Wikipedia:Reference desk/Archives/Science/2010 January 19

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January 19

Circuit Problem

Imagine some resistors set in parallel in a circuit (there may be more elements to the circuit). Kirchoff's law says that, for any path the current might take, it's change in potential must be the same. Why is this true (ie what forces the electrons all to lose the same amount of potential (or energy or wtv))? —Preceding unsigned comment added by 173.179.59.66 (talk) 00:26, 19 January 2010 (UTC)

I'm not sure it is correct to attribute this to a "force". An electron travels through the path of least resistance, so as it loses potential it increases the resistance of the path it took in the conductor, mainly due to heat. This means the next electron behind it won't take exactly the same path, it will take the next best path. This all happens at the speed of light, so when a current is actually flowing through all the parallel resistors it only makes sense that all the electrons lose the same potential. When any one electron has more or less potential then the others around it, it takes a slightly more or less (respectively) "difficult" path in the circuit and then loses more or less potential until it is equal. Otherwise all the current would ravel through the path of absolute least resistance, regardless of how many resistors are in parallel. Sorry my explanation is a little obtuse, maybe someone has a more elagant answer.Vespine (talk) 01:10, 19 January 2010 (UTC)

This sounds a bit like a homework question, so think about what would happen otherwise. If some lost less potential, you'd have electrons gaining potential as they travel through the loop. A 5V battery can't give a potential higher than that, it would be a violation of the conservation of energy. ~ Amory (u • t • c) 01:16, 19 January 2010 (UTC)

Empirical studies of emotion

Is there any scientific or experimental backing to confirm that the words we use to describe emotion are valid and actually reflect objective reality? For example we have common words that describe colours, and these are underpinned by scientific studies of colour in terms of the spectrum and three colour-detecting cells in the human retina. Have any underlying dimensions been experimentally discovered for emotions? Or are we just stuck at the qualitative level? 89.240.50.241 (talk) 00:52, 19 January 2010 (UTC)

Have you checked our Emotions article? Mitch Ames (talk) 00:55, 19 January 2010 (UTC)

You can't quantify emotion any more than you can explain how chocolate tastes. There is a thing called internal validity that measures how a term is used by different people at different times. That is to ensure that what you're calling 'anger' isn't a scattershot representation of all sorts of different negative moods. That sort of thing. Vranak (talk) 05:50, 19 January 2010 (UTC)

Well we can quantify emotions. I think it is commonly accepted that fear is associated with the fight-or-flight response, which is activated by the sympathetic nervous system; thus we could do a controlled study where adrenaline and its metabolites are measured from samples of blood taken, place it on a graph where subjects report a specific emotion. Look at Graph B on this picture to see what I mean (this is a measure of amphetamine though, not adrenaline).

If you mean that we can never "know" what a person is feeling, then we are talking about something else known as the problem of other minds. This doesn't mean we can't quantify things, as the OP already mentioned that the colour spectrum is always the same, although we can't "know" what other people are actually seeing (or whether they aren't a philosophical zombie). (Sorry for the scruffy structure of this post, in a hurry) --Mark PEA (talk) 10:46, 19 January 2010 (UTC)

The science on this goes all the way back to Darwin's book The Expression of the Emotions in Man and Animals. Also very influential is Paul Ekman's work showing that cultures all across the world use very similar facial expressions for basic emotions. Looie496 (talk) 18:08, 19 January 2010 (UTC)

So the answers are No, Yes. 78.151.106.238 (talk) 19:13, 19 January 2010 (UTC)

Huh? The answers are yes there is experimental backing (going back to Darwin) that the words we use reflect experimental reality, yes underlying dimensions have been discovered (by Ekman among others), no we aren't just stuck at the qualitative level. For a guide to research on the underlying neural bases of emotion, the books and articles by Joseph LeDoux are a good place to start. Regards, Looie496 (talk) 19:34, 19 January 2010 (UTC)

From what I've read in the Ekman article, it seems that he has only shown that his categories have Social reality, not the underlying physiological mechanisms as with colour and cells in the retina. Money now or belief in witchcraft in the past had similar universal social reality but with no underlying physiological basis. So the answers are still No and Yes, with the possible exception of fear. Believing social reality to be objective truth is what the far right do. 92.29.57.199 (talk) 11:19, 20 January 2010 (UTC)

Well, he showed more than that. Social reality would mean, for example, that all members of a given community understand a smile in the same way. What Ekman showed is that isolated cultures from all across the world understand a smile in the same way. That takes us from social reality to biological reality, as I understand it. Certainly Ekman thought that that was what he had done. Looie496 (talk) 17:40, 20 January 2010 (UTC)

People from different cultures believe in witchcraft or money, and neither have an underlying physiological mechanism. As far as I am aware Ekman never demonstrated a physiological mechanism for emotion, as with colour and retinal cells. 92.29.57.199 (talk) 21:34, 20 January 2010 (UTC)

illusion of wheel's direction

how do we get an illusion of a wheel of a car moving in backward direction,when car is at great speed. —Preceding unsigned comment added by Myownid420 (talk • contribs) 02:28, 19 January 2010 (UTC)

See Wagon-wheel effect. Nanonic (talk) 02:37, 19 January 2010 (UTC)

Damn, too slow! 218.25.32.210 (talk) 02:37, 19 January 2010 (UTC)

There is an absolutely brilliant depiction of the Wagon-wheel/stroboscopic effect on YouTube.HERE The film/video camera shutter is synchronised with the Helicopter rotors rotation. As a result the main rotor appears stationary as the helicopter flies around. --220.101.28.25 (talk) 10:00, 19 January 2010 (UTC)

In respect to , it's not that the effect occurs, but rather than the picture actually does reverse -- if we want to demonstrate the illusion, why does it have to make it happen artificially? (For example, This spinning girl illusion works without "cheating.") DRosenbach ^{(Talk | Contribs)} 13:18, 19 January 2010 (UTC)

Uh, that's a completely different effect. 17:35, 19 January 2010 (UTC)

That image isn't cheating: the whole idea is that the two directions of motion are aliased with the frequency of update in the recording (be it a film or a GIF) and thus are indistinguishable. Given only the final product and no contextual clues, it's impossible to say whether it "actually" reverses or not. --Tardis (talk) 18:46, 19 January 2010 (UTC)

Yep - DRosenbach is not understanding the problem. The spinning girl illusion is due to a lack of depth information - the silhouette of a clockwise rotating dancer looks identical to that of an anticlockwise rotation - so your brain can't understand which it is and flips back and forth between representations. The animated GIF is true temporal aliassing - which is a completely different illusion. SteveBaker (talk) 20:14, 19 January 2010 (UTC)

In computer graphics, we call this "temporal aliassing".

The easiest way to think about this is to imagine a wheel with three identical, equally spaced, spokes. In a TV or movie image or computer graphics or something, if the wheel rotates clockwise exactly 120 degrees from one still image to the next then every picture of the wheel would appear to be identical - even though a different one of the spokes would be at the top of the picture each time. Hence, it would not appear to rotate even though it's spinning really fast. However, if the wheel were to rotate only 119 degrees each time then there would be a visual conundrum: Did the wheel rotate 119 degrees clockwise - or one degree anticlockwise? In either case, the resulting series of images would be just the same. Our eyes & brains seem to prefer the slower rotation - so a wheel that's spinning at 119 degrees per frame seems to be rotating slowly backwards. As the wheel slows down, this effect persists - so if it rotates 100 degrees clockwise, our brains will insist that it's rotating 20 degrees anticlockwise...all the way down to 60 degrees. At 60 degrees per frame, we would get the same image whether we rotated 60 degrees forwards or 60 degrees backwards...the image would be identical. Now our poor brains can't figure out what's going on and instead of seeing rotation, we see a kind of flickery 6 spoked wheel! Once you get below 60 degrees per frame, we again have two interpretations - 59 degrees clockwise or 61 degrees anticlockwise. Again, our brains prefer the lower number - so FINALLY, we see what's really going on - a wheel rotating clockwise at 59 degrees per frame.

The angle below which everything looks normal is therefore exactly half of the spacing of the spokes. If you have a 4 spoked wheel, the anomaly happens when it's spinning at 45 degrees per frame or more...for a 36 spoked wheel, it's only got to be rotating at 5 degrees per frame to look bad. That's why the effect is called the "Wagon wheel effect" - because in the days of early cinema, we had maybe only 24 frames per second - and the stage coach in the cowboy movies that were popular back then only had to rotate fairly slowly to provoke the problem. Wagon wheels have a lot more spokes than most other kinds of wheel! It is probably also the case that filming out in the bright sunny desert where most cowboy movies were made means that the shutter time on the camera had to be kept short - that reduces the effect of motion-blur which greatly enhances the effect. In computer graphics, it takes a lot of effort to simulate motion blur and (in effect) we have an infinitely short "shutter time" - that means that this effect, which had gone largely unnoticed through the era of cars and modern TV cameras is now beginning to show up again.

What's kinda mind-blowing is that if you merely paint one of the spokes a different color - the illusion more or less vanishes. By breaking the rotational symmetry, the wheel now has to rotate 180 degrees per frame in order to cause this effect - and that's a really fast-moving wheel. We use this technique in computer graphics to try to break the illusion - making all of our wheels asymmetric whenever we can (painting the word "GOODYEAR" in white on the sides of tyres is a good example of that).

SteveBaker (talk) 20:11, 19 January 2010 (UTC)

SteveBaker that may be the best RefDesk response ever. Cuddlyable3 (talk) 20:56, 19 January 2010 (UTC)

Nah - I forgot to mention the Nyquist limit and the 'half the sampling frequency' thing - which ties in nicely with half of the angle of rotational symmetry. SteveBaker (talk) 02:55, 20 January 2010 (UTC)

OK...I thought it was an issue of, "if you keep looking at this, it will switch," and that's why I compared it to the spinning/oscillating girl. With my understanding of it, and that's an apparently incorrect understanding as you explain it, my rationale, which is now false, was as follows: If it's only that after a few seconds of watching the little GIF file above that it appears to switch, why does it appear to go in the opposite direction even if one doesn't look at it for the first half of the video. DRosenbach ^{(Talk | Contribs)} 02:42, 20 January 2010 (UTC)

Nope - this is something completely different. If my three-spoked wheel example has the wheel rotating at 110 degrees per frame, the backwards 10 degrees per frame that you think you're seeing is a rock-solid effect, you can't keep looking at it and see it 'switch'. The GIF is changing direction because the animation is slowly increasing in speed until it hits the temporal aliasing speed - then, although the speed is still increasing, it appears to slow down, stop and then reverse. You can visualize that in the same way we did with the three-spoked wheel. Imagine a video shot out of the window of a car that's driving along parallel to a really long picket fence with vertical strips every 12 inches. If you drive at 12 inches per frame, the fence seems stationary - if you drive at 11 inches per frame, it seems to be moving backwards - at 6 inches per frame, you see twice the number of fence posts - but kinda flickery - at below 6 inches per frame, everything looks normal. In the GIF animation, the green waves are like the fence panels. SteveBaker (talk) 02:55, 20 January 2010 (UTC)

Thanx! (even though this wasn't my question :) DRosenbach ^{(Talk | Contribs)} 04:10, 21 January 2010 (UTC)

This is more than just the "wagon-wheel effect" from old westerns. I saw an ultra-modern car TV ad the other day, and the same thing was going on. One would think with digitization they could make it "look right". But maybe people are so used to seeing it, that if it looked "right" they would think it looked phony? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:15, 21 January 2010 (UTC)

circuits

what will happen if we put a resistor of,say, R₁ and a simple wire say copper wire in parallel in a circuit made up of copper wire,with a battery and a switch only. what will be the resistance in the circuit.could it be solved like that

1/0 + 1/R1 = 1/Rp     (as the resistance of copper wire is 0)

where R_p is total resistance in parallel. —Preceding unsigned comment added by Myownid420 (talk • contribs) 02:51, 19 January 2010 (UTC)

The resistance of a copper wire is not zero, see here for some numbers. From my knowledge of electronics, what you seem to be suggesting would most likely result in a short-circuit. Such a circuit would have close to (but not exactly) zero so you can pretty much ignore the resistor since almost all the current is going to flow through the copper wire. Also, you probably shouldn't try to divide by zero. - Akamad (talk) 03:06, 19 January 2010 (UTC)

The current will be large and limited by the resistance in the battery. As Akamad said you can ignore the parallel resister. If there is no resistance in the wire or battery the current will still be limited by inductance, and will grow linearly with timeGraeme Bartlett (talk) 08:12, 19 January 2010 (UTC)

plate changing speeds

Is this possible the plate movement will start out slow then end up moving fast? Because Africa 100 million years ago move faster now it slow to 2 cm/year. Is this possible Antarctica could eventually move as fast as Australian plate? WHat changes the speed motion? Could Australia eventually slow down?--69.228.145.57 (talk) 04:49, 19 January 2010 (UTC)

It is possible, and the direction of movement could change over time. What happened in the past can be found by the geomagnetic reversal timing signatures on the ocean floor. Predicting the future is more difficult. One book I read stated that the circulation in the mantle is turbulent and so it varies over time and is not simply predictable. Graeme Bartlett (talk) 08:42, 19 January 2010 (UTC)

nuary 2010 (UTC)

Tree of Life in circular form

A question rather than an answer from me for a change. The current Evolution articles' template features a diagram of the "Tree of life" in a space-saving circular layout, and in recent years I've seen other similarly circular versions elsewhere. Does anyone know where this general circular layout of it originated? (The reason I ask is that, while desk-editing a school science textbook in 1990, I was asked by the authors to design and/or source a number of diagrams and other pictures, including a very simple Tree of life, and came up with just such a near-circular layout in order to save space on the page. Although I had no previous example consciously in mind it seems very unlikely that circular Trees of Life weren't already in use and quite probable that I'd seen one before.) 87.81.230.195 (talk) 04:59, 19 January 2010 (UTC)

It has developed gradually. At [1] you can see Darwin's own sketch where the branches from the roots go in different directions. This hand-made tree: [2] from Science in 1997 uses a similar space-saving layout. The circle appears naturally as you add more and more branches. The web-based generator for the image you refer to can be found at [3]. The company behind it claims it's a novel type of visualization, so according to them the style orignated in 2006. Though in my opinion, the main driver is large tree-of-life databases. EverGreg (talk) 09:45, 19 January 2010 (UTC)

Some more examples: Carl Woese in 1988 (figure 4) [4] Cover of Molecular systematics 1996: [5]. There's also an example you may have come across in school. There's a circular diagram where each kid in class starts off in the centre and then moves outward in a circular tree according to genetic properties such as gender, ability to roll your tongue e.t.c. It's not a phylogenetic tree, but gives an image of genetic similarity. EverGreg (talk) 10:06, 19 January 2010 (UTC)

Thanks for those suggestions, EverGreg, but some of those examples are, like Darwin's familiar original (published, incidentally, by the same firm I was working for), radial rather than circular, while the circular ones postdate my own usage. I certainly never encountered your school exercise (which would have to date back nigh-on four decades for me to have done so). Surely someone can come up with a good pre-1990 example to save me from the hubris of suspecting I may have originated it myself? 87.81.230.195 (talk) 10:56, 19 January 2010 (UTC)

Electrical Heating Distribution

So the above thread about heat pumps has me wondering about electrical heating in general. In what parts of the world is electrical heating commonly used to heat buildings? Here in (Suburban) Minnesota gas heating is the norm, and electrical heating is pretty much unheard of, except for maybe a small space heater in an ice shack or something. I understand that in the UK it's pretty common to take advantage of lower energy prices at night with a storage heater. We also had someone from Australia and Texas say that they had electrical heating. It seems to be that electrical heating is more common more temperate places. Do southern Europeans use electrical heating on a large scale? What about northern Europeans? I assume that Russians use natural gas (because they have enough of it), but I don't really know. What about in developed Asian countries like Japan? Buddy431 (talk) 05:23, 19 January 2010 (UTC)

Electric heating is cheap to install, so low cost systems in Australia use a simple fan over hot element heating. More sophisticated systems could be in slab or floor eating or the storage system using off peak electricity you mentioned. Reverse cycle systems can be quite efficient giving a gain of 4x the energy consumed. To use gas, reticulation infrastructure is needed in the form of plumbing or big gas bottles. Some do use this. Coal in furnaces is rare, and in the past there used to be oil heaters. Before this burning wood in fireplaces or stoves was common. Graeme Bartlett (talk) 08:09, 19 January 2010 (UTC)

I had electric baseboard heaters when I lived in Tennessee. And I wasn't the only one. I knew several people, especially those who were living in trailers who had electric heat. Dismas|^(talk) 09:51, 19 January 2010 (UTC)

In some parts of canada hydroelectric electricity is cheaper than gas. (Probably due to subsidies.) So electric heat is used. Otherwise electric heat is used when the installation cost of a gas burner is more than the savings of using gas vs electricity. Electric heat is very cheap to install. U.S. view: This is typically in the south where it doesn't get that cold. You have sort of a continuum - in the north, all gas. No A/C, so it's usually radiators (water). In the middle it's electric heat, and no A/C at all. In the south you have A/C (meaning the ductwork is anyway already there), so they use a central heat source, and they do gas. This is generalizing a lot of course. Also some places do not have gas service, and oil in not available. So electric is the default. These days, even in the north new construction comes with A/C, and the price of electricity has gone up more than gas, so it's pretty much all gas if it's available. Ariel. (talk) 10:27, 19 January 2010 (UTC)

Electrical heating is clearly the norm in Norway, a developed country in the north. Historically, we had very cheap hydroelectricity, you certainly don't need subsidies for this. Prices do rise as transmission capacity to the rest of Europe improves, though. There are (almost?) no distribution nets for gas in Norway, and I don't think it would be economic to build those; gas is piped from Norway's large sub-ocean gas fields via stations on the coast across the North Sea to Britain and the Netherlands. Large buildings do use oil for fuel though. Many single-unit houses have wood ovens as a supplement. I think electricity is the norm in Sweden and Finland as well. Jørgen (talk) 12:55, 19 January 2010 (UTC)

Electricity prices for the Nordic countries are here, in EUR/MWh, it would be interesting if some US users could compare this to their local heating prices (assuming 100% electricity efficiency). The electricity market in Norway is very competitive, I think the end-user prices are very close to the "market trading" prices (though transmission cost of 0,39 NOK/kWh (ca 7 US cents) comes in additition (at least that's the price in my area)) Jørgen (talk) 13:11, 19 January 2010 (UTC)

Here is a relatively informative article per your question, as you can see from the graph $.07 US/kwh is pretty darn low, a price almost no one in the US has seen since 2005. Depending on the natural gas spot market in the US, the price tends to be around 1/3 as much to get a BTU from NG compared to electricity (assuming the NG furnace is of modern efficiency). --Jmeden2000 (talk) 16:52, 19 January 2010 (UTC)

In some parts of Russia and Ukraine, they still use coal gas... 24.23.197.43 (talk) 07:22, 23 January 2010 (UTC)

difference between sea and ocean

what is the technical differnce in the definition of a sea and an ocean?Denito (talk) 07:46, 19 January 2010 (UTC)

Sea is small and Ocean is big. eg sea of Galilee is pretty miniature, but famous. The oceans currently on earth are pretty fixed in number, but perhaps your definition request is important to naming oceans in the geological past of earth, or on other planets. The Sea of Marmara is claimed to be the smallest sea, but sea of Galilee is smaller. According to Wikipedia a Sea is large, and an ocean is major. Graeme Bartlett (talk) 08:02, 19 January 2010 (UTC)

Even worse though, while sea of Galilee is a traditional name, it is actually a freshwater lake. Googlemeister (talk) 14:41, 19 January 2010 (UTC)

To further confuse things, some seas are part of a larger ocean (for example, the Carribean Sea is part of the Atlantic Ocean; the Andaman Sea is part of the Indian Ocean), whereas other seas, such as the Baltic Sea are separate bodies of water that are connected to oceans. See marginal sea and mediterranean sea. Gandalf61 (talk) 10:31, 19 January 2010 (UTC)

Oceans abut and separate continents. A sea is just some water on which one can sail a boat. Cuddlyable3 (talk) 13:15, 19 January 2010 (UTC)

Hmmm. The Bering Sea separates North America and Asia; the Red Sea lies between Asia and Africa; and the Mediterranean Sea has coastlines in Europe, Africa and Asia. But they are not oceans. Gandalf61 (talk) 15:10, 19 January 2010 (UTC)

Indeed. I did not claim that oceans have a monopoly on what they do. Cuddlyable3 (talk) 20:44, 19 January 2010 (UTC)

Because "ocean" is of European origin, it should be obvious that the use came from early Europeans. Add to the concept of an ocean the earlier fact that the world was flat, an ocean was the body of water that, if you sailed through it, led to the edge of the world. The world consisted of Europe, Asia, and Africa. The four oceans (just four at the time) were to the north, east, south, and west of the world. Once the world was proven round, there was no need to change the name. -- kainaw™ 15:24, 19 January 2010 (UTC)

Not to get too humanities on you, but that brief history of European knowledge of geography is ridiculously inaccurate. The Earth was known to be round in ancient and medieval times: for example, see our article on mappa mundi. 86.178.230.208 (talk) 17:20, 19 January 2010 (UTC)

I think there is also considerable geographical variation in the use of the term. I've noticed that Americans use the word "Ocean" in many contexts where the British would say "Sea". That may be because the USA is bounded by a couple of oceans where the Brit's have the North Sea on one side and an Ocean on the other. But it's only a matter of linguistics - there isn't any science behind it, beyond some vague concept of size. However, people still talk about "Sailing the Seven Seas"...when they probably mean something like "Four oceans and three seas". SteveBaker (talk) 19:11, 19 January 2010 (UTC)

To be more "humanities" in my answer... The English term "Ocean" comes from the Greek Oceanus. It is a concept of a Greek god represented as a world ocean upon which the world floats. The "flat" world concept is a simplification of the of concept of a round world floating in Oceanus. Many cultures named the coastal waters, but continued to refer to the unknown waters as being part of Oceanus, or an Ocean. The modern view of the world ocean is slightly romanticized with the Greek concept of an ocean. Atlantic comes from Greek Atlas, an offspring of Oceanus. Arctic comes from Greek Arktikos - the great bear in the northern stars. Antarctic is away from the bear. Pacific was named a long time later with a Latin name. It seems to me that Magellan should have known enough to give it a Greek-based name. However, the concept of an unknown ocean is what is different about the oceans and the seas. In modern times, very little is unknown. We just continue to use the terms here and there out of tradition. -- kainaw™ 20:22, 19 January 2010 (UTC)

--Mr.98 (talk) 20:37, 19 January 2010 (UTC)

Did you consider looking at Ocean, Oceanus, World ocean, or Atlas (mythology) before requesting a citation? -- kainaw™ 21:05, 19 January 2010 (UTC)

Our article Oceanus attributes that view to some scholars. Do you have a good secondary source we could use to improve the article? Our article World ocean doesn't really talk about it, because it is discussing the actual, existent world ocean. Our article Ocean briefly mentions the idea under the heading culture, but has no sources. Our article Atlas of course mentions that he was considered Oceanus's son, but I don't think anyone was disputing that. It says nothing about this (presumably old even to the ancient Greeks) conception of the world. None of these articles mention four oceans to the north, south, east and west of the world. So maybe Mr.98 did read the articles. In any case, some citation would be welcome to improve these articles (as well as our collective answer). 86.178.230.208 (talk) 18:43, 20 January 2010 (UTC)

I just don't buy the explanation you're giving for how the distinctions came about in our modern world. The original poster is asking about how we might define things today, and appealing to Greek myths is probably incorrect. Geography went through quite a few changes since the Greeks. --Mr.98 (talk) 21:51, 20 January 2010 (UTC)

I think our definition on the ocean page is pretty good. "An ocean is a major body of saline water, and a principal component of the hydrosphere." Now, obviously the line between what isn't a principle component of the hydrosphere or not is somewhat arbitrary, but the acknowledged oceans dwarf any candidate large seas considerably. The smallest ocean is some five times larger than the largest sea, while the rest of the oceans are some 20X larger. IMO the only questionable inclusion is whether the Arctic Ocean counts as an "ocean" or not. The Arabian and South China seas are both very small by comparison to the other oceans. --Mr.98 (talk) 20:37, 19 January 2010 (UTC)

Well...kinda...but the division of a more or less contiguous irregular shape into regions is entirely arbitary anyway. Where exactly the South China sea ends and the Pacific starts is a totally arbitary line. SteveBaker (talk) 02:40, 20 January 2010 (UTC)

Agreed for the most part. (In some cases, underlying geology does make certain waters have a different character than others, I believe, which would seem like a good reason to delineate them, if you were a sailor.) --Mr.98 (talk) 21:51, 20 January 2010 (UTC)

Oceans occur in the unlikeliest places. Thomas Babington Macaulay talked of The old philosopher is still among us ...blinking, puffing, rolling his head, drumming with his fingers, tearing his meat like a tiger, and swallowing his tea in oceans. -- Jack of Oz ... speak! ... 00:29, 20 January 2010 (UTC)

Is one difference that all the oceans on our planet connect together wrapping around the planet while the seas are mostly disconnected from being a solid unit, themselves separated from each other either by oceans or by land? --Neptunerover (talk) 09:08, 20 January 2010 (UTC)

Hmmmm. Black Sea, Aegean Sea, Mediterranean Sea, Ionian Sea and Adriatic Sea. Cuddlyable3 (talk) 13:56, 20 January 2010 (UTC)

No. It really doesn't take much effort to find counter-examples for those kinds of propositions (it would be nice if you did that rather than just posting wild speculation). For example:

• The Mediterranean Sea does not connect to any oceans directly because the Alborean Sea is in the way.
• The Alborean Sea does connect to the Atlantic ocean but only via the straights of Gibralta (is that a 'connection' or not?).
• The Aral Sea is completely land-locked and doesn't connect to any other bodies of water whatever.
• The Sargasso Sea is completely surrounded by the Atlantic ocean and touches no land or other regions of water. It's boundaries are defined by ocean currents and as such, it doesn't even stay in the same place from one year to the next!
• The Argentine Sea is nothing much more than an arbitary strip of water that is some unspecified number of miles wide adjoining a vaguely delimited stretch of coastline on the edge of the Atlantic ocean.

There is no solid rule here - it's a mess. Which is fine if you are just giving random bits of water pretty names - but has zero scientific meaning.

SteveBaker (talk) 14:06, 20 January 2010 (UTC)

Tsk, tsk. "The ALBORAN Sea does connect to the Atlantic ocean but only via the STRAITS OF GIBRALTER." Cuddlyable3 (talk) 17:02, 20 January 2010 (UTC)

Where is the "Alboran Sea", anyway? On my map, there's not such a thing, and the Straits of Gibraltar connect the Mediterranean directly to the Atlantic Ocean. Has that region's geography undergone some major tectonic changes? 24.23.197.43 (talk) 07:19, 23 January 2010 (UTC)

With the exception of oddities like the Sea of Galilee, seas and oceans are all saltwater, right? Misnamed things stay that way. Like Cape Cod, which is not a cape, it's a peninsula. Or, thanks to the canal, it's an island. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:19, 20 January 2010 (UTC)

When you come right down to it - geographers have a hard time of keeping names and definitions in order. (I write this from somewhere in the middle of the island of northandsouthamerica - a piece of land surrounded entirely by water). SteveBaker (talk) 00:09, 21 January 2010 (UTC)

And as with Cape Cod, the canal probably creates two islands out of one. Meanwhile, ponder this, and not just the bizarre fact that most of us live "in continents": Sometimes within a continent you'll find a lake that's self-contained. For example, Crater Lake in Oregon. That body of water has an island within it, an extinct volcanic cone. That island has various little pools of water. So that island also has small "lakes" within it. And some of those little pools have little bitty islands within them... and so on. Hey, why do I suddenly feel like this should be on the math page? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:38, 21 January 2010 (UTC)

Does depth have anything to do with it? Are there any seas as deep as the shallowest ocean's maximum depth? --Neptunerover (talk) 15:50, 21 January 2010 (UTC)

facebook

how do i get annoying stuff like picture of the day , poker ect to stop appearing on my updates? —Preceding unsigned comment added by Killspammers (talk • contribs) 14:24, 19 January 2010 (UTC)

Do you mean on your newsfeed (items that your friends have posted), on your wall (items that applications have posted whilst you're using them) or on your notifications? If you are asking how to hide certain application updates from friends appearing on your newsfeed, you can hover over the item and a 'Hide' button will appear. On clicking this you will get the option to either hide all posts from this user or all posts from this application. You can also do this by clicking 'Edit options' on the footer bar at the bottom of your feed. To stop applications that you use posting to your wall automatically you have to alter the settings for each of these individually. Open an application and hover over 'Settings' on the header bar at the top of the screen, each application has it's own settings page which you would then be able to see and open. Click on this and go to 'Additional permissions' and untick 'Publish recent activity to my Wall'. If you are asking how to stop certain applications appear in your notifications - click on the notification icon in the bottom right of the screen, click 'See more' to go to the notification settings page and untick those applications you don't want to recieve information from on the right hand side. HTH. Nanonic (talk) 15:17, 19 January 2010 (UTC)

no i want to delete the application from my facebook. how do i do it —Preceding unsigned comment added by Killspammers (talk • contribs) 15:57, 19 January 2010 (UTC)

Well, you can start by having a look at facebook's own help on this]. Nanonic (talk) 16:33, 19 January 2010 (UTC)

cyclisation of tryptophan

From the indole article: "Since the pyrrollic ring is the most reactive portion of indole, nucleophilic substitution of the carbocyclic (benzene) ring can take place only after N-1, C-2, and C-3 are substituted."

Is this really true if intramolecular substitution is taking place? Say the C2 site is protected, and C3 site is already occupied. I think if the amino group is protected (maybe by simple acid) the carboxy group will attach on the benzene ring. Can someone confirm this? If so, I'm going to change the article. John Riemann Soong (talk) 15:07, 19 January 2010 (UTC)

Intramolecular effects can beat intrinsic reactivity, but that doesn't change the fact of the intrinsic reactivity. The result for any specific reaction is always a balance (and rationalization based on) of all competing effects. DMacks (talk) 18:50, 19 January 2010 (UTC)

Yes, but that is a preference for substitution, right? I don't think the article should be speaking in absolute terms. John Riemann Soong (talk) 20:22, 19 January 2010 (UTC)

Woman sentenced to 4 years for torching boyfriend's penis

how is it possible she got only 4 years? why didnt they give her 20 to 40 years or even life ? if a man raped her hed get like 10 years but she does something a million times worse and gets only 4 years? http://www.cbc.ca/canada/montreal/story/2007/02/28/qc-andreerene.html

Your opinion is that it was "a million times worse" than rape. Others may disagree with you. In any case, to go with your analogy, I'm not sure what the standard sentence for rape is in Canada, but I'd doubt it's anything like "20 to 40 years or even life". Does anyone know? --Dweller (talk) 16:08, 19 January 2010 (UTC)

According to this website, the maximum possible sentences for sexual assault crimes range depending on the exact conviction, from 6 months to life. The judge gets a lot of discretion as to what exact sentence is issued though. It article implies that the sentencing had a lot to do with mitigating circumstances—the defendant's history of abuse, psychological problems, etc.—which are often taken into account for such things. Whether it is a truly just sentence or not, I don't know, and I'm sure informed people would differ. --Mr.98 (talk) 17:56, 19 January 2010 (UTC)

Personal opinions but I don't give a shit; "mitigating circumstances" of the rapist should have zero influence on their sentence. I don't give a shit if the rapist is temporally mentally insane or whatever the fuck other excuses they boil up - rape is rape and imo rapists should be locked up for life.

The Wikipedia Science Reference Desk isn't a discussion forum for opinions, debates, and chats about current events. Perhaps you could find a suitable internet forum for this type of question? TenOfAllTrades(talk) 16:10, 19 January 2010 (UTC)

(Also where's the science in this question? I suppose there's Fire involved but still... 194.221.133.226 (talk) 16:17, 19 January 2010 (UTC)

I did not find any information out there, other than your link, about this 2007 sentencing, but I would guess that, under the Canadian Criminal Code, section 268, she was probably charged with "aggravated assault", for endangering the life of the complainant, which means she can be imprisoned for up to 14 years. By contrast the penalties for rape in Canada (page 4 of the PDF) are maximums of 10 years ("sexual assault"), 14 years ("sexual assault with a weapon, threats to a third party, or causing bodily harm"), or life ("aggravated sexual assault") — the latter meaning that the rapist also "wounds, maims, disfigures, or endangers the life of the complainant". Those are the maximums — I didn't find any information about why in this specific case she got a lesser prison term (assuming I was even right about the charge brought). I learned two things looking this up — the word "rape" is no longer in the Canadian criminal code; and the first rape law in the USA reduced the penalty significantly if the female victim were single (!). Comet Tuttle (talk) 17:56, 19 January 2010 (UTC)

so why wasent she givin the maximum sentence 14 years? also if you would rather get your genitals set on fire than get raped u need your head examined. —Preceding unsigned comment added by 67.246.254.35 (talk) 18:44, 19 January 2010 (UTC)

Because a judge, probably in light of the aforementioned mitigating circumstances, decided to sentence her otherwise. --Mr.98 (talk) 19:01, 19 January 2010 (UTC)

The general idea is that you want to punish unjustified, capricious malice. It was the opinion of the sentencing parties that Ms. Flame didn't have that much malice. Probably they thought she was somewhat justified. She evidently thought she was justified at the time of doing it, and that would be good enough for me if I were a juror. Vranak (talk) 20:30, 19 January 2010 (UTC)

At least in Germany, and I guess in many other countries, first offenders usually get sentences much below maximum. One reason is that the public prosecutors and judges are civil servants with a life career, i.e. they are professionals and do not have to play to public sentiment. --Stephan Schulz (talk) 22:15, 19 January 2010 (UTC)

I have tried to find the case on the court's website, but it doesn't seem to be there. (If anyone else wants to try, this seems to be the right site, but searching for René under Court of Quebec Criminal division doesn't find anything - the website is in French, however, which is a language I don't actually speak, so a French speaker may have better luck.) --Tango (talk) 01:50, 20 January 2010 (UTC)

Nothing is worse than rape. /thread —Preceding unsigned comment added by 82.43.91.83 (talk) 22:05, 19 January 2010 (UTC)

Murder? Mass murder? Torture? Child abuse? Genocide? You are entitled to your opinion, but it is far from a universally held one. --Tango (talk) 01:37, 20 January 2010 (UTC)

I would rather all those things happen than rape, I would kill myself before rape. Yes, it's not a universally held opinion as you pointed out.

Again, this is not a debate forum. Please stop it. --Anonymous, 01:50 UTC, January 20/10.

I initially read the question as "touching" and the punishment seemed, well, excessive. Edison (talk) 18:02, 20 January 2010 (UTC)

I wonder what the punishment would have been if she coldcocked him? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:38, 20 January 2010 (UTC)

Autocrine signalling

From what I understand, autocrine signalling is where a cell releases a transmitter to purely act on its own receptors, so that it can talk to itself. Is there any good reason for this, or is my premise wrong (i.e. a cell never wants to talk just to itself)? At first glance it appears to be inefficient, probably analogous to sending yourself a text message when you could just store it in the draft folder and avoid the SMS cost. Or writing down "pour yourself a glass of water" and reading it, instead of just pouring yourself a glass of water. --Mark PEA (talk) 17:30, 19 January 2010 (UTC)

I suppose you've never written a todo list? My first thought about its utility is that it lets the cell react over an extended period of time (the lifetime of the transmitter) to even a transitory stimulus. --Tardis (talk) 18:39, 19 January 2010 (UTC)

Well the reason humans write todo lists is because their memories can fail them, otherwise they would just "remember" their todo list (it's the same reason why I think in my head, as opposed to speaking all my thoughts, because that would be a waste of energy*). Also I'm not denying that it has utility, it just seems there would be a more effective way of doing this rather than synthesizing large numbers of receptors and transmitters, releasing them to the outside, and then detecting their signal again. Of course this is useful in paracrine signalling or synaptic signalling, where autoreceptors can be used to maintain negative feedback systems. But for 100% autocrine signalling it is a waste of energy.

*Of course there are reasons to talk to oneself, not for self-communication but to assess one's voicebox, or just being an irrational, drunk idiot :) --Mark PEA (talk) 21:10, 19 January 2010 (UTC)

There are many biological processes in which amplification of a signal must occur: autocrine signalling is one mechanism for this. Of course it is "inefficient" from an engineering standpoint--- one more example of the difference betweened designed and evolved complex entities. alteripse (talk) 19:14, 19 January 2010 (UTC)

(ec) I might speculate that this is an example of evolution deciding to 'reuse its code', as a programmer might say. Rather than having to evolve a whole new set of signalling proteins to trigger some sort of signalling cascade in the middle of an existing pathway, autocrine signalling means that a cell can just use already-existing genes and proteins to trigger a signal in the 'usual' way from an 'external' stimulus. While it might not appear to be the most efficient method, it works. (Consider this — let's say that you are standing in front of a photocopier, and you just happen to need a sheet of blank paper. One solution is to try to figure out how to unlatch and open the paper trays, locate the pages of the correct size, remove a single sheet, make sure everything is closed back up properly, and declare success. Another solution is to just push the copy button on the front panel without putting an original on the glass. Presto — out comes the sheet you wanted, no diassembly or fiddling required. Evolution has a habit of reusing old methods with minor tweaks; it's 'easier' than generating whole new pathways from scratch.)

I'll also note that the definition of autocrine signalling is often a bit broader than simply a single cell acting on itself. It can also include cases where a particular cell signals not just to itself, but also to other cells of the same type. The applications of that sort of signalling are more obvious. Among other things, it allows groups of cells to 'assess' their surroundings by 'polling' their neighbors. A cell can 'sense' whether (for example) a lot of its neighbors are stressed out and respond accordingly. TenOfAllTrades(talk) 19:23, 19 January 2010 (UTC)

Yes, I can understand it in this sense, although my understanding is that this is a form of paracrine signalling. All the answers still seem to be evidence of Unintelligent Design, as I think with the massive amount of junk DNA, the cell could easily have some genes which allow it to talk to itself intra-cellularly that use less energy than this current way. Of course all of this relies on the premise that autocrine signalling is used purely for self-talking, which it probably doesn't (thus, I'd rather it were called pseudoautocrine signalling, since some paracrine signalling is thrown in). --Mark PEA (talk) 21:10, 19 January 2010 (UTC)

In general, autocrine signalling refers to messages between cells of the same type (including messages sent and received by the same cell), whereas paracrine signalling involves signalling between cells of different types or lineages. TenOfAllTrades(talk) 21:57, 19 January 2010 (UTC)

Thanks, my original premise was wrong then. (Retrospectively I now notice that the autocrine article actually states that this type of signalling is amongst the same type of cells). --Mark PEA (talk) 23:48, 19 January 2010 (UTC)

While autocrine signaling may involve more than one cell, there is a decent argument for a cell signaling itself in this way. For example, T cells use IL-2 in an autocrine loop, upregulating their high-affinity IL-2 receptor when stimulated. The extracellular loop provides a mechanism for nearby cells to sense and modulate the T cell's activation. Similar thing can happen with type I interferon signaling - if RIG-I is activated by dsRNA, interferon beta is one product, which may act in both autocrine and paracrine fashion to promote antiviral responses in both the original cell and its neighbors. I don't think your original premise was wrong at all, if I understood it correctly. -- Scray (talk) 01:48, 20 January 2010 (UTC)

In your scenario... (1) stimulus tells cell to to signal to itself → (2) cell produces & releases transmitters → (3) transmitters bind to membrane receptors → (4) receptors activate signalling pathways, which tell the cell to synthesize more receptors (upregulation).

My original question was asking why not just have a scenario where... (1) stimulus tells cell to "signal to itself" → (2) cell activates signalling pathways directly (that receptors in the step 4 above activate), which tell cell to synthesize more receptors. Of course, the answer seems to be that the autocrine signalling also signals to other cells (which opposes my original premise), or that evolution just hasn't had the selection pressure to create new code to do it a slightly more efficient way. --Mark PEA (talk) 10:32, 20 January 2010 (UTC)

Not only that, Mark, but in a case in which a type of cells is already set-up to receive an external message via SIGNAL A, it would be pretty efficient for that cell type to simply release signal A to set off the desired chain of events, rather than develop an entirely new intracellular pathway (and this rationale would suffice even if your autocrine example is a single cell, such as a lonesome leukocyte, etc. DRosenbach ^{(Talk | Contribs)} 04:20, 21 January 2010 (UTC)

Technical vs managerial career track

I'm hoping you RefDesk folks can refer me to some essay, website, book, etc that discusses the choice faced by a scientist or other technical worker when presented with the opportunity to move into management. (I'd love to discuss this with someone, but I understand the RefDesk isn't the place for it). ike9898 (talk) 17:41, 19 January 2010 (UTC)

See Dilbert (sorry). Looie496 (talk) 18:00, 19 January 2010 (UTC)

I'm not familiar with any books confronting this career choice, but googling manager career site:slashdot.org will yield many threads on the subject. Warning: Many "contributors" are grousing computer programmers who believe all management is counterproductive micromanagement. If you're looking for books on technical management (rather than focusing on the career choice which was your actual question), The Mythical Man-Month is considered a classic of software development management. Comet Tuttle (talk) 18:33, 19 January 2010 (UTC)

Managers get paid more and they are the boss. 78.151.106.238 (talk) 19:08, 19 January 2010 (UTC)

In my particular situation (US government), the difference in pay is small and and in my current situation as a researcher, I have a fair degree of autonomy. Both these factors reduce the advantages of moving into management. ike9898 (talk) 19:21, 19 January 2010 (UTC)

That may be true now, but think what will happen in the future. My guess is that in the long run you will be earning more money and having more status. 78.151.106.238 (talk) 20:38, 19 January 2010 (UTC)

If you like long meetings, presenting in front of groups, and having to nag deadbeats who are late to work and who slack off, then, by all means choose management. If you don't like those things and like to create things of value yourself, then choose the technical path. Technicians can pat themselves on the back and say, "I built that web site" or "I made that program." Managers aren't bad people. Some take joy in befriending their employees and rewarding them when they succeed. But eventually, you have to discipline them, too. That's not always a fun thing to do.--Drknkn (talk) 19:33, 19 January 2010 (UTC)

Its just as easy to spin that the other way - technicians would tend to do more repetative work with less responsibility, hence more boredom and lack of fulfillment. There are many different styles and fads of management or (not the same thing) leadership - autocratic, consultative, etc etc. Take your pick. And you can build something without doing the labouring yourself - hence you build bigger and more impresive things. 78.151.106.238 (talk) 20:38, 19 January 2010 (UTC)

Engineers are people who can do what they don't control. Managers are people who control what they can't do. Cuddlyable3 (talk) 20:39, 19 January 2010 (UTC)

Its difficult to recommend a book without having more information on what kind of management you see yourself doing, and what aspect of management interests you. Could you supply more details please? 78.151.106.238 (talk) 20:49, 19 January 2010 (UTC)

More details as requested:

• The most sensible and accessible type of management for me is management in government research agency. Such managers are involved in research in a sense, but they interact with the research indirectly, never hands-on.
• I'm not interested in management in particular, but I have the type of personality that I can get interested in also anything (e.g. editing the Wikipedia article on Ladies' Home Journal - I am a hetero male and do not read this magazine!)
• It seems to me that windows of opportunity to switch tracks are limited. I'm concerned that I might regret letting such a window pass me by.
• It seems that many older people, even older technical people, have less patience, interest and competence with new technology. Presumably, someday I'll be one of those people.

ike9898 (talk) 21:11, 19 January 2010 (UTC)

Thank you for assuaging natural worries about how reading too much might be influencing you, though that was TMI. Cuddlyable3 (talk) 12:03, 20 January 2010 (UTC)

What?? ike9898 (talk) 14:35, 20 January 2010 (UTC)

The small print comment is about your macho declaration about not reading a ladies' magazine. Some people would be shy about such things. Cuddlyable3 (talk) 16:49, 20 January 2010 (UTC)

Oh, OK. I offered the information to make it clear that I can get interested in things I have no good reason to be interested in. ike9898 (talk) 17:17, 20 January 2010 (UTC)

So now the question is, what sort of management do managers do in a government research agency? 78.149.139.201 (talk) 23:37, 19 January 2010 (UTC)

It is difficult to give the reply requested as a) from what the OP has said the OP may have been offered a supervisory job or perhaps a project management role rather than an executive management role, b) there's plenty of management theory but nearly all the time managers never refer to it according to personal experience and Mintzberg, c) the stuff you read in textbooks will probably have little relation to what you actually do, d) there is an enormous amount of worthless garbage written about management or business, particulary popular American books I have to say. But, bearing that in mind you could have a look at Fayolism. Something to remember about Fayol is that the english version does not give enough or any emphasis to feedback and checking, both vital - interested to see that the article says this was due to a mistranslation of "checking" as "control" in English. The autocratic leadership style of that time is rightly far out of date. Do not mistake leadership for management - a common mistake. I've seen bad ignorant managers believe that (coercive) leadership is all that needs to done while the organisation falls to pieces because no management is being done. I remember reading this: Writers on Organizations by D.S. Pugh and David J. Hickson. I found this a few minutes ago www provenmodels dot com which gives details of many familiar thories, although it still makes the same mistake about Fayol. Wikipedia says its on its blacklist, do not know why, perhaps it is a Wikipedia rip-off, but at least it packages it in a nice way. This is mentioned in a couple of articles http://www.amazon.co.uk/Organization-Theory-Design-Understanding-Organizations/dp/0324422717/ref=sr_1_4?ie=UTF8 never read it myself. The reviewer Stan Felstead has reviewed a lot of management books http://www.amazon.co.uk/gp/cdp/member-reviews/A39KA7J326RUCV/ref=cm_cr_dp_auth_rev?ie=UTF8&sort_by=MostRecentReview Update: If you like history I've found Management Thought by Jayanta K Nanda, which can be read in full online in Google Books. I'd like to read it myself. 92.29.57.199 (talk) 16:05, 20 January 2010 (UTC)

I see that Henry Mintzberg, perhaps the greatest living star of management theory, has recently had a book titled Managing published, in 2009. So although I've never read it myself, it would probably be worth reading. The first part of it that I read on Amazon mentions "evidence-based" books - unfortunately the majority of management books published are dross that is not evidence based. Rarely if ever do you find books that offer insights based on someone's personal experience without reference to academic publications - they are always garbage written in the first-person like a memoir and full of waffle. One thing that they never taught me in all my business training was how to handle the paperwork, and how important the mundane task of having a good up to date filing system is, so that the facts you need are readily at hand and quickly retrievable. 78.147.245.100 (talk) 11:59, 22 January 2010 (UTC)

Gaussian and SI Units of Charge

Hello everyone. Looking over pages for various units, I'm a little confused on how the relationship between coulombs and statcoulombs. Basically, if Coulomb's Law is defined differently in SI and gaussian units, the units on force must still be the same (mass length/time²). Setting the two forms equal to each other, I get a formula somewhat different to the one at the bottom of the statcoulomb page. I obtain

$1\;{\textrm {statcoulomb}}={\frac {1\;{\textrm {coulomb}}}{\sqrt {4\pi \epsilon _{0}}}}$

substituting in $1/\epsilon _{0}=10^{-7}c_{0}^{2}$ and throwing in a factor of ${\sqrt {10^{9}}}$ for converting kilograms to grams and meters to centimeters, I get 1 statcoulomb = 2997924580 coulombs, ie the exact opposite of what the page says (and opposite everything that every other conversion table I've looked at said). What's wrong with my derivation? Thanks :) Bennybp (talk) 18:10, 19 January 2010 (UTC)

If you have two numerical values a and b for the charge, in SI coulomb and statcoulomb respectively, and numerical values f and g in SI and Gaussian force units, and numerical values r and q in SI and Gaussian distance units, then the equation for two charges of the same size is

$f={\frac {1}{4\pi \epsilon _{0}}}{\frac {a^{2}}{r^{2}}}$

$g={\frac {b^{2}}{q^{2}}}$

Obviously, g = 10⁵f and q = 10² r, so

${\frac {1}{4\pi \epsilon _{0}}}{\frac {a^{2}}{r^{2}}}={\frac {b^{2}}{r^{2}}}\cdot 10^{-5}\cdot 10^{-4}$

If b=1, then $a={\sqrt {10^{-9}\cdot 4\pi \epsilon _{0}}}={\sqrt {10^{-9}\cdot 4\pi {\frac {1}{4\pi \cdot 10^{-7}\cdot c^{2}}}}}={\frac {1}{10\cdot c}}$

It seems like you forget that if you have a larger unit of charge, the numerical value for a given real charge is smaller ;-)

Icek (talk) 06:51, 22 January 2010 (UTC)

That makes sense. Looks like I need to crack open my high-school math book again. Thanks a bunch! --Bennybp (talk) 06:23, 24 January 2010 (UTC)

Relation between angular velocity and torque

What is torque formula of roatating equipment, if equipment rotate at constant angular velocity? —Preceding unsigned comment added by Mananmodi11 (talk • contribs) 18:24, 19 January 2010 (UTC)

If the angular velocity is constant, the net torque is zero (just as if the net linear velocity is constant, the net force is zero). In real life, if there is a decelerating torque due to friction, that means you'll need to apply an equal and opposite torque to maintain the angular velocity. -- Coneslayer (talk) 18:30, 19 January 2010 (UTC)

That is true for an isolated body. A rotating part of equipment that transmit power, such as a gearwheel in a clock or a car transmission, can have constant angular velocity while exerting a high torque. Cuddlyable3 (talk) 20:34, 19 January 2010 (UTC)

What? It's the net torque on the "part of equipment" that then needs to be 0, not the torque it exerts on other things. Of course, there's an equal and opposite torque applied to it by the driven object, but there's also a torque applied to it by the "upstream" source (eventually by an off-center spring or gasoline explosion or…), and at constant angular velocity they add to 0. --Tardis (talk) 20:46, 19 January 2010 (UTC)

Indeed. The car's transmission exerts a torque on the car's wheels and has a torque exerted on it by the car's engine. If the transmission has constant angular velocity, then those torques must cancel out. --Tango (talk) 01:06, 20 January 2010 (UTC)

So if we couple a Bugatti Veyron engine to SteveBaker's Mini and break its gearbox (sorry SteveBaker), was the net torque on the gears zero? Cuddlyable3 (talk) 11:52, 20 January 2010 (UTC)

Probably not. I've never tried connecting a gearbox to an engine too powerful for it, but I expect the gears would spin faster and faster until they broke. If their angular speed is increasing, there must be a non-zero net torque. --Tango (talk) 12:54, 20 January 2010 (UTC)

The over-powered mini was being driven at constant speed up a steep hill when the errr...dysfunction manifested. That's my story anyway. Cuddlyable3 (talk) 16:42, 20 January 2010 (UTC)

The easiest thing is to think of Torque as being the rotational equivalent of Force in the linear realm. When you apply a net force to an object you get an acceleration - but in the real world, friction and drag provide opposing forces that increase with speed. At high enough speed, the friction and drag equal the propulsive force and the speed levels off. Same deal with torque - when you apply an unopposed torque, the object spins faster and faster - but eventually, friction and drag provide opposing torques that increase until you get a constant rotational velocity. SteveBaker (talk) 02:31, 20 January 2010 (UTC)

:rolleyes:

${\mbox{power}}={\mbox{torque}}\times 2\pi \times {\mbox{rotational speed}}$

where rotational speed is in revolutions per unit time. See torque. --Heron (talk) 19:29, 20 January 2010 (UTC)

I know that the OP said "constant angular velocity", but, to expand on SteveBaker's comment and answer the question implied in the heading, when the torque is unapposed it is equal to rate of change of angular momentum i.e. torque = moment of inertia times rate of change of rotational speed. (assuming a fixed axis of rotation) Dbfirs 17:57, 22 January 2010 (UTC)

The path of the moon through the sky

Would the path of the moon through the sky, from moon-rise to moon-set, always be part of a circle if viewed through a very large sheet of glass that was set vertical and parallel to the imaginary line from moonrise azimuth to moonset azimuth? I mean, an arc of a circle and not some other curve. 78.151.106.238 (talk) 20:32, 19 January 2010 (UTC)

Almost entirely, yes. It is based on the rotation of the Earth and the current tilt of your view in relation to the moon. It is slightly (very slightly) skewed because the moon is also orbiting the Earth. It isn't enough that you'd really notice over a single night. -- kainaw™ 21:37, 19 January 2010 (UTC)

No, it would be part of an ellipse, I think. It is a circle on the sky, but when you project it onto a plane (the glass) you'll get an ellipse unless your eye, the glass and the moon are lined up just right. You've mentioned where the glass is with respect the moon, but not where your eye is. --Tango (talk) 01:14, 20 January 2010 (UTC)

No -- and it's not even "a circle on the sky." While above (or below) the horizon, the moon moves forward in celestial longitude and right ascension. Between rising and setting, the movement is enough to make its path vary significantly from a segment of a circle. Only an outer planet at stationary retrograde/direct (or a star) would closelt approximate a segment of a circle; and while the inner planets at stationary would move enough to distort a circle, the distortion would be small enough that "circle" would be a reasonable term. But the moon moves too fast, and is never stationary. (The exception would be when it is above or below the horizon very briefly, as it would be during certain times of the month in high terrestrial latitudes.)

unlikeliest thing to happen that did in fact happen? (that we know of)

Hi,

"Of all the things that were unlikely to happen, but did anyway, which one had been the unlikeliest?" (that we know of)

is my question even meaningful, or does it misconstrue statistics? (this is not homework). Thanks. 84.153.196.174 (talk) 20:55, 19 January 2010 (UTC)

That your particular sperm fertilized the egg, against compitition from millions or perhaps billions of other sperm. That is probably the most unlikely thing in anyones life. 78.151.106.238 (talk) 20:58, 19 January 2010 (UTC)

This fingerprint is very very unlikely to be here. Cuddlyable3 (talk) 11:41, 20 January 2010 (UTC)

No, it's the most certain thing in anyone's life. Cuddlyable3 (talk) 11:43, 20 January 2010 (UTC)

Anything after the event has taken place is the most certain thing, no matter how extremely unlikely it was before the event. 92.24.85.238 (talk) 11:41, 21 January 2010 (UTC)

Don't all sperm have the exact same DNA? What makes this not a distinction without a difference? 84.153.196.174 (talk) 21:00, 19 January 2010 (UTC)

No. They each have a different (overlapping) half of the source's DNA. --Tardis (talk) 21:04, 19 January 2010 (UTC)

What humans naturally consider "unlikely" is actually the most likely. For example, coincidence is considered unlikely, but high levels of coincidence are statistically very likely. I used this concept in a utterly pathetic novel I worked on for many years in which it was easy to identify when future people attempted to manipulate the past because they tended to remove coincidence and randomness. I used an example of asking a person to arrange blocks in a random manner to make it appear that the blocks simply fell out of a box. There will always be clear statistical identifiers when the humans arrange the blocks "randomly" and when they are actually just dumped from a box.

So, what is the purpose of this rambling nonsense? The most unlikeliest thing would be the complete absence of anything we consider unlikely since unlikely things happen all the time. -- kainaw™ 21:15, 19 January 2010 (UTC)

Humans, as opposed to physicists..? There's something funny about this, anyway. In what you call human terms, to be worth mentioning, unlikely things must be both unlikely and significant. Mere randomness like a particular fingerprint or Feynman's numberplate (mentioned below) don't count. The unlikely events which really count are the ones which contain knowledge, and knowledge is what probability tends towards (convergent evolution of ideas or genes). So what we call unlikely is finely balanced between the probable and improbable, and "most unlikely" doesn't make much sense because it's all a bit subjective; context matters, the context of type of events to include. 81.131.36.185 (talk) 12:21, 20 January 2010 (UTC)

One runs into trouble with this kind of thing quickly because the odds of specific things happening are often low but the odds of general things happening are high. For example: starting with the initial set of conditions shortly after the Big Bang, what are the odds that some of the matter would coalesce into our Moon, and some of the other matter would coalesce into an asteroid, and that asteroid would smack into our Moon? Yet, the odds that moons will form, and that asteroids will form, and some asteroids will hit some of those moons, are quite high. Delineating the scope of the analysis is really rather important, or else you end up with ridiculous (and meaningless) answers. --Mr.98 (talk) 21:19, 19 January 2010 (UTC)

Peel an orange and look closely at the patterns the fibres make on the surface of the segments. What were the chances of exactly that pattern occurring? So small as to be virtually impossible. And yet it happened. The closer you look at something, the unlikelier it was. Or as Terry Pratchett put it: 'Scientists have calculated that the chance of anything so patently absurd actually existing are millions to one. But magicians have calculated that million-to-one chances crop up nine times out of ten.' Neurotip (talk) 21:52, 19 January 2010 (UTC)

The chances of that particular pattern emerging are very small. But the chance of some pattern emerging is 100 percent. It's kind of like with the lottery. The odds of you winning it are very small. But the odds of someone winning it are very high. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:51, 20 January 2010 (UTC)

You know, the most amazing thing happened to me tonight. I was coming here, on the way to the lecture, and I came in through the parking lot. And you won't believe what happened. I saw a car with the license plate ARW 357. Can you imagine? Of all the millions of license plates in the state, what was the chance that I would see that particular one tonight? Amazing! - Richard Feynman

Law of Truly Large Numbers may also be relevant. --Mark PEA (talk) 22:27, 19 January 2010 (UTC)

It's an interesting question. If the energy of the universe is finite, then the number of possible quantum states of the universe is finite, so there must be a nonzero minimum probability for any possible state -- but I wouldn't begin to know how to estimate it. Looie496 (talk) 00:11, 20 January 2010 (UTC)

Yes, but there is no point looking at the probability of the universe being in a particular state. You need to look at the probability of the universe being in one of a set of states. We don't care, for example, if the oxygen molecule one metre to my left were actually 1.01 metres to my left. This is related to the concept of entropy. Not taking this into account leads to a lot of false claims about the unlikelyness of events. Imagine if I were to take a well shuffled deck and deal two cards face up and it turns out to be 2 7's. You may think that was unlikely and work out that the odds of getting those two cards was 1/52*1/51, or 0.04%, which is extremely unlikely and we may suspect that the deck wasn't properly shuffled. You should, however, note that it doesn't matter what order the cards came down in, so you should double the probability. You should also note that it doesn't matter what suits the 7's are, so you should multiply the probability by 6. You should then note that it doesn't actually matter that they were 7's, you would have been just as surprised by any pair, so you should multiply the probability by 13. Once you do all that you are left with the probability of two randomly chosen playing cards being a pair, which is 5.88%. Far higher than the 0.04% we started with. The chance of getting a pair is actually better than 1 in 20. It isn't very unlikely at all, so we shouldn't have been that surprised. The reason we were was because we were distinguishing between outcomes that were actually the same for our purposes. --Tango (talk) 01:03, 20 January 2010 (UTC)

If you apply the Bekenstein bound to the observable universe (which may or may not make sense) then it would argue that the universe has no more than 2^(10124) possible configurations given its current size. Of course that is an incomprehensibly large number. Dragons flight (talk) 01:05, 20 January 2010 (UTC)

Any event that just happened is the most improbable. If you take the big bang as a certainty - then the probability of a particular subatomic particle being at a particular place a picosecond later is less probable - the probability of some other subatomic particle being at some other place a second later is less probable still. The longer you go out in time, the less probable any given thing is.

The probability that I just flipped a coin and it came up heads is so astronomically improbable that at the instant I did it, that was the least probable thing that's ever happened in the entire history of the universe (apart from the uncountable number of other things that happened at that precise instant). For that coin to come up heads, I had to happen to pick up that coin at that 7/11 store because I happened to run out of milk because my son happened to have visited because...(time passes)...humans happened to evolve because...(more time passes)...the first self-replicating molecule appeared because...(because, because, because)...because that subatomic particle was here a picosecond after the big bang and not a bazillionth of a meter to the left.

But this is a kinda useless conclusion. What we generally mean when we say "What are the odds that this coin will come up heads?" is more like "Given that this coin is here at all and given that there is a sentient being present to toss it and observe the results...what are the odds that it'll come up heads?" - which reduces the unimaginably long odds to something closer to 50/50.

So the question we're being asked fails to allow a reasonable answer because it doesn't specify enough preconditions that we're allowed to assume. What is the probability of a coin coming up heads given that coins exist and people exist to toss them is a really high probability. The probability of a coin coming up heads given the existence of life on earth is a much lower probability and the probability given only that galaxies formed in the early universe is much MUCH lower still.

Hence, there simply isn't a good answer - and we shouldn't pretend otherwise. SteveBaker (talk) 13:40, 20 January 2010 (UTC)

Agreed - the problem stems from observer bias. Humans perceive randomness when there is in fact order; and they perceive order from systems which are statistically spread or indeterminate. Short of an elaborate mathematical definition for certain randomness measures, like deviations from expected values, or spectrum of those deviations (ad nauseum, deviations from expected deviations from expected deviations...), "degree of randomness" is poorly defined. High entropy is often equated with randomness - but this is a mistake of plain english language that doesn't really mean the same as scientific language. As alluded to in the Hitchhiker's Guide to the Galaxy, a really hot cup of tea is awfully high entropy - but it's not really very "unlikely" as far as human perception goes. In truth, it's because our limited capability to perceive certain aspects of the tea, like the individual motions of the billions and billions of individual tea molecules. If we could perceive and conceive those concepts - in actuality and not in abstraction - then we would be blown away every time we looked at a gust of wind or a warm fluid or even a solid object. How unlikely that Molecule #46983743 has "chosen" to collide with molecule #3298210932! What's the probabilty! The Dick Feynman quote really hits this point hard - who cares if an event is random if it is insignificant? But that's really just restating that we evaluate probabilities through the bias of being a human observer - with human preconceptions about what is "signficant." Nimur (talk) 17:32, 20 January 2010 (UTC)

So could things be a bit simpler...What is the highest-odds (major) sports betting outcome? (E.g. a 15000/1 horse romping home to victory in the Grand National?). 194.221.133.226 (talk) 15:35, 20 January 2010 (UTC)

It's more probable than a certifiably dead horse winning the race. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:49, 20 January 2010 (UTC)

Like most things, the probablility isn't zero. Consider a prize-winning racehorse, running at the limits of it's ability gets clear of the pack - suffers a sudden heart failure 5 feet from the tape - momentum propels it to victory (of a sort). SteveBaker (talk) 00:03, 21 January 2010 (UTC)

Well, the Grand National article lists the longest shot winners at 100 to 1, the same as Man o' War's only loss (to Upset, fittingly enough). Buster Douglas vs. Mike Tyson was only about 45 to 1. Clarityfiend (talk) 00:37, 21 January 2010 (UTC)

Greece won Euro 2004 as a 150-1 underdog, according to the BBC. Clarityfiend (talk) 02:53, 21 January 2010 (UTC)

The probability of everything that has occurred is one. Just because proscribed probability might put the chance of something happening at some fraction of one, that estimate is disproved when the event occurs. In short, statistics is a load of rubbish. Useful rubbish, but it it makes no contact whatsoever with the real world. Vranak (talk) 19:58, 21 January 2010 (UTC)

Go back to the question: "Of all the things that were unlikely to happen, but did anyway, which one had been the unlikeliest? (that we know of)." So: 1) things, 2) that happened. The answer would have to be something that has happened only once, and in the longest period of time. The answer is: The big bang. By definition, for anyone to ask this question, the big bang -- or some other creation event -- would have had to have occurred, but that doesn't change the fact "(that we know of)" that the big band has occurred only once in all the history of the universe, making it the most unlikely event to happen "but did anyway." Every other event that has happened has either happened more than once or more recently.

escaping black holes

Is it correct that a virtual graviton (gravity carrier) can escape out of black hole, whereas a real or actual graviton (gravity wave carrier) cannot?? 89.138.153.164 (talk) 21:00, 19 January 2010 (UTC)

Perhaps. --Neptunerover (talk) 02:07, 20 January 2010 (UTC)

I think that can be paraphrased as how can one tell? It's true on the straightforward model of a black hole as a gravity well but who knows what model will end up being accepted. I'm pretty certain we'll never be able to do an experiment to find out! See Hawking radiation for this general area, there's no reason to suppose gravitons would act any differently. Dmcq (talk) 10:55, 20 January 2010 (UTC)

Resistance/Stress

Does the resistance of a wire vary when the stress is changed, and is there a formula to relate the 2? Various circuits I've been building with potential dividers have seemed a bit odd and I was wondering whether the stress of the wire could affect it's resistance. Harland1 (^t/_c) 21:40, 19 January 2010 (UTC)

Yes, the stress on a wire causes strain which changes the length of the wire, and resistance varies with length. (A strain gauge works on this principle. By measuring the change in resistance of the strain gauge it is possible to determine the strain of the component to which the gauge is attached. Using knowledge of the elastic modulus of the material it is then possible to determine the stress experienced by the component.) Dolphin51 (talk) 21:50, 19 January 2010 (UTC)

There is a formula that relates the resistance R of a piece of wire of length L, the resistivity $\rho$ of the metal, and the sectional area A of the wire. See Resistivity#Explanation. Dolphin51 (talk) 11:18, 20 January 2010 (UTC)

Note that under strain, the resistivity may not be isotropic (the same in all directions) anymore: together with its inverse, the conductivity (see that article), it becomes tensorial. Effectively, numbers become matrices. — Pt _(T) 18:18, 21 January 2010 (UTC)

Relationship between moon phase and the azimuths of moonrise or moonset

Do moons with the same phase have the same azimuth of moonrise or moonset? And in this diagram here, http://hal.physast.uga.edu/~jss/1010/ch2/02-21.JPG it appears that a new moon rises higher in the sky than a full moon. Is that correct? I assume that the information given in the diagram applies to any time of year and any location (more or less) in the northern hemisphere. 78.151.106.238 (talk) 21:57, 19 January 2010 (UTC)

Since the moon's orbit is close to the Earth's orbital plane, and since the azimuth is measured with respect to the Earth's North Pole, I would assume it depends strongly on the season. Dragons flight (talk) 22:10, 19 January 2010 (UTC)

It looks to me as though the diagram applies to someone on the equator at the time of one of the equinoxes. Presumably they have done this for simplicity. The season and latitude of the observer makes a huge difference to azimuth as well as the rising and setting times of the moon. The new moon in winter will culminate low in the sky; the full moon in winter will culminate high in the sky, and vice versa.--Shantavira|^{feed me} 10:18, 20 January 2010 (UTC)

The moon's phase has nothing to do with the apparent position of the moon-in-itself -- it's a combination of the positions of the moon AND the sun. Therefore, the moon's apparent position is not unilaterally equatable with the moon's phase. Answer to your question: No.

Is a table available anywhere of the daily azimunths, ideally with the phase as well? 92.29.130.174 (talk) 12:09, 23 January 2010 (UTC)

gene concepts

Question removed: See talk page SteveBaker (talk) 04:56, 20 January 2010 (UTC)

EADS Astrium orbital power

Why exactly wouldn't it be dangerous [6] to be hit from orbit by 20 kilowatts of infrared laser beam? 81.131.45.171 (talk) 22:43, 19 January 2010 (UTC)

Probably because the beam would be quite spread out by the time it reached the ground. I can't find any details, though. --Tango (talk) 23:49, 19 January 2010 (UTC)

Per Tango, I don't know the details of the beam in question but it almost certainly has to do with the spreading of the beam by the time it reaches Earth's surface. Bright sunlight deposits roughly 1 kilowatt (kW) per square meter on the Earth's surface. If the beam is spread out over at least twenty square meters (a disc about 2.5 meters, or about eight feet, across) then the beam is no more intense than sunlight. That's not going to cook much. TenOfAllTrades(talk) 00:33, 20 January 2010 (UTC)

It'll be safe at this experimental scale - but a serious multi-megawatt setup could certainly cook if you got in the way of it, so you'd have to take precautions in the event that the satellite lost stability or something. Aside from simply radioing commands to the satellite in the event of problems with the incoming beam, I'd place a mirror on the ground detector to reflect a tiny fraction of the laser power back to the satellite. The satellite would be designed to cut off the beam if it doesn't "see" it's own reflection in that mirror. Ideally you'd want the cutoff to be a passive system - if the satellite doesn't actively assert that the beam is on-target, it's shut off automatically. That way if it drifts off-target, the power gets cut off even if the ground station goes AWOL or the satellite has lost on-board power - or both. SteveBaker (talk) 01:46, 20 January 2010 (UTC)

Good God yes. Something like this, it definitely needs to be fail safe. Apart from the judgement of the satellite's systems, based on reflections it can see, I'd have it sent regular radio messages saying "keep going", so that a change or halt in the radio messages (secure and encrypted from specific sites) would cause it to stop immediately. Not just ideally: I wouldn't sign off on a deadly thing like that up without fail safe systems. If it has to be told to stop in the event of failure, that's a recipe for disaster. 86.178.230.208 (talk) 17:48, 20 January 2010 (UTC)

That mirror should be a Corner reflector to avoid a tricky aiming problem. Cuddlyable3 (talk) 11:30, 20 January 2010 (UTC)

A multi-megawatt infrared laser would probably be even more spread out - if it was spread out to a disc a little over 100m in diameter (which sounds plausible to me) then it would still be no brighter than the sun. --Tango (talk) 04:10, 20 January 2010 (UTC)

Then what would be the point of it? Why not just stick some solar panels out there? That doesn't make sense. SteveBaker (talk) 04:38, 20 January 2010 (UTC)

Night. Cuddlyable3 (talk) 11:31, 20 January 2010 (UTC)

The 1kW/m² figure is a maximum. You only get it at noon near the equator. With a laser beaming the energy from space you get it 24/7 anywhere you want. But basically you are sticking solar panels out there - that's what the receiving station is, a big array of solar panels (optimised for the frequency of the laser, presumably). --Tango (talk) 07:21, 20 January 2010 (UTC)

I'm a bit puzzled by how a satellite can stay out of the earth's shadow 24/7 when the moon doesn't (but not entirely unbelieving). 81.131.36.185 (talk) 12:25, 20 January 2010 (UTC)

You put it at an appropriate Lagrange point. You may well need relay satellites to reach a receiver 24/7, though, since lasers do require line of sight. An alternative is to just put it in a geostationary orbit and accept that it will be in shadow for a short period occasionally. According to this source, that period is at most 70 minutes and is no time at all for most of the year (it's only near the equinoxes that they pass through the Earth's shadow). --Tango (talk) 12:51, 20 January 2010 (UTC)

You can also use a less-exotic sun-synchronous orbit. --Tardis (talk) 15:48, 20 January 2010 (UTC)

Why would that help? --Tango (talk) 21:14, 20 January 2010 (UTC)

Something in a dawn-dusk orbit (see the article) always sees the sun. --Tardis (talk) 15:42, 21 January 2010 (UTC)

That still doesn't make sense. If the beam is really no brighter than the sun, then why not just take the money you were going to spend on getting a spaceship to a Lagrange point and make two solar panels, that way you've don't have to worry about nighttime because panel #2 saved it up to a battery. APL (talk) 04:57, 21 January 2010 (UTC)

Yes, exactly. Large-scale storage of electricity is difficult - but nothing like as difficult as a spaceship! I thought the plan was (ultimately) to launch a few square kilometers of solar collecters to the Lagrange point and beam gigawatts of power down to a relatively small earth-based receiver. If you can only get a few times brighter than the sun, then there seems very little point in doing this. SteveBaker (talk) 14:31, 21 January 2010 (UTC)

Well, I don't know what the maximum safe level would be. You can probably have more IR than you can sunlight, since it is the UV from the sun that does most of the damage to humans. Really high power transmission would be great, but I would be surprised if it ever got planning permission. Most plans I've seen have stressed that the beam would be harmless even if it went off-target. Even with a 1kW/m² beam you would get several times what you would from the sun. You can get a more efficient receiver due to it working over a narrower range of wavelengths and you get the beam constantly at full power with very few breaks (depending on the orbit of choice - I think geostationary is my favourite, which has a few short breaks around the equinoxes). --Tango (talk) 17:59, 21 January 2010 (UTC)

Just noticed this, I'm surprised no one made a Sim City 2000/Sim City 3000 reference with their satellite microwave power plants which could of course misfire and obliterate much if your city. Looking at the SC2k article also pointed me at Space-based solar power which no one has mentioned and provides some info on things like targetting systems although fairly limited info on lasers and nothing on this particular proposal. Incidentally while only of minor relevance since the numbers above were just guesstimates, if the satellite is transmitting 10-20kW you're not going to receive that on the surface of earth. According to the talk page, you may lose about 1/3. Nil Einne (talk) 00:32, 20 February 2010 (UTC)

Where do Squirrels go in the Winter?

Also, why does DC have black squirrels? —Preceding unsigned comment added by 199.172.169.21 (talk) 23:29, 19 January 2010 (UTC)

Do they go anywhere? We have squirrels all year round, and the article seems to indicate that they build fairly permenent dens. As for black squirrels, check out their article. They're just a subgroup of the Eastern Gray Squirrel, and can occur wherever gray squirrels are found, though have larger populations in certain areas, including Washington DC. The article says they were introduced in the early 1900's at the Smithsonian National Zoological Park. Buddy431 (talk) 23:51, 19 January 2010 (UTC)

Squirrels don't go anywhere. They are well known for hiding nuts for the winter - they wouldn't do that if they weren't staying for the winter. --Tango (talk) 00:31, 20 January 2010 (UTC)

I don't believe squirrels migrate nor hibernate. I've seen them in the mountains all year round. --Neptunerover (talk) 00:52, 20 January 2010 (UTC)

Likewise in the city, here in Toronto. Actually, what they like to do in winter is break into the attic of my house... --Anonymous, 01:54 UTC, January 20/10.

I used to live in the Lower East Side of Manhattan, and on the way home from elementary school down the FDR Drive, I would often see a bunch of black eastern gray squirrels in the lawn of the Peter Cooper Housing. DRosenbach ^{(Talk | Contribs)} 02:54, 20 January 2010 (UTC)

It is utterly untrue that black squirrels are a phase of Gray Squirrels. In my town, we have gray squirrels. The next town has black squirrels. They do not apparently interbreed. Black squirrels do not grow up to be gray squirrels, nor conversely. Someone should do the genetic analysis and confirm the disparity. Edison (talk) 05:17, 20 January 2010 (UTC)

You might want to read the article on the Black squirrel. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:58, 20 January 2010 (UTC)

What's utterly untrue is that it's utterly untrue. Maybe you haven't seen them breed because you were barking up the wrong tree. DRosenbach ^{(Talk | Contribs)} 14:24, 20 January 2010 (UTC)

There are a few black squirrels around here, and all of our squirrels are Red Squirrels, not Grey Squirrels. Googlemeister (talk) 15:34, 20 January 2010 (UTC)

I'm curious how you're so adamant on the mating practices of local squirrels? How much squirrel mating do you have to observe before you can make confident proclamations on the habits and prejudices of the entire local squirrel population?

Besides, even if you're right that they don't interbreed, that's not a solid indication that they're incapable of it. Perhaps if squirrel 'tail' is plentiful (Get it? Get it?) they just stick to their own. APL (talk) 15:39, 20 January 2010 (UTC)

We have the article about the black squirrel vs. the personal observations (a.k.a. "original research") of one user. That doesn't say which is right. But it does suggest that he needs to find some citations. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:46, 20 January 2010 (UTC)

Then again, when I look at the tree squirrel article, it becomes clear that North America has many types of similar looking squirrels with overlapping ranges. It's entirely possible that the "gray squirrels" edison is refering to are not in fact Eastern Gray Squirrels, in which case they are truly different (though closely related) species. Buddy431 (talk) 21:15, 20 January 2010 (UTC)

It's weird, I was just talking with my friend about this yesterday. I have a further question - where do squirrels sleep when it's not winter? Do they all have nests or something somewhere? Do they just nestle in some big coniferous somewhere? Do they just sleep sitting on a branch? What do they do when a basement or attic is not available to them? TastyCakes (talk) 15:53, 20 January 2010 (UTC)

Again, read the article: eastern gray squirrel. They build nests known as dreys, in trees or other suitable places (like attics). Depending on where you live, you may be thinking of a different type of squirrel, in which case you'll have to read the appropriate article.Buddy431 (talk) 16:06, 20 January 2010 (UTC)

Yes -- here's a close-up photo. Similar nests can be seen throughout NYC and northern Jersey (other places as well, but I try not to leave the area and sometimes even feign ignorance that other places even exist :) DRosenbach ^{(Talk | Contribs)} 04:26, 21 January 2010 (UTC)

I can accept the black squirrels being a "subgroup" of the more common type, as our article says, but elsewhere I have seen the unlikely claim that the dark fur is a "phase" of the lighter squirrel. I took this statement to mean a "growth phase," with black squirrels later becoming gray squirrels or vice versa. Or does it mean a stable fur color? Since I live near a boundary between the ranges of the two groups, I see black squirrels to the north and the more common type to the south. It is rare for a black one to cross over the boundary zone. One block may have 3 gray ones and no black ones out foraging in one town, and conversely in the next town. There could be interbreeding with mixed litters of black ones and gray ones, but we do not see blended colors (intermediate shades). In many years of observation, I have never seen them hanging around together. A particular street is the approximate borderline, stable over many years plus or minus a block or two. The black squirrels might flourish more in more heavily wooded areas. Some genetic testing would be informative. The black squirrels in different regions need not be the same genetic subtype. There are also towns with white squirrels. In some cases, such as Kenton, Tennessee the presence of white squirrels is a point of pride for the town and active measures are taken to protect them and keep others out. Apparently not all white squirrel populations are albinos. As for where they go in winter, they are fond of gnawing their way into attics. Others insulate nests or pockets in dead trees with leaves and survive there, then come out to eat some snow and raid bird feeders and garbage cans of the plastic variety. Some refer to them as "tree rats." Chipmunks of "ground squirrels" hibernate, but gray squirrels don't. Edison (talk) 17:59, 20 January 2010 (UTC)

"Phase" is used in place of "race" or "subspecies", especially where the subgroup isn't geographically or otherwise isolated. It's pretty much equivalent to the word "breed", which is normally only used in domesticated species. Matt Deres (talk) 21:28, 20 January 2010 (UTC)

Black and gray eastern gray squirrels being the same species doesn't imply there would be shades in between. Some traits are either on or off, for example when the trait is determined by a single gene. It also doesn't imply that all populations of eastern gray squirrels would have similar distributions of gray and black. If the gene pool in one area has a lot of black squirrels, that's not likely to change over time unless there's selective pressure. And the selective pressures might be different in different areas, since as the article says the black ones are more successful in dark woods. Rckrone (talk) 21:49, 20 January 2010 (UTC)

All the black squirrels I've ever seen had tufted ears. There were gray squirrels (w/ white bellies) around too, but none of the different types (there were even red 'downtown' squirrels) seemed to associate with each other at all. --Neptunerover (talk) 16:10, 21 January 2010 (UTC)