Wikipedia:Reference desk/Archives/Science/2009 March 7

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Science desk
< March 6 << Feb | March | Apr >> March 8 >
Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

March 7[edit]

My penis is multicoloured (this is not a joke or vandalism)[edit]

Seriously. My penis is a mixture of Olive skin and my regular skin colour, which fits between type II and type III in this because I have dark brown hair and dark blue eyes. Seriously, my penis is multicoloured in random patches. This is not a joke. Is this normal? Not that any girls have ever complained about it, but I have some cousins on my father's side whom I've noticed actually have more olive coloured skin than myself. Weird that.--Get 'Em Out By Friday (talk) 00:08, 7 March 2009 (UTC)

Could it be the result of circumcision, which can leave darker skin closer to the base? arimareiji (talk) 00:14, 7 March 2009 (UTC)
Not circumcised.--Get 'Em Out By Friday (talk) 00:31, 7 March 2009 (UTC)
If you feel you have some medical condition that needs attention, see a doctor. It you simply want to know if anyone else has a penis that has more than one skin tone - yes. It occurs in other men. -- kainaw 01:17, 7 March 2009 (UTC)
From my corrupt youth, I remember that the character nicknamed "Pinto" in the movie Animal House got his nickname from having the same condition. (talk) 06:08, 7 March 2009 (UTC)
However, in the original National Lampoon story, Pinto got the discoloration on his penis because he'd gotten tar on it, possibly while masturbating. --LarryMac | Talk 13:49, 9 March 2009 (UTC)

Is the Yangtze River drying up?[edit]

In the Ganges River Article, it states that the Ganges River may dry up in 2030 because of receding Himalayas glaciers. Is the Yangtze River in China going to dry up too? When will the Yangtze River completely dry up? Sonic99 (talk) 04:53, 7 March 2009 (UTC)

A government official claims in China Daily the recent drying is due ot lack of rainfall and climate change is blamed. Elsewhere, human activity such as damming are blamed for the Yangtze's tributaries running dry. Glacier melting has been suggested as future problem for the Yangtze but it is not actually happening yet and it is expected that melting glaciers will first cause flooding before causing drying as they run out of material to melt. SpinningSpark 11:54, 7 March 2009 (UTC)
No, the last part is wrong. Glaciers primarily melt in high summer, when water levels are naturally low. Floods typically occur in spring, when seasonal snow melt occurs. So melting glaciers will increase average flow level (all other things being equal), but not usually cause floods. --Stephan Schulz (talk) 12:11, 7 March 2009 (UTC)
That's not what the source says, to quote;
"The rapid melting of Himalayan glaciers will first increase the volume of water in rivers causing widespread flooding," said Jennifer Morgan, director of the WWF's Global Climate Change Programme. "But in a few decades this situation will change and the water level in rivers will decline, meaning massive economic and environmental problems for people in western China, Nepal and northern India."
You are confusing the normal annual cycle of melting and the permanent destruction of glaciers due to global warning. The first is in equilibrium, the second is not. SpinningSpark 12:17, 7 March 2009 (UTC)
No. The long-term reduction of glaciers is overlaid by the seasonal cycle. Even now, most glaciers gain mass in winter. It's just that they lose more of it in summer. If you look at your source (the WWF report here), you will notice that they talk about all areas that are affected by Himalaya glacial run-off, and that that particular piece (increased flooding) applies to the Indian side. There, floods are not primarily resulting from snow melt, but rather are triggered in high summer, when the Monsoon brings massive amounts of precipitation. In that case, seasonal rains and maximum glacier melting coincides. But that does not apply to the Chinese river systems. --Stephan Schulz (talk) 17:24, 7 March 2009 (UTC)
I'm not sure about the Yangtze, but the Huang River is increasingly experiencing more days without water flow each year, due in part to the desertification around the Gobi Desert and receding Himalaya glaciers, both affected by climate change. The Three Gorges Dam on the Yangtze (Chang Jiang) may be able to control water flow for a period of time, however. I've read that the melting of the Himalayan glaciers will affect the main source of water for over 500 million people. ~AH1(TCU) 00:24, 8 March 2009 (UTC)
The WWF report doesn't say when the glaciers and river water will completely disappear in China. It discusses about the glaciers on the Indian side will vanish within 40 years and that isn't a long time from now. The Indian government better do something quick like reducing their population or else they'll be in very deep trouble. Sonic99 (talk) 00:42, 8 March 2009 (UTC)

perpetual motion machine[edit]

without thermal energy utilisation is it possible to make PMM? —Preceding unsigned comment added by Gbhavsar (talkcontribs) 08:03, 7 March 2009 (UTC)

It is not possible to make a perpetual motion machine. Dragons flight (talk) 11:13, 7 March 2009 (UTC)
I think that the questioner may be asking if a perpetual motion machine would be possible if thermal losses could be completely eliminated. It is not possible to eliminate losses entirely due to the second law of thermodynamics. Speculating on whether perpetual motion machines could exist if the second law did not exist is meaningless and unanswerable. If the impossible were possible it might be possible, but as its impossible, it ain't. SpinningSpark 11:27, 7 March 2009 (UTC)
A perpetual motion machine isn't just something in perpetual motion (a pendulum on the moon would satisfy that, to within a negligible margin of error), it has to actually do something. That means there aren't just accidental losses, there is intentional extraction of energy. That energy has to come from somewhere. --Tango (talk) 13:48, 7 March 2009 (UTC)
I'd say a device that does nothing more than stay in motion forever is also a PPM. The pendulum example would eventually slow and stop (although it might take longer than the life of the universe). Even the orbits of the Moon. Earth, and stars would decay eventually. StuRat (talk) 14:02, 7 March 2009 (UTC)
Our article disagrees with you. --Tango (talk) 14:05, 7 March 2009 (UTC)
Well, it's just a matter of words - linguistics, not science. When the free energy nuts talk about 'perpetual motion machines' - they are referring to the 'over unity' variety - from which energy could hypothetically be extracted. This 'first' kind of device is definitely - without any doubt whatever - quite utterly impossible. The 'second' kind is the idealised machine which has no friction, no air resistance, and never physically changes (eg it doesn't wear out or anything) - this enables it to be in motion perpetually. The spinning of the earth - the orbiting of the moon - these are all oft-cited examples. Sadly, none of them are that because there are other bodies in the universe causing tidal effects and other gravitational effects, there are tiny TINY amounts of gas and dust in even the hardest inter-galactic vacuum that will eventually cause drag and so forth. So machines of this second kind are acceptable to science as purely theoretical possibilities - although they may not be possible in practice. However, we must be ETERNALLY vigilant. The nut-jobs simply LOVE to cite the existance of "perpetual motion" of the second kind as "proof" that perpetual motion is indeed possible - and therefore they claim to be able to design whack-job "perpetual motion machines" OF THE FIRST KIND to make 'free energy'.
So there are two problems:
  • People confuse machines of the first and second kinds because (stupidly) we use the same words for each.
  • People ignore the PRACTICAL problems with the second kind of machine which mean that they do not in fact work PERPETUALLY anyway.
SteveBaker (talk) 15:26, 7 March 2009 (UTC)
I'm pretty sure the second kind is theoretically impossible too. If nothing else, anything with any moving parts whatsoever (technically, anything with jerking parts) will emit gravitational radiation and slowly lose energy. — DanielLC 17:08, 7 March 2009 (UTC)

Does electric current count as "motion?" A superconducting magnetic energy storage unit is said to have no decrease in current over time, as long as you keep it chilled and do not intentionally remove energy. Edison (talk) 20:50, 7 March 2009 (UTC)

Again with the linguistics! Whether we call electric current "motion" or not is irrelevant - what really matters is whether it can indeed go round and round in a superconductor forever without additional energy input. Again, I suspect that in theory it does - and in practice it won't...exactly why it won't in practice, I'm not sure...but I'd bet actual money! SteveBaker (talk) 01:21, 8 March 2009 (UTC)
you may have to wait a long time to collect though SpinningSpark 03:50, 8 March 2009 (UTC)
I'm fairly certain it will still generate cyclotron radiation. — DanielLC 05:11, 8 March 2009 (UTC)
Yes - and since electrons have mass (albeit exceedingly tiny), they must generate their own teeny-tiny gravitational waves...hence, per DanielLC's previous post, they ought to be (s-l-o-w-l-y) losing energy that way too. SteveBaker (talk) 07:55, 8 March 2009 (UTC)
I would like to point out (for the general reader's sanity benefit) that physicist have a fairly standard definition of PMM of first, second, and third kind and what SteveBaker defines here as second kind is usually defined as third kind while SteveBaker's first kind can be standard first kind or standar second kind, depending on which law of thermodynamis is actually being violated. See perpetual motion#classification. Dauto (talk) 17:40, 9 March 2009 (UTC)

why is there no article about biological (genetic) basis of breeding?[edit]

The breeding article is suspiciously silent on the topic. Since Darwin used breeding as an easy to understand example for evolution, this important topic should be covered in wikipedia Northfox (talk) 10:14, 7 March 2009 (UTC)

Please, be bold and write this article! Lova Falk (talk) 10:24, 7 March 2009 (UTC)
The breeding article is merely a disambiguation page, that is, an index to other pages. You might want to look at breed and selective breeding (which specifically refers to Darwin) and several other of the linked articles. SpinningSpark 11:19, 7 March 2009 (UTC)
thanks for the articles, SpinningSpark. But I find that they are somewhat contradictory.
Selective breeding says:
Charles Darwin discussed how selective breeding had been successful in producing change over time in his book, Origin of Species. The first chapter of the book discusses selective breeding and domestication of such animals as pigeons, dogs and cattle. Selective breeding was used by Darwin as a springboard to introduce the theory of natural selection, and to support it.
breed says:
Thus, all specimens of the same breed carry several genetic characteristics of the original foundation animal(s).
The first is often used as evidence for evolution (the breeder just 'speeds up' nature, eventually leading to new species), while the second one states that the bred animal contains just a subgroup of the wild gene pool. This is just my little WP:OR, so I thought that there would me a more fundamental, well referenced article. Well writing it myself is easier said than done. There are some editors that allow no tainting of their beloved theory and its icons. Been there, done that. Northfox (talk) 12:45, 7 March 2009 (UTC)
That's not contradictory. There are two stages in selective breeding, first you breed for the characteristics you want and then you breed to keep those characteristics. The first stage is, essentially, accelerated evolution, the second stage is more of an attempt to prevent evolution. --Tango (talk) 13:51, 7 March 2009 (UTC)
While artificial selection (which, when done intentionally, is called "breeding") is a good analogy to natural selection, it doesn't do anything to "speed up" mutations, which are another important element in evolution. Thus, you can't rapidly create a new species by breeding alone, since you still would need to wait thousands or millions of years for the mutations to occur which you could then select to breed a new species. I suppose you could speed this up by exposing the organisms to mutagens, but that would also make a large portion of them get sick and die. Genetic engineering offers a more practical way to introduce selected "mutations". StuRat (talk) 13:50, 7 March 2009 (UTC)
Your timescale is way off, StuRat. There are plenty of mutations that occur with every single generation. You certainly wouldn't have to wait thousands or millions of years to get enough of them for speciation if you have the right selection criteria. In the lab, artificial species have been derived with selective pressure across as few as 8 to 40 generations from a last common ancestor. In flies, that is around 3 months to a year. Rockpocket 22:20, 7 March 2009 (UTC)
I don't think the term "breeding" is normally applied to flies, but rather to larger animals with much longer lifespans (either pets or work/food animals). Therefore, the time for a new species to arise would be much longer. I'd be interested to see any source you have showing a new species of pets or work/food animals created from breeding alone, in fewer than 1000 years. StuRat (talk) 00:16, 10 March 2009 (UTC)
There is an argument that over time, selective breeding is just a variation on natural selection. Animals and plants are effectively evolving to exploit a niche where they are symbiotic with humans. In primitive societies, dogs which are good with children are more likely to be looked after, fed, exercised and ultimately to have puppies. There is an evolutionary pressure to be good with children. SteveBaker (talk) 15:04, 7 March 2009 (UTC)
Alternately, look at human preferences in breeding amongst themselves to see the same pattern. That which we consider "attractive" (symmetric face, symmetric body, good stature, and wide hips among other factors) tends to coincide with having "good genes" for breeding and/or reproduction. Quick thought experiment: Imagine breeding with one of the people pictured here. Now imagine breeding with someone with obvious deformities, or signs of Down syndrome, by comparison. Whether or not this is fair, it's how we're programmed. arimareiji (talk) 15:33, 7 March 2009 (UTC)
(**Removed links and ambiguous commentary with respect to photographs of real people.) If you wish to illustrate "breeding" examples with real people, you should have their permission for the use in this context. And you should make your point clearly and unamibigously. // BL \\ (talk) 16:17, 7 March 2009 (UTC)) Comment now makes no sense as text and links I removed have been reinserted. See the discussion at Ref desk on my talk page. // BL \\ (talk) 17:25, 7 March 2009 (UTC
One thing has always puzzled me. Why is it that pure-bred animals do not breed entirely true unless the parent animals are specially selected as best-of-the-breed? If two average pure-bred animals reproduce, the offspring have worse breed characteristics than the parents. After two or three generations of this, the offspring become quite nondescript. I think the same is true of genetically-engineered plants. How does this relate to evolution? – GlowWorm.
Our article Purebred says: A puppy from two purebred dogs of the same breed, for example, will exhibit the traits of its parents, and not the traits of all breeds in the subject breed's ancestry. That would seem to contradict your statements that purebreds don't "breed true". // BL \\ (talk) 19:18, 7 March 2009 (UTC)
Purebreds are usually so inbred that I would expect they are homozygous for pretty much all genes relevant to the definition of the breed, so offspring would have those same characteristics. It is, however, possible to have an animal that has all those same characteristics, but is heterozygous in those genes that are relevant and where the desired characteristic is dominant (you have to fudge it slightly for those characteristics not determined by a single gene, which is probably most of them!). If two such animals bred then, assuming (completely unrealistically, for the sake of easy calculations) the breed is defined by a single gene, they would have 75% offspring of the same breed and 25% not (for genuine breeds, it will be far more complicated, but the general idea is the same). --Tango (talk) 19:28, 7 March 2009 (UTC)
Yes that's basically it as I understand it. In certain types of breeding, like chickens for food, the grandparents are actually more valuable than the parents: you set it up so that a grandparent breeds a parent who can breed chickens to be eaten of a consistent type. The chickens to be eaten do not breed true and thus can't be parents themselves. Thus the breeder maintains the intellectual property by keeping the grandparent types under lock and key, selling off parents who can create the chickens that are actually eaten. So the business model works—breeders sell producers to chicken farmers, who take the produced chickens and sell them as food. After awhile, they need new producers, and are forced, by the genetics of it, to get them from the breeder again, as they cannot create producers with the genetic stock on hand. (What blows my mind is that they were able to work this out with just a little knowledge of Mendelian ratios in the 1920s and 1930s and a lot of trial and error.) -- (talk) 20:46, 7 March 2009 (UTC)
"True breeding" is an entirely artificial, subjective concept. If two stud animals were entirely homozygous for the same alleles at every locus, their offspring will (the vast majority of the time) be exactly the same as them, phenotypically speaking. If you define these two animals as "best of the breed" then most of the offspring would also be also be "best of the breed". In reality, the stud animals will not be homozygous at every locus, and so only a proportion of the "best" alleles will be passed on, and offspring will be genetically "inferior" to the artificial standard. However, its also possible that the offspring could have a "better" assortment, in that it got the "best" alleles from both parents and none of the inferior ones. This explains why (in any species that is artificially bred) the cost of the offspring from two best in breeds are so high. It increases you chances of getting an even better specimen, but more often that not all you do is dilute out the genetic combination that makes the two parents so special and you get a good, but not as good, assortment. Rockpocket 21:53, 7 March 2009 (UTC)
In evolution, perhaps the maintenance of a "good bloodline" works like this. If there is an environmental change, the particular members of a species that, by chance variation, are best suited to survive, will live longer and produce more offspring than those members not as well suited to the change. Assuming the environment then ceases its alteration (for simplicity), in each generation of the species there will be an automatic selection of the best-of-the-breed. Those best able to survive will gradually prevail until all members of the species are "best-of-the-breed" in the characteristic(s) suited to the changed environment.
The environmental change could be a climate change, the entry of a new predator, parasite, or disease, or some other adverse change. Or an indigenous predator, parasite, or disease may adapt to a new prey - the subject species. If the environment changes more rapidly than any members of the species can adapt, the species will become extinct.
In human-produced pedigree animals or plants, the "best-of-the-breed" must be re-selected by humans each generation. There is no automatic selection by the environment.
In natural selection, those members of a species best suited to survive might have only a slightly better longevity, and consequential generational relative increase in numbers, over other members of their species. But in the course of thousands of generations, those best suited will eventually be the only ones in existence. I once saw some figures on that. It was assumed that those best suited to survive had only a very slight advantage, say a 0.1% increase in numbers over the others, in each generation. Over a sufficient number of generations, the ones best suited would be the only ones to finally survive. The rest would die out, getting down to the last one to die. But a thousand generations is not long in evolution - in humans it is only about 25,000 years. So some of the tiny minor variations between members of a species can be extremely important in time.
Of course, many things in the environment are changing all the time, Some members of a species may be better suited to one change, and other members of the same species may be better suited to another change. That greatly complicates the matter. But I think the basic principle, and the difference between human selection and natural selection, is as described above. Human selection will produce permanent change only if it is continued for a great many generations, using selected "best-of-the-breed" specimens to produce each new generation.
I don't know where genetic engineering would fit in this. Perhaps the genetically engineered species should just be considered a separate species. – GlowWorm.

One thing I would add to the above. A slight variation that increases survivability would have to be inheritable. It was not inherited to begin with, so, like the rest of this hypothesis, further thought and practical investigation is needed. – GlowWorm.

Ah - the inevitable post from our closet creationist! Indeed, for the beneficial variation to be passed on, it has to be genetically based and therefore inheritable. But then you make the dangerous leap of saying "If was not inherited to begin with..." - but why would you think that is not the case? Well, there are two possibilities here: Firstly that it IS inherited - but that it requires a combination of genes from mother and father that have simply not come together before. Secondly, the variation might indeed not have been inherited in the sense of coming directly from the genes that made mother and father what they were - but instead be a random mutation caused by a copying error in the DNA replication that made sperm or egg - or a mutation caused by some kind of mutagen such as environmental chemicals, radiation, etc - or perhaps as a result of viral DNA segments being inserted into the DNA just prior to copying. So your last sentence doesn't really hang together. We know the reasons why there is variation over time and how those changes get preserved over the generations. We're not discussing the source of the variation - but rather the reasons for those particular variations to be selected (ie either artificially or naturally or some odd hybrid of the two). SteveBaker (talk) 07:51, 8 March 2009 (UTC)
Assuming a wife is faithful to her husband, and excluding identical twins,why are siblings not exactly alike except for differences due to age and gender? I am sure science has provided no proven reason for this. I don't like to see a dogmatic stand taken on an unproven hypothesis. But regardless of the reason for the variation, some of the differences will have an affect on survivability, however slight. – GlowWorm.
I am sure science has provided no proven reason for this. I am astonished that you could be so ignorant of the work of Watson and Crick, Gregor Mendel and many others. The reason for the differences in siblings has been well established by science to be due to them not having the same DNA. The process of DNA combination between parents is well understood and has been investigated by many working in genetics. It is certainly not an unproven hypothesis. SpinningSpark 10:44, 8 March 2009 (UTC)
If my senses didn't tell me better, GlowWorm was being sarcastic, or just a wind-up merchant. The concepts of chromosomal crossover and independent assortment are widely taught to 14-16 year olds in school (in the UK at least). Here are a couple of nice simple animations that would be typically shown: [1] [2] --Mark PEA (talk) 11:45, 8 March 2009 (UTC)
My education in science ended at age 13, except for some later training in electronics in the Air Force. I may not be up on book larnin', but I can take an outsider's view of science. As an earlier poster remarked, education tends to a give tunnel view of the subject learned. Also, well educated persons often take an arrogant attitude about their knowledge of other men's ideas, but they have no original thoughts of their own, not even farther down the tunnel. They are not creative; they are mere memorizers. In a few minutes, I will post on this thread some original ideas of my own about evolution. – GlowWorm.
13? How come? --Tango (talk) 22:19, 8 March 2009 (UTC)
I often feel the same way about professional athletes. All the training makes them so arrogant about their own abilities that it makes it obvious they don't really have those abilities. What good is training, anyway? arimareiji (talk) 22:28, 8 March 2009 (UTC)

(Experts should look away because I'm about to horribly simplify this for the purposes of explanation)
So let's explain to GlowWorm how come two (non-identical) brothers or sisters end up being different. The DNA in our cells is wound up into 23 separate paired 'chromosomes' comprising tens or even hundreds of thousands of 'genes' - and it's 'genes' that pretty much determine how we're going to turn out. When a cell divides, the DNA is duplicated and hence each cell has an identical copy of all of that stuff. When a mommy and a daddy who love each other very much make a baby - the baby gets 23 chromosome pairs - and a complete set of genes but it's random whether a particular set of genes on those chromosomes comes from the mother or the father.
So if (say) there is gene for eye color and a gene for hair color is on (I have no idea whether that's true or not...but it'll be something like that) - and if mommy is a blue-eyed blond and daddy is a green-eyed redhead - then in a large family, on average, roughly half of the kids will get that hair color gene from their mother and half will get it from their half of them will have blue eyes, the other half will have green eyes - half will have blond hair and half will have red hair. But that means that there are 4 possible types of kid - blue/blond, green/redhead, blue/redhead and green/blond. (In practice, it's nowhere NEAR as simple as that...but this is the basic mechanism). Now, if there is a third, for example - then because that too can come from either mommy or daddy - you'll have eight possibilities for the kids: blue/blond/boy, green/red/boy, blue/red/boy, green/blond/boy, blue/blond/girl, green/red/girl, blue/red/girl and green/blond/girl (phew!). Add in the gene for colorblindness - now you have 16 possible children, add in the gene for hating the taste of broccoli and you have double the number of possibilities for each additional gene you consider. Each characteristic from a separate gene doubles the number of 'types' of kid. So the total number of different children that a pair of unrelated parents might have is 2x2x2x2x2x2x2x2x2x2x2x2x....2x2x2x2x2x2x2x2x2x2x2x2...the number of 2's in that huge number is something like the number of genes. There are 10's of thousands of two people could have more 'kinds' of child than there are grains of sand on all the beaches of all of the oceans of all of the planets of the galaxy. So it's no surprise that our children turn out differently...unless they are 'identical' because they came from the same fertilised egg and therefore have the same mix of mommy-genes and daddy-genes.
In truth, that's a horrible over-simplification because (for example) some genes control the 'expression' of others so you might inherit the gene for blue eyes - but the gene for red hair might turn it off and you might get something totally different like brown eyes as a result...and genes are typically inherited in groups - but that's the simple view of why all of the kids of a particular pair of parents come out slightly different...yet all of the kids look like their parents (somewhat) because they picked up all of their genes from one or them.
I hope this helps. (And now I'm going to get my response shot to hell by the experts!)
SteveBaker (talk) 02:05, 9 March 2009 (UTC)

Prevailing winds in Israel?[edit]

Excuse me - does anyone know anything about the prevailing winds in Israel - in other words, what direction that weather fronts tend to move in there? I've been looking around online, and the best source I could find was this map. It looks like Israel should be just on the edge between the trade winds and the westerlies, but I'm unable to figure out which the region tends to belong to. Can anyone help me out with this? Thanks. --Brasswatchman (talk) 19:21, 7 March 2009 (UTC)

Given that Israel is on the Mediterranean, and smack in the middle between major continental land masses, I doubt that the idealized global wind map has any value. Winds will be very much dominated by local effects. --Stephan Schulz (talk) 22:41, 7 March 2009 (UTC)
According to the seasonal weather search for various locations in Israel on, average wind direction varies throught the year and for different locations, from west to northwest to east. ~AH1(TCU) 00:17, 8 March 2009 (UTC)
So I guess there's no real telling, then. Okay. Thank you both very much. --Brasswatchman (talk) 00:53, 8 March 2009 (UTC)

Work done by magnetic fields[edit]

It's true that work can never be done on a charged particle that is moving through a magnetic field correct? But a magnetic field can do work on a conductive piece of matter right? ScienceApe (talk) 22:33, 7 March 2009 (UTC)

I don't know what makes you think that no work is being done on a charged particle moving through a magnetic field. There is a force acting on the charge given by;
q is the charge
v x B is the vector cross product of the charge velocity and the magnetic field flux density
so clearly work is being done unless the charge is stationary or moving in the same direction as the field. Similarly work is done by a magnetic field on a conductor only if there is current flowing in it and the conductor "cuts" through the magnetic field, that is, moves in a direction not aligned with the field. In this case the force is given by,
where is the component of field perpendicular to the current.
SpinningSpark 03:44, 8 March 2009 (UTC)
Work is force acting through a distance. As your formula shows above, the force is always perpendicular to the particle's velocity. No work is done on the particle by the magnetic field.—eric 03:56, 8 March 2009 (UTC)
SienceApe, Yes, that's correct (if there is an electry current flowing through the wire), but with a caveat: The work is actually done by the electric field necessary to keep the current flowing. Dauto (talk) 04:11, 8 March 2009 (UTC)

Apart from the work which could be done on a charged particle by a magnetic field, work could be done on the same charged particle by an electric field. Edison (talk) 05:01, 8 March 2009 (UTC)

Species commonly known by binomial name?[edit]

I noticed in the article for Boa constrictor it notes that the species' common name is the same as its binomial name, which is unusual. Are there any other species for which this is true? (Other than bacteria, of course.) I'd like to see those for which the common name is the full binomial name, not just the specific name, since the latter is far more common. (talk) 23:16, 7 March 2009 (UTC)

This is true of Homo habilis and Homo erectus in my experience. Algebraist 23:19, 7 March 2009 (UTC)
Lots of bacteria are, or at least by abbreviations of the binomial name. E. coli for example, short for Escherichia coli. Lots of species that simply don't have a common name due to not being very common - extinct species, like the ones Algebraist mentions, as a good example of that. --Tango (talk) 23:26, 7 March 2009 (UTC)
Tyrannosaurus rex, orca (although some call it Killer Whale, orca is becoming more popular). ScienceApe (talk) 00:31, 8 March 2009 (UTC)
Have you really seen 'Orcinus orca' used as a common name? Algebraist 00:35, 8 March 2009 (UTC)
I recall seeing the name as Orca orca a long time ago. ScienceApe (talk) 01:57, 8 March 2009 (UTC)
This is a great question, apart from Boa constrictor I can't think of any extant species that commonly goes by a full binomial name. Rockpocket 01:00, 8 March 2009 (UTC)
Its pretty weak, but perhaps Pichia pastoris might be another? Rockpocket 01:08, 8 March 2009 (UTC)
The downside of that one is that it makes the lab smell like feet. Ugh. Saccharomyces cerevisiae smells so much better.... TenOfAllTrades(talk) 01:16, 8 March 2009 (UTC)
I have one! Aloe vera. Rockpocket 01:12, 8 March 2009 (UTC)
Great question, and this (Aloe vera) is the best response I've seen. --Scray (talk) 03:50, 8 March 2009 (UTC)
I think T.Rex, E.Coli, Homo Habilis and such are cheating - they just don't have common names - they were named by scientists and the scientific names have stuck. I think Boa Constrictor is actually pretty unusual. SteveBaker (talk) 01:13, 8 March 2009 (UTC)
Model organisms used in lab work are popular candidates. Since Pichia and E. coli have already been mentioned, let me throw in the nematode C. elegans.
I'd also be tempted to argue that baker's yeast – Saccharomyces cerevisiae – might be a legitimate candidate. When baker's yeast is used out the real world, most people aren't thinking of it as a living organism — it's just an 'ingredient'. I suspect that when people talk about Saccharomyces as a living creature rather than a kitchen aid, it's more often referred to by its binomial name. TenOfAllTrades(talk) 01:16, 8 March 2009 (UTC)
Not sure this is as pure and example as the Boa but how about Glis glis aka the Edible Dormouse. In the UK around Tring in Hertfordshire and Buckinghamshire where it has become naturalised following escape from the Rothschilds Estate it is only known by its binomial name. Use Edible Dormouse and you are likely to get blank looks. See [3] Tmol42 (talk) 01:38, 8 March 2009 (UTC)
Aha ha ha! Classic Daily Mail: "The area contains many highly desirable and expensive properties and some residents even fear their house prices could suffer." :D (talk) 17:15, 8 March 2009 (UTC)
In the spirit of Aloe vera above, perhaps Ginkgo biloba counts? I seem to recall hearing something about how it improves your memory or some such… I'm not quite sure. – 74  07:15, 8 March 2009 (UTC)
Does Echinacea count? It's a genus with several species, but at least the binomial name is commonly used. (talk) 08:38, 8 March 2009 (UTC)
Same for Acacia and Eucalyptus. --Mark PEA (talk) 11:18, 8 March 2009 (UTC)
And gorilla. --NorwegianBlue talk 11:45, 8 March 2009 (UTC)
As has been emphasized a few times, the question was about binomial names, therefore these last few don't qualify. Ginkgo biloba does seem like another winner. By my count, that's 3: Boa constrictor, Aloe vera, and Gingko biloba. Did I miss any? --Scray (talk) 16:44, 8 March 2009 (UTC)
Gorilla sort of counts since the binomial name is Gorilla Gorilla. --Tango (talk) 18:44, 8 March 2009 (UTC)
I'd dispute the Ginkgo. The books all say its common name is the 'maidenhair tree', but even if you discount that, I would argue that its common name is 'ginkgo', not 'ginkgo biloba'. --ColinFine (talk) 19:29, 8 March 2009 (UTC)
One organism that goes by its binomial name in Norway, is Gyrodactylus salaris (link to various news items). And since model organisms were mentioned above, let's not forget Drosophila melanogaster. --NorwegianBlue talk 19:51, 8 March 2009 (UTC)
D. melanogaster is commonly called a "fruit fly". However, I'd say that Tyrannosaurus rex should qualify. It's a well-known beast and the only way its name is shortened in common use is by reducing the first word to an initial, which is also scentific practice as in E. coli. --Anonymous, 20:27 UTC, March 8, 2009.
I've never heard the term "maidenhair tree" (131,000 hits on Google), but I see "Ginkgo biloba" all the time (2,290,000 hits on Google). I agree that Tyrannosaurus rex is the common name (but less compelling than some of the others since it's extinct and thus has had less chance than some of the others to have a common name, IMHO). --Scray (talk) 00:08, 9 March 2009 (UTC)
Agree with scray about Ginkgo biloba vs maidenhair tree. Also Aloe may sometimes be used in place of Aloe vera the same as Boas for Boa constrictor (although both are these may be confusing because they are also frequently used to refer to other members of the group). It's worth remembering that we're only refering to English here. Ginkgo biloba does have a common name in Mandarin and probably other Chinese dialects/languages Nil Einne (talk) 04:34, 9 March 2009 (UTC)

I did say "other than bacteria", since things like E. coli and Staphylococcus aureus seemed too obvious. But thanks for all the suggestions. The count is now Boa constrictor, Tyrannosaurus rex, Aloe vera, Glis glis and Ginkgo biloba? (talk) 02:45, 9 March 2009 (UTC)

This question has cropped up before here and here. – 74  03:47, 9 March 2009 (UTC)
Nice pickup, but the current discussion appears to be both more legible and more complete. --Scray (talk) 04:24, 9 March 2009 (UTC)
The OP seemed to be looking for a definitive answer; I was just establishing some baselines that show we're doing pretty good. – 74  04:43, 9 March 2009 (UTC)
I thought public logs of #wikipedia were verboten?! *ducks incoming meteor of wrath from Bureaucrats* (talk) 10:17, 9 March 2009 (UTC)

Salvia divinorum Mikmd (talk) 15:20, 11 March 2009 (UTC)