Wikipedia:Reference desk/Archives/Science/2008 August 5

= August 5 =

Apparent Incandescence of Planets
When viewed from earth, why do the planets of the solar system appear to be incandescent, as if they were stars? [This paragraph has been corrected by the originator. Sorry, folks, I didn't express myself right.]

We know that all the planets are below the temperature of incandescence.

Similarly, the earth's moon has a glowing appearance, rather like a fluorescent lamp. But men have walked on the moon and found it did not glow when the observer is close to it.

Things should get dimmer as they become farther away, not brighter. We know that from observation of things on earth. That also conforms with the principle that radiant energy decreases with the square of the distance.

What is the solution to this paradox? —Preceding unsigned comment added by Andme2 (talk • contribs) 04:26, 5 August 2008 (UTC)


 * Planets and moons shine because they reflect the light of the Sun, in varying amounts according to their albedo. Watch the moon throughout a month though, you will see large parts of it that don't glow brightly - those are the parts turned away from the Sun. (Oh and they're not the Earth's planets, they revolve around the Sun) Franamax (talk) 05:01, 5 August 2008 (UTC)


 * Are you suggesting that we don't own the entire solar system? I find it strange that your definition of ownership would depend so heavily on gravitational attraction.  Does that mean that the Earth owns your car and your house?  Human-made paperwork notwithstanding, Earth is certainly outcompeting you on net induced gravitational force acting on everything you think you possess.  Or, you can adopt a philosophy that ownership transcends gravitational attraction... Nimur (talk) 05:06, 5 August 2008 (UTC)


 * Well on the few occasions when I've taken my car off the Earth's surface, Earth has exercised its prior claim to ownership pretty darn fast. I haven't tried launching a house yet, for one thing if I didn't have gravity, I would have wasted all that money on floors. Not to mention toilets with pipes that go downwards... Franamax (talk) 05:57, 5 August 2008 (UTC)


 * And since there is a chance you're serious: 1) ownership implies control, so Earth tells the Moon what to do, but it sure doesn't tell Ganymede when it's bedtime; 2) ownership implies relevance, if my car doesn't have me around it's not much good (since I'm the only one who has the keys), whereas if Earth's not around, Jupiter still works just fine; and 3) philosophize all you want, the Earth is what you're made from and the Earth is where you're gonna end up, all nice and molecule-like. Write your paperwork up, it's gonna end up as dirt too eventually. Of course, there will always be a Wikipedia :) Franamax (talk) 06:14, 5 August 2008 (UTC)
 * Wait, wait a second... How can you be so sure we came from Earth when even NASA is trying to find out if we really came from Mars?  —Preceding unsigned comment added by 71.100.162.249 (talk) 20:58, 5 August 2008 (UTC)


 * They seem bright because you are looking at them contrasting with a black night sky. If you look at the moon in the day time (easy) or at the planets in day time - you need to have binoculars at least and know where to look you will find that the moon and planets are much dimmer looking.  Only Venus is really bright, and that is because it is very white and closer to the sun. Graeme Bartlett (talk) 06:50, 5 August 2008 (UTC)


 * "But men have walked on the moon and found it did not glow when the observer is close to it." Actually, the Moon's surface reflects about 12% of incident light, giving it an albedo similar to that of worn asphalt.
 * Anyone who has looked through a telescope knows that the planets are far, far dimmer in terms of surface brightness than any star. No amateur telescope can show the disc of any star except the Sun; hence, stars appear to have about the same surface brightness regardless of magnification.  Planets rapidly dim when the magnification is increased.  --Bowlhover (talk) 07:23, 5 August 2008 (UTC)


 * First, each point on a planet or Moon does get dimmer as distance increases. However, you also can see more of the surface of such an object as you back off, up to the point where it all fits in your view.  Backing up beyond that makes the object seem smaller, but this essentially squeezes all the reflected light down to a smaller and smaller area, such that the total amount of light that hits one rod or cone in your eye, in theory, remains the same, if there's no dust in between to absorb the light.  This continues until the light from the planet or Moon only hits one rod or cone.  From that point on the total amount of light hitting that point in your eye decreases with distance.  However, the nearby planets and our Moon aren't far enough away for that to happen, while all stars except the Sun are. StuRat (talk) 12:18, 5 August 2008 (UTC)


 * "However, the nearby planets and our Moon aren't far enough away for that to happen" Just to clarify, all planets except Earth are seen as points with the naked eye.  There are exceptions, but those are rare.  --Bowlhover (talk) 21:13, 5 August 2008 (UTC)


 * Using my def of a point light source as one where all the light hits a single rod or cone in the eye, the nearest planets don't qualify. StuRat (talk) 17:09, 6 August 2008 (UTC)


 * By the def, not even the stars are point sources. The lens can't focus light perfectly, but even if they could, the Airy disk would spread out the light.  These two factors are the reason bright stars like Sirius appear larger than dim ones like Gamma Trianguli.  It's true that planets should appear much larger than stars, but only the actual appearance of stars and planets is relevant to the question.  --Bowlhover (talk) 20:28, 6 August 2008 (UTC)


 * Another effect to consider is that our eyes dilate or contract in an attempt to make everything appear equally as bright, so that something like the Moon, which isn't very bright at all, seems bright when viewed at night. When you see the Moon during the day, you can really compare it with the Sun, and see how dim it really is. StuRat (talk) 12:22, 5 August 2008 (UTC)


 * Yet another effect is the night vision that only becomes fully effective after 30 minutes in the dark. Judging from http://webvision.med.utah.edu/imageswv/KallDark1.jpg, the eye's sensitivity threshold decreases by a factor of 60 000 after half an hour.  Pupil dilation has a significant effect only in the first few minutes of dark adaptation, in which it allows 4-16 times the light-adapted amount of light to pass through (http://sightresearch.net/files/adaptation.htm).  --Bowlhover (talk) 20:07, 5 August 2008 (UTC)

Height of mountains
how are the height of mountains calculated? how accurate are these?Shraktu (talk) 04:39, 5 August 2008 (UTC)


 * It could be done by dead reckoning, by pressure altimeters, or by triangulation. In modern times, GPS and RADAR are some other options.  Nimur (talk) 05:03, 5 August 2008 (UTC)
 * Here's an article from Slate, but it's not actually all that informative... Nimur (talk) 05:23, 5 August 2008 (UTC)


 * When I was in high school I was taught that 0 m starts at the geoid level. --Kjoonlee 06:03, 5 August 2008 (UTC)
 * Yes it is not that easy to calculate exactly where the geoid is for a mountain a long way inland. This has been a diffulcult job for surveyors.  It will involve taking precise measures of the vertical and comparing it with the known 0m datum at many points on a path to the top of the mountain. See if geodesy has anything. Graeme Bartlett (talk) 06:44, 5 August 2008 (UTC)
 * You may want to read Mount Everest for some info on the height and various ways it was measured Nil Einne (talk) 08:52, 5 August 2008 (UTC)


 * I believe triangulation is the most frequently used method. It has the advantage of not requiring a physical presence on the top of the mountain - don't forget that even today some mountains have not yet been climbed. Professional triangulation can also be amazingly accurate - the Great Trigonometric Survey of India in the 19th century measured the height of Mount Everest to be 8,840m, even though they were measuring from the border of India, about 150 miles away. This is within 0.1% of the current official height of 8,848m. Gandalf61 (talk) 08:58, 5 August 2008 (UTC)


 * You need some kind of zero point base to measure from, usually "sea level", which is a vague term at best. See Datum (geodesy). Pfly (talk) 09:18, 5 August 2008 (UTC)


 * Well, yes, but that is true of all the methods mentioned - they only actually give you a height relative to a base line. You then need some convention for defining the elevation of the base line - so you use a geodetic system. In the 19th century you put your base line near the coast (the Great Trigonometric Survye of India established its base line at Chennai) and measured its elevation relative to local mean sea level, which you averaged over several years. A modern survey would use the World Geodetic System. Gandalf61 (talk) 09:40, 5 August 2008 (UTC)

The height of mountains being above sea level means that on Mars or the Moon the mountain hieghts would be undefined, and that on Earth, as the hypothesized sea level rise progresses, all mountains would need periodic adjustments down in their reported heights. Seems odd. Edison (talk) 13:40, 5 August 2008 (UTC)


 * Yea it is non-ideal. Another thing is that a mountain like Mount Hood seen from Portland looks much taller than Pikes Peak seen from Colorado Springs, even though Pikes Peak is actually higher. But Portland is nearly at sea level and C-Springs is something like a mile high. But then, measuring elevation from sea level makes sense given human history and culture. Measuring from the center of the Earth might be more... scientific? Still, it's more useful to know how far above sea level your house is as a hurricane approaches, for example, than how far your house is from the center of the Earth. I agree it is odd though. "Sea level" is not the most stable and well-defined baselines. On the other hand, mountains are not exactly stable either, with their height changing not only from erosion but from larger scale uplift and sinking of land. This kind of height change may usually be slower than sea level change, but in some cases it happens catatrophically fast! Pfly (talk) 16:22, 5 August 2008 (UTC)

Semiconductor Resistivity
What is the "Four Point Probe Method" in measurement of Semiconductor Resistivity?Shraktu (talk) 06:27, 5 August 2008 (UTC)


 * I think you are looking for Four-terminal sensing --Dr Dima (talk) 06:33, 5 August 2008 (UTC)

Applications of Chem kinetics
do you know any websites on the applications of chem kinetics? Jaydilite2008 (talk) 12:10, 5 August 2008 (UTC)

Chemical kinetics would be a good place to start. EagleFalconn (talk) 13:18, 5 August 2008 (UTC)

Kissing scenes in movies - health risks?
In movie production, how do they prevent diseases from being passed from one actor/actress to another when they kiss? It doesn't look like there a lot that can be done when you see open mouths touching each other. On the other hand, if you kiss enough random people, sooner or later you'll catch something. Are actors and actresses really risking their health when shooting kissing scenes or do they have some kind of high-tech tricks not visible to the viewer that prevent disease transmission? —Preceding unsigned comment added by 71.185.73.240 (talk) 14:26, 5 August 2008 (UTC)


 * They are really kissing, if that's what you're asking. They probably do occasionally pass colds on to one another that way. But it's not much of an epidemic—the sum total of people kissing in movies per year is really just a handful. --98.217.8.46 (talk) 15:06, 5 August 2008 (UTC)


 * Plus during the filming of any one movie an every-day character I wouldn't expect will kiss more than 5 or 10 of their fellow actors on the movie. Given that shooting a movie can take anything from weeks to years it's hardly like the actor will be kissing significant numbers of individuals so I doubt the risk will be notably higher than the general population. 194.221.133.226 (talk) 15:14, 5 August 2008 (UTC)


 * Yeah, kissing is not risk-free, but it's not much different than shaking hands or other forms of close contact. Kissing is pretty scant but touches on the health aspects. Friday (talk) 15:15, 5 August 2008 (UTC)


 * The diseases spread via kissing are usually upper respiratory tract infections such as the common cold and influenza. Most people in good shape will recover from these within a week or two. Slightly more rare are the diseases such as infectious mononucleosis (kissing disease, mono etc) which are still usually non-fatal but take longer to recover. The risk is there but I suppose it's part of the job. — Cyclonenim T@lk? 17:12, 5 August 2008 (UTC)


 * Lots of movies have prolonged tougue-wrestling scenes. There are maladies more serious and persistent than colds and flu which could be spread by such contact. I wonder if standard contracts at mainstream studios require medical certification that the co-star is free of herpes, Infectious mononucleosis, Hepatitis B and venereal disease in general? The the Columbia University health information site "Go Ask Alice" says these could be transmitted by kissing, although they call it "highly unlikely." Edison (talk) 19:19, 5 August 2008 (UTC)


 * How do they prevent that? For the most part, they don't. I mean, if someone has a terrible cold, I'm sure they avoid filming the kissing scenes to try and ensure they don't have two sick actors on the set, which'd be a waste of time and money. Likewise, if someone has a herpes flare-up, I'm sure they avoid kissing for obvious reasons. And of course, actors and directors tend to get medical check-ups before filming begins (for insurance purposes), so if they have any even remotely serious communicable diseases, chances are that they're known and being dealt with. But apart from situations like this, I don't think it's a major concern, any more than kissing someone on a date is. I mean, I'm sure some people just don't kiss anyone if they can avoid it, but for most people -- whether they're in front of a camera or not -- kissing is not first and foremost thought of as a health risk. I mean, if you're going to be worried about that kind of thing, chances are that you'll also want to avoid shaking hands with people, eating out, engaging in many sports, etc. -- at which point one kind of has to wonder if you're suffering from mysophobia or something. It's not really a very reasonable concern, all things considered. -- Captain Disdain (talk) 00:41, 6 August 2008 (UTC)

Do newspaper inks contain cyanide?
Do the inks commonly used to print newspaper and newspaper inserts contain cyanide? —Preceding unsigned comment added by 71.185.73.240 (talk) 16:18, 5 August 2008 (UTC)
 * This may help you. — Cyclonenim T@lk? 17:09, 5 August 2008 (UTC)
 * Cyanide is a very dangerous chemical. I wasn't able to find any reference to it on any website discussing the dangers of newspapers/inks/etc.  On the other hand, I did not find an itemized list of the chemicals in ink. ---J.S  (T/C/WRE) 17:47, 5 August 2008 (UTC)
 * According to the link I just gave (albeit not in the free abstract), ink used in newspapers in the U.K. contains acetonitrile which is a cyanide.
 * Saying that acetonitrile contains cyanide is like the old trope about salt being made up of sodium, an caustic and explosive metal, and chlorine, a poisonous gas. While true in the sense that salt contains sodium and chlorine atoms, they exist in salt as (mostly) harmless ions, not as the poisonous elemental forms. Likewise with acetonitrile. Though it contains a cyano group, which is like the cyanide ion, the cyano group is covalently bonded to another carbon atom, which completely changes its reactivity versus the cyanide ion. While not completely harmless, acetonitrile is very different from the cyanide ion in the way it behaves in your body. It's like the difference between putting a cotton ball (cellulose) into your coffee and putting a teaspoon of sugar (sucrose). They may both be carbohydrates containing glucose groups, but what those glucose groups are attached to and the way they are attached makes a world of difference. -- 128.104.112.147 (talk) 20:49, 5 August 2008 (UTC)


 * Is it possible that Potassium ferricyanide or Prussian blue are used?87.102.5.5 (talk) 17:52, 5 August 2008 (UTC)

is this snake poisons —Preceding unsigned comment added by 71.3.150.136 (talk) 18:40, 5 August 2008 (UTC)

Strictly speaking, yeah, I guess its possible. However, acetonitrile and cyanide should not be confused. Acetonitrile is a very common organic solvent, cyanide is an ion. Acetonitrile has been known to breakdown into cyanide in human metabolic processes, however, and thats likely where any toxicity from newspaper ink would come from. EagleFalconn (talk) 20:00, 5 August 2008 (UTC)
 * Seems that nearly all the solvent from the ink would evaporate (otherwise the ink would never dry!), and that toxicity from the ink could be due to all the pigments too. Even the cited article above talks about a very different toxic chemical than acetonitrile. DMacks (talk) 20:58, 5 August 2008 (UTC)

The answer may be YES - see http://holmfirthtypo.blogspot.com/2006/04/complete-history-of-typography-part-3.html 87.102.5.5 (talk) 21:54, 5 August 2008 (UTC) "Pigments that may test positive for “free cyanide” under some test protocols include CI Pigment Blue 27, CI Pigment Red 169, as well as PMTA green and violet pigments" I'll leave the rest to you.87.102.5.5 (talk) 21:55, 5 August 2008 (UTC)

In my completely unprofessional, non-warrantied opinion: Don't get too worked up about tiny doses of cyanide. Cyanide is everywhere; the body has ways to deal with it. It's very toxic in the sense that it doesn't take much to kill you, but in the sense of nasty things happening to you from doses that don't cause symptoms, I'd be much more worried about benzo(a)pyrene, which one of the links suggests is in the ink. --Trovatore (talk) 22:03, 5 August 2008 (UTC)
 * I really should emphasize here that I'm not at all sure that what I write above is true -- this is a vague impression not based on anything solid. If anyone actually knows something about it I'd be interested to hear. --Trovatore (talk) 22:51, 5 August 2008 (UTC)
 * Toxicity from newspaper ink has been related to Antimony -- whether it still is, don't know and the article doesn't say. Julia Rossi (talk) 02:09, 6 August 2008 (UTC)
 * I think that must be slight wrong - antimony can be toxic - but surely would only affect those that worked with it ie the printers/typsetters/typemakers - occupational hazards.
 * I doubt there is (or was) any risk from antimony to the average reader.
 * But I could well be wrong. —Preceding unsigned comment added by 87.102.5.5 (talk) 02:27, 6 August 2008 (UTC)
 * Not the reader, but in other ways, so not for wrapping fish and chips or using on the body because it can be metabolised. Julia Rossi (talk) 06:07, 6 August 2008 (UTC)


 * Well, here's what I meant about cyanide. If someone forced me to make a choice between taking 100 mg of cyanide, or 100 mg of benzo(a)pyrene, I'd take the latter. It would quite possibly (probably? certainly?) give me cancer at some later time, but the cyanide would be certain death immediately. On the other hand, if the choice were between 1 mg of cyanide or 1 mg of benzo(a)pyrene, based on my current state of knowledge and belief, I'd take the cyanide, expecting it to be essentially harmless, whereas the hydrocarbon could still give me cancer even in the much lower dose.
 * So what I'm kind of curious about is, am I right about that? Does anyone really know? --Trovatore (talk) 08:21, 6 August 2008 (UTC)
 * It seems you want to avoid cancer, but not as much as instant death - I think your analysis is correct - though of course nobody really knows how much an increased chance of cancer from eating 1mg of benzopyrene - but 1mg of cyanide is not lethal (Cyanide poisoning). Actually you quite a good chance of surviving 100mg of cyanide - but not guaranteed. It's a probability choice and science can only help so much.87.102.5.5 (talk) 10:29, 6 August 2008 (UTC)

Logical human thought
I have a computer program which reduces multiple state equations to minimum form. When I record sensor data into a table as states of an independent variable for each sensor concurrent with some event and use the program to create a rule from the data, in some cases the rule that is created is very easy for a human to comprehend. I consider this process, therefore a form of simulated [logical] human thought. Is there any published objection to defining this process in that way? —Preceding unsigned comment added by 71.100.162.249 (talk) 19:27, 5 August 2008 (UTC)


 * The Chinese room argument? --Bowlhover (talk) 21:21, 5 August 2008 (UTC)
 * All of what I have read and skimmed through so far suggests Searle knew nothing of the process of logical equation reduction or that the human mind can apply it to memory of past events to formulate rules. Thanks for the reference. The student I am dealing with is at that age where whatever is read is accepted on face value without question as to whether it is true. Thanks. —Preceding unsigned comment added by 71.100.162.249 (talk) 22:12, 5 August 2008 (UTC)
 * True, but Searle used speaking Chinese as a random example of a human activity that computers may eventually do following code. Speaking English or reducing equations would have worked just as well.  --Bowlhover (talk) 22:25, 5 August 2008 (UTC)
 * But conversely Searle's argument makes a different point: What might a human do in such a situation to prove they are human and not computer? "For if we believe that Searle has proven that the man in his room (or more precisely, the system of the "rulebook-plus-man") doesn't understand Chinese, then Searle has also proven that a Chinese person doesn't understand Chinese. After all, no individual cell in a Chinese person's nervous system understands Chinese, and all of these cells obey the "blind" laws of biology (This argument doesn't work so well against dualists, but Searle, and many of his fans, claim not to be dualists.), just as surely as the man in Searle's room blindly follows the rulebook." -- A Refutation of John Searle's "Chinese Room Argument" by Bob Murphy. Murphy's refutation of Searle's argument applies regardless of the human activity. —Preceding unsigned comment added by 71.100.162.249 (talk) 06:31, 6 August 2008 (UTC)

electro etching of copper with copper suphate soln
can it be done? —Preceding unsigned comment added by 79.76.159.153 (talk) 20:50, 5 August 2008 (UTC)
 * With a current and an electrode most any conductive solution can be used to effect electro etching. Ferric hydrochloride, however, works without any current at all. —Preceding unsigned comment added by 71.100.162.249 (talk) 21:03, 5 August 2008 (UTC)

Rise time
What is the shortest mans rise time recorded? —Preceding unsigned comment added by 79.76.159.153 (talk) 21:24, 5 August 2008 (UTC)
 * Did you mean 'mains rise time' or 'shortest man's rise time'?87.102.5.5 (talk) 21:35, 5 August 2008 (UTC)
 * Haha, there are so many things this could mean! Is it about climbing something? Springing to one's feet? Getting an erection? We may never know... —Keenan Pepper 00:46, 6 August 2008 (UTC)
 * Even the earliest ever time the world's shortest man got out of bed... ; ))  Julia Rossi (talk) 01:48, 6 August 2008 (UTC)
 * Maybe the OT has drowned someone and fears early detection? --Ayacop (talk) 08:45, 6 August 2008 (UTC)
 * Mr. He Pingping claims to be the world's "shortest man" at 2.4 feet (73 cm). How quickly could one get a rise out of him? Perhaps by pointing put that Mr. Lin Yik-chic is only 67.5 cm tall . Edison (talk) 14:08, 6 August 2008 (UTC)

No no. I mean shortest time for man to get eerection —Preceding unsigned comment added by 79.76.167.200 (talk) 23:31, 6 August 2008 (UTC)
 * One of Kinsey's studies probably has the answer.. Suntag (talk) 17:21, 7 August 2008 (UTC)
 * What are you counting as the starting point? Beginning of stimulation? In which case, it's zero, since it's not uncommon to get erections without any stimulation at all (especially during puberty). If you mean from the penis starting to become erect and becoming fully erect, it's probably difficult to define exactly. --Tango (talk) 02:40, 10 August 2008 (UTC)

Question of utmost seriousness
Scenario: You take out a 500ml can of beer from the fridge where it has been sitting for the last 24 hours. You notice that its temperature is exactly +2 deg C. Unfortunately, because of the condensation on the can, it slips from your hand and falls a distance of exactly 1m to the floor. Miraculously, the can does not burst (although it may be dented), and all seems well. However, you quickly realize that if you try to open the can immediately, it will almost certainly mostly be lost in froth due to out gassing of the CO2.

Now the Q: If you were to return the can in question to the aforementioned fridge (with a temp of +2 deg C), how long would the can need to remain there before you could once again get it out and open it without any frothing and enjoy it at its best?

BTW its not homework-- I just done it ! :( —Preceding unsigned comment added by 79.76.159.153 (talk) 21:42, 5 August 2008 (UTC)
 * I'm guessing at this but I believe it is the same problem that requires cooling in the first place to remove the heat (in this case caused by the fall to the floor) it has acquired. Once the heat is lost there may be an additional time period for the molecules to forget their trauma and to go back to sleep since some of the energy from the fall was not turned into heat but into "nervous" molecules. I'd say give them another week. —Preceding unsigned comment added by 71.100.162.249 (talk) 22:20, 5 August 2008 (UTC)
 * A week? That's pessimistic! It's not really to do with heat or energy, it's just the dissolved gas coming out of solution, you need to give it time to dissolve again. I'm sure someone has done a detailed study on the problem, but in my experience about 20 minutes should do it. If it's been really shaken up, then maybe a little longer, but a simple fall wouldn't normally shake it up much. --Tango (talk) 22:54, 5 August 2008 (UTC)


 * I have spent many years pondering this issue. The first question is why shaking (agitating) the can makes it froth.  The increase in temperature is a red herring (the increase in temp from dropping it is orders of magnitude less than the variability in the fridge).  Frothing requires nucleating agents: in this case, this is small bits of dust etc that are present inthe liquid.   Under calm circumstances, these particles adhere to the sides of the can; but if you shake or drop the can they become suspended and become much more effective nucleating agents: FROTH!  Anyone got any comments? Robinh (talk) 07:15, 6 August 2008 (UTC)
 * Or, could it be that shaking it causes bubbles of air to get mixed into the liquid and those act as nucleation sites? --Tango (talk) 08:00, 6 August 2008 (UTC)


 * Both small bubbles and particulate matter can act as nucleation sites. Most commercial mass-market beers are filtered to remove the vast bulk of particulate matter.  (Exceptions exist, of course.  Trappist ales are perhaps the most dramatic example, though you'll only find those in glass bottles, not cans.)  That leaves bubbles.  Most will rise to the top of the beer after the can is allowed to stand undisturbed for a few minutes.   I would also recommend flicking the can sharply a few times around its circumference with your finger; this will dislodge some of the bubbles which would otherwise remain stuck to the side of the can. TenOfAllTrades(talk) 13:17, 6 August 2008 (UTC)

From my experience, I'd think a few hours should be more than enough. --Kjoonlee 11:19, 6 August 2008 (UTC)


 * From my experience, holding your mouth over the opening as you pull the tab stops waste and saves time. DuncanHill (talk) 11:36, 6 August 2008 (UTC)

I don't have a clue how but tapping the beer (if in a can) several times on the top seems to prevent fizzing up by a large degree. I'd love to know the science to that, actually, but it always works for me even if I shake it up loads. — Cyclonenim T@lk? 14:05, 6 August 2008 (UTC)


 * I used the "tap the can" method as the basis for a high-school science experiment. I did an exhaustive study with different types of taps, different lengths, different amounts of shaking (I even built a shaker to ensure all cans were shaken just as much) and I had controls that were not shaken, but sat there for the same length of time as those getting tapped.  Just out of a pure guess, I also used a "turn the can upside down" think my grandmother used.  I measured spray by opening the cans in a small fishtank with a lid (I cut holes in the plastic lid and used rubber gloves - so I could trap all the spray).  In the end, I found that tapping the can for about 5 seconds stopped most of the spray.  Also, turning the can upside down slowly and then upright again had the same effect.  Finally, leaving the can sitting there for about 5 seconds had an equivalent effect.  So, my conclusion was that it takes about 5 seconds for much of the fizzing to cease inside the can.  If you like, you can spin around three times on one foot while singing Old McDonald.  What you do during those few seconds isn't the key.  It is merely the length of time.  In the end - I got second place.  I'm still a bit pissed about it.  I was told that I got second place because the science teacher disagreed with my conclusion.  She was certain that tapping the can had some sort of physical effect on causing the bubbles inside to burst and reduce fizzing. --  k a i n a w &trade; 17:20, 6 August 2008 (UTC)
 * [unsure of etiquette WRT editing out-of-chronological order]. Anyway, see Mpemba effect for a similar phenomenon of teachers not believing a student.  Robinh (talk) 08:24, 8 August 2008 (UTC)


 * Ahahahaha! Welcome to the world of research :) Now you just need to replicate your results, publish your research, wait for (or encourage) others to independently replicate your results, and then you're home dry. But your teacher still probably won't believe you for another 20 years. 79.66.38.215 (talk) 23:25, 7 August 2008 (UTC)

OK AS the OP, i have to say that none of the above time estimates seem to concur with my experience. I have found that if I drop a can of lager from 1m or less, I have to leave it in the fridge for a considerable number of hours (may be 5 hours) before I can open it without frothing. Is lager different from other beers in this respect? —Preceding unsigned comment added by 79.76.225.183 (talk) 01:00, 8 August 2008 (UTC)
 * Lager is usually fizzier than ale, so I would expect it to need longer. --Tango (talk) 02:43, 10 August 2008 (UTC)

Harmful bacteria
I heard it said recently that the human mouth contains more harmful bacteria then the rectum or colon. Is that true or false? —Preceding unsigned comment added by 79.76.159.153 (talk) 23:16, 5 August 2008 (UTC)
 * Define harmful. There are normally orders-of-magnitude more bacteria near the exit of your alimentary canal than near the entrance, but I do not know how you would like to determine which are harmful and which are not. You would not want any of them in your blood stream, that's for sure. It depends on your immune system just how much harm any of them would do when given the opportunity. --Dr Dima (talk) 00:18, 6 August 2008 (UTC)


 * Well, oral bacteria in the bloodstream can possibly cause myocardial infarction. How much shit would you need to eat cause that? —Preceding unsigned comment added by 79.76.159.153 (talk) 00:31, 6 August 2008
 * Eating something does not automatically put it into your bloodstream. For a fair comparison you'd need to be injecting it. Probably a bad idea. APL (talk) 02:05, 6 August 2008 (UTC)


 * I'm not sure. I've been told that there are more bacteria per square centimeter on one's tongue and teeth than anywhere else in a healthy human body.  Maybe that's totally wrong, but it is widely circulating idea at least.  Dragons flight (talk) 00:29, 6 August 2008 (UTC)


 * It all depends whether you mean "(more harmful) bacteria" (i.e. bacteria that are more harmful than others), or "more (harmful bacteria)" (i.e. a greater number of bacteria that are harmful at all, even if only slightly). —Keenan Pepper 00:42, 6 August 2008 (UTC)


 * To 79.76: How much shit you would need to eat depends on how deep a shit you are in right now. Please use more appropriate terminology next time. To other readers: you may want to read Gut flora article. It clearly states the usual numbers of bacteria in human gut, as well as the more common genera of bacteria found normally in the gut. Clostridium, in particular, is a well known human pathogen, and many others are opportunistic pathogens. So, colon wins! --Dr Dima (talk) 01:13, 6 August 2008 (UTC)


 * Clostridium species, especially the dangerous ones like C. botulinum and C. perfringens, are pretty much everywhere in nature, though. They aren't harmful without special circumstances, though in those situations they're quite lethal.  SDY (talk) 02:04, 6 August 2008 (UTC)

The gut flora article is missing all the plant viruses see. And probably bacteriophages as well. --Ayacop (talk) 08:39, 6 August 2008 (UTC)