Wikipedia:Reference desk/Archives/Science/2010 August 30

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August 30[edit]

Fishtank blind spot[edit]

I notice that I'm able to see through my rectangular prism fishtank and see someone else looking into the opposite broad side, but I can't see through from my broad side at anyone peering through the two short sides, and vice versa. Why does this happen and at what angle between the glass panels does this 'blindspot effect' begin? If anyone has a pentagonal, hexagonal, etc. tank, perhaps you could register your visual experience -- I only see such shape tanks in the pet shop and they are empty so the effect doesn't apply. DRosenbach (Talk | Contribs) 01:42, 30 August 2010 (UTC)

If I'm reading this right, then my first thought would be Total internal reflection. I have nothing more to add...I'm not much of a scientist. Vimescarrot (talk) 01:47, 30 August 2010 (UTC)
(EC)I believe this is caused by an effect called total internal reflection. I don't know the answers to your specific questions, but that's a start. Carrot bet me to it! lol. Vespine (talk) 01:48, 30 August 2010 (UTC)
When light passed from one material to another, it's bent. If the amount of bend exceeds the angle required to exit the material then it's bent back - just like a perfect mirror. When you look through the parallel sides - the light is exiting at close to 90 degrees to the air/glass and glass/water boundaries - and the light coming from the person on the far side of the tank goes right through - so you can see them. When you look through two sides that are at right angles, the light will be passing through those boundaries at something more like 45 degrees - which is about the critical angle at which the light is totally reflected. It'll likely bounce around inside the tank until it's absorbed. SteveBaker (talk) 02:11, 30 August 2010 (UTC)
Without trialling this, I'd suggest the light would reflect off your broad side as it's beyond the critical angle thus the TIR mentioned, but I'd predict someone at the other short side would be able to see the reflection on that broad surface, i.e., the light would pass back out the other short side rather than being reflected around inside the tank indefinitely or until absorbed (could also depend on the absolute size of your fish tank which surface it left from). It would also depend on the angles of the incident light. If you put the person back and to the side rather than directly side on, and maybe vary your viewing position along that broad surface, you may be able to see them. FWIW the critical angle for water-air is about 49°, so if you're viewing angles are roughly 45°, it's more the glass-air boundary with a critical angle of about 42° (depending on the glass) that's causing you grief. --jjron (talk) 16:18, 30 August 2010 (UTC)

Electrocution?[edit]

What will happen if a piece of metal (say aluminum, conductor) is kept on a thick plastic/rubber matting ( insulated from earth ). A man stands barefeet on this aluminum plate. And a wire introduces high voltage (say 220 v) into the aluminum plate. Will the man get a shock ?  Jon Ascton  (talk) 03:43, 30 August 2010 (UTC)

First a disclaimer, do NOT attempt to perform ANY experiments with high voltage, it is extremely dangerous and quite easily lethal. What theoretically SHOULD happen and what could and might happen are two very different things. As for your question, if the person is electrically isolated from anything else, then no, there should be no electrocution. This is the same reason why birds can easily sit on bare high voltage wires without suffering any effect.Vespine (talk) 03:57, 30 August 2010 (UTC)
Yeah, I have seen birds sitting that way, safely. This video (from an item above in RD) http://www.facebook.com/video/video.php?v=148725461813437&ref=mf the guy's got killed because he is standing on a steel platform (roof of train) though it's a matter of inquiry if he is wearing shoes and why didn't insulation interfere in that case.
In one story of Stephen King, Quitters, Inc. a rabbit (or hare) is electrocuted while sitting on a metal platform (unearthed). Goof ?  Jon Ascton  (talk) 04:41, 30 August 2010 (UTC)
In the train example, even if he were wearing shoes, the train cable has a very high voltage and it's not unreasonable to think that the electricity would simply arc around the soles of his shoes. Dismas|(talk) 04:53, 30 August 2010 (UTC)
yes, shoes seem not to be as good insulators as you would perhaps think, I suspect a lot of people who are electrocuted aren't necessarily barefoot. I have seen purpose built insulating floor mats rated to just a few hundred volts and they are made of heavy rubber about an inch thick. As for the rabbit, unless there's something we're missed, that does indeed seem like a gaff, earthing the plate by the way would still make no difference, it's the rabbit that needs a path to earth. Stepping on and off such a platform would be when you would get the shock, but if you jumped on and off in one go you would be alright, again: definitely NOT something you should try for yourself. Vespine (talk) 05:58, 30 August 2010 (UTC)
Any electromotive force has two output terminals. In his question, Jon Ascton says a wire introduces high voltage into the aluminum plate. OK, so one terminal is connected by a conductor to the plate. That makes us wonder if the other terminal is connected to anything. Whether or not the man on the plate is at risk of electrocution depends entirely on whether there is a risk of him becoming connected to the other terminal. If he is not connected to the other terminal there is no closed circuit in which current can flow and he is not at risk of electrocution. If he is connected to the other terminal, or if the other terminal is connected to Earth and he touches something other than the aluminum plate or insulating rubber matting, zappo! Dolphin (t) 06:27, 30 August 2010 (UTC)
Strictly speaking, if you have enough voltage, you don't need a closed circuit. A human body has a certain self-capacitance. That is, even with nowhere for them to go, a certain number of charge carriers will flow in or out of the body as the voltage changes. Hook up an AC voltage source, and they'll flow both in and out, repetitively. Now you've got a current, even with nowhere for it to go. --Trovatore (talk) 07:45, 30 August 2010 (UTC)
See Displacement current. This current does find its way to the other source terminal. Cuddlyable3 (talk) 10:15, 30 August 2010 (UTC)
I agree entirely with the comment about human self-capacitance. I can remember taking a class of 14-year olds to the Science Museum in Paris (Palais de la Découverte), where one of the workshops the staff put on for them could be described as "playing about with a BIG van der Graaff generator". So, as one does, they got a couple of kids to come and volunteer, and made their hair stand on end (this video shows the same sort of demonstration). As I was the teacher and I knew what was going to happen, I was paying more attention to the safety rules the staff were giving the kids. To be charged up to half-a-million volts or so, the kids were stood on plastic podia a bit less than a metre (say 2½ feet) high – you can see the same thing in the video. The one thing the staff insisted on was to say "you can come off the podium any time you like, but please tell us first." (I assume they had a special teenager-discharging capacitor in the podium that they could connect up through a decent-sized resistor as needed)
Now the charge you get from a van der Graaff generator is DC, a one-off with no external current source, but still enough to give you a nasty shock if you discharge it through the body's internal resistance: it seemed to take a second or two to discharge the kids safely through the podium, and they were charged up to far more than the breakdown voltage of a small air gap as they would have had if they tried to step off the podium fully charged. If that had been AC with a external current source, it could easily have reached fatal currents even without a route to earth. Physchim62 (talk) 10:48, 30 August 2010 (UTC)
The question nominates 220 volts. Dolphin (t) 11:52, 30 August 2010 (UTC)
It should be OK - but the devil is in the details. For example - if you were to step onto or off of the plate, one foot at a time - then for a moment, one foot is grounded and the other is on the plate - and you'd get zapped. But you see birds sitting quite happily on 10,000 volt power lines - and this is the exact same problem. SteveBaker (talk) 13:31, 30 August 2010 (UTC)
But from my personal observation birds do not sit on the really high voltage transmission lines, 110kV for example, at least not that I have ever seen. 65.121.141.34 (talk) 13:59, 30 August 2010 (UTC)
Linesmen who connect themselves to high voltage lines are aware of corona discharge, described as like a swarm of insects buzzing around them. Cuddlyable3 (talk) 15:11, 30 August 2010 (UTC)
As a teen I once touched a metal electrical outlet plate that was "grounded" to 110V AC, while sitting on a chair of polyurethane of the like. I became curious about it because the metal looked smooth, but felt rough, and took some time rubbing and staring at it trying to figure out the incongruency. I resisted the suggestion to test my idea about electrical leakage with a ground... but my friend who declared that "there can't be anything wrong with the wiring, my Dad put it in himself!" used a metal pole to quickly determine the truth. This is why the U.S. uses 110 V wiring. ;) Wnt (talk) 15:38, 30 August 2010 (UTC)
On the question of shoes mentioned a bit earlier, it depends on the material of the sole. Leather soles are going to do a poor job but most man-made materials are good insulators if they are thick enough for the voltage in question. Don't trust your life though, to footwear that is not specifically designed for insulation - the slightest flaw in a material at high voltage can lead to dielectric breakdown, and in this case, the death of the wearer. SpinningSpark 15:38, 30 August 2010 (UTC)

Starched shirt[edit]

If starch is a polysaccharide (a bunch of sugar molecules), then why doesn't a starched shirt stick to my torso?--72.145.144.203 (talk) 05:30, 30 August 2010 (UTC)

For the same reason bread does not. Starch has different properties than sugar due to the long lengths of the sugar chains. Just like water has different properties than either hydrogen or oxygen, sugar has different properties than starch. When compounds interact chemically they form new compounds with very different properties. --Jayron32 05:37, 30 August 2010 (UTC)
  1. If I wash a starched shirt, will the starch come off?
  2. Do I need to sprinkle starch on a shirt after every wash?--72.145.144.203 (talk) 05:40, 30 August 2010 (UTC)
  1. Yes. Starch will wash out everytime you wash it.
  2. Yes, if you want it to retain that starched look. Spray starches are availible in aerosol cans, which are fairly easy to use.
Starch#Industrial_applications discusses the use of Starch in laundry. --Jayron32 05:45, 30 August 2010 (UTC)
Thanks for the answers.--72.145.144.203 (talk) 05:50, 30 August 2010 (UTC)
I love this question. A great example of the old curricular school subject "Domestic Science". Richard Avery (talk) 06:38, 30 August 2010 (UTC)

Eric Harris[edit]

did Eric Harris shoot Dylan Klebold ? —Preceding unsigned comment added by Tomjohnson357 (talkcontribs) 10:22, 30 August 2010 (UTC)

Wikipedia has an article about these great Americans. Cuddlyable3 (talk) 11:08, 30 August 2010 (UTC)

it dosent help —Preceding unsigned comment added by Tomjohnson357 (talkcontribs) 14:43, August 30, 2010 (UTC)

According to the article linked to by Cuddlyable3 above, they committed suicide. In other words, each probably shot himself. — QuantumEleven 14:13, 30 August 2010 (UTC)
Yes, it does help. Right there in the introduction. It says that they both committed suicide. If Harris shot Klebold then himself - then Klebold couldn't have committed suicide. SteveBaker (talk) 14:12, 30 August 2010 (UTC)
This shouldn't be filed in the Science section. Though the two might properly have placed themselves outside the scope of Humanities, it would seem the closest category. Wnt (talk) 15:26, 30 August 2010 (UTC)
Dylan's official autopsy report ruled (here) it a suicide. There was some speculation, given that he was shot by a single bullet in the left side of the head (rather than the right). However, it turns out that other footage showed him shooting a gun with his left hand, so it seems at least probable that he shot himself. As far as I know, there's no footage of them actually committing suicide. Buddy431 (talk) 19:28, 30 August 2010 (UTC)
And at all who rushed in saying "yes, they obviously shot themselves, look at our articles" (that has about one line about them killing themselves and doesn't say anything about how it was done), I say shame on you. A basic Google search would have shown that we don't really know for sure whether either of them shot themselves, and that there is legitimate controversy especially over Mr. Klebold. Especially you Steve: arguing from a linguistic standpoint? Over a single sentence that's been in our article for who knows how long, and would still be substantially correct even if one had shot the other? For shame. Buddy431 (talk) 19:34, 30 August 2010 (UTC)
For shame? WTF? Read what I actually wrote - not what you think that I wrote. I said that our article does contain that specific information...and it does. It doesn't take more than a single sentence to answer the OP's question. You may care to dispute whether our article is correct or not - but DO NOT reprimand me for doing precisely what the Ref Desk's mandate is - which is to find data primarily within the encyclopedia and tell our OP's where to go read it for themselves. If you think the article is incorrect then go there and fix it - but meanwhile, what I wrote is true, correct and in line with what we do here at the reference desks. You should not come here and put me down for doing what you have completely and utterly failed to do. You talk about some nebulous google results without pointing to where they actually are - we don't know whether your answer is backed by reputable sources or from some bunch of random conspiracy theorists. Now apologize dammit. SteveBaker (talk) 19:36, 31 August 2010 (UTC)
Sounds like a great piece of information (that the details of who shot whom or whatever is not known) to add to the relevant wikipedia articles. With WP:RS citations for alternative theories or at least statements that the exact sequence of events isn't known, or is disputed, or... DMacks (talk) 20:59, 30 August 2010 (UTC)
It sounds from the autopsy reports ("consistent with a self-inflicted gun-shot wound") and the description of who was carrying what weapons pretty clearly to have been suicide. Wikiscient (talk) 09:20, 1 September 2010 (UTC)
Eric was carrying this
Dylan had the TEC-9
Oh, wait, the "wound was consistent with 9mm ammunition" but they were both carrying 9mm weapons. And Dylan had the TEC-9; Eric was carrying the carbine, which is a lot less easy to fire into the left side of your head, aiming slightly downwards! Wikiscient (talk) 10:14, 1 September 2010 (UTC)
The autopsy and other reports concluded that they committed suicide - that each shot himself. Given the notoriety of the case, they would have put their best experts onto resolving this matter - so I don't think your opinions and guesses based upon the flimsiest of evidence stack up against that amount of expertise. Rather than guessing - and confusing our OP with highly in-expert opinions, I strongly suggest you read those reports. SteveBaker (talk) 12:46, 1 September 2010 (UTC)
Relax, Steve. Your response is addressed exclusively to me, does not discuss the OP's question in any way, involves your own opinion as to what "they" would have done, and suggests that you have not looked very closely at the cited sources yourself. If you would like to comment further on my response to this question or my behavior at this desk generally, please do so on the talk page or on mine, not in answer to an OP. Wikiscient (talk) 13:04, 1 September 2010 (UTC)
The autopsy report link does bring some science into this: unfortunately, the science is only that the wounds were "consistent with" self-infliction. That does not mean that they were proved to be suicide. Note that both wounds were "through-and-through", so ballistics can only be done by figuring out which bullet went with which suicide and digging it out of the wall. I don't know if this was done - there must have been a lot of bullets in those walls. But apparently DNA can be extracted from bullets [1] so even if all you had was a box of loose bullets from the room and the ballistics samples from the guns, you still should be able to figure out whether each boy was shot with his own gun. I don't know if anyone has done that, or if anyone cares. Wnt (talk) 18:20, 1 September 2010 (UTC)
And I maintain that we probably will never know for sure who actually shot Mr. Klebold, and that at some point it doesn't really matter. They certainly "Killed Themselves" in a collective sense, which is probably the best we can do in this case, especially after over 10 years. Buddy431 (talk) 23:26, 1 September 2010 (UTC)
The OP's question can be put as "Whose finger pulled the trigger?" that caused Dylan's death for which there is no living witness. The autopsy reports can not definitively rule out either Eric or Dylan as answer to the question. The only way it might be found is by a further forensic investigation. A hypothetical line of investigation is to try to find the lethal bullet that might both be traceable to one boy's gun and carry a detectable DNA trace from Dylan, as Wnt noted. Any such forensic investigation seems unlikely because of its minute chance of success, and the unnatural expense of employing a Crime lab where there is no prospect of an arrest. Wikipedia cannot speculate what if anything such investigation might discover. The question is likely to persist unanswered, like the theory of the shooter on the grassy knoll.
Non-americans may find it hard to understand how 18 and 17 year old boys could possess semi-automatic weapons. American gun law (see article) is based on the Second Amendment to the United States Constitution or Bill of Rights that protects a citizen's right to buy a gun from a dealer like Guns "R" Us in order to repell invasions by British redcoats. Cuddlyable3 (talk) 12:45, 2 September 2010 (UTC)

Water and Electricity[edit]

Water is generally presumed to be bad conductor of electricity, but I am sure if one is in a bathtub and a heater falls into it, one is dead. How ?

Added section heading -- 174.21.233.249 (talk) 16:34, 31 August 2010 (UTC)
Pure water is indeed a relatively poor conductor, but nearly all water outside of purified/distilled de-ionized water in a laboratory or similar specialized setting contains additional substances (mostly 'salts') which, even in trace amounts, provide ample ions with which to conduct electric current. 87.81.230.195 (talk) 16:54, 31 August 2010 (UTC)
Tap water has all sorts of stuff that the government put in it to clean it, plus it washed some salt off of your body. —Preceding unsigned comment added by 174.91.10.238 (talk) 17:03, 31 August 2010 (UTC)

By the way, don't be so "sure" about that heater killing you. It very well could, but you could saved by GFCI protection (or whatever they call it in your country), and predicting the flow of electricity in a mass of water is not so simple. Mythbusters did some experiments on this. --Anonymous, 19:53 UTC, August 31, 2010.

Any way to cut a steel cable with common tools?[edit]

Can you cut relatively thin steel cables using tools people are likely to have at home? I've tried cutting a thin cable but was surprised that even though it looked about the same diameter as a comparable galvanized wire, it's a lot harder to cut. Stores that sell steel cables have hydraulic cutters, but most people don't have a reason to buy and keep one at home. Any suggestions? —Preceding unsigned comment added by 96.227.60.170 (talk) 12:47, 30 August 2010 (UTC)

Good-quality lineman's pliers or diagonal pliers, or a hacksaw. Mitch Ames (talk) 13:07, 30 August 2010 (UTC)
Bolt cutters work pretty well and would be the first tool I'd reach for. If you have an angle grinder with a decent cut-off blade, you'd get through it with that too (wear eye protection - there will be lot's of pretty sparks!) - I suppose you'd eventually get through it with a Dremel tool with a cut-off disk - but it might take a while. Failing that, often you can untwist the cable such that the individual wires can be cut separately - and then all you need is a pair of wire-cutters and a lot of patience! If all else fails, a hacksaw will (eventually) get you through it. SteveBaker (talk) 13:25, 30 August 2010 (UTC)
Bend it many many times, and it'll break. It's possible to do it pretty accurately if you use two pliers to do the initial bend. Ariel. (talk) 17:47, 30 August 2010 (UTC)
The article Fatigue (material) describes Ariel's method of breaking by repeated bendings. The stress you apply needs to exceed the Fatigue limit of steel. Cuddlyable3 (talk) 19:20, 30 August 2010 (UTC)
Sounds like it could be made from strands of tempered high-carbon steel much the same as Piano wire. If you have a domestic gas cooker (or some such) and heat a small loop to cherry red and take it out the flame s-l-o-w-l-y, that will de-temper it and thus easer to sever. --Aspro (talk) 22:42, 30 August 2010 (UTC)

Deep Blue vs. Deep Blue[edit]

(I questioned whether this was "Computing" or "Science," and decided on "Science," since it is not, like most of "Computing," a practical question.)

If Deep Blue were to play chess against another Deep Blue, is it likely that one of them would be the winner (rather than a draw), and if so, what would determine which one was the winner? (E.g., random chance, or who goes first, or ...?)

(This need not be specific to Deep Blue's architecture — feel free to apply to other super chess A.I.s. that play against identical algorithms or machines. That is, it is not Deep Blue vs. Deep Junior that I am interested in, but Deep Blue vs. Deep Blue or Deep Junior vs. Deep Junior.) --Mr.98 (talk) 15:31, 30 August 2010 (UTC)

The received wisdom in chess is that the white pieces have a slight advantage, but the majority of grandmaster games end in draws. So I would say the most probable outcome of like machine playing like is a draw. However, if the machine has a flaw against a particular defence, the Sicilian Defence say, then that can be exploited by always playing the Sicilian Defence when black. Such tactics can be used against a human of course, but humans tend to learn from their mistakes after a while (albeit a long while in some cases) so the answer might come down to whether the machines are capable of learning from their mistakes. Such a pair of machines might produce some novel and interesting games. However, Deep Blue, had no such capability, except by human programming between games to eliminate previous mistakes, and would fall into the same trap over and over again. Deep Blue achieved the results it did mostly through brute force computation of positions. If Deep Blue had the programming to exploit the mistakes it itself made then the winner would be black or white depending on whether the mistake was with the white or black pieces. If however, it did not have such programming (most likely, since if the programmers allowed for a particular mistake to be exploited they would likely program Deep Blue not to make the same mistake itself) then the likely result would be that the mistake, even when made, would be overlooked by the opponent machine and a draw would result. SpinningSpark 16:05, 30 August 2010 (UTC)
I don't remember if it was the first or second Deep Blue match, but the one that I watched a documentary about pointed out that the programmers continued "improving" the program in Deep Blue throughout the match. In that sense, the human programmers could learn from mistakes and try to improve the performance. At that point, Deep Blue is just a tool and it is a game between the programmers of one tool against the programmers of another tool. -- kainaw 16:14, 30 August 2010 (UTC)
They were not allowed to make improvements while a game was ongoing. The improvements were made between sets of games - although Kasparov famously claimed that IBM were cheating to explain his loss of the match. SpinningSpark 16:30, 30 August 2010 (UTC)
It should of course be noted that there are routine computer-on-computer chess matches ([[i.e. World Computer Chess Championship, Chess Engines Grand Tournament, etc.), though generally not with the same program against itself. I'm sure that such games have been run though. Anyway, I see no reason why we could predict one outcome over another; a chess game is typically quite assymetric, such that I'm not sure that it would make much of a difference that both sides are running the same engine. I could be wrong though. Additionally, some engines can "learn" (such as by adding positions to a Transposition table), which, as Spinningspark, might make an interesting set of games. In this regard, though, there's nothing special about having identical machines, other than that they'll assign the same values to the same positions. Buddy431 (talk) 19:17, 30 August 2010 (UTC)
Chess remains only partially solved (in the game theoretical sense). Solving it seems somewhat controversial, but according to the Solving chess article only time will tell the answer to your question: "It is thus theoretically possible to "solve" chess, [however] the time frame required puts this possibility beyond the limits of any feasible technology." Wikiscient (talk) 19:31, 30 August 2010 (UTC)


You can pit chess computers against each other and find out! Many chess programs allow you to pit computer opponents against each other. Many even allow you to choose the engine - for example, GNU Chess/XBoard allows you to install any chess computer engine that speaks Chess Engine Communication Protocol. See our list of chess engines and the free and open-source software ones - there are dozens of common engines that can be "hot-swapped" in to an XBoard graphic chess interface. These engines can play against each-other or against humans. You might also want to read about how chess is "rated": Chess rating system. "Winning" is too simplistic - chess ratings are statistical monstrosities based on performance over many games. At best, you could determine whether an algorithm, playing against itself, were consistently susceptible to the same attacks, or if it were only susceptible to random strategies. And, you could compare different algorithms against each other. Chess engines often have tunable parameters, like "search depth", that will affect their performance on various hardware; so if you want to set up a maximum computer-time limit, your hardware will affect the outcome as much as the software engine. Nimur (talk) 19:33, 30 August 2010 (UTC)
As this is a game theory question, you might also consider asking at the Math desk. Wikiscient (talk) 19:45, 30 August 2010 (UTC)
You should read Feng-hsiung Hsu's book "Behind Deep Blue". He was the leading designer of the machine. It's an interesting read (not least because Hsu claims not to play chess - or even be particularly good at it!) He describes how they would routinely use Deep Blue to play against itself in order to find bugs, tune performance and automatically create certain tables that the machine used. Chess isn't a symmetrical game - there is a big difference between playing white and playing black - normally, white is on the offense and black is defending - so a machine that was better in defense than offense might well win more often against itself when playing black than white...for example.
More than that, in a sense, Deep Blue is always playing against itself - what happens when it is trying to figure out a move is that it will mentally try every possible legal move - then use it's own algorithms to try to guess the best response it's opponent could come up with. That way it can see which of move produces the weakest "best possible" response from the opponent. But since it's own algorithms are this imaginary opponent - it is reasonable to say that it's always "playing against itself".
SteveBaker (talk) 19:18, 31 August 2010 (UTC)
Interesting responses, thanks! --Mr.98 (talk) 00:55, 1 September 2010 (UTC)

Cactus / Agavaceae[edit]

Cactus, can be found in many areas of Yemen.

I've just uploaded this cactus image, but don't really know the scientific and public names for it. Can anyone help?--Email4mobile (talk) 16:19, 30 August 2010 (UTC)

maybe a member of Agavaceae, technically speaking not a cactus --69.246.200.56 (talk) 16:43, 30 August 2010 (UTC)
In this case, I've to rename the file and description. Can any admin do that for me? Thanks in advance.--Email4mobile (talk) 17:20, 30 August 2010 (UTC)
You have uploaded it to Commons, not here on Wikipedia so you need to ask on Commons. The best thing to do is upload it again with the correct name and then request speedy deletion of the old file. Instructions here. SpinningSpark 18:13, 30 August 2010 (UTC)

Definitely not a cactus, I marked Agavaceae] in the title, apologies if that is bad form. For a common name I'd say Century plant, but that is also a common name for a new-world yucca. SemanticMantis (talk) 20:15, 30 August 2010 (UTC)

Note that yuccas are also agavaceae. What they're not is agaves. The picture looks to me like an agave.
In fact the whole landscape is remarkably similar to Southern California. I had no idea Yemen looked like that For comparison, a picture of an agave that I took in Griffith Park: http://www.flickr.com/photos/30973445@N02/4695022211/ . --Trovatore (talk) 21:05, 30 August 2010 (UTC)
Thanks all. I think that photo represents exactly the same type we have in Yemen, Trovatore. I will upload it again with the name of agave, unless you don't have further comments.--Email4mobile (talk) 21:52, 30 August 2010 (UTC)

Is it possible to test if the universe/multiverse is infinite?[edit]

If reality was infinite, what would we expect to find? 148.168.127.10 (talk) 18:32, 30 August 2010 (UTC)

This is more philosophy than science. If you cannot detect something in any way and it cannot detect you in any way, does that something exist? The universe can expand faster than the speed of light. We can only detect a small portion of what might exist due to the limitation of the speed of light. Similarly, only a small portion of the universe can detect us due to the limitation of the speed of light. If you decide that anything that is mutually excluded by the speed of light doesn't exist, the universe is what we can detect and it is finite, but growing. If you decide that things we cannot detect (and cannot detect us) do exist, it is not possible to know if the universe is infinite or finite because we have no means of detects what might be the edge of the universe. Step this up to the theory of multiverses and you just make the problem more complicated with the same stipulation. If you limit this what we can detect, it is finite but growing. -- kainaw 18:40, 30 August 2010 (UTC)
Your second question begs the question: Is "universe" and "reality" the same thing? Can the universe be finite and reality infinite? Can the universe be infinite and reality finite? Notice that I ensured to include mutual detection in the answer above to handle many concepts of reality. What if something can detect us but we cannot detect them? What if something can change what we consider reality but we cannot detect it? Again, this falls more into philosophy than science. -- kainaw 18:44, 30 August 2010 (UTC)
A closed universe of the FLRW type would be expect to have a spacetime that is locally curved everywhere. We can observationally test for this. If we detect a non-zero positive curvature it would be strong evidence suggesting the universe is finite (even if it much larger than the size of the observable universe we currently live in). This would be akin to someone deducing that the Earth is round by watching ships sail over the horizon, even though they can't begin to see the shape of the entire Earth. It wouldn't be an absolute proof since the shape of the universe could change to something other than a FLRW type out beyond the regions we are able to measure, but it would be good evidence. So far though, it appears that the curvature of the universe is consistent with zero. This suggests either that the universe is infinite, or if it is finite then it is much much larger than the observable universe we are currently able to study. Dragons flight (talk) 18:58, 30 August 2010 (UTC)

Until we account for the missing mass (dark matter) then we are unlikely to be able to test very well for the cosmological periodicities which might indicate a closed space. Occasionally, someone will come up with evidence for periodicities but I'm not sure if there has ever been a literature review of those. Why Other (talk) 19:29, 30 August 2010 (UTC)

Nonsense post deleted. Cuddlyable3 (talk) 12:54, 2 September 2010 (UTC)

liquid air[edit]

If we assume that liquid air was stable at non-cryogenic temperatures at normal air pressure, would it be possible to breathe it? Googlemeister (talk) 19:26, 30 August 2010 (UTC)

No, because the assumption is invalid. You want Liquid breathing.
To be more precise, pressures at which non-cryogenic air is liquid are not compatible with mammalian cellular life. Even if they could be gradually equalized, the molecular moments of inertia necessary for many of the biochemical cycles (e.g. Citric acid cycle, etc.) and proper operation of proteins, enzymes, and nucleic acids would be fatally affected.
Even if those problems could be overcome, breathing liquid air would still suffer from a similar problem involved with breathing other oxegenated liquids: the inability to remove enough carbon dioxide at liquid viscosities. Removal of sufficient amounts of CO2 is a problem of the air commons as well as individual terrestrial animals. Why Other (talk) 21:57, 30 August 2010 (UTC)
There is no pressure "at which non-cryogenic air is liquid". At least if you believe this link, the critical temperature of air is −190 degrees Celsius, which I think qualifies as "cryogenic". Above that temperature, no matter how much you compress air, it will not liquefy (though it may acquire viscosity and other characteristics similar to that of a liquid). --Trovatore (talk) 22:45, 30 August 2010 (UTC)
Are you sure that temperature doesn't increase at high enough pressures? In any case, such pressures are fatal to mammals. Why Other (talk) 19:00, 31 August 2010 (UTC)
That doesn't even make sense. See critical temperature. --Trovatore (talk) 20:27, 31 August 2010 (UTC)
If air were liquid... it would be a liquid. I assume what you mean is, if a liquid had the oxygen content of air, or higher, could you breathe it? For that I refer you to liquid breathing, but for photos you'll need to turn elsewhere: [2][3] (but ignore all rumors of "blood substitutes", the idea is absurd and the experiments deadly)
Blood substitutes do show some promise for temporary surgical applications. Why Other (talk) 19:00, 31 August 2010 (UTC)

Why did clear polypropylene become whitish after melting & resolidifying?[edit]

I took a clear plastic container lid made out of polypropylene and cut it into small pieces and placed those pieces in the "dish" of a crushed and inverted aluminum soda can and placed the setup in a toaster (not microwave) oven at 450 F for 20 minutes until all the plastic was in clear liquid form. I took it out of the toaster oven and almost immediately as it hardened, it began to whiten to the point that when it was cool enough to handle, it was almost but not totally opaque; I could see the shadow of my finger through the ~5mm thick piece of plastic. What's the story there? —Preceding unsigned comment added by 166.137.11.190 (talk) 19:33, 30 August 2010 (UTC)

Two guesses: The original material was crystallized, and the melt was amorphous. Or perhaps you have lots of air bubbles in the melt. Also, all polypropylene I've seen has been opaque. Ariel. (talk) 20:20, 30 August 2010 (UTC)
We have an article on polypropylene that says "When polypropylene is biaxially oriented, it becomes crystal clear". I'd say that biaxial orientation is destroyed when you heat/cool small pieces of PP using a toaster oven and a crushed aluminum can. Also, I suspect that the Opacity_(optics) of the result might be due to the introduction of Crystallographic_defects. SemanticMantis (talk) 20:25, 30 August 2010 (UTC)

Candle dynamics / design, wicking[edit]

In short, if I use a piece of common jute twine as a `wick', what sort of candle could this support? (The goal here is to recycle old candle stubs into new candles, using commonly available household items).

I am familiar with capillary action in the simple context. Candle wicks work on this principle, but it seems to me that candle dynamics are not so simple. Several factors must come into play to make a self-sustaining candle, e.g. wick design, melting point/viscosity of the wax, diameter of the candle, and boundary materials.

The article states that braided cord works better, which makes intuitive sense, but I know from personal experience that twisted cords still wick, if not as well. The bigger issue is this: a mordant is applied to make most wicks, and "Without mordanting the wick would be destroyed by the flames and the flow of melted wax to the flame would cease."

I have a hard time accepting that mordants are strictly necessary, and the mordant article doesn't even mention flame-retarding effects.

Shouldn't there be some candle diameter/wick diameter/container material that would allow me to make a candle using some common type of cordage as a wick?

--Bonus question: if a mordant/ flame retardant is required, can some household compound be used for this purpose? —Preceding unsigned comment added by SemanticMantis (talkcontribs) 20:02, 30 August 2010 (UTC)

You can make a candle wick from a cotton ball, just take some, and twist it into a cord. Make sure it's real cotton though, not plastic (try to burn some). Jute might not work as well because it's coarse. A finer thread works better as a wick. It's not very hard to make a wick, and it does not require complicated calculations, or mordant. I've seen wicks made of fiberglass too, but they need a holder, so will work for oil, but not wax. Ariel. (talk) 20:17, 30 August 2010 (UTC)
Thanks, I'll try it. Still interested in the general principles at work, if not complicated calculations. SemanticMantis (talk) 20:31, 30 August 2010 (UTC)
In the 1960's candle wicks contained some lead to keep them upright, so that molten wax could rise in the wick and vaporize to burn efficiently. A mere piece of limp string might fall over in the pool of melted wax and be extinguished. The characteristics of the carbonized wick are important to the success of a candle. Modern wicks should still have a characteristic carbonized ash which stays upright to facilitate vaporization of the wax and efficient burning, even in the absence of heavy metals. Edison (talk) 01:49, 31 August 2010 (UTC)
Google books shows portions of lots of books with guidance on candle making. Braided wicks are said to be better than just twisted wicks, and the wick size must be appropriate for the candle diameter: too small and it will go out. Too big, and it will make a big sooty flame that will leave soot on the wall and ceiling. See [4] for instance. Edison (talk) 14:13, 31 August 2010 (UTC)

water (on any planet)[edit]

if you put water on another planet if its just a teaspoon or an ocean would life form. --83.71.85.217 (talk) 20:51, 30 August 2010 (UTC)

This was asked up here. Or, at least, it was a very similar question. Bus stop (talk) 20:54, 30 August 2010 (UTC)
Both IPs seem to be from similar areas. Are we doing students' homework here? HiLo48 (talk) 20:57, 30 August 2010 (UTC)
We don't know. Our article Abiogenesis will be of interest, though, as it says up toward the top, "There is no truly "standard model" of the origin of life." Comet Tuttle (talk) 21:00, 30 August 2010 (UTC)


For earth-like life, water is necessary, but not sufficient. Other materials are necessary for organic molecules to form: carbon and nitrogen, at least; and probably phosphor, sulfur, sodium, chlorine, and many other chemical elements. If you are willing to accept a very abstract definition of "life", then the specific requirements for it to exist are much more open to interpretation. Nimur (talk) 22:09, 30 August 2010 (UTC)
Do you mean phosphorus? --Chemicalinterest (talk) 22:10, 30 August 2010 (UTC)
Life is not created from simple compounds, although many would dispute this point. --Chemicalinterest (talk) 22:11, 30 August 2010 (UTC)
Define "simple". Simple prokaryote bacterias are made of water, fat, a few proteins, and some nucleic acid - (see bacterial cell structure) - they're essentially nothing but a flimsy bag full of simple chemical compounds. More advanced life-forms are just "additionally complicated" bags. DNA is a very complicated compound, by comparison to, say, H2O. But, it is naturally created from simpler sub-compounds called base pairs. In turn, these are created from simpler sub-compounds called nucleotides. Those are made up of individual organic molecules, which are made of individual atoms. At some point, we reach such simple compounds that the molecules can not be said to be alive. Where do we define this line? At what point does the chemical reaction cross the threshold of sufficient complexity to be called "alive"? And what about hypothetical life-forms that are not carbon-based? We have a discussion on the definition of life that brings up important definitions and presents many viewpoints on the issue of abiogenesis. Whatever your belief is about the origins of life - whether you think that life started on Earth, in space, or even if you are a creationist, you must have some kind of answer to the abiogenesis problem... and granted, this is a very challenging question. Most scientists believe that the presence of carbon, water, phosphor(us), sulfur, nitrogen, and so on, plus billions of years and exposure to lightning, cosmic rays, radiation, and solar heating, is a sufficient amount of time for a few of these atoms to "randomly" bump together in such a way to create a self-sustaining and replicating chemical reaction - the beginnings of the basic metabolism of a simple life form. Scientists debate exactly how long and what materials are absolutely necessary. Nimur (talk) 00:40, 31 August 2010 (UTC)
Much is said about the presumed improbability of a self-replicating molecule just popping into existence out of simpler compounds. But is it really that improbable? The important thing to remember when thinking about the abiogenesis issue is that in addition to a very large timescale, life might have formed in any drop of suitable liquid on any suitable body in the entire universe. Throughout the enormous number of random 'bumps between atoms' that have happened in the entire universe over the entire time since the big bang - only one of those had to result in a viable self-replicating molecule to result in life as we know it. It happened (probably) here on Earth because it must have done or we humans wouldn't be here. Using the 'anthropic principle' to explain things that we don't know the answer to is generally considered 'iffy' - but in this case, it's precisely the right answer. When we talk about "the entire universe" in this context, we don't even have to limit ourselves to "the observable universe"...whichever part we evolved in is by definition within the visible universe.
So let's crunch the numbers: There are 1023 stars in the observable universe - and the lower bound estimate for the entire universe is 1023 times larger - if an average star has 10 moons or planets with water - then there are 1047 possible places for life to form - if random chemical 'bumps' happen to every molecule in the surface of the planet about every few microseconds then over the past 10 billion years each one will have been bumped 1023 times - and if the volume of the earth's ocean is a reasonable 'typical' volume then there are 1023kg of water (plus loads of other 'stuff') - but we also know that life might have formed deeper in the Earth's crust - since Avogadro's number is 6x1023 we can probably estimate that there are 1046 molecules around on a typical planet that are doing the bumping. Multiply that out and you have 1047+23+46=10116 possible opportunities for that first self-replicator to have randomly formed. (I love how all of those constituent numbers are around 1023!)
If you seriously stop to consider the size of that number, it would be truly remarkable if some kind of self-replicator didn't spontaneously arise at least once at some point in the universe! (Of course, if the universe is infinite (which it very well might be) then the abiogenesis event has to have happened an infinite number of times - so it's not just overwhelmingly probable - it's an absolute certainty).
Just as with evolution - this process is completely inevitable and it would take a rather large intellectual leap to imagine constraints that would somehow have prevented this abiogenesis event from happening. We may not know the details yet - but the statistics are beyond reproach. We KNOW that the abiogenesis event had to have happened - it's just too improbable that it couldn't have happened.
SteveBaker (talk) 23:11, 31 August 2010 (UTC)
@Chemicalinterest: You are incorrect. Life is certainly composed (in part) of some exceedingly complicated compounds (although quite a lot of the composition is simple stuff). But that doesn't mean that life wasn't created from simple compounds...it obviously was. All of the atoms that make up our bodies ultimately came from basic elements formed in fusion reactions inside a star and thrown out into space in a supernova. It follows that even the most complex compounds such as DNA and RNA must have formed by some means from the most simple possible building blocks...the raw elements. The only real question here is what processes made that happen. SteveBaker (talk) 22:28, 31 August 2010 (UTC)
That covers the favorite topic of... evolution and the origin of life! I believe that their is more to life than 1018 carbon atoms and 104 nitrogen atoms and 1015 oxygen atoms, etc. etc. --Chemicalinterest (talk) 00:23, 1 September 2010 (UTC)
Well, you can believe all you want; but if you can't explain what "more" there is, then your belief isn't really scientific. Life really is just lots of very complicated, self-replicating chemical interactions. How complicated is it? So complicated that we can't re-create all of them in the best chemical laboratories (yet); or simulate them on the best and most powerful computers. But really complicated does not mean "happened because of magic." Life originated, and the reactions took place, because like all chemical reactions, the conditions were suitable for that set of reactions to occur. Nimur (talk) 18:20, 1 September 2010 (UTC)
You are correct in reference to the human body, but not the rest of the human. --Chemicalinterest (talk) 19:14, 1 September 2010 (UTC)

Cordless power supply[edit]

It glows! Without wires!

I was just wondering on how it would be possible to create a cordless vacuum cleaner... but then it hit me as quite obvious that how would it be supplied with power? Well, is this even feasible? 99.114.94.169 (talk) 21:59, 30 August 2010 (UTC)

Maybe it could be battery-powered. Bus stop (talk) 22:07, 30 August 2010 (UTC)
IIRC, someone was working on creating a cordless vacuum cleaner without a battery. It was run by concentrated electromagnetic waves. --Chemicalinterest (talk) 22:09, 30 August 2010 (UTC)
Are you referring to wireless energy transfer? (See photo.) Comet Tuttle (talk) 22:41, 30 August 2010 (UTC)
Roomba, not only cordless, but doesn't even need a person to push it around! Vespine (talk) 22:54, 30 August 2010 (UTC)
So its actually possible to transfer usable energy across an area without, say a wire? 99.114.94.169 (talk) 23:07, 30 August 2010 (UTC)
Yes, inductive charging is a proposed method of charging electric vehicles at charging stations. SpinningSpark 23:54, 30 August 2010 (UTC)
Already exists: http://www.google.com/products/catalog?q=cordless+vacuum+cleaner&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&cid=2577918473611675068&ei=9kV8TP7JG4PMnAeuk-yVCw&sa=X&oi=product_catalog_result&ct=result&resnum=1&ved=0CDQQ8wIwAA#. Runs on recharegable batteries. thx1138 (talk) 00:00, 31 August 2010 (UTC)
More generally, you may find the Wireless energy transfer article interesting. (And I think I recall that Nikola Tesla was a strong advocate of developing this technology, on a large scale and over vast distances). Wikiscient (talk) 00:45, 31 August 2010 (UTC)oh, comet already got this one Wikiscient (talk) 00:47, 31 August 2010 (UTC)
There's also powermat, but this is still charging batteries, you aren't replacing the batteries, you just charge them wirelessly. Vespine (talk) 01:26, 31 August 2010 (UTC)
There's no problem transfering usable energy across an area without wires: see PS10 solar power tower, which is rated at 11 megawatts output. The problem is getting in the middle of that energy transfer! Now a standard U.S. 12-amp vacuum cleaner consumes 1.44 kilowatts input, but let's imagine that the cordless model is smaller, and so only consumes one kilowatt. What's a kilowatt? It's the power of the Sun's radiation on a square metre (10 sq. ft.) of the Earth when the Sun is directly overhead: so imagine going sun-bathing at midday on a clear day in the tropics, and your whole body still isn't receiving a kilowatt (your exposed surface area is a lot less than a square metre). Now imagine the beam that has to power your vacuum cleaner, which is much smaller than you are, and imagine what would happen if you got in the way of the beam! Physchim62 (talk) 01:42, 31 August 2010 (UTC)
All that wirelessly transmitted AC is wonderful, unless you consider that electromagnetic radiation just might have bad effects on human tissues. I do not care to be in the middle of an electrical transformer. Edison (talk) 01:44, 31 August 2010 (UTC)
Cf. Waldo. But be careful that you don't find one of the bad truths. --Trovatore (talk) 02:04, 31 August 2010 (UTC)
You could run a vacuum cleaner on an internal combustion engine... No cords needed and you could have a vacuum cleaner that probably could suck your carpet clean off the floor. You would need to find a way to vent the exhaust out of the house though so you don't get carbon monoxide gas. Googlemeister (talk) 13:01, 31 August 2010 (UTC)
Here is a 1901 petrol driven cordless vacuum cleaner. Gandalf61 (talk) 13:18, 31 August 2010 (UTC)
There'll be no carbon monoxide if you use hydrogen as the fuel. Of course, there are a few technical problems with that too!
Another way to store energy on board a device is a tank full of compressed air, or liquefied air at cryogenic temperatures. Or it could be superheated water that is kept from turning into steam by the pressure in the tank. In each case the air or steam from the tank is used to drive cylinders as in a standard steam engine. At least two of the three versions of this system -- the compressed air and the superheated water -- have been used in real life for fireless steam locomotives in industrial facilities, and compressed-air power was even used for public transit vehicles (streetcars, mostly in Paris). But the need for a heavy tank and heavy equipment to recharge it makes all of these impractical for a small appliance too.
--Anonymous, 20:03 UTC, August 31, 2010.


That Tesla photograph always bugs me. There's clearly a wire leading out to the light-bulbs. Who's to say it's not powering them? (Tesla certainly wasn't above taking a staged photo if it got him some funding.) APL (talk) 14:49, 31 August 2010 (UTC)
A few days ago on Bargain_Hunt a manual vacuum cleaner appeared. It was basically a giant syringe. Here are some at the Museum of Welsh Life --80.176.225.249 (talk) 17:41, 31 August 2010 (UTC)

Mixing unknown chemicals[edit]

I'm writing an essay about why it is not a good idea to mix unknown chemicals in the laboratory (we do this every year for a different rule, as part of the "Laboratory Safety" unit). I'd like to provide a concrete example of a very dangerous reaction that could occur if random chemicals are mixed "to see what would happen", but I can't think of anything at the moment. Could someone help me out? BTW These should be chemicals you can find in a high school chemistry laboratory. 76.230.225.80 (talk) 23:04, 30 August 2010 (UTC)

This BBC article lists three bad products of mixing ammonia and bleach, depending on the proportions you used. Comet Tuttle (talk) 23:15, 30 August 2010 (UTC)
Bleach and hydrochloric acid is the classic example. The reaction produces chlorine gas, and people die from it every year (not many, it's in the single figures per year for the UK, with 60 million population, but all the same) Physchim62 (talk) 23:43, 30 August 2010 (UTC)
Pouring water into sulfuric acid is also used as a common example of a dangerous reaction that can happen in the lab. The reaction is highly exothermic so can boil and splatter acid onto anything nearby. Vespine (talk) 01:32, 31 August 2010 (UTC)
I thought of two chemicals which create a highly sensitive explosive compound when mixed, which once almost blinded me when an ounce of the mixture exploded in a glass jar when I merely started to unscrew the lid, but I decided that the information would only encourage bad behavior. I spent months removing glass shards from my hands. There are probably some still in there many years later. Edison (talk) 01:42, 31 August 2010 (UTC)
this? --Chemicalinterest (talk) 16:24, 31 August 2010 (UTC)
Hopefully Wikipedia can prevent injuries by reminding children not to make that stuff in a glass jar. Or anything else even conceivably explosive. I happen to know that you can leave a kid alone with a container of screw-cap test tubes and harmless reagents for less than five minutes, and end up with him barely avoiding blinding himself because while you weren't looking he filled up the tube, capped it tightly, and pulled out a lighter from his pocket... Wnt (talk) 21:41, 1 September 2010 (UTC)
Mixing concentrated sulfuric acid and either concentrated hydrochloric or hydrobromic acid seems like a clever way of getting "even more acidic or specifically corrosive" (maybe in analogy to aqua regia?). Except one tends to produce clouds of HX gas and the other maybe also lots of X2 vapor if I recall. That latter is a nice visual demo because of the colors. How about "I'll neutralize this strong ammonium hydroxide solution with conc. HCl!"? Start with slightly warmed solutions. You don't even need to get as far actually mixing them--just tilt one towards the other so the vapors start to mix--and you get a large white cloud forming that settles as a fine powder on all surfaces. As a bonus, you don't create a chemical waste problem: the powder is water-soluble and not corrosive--probably wash down the drain or trashcan disposal--and the concentrated reagents are not consumed, diluted, or converted into other hazardous materials. Obviously nobody should try these at home and/or without appropriate protective gear, etc. etc. DMacks (talk) 06:25, 31 August 2010 (UTC)
I mixed conc. HCl and dilute ammonium hydroxide to produce a slight smoke. X2 would probably not form for HCl, because H2SO4 isn't a strong enough oxidant. Bromine would be produced though. Nice toxic suffocating corrosive bromine vapor. oror --Chemicalinterest (talk) 16:27, 31 August 2010 (UTC)
Concentrated sulfuric acid and formic acid will give off carbon monoxide. There will be numerous other effects such as gumming up your equipment, explosions, gasses, really bad smells, toxins, taht could happen. Graeme Bartlett (talk) 11:47, 31 August 2010 (UTC)

The screaming jelly baby is a common school chemistry demonstration in the UK. It involves heating potassium chlorate in a boiling tube to melt it (to melt the KClO3, that is, not to melt the boiling tube!), then dropping in a jelly baby - a source of sugar, to be oxidised by the chlorate. CLEAPSS reminds teachers in its notes on potassium chlorate that while KClO3 + sugar is safe if performed according to the instructions, KClO3 + sulfur and KClO3 + phosphorus are explosive mixtures and are therefore illegal to prepare. See also Armstrong's mixture, which is primarily KClO3 + P.

Ben (talk) 16:39, 31 August 2010 (UTC)