Wikipedia:Reference desk/Archives/Science/2012 September 24

= September 24 =

Black rat taxonomy
Per Special:ArticleFeedbackv5/Black_rat/159109, why does the black rat have the same genus and species, i.e. Rattus rattus?Smallman12q (talk) 01:39, 24 September 2012 (UTC)


 * Because that's what Linneus named it. He, and others after him, did that for several type species: Bufo bufo and Gorilla gorilla are other examples. Dominus Vobisdu (talk) 01:47, 24 September 2012 (UTC)


 * Also Puffinus puffinus - which confusingly isn't a Puffin. AndyTheGrump (talk) 01:52, 24 September 2012 (UTC)


 * One of my favorite species is Gulo gulo. See also

Alces alces Anser anser Axis axis Bison bison Bubo bubo Bufo bufo Buteo buteo Capreolus capreolus Ciconia ciconia Cochlearius cochlearius Crocuta crocuta Dama dama Gallinago gallinago Gazella gazella Genetta genetta Gorilla gorilla Himantopus himantopus Huso huso Hyaena hyaena Iguana iguana Lutra lutra Martes martes Mercenaria mercenaria Meles meles Mephitis mephitis Nasua nasua Nycticorax nycticorax Oingo Boingo Oreotragus oreotragus Papio papio Porphyrio porphyrio Redunca redunca Salamandra salamandra Tadorna tadorna Tyrannus tyrannus Vicugna vicugna Vulpes vulpes''
 * and our articles reduplication and binomial nomenclature--although it does not seem we have info on reduplicated binomials. μηδείς (talk) 03:22, 24 September 2012 (UTC)
 * Tyrannus tyrannus? Most disappointing. I was hoping for something much bigger, scalier, and more likely to tear large chunks out of passing herbivores... AndyTheGrump (talk) 03:59, 24 September 2012 (UTC)
 * The bird called Tyrannus tyrannus could well be descended from a dinosaur. Maybe it should be called Tyrannosaurus Ex. ←Baseball Bugs What's up, Doc? carrots→ 04:11, 24 September 2012 (UTC)
 * It is undoubtedly decended from a dinosaur, see Origin of birds. Also, as birds are therapods (at least by cladistics), they are likely close cousins of T-Rexes, though not likely direct decendents.  -- Jayron  32  04:17, 24 September 2012 (UTC)
 * Danny Elfman would like to have a word with you... -- Jayron  32  03:31, 24 September 2012 (UTC)
 * Not interested. Tell him to send over Jenna and then we'll talk. μηδείς (talk) 03:39, 24 September 2012 (UTC)

There's also the Aha ha. μηδείς (talk) 03:51, 24 September 2012 (UTC)
 * And don't forget the Ladybug Ladybug. ←Baseball Bugs What's up, Doc? carrots→ 04:09, 24 September 2012 (UTC)

Among the cats are Uncia uncia, Caracal caracal, and Lynx lynx μηδείς (talk) 04:31, 24 September 2012 (UTC)


 * We've dealt with this on the ref desk before. Relevant WP pages are Tautonym and List of tautonyms. Deor (talk) 09:15, 24 September 2012 (UTC)
 * I was wondering why I couldn't find any reduplicated plant names. μηδείς (talk) 16:39, 24 September 2012 (UTC)
 * Does Rose is a rose is a rose is a rose count? --  ♬  Jack of Oz  ♬  [your turn]  19:34, 24 September 2012 (UTC)
 * Regarding plants: Botanical nomenclature is handled differently, by a different organization, with different naming rules, than animal nomenclature is. See also Nomenclature codes.  -- Jayron  32  19:46, 24 September 2012 (UTC)

ANTI MICROBIAL CLOTHING
I HAVE SEEN CLOTHES TREATED WITH A "ANTI MICROBIAL" FINISH. WHAT EXACTLY ARE THEY TREATED WITH? AND WHY DOSENT IT WASH OUT?--Wrk678 (talk) 02:31, 24 September 2012 (UTC)
 * We actually have it mentioned in our Textile finishes article, but it doesn't really answer your question. Try this link, I don't have time to read it but it looks like it has more information. Vespine (talk) 03:15, 24 September 2012 (UTC)
 * (ec) Is this (and this) the stuff you mean? (There are, in theory, an unlimited number of ways to make anti microbial clothing)  The link concerns attachment of layers of quaternary polyethylenimine to fabric with ultraviolet light. Wnt (talk) 03:16, 24 September 2012 (UTC)

hurricane, cyclone & typhoon
In terms simple enough to be understood by a child, please explain the differences between a hurricane, a cyclone and a typhoon. Please limit, if possible, to one paragraph.

Thank you, TLM80209 — Preceding unsigned comment added by TLM80209 (talk • contribs) 03:41, 24 September 2012 (UTC)


 * According to Tropical cyclone, they are regional terms used for the same type of storm. ←Baseball Bugs What's up, Doc? carrots→ 03:50, 24 September 2012 (UTC)


 * The answer is: They are the exact same weather phenomenon, but we use different names depending on what part of the world it occurs in. If it occurs near the Americas, it's a Hurricane.  If it occurs near East Asia, it's a Typhoon.  If it occurs near Australia or India, it's a Cyclone.  -- Jayron  32  04:13, 24 September 2012 (UTC)


 * However, note that "cyclone" is sometimes misused, in the US, to mean a tornado (see def 3). StuRat (talk) 04:30, 24 September 2012 (UTC)


 * Note that cyclone lists tornadoes as a variety; it is quite a general term and includes more than a "synoptic scale" (to quote the article without really understanding it) tropical cyclone. Even so, I don't feel like people in the U.S. have really called tornadoes "cyclones" since The Wizard of Oz (1939 film). Wnt (talk) 18:17, 24 September 2012 (UTC)
 * This article contains a reference to that term from a couple of weeks ago. Less common, but still used. It was first coined in reference to a tropical cyclone that hit India in the mid-19th century, and was soon picked up in reference to tornadoes. Both "tornado" (from Latin) and "cyclone" (from Greek) convey the idea of spinning rapidly. This USAToday article from 5 years ago states that the term "cyclone" is still used by the public (sometimes) in reference to a tornado, and that technically a tornado is a type of "cyclone", i.e. rotating cloud. The term used to be much more common. The Hall of Fame pitcher Cy Young always claimed that the "Cy" stood for "Cyclone", not for implying he was a rube. (That was Waddell or Marquard). ←Baseball Bugs What's up, Doc? carrots→ 01:03, 25 September 2012 (UTC)


 * Synoptic scale meteorology deals with large, continent-sized weather trends, contrast with mesoscale meteorology and microscale meteorology. The difference is akin to the distinction between (imperfect analogy): Macroeconomics and microeconomics.  -- Jayron  32  19:42, 24 September 2012 (UTC)


 * And to add to the confusion, in the USA a Hurricane force wind warning is issued for strong winds explicitly NOT associated with a tropical cyclone or hurricane. And "hurricane force" is the formal name for the highest wind speeds on the Beaufort scale. HiLo48 (talk) 04:41, 24 September 2012 (UTC)
 * A cyclone is a large weather pattern of rotating winds spiraling inward towards an area of low pressure in the center. When the winds become very strong, it is called a tropical cyclone. Americans call them hurricanes, while in Japan they're called typhoons...? I think you might be better off with a website for kids. Ssscienccce (talk) 02:49, 25 September 2012 (UTC)


 * As your friendly meteorology student here I would like to clarify that basically while all hurricanes/typhoons are cyclones not all cyclones are hurricanes/typhoons. A cyclone is basically any weather system that is rotating in a cyclonic direction, that is counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere. Mesocyclones, tornadoes, hurricanes/typhoons/tropical cyclones, Extratropical cyclones, and polar lows are all cyclones. The terms hurricane and typhoon refer exclusively to tropical cyclones (which are in come parts of the world known simply as "cyclones". Ks0stm  (T•C•G•E) 20:38, 25 September 2012 (UTC)

supernova
the article's intro says that most or all of the star's material is expelled, but in most examples nutron stars or black holes are left over after. what am i missing here?165.212.189.187 (talk) 16:14, 24 September 2012 (UTC)
 * Most is not a synonym for all. -- Jayron  32  16:24, 24 September 2012 (UTC)

That is one good (antonym of bad) observation, thank you. You forgot much is not a synonym for most, or is it?165.212.189.187 (talk) 16:37, 24 September 2012 (UTC)
 * Yes, but you never used the word much, so I had no reason to bring that up. -- Jayron  32  18:45, 24 September 2012 (UTC)
 * yes you did: the article says much whereas Op incorrectly replaced it with most, which means Op also missed that, or you both did.GeeBIGS (talk) 03:43, 25 September 2012 (UTC)
 * I looked at that source, and I didn't notice anything in it about supernovas that emit all their material. Can you really have a supernova and it doesn't leave anything behind, not even a Genesis planet?  I'm thinking, "bad edit". Thanks for your response below! Wnt (talk) 16:46, 24 September 2012 (UTC)


 * Type Ia supernova are believed to emit all of their material. They generate more energy than the gravitational binding energy of the star and heat the entire interior, with the implication that the entire star becomes superheated and blows away.  Compact objects  are not expected to remain after Type Ia supernova.  The more common core-collapse supernova (Types II and Ib / Ic) treat the core of the star and it's bulk differently, and generally are expected to leave compact core remnants, i.e. neutron stars / black holes, at the center of the explosion.  Dragons flight (talk) 19:11, 24 September 2012 (UTC)


 * PS. The cited source does say that the white dwarf in a Type Ia supernova is "completely disrupted", which is essentially the same as noting that all of the material is emitted. Though I would say that the point could be made clearer.  Dragons flight (talk) 19:23, 24 September 2012 (UTC)
 * "could be made clearer" is probably a completely true statement regarding 99.9999% of our articles on scientific or technical subjects. -- Jayron  32  19:39, 24 September 2012 (UTC)
 * Since we have 4 million articles, and perhaps even 1 million articles on science / technical topics (broadly construed), that leads me to wonder which 1 article do you think is completely clear? ;-)  Dragons flight (talk) 21:41, 24 September 2012 (UTC)
 * The one on transparency. ←Baseball Bugs What's up, Doc? carrots→ 00:25, 25 September 2012 (UTC)
 * I would have thought that no matter how the star broke apart, that there'd always be some spot in the middle which didn't know "which way to go" and would collapse back in for the lack of a bearing. How does the star get around that?  Does the stuff simply stay at such superheated temperatures for so long that its gravity can't hold it together? Wnt (talk) 20:08, 24 September 2012 (UTC)
 * The star is only held together by its gravity. When most of the mass is lost, there is nothing that keeps the superhot, superdense core together anymore, and it flies apart. --Stephan Schulz (talk) 20:15, 24 September 2012 (UTC)
 * Of course, but even a gas giant has enough mass to stay together. I suppose it's a matter of trying to understand how absurdly hot the gases of the exploding star become, and how long it takes them to cool off, and plugging it into some kind of scale height equation? Wnt (talk) 23:25, 24 September 2012 (UTC)
 * If the average speed of the gas molecules (which is what we mean by temperature) then enough molecules will have escape velocity that the remaining cloud of gas dissipates. You will get a kind of evaporative cooling, but as gas escapes the gravity reduces and the escape velocity comes down. I'm not sure which affect is faster, but you could certainly get down to a very small amount of gas remaining before it cooled enough to become gravitationally bound (and it wouldn't surprise me if you just end up with complete dissipation). --Tango (talk) 20:23, 25 September 2012 (UTC)
 * And add to that the possibility of Gamma-ray burst emission mechanisms (the reverse shock being the important part), and Supernova, and there's a good chance that the minor "cooled" remnant stuck in the middle will be disrupted in the aftermath of the supernova{OR}. Exactly how the disruption works is probably unknown, but it will probably be a phase of decreasing degeneracy followed by a more or less classical expansion driven by the heat at the core. Asymmetry and reverse shock, given their magnitude and the diameter of a hot, non-degenerate target, should be more than enough to disrupt anything that survives both phases. - ¡Ouch! (hurt me / more pain) 08:38, 26 September 2012 (UTC)

Drawing faster than your own shadow
Lucky Luke is famous for drawing faster than his own shadow. I've come to think, doesn't practically everyone draw faster than their own shadow? I mean, when you move your arm, light moving from the sun (or other similar light source) hasn't yet reached the place where your arm used to be, so the corresponding place in the shadow stays dark. On the other hand, light that previously reached the place where your arm is now is still moving towards the background, so the corresponding place in the shadow is lit. Of course, given that the speed of the light is so great, this happens so fast that the human eye cannot really distinguish between it and instantaneous movement of the shadow. The speed of your movement doesn't matter - for there to be noticeable difference, your shadow should be a great distance away. On the other hand, the event portrayed in the parody comic "Rocky Luke" - drawing slower than one's own shadow - is impossible. Have I got this right? J I P &#124; Talk 18:12, 24 September 2012 (UTC)


 * Correct. I suppose a person might try to force some order onto the comedy, if desired, by saying that a slow motion view of the draw should see a noticeable difference in the rate of the draw, i.e., that the person should draw at something on the order of the speed of light (so that say a 1 foot motion to draw is only half completed by the shadow four feet away, making your speed 1/8 light speed). Wnt (talk) 18:21, 24 September 2012 (UTC)


 * And note that from the POV of the person drawing, their view of their distant shadow is delayed by the speed of light over twice the intervening distance, as first their shadow must travel that distance, and then the image of their shadow must make the return trip to their eyes. StuRat (talk) 18:45, 24 September 2012 (UTC)
 * So actually no one can even theoretically see his/herself as drawing faster than his/her own shadow, but an outside observer could see such a person drawing faster than his/her own shadow? J I P  &#124; Talk 18:48, 24 September 2012 (UTC)
 * No, that's exactly wrong. A person sees himself drawing slower than his or her shadow as light has to travel twice the distance between himself and his shadow.  A person who was situated opposite a person and their shadow (i.e. going light-artist-shadow-observer) would see the shadow draw first, before seeing the person draw, while an observer situated between the two, but off to the side a bit, would see them draw simultaneously.  An observer situated behind the artist would see the artist draw first, then the shadow.  These three situations are a demonstration of relativity of simultaneity.  -- Jayron  32  19:24, 24 September 2012 (UTC)
 * Wait a minute - see the shadow draw first? Simultaneously, I can picture, but how is the light going to the shadow going to outrace the light to the observer, even if you put some slow glass in there somewhere? Wnt (talk) 20:05, 24 September 2012 (UTC)
 * The artist-observer-shadow (assuming the shadow falls on a wall or other similar opaque object) is always going to make a triangle, and the relative lengths of the legs of the triangle determine how long the light takes to reach the observer. Insofar as one can construct a triangle where the distance from the shadow to the observer is the shortest of the three legs, there will be many situations where the observer can see the shadow draw first.  There are also constructions where one could see them draw simultaneously, or where one could see the artist draw first.  -- Jayron  32  20:19, 24 September 2012 (UTC)
 * Ummm, you do remember that the light has to go from the "artist" to the shadow before the shadow does anything at all? One of us is seriously confused at this point... Wnt (talk) 21:59, 24 September 2012 (UTC)
 * Indeed - see triangle inequality. The shortest distance between two points is a straight line, so the direct route from artist to observer has to be quicker than going via whatever the shadow is being cast on. --Tango (talk) 20:26, 25 September 2012 (UTC)
 * I think, somewhere along the line, someone misinterpreted which sense of the word draw is being used here. Luke is a quick-draw artist, but as far as I know not an "artist" in the sense of creating visual representations. --Trovatore (talk) 20:49, 24 September 2012 (UTC)
 * In any event, the above observations are failing to take into account the limitations of the observers; human photosensory capability and visual cognition processing, while seemingly instantaneous to our perception, are in fact many orders bellow the speed the light and as a result, at any distance where a human shadow would be seen by the person generating it, the movements occur simultaneously, to human perception. That is, no human being has the capability to detect the minute difference in time between the movement of the person generating the shadow and the movement of the shadow itself as a result of the upper threshold on the "refresh rate" of the human photosensory package (and if they could, they'd be perceiving light in a very different way from how we experience it).  In fact, not only is the human nervous system not capable of parsing data into discreet enough chunks to make this detection, but so is all but our most advanced photonics technology.  Of course, I assume when people use the term "observer" above that they are using it in the sense common to the physical sciences -- a theoretical thought experiment construct not constrained by our physical limitations -- but the distinction is still worth making when answer the OP's question. Snow (talk) 22:34, 24 September 2012 (UTC)
 * Luke draws his gun faster than his shadow can. If his shadow were to try to get the drop on Luke, Luke would shoot the shadow dead. --Trovatore (talk) 22:39, 24 September 2012 (UTC)
 * Maybe not! Since the amount of time between the start of the events is so small and the air between the two shooters is not perfectly uniform, there's every chance that the shadow's bullet will strike Luke first, simply if there was the smallest difference air density anywhere along the trajectory of the bullets (which, when we're looking at things on this scale, there would be). However, both are going to get "hit" if either of them is, since the reaction time between the two actors could not be significant enough to change this outcome, even if the shadow could operate independently.   Lucky for Luke (pun totally intended) shadow guns have notoriously bad stopping power.  Snow (talk) 22:56, 24 September 2012 (UTC)
 * I agree with Wnt that it's not possible to see the shadow first, as the only way for this to happen is if the hypotenuse is longer than the sums of the other two sides of the triangle, which isn't possible. - Akamad (talk) 22:18, 24 September 2012 (UTC)


 * The point in the whole faster-than-his-own-shadow thing is that he can shoot before his shadow draws. Here is a famous image: (the bullett hitting before the shadow draws has issues but let's not go there). PrimeHunter (talk) 22:48, 24 September 2012 (UTC)
 * If you think that's fast... Cool Papa Bell could turn off the bedroom light and be in bed before the room got dark. ←Baseball Bugs What's up, Doc? carrots→ 23:02, 24 September 2012 (UTC)
 * Nay, that's just outrunning electrons. Depending on the inductance of the circuit it's possible any old lady could do it.  (Not one that passes the building code though ;) ) Wnt (talk) 23:15, 24 September 2012 (UTC)
 * Good point. You can maybe outrun the house current, but you can't outrun the building inspectors. ←Baseball Bugs What's up, Doc? carrots→ 00:24, 25 September 2012 (UTC)

Doppler effect
Hi all. From wave physics we have that for a source of a frequency fs moving at speed vs towards a stationary observer, the observer perceives a frequency fobs of $$f_{obs}=\frac{v}{v-v_s}f_s$$. For an observer moving at speed vobs towards a stationary source of a frequency fs the observer perceives a frequency fobs of $$f_{obs}=\frac{v+v_{obs}}{v}f_s$$, where unsubscripted v is just the speed of sound. If one is moving away from the other, we can just set either vobs or vs negative, and we can combine these two formulas into the general $$f_{obs}=\frac{v+v_{obs}}{v-v_s}f_s$$. My question is, since motion is relative, why the distinction between a moving source and a moving observer? For example, if an ice cream truck was moving towards a stationary me at a speed of 5 m/s emitting a proper frequency fs, wouldn't it be the same as me moving at 5 m/s towards a stationary ice cream truck emitting the same frequency? Thanks. 24.92.74.238 (talk) 20:07, 24 September 2012 (UTC)
 * Motion is not relative in that scenario. The sound propagates at a constant speed with respect to the atmosphere, which forms an absolute reference frame. Looie496 (talk) 20:17, 24 September 2012 (UTC)
 * Note that the "v-vs" can go to 0, creating an "infinite frequency", i.e. a sonic boom or shock wave not covered by this mathematics when it exceeds the sound barrier. But for the hypothetical observer (who we imagine as having no physical effect on the system himself, like a ghost) the frequency merely doubles when he approaches at the speed of sound.  (Question: is it possible to design an instrument boom at the front of a real supersonic aircraft so that it hits undisturbed air from in front of the shock wave and takes recording studio quality sound of the peace and quiet it is about to destroy, for miscellaneous espionage purposes?) Wnt (talk) 23:31, 24 September 2012 (UTC)


 * Motion is relative, but the effect depends on the relative speeds of the emitter, receiver and medium, not just the emitter and receiver. -- BenRG (talk) 03:27, 25 September 2012 (UTC)