 22 October 2008 (UTC)

Do you mean the Jet stream? Or do you mean Wind tunnels used to test the aerodynamics of Jet aircraft? --Jayron32.talk.contribs 10:34, 22 October 2008 (UTC)

Osmosis Experiment

Hi all I am doing the age old osmosis experiment where u chuck discs of potato into different molarities of sucrose solution and record the change in mass. However one of the questions I have to answer is: 'When you dry the discs with a paper towel before putting them in the solution should you try and get them as dry as possible by squeezing all the water out?' Well I presume the answer is no, but I can't really think of a good explanation why not. Would squeezing the discs be a bad idea as it would damage the cell membranes of the potato cells and therefore when the discs are put into a very dilute solution/water the cells will not be able to take up water because their membranes have been ruptured and the water will just come out of the cell (I'm picturing a burst water balloon here!) even though water should diffuse in. Hope this makes sense and please share your thoughts! Thanks. —Preceding unsigned comment added by 139.222.241.40 (talk) 11:01, 22 October 2008 (UTC)

Your impressions of the situation look accurate to me. Causing excess cellular damage would likely ruin the experiment as described. --Jayron32.talk.contribs 12:22, 22 October 2008 (UTC)

This is just a random idea I just had, so I can't say I've tried it experimentally (but it's based on the principle behind plastination so it's not like it's never been done), but if you want to get those potatoes really REALLY dry, submerge them in acetone. The water should diffuse into the solution, and the acetone should enter the cells. When you remove the slices, leave them out to dry in a warm place: all the acetone should evaporate. Compare the weight difference with the potatoes you put in the most concentrated solution. For a real difference in weight, put the acetone-dried potatoes in deionized water and see how much they take up. If you decide to try this experiment, do it underneath a fume hood and make absolutely sure you're nowhere near any ignition sources. --Shaggorama (talk) 08:41, 23 October 2008 (UTC)

When you carry out the experiment you will find that some of the disks gain weight, others lose it, depending on the concentration of the sucrose solution. What happens when their neither gain nor lose weight? What is the actual purpose of your experiment? What are you trying to find out? The answer to this question should provide you with an answer to why you don't want the disks dried out. Theresa Knott | The otter sank 15:26, 24 October 2008 (UTC)

Discoveries made on space

From Feynman, What do you care what other people think?: "In the newspaper I used to read about shuttles going up and down all the time, but it bothered me a little bit that I never saw in any scientific journal any results of anything that had ever come out of the experiments on the shuttle that were supposed to be so important".

Is there any notable discovery made on space? Or any notable discovery based on data gathered on in space? Mr.K. (talk) 12:12, 22 October 2008 (UTC)

Yes, innumerably many so. See our article on NASA spinoffs for a start on the practical applications. Also, "in space" rather than "on space" is the correct usage. — Lomn 12:45, 22 October 2008 (UTC)

This article lists many discoveries made for space. Mr.K. (talk) 13:10, 22 October 2008 (UTC)

See also this RefDesk thread from last summer, where I asked a similar question: Wikipedia:Reference_desk/Archives/Science/2008_July_1#Space_program_benefits. jeffjon (talk) 12:47, 22 October 2008 (UTC)

Yes, that answers my question. Mr.K. (talk) 13:10, 22 October 2008 (UTC)

A lot of these are from the Aeronautics part of National Aeronautics and Space Association. The ones that are related to space exploration seem to be stuff that they developed in order to make space travel easier, rather than principals learned from the experiments themselves. Although they are useful, you will find similar things in extreme sports. Nobody talks about car racing as scientific, even if it did improve tires and engines. — DanielLC 15:13, 22 October 2008 (UTC)

Also, it would be fair to acknowledge the contributions made with scientific instruments installed and serviced by the shuttle, most notably the Hubble Space Telescope. --Sean 15:16, 22 October 2008 (UTC)

There's also the notion that patience needs to be practiced here. Initial forays into space are needed to set up future success. An arguement can be made that the progress has stalled somewhat, but one cannot judge the success or failure of the space program merely on short-term financial returns. If, 200 years from now, we are able to mine mineral wealth on asteroids, we may well see the early space program as entirely vital to that development. We don't have enough history to judge the situation on yet. Indeed, its if we judged all of the Age of Exploration only on Columbus's first voyage. If we said "Look, all this guy brought back was some trinkets and a nasty case of syphilis" then it may not have been judged a success. One could make the case, with the exponentially hard task of exploring extraterrestrial space, we are still at the "proof of concept" phase of space exploration, and may be there for many decades to come. The real returns of space travel may not be realized in our life time, but that does not mean that the entire project has been a failue... --Jayron32.talk.contribs 15:45, 22 October 2008 (UTC)

Of course, Columbus was not really doing his work for its own sake. He was looking for a trade route, which would have been worth a lot. It wasn't exploration for exploration's sake. For the record, most scientists hate the idea of funding science for its own sake as the only justification. Why? Because there's no way to tell what an appropriate budget expenditure is for something like that; there's no way to pressure politicians for more funding than they currently have. --98.217.8.46 (talk) 01:49, 23 October 2008 (UTC)

The thing is that NOT ONE of those 25 things in our NASA spinoff article are inventions that were made in space. They were made right here on earth for the purpose of sending people to space. Feynman was exactly right - it's very hard indeed to find any significant science that's been done by humans in orbit. NASA consumes around 20 billion dollars a year. Do you seriously imagine that a research organization funded to the tune of 20 billion dollars per year (in modern dollars) for a period of 50 years would have come up with just 25 (mostly rather mediocre) inventions? That's $40,000,000,000 per invention! Worse still, most of those are not even "inventions" - they are mostly minor improvements of well-known technologies. Did we really spend $40bn to invent the LED? Well, LED's are rather important - perhaps that was worth it? ...but um...actually...NASA didn't invent the LED - go ahead, read "LED" - it was invented by some British guy in 1907, or perhaps by a Russian guy in 1920, maybe perfected by "the Radio Corporation of America" in 1955 and finally became mass-manufacturable in 1961 - thanks to a couple of guys at Texas Instruments. In truth, NASA's $40bn contribution has been to make them a teeny-tiny bit brighter by growing crystals in orbit to avoid certain imperfections. Of course that's a completely infeasible way to make LED's - and it would be cheaper by far just to use two regular earth-grown LED's...NASA's PRACTICAL contribution to LED technology is precisely zero.

What does it REALLY take to make an invention? I worked on the team that invented the CD-ROM. I think that rates about as highly as the entirely trivial NASA "invention" of the cordless vacuum cleaner. There were about 50 engineers working on the project within Philips and SONY over a few years. A few millions of dollars for an invention that's at least as intellectually difficult and generally vastly more useful than portable vacuum cleaners.

The fact of the matter is that the idea that spinoffs are a justification for the existence of NASA is really very silly. As usual, Feynman is right...good science doesn't happen in space - and even if it did, 20 billion dollars a year would produce vastly bigger returns if it were directed at pure research down here on Earth. That's not to say that NASA shouldn't exist - I think they're very important - but please, let's not kid ourselves that they are earning their keep with spinoffs - that's just laughable.

SteveBaker (talk) 05:24, 23 October 2008 (UTC)

I mean, if you really want to find published research, all you have to do is look. --Shaggorama (talk) 08:30, 23 October 2008 (UTC)

Does the wavelength of light change in a time varying magnetic field?

I am part of a research project which requires the use of optical fiber to send a constant frequency clock through a 3 Tesla pulsed magnetic field. There has been a debate centered on the idea that the varying magnetic field will shift the frequency of the light in the optical fiber adding jitter to the encoded clock. I have not been able to find any research on anything similar. My simple understanding of the wave properties of light are that it is composed of "B" field and "H" field components. As these propagate down the fiber, the magnetic field component would receive a local temporary "bias", but since there is not a corresponding shift in the electric field, the wavelength of the light should be unchanged. Monkeyfire (talk) 16:20, 22 October 2008 (UTC)

Due to the glass or impurities in the glass you may get some sort of low level effect. Even if the field causes vibration in the fibre, this can affect the light traveling though, with phase or amplitude modulation. With intense enough fields you will get a distortion of space with a general relativistic effect. To a first approximation though the electromagnetic effects will be linear and add without affecting each other. If you use frequencies close to absorption lines due to impurities you will likely get the biggest effects due to changes in magnetic field. Graeme Bartlett (talk) 21:12, 22 October 2008 (UTC)

More specifically look at Magneto-optic effect. Here a magnetic field causes a delay in circular polarized light. This will affect the wavelength. Graeme Bartlett (talk) 01:25, 23 October 2008 (UTC)

Internal organs

While watching replays of an American football game, I saw a bit about a player having a spleen injury; they didn't say what it was exactly, but I'd guess a ruptured spleen. We hear about ruptured spleens occasionally, and very occasionally about gall bladder injuries, but why do some organs (for example, the pancreas) never get injured this way? Or do they get injured, and I simply don't remember hearing about it? Nyttend (talk) 17:10, 22 October 2008 (UTC)

According to Pancreas#Diseases of the pancreas (a section that needs to be rewritten so as to actually summarise the article it's meant to be a summary of...), a punctured pancreas is a serious injury, however I've never heard of one either which probably means they aren't very common. It may be due to the relative positions in the body, perhaps the spleen is less protected. --Tango (talk) 17:17, 22 October 2008 (UTC)

The spleen sits under the lower left rib cage margin, so in principle is well protected unlike the pancreas in upper abdomen. To injur some organ as implied above, it needs to be compressed between things, and the pancrease is burried under loads of squishy guts that would absorb most blows. By contrast one American Footballer landing on another's chest may crack a rib, the sharp end of which may cut the spleen. Also will depend upon how friable the various organs are - maybe the spleen will tend split easily for a blow landing below & under the rib cage. Anyway that's my best guesses David Ruben ^Talk 19:41, 22 October 2008 (UTC)

According to the Grey's anatomy links from our articles on spleen and pancreas, the spleen weighs 2 or 3 times as much as the pancreas. Perhaps the larger size makes the spleen more susceptible to damage? Wanderer57 (talk) 01:31, 23 October 2008 (UTC)

speed of ripple vs speed of sound

The article speed of sound discusses the speed of sound, a longitudinal wave. A ripple on the surface of water is a transverse wave. Does it have a constant velocity? Do we have an article discussing the velocity of transverse waves? RJFJR (talk) 20:11, 22 October 2008 (UTC)

Actually, a ripple on the surface of the water is a surface wave. The characteristics of a surface makes it behave distinctly different from a transverse wave. The velocity of transverse waves is calculated exactly like all other waves. Velocity = Wavelength * Frequency, or v = λ*ν --Jayron32.talk.contribs 20:24, 22 October 2008 (UTC)

I think part of the question was whether the product is constant. If you throw a pebble into a lake, you will create a wave which travels at a certain speed. Same thing if you throw a big rock into the lake. Will the velocities of the two waves be equal? (No lake nearby, can't do the experiment right now). --NorwegianBlue ^talk 20:36, 22 October 2008 (UTC)

It's an excellent question and I'm watching this space... --Tango (talk) 21:52, 22 October 2008 (UTC)

I can't remember well, but I *think* that in the general solution the velocity of propagation is constant, but dependent on wavelength. Of course, they probably derive that from an equation that assumes those two things anyway, so I'm not sure how useful it is. Confusing Manifestation(Say hi!) 22:17, 22 October 2008 (UTC)

For a surface wave the velocity is not constant, and longer wavelengths travel much faster, eg tsunamis are much faster than normal ocean waves or ripples. Read Ocean surface wave#Science_of_wavesGraeme Bartlett (talk) 01:56, 23 October 2008 (UTC)

There it is! Thank you. (It includes the note on the effect of depth of water that I was also curious about). RJFJR (talk) 13:32, 23 October 2008 (UTC)

Spurs

What's going wrong? —Preceding unsigned comment added by Tony May (talk • contribs) 22:14, 22 October 2008 (UTC)

You're going to have to be a *lot* more specific than that. What spurs? Where? What makes you think something's going wrong? What *appears* to be going wrong? Confusing Manifestation(Say hi!) 22:20, 22 October 2008 (UTC)

Why do I get the feeling this question is about the terrible start to the football season for the British club Tottenham Hotspur (a.k.a. the Spurs) However, I don't think it has anything to do with science. —Cyclonenim (talk · contribs · email) 22:27, 22 October 2008 (UTC)

It might, if the Daleks have slipped them a tailored pathogen so as to clean up in wagers. —Tamfang (talk) 02:27, 23 October 2008 (UTC)

I accidentally an entire spur! Mac Davis (talk) 03:33, 23 October 2008 (UTC)

Maybe bone spur? RJFJR (talk) 13:35, 23 October 2008 (UTC)

"Natural" and "artificial" selection in humans

In humans, is it possible to cleanly distinguish natural from artificial selection? NeonMerlin 23:08, 22 October 2008 (UTC)

Since humans are, by any definition, "natural", what are you asking? Saintrain (talk) 00:42, 23 October 2008 (UTC)

What he's getting at is that the "artificial/natural" distinction is usually one of human agency or not. I would say, "it really depends on your definitions of artificial and natural selection here." The differences between the two are not really scientific in nature—humans exist as part of the "natural" world, and human agency does not have any particularly non-natural component than, say, termite or chimpanzee agency. Keep in mind that even trying to determine the most extreme form of human agency into human selection, eugenics, is fraught with definitional difficulties. --98.217.8.46 (talk) 00:49, 23 October 2008 (UTC)

Only if you're against it. Mac Davis (talk) 03:32, 23 October 2008 (UTC)

Even if you are "for" eugenics you can have trouble defining it. Only sloppy propagandists are happy with defining a term as everything under the sun. --98.217.8.46 (talk) 12:32, 23 October 2008 (UTC)

I don't think you can distinguish the words "natural" and "artificial" cleanly under any circumstances. What does it mean when you buy a food item that claims "No artificial coloring or preservatives"? Would cyanide be considered "natural"? Actually, there are bacteria and algae that produce the stuff - so yes...it's perfectly natural. Because humans are "natural" animals - why should the processes we engage in be any less "natural" than the ones produced by animals. Silk worms make silk - and it's "natural" - humans produce something that's pretty similar - and it's "artificial"...why? If you answer that anything that humans do is "by definition" artificial - and anything we had nothing to do with is "natural" - then by that definition, all human selection is "artificial" because simply because humans are responsible SteveBaker (talk) 04:51, 23 October 2008 (UTC)

The OP may be interested in reading the works of Jared Diamond, particularly The Third Chimpanzee. As others have noted above, the distinction between artificial and natural selection is at best a tough one to make, but Diamond argues (somewhat convincingly) that some of the things we assume to be responses to natural selection have significant cultural components. The example he uses is skin colour, which while it obviously varies grossly in proportion to the amount of UV light a population would be exposed to, also displays quite a lot of variation that cannot be explained by that. Matt Deres (talk) 16:17, 23 October 2008 (UTC)