Wikipedia:Reference desk/Archives/Science/2013 May 20

= May 20 =

Throwing one's hands in the air
When humans get excited, they tend to put their arms up. Three prominent examples are in worship services (e.g., File:Zhromko.jpg), at music festivals, and at sporting events. Why do they do this? Magog the Ogre (t • c) 00:21, 20 May 2013 (UTC)
 * When humans get excited, they do lots of things, they dance, they cheer, they clap, it's partially cultural, but I can't actually see what needs an explanation? What else can humans do when they get excited? All we have are arms, legs and voices. Unless you also have a lighter, a phone or a vuvuzella... Vespine (talk) 01:13, 20 May 2013 (UTC)
 * I've inserted a picture showing another type of excitement. Looie496 (talk) 01:26, 20 May 2013 (UTC)
 * @Vespine, I do not think it is cultural. I have observed it across cultures, and it comes quite naturally in some situations. Magog the Ogre (t • c) 04:27, 20 May 2013 (UTC)
 * I said partially cultural. There is a cultural component which would help determine exactly how people will react to exciting situations. Look at the history of Applause for example: Within each culture, however, it is usually subject to conventions.. Watching the world cup soccer staged in different countries can also reveal how different cultures react in exciting situations, they're not all precisely the same. Of course I'm NOT saying there aren't common components which aren't cross-cultural, of which lifting one's hands certainly might be one of the most "basic". Vespine (talk) 04:53, 20 May 2013 (UTC)


 * I once read the following, describing a certain unnamed culture: When speaking, they gesture frantically with their hands in an attempt to distract your gaze from their ugly faces, upon which are clearly etched the marks of their moral and intellectual degeneracy. --   Jack of Oz   [Talk]  05:03, 20 May 2013 (UTC)
 * I once read in a scientific text that the reason rattlesnakes evolved rattles was because all snakes naturally shake their tails when excited, given they have nothing else to shake. μηδείς (talk) 08:30, 20 May 2013 (UTC)


 * I suppose it's possible that this is a gesture that's intended to show the opposite of "defensiveness". You're much more vulnerable to attack with your arms waving up in the air - and you can more clearly see that a person isn't armed.  Perhaps this is a way for body-language to say "I'm excited, but not in an angry or threatening way." ?? SteveBaker (talk) 15:35, 20 May 2013 (UTC)


 * Or an urge to be associated with the win or celebration. Like "I am also part of this victory";  "I was on/cheering for the winning side" ; "I voted for you so don't put me in jail" etc.165.212.189.187 (talk) 18:28, 20 May 2013 (UTC)


 * Just don't get carried away with it. ←Baseball Bugs What's up, Doc? carrots→ 23:18, 20 May 2013 (UTC)


 * I remember reading a paper claiming that having an "open" or "closed" posture had an effect on behaviour and self-esteem. The study claimed that people who were more confident had an open posture, and that having an open posture led to increased confidence. It had people stay in closed or open postures for 10 minutes prior to being given a job interview, and the people who had a closed posture performed much worse than those having an open posture. Personally I found the methodology dubious for this particular study, but it is indicative of an attempt to link posture and confidence. It could be that when one is celebrating, they are feeling more confident and thus adopting an open posture is natural, according to this way of thought. This is merely idle speculation but it might open some avenues of research. Look up scientific papers on posture and self esteem / confidence. Superficially, Google will yield a lot of pop-psychology self help on the subject as well. — Preceding unsigned comment added by 64.201.173.145 (talk) 21:00, 21 May 2013 (UTC)
 * There's a Ted speech about it here (although she's talking about "triumph" throwing your hands in the air, not exacerbated throwing your hands in the air). Incidentally chimps do the same thing. We're a lot more hard-wired than some would suggest. Shadowjams (talk) 02:44, 25 May 2013 (UTC)

Decay product
Why does decay product is referred as 'daughter', not 'son' ? Concepts of Physics (talk) 13:00, 20 May 2013 (UTC)


 * The most likely reason is that in many cases it can go on to be the mother atom of a subsequent round of decay. -- 71.35.111.68 (talk) 16:17, 20 May 2013 (UTC)


 * No reason, just somebody started doing it that way and it caught on. Gender language, when assigned to anything regardless of it's actual sex (if any) is often arbitrary. StuRat (talk) 06:43, 21 May 2013 (UTC)


 * Here is a reason: only the female gender can give birth, thus it would volate that principle to call the decay product a son, as opposed to a daughter. Plasmic Physics (talk) 11:54, 21 May 2013 (UTC)

Mysterious lack of airspeed
This 1958 advertisement for Delta announced their nonstop DC-7 service, Atlanta to New York, took 2 hours, 39 minutes. My calculator tells me that's an average speed (assuming 760 statute miles from Atlanta Hartsfield to New York LaGuardia, per Google Earth) of about 286 statute miles per hour. Well and good, but a google search for today's nonstop flights reveals that 2 hours 10 minutes is the fastest scheduled time on a Boeing 737, or a speed of about 350 statute miles per hour. WTF? The article DC-7 gives a cruising speed of 359 mph for that 4-engine prop job, but the latest Boeing 737s have a cruising speed of 511 mph. Another couple of clicks shows that the DC-7 made the journey at an average of 80% of its cruising speed; yet the Boeing 737 travels at an average of only 68% of its cruising speed for the same journey. Thus the trip is only half an hour faster in 2013 than in 1958. Why so slow? Textorus (talk) 15:02, 20 May 2013 (UTC)


 * Some possibilities:
 * Airliners aren't at cruising speed for the entirety of the flight. The approach phase, particularly, is slow and often circuitous. However, that "less than cruising speed" speed is probably comparable between the DC-7 and a modern jetliner (at least more comparable than their cruising speeds), which means the modern jetliner will proportionally experience more delay relative to its theoretical minimum travel time.
 * Airliner routing is different over a 55-year span. The DC-7 didn't have to contend with either the volume of other aircraft in the airspace or the post-9/11 security measures that a modern jetliner encounters, both of which restrict the path an aircraft can take. More restrictions mean a longer flight, generally.
 * The definitions of "departure time" and "arrival time" may have shifted (this one is just speculation on my part). What is "departure time"? When no new passengers are admitted aboard? When the cabin door is shut? When the plane begins to move? When it actually leaves the ground? That's 15 to 30 minutes of possible range right there, and if the 1958 definition doesn't match the 2013 definition, it's potentially a significant input. &mdash; Lomn 13:56, 20 May 2013 (UTC)


 * (ec) Travel times are usually derived from gate-to-gate times. So undocking, pushing back, taxing, runway wait times, takeoff and acceleration times, plus the equivalent on landing all add to the total time without adding commensurately to average speed.  Add that to the much higher traffic densities and larger taxiing distances for modern airports, and you should see why it is at least plausible that on shorter trips the times may not have improved much, despite the cruising speed increasing substantially.  The large difference between your calculated speeds and the aircraft's cruising speeds tips one off to this.  — Quondum 14:04, 20 May 2013 (UTC)


 * Departure from Atlanta was relatively straightforward in 1958: roll away (no pushback, since there were no jetways), taxi a mile or so to the end of the active runway, wait for maybe one or two take-offs and landings, and go. Nowadays it's possible to taxi five miles at Atlanta and wait for a dozen planes ahead of you. It's not as bad in terms of distance at LGA, but it's more congested - waiting for a gate (no pulling up on an empty ramp space anymore).  Acroterion   (talk)   14:19, 20 May 2013 (UTC)


 * As Quondum and Acroterion both note, the gate-to-gate time includes an awful lot of time spent not cruising, particularly on a shorter flight. Try working the math the other direction, and see what you get.  A 760-mile journey at the DC-7's 359 mph gives 2:07 cruising time; if the total time is 2:39, then that's 32 minutes of taxiing, approaching, and so forth.  A 760-mile journey at the 737's 511 mph gives 1:29 cruising time; given a total travel time of 2:10, there's 41 minutes of 'non-cruising' time.
 * Granted, that sort of back-of-the-envelope isn't quite realistic – aircraft obviously don't jump instantaneously from the runway threshold to full cruising speed and altitude – but it's not a ridiculous result. Nine minutes difference in the 'non-cruising' time can be down to differences in the way departure and arrival times are defined, increased traffic and delays at the two airports, changes in permitted routes, and the fact that many airlines have slightly reduced their cruising speeds to save fuel. TenOfAllTrades(talk) 15:14, 20 May 2013 (UTC)


 * I fly on a regular basis between London and Amsterdam. The flight is timetabled at a little over an hour.  However, at Schiphol the plane will often take 20 minutes to taxi between terminal and runway (so much that it sometimes seems like we are going all the way there on the ground), and then spend less than 40 minutes in the air.  Heathrow is a busier airport with fewer runways and sometimes long waits for other aircraft ahead.  Astronaut (talk) 18:14, 20 May 2013 (UTC)


 * Another possibility that nobody so far has mentioned is that the Boeing's 511-knot cruising speed is only achievable at high altitude (above 25,000 feet) -- below that level, it drops off sharply so that near sea level, the V(ne) (that's the MAXIMUM safe speed) is only 330 knots! (This is true of ALL jetliners, as a matter of fact -- the engines produce less power at low altitude, and the denser, more turbulent air puts unacceptable stress on the airframe.)  And since for such a relatively short flight, the plane spends a greater part of the journey at low altitudes, even its average FLYING speed will be lower because of this.  (Not to mention the time spent in the holding pattern at the outer marker while waiting to land.) 24.23.196.85 (talk) 04:59, 21 May 2013 (UTC)

Thanks, guys, for all the responses. I suppose the relatively slow speed (to my mind) of the jet flight is due to some combination of all the points mentioned above. I see that for comparison, today's best flight time between Atlanta and Dallas (730 statute miles) is 2:25, or 61% of the 737's cruising speed, on average - even worse than to New York! Though from EWR to LAX (~2455 miles), the Boeing gets up to 88% of cruising speed, speaking on average once again - so it seems that the longer the flight, the more efficien the jet plane is.

NEW QUESTION then: Aren't we wasting a lot of fuel and money flying jets on short-to-medium routes? Wouldn't it be better to go back to propeller craft, which - correct me if I'm wrong - don't use nearly as much fuel and get you from A to B in nearly the same time? Wouldn't that help save the airlines, the economy, the trees, the whales, etc.?? Textorus (talk) 19:35, 21 May 2013 (UTC)
 * Yes, that's all true, but the key issue is whether consumers will accept turboprops; industry experience has shown that consumers prefer jets, all other things being equal. A casual google search suggests that the industry may be moving back towards turboprops for regional routes. &mdash; Lomn 19:53, 21 May 2013 (UTC)
 * Interesting articles, thanks. Textorus (talk) 00:36, 23 May 2013 (UTC)
 * Turboprops airplanes are also more prone to air bumps and resulting vomits.. Electron9 (talk) 01:50, 24 May 2013 (UTC)
 * Not really -- this is because of their generally lower cruising altitude, which is also the case for jets on shorter flights like Atlanta to Dallas. (I remember one particular flight from LAX to SJC in a Bombardier CRJ where they kept the seatbelt light on the whole way from takeoff to landing because the turbulence was so bad and they couldn't find an altitude with smooth air, even at FL280 -- they kept changing altitude every few minutes, but the plane just kept bouncing up and down like a cork on choppy water!) 24.23.196.85 (talk) 06:06, 24 May 2013 (UTC)
 * Note that, while earlier jet engines were not fuel efficient, modern high-bypass jet engines compare pretty well with turboprops. Wickwack 121.215.140.49 (talk) 10:13, 22 May 2013 (UTC)

Human body
What is it called the upper part of the human foot? Thank you.175.157.180.68 (talk) 15:03, 20 May 2013 (UTC)


 * The top is the dorsal, unlike the underside 'plantar' surface (where one gets plantar warts – better known as verrucas). As it the foot, it is therefore the  dorsum pedis. Does that help?Aspro (talk) 15:19, 20 May 2013 (UTC)


 * Wikipedia has an article on foot.--Shantavira|feed me 15:29, 20 May 2013 (UTC)


 * It's called the instep. μηδείς (talk) 18:41, 20 May 2013 (UTC)

Original Earth-Moon distance
Hi: I looked up the entry for the Moon, trying to read what was the original distance between the Earth and Moon. I did not see it in the story. Did I miss it or is it not there? Thanks for you help. Red.leaf.flyers (talk) 16:53, 20 May 2013 (UTC)
 * It depends on which model for the Origin of the Moon you are working with. One of the dominant models is the Giant impact hypothesis, in which case the original distance between the Earth and Moon was 0 km, insofar as they were once the same body.  -- Jayron  32  17:06, 20 May 2013 (UTC)
 * In a giant impact, material would be ejected into Earth orbit, where it would eventually coalesce to a ball. It is a bit hard to say where the orbit would be, but simulations suggest 3-5 Earth radii (20.000 - 30.000 km). An impact would have a hard time lifting enough material higher than five radii. Closer than about three Earth radii would put the impact ejecta inside the Roche limit, giving the Earth rings rather than a moon. 88.112.41.6 (talk) 17:39, 20 May 2013 (UTC)
 * Hang on, are you saying that since its formation, the moon has migrated from 3-5 earth radii away, to its current position 60 earth radii away? I'm not saying you are wrong, I just always imagined that the moon would have had to form very roughly around it's present position. However I can see now how that doesn't quite make as much sense as I thought it did... Vespine (talk) 06:54, 21 May 2013 (UTC)
 * According to Italo Calvino, it used to be close enough to climb up to it from a small boat, by way of a ladder. See La distanza della luna, the first vignette in Le cosmicomiche.  It's available in English translation if necessary.  Seriously, of course it's off-topic for this desk, but I very strongly recommend it. --Trovatore (talk) 06:57, 21 May 2013 (UTC)
 * On the topic of the Moon in fiction, Domingo Gonsalves harnessed large geese and tagged along for their annual migratory flight to the Moon circa 1638. Nimur (talk) 13:12, 21 May 2013 (UTC)


 * At it's current rate of motion, 3.8 cm / yr, the moon would migrate 25 Earth radii in the age of the Earth. However, that is almost certainly a lower bound as the rate of migration should have slowed over time.  Dragons flight (talk) 07:57, 21 May 2013 (UTC)


 * It is actually possible to very roughly estimate this initial distance of roughly 30,000 km using a back of the envelope calculation. It boils to the fact that you have an impactor that had a similar orbit as the Earth, so it comes in from infinity at zero relative speed, and therefore the impact happens at escape velocity. If you where to give the ejecta that velocity, it would escape at infinity but, of course, a significant fraction of the impact energy is not available as kinetic energy. Then because the Earth radius is the quantity with the diemnsions of length, what happens is that if you make some rough approximations then whatever fraction is available, you find that the distance ends up being the Earth radius times some dimensionless factor, and that factor is not going to be very large like 100 or very small like 0.01. Count Iblis (talk) 11:48, 21 May 2013 (UTC)
 * As I am an amateur purveyor of all lunar literature, I have a fascinating text, Strange World of the Moon (authored by V. A. Firsoff in 1959) that makes an excellent chapter of dimensional analysis and inference about the origin of the moon. Needless to say, the book and its science predates manned spaceflight to the moon - or in fact, any spaceflight to the moon - so many of its conclusions have since been refined or refuted by better selenological evidence.  In addition to the Giant Impact hypothesis, the author considers several other possibilities: tandem formation from a primordial nebula; capture of a separate celestial body; massive ejection by volcanic or other paleo-Earth processes; or simply large-scale fluid flow during Earth's formatory molten-rock era.  From first principles of physics, and based on knowledge of orbital mechanics and basic facts of gravity, none of these alternate formation theories seem to sit well with the author; it quickly becomes clear why Giant Impact hypothesis gained traction in the following decades.  However, even in 1959, it was easy to see that this was no ordinary impactor; the momentum necessary to eject a moon-sized object would have to be planetary in size.  Evidence of the geochemistry of moon rocks - only possible after our first sample return missions in the late 1960s - strengthens the case; and many scientists now believe that the impactor may have been Mars.  This is difficult to prove; but is widely accepted as "more plausible" than a mysterious impactor that has long since disappeared.  For example, NASA's current science webpage at Solar System Exploration: Earth and Moon origin, asserts that the impactor would be "Mars-sized," without naming any names.   Nimur (talk) 13:30, 21 May 2013 (UTC)
 * As an ex-aspiring astronomer who still reads popular accounts of the current art, I think you're slightly misinterpreting the proposed scenario. It isn't that another planetary body performed a hit-and-run on Earth, knocked off the Moon material, and went on its way largely intact (perhaps as Mars). Rather, the idea is that a (Mars-sized) proto-planet (sometimes dubbed Theia), stuck the proto-Earth, rendering both largely molten, and merged with the Earth: a good deal of the material splashed off from the impact then coalesced to form the Moon with much of the rest falling back to the now somewhat enlarged Earth. Only a relatively little debris would have escaped the Earth-Moon system, and the resulting materials of both the Earth and Moon would be similar but not identical blends of the original two colliders. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:05, 21 May 2013 (UTC)
 * Yes, and the impactor could plausibly have come from L4 or L5 as pointed out here. Count Iblis (talk) 15:16, 21 May 2013 (UTC)
 * I'm familiar with several variations on the theme. I think, based on factual evidence alone, there's still a lot of wiggle-room for scientific disagreement.  It is my opinion that there are not very many conclusive facts about the early formation of the Earth-Moon system; rather, there are several competing theories and hypotheses supported by our sparsely-available evidence; each scenario varies in degree of plausibility.  Nimur (talk) 22:09, 21 May 2013 (UTC)
 * Did I hear someone mention Immanuel Velikovsky? --   Jack of Oz   [Talk]  23:35, 21 May 2013 (UTC)
 * A billion years from now interesting things could happen. Count Iblis (talk) 00:23, 22 May 2013 (UTC)

As explained here, General Relativity makes the solar system relatively stable: "These results also answer to the question raised more than 300 years ago by Newton, by showing that collisions among planets or ejections are actually possible within the life expectancy of the Sun, that is, in less than 5 Gyr. The main surprise that comes from the numerical simulations of the recent years is that the probability for this catastrophic events to occur is relatively high, of the order of 1%, and thus not just a mathematical curiosity with extremely low probability values. At the same time, 99% of the trajectories will behave in a similar way as in the recent past millions of years, which is coherent with our common understanding that the Solar System has not much evolved in the past 4 Gyr. What is more surprising is that if we consider a pure Newtonian world, the probability of collisions within 5 Gyr grows to 60 %, which can thus be considered as an additional indirect confirmation of general relativity." Count Iblis (talk) 00:41, 22 May 2013 (UTC)