Wikipedia:Reference desk/Archives/Science/2009 January 27

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January 27

Errors in casting plastics

Hi - I need a piece of terminology - what's it called when a mold produces a bad casting and you get something that's not the shape you intended?

Thanks,

Adambrowne666 (talk) 00:55, 27 January 2009 (UTC)

A dud ? I'm not sure if a malformed plastic casting has a specific name. StuRat (talk) 03:28, 27 January 2009 (UTC)

One type of imperfection in casting is flash, though this may be removed to obtain the shape you intended. -- KathrynLybarger (talk) 03:39, 27 January 2009 (UTC)

Thanks, yeah, probably there's no global term - I'm gonna go for a 'miscast', I think. Adambrowne666 (talk) 04:14, 27 January 2009 (UTC)

Id call it a blob--GreenSpigot (talk) 13:52, 28 January 2009 (UTC)

I read through two rather large online glossaries to do with metal casting, and although there were lots and lots of words for the particular defects, I couldn't find a general one. There were many places where they might have used such a word if it existed, but they always just called it a defective casting. I expected to find some nice, slangy wordling, something like "glippet" or "pfnisch", but no dice. (I should imagine that the terminology of metal casting would have transferred to plastic casting more or less entire.) --Milkbreath (talk) 14:11, 28 January 2009 (UTC)

I don't know officially, but I would say 'dud', 'reject' or 'miscast' (to repeat 2 already-mentioned terms) - I actually doubt they would coin a new term for it because there are very common words that would be suitable. I know in anything that I've ever manufactured (computerised engraving, plastics assembly, signage) we could just say 'dud' or some expletive. Rfwoolf (talk) 22:30, 2 February 2009 (UTC)

Spontaneous absorption of water waves

What is the formula for the rate at which deep water surface waves (both gravity and capillary) are absorbed by the water and the air above it, if they do not run into anything?

129.2.43.42 (talk) 01:22, 27 January 2009 (UTC)Nightvid (unregistered)

Well, I was really hoping you'd get a good answer - because it's great question. But I've looked all over for an equation and I don't see one. From reading around the subject, some things become evident:

• Water waves at different frequencies and directions can be considered independantly.
• Waves move at different speeds and are attenuated at different rates depending on their frequency.
• Higher frequency waves are attenuated more rapidly than low frequencies.
• Wind has a huge effect on energy transfer into and out of waves.
• Tides make a big difference too...even in deep water.
• Breaking waves behave very differently from 'smooth' waves.
• When the water is more than 1.5 wavelengths deep - it may be considered to be a 'deep water' wave.

But I couldn't find a single, simple equation anywhere...which is surprising.

SteveBaker (talk) 01:30, 28 January 2009 (UTC)

soap

Good day!

I would like to ask what is a germicidal soap and what are its effects?! or shall we say what are its applications-for what and for whom...

Your answer would be greatly appreciated.

Thank you and God bless! —Preceding unsigned comment added by 125.5.144.109 (talk) 02:50, 27 January 2009 (UTC)

An antibacterial soap is one that tends to kill bacteria. This is usually unnecessary, as washing bacteria off your hands is sufficient. There are some negatives, as well:

1) It can kill off helpful bacteria that control other health threats, like fungus.

2) It can kill off helpful bacteria in septic tanks, which decompose waste.

3) It can cause bacteria to develop a resistance, which makes it more difficult to kill them when they really do pose a threat. StuRat (talk) 03:23, 27 January 2009 (UTC)

That's why there's an increasing move to switch to bacteriostatic rather than antibacterial soap. 76.97.245.5 (talk) 03:46, 27 January 2009 (UTC)

Although the evidence is still being generated, I believe that while washing of hands will suffice for reducing the microbial load (primarily through friction), there are some pretty nasty pathogens that require stronger means to more greatly ensure reduction in their counts. Case in point -- you want to definitely "nuke" Salmonella and MRSA, not just reduce their respective counts. I also believe that the levels of antimicrobials that would go from your hands to the septic tank are far below those needed to effectively reduce those bacteria. Lastly, the potential of antimicrobial resistance is a real issue -- and the jury is out on that. However, when you consider the degree of action needed to hold a microbe in stasis (e.g., bacteriostatic), rather than killing it (e.g., bacteriocidal), the probability of building up resistance to bacteriostats would far exceed the ability to develop resistance to bacteriocides! GVB012009 (talk) 19:53, 29 January 2009 (UTC)

Soap was invented around 3000 BC, During the 1970's someone thought "why don't we make soap that's BAD for bacteria." Apparently up to that time soap was enjoyed by bacteria as a nutritious food stuff. Bacteria fought back, hiring lobbyists who argue that use of antibacterial soaps should be restricted. —Preceding unsigned comment added by 76.125.8.141 (talk) 13:42, 27 January 2009 (UTC)

That was entirely unhelpful. Matt Deres (talk) 20:10, 31 January 2009 (UTC)

antibiotic resistance

Something has long bothered me about the antibiotic resistance discussions as applied to hand soap. The active ingredients usually used in antibacterial soap are triclosan or ethanol. However, it is physically impossible to use either of these compounds as internal antibiotics. The ratio required for ethanol (>60% by volume) would be fatal in the bloodstream, and triclosan is too insoluble in water to reach bactericidal concentrations in blood (normally it is suspended in an nonpolar solvent). Further, my understanding is that their chemistry and method of action is simply not related to any of the widely used internal antibiotics, so the risk of cross-resistance ought to be very low.

Hence my question is: Should people really worry about bacteria developing resistance to triclosan or ethanol? Would it matter? It would appear that even if bacteria developed resistance to hand sanitizer it would have little to no relevance in deciding how to fight an infection of that bacteria. Sure, it might be a little bad if hand soaps and the like lost their edge, but in the grand scheme of things being resistant to hand soap would appear to be independent of and far less troubling than resistance to things like methicillin. Dragons flight (talk) 05:36, 27 January 2009 (UTC)

No, the issue of resistance doesn't pertain, as the agents in hand soaps are antiseptics rather than antibiotics. - Nunh-huh 06:05, 27 January 2009 (UTC)

I think it's just a case of mislabeling. What they probably mean is that any surviving pathogens are likely to be very hardy and might be harder to kill with conventional methods. I agree that there is a lot of confusing (confused?) info out there. I read an article (reputable science site) where the interviewed researcher within 4 sentences first complained that increasing use of antibacterial cleaning agents in households would influence bacterial susceptibility to drugs, then he stated that although that had been shown in a petri dish an experiment conducted on an actual kitchen countertop failed to yield the same result. He followed that by saying if it were up to him he would only advocate use in hospitals because in a household you wouldn't need it anyway because the bacterial load was rather low whereas in hospitals it was high. Somewhere lower down was a comment that hospitals are breeding grounds for drug resistant strains. (So he advocates use of chemicals he suspects of increasing drug resistance in a place that already has a lot of that, instead of where it could not be shown to develop?) I read it several times, and then actually went and looked the guy up. He really was a researcher in a university lab. 76.97.245.5 (talk) 10:01, 27 January 2009 (UTC)

I have to disagree with both of the two previous posters.

@76.97.245.5: Sure - that was a bad report - but it doesn't mean that what the guy is saying isn't true - and it CERTAINLY doesn't mean that the reverse of what he says IS true!

@Nunh-huh: Your distinction between antiseptics and antibiotics is irrelevent.

But in general:

Whenever we provide some kind of stress factor in the life of a creature (be it a bacterium or an aardvarq), we're going to be affecting it's evolutionary development in such a way that it'll tend to be better at surviving in that stressed environment in the future. That's absolutely unavoidable - and it doesn't matter whether it's an "antiseptic" or an "antibiotic" - the result is the same. (From the lead paragraph of our Antiseptic article:

"Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction. They should generally be distinguished from antibiotics that destroy bacteria within the body, and from disinfectants, which destroy microorganisms found on non-living objects. Some antiseptics are true germicides, capable of destroying microbes (bacteriocidal), whilst others are bacteriostatic and only prevent or inhibit their growth. Antibacterials are antiseptics that only act against bacteria. Microbicides which kill virus particles are called viricides."

But it really doesn't matter. Antiseptics, antibiotics, disinfectants, germicides, bacteriocides, bacteriostatics, antibacterials, microbicides AND viricides - all apply stress to their intended targets and if they are anything less than 100% effective at preventing their chosen victims from ultimately reproducing - they WILL cause evolutionary pressure. (It's tough to be 100% effective because at the boundaries of the area the substance was applied over, there is guaranteed to be some place where it's present in non-lethal doses - and right there, a creature can survive and evolve tolerance)

Once you have evolutionary pressure - you'll tend to get resistant strains developing.

Hence, the rule is that you shouldn't use ANY of those things unless you actually need to. We got along just fine without antibacterial/whatever soaps, baby-wipes, TOYS(!), etc - and introducing them is a bad idea regardless of whether you happen to be able to induce evolutionary effects in the lab. Evolution is a valid scientific theory and you don't need to keep doing experiments to prove it. Just as we know that brand X bowling balls will fall if you let go of them without having to do the experiment - so we know that creatures will tend to evolve without doing the experiment. If you can't reproduce it in the kitchen but you can make it happen in the petri dish then you certainly need to ask why that is and set up experiments to find out why - but it shouldn't lead you to conclude that evolution doesn't work in the kitchen because extraordinary claims require extraordinary evidence. We should behave as if the hypothesis that evolution doesn't work on kitchen countertops is false until such time as someone proves it and manages to explain why.

So, with what we currently know (which is all we ever have to go on) - we shouldn't use these products in the kitchen because the consequences of failing to do so are not severe. But we may be forced to use them in hospitals where the consequences of infection are vastly more serious because of all of the sick people spreading nasty bacteria everywhere - and all of the open wounds and so forth. Resolving the issue of bacterial and viral resistance to antimicrobials in hospitals is a serious one - but it's not relevent to the question of whether we should make matters worse by using them when we don't need to in our own homes.

SteveBaker (talk) 14:24, 27 January 2009 (UTC)

Steve, There's some kind of flaw in this argument, in its most general form, isn't there? I see some sort of assumption that organisms have an unlimited capacity to cope with any number of evolutionary pressures. In practice if you put a pressure on a zillion parameter system sure it will adapt to that pressure but the adapted point will not be as optimal at some other things as the unpressured system. So your bacteria may adapt to survive repeated exposure to 55% alcohol when it couldn't before but it will be worse at something else. Which depending on your reliance on the hard soap may or may not be a worse situation than before. Sure if you are talking about an antibiotic you need to cure someone you don't want to stress it that way but if you are talking about something which doesn'r really matter I find it hard to buy the argument.--BozMo talk 15:03, 27 January 2009 (UTC)

Sure - the bacterium that's resistant to dilute alcohol will be worse at something else - but in evolutionary terms, it only has to be better off than it's competition. So every time you use dilute alcohol, you'll wipe out more of the 'capable' bacteria and give the resistant (but otherwise worse) ones room to grow and thrive. The problem is that the 'worsening' may be (say) the loss of the ability to metabolize pink food coloring or something. That loss isn't measurably to our gain - and we can't control or (easily) predict what that 'worsening' might be. Worse still, when you set loose a new set of genes, you don't know WHAT the effect will be. It could just as easily result in a change of the 'coating' of the bacteria and thereby cause all of us humans to lose our antibody-resistance to the darned thing. SteveBaker (talk) 16:36, 27 January 2009 (UTC)

Agree but AFAICT in general "big" stresses (e.g. surviving in salt water or Dettol) seem to take a lot out of bacteria: they don't seem to ever manage one of these and still be able to compete with other bacteria well when the stress is absent. --BozMo talk 21:05, 27 January 2009 (UTC)

Lots and lots of things can place an evolutionary pressure on bacteria though, and almost no one worries about their impact. For example, ordinary (non-bactericidal) bar soap, dish soap, and laundry detergent will all remove bacteria. Presumably this creates an evolutionary pressure for bacteria that cling more firmly to their environment to avoid being washed away. However, you'll never hear people advocate that we stop using soaps entirely. Similarly, the wide spread use of food preservatives presumably encourages "preservative resistant" bacteria, but I've never seen people get crazy about preservative resistance the way some people do about hand soap. It just strikes me that the way some people focus on antibacterial hand soap is way out of proportion to the danger. Dragons flight (talk) 15:41, 27 January 2009 (UTC)

That's true - but the things you've described are truly necessary to us. Antimicrobial washing up liquid is of negligable benefit - it's purely an advertising bullshit thing - and we don't need to use it. Food preservatives, however are necessary to our way of life. SteveBaker (talk) 16:36, 27 January 2009 (UTC)

For an example of where antibacterial soaps should be used, hand-washing in areas prone to MRSA comes to mind: MRSA#Hand_washing. StuRat (talk) 15:14, 27 January 2009 (UTC)

Despite SteveBaker's assertions and theoretical dissertation, the facts are: there are no significant clinical effects that can be attributed to "antiseptic resistance", and there are significant clinical consequences of "antibiotic resistance". - Nunh-huh 07:26, 28 January 2009 (UTC)

Of possible relevance: Hand washing with soap significantly reduces the spread of pneumonia and diarrhea, the two leading causes of death worldwide among children younger than age ive. In a study funded primarily by P&G Beauty, a division of Proctor & Gamble, researchers examined 900 households in squatter settlements in Karachi, Pakistan. Although the public health benefits of clean hands are clear, whether poor communities by themselves can afford to purchase soap regularly remains uncertain.

Number of pneumonia cases (per 100 person-weeks) among households that washed-

With antibacterial soap: 2.42

With plain soap: 2.20

Without soap: 4.40

Number of diarrhea cases among households that washed-

With antibacterial soap: 2.02

With plain soap: 1.91

Without soap: 4.06

(Source: The Lancet, July 18 2005) (as reported in Scientific American, October 2005) —Scheinwerfermann ^T·_C01:57, 30 January 2009 (UTC)

Interesting. That shows that antibacterial soap isn't quite as good. I wonder why ? Either some bacteria are killed which helped to control the baddies, or perhaps people don't wash their hands as thoroughly, thinking the antibacterial action will do the job for them. StuRat (talk) 05:36, 30 January 2009 (UTC)

question about HIV/AIDS

how does science, technology and communications address issues of HIV/AIDS and gender mainstreaming —Preceding unsigned comment added by 196.33.11.13 (talk) 12:21, 27 January 2009 (UTC)

This sounds like a homework question to me. On the off chance it isn't, perhaps you would care to provide a little more information about what, specifically, you're interested in? -- Captain Disdain (talk) 12:47, 27 January 2009 (UTC)

Writing a college essay involves first determining what the question means. College professors are often not models of clarity. I think they sometimes get fed up and try to trip the class up. Sometimes they actually think what they wrote makes sense, not realizing that they're begging the question. Sometimes they're drunk when they write it, I suppose, which would explain a lot. The second step is to guess what the professor wants to see. This is important only to the extent that your grade is important. You can learn the material thoroughly and become the most proficient person in the world in your pursuit and still get only a "C" if you don't follow this second step. Often, too, your paper will be graded by a graduate student with a checklist looking for key concepts and facts, and you should try to guess what these will be. In this case, we start at a disadvantage because the grammar of the question is bad ("does" should be "do"), so we can look forward to getting marked off for correct English, always frustrating. Another problem is the jargon. What is an "issue"? Professors love that word. I've never been able to tell whether they use it because they think it has a meaning, because they want to leave things open-ended, or because they're just being bloody-minded. And good luck figuring out what "gender mainstreaming" is. That really pisses me off. I'll bet your professor just got done having a big argument with his mistress over the term, and he wants to see what you'll all say about it so he'll have more arrows in his quiver the next time it comes up in a symposium. Anyway, good luck, and don't sweat it. Think it's easy, and it will become easy. --Milkbreath (talk) 12:57, 27 January 2009 (UTC)

...OR...

You could just say:

Please do your own homework.

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

SteveBaker (talk) 14:03, 27 January 2009 (UTC)

There's nothing wrong with telling people generally how to go about thinking of how to answer questions when it is clear that's probably what is at stake here. Saying "do your own homework" is concise but it isn't always the most useful answer (and I mean "useful" here in the true sense, not in the sense that giving them the answer would be "useful" in the long run). Teach a man to fish, and all that. --140.247.241.150 (talk) 17:51, 27 January 2009 (UTC)

I too thought "gender mainstreaming" was just meaningless jargon, but truly we have an article on everything. Gandalf61 (talk) 17:01, 27 January 2009 (UTC)

Silly me. Now that I know it's about differential implications.... --Milkbreath (talk) 17:28, 27 January 2009 (UTC)

If it was about differential integrations it would be much easier, by the Fundamental Theorem of Calculus. You could probably submit the question, (+C), and not get a C+ ... Nimur (talk) 18:32, 27 January 2009 (UTC)

Vines climbing around a tree

Why do vines climb upwards around a tree in a clockwise direction(if looked from above)? —Preceding unsigned comment added by 202.70.74.137 (talk) 15:15, 27 January 2009 (UTC)

You may have selection bias. I spent three years trying to tame the wisteria on my trees. It grows wherever it likes, in whatever direction it likes. -- kainaw™ 15:17, 27 January 2009 (UTC)

Apparently this is an active area of research; try googling "vines clockwise". It seems most vines twist counterclockwise, but that we haven't figured out why yet. Perhaps something to do with the chirality of biological molecules. --Allen (talk) 15:37, 27 January 2009 (UTC)

Why are 90% of people right handed? Why do most sea shells twist in one direction? Why do (nearly) all of us have our hearts, livers and pancreases on one particular side? Why do ALL animals and plants have the same chirality of biological molecules? If there is not advantage to one asymmetry over the other - why isn't there a 50/50 mix? The reason is that we're all descended from a single individual. So in this case, once the gene for a particular direction of twist got to become the ancestor of all modern vines - only an evolutionary change in the twist-direction gene could cause opposite-direction-twist to happen. Since there is likely to be ZERO evolutionary benefit to twisting in the opposite direction to all of the other plants - that gene would not reproduce preferentially to the 'normal' direction and could easily simply fade from the gene pool because it's so rare. Genes only spread when there is some benefit to the creature that possesses that gene. Left-handedness in humans is a bit different - it is thought to hang around because we are tribal creatures and there is a benefit to every community of humans to have a few left-handed people because our brains are wired up differently. Hence communities in which left-handedness dies out are at a disadvantage compared to those where it remains - and hence there are always a few lefties around (including an unreasonably large percentage of US presidents, architects and 3D computer graphics people!). SteveBaker (talk) 16:23, 27 January 2009 (UTC)

Before we compare to handedness, we could at least provide a non-google reference that it's intrinsic to the plant and not the environment. There seem to be a lot of news stories re-hashing this same research. [1] [2] APL (talk) 17:12, 27 January 2009 (UTC)

I agree with APL. Steve's explanation sounds plausible, with the quibble that vines are not a monophyletic group, so any shared twist-direction gene would probably be doing more than determining twist-direction. But most researchers seem to agree that vine twining is an unsolved question. Same with handedness... there seem to be multiple active hypotheses for the proportion of left-handedness. And Steve's explanation requires group selection, which is controversial. --Allen (talk) 20:24, 27 January 2009 (UTC)

I wonder if the OP is from a hemisphere opposite Kainaw's, though; there's part of me that remembers an experiment with toilets flushing a different direction in the northern hemisphere from the southern, and wondering if vine growth has to do with the rotation of the earth. —Preceding unsigned comment added by DTF955 (talk • contribs) 17:59, 27 January 2009 (UTC)

Er - you do know that the toilet-flushing thing is a myth don't you? The coriolis forces are VASTLY too tiny to produce either that - or the vine rotations...so no. SteveBaker (talk) 18:31, 27 January 2009 (UTC)

Ohh, now I donno about that…surely if the Coriolis forces are strong enough to create left- rather than right-hand traffic in Australia and New Zealand, they're strong enough to make water spiral the wrong way down the sink. ← The preceeding text is a joke. It is not intended to inform or educate. —Scheinwerfermann ^T·_C21:01, 27 January 2009 (UTC)

Vine-twisting direction seems to have been noticed only quite recently. I wonder why botanists did not notice it generations ago. What else is being overlooked in botany? And what is being overlooked in other branches of science? Medical school students are told to pay attention to details about a patient and his ailment; but that does not seem to be stressed for college students in other areas of learning. In everyday life we ignore many, many, small details - we would go nuts if we paid great attention to everything. But in science, and in professions, attention to details within the area of interest is needed. (The transistor was discovered by investigating a small detail in the action of diodes.) On the other hand, a scientist should not become so immersed in details that he overlooks the big picture. In this regard, details may be sought in order to support a pre-existing conjecture. For instance, Darwin studied details in biology with a predetermined objective. He wasn't just accumulating facts (though that can be useful to aid further work in science by others). Darwin's predetermined objective was to place evolution on a firm basis. Thus, there are two goals in science. One is to accumulate facts. The other is to put 2 and 2 together to make 5 (idea synthesis). Sometimes the "accumulating" approach in science leads to the other approach – the very act of accumulating related facts can bring to light an overall concept that was not seen at all before. Even in everyday life a serendipitous juxtaposition of seemingly unrelated facts will occasionally reveal an overall concept not seen before. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:22, 27 January 2009 (UTC)

It's not a recent discovery, Charles Darwin wrote about it. I always thought it was because the plant was phototropic following the sun as it went around the sky. Graeme Bartlett (talk) 20:12, 27 January 2009 (UTC)

Surely that would only work if they were growing an entire loop around the tree each day? I don't think they grow that fast. --Tango (talk) 20:19, 27 January 2009 (UTC)

No, it could just be that they're influenced at some critical point. But the articles I link indicate that the influence of the sun's motion has been ruled out as the cause. APL (talk) 20:25, 27 January 2009 (UTC)

Yeah - I mean it would work during the summer at the North or South polar regions where the sun doesn't set for months at a time - and it couldn't possibly work near the equator where the sun doesn't "circle" a tree but ascends pretty much vertically into the sky - across the zenith and vertically back down again on the opposite side. The acid test would be whether the same plant would coil in the opposite direction when planted in the southern hemisphere...that's worth thinking about...just so long as nobody else says the word "coriolis"! SteveBaker (talk) 21:51, 27 January 2009 (UTC)

Actually -- and it's surprising to me, too -- the [CENSORED] effect was one of the hypotheses of these Australian researchers. --Allen (talk) 22:08, 27 January 2009 (UTC)

Puh!...botanists...what'ya gonna do? They aren't even proper biologists. May I refer you to this handy chart and invite you to place botanists on that scale! That effect relies on the magnitude of two properties - speed of motion and North/South distance travelled - two properties that a vine has in astoundingly negligable quantities! Bozo's. :-) SteveBaker (talk) 01:03, 28 January 2009 (UTC)

Botany is scorned because it has not progressed much beyond description and classification. The reason it has not progressed much is because it is very difficult. Physics is child's play compared to botany. – GlowWorm —Preceding unsigned comment added by 98.17.34.148 (talk) 16:42, 28 January 2009 (UTC)

It's not a matter of difficulty. We were talking a few days ago about economists and I was saying that what they do isn't really science. That doesn't make economics 'easy' - it just means that they aren't doing science while they are doing it. Botany is indeed mostly a matter of 'stamp collecting' with relatively little actual science going on. That doesn't make it less worth-while or less difficult - it just means that it's mostly not 'science'. Hence, it comes as no surprise to me that some botanist would make the incredibly stupid suggestion that coriolis forces caused this when the briefest glance at what that force actually IS would make it blatently obvious that it cannot be the culprit. A proper scientist might do an experiment - but when a back-of-envelope calculation shows the effect has to be utterly negligable, one would not consider doing THAT experiment until all other reasonable lines of inquiry had been excluded. If it we're me, I'd want to try to make one grow the other way by having artificial lighting that moved in the opposite direction to the real sun in the vine's habitat. I'd look to see if there were EVER a vine that grew the opposite way and do a DNA study to try to isolate the 'clockwise' gene. I'd try a whole bunch of much more likely things before I'd EVERY go on record as saying that coriolis was even the remotest possibility. So this particular botanist is not behaving like a proper scientist and is showing a lamentable lack of scientific knowledge. SteveBaker (talk) 19:27, 28 January 2009 (UTC)

Botanists are just a cross-section of humanity, and as with reference desk authorities you get the whole spectrum from awesomely wise to thick as two bricks. Left- and right-handedness in creepers has been known since our ancestors started oozing around on dry land. Even Flanders and Swann wrote a ditty celebrating the phenomenon
Said the right-handed Honeysuckle to the left handed Bindweed
oh let us get married if our parents don't mind we'd
be loving and inseparable, inextricably entwined we'd
live happily ever after' said the Honeysuckle to the Bindweed..
Rotational (talk) 09:48, 29 January 2009 (UTC)

Help on Forces

Does Contact force exist even when there is no gravity. Bold text CAN YOU DIFFERENTIATE NORMAL CONTACT FORCE FROM CONTACT FORCE??? And further more...what is the newtons third law pair for contact force acting on the feet of a gecko that clings to a wall which is perpendicular to the ground??? —Preceding unsigned comment added by 123.49.43.236 (talk) 17:52, 27 January 2009 (UTC)

Certainly. Gravity is just a force - you could substitute a different force. Magnetism, say. Also, that nice Mr Einstein told us that acceleration and gravity are indistinguishable for all laws of physics - so in deep space an object accelerating at 1g would produce exactly the same effect. The teeny-tiny hairs in the gecko's foot are sticking to the glass through Van-de-Waal's forces at the atomic level. SteveBaker (talk) 18:30, 27 January 2009 (UTC)

See Sticky Secrets of the Gecko and van der Waals force ciao Rotational (talk) 10:04, 29 January 2009 (UTC)

It seems really unlikely that in any circumstance, the Contact Force would be in any other direction than normal. Does anyone know of any counter-examples? If there are any, they are probably not in macroscopic, "standard" situations. Nimur (talk) 18:39, 27 January 2009 (UTC)

I think there is some confusion here between contact force and normal force. Our contact force article explains the difference as follows: "A contact force has two components. The part of the force that lies within the plane of contact is friction ... The part of the force that is perpendicular to the plane of contact is called the normal force." For example, an object in equilibrium on a rough sloping surface experiences a contact force that is not normal to the surface (the contact force must be vertical so that it is equal and opposite to the object's weight), but the normal force is always, by definition, normal to the surface. Gandalf61 (talk) 10:36, 28 January 2009 (UTC)

I'd better review my basic physics terminology... Nimur (talk) 15:15, 28 January 2009 (UTC)

Most stuff eaten at once and eating things whole

Since I'll be gone on April Fools Day, I ask this question now that was on my mind.

The song about the old lady who swallowed a fly has her eating huge amounts of things at once, apparently whole (though it's not said for sure; she's likely nuts as it is, so she could have odd ideas about what can catch what, but anyway...).

My questions are: 1. How much is the most one person has eaten at one time? I've heard of ten-pound burgers someplace, I think. 2. I doubt one could even get a cat down one's throat, so we'll go with a bird; suppose someone was able to swallow a very small bird whole; how long would it survive in the stomach before being attacked by the stomach fluids and killed? Long enough to find the spider?

Take note - anyone who claims this question is asking for medical advice will be laughed at for days. :-)Somebody or his brother (talk) 18:08, 27 January 2009 (UTC)

Well, our stomach article states "in humans, the stomach has a relaxed volume of about 45 ml, it generally expands to hold about 1 litre of food, but can hold as much as 4 liters." Certainly the limiting factor is the circumference of one's esophagus. According to this article average diameter is 2-3cm (.78-1.1 in), so 6.3-9.4 cm (2.4-3.5 in) circumference. -- MacAddct1984 ^{(talk • contribs)} 18:30, 27 January 2009 (UTC)

Surely the esophageal cross-section is not of fixed size? Nimur (talk) 18:37, 27 January 2009 (UTC)

Yeah, it must expand to a point, I couldn't find much about it though. If a bird did manage to get down someone's throat, I'm sure finding and eating an already decomposing spider is the last thing on its mind. Also, we happen to have an article on There Was an Old Lady Who Swallowed a Fly. -- MacAddct1984 ^{(talk • contribs)} 18:43, 27 January 2009 (UTC)

Wow, there is an article on everything here. :-)Somebody or his brother (talk) 19:21, 27 January 2009 (UTC)

Not forgetting 'a waffer thin meent' [3] Laughed at for days, eh? - ooh, blimey!! Richard Avery (talk) 19:41, 27 January 2009 (UTC)

66 hot dogs in one sitting. You might also want to check competitive eating. Clarityfiend (talk) 20:04, 27 January 2009 (UTC)

Please see the International Federation of Competitive Eating Records List. These guys are pretty much the authority. The most impressive item on the list in my opinion is the 21 lbs of grits eaten in 10 minutes. Anythingapplied (talk) 20:51, 27 January 2009 (UTC)

Hmmm...less than 2 pounds of chocolate in 7 min.? On the other hand, 65 hard boiled eggs, and by a woman. In your face, Cool Hand Luke. Clarityfiend (talk) 00:13, 28 January 2009 (UTC)

In my old school times a guy tried to eat two krapfen at once, but suddenly became red and almost died.--pma (talk) 00:55, 28 January 2009 (UTC)--pma (talk) 00:55, 28 January 2009 (UTC)

Does this count as "whistling"?

Hi. I know a method of "whistling" different from conventional whistling. Place the tip of your tongue loosely on top of your lower teeth, then place your upper teeth loosely on top of your tongue, and very slightly behind your lower teeth. Pucker your upper lips up towards your nose, close your jaws slightly, then blow a steady stream of air through your upper teeth and the gap in your lips, while slightly puffing your central and upper cheeks. It should make a high-pitched sound. Now, I find that using this method, I cannot control the pitch of the whistled note, and it isn't always continuous. However, would this still count as whistling or not? Thanks. ~AH1^(TCU) 19:17, 27 January 2009 (UTC)

See Whistling#Types. Seems to me like it's still whistling, unless by "still count" you mean you're planning to enter a whistling contest and don't want to be disqualified. Coreycubed (talk) 19:50, 27 January 2009 (UTC)

Whistling can be done lots of ways, even with a whistle, your hands, or a blade of grass. To decide if something is whistling or not all depends on the noise that is made. If it makes that high pitch whining "whistling" noise then it is indeed a whistle regardless of how you do it. Even when a teapot makes that noise it is considered to be whistling. Anythingapplied (talk) 22:43, 27 January 2009 (UTC)

Autoclaving liquid

When autoclaving liquid, one is always instructed to use an oversized container so that the liquid will not escape if it starts to boil. When you use the 'liquid' cycle on the autoclave, at the end of the cycle the pressure drops slowly to prevent boiling over.

My question is, in practice does liquid (an aqueous solution such as microbial media) commonly boil in a autoclave run on the liquid cycle? That is, is the oversized container really just a redundant precaution, and the liquid will not boil as long as the autoclave works correctly? ike9898 (talk) 21:08, 27 January 2009 (UTC)

There might be some liquid expansion issues but I think you've answered your own questions. In practice many things can go "wrong". Preparation can determine if the "wrong" event is a) of no consequence or b) requires the process to be repeated without getting anything "wrong". If a redundancy doesn't cost anything, for example grabbing a moderately larger dish over a smaller one, than there is no reason not to take the extra precaution.--OMCV (talk) 01:21, 28 January 2009 (UTC)

Usually the problem with boiling is that the pressure drops much faster than the temperature does. Theoretically if the autoclave is working and designed properly it wouldn't happen, but in practice people get antsy and try to open the door too soon or the control isn't exactly 100%. I know with the media I've autoclaved (been a few years, though!) it wasn't unusual to see it churning a little bit when I took it out, albeit not enough to boil out of anything. I may have been a little trigger-happy with the door, though. SDY (talk) 01:17, 28 January 2009 (UTC)

I used to make LB all the time and, while I couldn't tell what was going on once the doors shut, I would often see evidence of broth that had crept up the inside of the flash. Also, after taking out the flasks, the slightest movements would cause it to bubble up rather violently. -- MacAddct1984 ^{(talk • contribs)} 18:14, 28 January 2009 (UTC)

Thanks, all. I'm basically being cheap and trying to avoid bigger flasks, but I think I'm going to just bite the bullet buy them. It's better than making a mess and/or ruining an experiment. ike9898 (talk) 19:36, 28 January 2009 (UTC)

From my experience, the liquids boil anyway even on the liquid setting in an autoclave. When autoclaving agar mix I avoided boiling over by only filling the bottle half full. When removing a freshly autoclaved bottle, it is completely normal that the liquids are superheated and will boil when disturbed. Put your bottles of media in one of those heavy duty plastic autoclave-safe bins to keep boiled over liquid from spilling inside the autoclave. Bigger flasks are nice because the extra volume keeps the liquid piping hot while pouring plates. (Cleaning out congealed agar from inside a bottle is no fun) Something to keep in mind is that when choosing a large size container, pick one that is easy to pour while wearing something to keep your hands from being burnt. The typical 1L glass bottles can be difficult to handle while wearing oven mitts. I would suggest donning a mitt and visiting the lab next door, filling up a bottle with water so it mimics the weight of a full bottle and practice holding and pouring to get a feel for what you can grip. Sifaka ^talk 20:06, 29 January 2009 (UTC)

osmole confusion

I`m just reviewing some renal stuff, and I`ve realized I`m confused on a pretty question:

If I took 500 sodium molecules and put them in 1 L in one container. In another contained, I put 500 glucose molecules.

Which would have the greater osmolality?

--Cacofonie (talk) 21:39, 27 January 2009 (UTC)

Did you review osmolarity? The first paragraph has a discussion of a similar question. See also molality within the concentration article. On a related note, you probably mean "sodium chloride" or some other sodium salt since pure sodium would be pretty reactive in water (which is what I assume you are dissolving in, since you didn't specify). --- Medical geneticist (talk) 23:27, 27 January 2009 (UTC)

Besides the fact that sodium doesn't really form molecules. If you're talking about sodium chloride I guess you could consider a pair of Na+ and Cl- as one "molecule", at least for the purpose of molarities. Confusing Manifestation(Say hi!) 04:16, 28 January 2009 (UTC)

Actually, see Van't Hoff factor. Sodium chloride has a colligative molarity double its measured molarity because it is not a molecule, but rather, an ionic substance. Strong electrolytes like NaCl have Van't Hoff factors equal to the number of discrete particles they form in solution, for sodium chloride each "NaCl" formula unit (which are not molecules) results in TWO discrete particles, an Na+ and Cl-. Non-electrolytes, like glucose, have a Van't Hoff factor of exactly 1, since they don't dissociate at all in solution, so one mole of glucose molecules produces exactly one mole of particles in solution. So a 1 molar solution of NaCl will have double the osmolarity of a 1 molar solution of glucose, because dissolving 1 mole of NaCl in a liter of solution will produce double the number of particles that dissolving 1 mole of glucose will. --Jayron32.talk.contribs 04:41, 28 January 2009 (UTC)