Wikipedia:Reference desk/Science

Wikipedia:Reference desk/headercfg

April 16

Total number of people

What is the total number of people to have ever lived and how many people die and are born each year? 71.100.175.14 04:01, 16 April 2007 (UTC)

I don't know off the top of my head, but I just typed "total number of people to have ever lived" into Google, and the first lotsa hits look relevant... —Steve Summit (talk) 04:03, 16 April 2007 (UTC)

The first question has been asked several times recently. Estimates vary of course, but somewhere in the region of 100 billion, as I recall. Clarityfiend 04:31, 16 April 2007 (UTC)

No need to recall or guess. It's all here, in our very own Wikipedia. JackofOz 04:45, 16 April 2007 (UTC)

See

Wikipedia reference desk Science Archive September 2006

How many humans have ever lived.

http://en.wikipedia.org/wiki/Wikipedia:Reference_desk_archive/Science/2006_September_27

202.168.50.40 05:15, 16 April 2007 (UTC)

Reason for asking:

From the above and according to Ramsey at the Department of Mathematics at the University of Hawaii so long as the total number of people that have ever lived (have been born) is less than 781,250,000,000 only Seven Degrees of Separation are required to link every single human who ever lived assuming that each person still knows at least 50 other people. Drop that number to 5 contacts and the Degrees of Separation only jumps to 16. 71.100.175.14 06:51, 16 April 2007 (UTC)

There must be additional assumptions. I believe that figure would only be true if those fifty people are essentially distributed at random around the world. Take an extreme case: an isolated island with 51 people, where everyone knows everyone else, but has never met anyone not from the island. Each one of those islanders knows fifty people, yet you could trace through as many degrees as you would like and they would never be connected to you, for instance. In reality, contacts tend to be clustered around geographic connections (and to a lesser extent, cultural, professional, and so on). — Knowledge Seeker দ 08:52, 16 April 2007 (UTC)

Aren't you forgetting something? Those people had to have come from somewhere and it is the link with the people from which they came that links them to everyone else when you include previous living persons. 71.100.175.14 22:01, 16 April 2007 (UTC)

Of course, that's a gross oversimplification; the seven degrees of separation calculation is not – I'm sure – meant to be taken literally. If we take the maximum human lifetime to be of the order of 120 years, with seven degrees of separation there's no way to be linked to anyone from more than 840 years ago.... TenOfAllTrades(talk) 12:55, 16 April 2007 (UTC)

Did you actually do the math? The estimated total number of humans ever born going back a million years based on only an average 25 year life span falls well within Seven Degrees of Separation with 50 contacts per degree. 71.100.175.14 21:42, 16 April 2007 (UTC)

Er, how do you have a contact with someone who died before you were born? TenOfAllTrades(talk) 22:18, 16 April 2007 (UTC)

By simply specifying that your application of DoS is not limited to the living but also included the dead just as you can specify that you have a hereditary relationship with your great, great, great, great, great grandmother who I am assuming is no longer living. 71.100.175.14 22:43, 16 April 2007 (UTC)

By that token, any living creature can be connected to any other living creature with only two degrees of separation, via the universal common ancestor... SamSim 19:52, 19 April 2007 (UTC)

The total number of people who have ever existed is probably between 70000000000 and 100000000000. There are estimated to be around 4 deaths and 6 births each second, whch is about 125000000 and 190000000 each year. But of course these are all estimates, especially since people disagree on how long humans have existed for.

Do certain squirrel species commit suicide? (or for that reason any species, other than the human species?

I am researching on the subject of suicide. Currently wondering if there are other species (alive or extinct) that are capable of committing suicide. I've searched google, but instead landed up in blogs that describe how squirrels cross the road and get killed...or something like that. Are animals or insects as such capable of bringing an end to their own life?Arun T Jayapal 09:32, 16 April 2007 (UTC)

I don't know of any animals besides humans who commit suicide for the pure sake of ending their lives, but bees die when they sting something (sacrifice themselves to scare away what might threaten the hive), deer stare stupidly at headlights and get run over instead of stepping aside (what is that, fear? Confusion? I'm not sure actually). And, of course, there are always wonderful, cute, tiny, suicidal lemmings (mythically suicidal at least, they don't actually mean to kill themselves). But squirrels? I'm willing to be they're just dumb. I say don't worry if you run one over, do your part to help natural selection ;-) Someguy1221 10:07, 16 April 2007 (UTC)

I believe deer are exhibiting an inappropriate survival response to "freeze" so the "predator" (car) won't see them. Nothing in their evolution prepared them for dealing with cars, so they react to them like they would to a predator they know they can't outrun. If that was actually the case, freezing and hoping the predator doesn't detect them would indeed be their best chance at survival. StuRat 14:48, 16 April 2007 (UTC)

Possibly related to this is Learned helplessness, which shows that at least animals can learn some sense of futility. The basic experiment taught dogs (through conditioning) that the sound of a bell would be followed by an electric shock. Dogs that had a means of escape from the start would quickly learn to use it when the signal was given. Dogs that did not have this possibility of escape during learning would not not use it when it was introduced later on. In this way an animal could at least commit suicide through inaction, rather than action. A lot of behavior surrounding learned helplessness seems to correlate to human concepts like clinical depression and optimism, which suggests that animals can at least suffer suicidal emotions, even if they are unaware that death might stop the pain. risk 22:25, 16 April 2007 (UTC)

It's the same with hedgehogs and cars. They roll into a ball for protection when they see the headlights - which is not much use vs. a wheel. I think it's the same with armadillos - maybe one of the Americans here can confirm that they are regular roadkill victims (I think I read that). --Kurt Shaped Box 22:30, 16 April 2007 (UTC)

Hmm. Why do bees die after they sting?Arun T Jayapal 13:06, 16 April 2007 (UTC)

Bees die after they sting because the stinger is barbed in order to remain lodged in the skin of the victim when the bee flys away, and when the stinger pulls out, the venom glands come with it in order to continue pumping venom into the victim. This removal of the stinger / venom gland results in a mortal wound for the individual bee. This is a classic case of Altruism in the evolutionary sense. -Czmtzc 14:02, 16 April 2007 (UTC)

That definetly qualifies as a suicide.

—The preceding unsigned comment was added by 84.187.59.188 (talk) 23:08, 16 April 2007 (UTC).

If you mean do healthy animals commit suicide, I think the answer is no. But this would depend on if they knew their actions would result in death. Do animals have a sence of life and understand that they may die at some point - and if they do, do they click that they could end their own life sooner? But there are cases where sick animals will do things that cause them to die faster, like an indured whale beaching itself for exapmple. I think that somewhere along the line its happened, but don't know if you'll find much info on it. Think outside the box 11:29, 16 April 2007 (UTC)

My dog acctually commited suicide after its pups were born. we paid more attention to the puppys (but still kept spoiling him) but he wanted all the attention so one day he just looked at us then ran straight into the tires of a incomming car. now before you say anything this dog was smart he knew what cars did and he would never go near the road for this reason. this is why i belive that he committed suicide that day its the only explanation for his actions =( User:Maverick423 If It Looks Good Nuke It 13:50, 16 April 2007 (UTC)

I wonder if dogs ever suffer from post-partum depression ? StuRat 14:54, 16 April 2007 (UTC)

As for suicidal animals, there are many species that die after they have "served their purpose" (usually mating for males and giving birth/laying eggs for females), however, this is typically accomplished by some biological mechanism (not well understood) other than intentional suicide. Knowing whether you are a net help or hindrance to your relatives is complicated, so requires a fair amount of intelligence to determine. This may be why the decision of when or if to commit suicide isn't left up to less intelligent animals. I can think of one possible exception. I believe in many species a sick individual will leave the group and "go off to die". This death will then take place due to predation, starvation, dehydration, exposure, etc. StuRat 15:02, 16 April 2007 (UTC)

You know i acctually seen that in many documentrys of animals. when a preditor can nolonger hunt with its pack, it ussally goes off to die like StuRat said, i belive one of the documentries acctually stated that this is equivallent to committing suicide in the animal kingdom as the animal that leaves knows it has no chance or surviving on its own with out its pack. Perhaps a articl on Animal Suicide is in order? User:Maverick423 If It Looks Good Nuke It 15:28, 16 April 2007 (UTC)

male angler fish.

Don't the rest of the pack actively drive the 'no longer useful' animal away, instead of it choosing to leave of its own accord? I've certainly read anecdotal accounts of this amongst gulls (if one bird is sick or injured, the rest will attack it until it either leaves or is killed) - the sickly flock member presumably being a liability to the rest. Apparently, albino gulls are subject to a lot of 'social pressure' too (this was actually cited in a scientific paper I read, though I cannot recall the details now)... --Kurt Shaped Box 22:25, 16 April 2007 (UTC)

I'd like to see that cite. I don't doubt you, but it sounds counter-intuitive to me. Part of the benefit of living in a herd/ flock/ school is that you reduce your individual risk of predation because there are so many others around. If I was an antelope in the Serengeti, I'd be quite in favour of there being a few lame animals in the herd for when the cats start hunting; if there are easier targets sround, I might be left alone. Matt Deres 20:32, 17 April 2007 (UTC)

In some cases female Black Widow spiders and Praying Mantis' devour the male after copulating. I guess you could say that the male commits suicide by doing that. SteveBaker 23:08, 16 April 2007 (UTC)

Infected ants sometimes leave the colony and subsequently die.Polypipe Wrangler 06:22, 17 April 2007 (UTC)

Quantifying article

In article Center pivot irrigation there are no factual data given. Does someone know some data that quantify such an irrigation system? E.g. typical, average, even record length of array (yards or meters). Speed of rotation. Quantity of water pumped. Etc. etc. VanBurenen 14:27, 16 April 2007 (UTC)

A tree named Sag

According to our article about Purandhar as well as this page, "Some parts of Purandhar are covered with forest, which is composed mostly of Sag, Teak, Oak, and Mango trees." I've never heard of a type of tree called "Sag", however. Nor does Wikipedia have an article on such a type of tree. The closest I could find was Amaranthus dubius, a weed which is sometimes referred to as "Khada sag". Anyone have any clues as to what this "Sag" is referring to? Kaldari 16:36, 16 April 2007 (UTC)

Looks like it may just be another name for Teak actually. Kaldari 16:43, 16 April 2007 (UTC)

Maybe a misprint of Sal?—eric 17:31, 16 April 2007 (UTC)

Emphysema death breakdown

What is the breakdown of emphysema death causes? [Mαc Δαvιs] ❖ 16:54, 16 April 2007 (UTC)

By far the leading cause of emphysema is cigarette smoking [1]. Air pollution and occupational exposure to airborne toxins round out the bulk of the remaining cases. About 2% of cases a attributable to A1AD, a genetic disorder. Have you Googled for numbers? TenOfAllTrades(talk) 02:51, 17 April 2007 (UTC)

I don't know jack about the beanstalk

Would the cable of the space elevator rise perfectly vertically or would it bend? If the latter, roughly how much? Clarityfiend 16:57, 16 April 2007 (UTC)

Speaking generally and ideally, the cable remains taut and vertical. From a practical engineering standpoint, a completely rigid structure is a bad idea and so some flex would certainly be allowed for and expected. Also note the article subsection on cable lean. — Lomn 17:28, 16 April 2007 (UTC)

If anchored at the equator, An ideal beanstalk will be vertical. If not anchored at the equator, it will not, but I'm not sure what will happen instead. -Arch dude 20:40, 16 April 2007 (UTC)

Yet another reason it hasn't been built yet : ) Nimur 20:43, 16 April 2007 (UTC)

I believe that one of the reasons why ship-born earth-side designs are looking good because it would be possible for the ship to move out of the way of major storm systems to avoid damage to the cable. It seems unlikely that the space-side end would be able to keep up - so I deduce that the cable is indeed allowed to lean somewhat. But since the cable would be considerably more than 35,000km long, the base would have to move an awful long way before there was any significant angular shift in the cable! You have to have a mental image of a cable that's three or four times the diameter of the earth! From that, perspective, a bend of a few kilometers - or even maybe a hundred kilometers is pretty negligable when distributed along the entire length. The tricky matter is whether very low frequency oscillations might be induced by wind shifts happening at close to the cables resonant frequency. Our article suggests that a one-degree lean might occur due to the coriolis effect on the 'climber' as it ascends the cable. SteveBaker 23:00, 16 April 2007 (UTC)

Viruses

I am writing a paper on viruse, and am a little confused!! Can viruses be destroyed by phagocytosis, or does this only apply to bacteria? Hope someone can help 81.101.49.156 19:40, 16 April 2007 (UTC) Chrissy

Virtually any foreign matter can be consumed by phagocytes, viruses included. And like bacteria, viruses can be attacked by free roaming antibodies. Viruses can also be eliminated by the additional method of Natural killer cells destroying infected cells, to prevent new viruses from forming from it. Someguy1221 21:00, 16 April 2007 (UTC)

Thankyou for clearing that up for me 'someguy', much appreciated 81.101.49.156 22:16, 16 April 2007 (UTC)Chrissy

Hydroponics and Tequila

I've been reading up on hydroponics, and I recall an episode of the Colbert Report where a guest (I think it was Neil Young) proudly declared to have smoked pot that was hydroponically grown in tequila. The more I read about hydroponics, the more this strikes me as impossible. As I understand it the nutrient solution for hydroponics needs to be carefully controlled in terms of acidity and mineral concentration, and chucking spirits in there seems like a sure fire way to kill the roots. Is this at all possible? And if it is, does it have any effect on the crops? I somehow doubt that this will lead to tequila flavoured strawberries, even if it does work. risk 22:11, 16 April 2007 (UTC)

Maybe he actually meant hydroponically grown in Tequila? Vespine 22:35, 16 April 2007 (UTC)

Or, I suppose, you could add one drop of the alcoholic drink of your choice to each gallon of water, which shouldn't kill the plants, but this certainly wouldn't affect the flavor of the plants which grow in it, either. StuRat 22:50, 16 April 2007 (UTC)

Or maybe he was joking? It would not be unexpected to hear a comidic exageration the Cobert Report. -Czmtzc 11:50, 17 April 2007 (UTC)

I don't think that was the case, but I may have missed it. In any case, it turns out that it was Toby Keith [2] and it was Willie Nelson's pot. Apparently Nelson got busted a week later, too. risk 12:51, 17 April 2007 (UTC)

What's the age record for herring gulls?

Today, I encountered a gull that must be at least 25 years old now. I remember first seeing him as an adult when I was a boy - he has *very* distinctive plumage (looks like he has some sort of pigment disorder - large areas of his wing plumage are snow white, instead of grey, in a very distinctive pattern). I hadn't seen him for three years or so (he used to nest around here regularly), so I just assumed that he was dead and gone - but today, I saw him sat up there on his favourite perch (well, rooftop), watching the world go by. I'm certain that it's the same bird. Has anyone ever heard of an older member of this species? --Kurt Shaped Box 22:44, 16 April 2007 (UTC)

Now how did I know who asked this question as soon as I saw the title ? Isn't it possible that the pigment disorder is inherited and it's offspring has also inherited it's favorite perch ? StuRat 22:53, 16 April 2007 (UTC)

It's certainly possible Stu - it did appear that it was the same bird though. The particular pattern of white and grey on his wings was exactly as I remembered it. What are the chances of a pigment disorder manifesting itself identically, even if it is inherited? --Kurt Shaped Box 23:04, 16 April 2007 (UTC)

There could be some selective memory at work, your memories of that bird from 25 years ago may have been adjusted to match the current bird. Do you have any photos of the earlier bird to ensure that you recall it correctly ? StuRat 00:46, 17 April 2007 (UTC)

First, I will assume good faith, and that your memory is not faulty. According to this site Top ten bird lifespans of North America, the age records for the top ten range from 30 - 50 years. The birds in the list are all sea birds too. I personally do not think it is unreasonable that you may have a 26 year old bird. -Czmtzc 11:48, 17 April 2007 (UTC)

Thanks for that guys. I'm willing to accept that it may be selective memory on my part - but it would be nice to think that the big guy was still alive and kicking. I have fond memories of throwing food into the air for him to catch from back when I was a kid. Because he looked slightly different to the rest, I singled him out and made sure that I always threw food in his direction. That's all it takes to make a gull start hanging around near your house (for those that might want a gull hanging around near their house). --Kurt Shaped Box 18:45, 17 April 2007 (UTC)

Just in case you want them to "decorate" your car for you ? StuRat 07:03, 19 April 2007 (UTC)

Eris

From looking at Eris and the Definition of 'planet', how is Eris not a planet? Teak the Kiwi 23:21, 16 April 2007 (UTC)

The definition of planet is somewhat subjective; the IAU has sought to quantify it as follows:

• is in orbit around the Sun,
• has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape, and
• has "cleared the neighborhood" around its orbit.

See 2006 definition of planet for some details. In my opinion, these are vague enough to allow astronomers some argument-room. Nimur 00:09, 17 April 2007 (UTC)

I still don't understand, it looks close to a sphere, it is in orbit a round the sun, and from what I can figure out it has 'cleared it nieghborhood' (Its not like Ploto and Charon). If it is higher mathematics than Algebra I, just say so. Teak the Kiwi 03:07, 17 April 2007 (UTC)

Eris is classified as a dwarf planet - the difference between that definition and that of a true planet is thr third one (above) "cleared the neighborhood". Since Eris has been classified as a dwarf, it must be that it has not cleared it's neighbourhood. SteveBaker 03:43, 17 April 2007 (UTC)

That is indeed the case. It is clearly demonstrated at List of solar system objects by planetary discriminant. The discriminant is used as the measure of clearance. The lowest discriminant for the now-accepted planets is 24,000 (Neptune), whereas that for the minor planets is no higher than 0.33 (Ceres). Eris's discriminant is only 0.10. By this measure, Eris is nowhere near clearing its neighbourhood. JackofOz 03:59, 17 April 2007 (UTC)

The definition is horrible. It was an attempt to avoid having very many new planets and at the same time include no completely arbitrary size restriction. The whole story is an example of the Paradox of the heap, where an essentially fuzzy definition (being large) is made precise. Do you remember the old sience fiction stories about mirror earth? The existence of such an object (there is none, I know, thank you) would make earth a dwarf planet under this definition. A raindrop floating around in free space is a dwarf planet by this definition. It is really unspeakably horrible. —The preceding unsigned comment was added by 84.187.17.11 (talk) 13:06, 17 April 2007 (UTC).

I disagree. A raindrop floating in free space (part of it would vaporize and the rest would solidify pretty quickly, so it would rather be a hailstone) isn't round because of gravity but because of surface tension, therefore it wouldn't be a planet according to the definition. And with a mirror Earth Earth's orbit wouldn't be stable, and I would consider such a planetary system to be still in development - I think the chances are quite high that the two bodies collide within a few million years. Icek 17:31, 17 April 2007 (UTC)

Yeah - there is no way a raindrop can qualify because it can't hold a spherical shape under it's own gravity, it would be completely unable to clear it's neighbourhood. Sure - they become spherical due to surface tension - but that doesn't make them planets. The "spherical under own gravity" requirement effectively puts a minimum size on what qualifies as a planet - so there is an implied lower size limit. But this is all irrelevent in the grand scheme of things - labels like 'planet' are arbitary - there are bound to be corner cases that cause difficulties. We get this kind of issue come up here every day or two on the science desk and the answer is - in truth - "This has nothing whatever to do with science - it's a branch of linguistics." SteveBaker 00:46, 18 April 2007 (UTC)

April 17

Whites of eyes

Is it true that humans are the only animals to have whites eyes (outside of the iris)? zafiroblue05 | Talk 00:04, 17 April 2007 (UTC)

Sclera, the white part of the eye, does not say! I think other animals definitely have a sclera, but I don't know if it's white. I can't get a good image of many animal eyes to check... Nimur 00:27, 17 April 2007 (UTC)

Nope - first pic I found. --Kurt Shaped Box 00:26, 17 April 2007 (UTC)

While many other animals have sclera, the sclera in humans typically take up a much larger portion of the visible eye than in other animals. At least one biologist has suggested that having larger sclera was evolutionarily advantagious to humans as it made emotions easier to read (pretty speculative though). Someguy1221 00:33, 17 April 2007 (UTC)

I don't know about reading emotion - but it does make it a lot easier to see what direction other people are looking. SteveBaker 01:35, 17 April 2007 (UTC)

Every dog I've seen has a white sclera. However the iris and pupil take up almost all the space in the visible eye socket, so you can't see it unless the animal diverts its eyes. [Mαc Δαvιs] ❖ 02:11, 17 April 2007 (UTC)

I have seen dogs, etc. move their eyes just enough so that you can see a little bit like [Mαc Δαvιs] said. Teak the Kiwi 03:09, 17 April 2007 (UTC)

You can see it in this image Image:Staffordshire Bull Terrier - Labrador Cross.JPG. SteveBaker 03:36, 17 April 2007 (UTC)

cute !

What horrible bloodshot eyes, obviously from too much drinking and paranoia. [Mαc Δαvιs] ❖ 17:57, 18 April 2007 (UTC)

Prostate health

How many times per week/day should a man ejaculate to maintain optimum prostate health? —The preceding unsigned comment was added by 88.109.222.205 (talk) 00:09, 17 April 2007 (UTC).

Too much can decrease your overall sperm count. But in all seriousness, you don't need to ejaculate weekly or daily to maintain your prostate. bibliomaniac15 00:36, 17 April 2007 (UTC)

According to a study done by the Cancer Council Victoria in Melbourne, men who ejaculated 5 or more times per week were 30% less likely to develop prostate cancer[3], as it also states at prostate. Somebody said something mean to me several days ago when I said it is unhealthy to never ejaculate in a question about abstaining. Check that one too for some quote and references. [Mαc Δαvιs] ❖ 02:06, 17 April 2007 (UTC)

Inverted glass with water holds a card

If you fill a glass with water, place a card over it and turn it upside-down, you can remove your hand from the card and the card will remain in place. I understand that this has to do with the air pressure below, but

• Is the pressure of the water above the card really less that the pressure of the air below it?
• Is the density less? (obviously not)
• Why does the glass need to be filled with water? Wouldn't it be even easier with air? (obviously not)

Clearly I haven't precisely understood the experiment (you can view a video of it here). Can someone explain it to me a little better (or is there an article on it?). Thanks!

-- Josh, 02:03, 17 April 2007 (UTC)

Uh! I think you may be misunderstanding what is happening. The glass is actually like a gigantic straw. You can drink from the straw because when you remove air from the top, a vacuum is created, and the fluid rushes up to fill that space, right into your mouth. In the glass, if the water (and card) tries to fall out, there is a vacuum of empty space at the top, and that sucks the water back up in again. [Mαc Δαvιs] ❖ 02:10, 17 April 2007 (UTC)

Also need to consider the surface tension of the water. To make it work, may need to have the glass to be within certain limits on the ratio of diameter, water depth, and empty space above the water. DMacks 02:12, 17 April 2007 (UTC)

Can this sort of thing be generalized for all fluids? Or is this a water specialty?--Ķĩřβȳ♥♥♥ŤįɱéØ 02:20, 17 April 2007 (UTC)

Atmoshperic pressure will support a column of 760mm of mercury as in a barometer, or a column of water about 30ft high. The card just allows the air pressure to act evenly over the body of the water with which it is in contact. Otherwise any light disturbance on the water surface would cause the water to pour out.

Fill a tumbler under water and then raise it above the surface. The same effect is seen, but a bit of water sloshing in and out in this case is unimportant-- its not going to destabilise the whole thing.

I presume the narrower the glass tumbler the easier this is to perform as the water cannot move about so much sideways.

Of course in very narrow tubes, the capillary effect takes over.

In regard to vacuums sucking water up a straw, isn't it more accurate to say the pressure of the surrounding water pushes water up the straw because when the person sucks (ie. inhales the air in the straw), there's suddenly a space for the water to go into? JackofOz 03:38, 17 April 2007 (UTC)

Correct. Suction is not an actual force, but more accurately, it's not that the water has someplace to go, but rather that there is no longer anything pushing it back (minor distinction). However, the water is actually pulled up slightly by the walls of the straw, although this effect is primarily observable in narrow tubes (as the unsigned comment above states. Someguy1221 03:48, 17 April 2007 (UTC)

The water serves two functions in the experiment:

• It makes a nominal seal so that the fluid inside the glass can't exchange with the fluid (gas) outside the glass, and

• It makes the experiment much more dramatic.

The glass could be filled with anything that allows the formation of a seal and has a denisty low enough that the atmospheric pressure pressing up on the card bottom can overcome the weight of the stuff inside the glass.

Atlant 12:58, 17 April 2007 (UTC)

If you believe the effect depends only on the sealing you are completely wrong. The pressure of the water is the same as the pressure of the air when you fill it in the glass. If you turn the glass around, the original pressure plus the weight of the water is pushing from above and the same atmospheric pressure is pushing from below and the card will move downward. However: The capillary effect glues the edges of the card to the glass, and the card will bend instead of moving downward. Now the crucial effect comes into play: Water is essentially incompressible. The water will lose its entire internal pressure while extending only by a tiny fraction of its volume. The air pressure continues to push from below and keeps the card from falling. The experiment cannot work with air in the glass, even if you seal the edges with water, because the air will simply have the same pressure as the air outside (It does work with light cards, because of capillary force alone, but you can put small weights on the card in both cases to see a difference).

Did I say that it depends only on sealing? Someone asked why water; I answered that. One of the reasons "why sater" is that water forms an adequate seal (for several reasons) to keep the water from escaping the glass in small runnels acted-on by gravity. If you think that doesn't matter, try doing the experiment with Helium II superfluid instead of water and let me know what happens.

Atlant 17:14, 17 April 2007 (UTC)

You said anything that allows the formation of a seal and that is not to heavy. I don't want to be offensive, but you wrote that just two paragraphs higher. As for Helium, my guess is that the card will fall down. However, my kitchen sink seems to be out of helium today. —The preceding unsigned comment was added by 84.187.32.191 (talk) 20:31, 17 April 2007 (UTC).

And I stand by that statement ("allows the formation of a seal and is not too heavy") and haven't seen anyone disclaim it. I think I'm missing your point. Rather than debate what I said, why don't state your point (again?).

Atlant 13:28, 18 April 2007 (UTC)

Here's how I think about it. (And it's a fun experiment, which you should all try, but don't make the same mistake I did just now, namely holding the inverted glass+card too high above the sink, assuming it'll work the first time, because when the seal fails and the water comes splooshing out all at once, it splashes out of the sink all over your shoes. But I digress.)

If you fill a long, thin tube or pipe with water, and seal it at the top, you will discover that the water trickles out very slowly, if at all. You can describe this in terms of suction or in terms of pressure, but it's also just a question of mass transfer. If the water is going to trickle out of the bottom, it has to be replaced by air. (And, indeed, if the long, thin tube is transparent, and the water is managing to trickle out, you will see bubbles slowly rising, moving opposite the water flow, collecting at the top as the water level lowers.)

There's no magic involved here; we don't have to posit a special force which somehow defies gravity and keeps the water in the tube (or glass). If the tube or glass were filled with clay, or cement, or silly putty, or jell-o, or blackstrap molasses, or tapioca pudding, or ice, or some other solid or very viscous liquid material, we wouldn't be at all surprised if it didn't come out. Is it defying gravity? What's holding it up? Why, we're holding it up: we're holding the tube or glass, and the stuff inside is stuck to the tube or glass, so it doesn't fall down. Simple as that.

Well, almost. Clearly there's a difference between solid materials like clay and cement and jell-o and ice, and viscous materials like silly putty and molasses, and liquids like water. Also clearly there's some kind of a difference between a thin tube or pipe, versus a wider-mouthed glass or jar. But where's the crossover point between a thin tube or a thick liquid where the effect obviously works, versus a thinner liquid or a wider vessel where we would expect the liquid to run out? Clearly there's a continuum.

And there's one more factor to consider, which several others have noted: surface tension. Water tends to stick to itself, and to the walls of the vessel it's in. Among other things, this makes it even more difficult for (say) those bubbles to rise, moving opposite the water flow, in that long, thin, transparent tube I was hypothesizing. And the surface tension also plays a role at the bottom of the column of water, at the bottom end of the tube or glass you're expecting it to flow down out of. Obviously, you would think, all the dumb water has to do is pick a side, with the water flowing down out of one side, and the air rising up the other. But the water is too stupid to make this choice. Every spot on the bottom surface of the water wants to flow down and out just as much, and because all of it is trying, none of it can. It's a lot like commuters trying to exit a subway car at a crowded station, when there are so many people waiting on the platform impatient to board that the disembarking passengers can't get past them.

So where does the card come in? We may believe that water can stay "upside down" in a thin tube that's closed at the top, as long as the tube is sufficiently long and thin (whatever that means). But clearly a glass is not long and thin enough, as we can easily prove by holding one upside down while it's full of water and noticing that the water does come rushing out.

As I think of it, the card acts as a surface tension enhancer. Since the card is relatively inflexible (even when wet), it reinforces and enables that simultaneous impatience of every point along the bottom surface of the water to be falling out at once. The water can't bulge downward (beginning to flow) at one point, while simultaneously bulging upward (about to form a rising bubble) at another, because the dumb inflexible nonporous card is in the way.

So what holds the card up? Well, it doesn't weigh very much, so the surface tension of the water does the trick. We don't normally think of water as an adhesive, but surface tension definitely makes it a weak one, as you can realize if you think about one of the ways you pick up a tiny object, too little to grasp between your fingers: just lick one finger and touch, and the object sticks to your finger.

(Disclaimer: this has been a speculative, armchair explanation, with no actual scientific sources cited or even consulted. Apologies if anyone is offended by my lack of rigor.) —Steve Summit (talk) 02:47, 18 April 2007 (UTC)

emfs and internal resistance

If I had a circuit consisting of a battery with internal resistance that is hooked up to a variable resistor, and I know the terminal voltage of the battery and the current in the wire at a set resistance, would it be possible to determine the emf of the battery?

Thanks --K=.5mv^2 02:08, 17 April 2007 (UTC)

The emf of the battery is just the open circuit voltage of the battery as measured with a voltmeter. You dont need any other stuff. However, if you are not allowed to open circuit the battery, see Internal resistance #Batteries. (replacing the apparently useful comment of a banned user Rockpocket 20:59, 17 April 2007 (UTC))

Just to put a finer point on Rockpocket's answer, the reason you can (usually) accurately measure the EMF with just an ordinary voltmeter is that voltmeters normally have an input resistance that is many orders of magnitude larger than the internal resistance of the battery. If that isn't the case for the specific voltage source you're trying to measure, you'll either need to calculate (as you suggested in the question) or use a different instrument such as an electrometer.

Atlant 13:01, 17 April 2007 (UTC)

Knife into head

I was wondering how easy or hard it is to stab somebody with a sharp knife, and penetrating their head. If you wanted to kill somebody and you had snuck up behind them, could you easily just smash the knife blade through their skull or not? I don't think the bone could be strong enough, because of the force of impact and concentration (knife point) is fairly unoptimal for the target. [Mαc Δαvιs] ❖ 03:09, 17 April 2007 (UTC)

I would expect it would depend on where you hit the skull. If you hit at a weak spot, straight on, it would go in. If you hit at a strong point, at a slight angle, it would be deflected (but still cut the scalp up). Also, I expect a human cadaver would be needed for the experiment, as animal skulls of the same size tend to be much tougher. StuRat 04:25, 17 April 2007 (UTC)

If they were standing up, I don't think the knife will go through, but you'll rip their scalp and push their head forward. --Ķĩřβȳ♥♥♥ŤįɱéØ 04:28, 17 April 2007 (UTC)

Ah, so then it would be better if you hit the rest of their body? Where would be best anyway? [Mαc Δαvιs] ❖ 05:33, 17 April 2007 (UTC)

---

Wikipedia does not provide Criminal Advice. We do not provide advice on how to kill a person most effectively, how to infiltrate your apartment while being surrounded by SWAT teams, or how to make meth in your kitchen. Ask a professional criminal instead.

---

All jokes aside though, I guess somewhere near major arteries would be a good spot. --antilived^{T | C | G} 05:53, 17 April 2007 (UTC)

Some martial arts defend against attacks of the knife held with the ice-pick grip and attacks to the head (or other parts) with said knife. BTW, take a look at where the Frontal bone and Parietal bone join... it is a spot of weakness. I suspect it is possible, if done at the right angle with the right instrument. If I tell you any more they would send someone to kill me ;-) Root⁴(one) 06:38, 17 April 2007 (UTC)

I was told by a police officer that cutting the groin is probably the easiest way to kill someone with a single knife cut - obviously due to outbleeding. 213.48.15.234 07:33, 17 April 2007 (UTC)

"If in doubt, aim for the groin." - effective on most men --antilived^{T | C | G} 09:37, 17 April 2007 (UTC)

Oh yes, you can't underestimate the "OH MY GOD YOU JUST STABBED MY GROIN" effect. Why isn't there an article on that? 213.48.15.234 11:18, 17 April 2007 (UTC)

Probably women. [Mαc Δαvιs] ❖ 18:36, 17 April 2007 (UTC)

Professionals in this business have been called "cutthroats" for centuries, I am inclined to believe that this is no coincidence. —The preceding unsigned comment was added by 84.187.17.11 (talk) 12:49, 17 April 2007 (UTC).

I suggest you Nuke them... using micro waves or something. might not be as fast but it looks alot cooler then stabbing... and how can we all forget the neck?? slashing the neck the only one that mentioned it was mr 84 ^^^. User:Maverick423 If It Looks Good Nuke It 13:25, 17 April 2007 (UTC)

No, actually it wouldn't look that cool. They would feel burns underneath their clothing. Have you checked microwave gun? [Mαc Δαvιs] ❖ 18:36, 17 April 2007 (UTC)

Guess not, because that's not an article yet. http://powerlabs.org/uwavexp.htm is the first thing that comes to mind. He's starting a page on the new one soon. [Mαc Δαvιs] ❖ 18:38, 17 April 2007 (UTC)

Done!!!! still working on it though. microwave gun User:Maverick423 If It Looks Good Nuke It 16:24, 18 April 2007 (UTC)

Yep its been talked about before maybe it deserves its own article =P if you recall last time i tried to burn stuff outside using a microwave which didnt work =( the chips and all that stuff burnt up before it did any damage. anyways a knife to the head is kinda primitive dont you think i mean with the tech we got now adays we can imaging some pretty fun (for the person using it) ideas on how to umm end a life. User:Maverick423 If It Looks Good Nuke It 21:34, 17 April 2007 (UTC)

I think the best thing for the Microwave Gun is a redirect to Active Denial System. I have mentioned this at the Talk Page. Nimur 17:10, 18 April 2007 (UTC)

well i found a place where a guy was talking about other potental uses for this kind of gun. it included this being used as a faster way of melting glue like a glue gun. im not sure its a relyable source but its a pretty good idea. who knows it might be a future device one day. well enough chit chat heres the link http://www.whynot.net/ideas/1085 u tell me what u think its on my talk page ok. User:Maverick423 If It Looks Good Nuke It 20:37, 18 April 2007 (UTC)

I've hacked up a lot of chickens in my day, and even their puny bones take a good whack with a cleaver to get through. A human skull is probably enough trouble that you should probably just let go of your anger, and remember that the best revenge is living well. --TotoBaggins 13:34, 18 April 2007 (UTC)

Prevalence of freezing temperatures on Earth

Hi

I'm looking for some numbers for an introduction about how common temperatures below OC are on Earth. I'd love to be able to say "90% of the Earth's terrestrial environment experiences temperatures lower than 0C each year" or something like that. Does anyone have any insights and/or references about this? Thanks heaps for your help!

Aaadddaaammm 03:10, 17 April 2007 (UTC)

That's an interesting question. I've never seen that information presented that way. But if you look up information about climate zones, such as the Köppen climate classification, you can find maps showing how much of the Earth's land area has each major type of climate, and you can find how the climate types are defined. (And a Google search on things like "climate" and "map" will take you to more pages.) That'll take you part way toward an answer, although getting from a map to an accurate percentage of areas won't be easy. (Ocean maps with climatic information are harder to find; you may have to settle for land only.) --Anonymous, April 17, 2007, 03:45 (UTC).

Thanks for your reply - I did consider this kind of approach, but decided it was a bit too rough for my report. I really just want a throw-away statistic to get the paragraph started, and don't want to have to justify my calculations too much. Does anyone else have anything to offer on this question? Aaadddaaammm 01:17, 18 April 2007 (UTC)

CMOS and CCD image sensor comparison

If CCD is better than CMOS sensor, then why almost all professional SLR digital camera use CMOS as their sensor? roscoe_x 06:10, 17 April 2007 (UTC)

From Charge-coupled device, "Since a very-high-resolution CCD chip is very expensive as of 2005, a 3CCD high-resolution still camera would be beyond the price range even of many professional photographers." --Wirbelwindヴィルヴェルヴィント (talk) 06:28, 17 April 2007 (UTC)

Just backing up what Wirbel said, CCDs are not cheap! 213.48.15.234 07:34, 17 April 2007 (UTC)

Then would it mean Canon Ixus is better than Canon EOS? If not, what make the EOS better? roscoe_x 08:21, 17 April 2007 (UTC)

Because the sensor is much, much, much, much bigger and hence able to receive more light and hence higher SNR ratio and hence less noise and hence less detail diminishing noise reduction. Also, not almost all professional DSLR's are CMOS based, you forgot all the Nikon ones (among others). --antilived^{T | C | G} 09:35, 17 April 2007 (UTC)

spring !

im searching for a way to figure out the optimal proportion for a helical spring to propulse a person (lets say 150 lb)kind of like a trampoline and how many of those i would need

the thing is i want to figure out what the smalest amount i could use and still have a smooth unwinding and not take more than about 1 1/2" for the spring to be able to push back the weight

i also need to find out wich material would be good

clockwork fromage —The preceding unsigned comment was added by 216.113.96.143 (talk) 06:20, 17 April 2007 (UTC).

The only thing that immediately springs (sorry NPI) to mind is that of a recoil spring in a (very) large field gun

/cannon. —The preceding unsigned comment was added by 88.111.93.83 (talk) 22:21, 17 April 2007 (UTC).

There are equations that can help predict the behavior of a spring, including Hooke's Law. There are also calculators that can help you play what-if. As you can see, there are more variables than you have specified, so it's hard to give a definite answer without knowing more about the application you have in mind. How big around can the spring be? With what force are you trying to propel this person? Does the person's weight compress the spring, or does something else? Are you going for distance? How does balance factor in?

Also, before you go propelling any human beings, please think about safety. Human beings who are propelled can fall on their faces, twist their ankles, and plenty of other things. --Dvortygirl 03:32, 18 April 2007 (UTC)

See also Spring Shoes – b_jonas 20:59, 18 April 2007 (UTC)

Genetics of ear-wiggling?

Some time after I wrote this article, others added these unreferenced claims:

1. "The general consensus is that the ability to wiggle your ears is thanks to one gene, which has been turned off for some people."
2. "Approximately twice as many men than women can wiggle their ears."

While I can attempt to describe the learning process from experience, I have no idea where I might verify or discredit these claims. Neither Auricularis nor Ear discusses these details of human ear motion. In the name of accuracy, thanks in advance for any direction you can offer. --Dvortygirl 07:19, 17 April 2007 (UTC)

Many of the facial muscles not normally accessible as voluntary can be learned. Ears are the same way, but not sure about the gene thing. [Mαc Δαvιs] ❖ 18:34, 17 April 2007 (UTC)

Effectiveness of 'low blow' against bear attack?

I reading one of those 'SAS survival guide' books a few years ago in which it was stated that as a last resort when being attacked by a bear, one should attempt to strike it repeatedly in the groin/testicular area. Just as a matter of interest - has anyone ever heard of anyone surviving a bear attack by kicking their assailant in the nads? This is the only reference I could find to someone attempting a groin attack on a bear - it didn't end well. --Kurt Shaped Box 11:39, 17 April 2007 (UTC)

Different strokes for different bears. It's not something with a high success rate. --Zeizmic 12:04, 17 April 2007 (UTC)

Have you seen the John West salmon commercial? - that seems to back it up quite well. Capuchin 12:39, 17 April 2007 (UTC)

LOL! I've been trying to remember what that advert was selling for ages now. Great to see it again. Thanks. :) It was a memory of that ad that made me start the original 'man vs. bear' thread some time back (which spawned several 'x vs. y in a fight to the death' imitators). --Kurt Shaped Box 18:39, 17 April 2007 (UTC)

Lets not forget that that commercial had a human wearing a bear suit. User:Maverick423 If It Looks Good Nuke It 13:36, 17 April 2007 (UTC)

But what if the bear likes it ? StuRat 17:05, 17 April 2007 (UTC)

You'll probably die in an even more horrible, lingering way than if the bear had just crushed your skull and gotten it over with? --Kurt Shaped Box 18:40, 17 April 2007 (UTC)

For some reason I don't think that precision strikes against large beasts would be effective, because when a 500 lb. behemoth of muscle and teeth is bearing down on you, you're only going to feel terror. Vranak

Bigger beast, bigger testicles to kick? --Kurt Shaped Box 22:44, 17 April 2007 (UTC)

I don't think testicles on animals are usually in a place you can readily kick, so it hardly matters. Vranak

Does everything sink when it goes below a certain depth in the ocean?

A log floats. If I were to drag it deep enough under water, would the water pressure from above force the log down to the bottom of the ocean, or would the fact that the cellulose molecules would always be slightly less dense than the surrounding water molecules mean that the log would always rise to the surface? Is there some point of neutrality at a certain depth that would hold the log stationary until Brownian motion bumped it either up or down enough? — Jonathan Kovaciny (talk|contribs) 13:42, 17 April 2007 (UTC)

The pressure at depth would have no directional vector (so would not force a log down/up or any direction) although it might cause the cells in the log to become more compressed and thus the log to be more dense. If the log became more dense than the surrounding water it would sink. Objects less dense than water will always float.David D. (Talk) 14:54, 17 April 2007 (UTC)

The same would happen to the water though, as the pressure (and depth) increase, the density will as well, so the water may become more dense than the object. In this situation, there would be a depth where the object becomes neutrally buoyant, and it would remain there. anonymous6494 16:35, 17 April 2007 (UTC)

Water will not compress as easily as wood (which has a lot of air space in the dead cell chambers) so the density of water will not increase as much as wood due to depth, if at all. Changes in water density are primarily due to temp and composition (salt and nutrients). There is a good figure here that confirms the density does not change significantly with depth. http://www.windows.ucar.edu/tour/link=/earth/Water/density.html&edu=high David D. (Talk) 20:09, 17 April 2007 (UTC)

No, not everything sinks when it gets to a certain depth. Some things always float (Styrofoam), some things always sink (lead cannonballs), some things will find a natural level within the water (some plants), and some will sink once they reach a certain depth (a submarine that implodes at that depth). StuRat 17:02, 17 April 2007 (UTC)

In the case of the submarine, it doesn't necessarily sink. At surface, the submarine consists of the metal hull and the air inside. When it implodes, the air part quickly rises and the metal part quickly sinks. So, to be annoyingly technical, the submarine separates into the parts that float and the parts that sink. --Kainaw ^(talk) 18:50, 17 April 2007 (UTC)

Or, if the submarine is at sufficient depth and the air content of the water is low enough, the air might dissolve into the water before reaching the surface. StuRat 19:21, 17 April 2007 (UTC)

I dont think things usually find a "natural level". If something is even a little compressable, and especially if it has gas pockets, then neutral buoyancy is an unstable equilibriam. Nearly everything ends up either floating or sinking - unconscious divers for example.Polypipe Wrangler 21:56, 17 April 2007 (UTC)

I'll take this opportunity to recommend again the excellent book, "The Flying Circus of Physics", which addresses questions like this in spades. One item is on the topic of why a crate will sometimes float face-up vs. corner-up in the water. --TotoBaggins 00:01, 18 April 2007 (UTC)

Most buoyant materials are relatively compressible. Water is relatively incompressible. So, yes, most things lose buoyancy as they sink, due to compression. Scuba divers are intimately familiar with this: as you descend, your wetsuit compresses and becomes less buoyant, and you have to continually add air to your buoyancy compensator to, er, compensate. (The compressed wetsuit also doesn't insulate as well, which sucks, because the water generally gets colder as you get deeper, too.)

Deep-rated submersible vehicles use special, noncompressible buoyancy materials, such as syntactic foam.

In answer to the original question, I suspect that most materials would sink past a certain depth, not because the extreme pressure "forces them down", but because the extreme pressure would eventually compress virtually any material below its buoyancy point. (There are exceptions, though they are few: deep-rated submarine pressure vessels and syntactic foam are two.) —Steve Summit (talk) 02:09, 18 April 2007 (UTC)

The question is not whether the material is compressible, but whether it's more or less compressible than water. If you have a chunk of something that's slightly more dense than water at atmospheric pressure, but less compressible than water, then it is possible that it would be negative buoyant at the surface, but that when it sinks to a certain depth, the water would have become dense enough to make it neutrally buoyant, and there it would stop. I think there are lots of solids that are less compressible than water. The rare property is going to be that the substance is more dense than water at 1 atmosphere, but by such a slight margin that it's less dense than water at the bottom of the ocean. --Trovatore 02:20, 18 April 2007 (UTC)

Good point. And this reminds me of Galileo's thermometer -- I wonder how applicable that is to this discussion? —Steve Summit (talk) 03:27, 18 April 2007 (UTC)

Collegues, pleaselook at the bathyscape article. A bathyscape consists of a tank of (relatively) incompressible oil tank, controllable ballast, and a heaviar-than water payload. If a substance is (relatively) incompressible, its tendancy to sink will not increase with depth. -Arch dude 03:29, 18 April 2007 (UTC)

No one seems to have mentioned Archimedes principle yet. —The preceding unsigned comment was added by 88.109.207.222 (talk) 10:08, 18 April 2007 (UTC).

At what depth will the pressure cause a bubble of air to sink instead of rise? How would i go about calculating this? User:andbir

microbiology

Why is it important to differentiate glucose nonfermenters from Enterobacteriaceae? —The preceding unsigned comment was added by 209.213.220.109 (talk) 16:08, 17 April 2007 (UTC).

My faith in science would be seriously shaken if I thought the future microbiologists of the world were getting their homework done by a bunch of Internet dweebs. --TotoBaggins 23:57, 17 April 2007 (UTC)

do fish like rain

I am curious to know if fish like rain, or how they react to rain. —The preceding unsigned comment was added by 69.236.22.85 (talk) 17:22, 17 April 2007 (UTC).

Well, it is rather obvious that fish don't mind getting wet. However, the raid has different effects on them. It creates a darker atmosphere when it couds over - making it harder to see (though they can smell just fine). If the water is warm, a thin cool layer of water floats on top of the warm water for a bit - most fish don't care for that. They stay in the warmer water. If it is cold, a thin warm layer of water floats on top of the cold water for a bit, which draws fish closer to the surface. Heavy rains will cause water levels to rise. Fish tend to rise with a rise in water levels. Then, if it is a river, the current picks up. The fish have to swim against it or get swept downstream. That's a just a few things to think about. There are surely a lot more - such as the effects of acid rain on fish. --Kainaw ^(talk) 18:47, 17 April 2007 (UTC)

I could also imagine the the action of raindrops impacting on water would increase the oxygen content a little bit.-Czmtzc 18:54, 17 April 2007 (UTC)

In brackish waters, as in the Florida Everglades, rain tends to decrease the salt content in the water (with high tides increasing it again). StuRat 19:17, 17 April 2007 (UTC)

Rain would make lots of noise too, making it harder to hear other things.Polypipe Wrangler 21:59, 17 April 2007 (UTC)

Hypoxic tents

I searched a bit on these tents but they are pretty much too expensive for a poor student like myself, are there any good low budget methods to have similar results?Bastard Soap 17:47, 17 April 2007 (UTC)

You could put together the component parts and it would be cheaper, but still expensive. You need an Oxygen tank, a Nitrogen tank, an air quality regulation system, and a semi air tight tent and constant refills for the gas tanks. Personally I would not want to use an amateur Hypoxic tent because I would not trust the oxygen concentration. What if your Oxygen tank ran out before your Nitrogen tank? You may never wake up. Czmtzc 18:02, 17 April 2007 (UTC)

Also, in the presence of pure oxygen, many normally nonflammable things become flammable, like human flesh. So, only those with proper training should handle oxygen tanks. StuRat 19:13, 17 April 2007 (UTC)

Tapping on the fishtank...

I used to have a terrible habit of tapping on the glass of a fishtank whenever I happened to be passing one (I guess to make the fish look at me - which never worked anyway). I've been told off on more than one occasion for doing so and told to stop as "you'll kill the fish". Why does tapping on the glass harm the fish? --Kurt Shaped Box 18:55, 17 April 2007 (UTC)

The thundering booms from your taps cause stress which reduce immunity levels which leads to disease and eventually death. --Kainaw ^(talk) 18:58, 17 April 2007 (UTC)

Can you give a source for that? It sounds like an urban legend to me. I know that there have been stress related diseases with pigs in very bad living conditions, but fish? Just from hearing sudden loud sounds?

(And pigs eat their own young if the conditions are stressful)! Nimur 17:18, 18 April 2007 (UTC)

They can sense that you're a reincarnated seagull? Clarityfiend 23:06, 17 April 2007 (UTC)

Sometimes I do feel like I was a seagull in a past life. Did I ever mention that I can copy gull noises so well that the gulls will sometimes respond to them? ;) btw, the response you replied to wasn't mine... --Kurt Shaped Box 23:10, 17 April 2007 (UTC)

Asymptomatic carriers

Hello, me again. I'd like a bit more information on disease carriers; specifically, whether an offspring of someone with a recessive disorder will 'carry on' being a carrier of the disorder through three more generations. Lady BlahDeBlah 20:28, 17 April 2007 (UTC)

If this is a disease that's inherited through simple mendellian genetics, the child of a carrier will have a one half chance of becoming a carrier himself. This can continue without end through any number of generations. Someguy1221 20:02, 17 April 2007 (UTC)

So...a carrier who marries a normal person and has a child, that child will still/could be a carrier himself, and so on. Right? The disease I'm particularly thinking of, if it'll help, is what I got here last time I asked a question: Leber's congenital amaurosis. Lady BlahDeBlah 20:28, 17 April 2007 (UTC)

Precisely. The child of a carrier and a noncarrier has a 50% chance of being a carrier, 50% chance of being a noncarrier. And any children who are carriers will have their own children follow the same probability. If a carrier were to marry another carrier, the children have a 50% chance of being carriers, 25% chance of being normal, and a 25% chance of inheritting the full blown disease. How long it's been since someone actually had the disease is irrelevent, and this is how you get carriers who have no idea that they even might be carriers. Leber's congenital amaurosis appears to be inherited in this fashion. Someguy1221 20:42, 17 April 2007 (UTC)

Just to clarify, there are actually as many as six genetically distinct forms of Leber's congenital amaurosis (caused by mutation in different genes, including retinal guanylate cyclase and the RPE65 gene). This leads to the slightly odd situation where two parents who appear to suffer from the same genetic disease, can produce completely unaffected children. See PMID 12015276 for details. Rockpocket 21:14, 17 April 2007 (UTC)

Colleagues, we are conflating Genetic disease with communicatable disease. A genetic disease is communicated via sperm or egg. The offspring will inherit the disease genetically from the father or mother via nuclear DNA, if the disease is "(nuclear) genetic", and from the mother, if the disease is mitochondlear. Under extremely rare conditions, the offspring might inherit a mitochondlear disease from the male parent. The offspring can become infected with a bacterial,viral, or fungal disease from the mother, completely independently from the act of conception: the mother and offspring are in intimate contact, permitting a pathogen to move from mother to offspring. In species where father and offspriong are in intimate contact, a pathogen can move from father to offspring. -Arch dude 02:34, 18 April 2007 (UTC)

I don't believe the person posing the question was referring of a communicable disease, due both to their use to the term recessive disorder and their clarification they are interested in Leber's congenital amaurosis. Rockpocket 03:19, 18 April 2007 (UTC)

Uh, yeah, I don't think my genetics Babelfish is working, Arch dude. Rockpocket's right, I was only referring to a specific disease. Lady BlahDeBlah 18:57, 18 April 2007 (UTC)

And genetic diseases are not "communicable". "Communicable" has a specific meaning in medicine, and it doesn't cover genetic transmission. - Nunh-huh 02:22, 19 April 2007 (UTC)

v = frequncy  ?

I was taught that "v" stands for frequency, measured in hertz. How come it's not in the article "v" ? --24.76.228.161 22:19, 17 April 2007 (UTC)

No its not 'v', its the greek letter 'ν' (nu) which admittedly looks a bit like a 'v' but isnt! For instance E=hν. The photoelectric equation. —The preceding unsigned comment was added by 88.111.93.83 (talk) 22:26, 17 April 2007 (UTC).

The greek letter nu (ν) is often confused for vee (v), so many texts choose to represent frequency by the letter "f" to avoid mistaking it for velocity or voltage (as velocity and voltage are typically represented by v and V respectively). Someguy1221 22:29, 17 April 2007 (UTC)

In Arial the characters are identical, unfortunately. The relevant link is Nu (letter). --24.147.86.187 23:38, 17 April 2007 (UTC)

I was wondering why it looked different when I was editing it but then it looked identical here...Someguy1221 00:00, 18 April 2007 (UTC)

Oh, that explains it all...thanks. --24.76.228.161 00:53, 18 April 2007 (UTC)

This is why I prefer to write E = ℏw ... er... make that E = ℏω. -- mattb 06:02, 18 April 2007 (UTC)

Dust Settles... Or Does It?

If you were to completely isolate your bedroom (airtight, no vibration, no light etc.), would the initial airborne dust particles eventually all settled down on something (bed, desk, chairs, floor), or would some remain airborne infinitely?--JLdesAlpins 23:25, 17 April 2007 (UTC)

If they are heavier than air, they should settle, yes. --24.147.86.187 23:39, 17 April 2007 (UTC)

Perhaps Brownian motion would play a role? --TotoBaggins 23:58, 17 April 2007 (UTC)

I suppose it's theoretically possible for brownian motion to keep particles airborne indefinitely - but it's really unlikely. We know that typical house-dust settles because clean, horizontal surfaces end up covered in dust - which must have settled out of the air. So 'normal' house dust would definitely settle out eventually. SteveBaker 23:59, 17 April 2007 (UTC)

I guess it depends on your definition of "dust". Presumably a particle of a similar size to the air molecules would easily stay airborne forever, and dust bunnies fall quickly, and somewhere in between something might stay aloft for a good while. --TotoBaggins 00:06, 18 April 2007 (UTC)

My sense is no, that microfine dust particles would stay aloft indefinitely, as minor variations in heat distribution in the structure of the house itself, from the sun and winds moving around outside, will keep the air moving, just a little. Vranak

Interestingly, your body heat is easily enough to stir up dust and pollution, so if you have the right imaging techniques, you can 'see' your own plume of circulating air stirring up the dust, even if you are sitting still. Carcharoth 10:41, 18 April 2007 (UTC)

An airtight room or chamber could still have temperature differentials, which would cause convestion. The outside temperature might vary 20 degrees F (11 deg C) each day. The current of air along the walls and especially along the window panes could probably stir up smaller dust particles. Edison 13:46, 18 April 2007 (UTC)

Furthermore wouldn't dust particles -- those that come from skin and hair anyway -- eventually decay down to such a small level that they would become a part of the air itself? That's what it smells like anyway, when I enter a house that's been sitting vacant for a while. The air inside definitely isn't clean and fresh, with all the dust settled out. Vranak

April 18

Hurricane names

Who gets the job of naming hurricanes? Do they have someone standing around with a book of baby names and write down random ones? bibliomaniac15 00:29, 18 April 2007 (UTC)

Tropical cyclone naming tells all. Rockpocket 01:01, 18 April 2007 (UTC)

Change in velocities of orbits

"In the elliptical orbit, the center of mass of the orbiting-orbited system will sit at one focus of both orbits, with nothing present at the other focus. As a planet approaches periapsis, the planet will increase in velocity. As a planet approaches apoapsis, the planet will decrease in velocity."

The above is taken directly from the Wikipedia article on orbits. I was wondering why the planet increases in velocity as it approaches periapsis and why it decreases in velocity as it approaces apoapsis. Thanks a lot 208.96.96.207 00:41, 18 April 2007 (UTC)

In a circular orbit, the force of gravity on a planet is always facing perpendicular to the direction of motion of the planet, and thus gravity cannot do work on the planet, and cannot change its velocity speed. In an elliptical orbit, however, on the approach to periapsis the force of gravity has a component in the direction of the planet's motion, and thus the planet speeds up. And on the way to apoasis, the force has a component opposite the planet's direction of motion, so it slows down. You could also interperet the change in velocity as a change in kinetic energy to exactly cancel the change in gravitational potential energy as the planet's distance from its star changes. You could also interperet it the correct way, with general relativity, but that would be nasty and unnecessary. Someguy1221 00:53, 18 April 2007 (UTC)

In a circular orbit, the force of gravity on a planet is always facing perpendicular to the direction of motion of the planet, and thus gravity cannot do work on the planet, and cannot change its velocity.

This is bullshit! Velocity is a vector and if gravity cannot change the velocity of the planet then the planet would move in a straight line and the planet would not be in a circular orbit. Obviously gravity can change the velocity of the planet. 202.168.50.40 01:11, 18 April 2007 (UTC)

Calm down, corrected now. Someguy1221 01:13, 18 April 2007 (UTC)

Goodness - that was a bit uncourteous. --bmk

Although the distinction between "speed" (a scalar) and "velocity" (a vector) is always made in physics and is a useful one when talking about these concepts, it mostly isn't made in other fields. In particular, people involved with space travel tend to say "velocity" even when they mean speed: for example, they speak of escape velocity rather than "escape speed", even though escaping depends only on kinetic energy and therefore only on speed. (Okay, speed and not being on a collision course.) --Anonymous, April 18, 2007, 08:40 (UTC).

Another good way to think about it is that the satellite's angular momentum is constant, so a shorter radius implies a faster velocity and vice versa. anonymous6494 16:17, 18 April 2007 (UTC)

which paper towel are strongest?

68.96.105.152 02:09, 18 April 2007 (UTC)

I would guess Bounty as they seem to be obsessed with proving this, but it is probably the only good thing about them. I think this might count as advertising though. You should test it yourself to make sure.

Self-testing is good, because that will let you narrow down the possibilities for what constitutes strongest. Does that mean "most weight supported" or "most scrubs before ripping"? Tearing in the plane or against it? Wet or dry? And so forth.... — Lomn 15:41, 18 April 2007 (UTC)

Chinese to English Geology Dictionary

Dear Wikipedians:

Does anyone know where I might find a good online Chinese to English geology dictionary or translator?

Thanks,

70.53.61.246 04:10, 18 April 2007 (UTC)

"Perfect" insulation

Let's say I have a big hollow ball made of some magnetic material or other. The shell of this ball is quite thick, and is completely airtight. Inside the ball is just plain old room temperature air from my garage. Now lets say I enclose this ball inside another ball in such a way that the inner ball is suspended by magnets, and I've completely evacuated the air from the outer ball. (I now have a ball floating inside a vacuum.) Just for good measure, I cover the outer ball with a mirror surface. Next, having nothing better to do with my money, I ship my ball down to Antarctica and drop it (gently) on the ice. Will the temperature of the inside ball ever drop? — Jonathan Kovaciny (talk|contribs) 05:45, 18 April 2007 (UTC)

Yes, because:

1) You can never completely remove all the air, so some conduction and convection will occur.

2) No mirror reflects all radiation, so some heat will be transferred by radiation, as well.

StuRat 05:54, 18 April 2007 (UTC)

This is just a variant of the perpetual motion machine. Perfect machines only exist in *expletive deleted* minds. Vranak

Even if you assume that you have a perfect vacuum, heat can still be lost through radiation instead of the normal heat transfer. And when you have two metal spheres like that, I can't help but think there's some sort of surface charge effect that would occur that might change the temperature over a long period of time, but I'm not sure if that'd happen. --Wirbelwindヴィルヴェルヴィント (talk) 06:18, 18 April 2007 (UTC)

I protest - this has nothing to do with perpetual motion whatsoever. This is a thermodynamic question, really. See blackbody radiation - if your outer shell is at a different temperature than the inner shell, the two will inevitably communicate energy via the radiation field between the shells, which will always exist. Entropy will increase, and your system will equilibrate! --bmk

It's related to the perpetual motion machine in that the idea is to create conditions that are unchanging. Which is a pipe dream. Vranak

I see that I just repeated most of Wirbelwind's comments - sorry! --bmk

No problem. I wanted a confirmation that I didn't make something up anyways =P --Wirbelwindヴィルヴェルヴィント (talk) 01:40, 19 April 2007 (UTC)

What planet is this?

Unknown Planet

I took this image in southern Uganda, looking west, north-west just after sunset (~8:00pm local time). I think that the cluster of stars just below the planet are the Seven Sisters (of Subaru fame). Also, Orion is just out of frame in the far upper left. I was a degree or two south of the equator. Thanks. --Cody.Pope 07:01, 18 April 2007 (UTC)

By using this neat online sky simulator and entering approximate Ugandan coordinates (0 N 33 E) and your specified time (17:00 UTC) and direction (azimuth 280), I determined that your planet is Venus. --bmk

BTW I doublechecked, and Orion is indeed up and to the left in the sky. --bmk

Genius! I knew there were tones of programs and scripts out there for this, but I has having trouble finding one. Also, this too confirms that my star cluster is indeed Pleiades. --Cody.Pope 08:07, 18 April 2007 (UTC)

Whenever you see a bright planet in the western sky shortly after sunset (or in the eastern sky around dawn), it's almost certainly Venus, which is the brightest object in the sky (after the moon) and never very far from the sun.--Shantavira 08:16, 18 April 2007 (UTC)

Genetic Tests

You sometimes hear of surveys about the genetic make-up of an area (like proving there's lots of Celtic genes in England for example), how would you get one of these tests for yourself to trace your ancestry? And what exactly can they test, is it only the direct male or female line?137.138.46.155 07:18, 18 April 2007 (UTC)

National Geographic offers a home kit through their website. They track only your paternal (if you're a male) or maternal line (via Y-chromosome micro-satellites or mitochondrial DNA, respectively). Your lineage would then go into their database, though. You could find out from whereabouts your line came. I believe the kit cost 100USD. Do a search for "genealogy project" on their website. --Cody.Pope 07:27, 18 April 2007 (UTC)

You should take a look at Genealogical DNA test. National Geographic tracks fewer markers than most commercial tests. To find actual links to commercial labs, see Genetic_genealogy. If you want advice or a personal recommendation on testing, drop me a note on my talk page. - Nunh-huh 02:18, 19 April 2007 (UTC)

Thanks, I was curious really, don't think it's worth paying out till I'm a bit richer, or the tests get better, as I already know my ancestry is North European.137.138.46.155 07:19, 19 April 2007 (UTC)

Is there a lot of vegetation in the South of China?

I saw in a satellite map a representation of methane emissions, most of the "methane clouds" were caused by zones with heavy vegetation, such as in equatorial areas. Despite that, the biggest one was allocated in southern China, in a circle-like area. My question is: Is there such a huge amount of vegetation or are the Chinese just producing a "special" kind of pollution there? Thanks. --Taraborn 10:06, 18 April 2007 (UTC)

Please show us the map,'South China'is too genernal.I can't give a nice prediction without enough info.Anyway,as I know,South China is one of the relatively developed area of China.The presence of heavy vegetation is less likely to appear in such area.--lowerlowerhk 21:06, 18 April 2007 (UTC)

Was it this one [4] ? -Haikon 17:43, 18 April 2007 (UTC)

Yes, that's exactly the map I saw :P --Taraborn 19:06, 18 April 2007 (UTC)

And it's mountainous!JoshHolloway 17:47, 18 April 2007 (UTC)

This map [5] shows "natural primary vegetation cover". It might also help to look at List of countries by population density. -Haikon 17:53, 18 April 2007 (UTC)

There were a lot of trees around that area a while ago, and mst of them are likely to still be there. I think I read somewhere that a lot of methane is produced by farm animals, especially cows. Which is why there is so much over India.

Also, aren't a billion people going to produce a fair amount of methane ? Perhaps to save the planet we should supply free Beano to the Chinese. :-) StuRat 23:15, 18 April 2007 (UTC)

Looks like it corresponds with population density pretty well, [6], with the strongest methane area over the Yellow River plain, China's "breadbasket", if I'm not mistaken. Pfly 02:31, 19 April 2007 (UTC)

Vitamin B - Thiamin as a mosquito repellant

Hi

I'm writing to you from South Africa and currently in hospital with malaria. My question however deals with thiamin as a bug repellent.

I recently saw an advert for a bugpatch that claims to allow small amounts of thiamin (vitamin B1) into the skin which apparently keeps mosquito's at bay? Wikipedia explains what Thiamin is, its chemical constitution, etc, but no mention is made of its mosquito or bug repelling qualities. Could anyone perhaps tell me:

1. If Thiamin is an effective repellant; 2. If yes, why this is so?; 3. if one cannot get hold of a patch etc, would simply ingesting thiamin (e.g. vitamin B) syrup be effective?; 4. how much would a person have to ingest for it to be effective?

regards —The preceding unsigned comment was added by Andrerabe (talk • contribs) 12:03, 18 April 2007 (UTC).

I remember that was big 20 years ago. Most of the 'alternatives' have been tested and found ineffective. --Zeizmic 12:18, 18 April 2007 (UTC)

There's no evidence that thiamine is effective as a mosquito repellent:

• Khan A, Maibach H, Strauss W, Fenley W (1969). "Vitamin B1 is not a systemic mosquito repellent in man". Transactions of the St. John's Hospital Dermatological Society. 55 (1): 99–102. PMID 4389912.{{cite journal}}: CS1 maint: multiple names: authors list (link)

• Strauss W, Maibach H, Khan A (1968). "Drugs and disease as mosquito repellents in man". Am. J. Trop. Med. Hyg. 17 (3): 461–4. PMID 4385133.{{cite journal}}: CS1 maint: multiple names: authors list (link)

Interestingly, acute thiamine deficiency can mimic and complicate malaria infection, which is especially important in Southeast Asian populations. I'm not sure how relevant that is to malaria patients in South Africa, but my understanding is that it's a major reason that patients are commonly supplemented with thiamine in Southeast Asia. --David Iberri (talk) 14:04, 18 April 2007 (UTC)

I would guess that's how the idea came about that thiamine worked as a mosquito repellent, from observations that people wearing thiamine patches came down with less severe cases of malaria. StuRat 18:41, 18 April 2007 (UTC)

Baset trailer

Is there such thing as a baset trailer? James S. 14:30, 18 April 2007 (UTC)

I doubt it; the discussion page has details. Why in the world would somebody use a gasoline electric generator to drive a car? This is adding an extremely lossy stage of energy transfer; if the same engine were used to directly power the car, the fuel efficiency would be immensely better. Nimur 17:25, 18 April 2007 (UTC)

There are many advantages to gasoline-electric hybrids:

1) They can have smaller engines, meaning less weight, since power for acceleration is provided by the batteries.

2) The engine can be run at the most efficient speed to charge the batteries, as opposed to the variable speeds needed for a gasoline only vehicle.

3) Gasoline is quick and easy to replace on the road, due to the existing infrastructure, while recharging an electric-only vehicle is not.

4) Gasoline-electric hybrids provide a longer range than electricity alone.

5) A well designed hybrid will have redundancy in that the vehicle can run on either gasoline or electricity alone, if need be, in case of a failure in either system. StuRat 17:52, 18 April 2007 (UTC)

6) All wheel drive is easier to accomplish with an electrically driven vehicle than gasoline (I'm not positive on this one). StuRat 17:50, 18 April 2007 (UTC)

In support of your last point, the Toyota/Lexus AWD hybrid SUV has no driveshaft to the rear differential ; there's just an electric motor located where the driveshaft would connect to the rear differential case. That arrangement saves the weight of the driveshaft, the U-joins, and the center differential.

Atlant 19:40, 18 April 2007 (UTC)

Heavy questions

Where did the heavy elements on Earth come from ? I am aware that heavy elements (over the mass of iron, I believe) come from supernovae. What I'm asking about is if we know which specific supernova(e) contributed to the Earth's supply. There are many sub-questions related to this:

1) I assume the supernova(e) in question must have been within our Milky Way galaxy. Is this correct ?

2) I'm assuming that heavy elements existed on Earth, in roughly the same ratio (except for those lost due to radioactive decay), since the Earth was formed some 4.3 billion years ago. Do we know this to be correct ?

3) Are heavy elements relatively evenly dispersed throughout the galaxy, by solar system, or is it uneven ? (I realize that planets, especially terrestrial planets, are heavily weighted towards the heavy elements.) If evenly distributed, this would lead me to believe that so many supernovae contributed that it would be difficult to track specific sources.

4) Can we date the age of heavy isotopes with long half-lives (say billions of years), by comparing the ratio of the original isotopes with the stable products, much like carbon dating ? If so, and if there is only one supernova source, or perhaps a small number, we might be able to match up supernovae remnants with those ages. Has this been done ?

5) I am assuming a supernova would need to be relatively close to our solar system to contribute a significant amount of heavy elements to Earth. Either that or many supernovae would be needed far away. Is this correct ?

6) Are there any candidate supernova remnants (like black holes or neutron stars), relatively near our solar system and over 4 billion years old ?

StuRat 17:41, 18 April 2007 (UTC)

Those are heavy duty questions. I think the presence of heavy elements is pretty sparse; combined with difficult detection due to low quantities (relative to say, Hydrogen). Our best detection tool is emission spectroscopy, but "new-age" astronomers/astrophysicists like to use long-time-interval image processing to detect wobbles and gravitational perturbations; and make inferences about mass and distribution, etc.

As far as the original source, I think the theory holds that our solar-system is a second-generation (or nth generation) of material from an originally larger star. I doubt that significant amounts of the material (especially heavy metals) came from outside the near solar vicinity. I don't know of any large 'candidate supernova' objects within a reasonable range; but if the time-scale is billions of years, a lot of speculation is naturally part of the theory, and you can start looking at extremely distant (millions of light-years) objects. As a bit of precaution, it is not a good assumption that stellar material (especially large quantities) could move even a significant fraction of the speed of light; so an element that formed 10,000 light years away might take millions (billions?) of years to "travel" to us.

In summary, I think the best estimate for where the material came from is "here" - i.e., this solar system; which has undergone a very significant time-evolution since its original creation. Nimur 17:53, 18 April 2007 (UTC)

But, if there was a supernova right in our own solar system, shouldn't there be a black hole or neutron star left over from it ? StuRat 17:58, 18 April 2007 (UTC)

If there were a supernova in the solar system, the Earth wouldn't be here. Speaking of which, what is a safe minimum distance to be from a supernova? From a regular run-of-the-mill nova? Clarityfiend 18:02, 18 April 2007 (UTC)

StuRat isn't suggesting that said supernova occured after the solar system formed. That said, see Supernova#Impact_on_Earth. Novae would probably have less impact, but their even more variable scale means that a lower limit can't really be imposed. — Lomn 18:10, 18 April 2007 (UTC)

It's worth noting (backing up to StuRat's question about a black hole in the vicinity) that a star could go supernova in the general region of the sun 5 billion years ago and not be anywhere nearby now. For example, Barnard's Star is presently ~6 light years away, but will have closed to 4 ly within 10,000 years. Scale that out to a few billion years and you're talking about the star being up to around one million light years distant when the solar system was formed. — Lomn 18:19, 18 April 2007 (UTC)

I think metallicity is the general concept you're looking for. As Nimur notes, it's more the case that the solar system (even the galaxy) is of generally later population. While particular supernovae may have contributed to the collapse of whatever dust cloud the solar system coagulated from, it simply isn't practical to assign individual supernovae to the distribution of metals. Rather, entire classes of older population stars exploded to form not just metal-rich individual stars/planets but entire metal-rich galaxies and galaxy clusters. — Lomn 17:59, 18 April 2007 (UTC)

Do other galaxies and clusters have roughly the same ratio of heavy elements ? StuRat 21:00, 18 April 2007 (UTC)

Of Hydrogen/Helium to metals? No. As noted in metallicity, the Milky Way has from 2 to 5 times the relative metal content of the Magellanic Clouds. Within the metals (say, Iron to Uranium)? I'm speculating, but I would expect that it's relatively constant, since (I think) any supernova produces stuff all the way up the periodic table. Theory suggests that this holds for even the oldest, originally metal-free Population III stars. — Lomn 21:11, 18 April 2007 (UTC)

To answer question 4, there are a number of radioactive isotopes with half-lives of hundreds of millions to billions of years. Check out Uranium-lead dating. Someguy1221 18:55, 18 April 2007 (UTC)

To answer #5: The sun is traveling with about 17 km/s through its stellar neighborhood. In 5 billion years, this leads to a distance of 2.8E+5 light years - so anything that was close back then isn't necessarily close to the sun now. Icek 01:29, 19 April 2007 (UTC)

Determining energy cost of household

Hi, I am wondering if anybody can help me calculate the energy cost of my household. I know how to do so for simple devices, like lightbulbs with clearly marked wattages, but how do I do such a thing for other devices? I'm particularly interested in how much energy it takes my washer and dryer run, but I don't see any useful info as to how to do such a thing anywhere on them

Update: thanks to everybody for replying, I found this site http://www.tribaluk.com/laundry.htm which lists Energy Consumption in kWh (60ø C) for various machines. What exactly does that mean? Does it refer to per cycle? What does the 60ø C mean? 4/19/07

Robin

Well, if all you want is the total energy, you can obviously just check your electric (and also maybe gas or fuel oil) bill! Or you could find and learn how to read your electric meter, to get more fine-grained answers. --Steve Summit (talk) 20:36, 18 April 2007 (UTC)

You could turn everything in the house off (the breaker board might help with that), record what your electric meter says, do a load of laundry, and then record again what the meter says. The difference in those numbers is how much juice it took to do the laundry. You could do it a few times and take the average if you wanted more accuracy. --TotoBaggins 21:01, 18 April 2007 (UTC)

If you really want to get per-device numbers, you need only a multimeter and a pocket calculator. I think there are also "user friendly" meters designed especially for this if you don't want to muck around with wires. -- mattb 21:02, 18 April 2007 (UTC)

Actually, no (to the first bit, that is): determining the power/energy used by a device requires measuring both the voltage and the current. Measuring the voltage is easy, of course (and to first order you don't even have to measure it, because it is what it should be), but measuring the current requires interrupting the circuit, and requires a high-current scale (amps or tens of amps) on your multimeter, which most small/inexpensive meters don't have. All of that is why a more convenient, clip-on ammeter is a splendid idea, except that I get the impression they're all inaccurate, or expensive, or both. (But I could be wrong.) —Steve Summit (talk) 02:56, 19 April 2007 (UTC)

My cheapest multimeter is rated for 10 amperes. That should handle most household devices save for your space heater, microwave oven, electrical stove, water heater, etc. -- mattb 03:06, 19 April 2007 (UTC)

See also clamp meter, but the problem is that you don't much care about the instantaneous reading but rather the time-integral of the reading. Some of the fanciest clamp meters can do this. There are also gadgets you can buy that you plug your appliance into; they then calculate this.

Atlant 12:18, 19 April 2007 (UTC)

The voltage and current ratings are marked on a lot of devices, but beware that those values are probably maximums and the actual usage will differ from that. anonymous6494 21:57, 18 April 2007 (UTC)

They also often don't account for all of the energy that's wasted as heat, either in the wires leading to the device or in the power supply for the device (if it has one). Someguy1221 22:08, 18 April 2007 (UTC)

Doesn't matter. Unless there's something very wrong with the wires (whether leading to the device or within it), substantial energy won't be dissipated in them. And the nameplate rating of a device normally reflects the current it actually draws, regardless of the use it'll get put to. For example, a 100 watt light bulb does indeed draw 100 watts, although it converts most of those watts into heat, not light. But my point is that the nameplate reading (to the extent that it's at all accurate in the first place) does reflect the amount of energy that is wasted (as heat or otherwise) in the rated device. —Steve Summit (talk) 02:56, 19 April 2007 (UTC)

The "nameplate" on a lightbulb or an electric heating device such as a range, toaster, space heater or hairdryer may accurately reflect the energy consumption, but on computers and motor appliance such as washing machines, the nameplate may overstate the average power consumption during operation. A utility electric meter has marked on it a "kh" factor which allows it to be used as a watt-meter to measure instantaneous power. Per Electricity meter , "The amount of energy represented by one revolution of the disc is denoted by the symbol Kh which is given in units of watt-hours per revolution. The value 7.2 is commonly seen. Using the value of Kh, one can determine their power consumption at any given time by timing the disc with a stopwatch. If the time in seconds taken by the disc to complete one revolution is t, then the power in watts is P = 3600×Kh/t. For example, if Kh = 7.2, as above, and one revolution took place in 14.4 seconds, the power is 1800 watts. This method can be used to determine the power consumption of household devices by switching them on one by one." Measuring amps, even with a high quality RMS clamp meter, is not an accurate way to determine energy consumption in AC circuits with motor load or electronic load. Volts times amps will generally overestimate the watts, due to the less than unity Power factor.Edison 15:26, 19 April 2007 (UTC)

Mercury

How much tuna would I have to eat to get my daily recomended value of mercury? What other foods are a good source of mercury?

Cute question. Some would call it a troll, not me though.

Anyway, methyl mercury comes from coal power plants. If you don't live around coal power plants, the local tuna won't have much mercury, so try to get it from the Eastern seaboard of the United States. There's a rather large number of coal-fired plants over there. Also, as the recommended daily intake of mercury is 0.0mg for men, 0.0mg for women, you may actually want to avoid tuna caught along the Eastern seaboard altogether. Unless of course you do have a deathwish. Vranak

The man's got a deathwish! adam the atomTEC 20:07, 18 April 2007 (UTC)

Sharks can contain even more mercury (as they are higher up the food chain; they eat the tuna which themselves contain mercury). Therefore, shark fin soup may be right up your street. Of course, sharks are endangered and the process for removing the fins is usually rather cruel (cutting off the fins while the shark is still alive often takes place) and assuming you live in the USA, importing shark fin or catching it in US waters is illegal unless you can import an entire shark carcass, which just happens to have its fins still attached. Laïka 21:21, 18 April 2007 (UTC)

Sadly, not even vegetarians are necessarily safe from mercury poisoning; in the 1960s and 1970s, methylmercury was a popular fungicide for treating wheat, especially in Iraq. People then made this wheat into bread and suffered from mercury poisoning, while the Chinese emperor Qin Shi Huang was killed because he believed that eating mercury would make him immortal; unsurprisingly, it didn't. Laïka 21:28, 18 April 2007 (UTC)

I think the proper way to interpret this question is "how much tuna fish can I eat per week without being in danger of mercury poisoning". I seem to recall a fairly low recommendation, something like 2 cans per week. StuRat 23:07, 18 April 2007 (UTC)

StuRat, that sounds outrageously low! I recall eating tuna fairly often as a kid, and I turned out alright... Nimur 00:05, 19 April 2007 (UTC)

Well again, it's going to greatly depend on where the tuna came from. East coast bad, far out in the Atlantic, or Pacific, good. Vranak

Also, it depends on the length of exposure. Mercury was used in hat making. After many (many) years of working with mercury, the mercury poisoning would take effect (baldness and insanity), hence the term "mad hatter". Those who wore mercury-laden hats all their life had very little effect. A single dose of mercury has no long term effects. I drank mercury once as a baby. It only resulted in a silver splotch in my diaper. --Kainaw ^(talk) 13:06, 19 April 2007 (UTC)

See here for some figures from the FDA. And here for toxicity information of methylmercury, the relevant compound, from the EPA. Icek 00:53, 19 April 2007 (UTC)

Hey i survived mercury exposure once. from thermomiters i acctually broke them to play with the chemical as they formed tiny little balls on the floor that rolled. its i mean it was quite fun =) and look at me no problems what so ever no insanity or nothing of the sort. and im still clearly alive =). User:Maverick423 If It Looks Good Nuke It 15:16, 19 April 2007 (UTC)

Mercury as the metal is much less toxic than when as an organometallic compound. Xrays showing people with lots of bright spots of metal inside are quite interesting(PMID 11519542) but the victims can recover, unlike Karen Wetterhahn. See our Mercury poisoning article for more info about these distinctions. DMacks 15:26, 19 April 2007 (UTC)

ah so there is a diffrence! all this time people kept telling me there wasnt but now i can prove them wrong! User:Maverick423 If It Looks Good Nuke It 17:08, 19 April 2007 (UTC)

The skull

Is the skull a single bone or a group of bones? Heegoop, 18 April 2007 (UTC)

22 bones. Check out human skull. Someguy1221 20:38, 18 April 2007 (UTC)

"Perfect" Black Hole insulation

Jonathan Kovaciny saids Let's say I have a big hollow ball made of some magnetic material or other. The shell of this ball is quite thick, and is completely airtight. Inside the ball is just plain old room temperature air from my garage. Now lets say I enclose this ball inside another ball in such a way that the inner ball is suspended by magnets, and I've completely evacuated the air from the outer ball. (I now have a ball floating inside a vacuum.) Just for good measure, I cover the outer ball with a mirror surface. Next, having nothing better to do with my money, I ship my ball down to Antarctica and drop it (gently) on the ice. Will the temperature of the inside ball ever drop?

Now suppose I increase the mass density of the inner ball until it becomes a blackhole. Now even the radiation cannot escape from the inner ball. Will the temperature of the inside ball ever drop?

202.168.50.40 22:45, 18 April 2007 (UTC)

Maybe --> Hawking radiation. Someguy1221 22:52, 18 April 2007 (UTC)

So many hypotheticals... I think the ("safe") practical answer is to call bluff on the "perfect insulation" which could clearly never be built in practice. (Perhaps the easy-way-out, but it's realistic). As for turning the problem into a black hole, it suddenly ceases to matter whether the system is insulated, because the insulation would be inside the event horizon. I think this is a gedankenexperiment that I want no part of. Nimur 00:09, 19 April 2007 (UTC)

Doesn't the temperature rise when the inner ball is collapsed? But the real object of the question is does temperature have meaning if it can't be measured? If no one is in the forest, does the falling tree make a sound? --Tbeatty 07:38, 19 April 2007 (UTC)

To first part, yes the inner ball cools down. Whilst there may be a vaccuum between the inner and outer balls, this only eliminates transfer of heat by convection (of course in practice no man-made large-scale volume vaccuum is perfert and a tiny heat transfer by convection will occur). Having a vaccuum layer does not prevent radiative loss of infra-red heat from the inner ball outwards. Your question also ingnores the strength of magnets needed to levitate the inner room - if they are electromagnets then heat will be generated. So yes the inner ball will heat up allbeit extremely slowly.

If you collapse the inner ball into a black hole, then Gay-Lussac's law would suggest its temperature reaches infinite, although this applies to an infinitely small volume, so no overall change in temperature in the wider orginal volume of space. However how are you going to suspend the black hole within the outer ball ? - Its going to take huge amount to power - (nolonger question few centimeters between inner & outer shell wall but outer wall to centre of the space). Crushing the inner ball into a black hole will take a fantastic amount of power (no black holes ever been created from just an atomic bomb explosion, and supanova are somewhat hot over an area rather larger than the earth!). Lastly, tiny black holes probably radiate off their mass as Hawking radiation and eventually explode! David Ruben ^Talk 13:41, 19 April 2007 (UTC)

Didnt they mention a particle accelerator that acctually creates tiny black holes? come out on a show think it was naked science. where they smash atoms at great speeds that they form tiny black holes. it was quite intresting.

April 19

Turning gray/green

Why do people sometimes turn gray or greenish when they are feeling nauseous? What's the mechanism behind the color change, why does it often coincide with that symptom? Just curious. --24.147.86.187 00:08, 19 April 2007 (UTC)

Probably decreased blood, the opposite of flushing (physiology). See pallor, which is sort of a stub article. Nimur 00:11, 19 April 2007 (UTC)

Unlike fish, frogs and reptiles, humans don't undergo short-term, physiological colour changes using melanin. They do undergo longer-term, morphological colour change (e.g. tanning) though. So all short-term colour changes in human are a result of haem, the pigment in our blood. Rockpocket 01:09, 19 April 2007 (UTC)

Male Contraceptive pill

So how close is this thing (or one of these things) to production in the USA? 75.161.134.92 02:07, 19 April 2007

Hmmm... given the possibilities for forced sterilization, I'd have to say hopefully a long, long way. Vranak

The issue of forced sterilization is no more relevant to the male pill as it is to the use of the female pill, as it will only be marketed if it is completely reversible. We are not talking about castration here, just hormonal modulation. For the last 5-10 years scientists have been telling us that it should be available in the next 5-10 years (e.g. [7]) However, the results of decade long studies are looking promising [8] and some experts are still talking about "the next few years" [9]. The trials are still preliminary, though, to its probably more accurate to say "it's still a long way from being commercially available" [10] Rockpocket 04:37, 19 April 2007 (UTC)

Even if its not reversible, its only forced sterilization if the recipient is unwilling. We're assuming people will take these pills voluntarly? Think outside the box 11:45, 19 April 2007 (UTC)

Me, I'm anxiously waiting Ethical Birth Control. And the return of Howard Johnson's. And Ethical Suicide Parlors. Until then, I suppose there's always Gossypol.

Atlant 16:20, 19 April 2007 (UTC)

Cell Division at Extreme Temperatures

I have a friend that claims that no known bacteria on Earth can reproduce above 150 degrees Celsius, since DNA is simply too unstable to replicate at temperatures that high. I've looked at the articles for cell division, mitosis, and DNA, but haven't found anything helpful. I'm pretty sure that the organisms that live near the hot vents at the bottom of the ocean reproduce at close to this temperature, but I'm not sure...any help? Thanks! --pie4all88 10:35, 19 April 2007 (UTC)

In the article about Hydrothermal vents it says: Other examples of the unique fauna who inhabits this ecosystem is a snail armoured with scales made up of iron and organic materials, and the Pompeii worm (Alvinella Pompejana), which is capable of withstanding temperatures up to 176 degrees Fahrenheit. Think outside the box 11:42, 19 April 2007 (UTC)

You'll want to check out our articles on thermophiles, hyperthermophiles, and Strain 121. Strain 121 is the most extreme thermophile currently known. It is capable of continued survival and reproduction at temperatures as high as 121 °C. TenOfAllTrades(talk) 13:52, 19 April 2007 (UTC)

Largest Bomb in Existence?

What is the largest existing bomb in terms of radius of explosion? I'd imagine it'd be a Hydrogen Bomb, but the article doesn't seem to say the answer. I have a friend who claims that someone (probably Russia, he said) has a bomb that is 23 times more powerful than what is needed to blow up the entire Earth, but I am skeptical. Thanks for the help! --pie4all88 10:35, 19 April 2007 (UTC)

I don't think the US military would be too keen on having that information public, but you may be interested in historical precedent: Tsar Bomba. Vranak

Just in case you were curious about non-nuke bombs, I went to Daisy cutter, officially called the BLU-82. That page states the following: It was the largest conventional bomb for several decades. That title is now held by the GBU-43 Massive Ordnance Air Blast bomb, which contains 18,700 pounds of explosive, although both these weapons were outstripped in weight and size by the T12 Cloud Maker penetration or earthquake bomb developed from the British Grand Slam bomb of World War II. The T12 weighed 43,600 lb, almost twenty metric tons. Dismas|^(talk) 10:57, 19 April 2007 (UTC)

Incidently, the "GBU-43 Massive Ordnance Air Blast" bomb, or the MOAB, is monikered "the Mother Of All Bombs".--JLdesAlpins 11:21, 19 April 2007 (UTC)

There is certainly no bomb large enough to blow up the entire Earth, much less "23 times more powerful" than that. That's a tremendous amount of energy, and the Earth is thought to have absorbed stellar impacts with energies far, far higher than any bomb that has been developed (e.g. Giant impact hypothesis, Cretaceous-Tertiary extinction event). If you want numerical estimates as to how much energy that would be, this page is pretty entertaining. --24.147.86.187 12:09, 19 April 2007 (UTC)

The above answers the question well -- there's absolutely no way for a human-scale bomb to actually "destroy the Earth". To back up to some earlier points, it's worth noting that "largest bomb" (such as the Tsar Bomba or Castle Bravo, the largest US bomb) is an entirely separate military concept from "most useful bomb". For example, the Trident missile carries eight half-megaton warheads. 4 MT is far less explosive force than a single large bomb could produce, but eight warheads are far more flexible than one. The conventional bombs cited by Dismas above are arguably even more effective than modern nukes, despite having drastically less yield, as political realities allow their use while prohibiting the use of nuclear devices. — Lomn 13:56, 19 April 2007 (UTC)

An issue to consider is that a nuclear bomb blast has multiple zones of effect. There is not a discreet radius where you can say the explosion stops. Rather you have radii with descending magnitudes of destruction. Take a look [HERE if you would like to see some interactive examples.-Czmtzc 14:49, 19 April 2007 (UTC)

It should also be noted here that the limiting factor here is not the strength of the bomb, but the curvature of the earth, which means that there is a simple maximum radius. I remember reading somewhere that this was 37 kilometers, but I suppose the exact number depends on the definition of the destructive range. risk 14:59, 19 April 2007 (UTC)

In the Texas City Disaster there was a huge unintentional bomb which exploded due to mismanagement and improper handling.. A ship loaded with 17,000,000 pounds (8,500 tons) of ammonium nitrate exploded in a harbor in 1947 and killed 581 people. The explosion followed a gradually increasing firewhich might have been due to careless smoking or spontaneous combustion. The explosion was comparable to that of 2 to 4 kilotons of TNT. A nearby ship with 2,000,000 pounds (900 tonnes) of ammonium nitrate exploded afterward as an aftereffect of the first explosion. Edison 15:19, 19 April 2007 (UTC)

Ah, but the largest artificial non-nuclear explosion in history seems to be the Halifax Explosion. A munitions ship packed with 2,653,115 kilograms (5,849,117 lbs) of explosives (benzol, nitrocellulose, picric acid, and TNT) collided with another ship, and the explosion killed over 2000 and devastated all buildings within a 2 km (1.24 mi) radius of the blast. − Twas Now ( talk • contribs • e-mail ) 19:30, 19 April 2007 (UTC)

photon

Is there a proof that photons exist? I think I have a proof they do NOT exist. By philosophy everything has a use or a goal. Something without use does not exist,said ancient philosophers. Photons have no use. Everything about atoms,e.g. atomic spectra,can be explained by normal, classical (Newton,Maxwell)laws. Rutherford and Bohr could not. But I can.

Verify? Do you want the simple spectrum of Hydrogen, in Dutch or French? I can e-mail it to the adres you give me.

Morp

The Photoeffect might be the proof?--Stone 11:17, 19 April 2007 (UTC)

Is light not made of photons? Think outside the box 11:39, 19 April 2007 (UTC)

Counterproof: another branch of philosophy says that everything need not have a use or a goal, ergo "useless" photons can easily exist. What makes photons useless, anyway? What makes atoms "useful" in this sense? In any case, photons are very useful in the fact that they are the force carrier for the electromagnetic force. Try imagining life without them. As for proof of their existence, try researching the early advances in quantum theory - unless energy is quantised in discrete packets (called photons), the Photoelectric effect cannot be explained, and Blackbody radiation produces an infinite amount of energy - obviously ridiculous. Icthyos 12:03, 19 April 2007 (UTC)

Einstein's explanation of the photoelectric effect is the classic, original proof. It cannot be explained using classical Maxwellian laws. If it could be, a generation of very unhappy and reluctant physicists would never have switched over to it. There are other effects that can only be explained by postulating a quanta of light. And the notion that "something without use does not exist" is just a silly axiom, one with no strong philosophical backing. In any case I don't see your assertion that photons "have no use" as being particularly well supported — you might a well say electrons "have no use", or atoms "have no use", or muons "have no use". --24.147.86.187 12:14, 19 April 2007 (UTC)

Stimulated emission and Raman scattering would be rather interesting to try and explain without an understanding of the optical quanta we call the photon... Also, it would be rather difficult to explain the workings and methods of the very real optoelectronic devices I've personally worked on (like the avalanche photodiode). -- mattb 14:28, 19 April 2007 (UTC)

Photons have no use? Now see here... Clarityfiend 18:29, 19 April 2007 (UTC)

Solar "Booms"

Is there any way to estimate the power in decibels of the sound waves in the Sun's corona?--JLdesAlpins 16:28, 19 April 2007 (UTC)

The decibel is a dimensionless measure of ratio. It's only meaningful when referenced to some point (like "-3 dB from peak power"). Maybe you're looking for dB(SPL) or dBA. -- mattb 17:21, 19 April 2007 (UTC)

What's the best way to stop a parrot from swearing??

I've mentiond my trusty hyacinth macaw on this board before. What I didn't mention is that she is an incredibly foul mouthed bird. I've never sworn directly at her but I have a temper and do tend to curse loudly and heavily into thin air when things go wrong and she's picked up on that. She says the 's-word', the 'f-word' and the 'c-word' a lot, over and over and over. It's quite embarssing when I have polite company, or when I take her out in her harness with me. She seems to swaer at strangers a lot, maybe because it's fun for her to see them react (they usually just think it's quite funny when she turns to them from my shoulder in town and calls them a 'f*cking c*nt', though she's said it to little kids too, which isn't so funny) or something.

The damage is probably done already but does anyone know a way I might discourage her from doing it so often? Anything that doesn't involve punishing my bird. --84.65.77.1 17:28, 19 April 2007 (UTC)

Electric shock therapy Its more then a solution to weak musles if that doesnt work Nuke it ;-) User:Maverick423 If It Looks Good Nuke It 17:54, 19 April 2007 (UTC)

It is very difficult to train an animal to "do what I say, not what I do." However, the bird may be trying to get attention. So, give it excessive attention when it says something nice and ignore it when it says something bad. If it isn't trying to get attention, find out what the bird is trying to get and give it to the bird when she is nice and don't provide it when she is bad. For example, I had a hedgehog who took to biting my hand to see if I had food. To stop it, I put food in my hand and, if she bit me, I'd make sure she saw me give it to another hedgehog. If she ran up to me without biting, I'd give it to her. She stopped biting in three days. --Kainaw ^(talk) 19:03, 19 April 2007 (UTC)

I also hope you learn not to swear out loud in front of the bird. This could be a good lesson to learn before you have kids that pick up the same language. As embarrassing as this may be in a bird, imagine if your kid's teacher called to complain that your kid is calling the other kids and teachers those names. StuRat 19:09, 19 April 2007 (UTC)

The bird's name isn't Ruby is it? There's a bird on YouTube that calls its owner a f*cking c*nt, quite funny if you ask me.

Honestly, the easiest and perhaps best option is simply to accept the bird's potty mouth.Vranak

The Law of Effect says "responses to stimuli that produce a satisfying or pleasant state of affairs in a particular situation are more likely to occur again in the situation. Conversely, responses that produce a discomforting, annoying or unpleasant effect are less likely to occur again in the situation." Having your attention, such as pleading with him not to swear, might be a "pleasing state of affairs." As a principle of Operant conditioning, this means that if you reward the parrot in some way, as by paying more attention, when he cusses, then he will cuss more. If you reward other vocalizations, and ignore curses, then the vocabulary should shift in the direction you want. It is hard to punish a bird without harming it or causing more undesirable behavior, and it is hard to be sure the punishment will not just lead to more of the undesired behavior, as well as making the animal hate and fear you. See Animal training for more info. From experience, promptness and consistency are important, along with patience and repetition. Like a child, the bird may note that your swear words are important, so controlling your vocalizations may be a necessary step toward controlling the birds vocalizations. Edison 21:47, 19 April 2007 (UTC)

Agreed. Bird hears human vocalizing loudly and harshly whilst behaving in a particularly animated manner - bird is interested by this. Bird doesn't know what sounds mean but knows that they probably have some significance to the creature it lives with. Bird attempts to use these new sounds - bird gets attention from companion creature. Bird likes attention, bird continues to make sounds, other creatures like the one the bird lives with show bird attention when bird uses new sounds. Bird likes attention - etc., etc., etc.. As birds go, hyacinth macaws are pretty high up there in terms of intelligence. --Kurt Shaped Box 21:56, 19 April 2007 (UTC)

Insulin and Blood Sugar

From what I understand, its bad for your blood sugar to rise rapidly because it releases insulin which stores fat, then why do bodybuilders who use growth hormone also inject insulin?

If you eat too much sugar, you store more fat. If bodybuilders take insulin hey don't need, and then eat enough carbohydrate to keep from being hypoglycemic, they store more fat. alteripse 20:55, 19 April 2007 (UTC)

Principle Rotation Axis in D_2d and D_3d Groups (Inorganic Chemistry & Symmetry)

How are the irreducible representations for point groups generated? My book says that A represents symmetry about the principle rotation axis and B represents antisymmetry. I'm ok so far. However, upon flipping to the character tables for D_2d and D_3d a few pages after that, here's what I see (I removed some impertinent info, such as E rows).

D2d	E	2S4	C2	2C2'	2σd
A1	1	1	1	1	1
A2	1	1	1	-1	-1
B1	1	-1	1	1	-1
B2	1	-1	1	-1	1

D3d	E	2C3	3C2	i	2S6	3σd
A1g	1	1	1	1	1	1
A2g	1	1	-1	1	1	-1
A1u	1	1	1	-1	-1	-1
A2u	1	1	-1	-1	-1	1

In the D_2d table, it shows that A and B are BOTH +1 under what I assumed is the principle rotation axis (the C₂). It almost appears that they are using one of the S₄ as the principle rotation axis, since under that column A's are +1 and B's are -1. Kinda weird, but I suppose it could be seen as the highest order axis.

But then, it looks like they are using the C₃ axis as the principle rotation axis in the D_3d group, despite the presence of two S₆ improper rotation axes (A's are +1 under S₆ and not C₃). Am I going crazy? (probably, but not even my professor could figure it out.) Thanks for at least reading this, even if you don't know the answer :) --129.21.126.178 19:55, 19 April 2007 (UTC)

Correction: In the last paragraph, A's are all +1 under C₃ and not S₆. I had them switched. Sorry --129.21.126.178 19:58, 19 April 2007 (UTC)

Diarrea and Weight loss

If I have diarrhea, will I lose weight other than water weight? Will everything I ate just come out without the calories being absorbed by the body?

Yes, you will lose weight, but it will cause malnutrition, so I wouldn't want to use this as a weight loss method.Czmtzc 20:34, 19 April 2007 (UTC)

It's not a good thing but it may simply be a precursor to more healthy digestive workings. If you've made an effort to improve your diet, and are seeing some liquid stool, stick with it. Vranak