Wikipedia:Reference desk/Archives/Science/2007 July 19

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1 July 19

[edit] July 19

[edit] Save energy by texting instead of eMailing?!?

Women’s Health magazine published a bunch of simple things we can do everyday to protect the environment (based on the new book, The Green Book: The Everyday Guide to Saving the Planet, One Simple Step at a Time). One of the tips is:

Text Him (or Her) Up

Instead of emailing to ask when he wants to meet at the restaurant, text him. It uses about 30 times less energy per message.

This seems like a pretty dubious claim to me - what do you guys think? SteveBaker 00:47, 19 July 2007 (UTC)

The sum total of saved energy would not be enough to remove the air from the brain of the person who thought this idea up.

Well technically, you probably are spending less energy to light the cellphone's screen than power a computer- but since your computer is probably on anyway, leaving it on while you use your cellphone spends more time and wastes energy on your cellphone. To be brutally honest though, that idea will save about as much energy as shaving your pencils with a swiss knife. --L^augh! 00:59, 19 July 2007 (UTC)

I think that the idea with that suggestion was that a cellphone has a small battery, while a computer is probably spending a lot of electricity to run. However, since your computer is probably already on, it's actually wasting energy. Bart133 ^{(t) (c)} 03:52, 19 July 2007 (UTC)

In my opinion, this is a gimmick by the service providers to get more people to start using text messages. They get paid for every text message (At least they do, in India). I have seen many such suggestions in general magazines, mainly because the writer of the article is not qualified enough to understand that what he / she reads / hears somewhere else may not be correct. The claim would be true only if one needs to power on the computer just to send a mail. But this fact is very obvious -- WikiCheng | Talk 06:54, 19 July 2007 (UTC)

Worthy of a Dilbert cartoon - almost as good as "smaller fonts take up less disk space". Gandalf61 10:33, 19 July 2007 (UTC)

Yeah, this is pretty stupid. Even though the computer uses more power, it most likely is on already. Also, you could probably type you message in and email it about 5x faster since you can generally type much faster on a keyboard then you can on a cellphone.--GTPoompt (talk) 20:24, 19 July 2007 (UTC)

(Saving Wikipedia disk space as instructed) That's pretty much what I've been thinking too - but then I wonder whether the cumulative load of trillions of emails has resulted in a ton of extra Internet infrastructure that could have been smaller/simpler otherwise - but then whether the cellphone network would be simpler if there were no text messaging. Seems like it's an incredibly difficult assessment to make - I can't imagine where you'd start gathering the data for such a claim. SteveBaker 21:04, 19 July 2007 (UTC)

And yet clearly someone did gather the data, because they didn't just claim that texting used less energy than email, they quantified it! I mean, that "30 times" figure has to mean something, right? --Steve Summit (talk) 21:44, 19 July 2007 (UTC) (Saving disk space on the confession that, yes, I'm being sarcastic.)

Oh - undoubtedly. If they'd said that emailing took 31.457 times more energy than texting then we'd know for sure that it was a totally bogus figure! "30 times" is right on the borderline of being oddly exact! SteveBaker 01:50, 20 July 2007 (UTC)

I think the consensus is that, while it's possible one method or another uses less energy, the amount of energy used to send an e-mail is so trivial we shouldn't be wasting our time thinking about it. If you print the e-mail out, however, then you probably use like 1000 times as much energy (in the manufacturing of the paper and ink, mostly). StuRat 02:51, 23 July 2007 (UTC)

It seems to me that most replies here equate "texting" with "emailing", which has never been my understanding; I've always used "texting" to mean SMS or other forms of phone-based texting, so the comments about a computer's power needs wouldn't seem to apply. Is this a regional terminology issue? jeffjon 20:50, 24 July 2007 (UTC)

The comparison is supposed to be between texting and e-mailing. I would take "texting" to mean "cell phone text messaging", too, although it could possibly also mean "instant messaging on computer". StuRat 06:12, 25 July 2007 (UTC)

[edit] Game without rules

It seems that every game has rules and that if something has rules that it is (or is treated as) a game. Are there any games that do not have rules and is there anything that has rules that is not a game? (Including any system such as law as being a rule and therefore the legal system a game.) 71.100.170.92 23:59, 18 July 2007 (UTC)

Calvinball --Trovatore 00:00, 19 July 2007 (UTC)

Unfortunately its only rule disqualifies it as being ruleless. 71.100.170.92 00:20, 19 July 2007 (UTC)

Actually - Calvinball does have one rule - you may never use the same rules twice. SteveBaker 00:46, 19 July 2007 (UTC)

Something that had no rules at whatever would not be an identifiable game - in as much as all games of that kind would (of necessity) be utterly identical. So: Here is a game called "Blank" which has no rules whatever: -Let us know how much fun it is! There are lots of games with very few rules (eg Go), or rules that can be changed by the players (eg Nomic) - or where rules change as a part of how the game is played (eg Lemma [1])- or which have rules you make up as you go along (eg Calvinball)- or which simply don't exist at all (eg Mornington Crescent (game)). Here is a game I played with friends in college: Take a chess set - set it up the usual way - but make the rule that no piece is allowed to move at all. Each turn, you may either redefine how a type of piece moves (eg pawns can only move if they start on a black square and they do so by moving three spaces diagonally in any direction) or you can move a piece according to whatever set of rules exists. If you lose your king, you lose - and if you are 'in check', you can't redefine the movement pattern of any of the pieces that have you in check. SteveBaker 00:35, 19 July 2007 (UTC)

Mao (game) has rules that are kept secret from new players. List of games with unspecified rules is of relevence. SteveBaker 01:06, 19 July 2007 (UTC)

And the second part of the question - things with rules that are not a game are everywhere. Our legal system - computer programming - electronics design - life itself! SteveBaker 00:39, 19 July 2007 (UTC)

Steve, please read WP:NPOV --L^augh! 00:57, 19 July 2007 (UTC)

Sorry, this is Wikipedia - we make up the rules as we go along. SteveBaker 01:06, 19 July 2007 (UTC)

Would you like to play the game of questions from Rosencrantz & Guildenstern are Dead? --Trovatore 01:18, 19 July 2007 (UTC)

"Oh! You mean....you pretend to be him, and I ask you questions!" -- MarcoTolo 02:07, 19 July 2007 (UTC)

Statement. One-love. Whose serve? --Trovatore 02:08, 19 July 2007 (UTC)

Since this is science desk, Science and Mathematics in particular have rules that are not a game. --Tbeatty 04:32, 19 July 2007 (UTC)

Well, anyone could always consider it a game if they chose, although I'm still waiting for a physicist to shout "PWNED" while receiving a Nobel Prize. Someguy1221 04:46, 19 July 2007 (UTC)

zOMG LAG. Capuchin 06:40, 19 July 2007 (UTC)

Yes, I would say so. After all, game theory, the mathematics to reason about strategy in games, is not used to reason about children's games but about real live, and a key point is that rules may emerge because it would be disadvantegeous not to follow them. Capitalism in its most extreme form is a game without rules. International politics may be an even better example: as there is no world police, there is no way to enforce compliance with international treaties -- except for the fact that you may be punished by other players for cheating one player. These other players enforce the rules not because they are rules but because the enforcement is a game move of advantage. (See altruistic punishment.) A very extreme example is the classic application of game theory: nuclear strategy. There are no rules in nuclear warfare, just the goal to get not too many of your own people killed. ("Mr. President, I'm not saying we wouldn't get our hair mussed. But I do say no more than ten to twenty million killed, tops. Uh, depending on the breaks." --General Turgidson in Dr. Strangelove). And, finally, the largest game ever, with no rules at all: Evolution. Pity that our article on Evolutionary game theory is just a stub. Simon A. 08:53, 19 July 2007 (UTC)

My understanding of evolution is that it most certainly does have rules. Anyways, it seems that anything people are involved in that is competitive, which often seems like damn near everything, will be understood or framed by some as a "game" regardless if it has any clearly defined rules or how serious it might appear to be (ex. "The Great Game"). In some games winning is all that counts; Love and War are often seen as games and if it's true that "all is fair" in them, then I suppose they have no rules. -- Azi Like a Fox 12:14, 19 July 2007 (UTC)

The laws of physics (biology/chemistry/math/whatever) are a set of 'default' rules that are inherent in every game we play. If we count them as "rules" in the context of this question then there can be no games that have no rules because the laws of nature are irrefutable and immutable. If we say "No - those aren't really 'rules' in this context" - then evolution has no rules. I just basically dislike equating an arbitary 'process' with a 'game' and laws of nature as 'rules'. Rules should be arbitary things that humans have imposed in order to restrict arbitary behavior to some subset that we call 'the game'.

Actually - it's not just humans. My dog has a clear set of rules for the 'pull rope and fetch' game.

Human and dog grab opposite ends of the rope - nobody pulls until everyone has a good grip.
If dog pulls rope from humans hand then dog holds the rope 6 inches from human hands - and moves it just out of reach if human tries to grab it - until human succeeds in grabbing it.
If human pulls rope from dog then human throws rope far away and dog has to run and bring it back at which point human grabs it or (optionally) dog may choose to invoke rule 2.
Game is over when either party drops rope without a fight.
(and this is the rule I'm least clear on) Scoring has something to do with the amount of growling involved - if you can employ ventriloquism in order to bark without causing rule 3 to be invoked, that's extra points?!?

But these are a clear set of rules - that were not thought up by a human. SteveBaker 19:59, 19 July 2007 (UTC)

TEGWAR. Corvus cornix 17:41, 19 July 2007 (UTC)

Many games in the List_of_fictional_games don't have any rules. Do they count?

[edit] Basis of distinction

In reference to SteveBaker POV (as in Perspective (cognitive), which is highly valuable, relevant to the question and sought after here within the context of this discussion) How does one distinguish (i.e., what rule might one use to distinguish) between something that has rules and is a game and something that has rules and is not a game? Julie Dancer 08:46, 19 July 2007 (UTC)

A game is an event which has a goal and/or a winner. Even our academics (passing from one grade to another) can be viewed as a game. Bidding for a project can also be viewed as a game. Planning and executing a theft is a game too :-) -- WikiCheng | Talk 12:20, 19 July 2007 (UTC)

In that context then, in absence of a rule to make the distinction, is there anything which has rules that can not be played as a game? Julie Dancer 12:33, 19 July 2007 (UTC)

I would say no, there would be nothing preventing someone from playing whatever as a game given cheng's definition. Can think of things that should not be played as a game and also things that in most cases would not be (for example anything involving going to the DMV- there might be rules to follow and a goal, but you would have to be fairly masochistic to view the experience as a game). 38.112.225.84 12:56, 19 July 2007 (UTC)

Yes, but what about a rule that makes such a distinction? Julie Dancer 14:49, 19 July 2007 (UTC)

It's really all in the mind. Take the classic Prisoners Dilemma "game". If you are an actual prisoner facing a life or death situation - then this is a situation with arbitary rules that is most definitely not a game! If you are a mathematician studying the prisoners' dilemma as a part of game theory - then (ironically), it's still not a game. If you play Prisoners Dilemma with a good friend in a pub over a couple of beers - then it's a game. The group who were testing the theory of altruism using an iterated version of the prisoners dilemma were doing serious research (using 'tit-for-tat' strategies within it) - but the people they asked to contribute computer programs to play it were treating it as a game - in that case, this thing was simultaneously a game and not a game. This is true of many things. Just think of the number of competitions there are for things like good cooking skills - which is a game when they say it's a game - and a chore to do if you don't feel like being the one whose turn it is to cook tonight. SteveBaker 19:43, 19 July 2007 (UTC)

So are you saying that the distinction is that in the presence of rules something is a game if you choose to play (or participate as a player) and not a game if you choose not to play (or to participate as a player)? If so then what about those situations where you are required to participate whether you like it of not in order to exist or to not be terminated? Is this the rule that you would use to determine whether or not the presence of rules did or did not entail the presence of a game?

For instance. Suppose I am a bus driver and I am told (given a rule) that if I see a knife or a gun then the passenger can not come on board or if on board must be told to leave but if same passenger hides the gun or knife so that it can not be seen by me then the passenger can come on board or remain on board unless I have already seen the knife or gun then the passenger must leave.

To me these rules amount to playing the game of deceiving the driver as official policy of the bus line and I choose to decline to play this game. If I decline then I cannot be a bus driver. I either play this game or I loose my job. Julie Dancer 21:05, 19 July 2007 (UTC)

No - not at all. I'm saying it's a game if you treat it as such - no more, no less. If winning isn't all that critical to you - then maybe it's a game. If playing it is life-and-death or losing your job or whatever - then it's not a game anymore - even though the rules are the same and the players are the same. To quote the Wiktionary: Game - A pursuit or activity with rules performed either alone or with others, for the purpose of entertainment. - that last bit says it all 'for the purpose of entertainment' - as soon as it's not entertainment anymore - it's no longer a game. Those same set of arbitary rules (which evidently aren't a game to the bus driver) might make perfectly good rules for children playing "bus driver and urban terrorist" in the schoolyard. My point is that it's not what the rules are that make it a game or not - it's purely the context in which those rules are being obeyed and the mindset of the participants.

This may not be entertainment for the driver but what about for the administration? If the administration finds it entertaining then it would seem to still be a game.

Take the Roman Colosseum. For whom was the death at the mercy of the Gladiator or the wild beast a game whereas for the Emperor, no doubt it was all merely entertainment.

In our own legal system, many including prosecutors, judges, clerks and defense attorneys in addition to the accused him or her self may see the entire process as a game to be played at someone else's expense. Nonetheless I agree that entertainment is probably the best rule for determining whether or not something that has rules is or is not a game. Julie Dancer 08:08, 20 July 2007 (UTC)

Is One Button a game? Nimur 06:58, 20 July 2007 (UTC)

And if it is, when does the game begin? According to some, everybody is already playing One Button, they just haven't won it yet. Nimur 07:00, 20 July 2007 (UTC)

To me, it seems that Julie and Steve use the word "game" in pretty much opposite meanings. Steve uses the everyday definition of "game", namely something that you do for fun. Julie uses the definition from game theory: everything where a set of rules is either set explicitely or can be abstracted from the circumstances that detemine who is wins and who loses. To me, the game theorists have a point, albeit one for a slightly cynical realist: A gambler plays a game, and a daytrader seems to do the same, and it's clearly not just for fun. Looking at maps and military strategy plans one can't help noticing that from generals' point of view, war looks like a game. And that it, in fact, is one is the great tragedy of all history. Simon A. 14:46, 20 July 2007 (UTC)

Then are you saying that the rule which distinguishes a set of rules as being or not being a game is the consequence of playing the game for the individual player or for the follower of the rules? Julie Dancer 16:40, 20 July 2007 (UTC)

[edit] Re:Magnets

I know that magnets' opposite poles attract each other (north attracts south), but why does a magnet's north pole points to the Earth's North pole? Shouldn't it be going the other way instead? --Zacharycrimsonwolf 12:16, 19 July 2007 (UTC)

Well, we call the pole towards which a magnet's north pole points as the north pole. As you mentioned, it is the earth's south (magnetic) pole which attracts the magnet's north pole. To put it in simple words, if you imagine earth to be a big magnet, the south pole of the earth magnet is near the geographic north pole and vice versa. See Magnetic_North_Pole. It states that 'the Earth's North Magnetic Pole is therefore physically a magnetic south pole' -- WikiCheng | Talk 12:30, 19 July 2007 (UTC)

The choice of the magnet's names of the poles comes from the direction they point when used as a compass. They were named before people realized that the earth acts as a giant magnet. -- JSBillings 12:57, 19 July 2007 (UTC)

Okay. That would mean the Earth's south magnetic pole is named the North Pole? Thanks. Cheers, Zacharycrimsonwolf 11:32, 20 July 2007 (UTC)

Yes, how they are named and how they actually behave are polar opposites. StuRat 02:42, 23 July 2007 (UTC)

[edit] project

can someone explain to me where to search for the abstract and implementation of any electrical project? i need to do an electrical project for my final year in college and i have already searched countless webpages in vain. i did not find a suitable project. can someone say where to search for a good electrical project (projects as advanced as the projects one can find in IEEE magazines). —Preceding unsigned comment added by 59.89.20.202 (talk • contribs)

Why not take one of those existing projects and add a clock to it? :) Or do some other novel adaptation that contributes something to the field, and catches your interest? MAKE magazine frequently has spiffy electrical projects, but they may be too simple for what you're looking for, but perhaps you'll find some inspiration there. --TotoBaggins 17:01, 19 July 2007 (UTC)

Solar powered garden light that turns on when it hears footsteps instead of turning on only when it is dark.Polypipe Wrangler 01:48, 20 July 2007 (UTC)

To expand on that last idea, also consider the use of passive infrared sensors rather than acoustic detection.

Atlant 12:03, 20 July 2007 (UTC)

You're probably looking for websites called "Electronic Circuits Archive" or "Schematic Archives." Here's a few:

the electric wave

web-EE archive

U. of Washington circuit archive

delabs

electronics-lab.com

circuit exchange int'l

Free Electronic Circuits

DMOZ links to more archives

And here's my links to some particularly fascinating examples

[edit] Causes of losing a wheel

I'm interested in knowing more about the technical aspects of the holding capacity of lug nuts on Wheel studs.

I've found a fascinating article at [2] explaining how bolts work, but I have two questions which I hope someone could answer in terms which are not too technical.

Apart from not being adequately tightened, what other factors, or conditions, might cause a nut on a car's wheels to loosen and eventually come off?
If a wheel stud does not completely penetrate and pass through to the other side of an open lug nut, will this reduce the holding force of the nut, and, if so, how might one calculate the reduction of holding power related to the depth of penetration of the stud? --JAXHERE | ^Talk 17:05, 19 July 2007 (UTC)

Lots of things can reduce the grip of the nut on the bolt:

If you somehow got oil or grease onto the threads - that would do it.
If they are over or under-tightened.
If they were overtightened sometime in the past.
If a nut with the wrong kind of thread were put onto the bolt - either now or in the past or if it somehow became cross-threaded either now or in the past (this was the case when I took delivery of my 1963 Mini which had seven cross-threaded wheel nuts on it - three of which were on one wheel!!).
Some old/large vehicles have threads that tighten up in the anticlockwise direction on one side of the vehicle to allow for the fact that the direction of rotation of the wheel can cause wheel nuts to loosen - so I suppose the nuts on that side of a 'normal' car would be more prone to this than those on the opposite side.
I suppose that if you've swapped wheels an insane number of times then the threads might start to wear out...seems unlikely though.
Corrosion of the threads is a problem because the rust doesn't have the strength of the metal - and even if the rust has been removed, the resulting loss of metal will reduce the quality of the contact between nut-thread and bolt-thread.
Certainly if the entire depth of the nut is not fully threaded onto the bolt. The actual math of a nut that's only partially threaded onto the bolt is going to be complicated. It's tempting to say that if the bolt only goes X% of the way through the nut then the nut must have only X% of the usual 'holding power' - but the thing about wheel nuts is the damage that happens to the threads on the bolt. When you over-tighten them (for example), you can actually distort the metal of the threads on the bolt so that the nut doesn't grip as well. Even after you correct the tension on the fitting - that distortion remains - weakening the grip of the nut on the bolt forever more after that. Similarly (I suppose), having the nut correctly torqued up - but with only half of the thread engaged is putting double the usual force on every centimeter of the thread - and that's like you over-torqued it. So you might find that you damage the bolt so the holding force of the nut is halved because there is half as much thread providing the necessary friction - but ALSO, you now have a damaged or weakened thread on the half that is engaged - so that could easily reduce the amount of grip even further.
You can use a commercial 'thread lock' compound ("Loctite" is the most popular brand) to improve the adhesion of nut to bolt.

Bottom line is whichever of those things you think you screwed up: "Don't Do That!" ...and if you did, consider getting a new set of wheel bolts. The ones I bought for my Mini only cost a couple of bucks each and they were pretty easy to replace. I would also recommend buying a torque wrench and tossing that into the toolkit in the back of your car so you can get the tension right even if you are putting on a spare tyre at the side of the road. SteveBaker 19:27, 19 July 2007 (UTC)

I'll bet more wheels fall off as a result of wheel bearing failure than lug nut failure. That is, someone botches the assembly of the wheel bearing, its castellated nut, the cotter pin, or what-have-you and the bearing falls apart on the road. Or the bearing freezes as a result of faulty lubrication and overheats, eventually causing something mechanical (like the stub axle) to break.

Atlant 12:10, 20 July 2007 (UTC)

[edit] Supporting principles

Thanks for the responses, everything seems to make sense, to me. Now the really tough part: Can you direct me to on-line authorative explanations of these concepts? The link I gave at the beginning is a part, but I'd hope I can find more, but the searches I've done so far hasn't uncovered enough. --JAXHERE | ^Talk 15:07, 20 July 2007 (UTC)

Our impact force and impact wrench articles discuss some of the physics involved in tightening bolts. StuRat 02:25, 23 July 2007 (UTC)

[edit] Reusing Nomenclature

Okay, so I know that if any given organism (living or extinct) is given two names, then the one published first is used; but what happens to the old name? In other words, if we discover the direct ancestor of Hyracotherium, can it be called Eohippus? If they definitely identify the oldest ancestor of humans that is not an ancestor of chimpanzees (assuming we haven't already) can it be called Eoanthropus? These are just examples; I guess they could call an insect Eohippus as well. Eran of Arcadia 19:30, 19 July 2007 (UTC)

I don't know about previously used names, but there are examples where the same name appears in two widely seperated family trees, i.e. there might exist a Sillius group of rodents and a Sillius group of insects. As long as they are sufficiently distinct organisms there is little chance of confusion. Often this occurs when the name itself is not very inventive, such as naming a group after the country in which they were first found. Sorry, I don't recall any specific examples. Dragons flight 01:58, 20 July 2007 (UTC)

What do you mean by "group" in that case? Can a genus name appear twice, or only higher levels? Eran of Arcadia 02:51, 20 July 2007 (UTC)

I don't have the time to go slogging through the primary source material at the moment, but Nomenclature Codes has links to the widely-accepted codes governing the naming of organisms. There are separate codes for animals (ICZN), plants and fungi (ICBN), and bacteria (ICNB). I would expect (or at least hope) that the Codes would contain the rules on re-use of names. TenOfAllTrades(talk) 02:46, 20 July 2007 (UTC)

Strictly speaking, only specific names may be shared among several species (in different genera), but all other ranks must be unique. There are so many rules that some violations are overlooked if they're benign, simply because scientist have better things to do. The Vianna code is coming online soon. I suspect old invalid names may be reused, but only with fairly unrelated organisms to avoid confusion. Bendž|Ť 21:05, 20 July 2007 (UTC)

That's a shame then, Eohippus is too cool of a name not to get a horse named with it . . . Eran of Arcadia 01:08, 23 July 2007 (UTC)

[edit] Need help with particle reactions

can anyone give me the net energy changes, or a method of working them out, and also the required conditions for the following events.

${\nu}_e + \hbox{n} \to e^{-} + \hbox{p}$
$\bar{\nu}_e + \hbox{p} \to e^{+} + \hbox{n}$
$\hbox{n} \to \bar{\nu}_e + e^{-} + \hbox{p}$

Cheers. Philc 19:36, 19 July 2007 (UTC)

You can get an idea by using E=mc², along with the mass of the neutron, proton, and electron. Your neutrino or antineutrino are approximately massless, though that is a hypothesis. The positron is the same mass as the electron. Your last reaction is the spontaneous decay of the neutron. GB 21:21, 19 July 2007 (UTC)

That only takes into account the mass changes, I want to also consider the kinetic energy of the particles on either side of events. Because also I don't know how much energy is required to initiate the reactions, and how much is released as KE. Philc 23:29, 19 July 2007 (UTC)

To Graeme, I don't think ignoring the neutrino mass is a hypothesis, it's more of an approximation (a very good one). As for knowing the KE of all the particles, that is tricky. The neutrino is not repelled in anyway, so there's not really a 'coulomb barrier' style activation energy. The neutrino I think can have any energy. Certainly in the three body decay (the third equation), you cannot tell how the energies will split. This was in fact some of the early evidence for a neutrino, had the neutron simply gone to e and p their energies would have been well defined, but the existence of the neutrino means they aren't. Sorry if that's not so helpful. Cyta 07:47, 20 July 2007 (UTC)

Number 3 is the spontaneous decay of a neutron - no initial kinetic energy is required, but all the mass difference goes into the kinetic energy or the products. You can work this out. For part 1 of the homework this is the neutron decay accelerated by neutrinos. The crosssection will be very low, but it may vary with the energy of the neutrino. Number 2 is your inverse neutron decay, you will have to supply enough energy to create the extra mass. You cna't know the kinetic energy of all the particles as Cyta says, instead tehre is a range of possible values as the energy is split between particles. see beta decay. I was saying that the idea the the neutrino is massless is a hypothesis. GB 07:57, 20 July 2007 (UTC)

I thought that with the observation of neutrino oscillation, the idea that the neutrino is massless is simply wrong? Algebraist 10:49, 20 July 2007 (UTC)

It's a shame you had to imply this is homework. It's Late July, I don't know of any schools that aren't on holidays, and I certainly am, I was purely wondering out of interest in a larger picture, I can explain to you if you want. I was looking at the possibility (purely playing with ideas in my head) of using the $\bar{\nu}_e$ and fast

n

generated during nuclear fission. Using the equations I listed:

${\nu}_e + \hbox{n} \to e^{-} + \hbox{p}$
$\bar{\nu}_e + \hbox{p} \to e^{+} + \hbox{n}$
$\hbox{n} \to \bar{\nu}_e + e^{-} + \hbox{p}$

by adding (1) and (2) you get;

$\bar{\nu}_e + {\nu}_e + \hbox{n} \to e^{-} + e^{+} + \hbox{n}$

if you add this to (3) you get;

$\bar{\nu}_e + {\nu}_e + \hbox{n} \to e^{-} + e^{+} + \bar{\nu}_e + e^{-} + \hbox{p}$

$\bar{\nu}_e + {\nu}_e + \hbox{n} \to 2e^{-} + e^{+} + \bar{\nu}_e + \hbox{p}$

if you add this to (2) you get

$\bar{\nu}_e + {\nu}_e + \hbox{n} \to 2e^{-} + 2e^{+} + \hbox{n}$

The electron and positron could then be tapped off using magnetic fields as they would move in opposite directions, therefore preventing instant annihilation.

What I was basically wondering is how much kinetic energy this chain of events would require to initiate, and pass through to the end, and how comparable that would be with the KE of $\bar{\nu}_e$ and fast

n

from fission, and the billions of ${\nu}_e\,$ flying in from the sun every second. Philc 11:25, 20 July 2007 (UTC)

Sorry about upsetting you with the homework suggestion. The minimum egergy required will be that required to form the two electrons and two antielectrons, which I think is 4*511keV or 2.022 MeV. However the reaction you describe would have an incredibly low cross-section. It is hard enough for one neutrino to hit a neutron, let alone two at the same time. You can see how slowly the detectors find neutrinos from the sun to get an idea of the low chance that a reaction occurs. Extrememly high energy neutrinos with energies in the EeV range have a much bigger chance of impacting matter. GB 11:59, 20 July 2007 (UTC)

Because of the nature of the reaction stages as opposed to all at once, it wouldn't require the neutrinos to impact simultaneously, but point taken on the non-likelihood of the reaction taking place. Do you have any idea where I can find out the kinetic energy of neutrons and antineutrinos from nuclear fission. I was assuming it was quite high, given that they are known as fast neutrons, and have to be mediated with boron. But since they were called fast neutrons simply to differentiate from slow neutrons, purely in the context of propagating fission reactions, I can't really assume that it is comparable to the energies required for particle reactions. Philc 13:25, 20 July 2007 (UTC)

In Nuclear chain reaction you can see U-235 + neutron -> fission fragments + 2.52 neutrons + 180 MeV. The energy is split between the different four to five particles, so there could easily be several MeV per neutron, so fast neutron would have the energy necessary. Neutrinos from the sun[3] seem to have a relatively low energy, below half a MeV, so they would not contrubute much to the reaction. GB 01:44, 23 July 2007 (UTC)

Ok, thank you very much. Philc 15:02, 24 July 2007 (UTC)

[edit] Electronics: Can something that requires 100mA run off of 500mA?

Hello, I play guitar and in the world of electric guitar there are foot pedals that you can switch on and off to use a desired effect, and I prefer powering them with an adapter. In this case, my Electro-Harmonix Small Clone chorus pedal says it requires 100mA of current. I went to 3 separate stores and they didn't have the exact adapter that the company would like you to have, but one store did have an Electro-Harmonix adapter that provides 500mA instead of the required 100. My question is, is this going to fry my pedal? Or does the pedal limit the current draw? I'm pretty sure it is limited and should be fine, but I don't want to take a chance cause this pedal was almost $90. Thanks! NIRVANA2764 20:34, 19 July 2007 (UTC)

It's no problem - the pedal will only pull the amount of current it needs. You need to be sure that:

The voltage is set correctly for the pedal.
That the power socket has the correct tip/ring polarity. There is usually a picture on the pedal that shows which is positive - most 'generic' power supplies have a way to get the wrong!
That you have ENOUGH amps avaliable on the power supply (which you do!)
If you plug it all in and it doesn't immediately work - unplug it REALLY QUICKLY and double check everything - with any luck you'll avoid damaging it.

Personally, I wouldn't buy an adaptor for another pedal - I'd go to WalMart or RadioShack (or whatever your local equivalent is) and buy one of those switchable power supplies that comes with a bazillion different connectors and can be switched to any voltage. Those are cheaper - have a range of connectors and are generally more flexible in terms of tip/ring polarity. My son has several effects pedals - and they all run off of these switchable power supplies. SteveBaker 20:53, 19 July 2007 (UTC)

Thanks a lot for your help. A lot of people are recommending universal adapters to me, and it seems like a good idea (they are cheaper than regular ones...don't know why though) but I have fried 2 of them to date, and I don't know why. Perhaps my pedal required more current than the pedal could supply. I would use them fine for a few months, then one morning, find them to be not providing any current to my pedal. The sticker on them would be warped, leading me to believe that they got overheated and just died out. I've asked many people and nobody can explain it. So now my philosophy is that I will buy only the adapter that the manufacturer suggests, because I'm tired of frying adapters. NIRVANA2764 20:58, 19 July 2007 (UTC)

Certainly you need to ensure that the adaptor can provide the current the pedal demands - and with some of them you have to read the fine-print on the packaging because some of them can deliver less amperage at higher voltages. Ideally, you want the adaptor to be able to produce roughly twice the amperage of the device it's driving in order that it should run fairly cool. If the adaptor is putting out close to it's maximum then it'll get hot and probably, it's lifetime will be shorter too. My son uses four 'COBY' 500mA supplies to drive four guitar effects pedals from various different manufacturers - and so far, none of them have died over more than a year of fairly frequent use. I'm running my laptop from a universal adaptor too - but it's running fairly close to its' maximum capacity for over a month now. It's hot and the label has warped and fallen off...so I don't expect it to last for very long. But the original supply for my laptop died and HP wanted $80 for a replacement. The no-name variable supply cost $20 - so I figure I'll still be ahead of the game when I'm on my fourth one! But buy universal adaptors with plenty of spare capacity for the pedal you have and they'll run cooler and last MUCH longer. SteveBaker 01:32, 20 July 2007 (UTC)

Questions about voltage and current are surprisingly frequent here on the Reference Desks. Here is a handy way to think about and remember the difference. It is traditional to use fluids in these analogies.

Suppose you have a recipe for Cherries jubilee that calls for one cup of 80 proof Kirschwasser. Suppose you are low on funds (and have a tin tongue to boot) and you try to use Budweiser instead of Kirschwasser. But when you try to ignite the flambé, it ain't gonna burn, because beer just doesn't contain a high enough concentration of alcohol for that.

Suppose that, stung by this demoralizing failure, you resolve to save your pennies until you have enough to head down to your friendly neighborhood liquor store to buy some of the real stuff. But they won't sell you a cup of it -- the smallest bottle of Kirschwasser they have is 500 ml, or a little over 2 cups. The burning question is: will the 500 ml bottle do? And the answer is, of course it will (assuming you can afford it). You can almost certainly find something to do with the extra 1.113 cups of liqueur when you're done with (or perhaps even as you're enjoying) that dessert.

Amps are like cups. Volts are like proof. It doesn't matter if your supply has too many cups; it only matters if it has too few, or if the proof is too low, or too high. Prost! —Steve Summit (toast) 02:38, 20 July 2007 (UTC)

[P.S. Stay tuned for our next exciting episode, in which we learn that watts are like hangovers.]

Wot?

Atlant 12:20, 20 July 2007 (UTC)

Another comparison: Watts are like beer, while Volt-amperes reactive are like the foam on the beer. Edison 20:55, 20 July 2007 (UTC)

I'm going to make a platinum plated spork - I mean that! SteveBaker 01:12, 21 July 2007 (UTC)

Now, now, it was a reasonable (if obscure) analogy: just as reactive current takes up capacity in your transmission lines without transmitting any useful power, so does the head take up space in your glass without providing any useful beer! —Steve Summit (talk) 01:33, 21 July 2007 (UTC)

[edit] What is the difference between sociopath and psychopath?

Right now, sociopath redirects to psychopath, and the psychopath article says that they are the same thing, just different terms. But the sociopath page has sort of an edit war with some users redirecting it to antisocial personality disorder and others changing back to psychopath. Which is correct?--64.149.176.55 21:25, 19 July 2007 (UTC)

Yes, those editors are demonstrating an approximately correct usage of the terms, sounds like. --Steve Summit (talk) 22:36, 19 July 2007 (UTC)

If memory serves, psychopath is an antiquated term, which has been replaced with sociopath. They might have slightly different shades of meaning, but I think that that's the gist of it. Raul654 21:30, 19 July 2007 (UTC)

"Psychopath" and "sociopath" are terms used in common parlance but the APA would say that these refer to persons with antisocial personality disorder (cf DSM IV). Donald Hosek 22:13, 19 July 2007 (UTC)

I think both Raul & Donald above are on the right lines, it might also be useful to compare dictionary definitions, these from Chambers Dictionary 1983 edition. " Psychopath - one who shows a pathological degree of specific emotional instability without specific mental disorder: one suffering from a behavioural disorder resulting in inability to form personal relationships and in indifference to or ignorance of his obligations to society, often manifested by anti-social behaviour, as acts of violence, sexual perversion, etc." " Sociopath - sociopathy - any of several personality disorders, resulting in asocial or antisocial behaviour. " DuncanHill 22:38, 19 July 2007 (UTC)

For what it's worth, DSM IV doesn't use either term, as Donald says, it does have antisocial personality disorder. DuncanHill 22:48, 19 July 2007 (UTC)

David T. Lykken illustrated the difference with the classic nature and nurture division: psychopathy is a psychological condition caused by natural conditions such as brain damage or atypical neural development, while sociopathy is a sociological condition caused by nurtural (is that a word?) conditions childhood abuse, poverty, extremely high/low intelligence (although of course most people would have a combination of the two, brought about by a combination of nature and nurture). Laïka 00:13, 20 July 2007 (UTC)

[edit] Relativity

Suppose there are two beams of light alongside each other, Beam A and Beam B. According to the special theory of relativity, the speed of light is the same from any ppoint of reference. Would Beam B be traveling at the speed of light from Beam A's point of reference? ¿SFGiДnts! ^{¿Complain! ¿Analyze! ¿Review!} 21:35, 19 July 2007 (UTC)

By talking about "beams of light", do you really mean, "the point of view of a photon inside a beam of light"? As it is you make it sound like you think of the beams as static entities, but they aren't. But in any case — yes, assuming they could be observers in a traditional sense, from their frames of reference they will measure one another as going the speed of light (assuming they are both in a vacuum). --24.147.86.187 22:47, 19 July 2007 (UTC)

Short answer, yes. Long answer, the question is ill-posed. Time would appear to stand still for a hypothetical observer moving at the speed of light and hence he would be unable to measure the speed of the second beam of light. So, technically it is not possible for any measurements to be made from the point of view of a beam of light. However for reference frames arbitrarily close to the speed of light you can still make the measurement and you will always find that light moves at light speed. ;-) Dragons flight 22:55, 19 July 2007 (UTC)

(edit conflict x2) Things get funny in special relativity if you pick a lightlike reference frame, since you end up with infinite time dilation. Essentially, for an observer moving at the speed of light, no time passes, and so questions like "how fast is something else moving relative to me?" become rather meaningless. —Ilmari Karonen (talk) 22:55, 19 July 2007 (UTC)

The main problem with the question is the misunderstanding of the special theory of relativity. The question uses the phrase "from any point of reference". That is not what the special theory of relativity states. It only applies to inertial frames of reference. A photon traveling at the speed of light is not an inertial frame. As the article the OP linked states: "Relativity theory depends on "reference frames". A reference frame is an observational perspective in space at rest, or in uniform motion, from which a position can be measured along 3 spatial axes. In addition, a reference frame has the ability to determine measurements of the time of events using a 'clock' (any reference device with uniform periodicity)." It is hard for a photon to measure time when time is standing still. -- Kainaw^(what?) 23:06, 19 July 2007 (UTC)

I knew I should have paid better attention in middles school science. :) ¿SFGiДnts! ^{¿Complain! ¿Analyze! ¿Review!} 00:09, 20 July 2007 (UTC)

IMAGINE you are a photon in a long line of photons moving in the same direction (all moving of course at the speed of light relative to someone not moving). Wouldn't the photon in front have to be moving at your same speed, and the one behind also moving at your same speed? So to each of you in the line there is no motion relative to each other. Isn't it the same for a photon out to the sides moving in your same direction? SO.. if you are motionless in your own frame of reference, an outside observer would appear to be moving in reverse at light speed right? According to relativity the outside observer would experience time standing still since he is going at light speed relative to you. But your world is motionless and time for you is normal? Confusing isn't it.

No it is not. This comes up on a weekly basis here. What it boils down to is this concept of "motion" and "speed". If you stop using those broken concepts it makes perfect sense. The one with the highest energy-to-mass ratio is "traveling faster". If it is 100% energy, it is "traveling at the speed of light". So, two photons are hopping along at the "speed of light" - which means they are 100% energy. They go in opposite directions, or the same direction, or in random circles and swirls. Does the fact that they are both 100% energy change? No. What if some guy is sitting at his computer trying to make this confusing? He is only about 10% energy. Does the movement of the photons change the fact that is he only about 10% energy? No. But he is relatively moving away from the photons? Big deal - he's still only about 10% energy. But I've always been given an example of a spaceship traveling through space! So - it was a bad example. He's still only 10% energy. But that isn't in the Wikipedia article! So - he's still only 10% energy. But I've read the Cryptonomicon! So - you have a high tolerance for bad prose. He's still only 10% energy. Regardless of your argument, it isn't confusing. -- Kainaw^(what?) 12:08, 25 July 2007 (UTC)