Wikipedia:Reference desk/Archives/Science/2009 April 26

= April 26 =

radical addition of alkynes
There are two (pencil and paper) subsyntheses I would like to make (well the reason I'm adding halogens is that I'm trying to attach the products onto an aryl group later, but that's not the issue). Can I check that the following ideas are valid:



First synthesis: I know alkene reactivity > alkyne reactivity, but would it be possible to use acid-catalysed hydration of just the alkene bond? If I set the temperature low enough, it would be possible to get a major product where I just added to the alkene bond but not the alkyne bond, right?

In addition, how would I design the reaction so I can "stop" at the alkene stage, and not do a double-hydrobromination? (My textbook says you can stop it for normal Marvkovnikov addition, without commentary on radical addition, such that you don't form geminal halides, but I have no idea how you would detect the optimal formation of your alkene product such that you could stop the reaction on time.)

In addition, does the overall idea of radical (anti-Markovnikov) addition of Br to an alkyne bond work? Are radical stability effects magnified such that the formation of 2-bromo product is limited? I assume that the radical addition for alkenes is much faster than the carbocation formation step, hence why the radical effect dominates, but is a radical on an sp-carbon going to be more unstable than say a radical on a secondary sp2 carbon? John Riemann Soong (talk) 08:34, 26 April 2009 (UTC)



Second synthesis: Assuming the validity of radical addition to an alkyne, this second synthesis seems to imply I would get a cis-product as well as a trans-product. I only want the trans-product. Is it possible to design a reaction that favours the formation of trans-product? (The formation of diastereomers isn't important for my first synthesis.) John Riemann Soong (talk) 08:34, 26 April 2009 (UTC)

Enhancement by implants
More and more often I would find a third arm or an implanted wlan interface to my computer very useful. Being in a hurry very often, I would greatly appreciate a way to put on my socks while continue to operate the keyboard, just as an example. Or to make a phone call, talking silently via some future-style nerve-reading interface while listening to some slow talking time-sucker on the normal phone.

I know this is far from practice, at least for otherwise healthy people (and thus this is not asking for medical advice), but what is the state of art for such enhancements? (Well, I know I could buy a headset for a start ...) 93.132.137.0 (talk) 11:45, 26 April 2009 (UTC)


 * Well - perhaps not as far as you think. If you'd be prepared to use your real hands for putting on your socks on, there is a guy who has demonstrated typing by thought alone . See Brain-computer interface for example.  At present, it's rather slow (eight characters per minute!) - but it's getting there.  There are plans to sell a starwars-themed toy that lets you control the motion of a ball moving up and down a tube by thought alone: .  So it's certainly possible. SteveBaker (talk) 14:54, 26 April 2009 (UTC)


 * The thing that has real prospects is "add-ons" to replace things that are missing, such as an amputated limb. The big problem with wholly new things like a third arm is that you don't have any brain circuitry to manage them.  There are some tricks that potentially could be used to reconfigure brain circuitry that has other functions, but none of them are likely to come into play very soon. Looie496 (talk) 16:47, 26 April 2009 (UTC)


 * The strange thing is that when I try to put on my socks while brushing my teeth and wanting to do even more in parallel (but not attempting for certainty of failure) I really feel like I could handle a third or forth arm. After all, I frequently pick up things with my feet. (Maybe I was a spider in some previous life.) As for the links from Steve Baker (thanks!), they made me realize I won't need any extra limbs implanted when there is/would be the possibility to steer some detached actuators instead --- a kind of real-science telekinesis. 93.132.137.0 (talk) 22:04, 26 April 2009 (UTC)

Earthrise on the Moon


Today's featured picture at Commons has the following caption: "Taken by Apollo 8 crewmember Bill Anders on December 24, 1968, showing the Earth seemingly rising above the lunar surface. Note that this phenomenon is only visible from someone in orbit around the Moon. Because of the Moon's synchronous rotation about the Earth (i.e., the same side of the Moon is always facing the Earth), no Earthrise can be visible from the surface of the Moon." I can understand this very well. However, would you always see the exact same scene? Would Earth appear to be basically a circle in the sky that doesn't move? Or would it move somewhat because the Moon isn't always precise-to-the-millimetre facing the same way? Just curious...Nyttend (talk) 12:55, 26 April 2009 (UTC)


 * It would appear as the Moon does from Earth, just larger -- that is, it would exhibit phases as well as size changes due to orbital eccentricities and the libration that allows us to see more than half the Moon. &mdash; Lomn 12:59, 26 April 2009 (UTC)


 * From the perspective of someone standing on the surface of the moon, the earth would stay in more or less the exact same place in the sky, hour by hour, day by day, year by year (it would move a little because the moon 'librates' - see image at right) - but as the long lunar day progresses from dawn to dusk to night, the earth would go through phases - just as the moon appears to go through phases from earth. SteveBaker (talk) 14:45, 26 April 2009 (UTC)
 * I haven't seen anything written about this, but the Earth would almost certainly have to move slightly, because the Moon's orbit is slightly elliptical rather than circular, and in addition is perturbed by the Sun. Looie496 (talk) 16:37, 26 April 2009 (UTC)
 * I think that's all covered by libration. -- BenRG (talk) 18:46, 26 April 2009 (UTC)
 * Also of course you would see evolving cloud patterns on the surface and a complete rotation every ~25 hours. It would be a lot more dynamic than the view we have of the Moon. -- BenRG (talk) 18:46, 26 April 2009 (UTC)

Googling on "libration in longitude", I found a page at demonstrations.wolfram.com that says the extent of this libration is 6°. Since the Earth's visual diameter as soon from the Moon is about 2°, it follows that there are parts of the Moon -- ones that we see roughly edge-on from the Earth's surface -- where you could indeed see the Earth rise. It would never come very high above the horizon, and later it would turn around and set in practically the same place, the whole cycle taking about a month. --Anonymous, 21:25 UTC, April 26, 2009.


 * That animation is hypnotic. I---must---turn---it---off!Edison (talk) 04:43, 27 April 2009 (UTC)
 * Yes - isn't that odd. SteveBaker (talk) 12:41, 28 April 2009 (UTC)


 * This "almost stationary" earth phenomenon was a critical element of Apollo's lunar surface S-band communications antennae, which where directional and set up to point to one spot in the sky (towards Earth). Nimur (talk) 15:09, 27 April 2009 (UTC)
 * Yes, but the Apollo missions each spent only a few days on the lunar surface. Given that the earth would make its apparent motion over an entire month, the amount of motion over a few days might well be little enough to make the assumption that it's stationary be a viable one. SteveBaker (talk) 12:41, 28 April 2009 (UTC)

SN 2005gj
A new article on an interesting supernova. I'm an astronomy amateur and would therefore appreciate review of the text by someone with a little more experience. Thanks, &mdash; Anonymous Dissident  Talk 13:32, 26 April 2009 (UTC)


 * Wikiprojects are very helpful for things like this. I suggest you ask at Wikipedia talk:WikiProject Astronomical objects. Looie496 (talk) 16:40, 26 April 2009 (UTC)
 * One of the missing info would be, is it in the Milky Way, in what galaxy, what distance? How fast did it rise and dim, to what magnitude (visible for whom?). All that theoretic stuff that now is in the article would just be a chapter. --Ayacop (talk) 18:20, 26 April 2009 (UTC)
 * Yeah, I know. But it's all that's out there, unfortunately. I know how far away it is, at least: 865m ly. &mdash; Anonymous Dissident  Talk 20:15, 26 April 2009 (UTC)
 * I just fixed the section header. Would you believe I accidentally linked to the wrong article? >_< &mdash; Anonymous Dissident  Talk 20:16, 26 April 2009 (UTC)

Rust spreads by catalysis or mechanical reasons.
I'm fairly sure I know the answer to this - but I need some evidence. At my local car club, we restore a lot of rusty old wrecks. Getting rid of rust is obviously important - but what I want to know is whether rust spreads because the rusty metal traps water and salt better than smooth metal - or whether it's because the existing rust is acting chemically as some kind of catalyst for reaction. It's obvious that rust starts as a little spot and then grows - it's just a question of what that mechanism is. I'm pretty sure it's not a chemical effect - but there is a big argument about it that needs resolving.

TIA SteveBaker (talk) 15:01, 26 April 2009 (UTC)


 * I think iron rust spreads because it's flaky. It exposes the material below to further rusting. (This is from something that I read about why iron and steel rust but aluminum doesn't. Catalysis was not mentioned.) --173.49.78.81 (talk) 15:38, 26 April 2009 (UTC)


 * Yeah - that's what I believe too - but I need some actual evidence. SteveBaker (talk) 15:56, 26 April 2009 (UTC)


 * As I understand it (which may not be very far), rusting is an example of electrochemical corrosion and any initial defect in the protective paint layer forms an anode with a current formed through the water (which is why salt water is so destructive because of its high conductivity). This link has some further explanation which you may find useful. BTW both chloride and sulphate commonly act as catalysts in rusting. Mikenorton (talk) 19:00, 26 April 2009 (UTC)


 * I agree - rust is electrochemical, so it will induce local static voltage in the electrically connected metal. Because the rust is a worse conductor than the "pure" iron (or steel/alloy), it has some resistivity and the voltage does not equalize; current flows; and this current encourages the further rusting.  (Those electrons have to go somewhere - and they go to the oxidation reaction, encourage it, and move along to the next spot).  You can weld on some extra metal like Zinc to preferentially absorb that current, but I've never heard of this being used on a land vehicle (I'm no auto-body expert though).  Anyway, I think this is neither mechanical (flaking) nor catalytic because the existing rust is actively participating in the electrochemical reaction throughout the entire connected surface.  Nimur (talk) 15:14, 27 April 2009 (UTC)

On high-speed tallow candles
The Dictionary of Misinformation(a trivia book dedicated to debunking common misconceptions), in a section about the claims that a botfly can fly at 800 mph, says that "a tallow candle will penetrate a board at such a velocity". Is this true? I recall the Mythbusters refuting a similar proposition about a straw penetrating through a tree trunk in a hurricane(about 300 mph wind speed), but 800 mph is more than twice that, so I'm not sure how to extrapolate from that to the presumably softer candle. 69.224.37.48 (talk) 18:38, 26 April 2009 (UTC)


 * So, imagine this botfly as it passed you at 800 mph, it would give you quite a scare as it cracked through the sound barrier —Preceding unsigned comment added by 86.4.190.83 (talk) 19:39, 26 April 2009 (UTC)


 * The Botfly thing has been debunked over and over (Here, for example) - one good reason being that it would have to consume more than it's own weight in food every few minutes in order to be able to produce that much energy.
 * But I wouldn't be quite so quick to dismiss the idea of the candle going through a board at 800mph. It's not the hardness of the candle that matters so much as the mass.  When any object hits any other object and is stopped - all of the kinetic energy that the moving object had has to go somewhere.  A candle weighs...I dunno...0.1kg let's say. At 800mph - 350 ms-1 it's going about a third of the muzzle velocity of a 50cal bullet with about three times the mass. But kinetic energy is proporitional to the SQUARE of the velocity - so it's going to deliver only about a third of the 'punch' of a modern 50cal bullet.  However, the target is a "board" - perhaps just a half inch of wood.  I've seen karate people smash "boards" with their open hands.  I think that an 800mph candle would go through a "board" like a knife through butter!
 * The Mythbusters did point out that a straw couldn't go through a tree trunk - but they did get them to penetrate a fair way into the trunk (a tree trunk is a lot thicker than a board) - and they found that a heavier projectile would do considerably more damage. A candle weighs maybe 50 times more than a straw, we're talking about it going almost three times faster - so perhaps 450 times more energy - and through a 1/2" board rather than an 8" tree...I think that's no problem at all!
 * SteveBaker (talk) 20:01, 26 April 2009 (UTC)


 * Hmm. I have some doubts that a tallow candle could even go through air at 800 mph.  Tallow is pretty soft. Looie496 (talk) 21:40, 26 April 2009 (UTC)
 * It would probably be seriously deformed (unless you shaped it to be very aerodynamic), but it is very difficult to stop something that is moving that fast - unless it had to travel a long distance through the air, I'm pretty sure it would make it in some form or other and, as Steve says, all that really matters is the mass, what form that mass is in is pretty much irrelevant. --Tango (talk) 22:54, 26 April 2009 (UTC)
 * Besides - the original "thought experiment" didn't say there was air - we may therefore assume the whole thing happen in a vacuum. At any rate, it's pretty much specified that the candle hits the board at 800mph...who knows how?  SteveBaker (talk) 02:49, 27 April 2009 (UTC)
 * The board is toast. Same as if the board moving 800 mph in vacuum hit a stationary candle. Same as if foam space shuttle insulation hit a carbon fiber wing surface at several hundred miles per hour. Edison (talk) 04:42, 27 April 2009 (UTC)


 * I'm confused - the tallow candle is propelled to high velocity by some external energy source? Is it possible that they are using the (archaic) usage of "candle" to mean "rocket"?  (This seems unlikely since they call it a "tallow candle", but a modern hybrid fuel rocket can work on paraffin with pretty good combustion).  Is the idea that at 800 mph, even something as soft as tallow can penetrate a solid object?  I'm also thinking that the flame exit velocity of a regular candle could actually be close to 800 mph (transsonic at high temperatures) in a very local sense; but I don't see how this convective flow would penetrate a board at 800 mph (unless the board is not combusting but is acting as a rocket nozzle or venturi tube... in that case, the flame gases could easily exit at 800 mph if confined to a small hole.  Nimur (talk) 15:28, 27 April 2009 (UTC)


 * Does it have to be recognizable as a candle after it hits the board? I think you would have a demolished board, and little bits of candle everywhere.  —Preceding unsigned comment added by 65.121.141.34 (talk) 20:01, 27 April 2009 (UTC)


 * To clarify, all the book says on this subject is the clause I quoted above, with no indication of how you'd accelerate the candle to that speed. I get the impression that it's supposed to remain intact while cleanly punching a hole through the board, but everything shattering into bits seems more likely. 69.224.37.48 (talk) 23:57, 27 April 2009 (UTC)


 * If a candle were attached to a rocket fired in space and accelerated to 800 mph (357 meters/sec), then detached from the rocket and made to strike a board, the board would become splinters and the candle would probably liquify or vaporize, or at least be smashed to small fragments. If it were in a stable axial trajectory, it might just blast a circular hole throught the board about the diameter of the candle, like a jet airliner smashing into the Pentagon at several hundred miles per hour. If you tried firing a candle from a gun, it might turn to melted tallow. It is low in density, and would decelerate quickly in air. It might be possible to accelerate it to 800 mph with a discarding sabot and high pressure air in a long tube, such as Mythbusters used to accelerate frozen chickens to smash into airplane windshields. The board should then be fairly close to the muzzle. Definitely do not try this at home. (But if you do I would like to see the video.) Edison (talk) 00:45, 28 April 2009 (UTC)


 * I've seen a demonstration (real-life, not on TV) of a soft tallow candle fired through boards. I don't know at what speed but it was definitely subsonic. It was fired from a home-made rifle!    D b f i r s   16:24, 28 April 2009 (UTC)


 * Are you sure it was a real tallow candle? And if anyone has a video of this, I'd love to see it. 69.224.37.48 (talk) 15:12, 30 April 2009 (UTC)

Battery Disposal
I decided to so some spring cleaning this weekend and my project turned up a ton of alkaline batteries. I raed on my the website for my community waste disposal agency that batteries manufactuerd after 1996 don't have lead in them and can be disposed of safely with regular garbage. Thing is, I have no idea how old these batteries are: no dates! are there any indicators I can look for to indicate lead safety? Thanks --Shaggorama (talk) 20:38, 26 April 2009 (UTC)


 * I have no idea about procedures in MD, but in the EU every supermarket provides receptacles for spent batteries. They all (I believe) contain heavy metals which is bad for the ears, not to mention refuse dumps :)  --Cookatoo.ergo.ZooM (talk) 22:19, 26 April 2009 (UTC)


 * I have never seen such a supermarket recepticle in the UK, although my local electrical shop will take them.--80.3.133.160 (talk) 11:32, 27 April 2009 (UTC)


 * You could buy a modern, non-lead battery and weigh it. Then weigh the old batteries. If any of the old batteries are heavier, they probably contain lead. This is not a certain test, of course. It would be best to dispose of all the old batteries as if they; contained lead. – GlowWorm. —Preceding unsigned comment added by 98.21.107.234 (talk) 18:08, 27 April 2009 (UTC)
 * If the batteries actually are labelled as "alkaline batteries" as you say, then they're pretty much guaranteed not to be lead-based - see alkaline battery. Lead-based batteries are, additionally, quite uncommon as small household batteries even pre-1996; and they generally are clearly labelled even going back into the 1980s. The danger of lead isn't a particularly new discovery. ~ mazca  t 13:14, 28 April 2009 (UTC)


 * Alkaline batteries usually contained cadmium -- not good for landfill. Large modern rechargeable torches often have sealed lead-acid batteries, again, not good for landfill.  It would be good to try to find a recycling facility if possible.    D b f i r s   16:33, 28 April 2009 (UTC)
 * No, there is no cadmium in alkaline cells. You are thinking of nickel-cadmium cells. --Heron (talk) 18:30, 28 April 2009 (UTC)
 * Indeed, Dbfirs does have a good general point though - even in the case of alkaline batteries, there's a possibility of mercury being used in small amounts, and that's no more pleasant than lead or cadmium. As a general rule it's always best to recycle batteries if practical - lead is not the only dangerous heavy metal involved. ~ mazca  t 19:31, 28 April 2009 (UTC)

Sod
What is the best and most durable sod? —Preceding unsigned comment added by 65.71.169.181 (talk) 21:09, 26 April 2009 (UTC)


 * For what purpose? --Tango (talk) 22:50, 26 April 2009 (UTC)


 * Best is a matter of opinion. You must explain to use what you define as being "best" to get an answer there.  As for most durable (and ignoring the astroturf answer), tall festuca is popular for high-traffic areas that require durable grass.  There are many types, so it is usually possible to find a type that grows in most areas that have sunshine. --  k a i n a w &trade; 23:25, 26 April 2009 (UTC)


 * Someone want to run with a politician-joke? Nimur (talk) 15:31, 27 April 2009 (UTC)


 * Didn't Strom Thurmond set the record for best and most durable. -- k a i n a w &trade; 17:33, 27 April 2009 (UTC)

The physics of water filling into a depression
Hi. This is from a question that didn't really get answered last time, but hopefullt this is answerable. Let's say you have a depression in the land, and water is starting to fill it. I want a general formula that calculates the amount of time needed for water to completely fill the depression. I know parameters such as the average and maximum depth of the area, the elevation at which the water is coming, the area of land filled, the length that the water initially needs to travel in order to meet the lowest point, whether the depression is dry or already has water in it, etc. Would I need any other information such as the salinity of the water, the temperature, the curvature of the Earth, the density of the rock, the air pressure in the depression, the wind direction and speed, etc? Does the formula, d = t2(a/2) (where d is distance, t is time, and a is acceleration (9.98 m/s)) be related to this formula? Thanks. ~ A H  1 (TCU) 22:39, 26 April 2009 (UTC)


 * Surely all the information you need is the volume to be filled and the rate at which the water is flowing in? Divide one by the other and you have your answer. --Tango (talk) 22:49, 26 April 2009 (UTC)


 * Perhaps, but I need to calculate the rate at which the water is filling in, from parameters such as the depth of the depression using a type of formula. So, how do I do this? ~ A H  1 (TCU) 22:53, 26 April 2009 (UTC)


 * If the water is falling in from above the depression, then Tango is entirely correct: flow rate and volume are the only necessary parameters. If you add in drainage, you may need to move up to a differential equation, but even then, salinity and all that should be irrelevant. &mdash; Lomn 01:14, 27 April 2009 (UTC)
 * The rate the water is filling it in is something you need to measure, you can't calculate it without far more information that it is reasonable to have (assuming you are talking about a real world situation, rather than some idealised one). You need to measure the cross sectional area of the river that is filling it in and how fast it is moving, multiply those together and you get the amount of water filling the depression per unit time. --Tango (talk) 12:17, 27 April 2009 (UTC)


 * If you want to know the depth of water as a function of time then you're going to need to learn some calculus. You need an equation describing the shape of the depression - then you're going to calculate the integral of that function - and this new function can then be evaluated to figure the rate of filling. SteveBaker (talk) 02:43, 27 April 2009 (UTC)
 * Don't ignore the flow of water through the soil into the aquifer. Newton-Raphson matrix methods might help in providing non-determinate solutions.Edison (talk) 04:39, 27 April 2009 (UTC)
 * Yes, if there is significant drainage then it gets more complicated. The drainage will depend on how filled it is already so you will, as Lomn says, need a differential equation. --Tango (talk) 12:17, 27 April 2009 (UTC)