Wikipedia:Reference desk/Archives/Science/2009 August 29

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

August 29

Alpha particle scattering experiment

If we perform alpha particle scattering experiment what will happen if electrons come across alpha particles? —Preceding unsigned comment added by Tipusultan11 (talk • contribs) 00:36, 29 August 2009 (UTC)

Electrons are not alive, so they cannot "come across" anything. They can be scattered elastically, though. Since the rest mass of an alpha-particle is much larger than that of an electron, the momentum of an alpha-particle in laboratory frame does not change significantly in that process. I assume you are talking about Rutherford experiment (a.k.a. Geiger–Marsden experiment), and you have read the article. --Dr Dima (talk) 01:26, 29 August 2009 (UTC)

An alpha particle is just a positively charged helium ion, He²⁺. So an alpha particle attracts electrons, and can bind with one electron to form an He¹⁺ ion, or bind with two of them to form a neutral He atom. Red Act (talk) 01:32, 29 August 2009 (UTC)

I think the alpha particles are moving too fast in this kind of experiment to stand much chance of capturing electrons. It is not impossible, though. --Tango (talk) 17:31, 29 August 2009 (UTC)

Unless the He++ e- pair can transfer energy to something the resultant He+ will be of such high energy that it would break apart again - the common method of losing energy would be to emit raditation, thus:

He2+ + e- >>> He+ + hv

83.100.250.79 (talk) 18:51, 29 August 2009 (UTC)

It is not easy to calculate rates of various He²⁺ + X <==> He⁺ + Y⁺ processes (photoionization and photorecombination, electron impact ionization and three-body recombination, charge transfer, etc.) even in a dilute gas or plasma; in a solid foil it is almost hopeless. However, Rutherford and his students used a foil so thin that electromagnetic interaction of an alpha-particle with electrons in the foil did not appreciably change the alpha-particle momentum, no matter what the end states were of that interaction. --Dr Dima (talk) 22:39, 29 August 2009 (UTC)

Parallax method

What is Parallax method? Please explain its use. —Preceding unsigned comment added by Tipusultan11 (talk • contribs) 00:46, 29 August 2009 (UTC)

The Parallax method is the use of two different vantage points to calculate the distance to an object. For example, if you stick a finger in front of you and open your eyes alternately, your finger moves with respect to the more distant objects in the background. It can be used to measure the distance to faraway objects, but the Parallax article does a very good job of explaining it (with diagrams), so I won't repeat that here. Awickert (talk) 00:55, 29 August 2009 (UTC)

I once saw a cow move its head from side to side while looking at me across a fence, as if it was using the parallax method to see how far I was away. I have done this myself in exactly the same way. Poor genius cow - turned into beefburgers. 89.243.198.115 (talk) 19:00, 29 August 2009 (UTC)

Uncertainty principle-another question

Uncertainty principle#Wave mechanics explains uncertainty principle of position and momentum of a particle.

It says: "If the wave (note by the poster: the wavefunction of the particle) extends over a region of size L and the wavelength is approximately λ, the number of cycles in the region is approximately L / λ. The inverse of the wavelength can be changed by about 1 / L without changing the number of cycles in the region by a full unit, and this is approximately the uncertainty in the inverse of the wavelength"

I think this is about one particle, but the above process includes changing the inverse of the wavelength without changing the number of cycles in the region by a full unit. If we are to measure only one particle, there seem to be no way of knowing the number of cycles in the region, on the other hand, if we are to measure a bunch of particles, capturing the shape of the wave seems possible, and therefore the wavelength and position. How should I understand this? Like sushi (talk) 08:35, 29 August 2009 (UTC)

You do need to repeat your measurement on many "identically prepared systems" in order to see evidence of the uncertainty principle, and you can by such repeated experiments build up a picture of the whole wavefunction. But knowing the whole wavefunction doesn't tell you the position and momentum because that information simply isn't there. Actual experiments aside, position and momentum can't be mathematically encoded in the wave function to better precision than what's given by the uncertainty principle. That's what the argument you quoted is meant to illustrate, I think.

Think in terms of systems, not particles. There's almost nothing that distinguishes the "fundamental" particles from any other system in quantum mechanics. The uncertainty principle applies to quantum systems regardless of the fundamental particles in them. I don't mean that it applies to the system indirectly by way of its constituent particles, I mean that it applies directly to the system as a whole. It's systems that are described by wavefunctions, not particles. Unless your system happens to consist of exactly one particle, the wavefunction of the system is not made up of wavefunctions of constituent particles. -- BenRG (talk) 13:17, 29 August 2009 (UTC)

You seem to be under the impression that the uncertainty comes from some difficulty in measuring the shape of the wavefunction. That's not the case. The uncertainty is an intrinsic property of the wavefunction even if we have a full knowlege of its shape. Dauto (talk) 13:23, 29 August 2009 (UTC)

Thank you for both. If we can build up the picture of the whole wavefunction, can we not tell the wavelength by measuring the distance between the peaks?

Like sushi (talk) 03:51, 30 August 2009 (UTC)

Only if the wavefunction is exactly periodic like a sine function in which case it would have infinite extension and you would pay your exact knowlege of the wavelength (and momentum) with complete uncertainty about the position. The particle could be anywhere along that sine wave. Simply cutting the sine function after some finite extension and setting the wavefunction to zero outside of that "box" doesn't solve the problem bacause you introduce other wavelegths into the fourier analysis of that modified wavefunction other than the original wavelength.In other words, you pay for your partial determination of the position of the particle with uncertainty about the wavelength (and momentum). That unavoidable feature of the fourier analysis is very much the spirit behind the uncertainty principle. Dauto (talk) 06:50, 30 August 2009 (UTC)

Sorry to bring up once more the constituent particles, but doesn't determining the shape of the wavefunction include determining the positions of each particles? I mean as parts of the picture like dots. ! I might have got it. The wavelength of the system can be known with the positions of particles, but not with the distribution of the positions of all particles in the system? That is what Mr. BenRG (I guess he is a man) means by "it applies directly to the system as a whole"?

(But where has "changing the inverse of the wavelength without changing the number of cycles in the region by a full unit" gone? I thought change in this limitation in the wavelength and the size of the wavefront at the distance have something to do with it.)

Mmmm... I don't know, but wavefunctions of particles are changes of some fields, right? Then as the field has no end, the wavefunction must have an infinite possibility of positions of particles, or have infinite areas of value zero? How does infinite areas of value zero influence the accuracy of determining wavelength?

Like sushi (talk) 08:01, 30 August 2009 (UTC)

I'm afraid I can't make head or tail of most of what you just wrote. I think you need to get all these wrong ideas out of your head and start from scratch. The wave function is not a wave in space. Particles don't have wave functions. Particles don't appear as dots or bumps in wave functions. A wave function and a quantum field are different things. You still seem to think that there's something special about particles and that you'll get a better understanding of quantum physics by starting with the particles. That's not true either. Forget about particles. In fact, forget about quantum mechanics for the time being. The uncertainty principle is a property of any kind of wave, not just a quantum wave function. To the extent that the frequency of a wave is well defined, the "position" (effectively the region where it's nonzero) is spread out, and vice versa. -- BenRG (talk) 10:31, 30 August 2009 (UTC)

I thought I might have got something, but that (you say) is wrong.

(Skip this if you are not interested in what I thought)I thought wavefunction spread in space (which has no end) and when observed, had one position like a dot (and can be seen as a particle). I thought observing a wavefunction might leave different dots and they could form a shape of the wavefunction.

So, what is Uncertainty principle?

It is a property of any kind of wave. And it is that "to the extent that the frequency of a wave is well defined, the "position" (effectively the region where it's nonzero) is spread out, and vice versa".

I don't know where to ask you to start, but one thing I feel not clear is what "position" is.

Like sushi (talk) 12:03, 30 August 2009 (UTC)

Okay, that paragraph (the one you believed) is pretty accurate, except that the wave function isn't defined in 3D space, it's defined in a "configuration space" where the points are different configurations of the system. When you do a measurement to find the state of the system you find some configuration where the wavefunction was nonzero. After the measurement you can treat the wavefunction as having "collapsed" such that it's zero everywhere except for a narrow peak around the configuration you actually got. This doesn't mean the system has collapsed to a point in 3D space, it means that the parts are fairly definitely in a particular arrangement, which might be spread out over a large area in 3D space. The dimensions of the configuration space are degrees of freedom (mechanics), arbitrary parameters that describe the arrangement of the system. You could call this the "position of the system", but it's not a point in 3D space; the system might occupy a large region of space. A point particle of the sort they talk about in undergraduate quantum mechanics (which is not quite the same as a particle-physics particle) can be described by three numbers giving a spatial position, so in a single-particle system you can identify the configuration space with 3D space. With two particles, though, the configuration space has six dimensions. With one rigid body it has six dimensions (three for position and three for angular orientation). With two rigid bodies it has twelve dimensions, and so on.

The classical time derivatives of the position and the angular orientation (momentum and angular momentum respectively) are not independent coordinates in the configuration space. Instead, they are the derivatives of the wave function with respect to the position or angular orientation. That means you can't have an object in a definite position or definite orientation, because then the derivatives don't exist and the momenta aren't well defined. There has to be some spread in the position. But the narrower the spread, the more the derivative varies, and so the less precisely the momentum or angular momentum is defined.

You can't work out the whole shape of the wavefunction by consecutive measurements on the same system because of the collapse, but you can work it out with independent measurements on a bunch of "identically prepared systems" (meaning, effectively, systems that all have the same wave function). However, even knowing the whole wave function you can't work out both the precise configuration and the precise time derivative of the configuration because they aren't both present in the wave function. Also, if you measure the "position of the system" then the wave function collapses to a narrow peak, meaning the momentum becomes very uncertain. If you measure the momentum then the position becomes very uncertain. -- BenRG (talk) 13:54, 30 August 2009 (UTC)

Well, it's true that in general a wave function can't be thought of as a function on 3D space, but for the simplest case of a single particle ignoring spin the only degrees of freedom are its position, so you can view the wave function as a function on space (or as a function on the momentum space).

To the OP: Uncertainty is as you said a property of any wave function. It follows mathematically from the way we define the momentum operator relative to the position operator. The Uncertainty principle#Derivations part goes into how you might prove that. Rckrone (talk) 19:17, 30 August 2009 (UTC)

I haven't thought that wavefunctions can have so many dimensions. So it has dimensions for positions plus dimensions for angular orientaions. What are these angular orientations? Do they have something to do with uncertainty?

I don't know what you mean by "parts" and "arrangement" in "...the parts are fairly definitely in a particular arrangement, which might be spread out over a large area in 3D space. The dimensions of the configuration space are degrees of freedom (mechanics), arbitrary parameters that describe the arrangement of the system."

And why collapse into "a narrow peak around the configuration" may not result in fairly accurate position and the wavefunction "might be spread out over a large area in 3D space"?

"you can't have an object in a definite position or definite orientation, because then the derivatives don't exist and the momenta aren't well defined". Derevatives are like, for example, tangent lines for a parabola, right? Then derivatives in the case of a definite position or definite orientation are not 0?

Like sushi (talk) 03:15, 31 August 2009 (UTC)

'Hottest' chilli pepper

We've been given a plant that is claimed to be the worlds hottest chilli pepper (not 100% sure though) and were wondering how to know when it's ripe?... They're green at the moment and look big enough but we're not sure whether that's the right colour and we don't know what variety it is... If anyone knows anything about the matter any help would be appreciated... Thanks —Preceding unsigned comment added by 83.33.75.101 (talk) 12:55, 29 August 2009 (UTC)

The "worlds hottest pepper" plants sold in department stores will turn orange or bright yellow when fully ripe. You can use them when still green as they're already very hot. --Digrpat (talk) 17:09, 29 August 2009 (UTC)

Bhut jolokia? Axl ¤ [Talk] 00:02, 1 September 2009 (UTC)

Hottest pepper

The above question inspired a desire in me to know what the spiciest pepper and spiciest foods are. Ks0stm ^(T•C) 17:18, 29 August 2009 (UTC)

See Scoville#List_of_Scoville_ratings. --Tango (talk) 17:32, 29 August 2009 (UTC)

Other flavours comparied with spiciness are substances like piperine from ground pepper and whatever it is that gives wasabi its flavour. I don't know what the most peppery/wasabi-y foods are, mind. Vimescarrot (talk) 17:51, 29 August 2009 (UTC)

Scoville scale generally measures only Capsaicin heat, and not piperidine (pepper corn) or Isothiocyanate (horseradish, mustard, and wasabi) are not generally measured on that scale. The methodology used to develop the Scoville scale could could be used seperately for piperidines and isothiocyanates, but it generally isn't necessary to develop a "mustard" scale or a "peppercorn" scale, since the botanical variation in these types of foods aren't as great as in the Chili peppers. Horseradish and peppercorn are just not known for having dozens of varieties, each with unique culinary uses, which would necessitate a "scale" for measuring them on. When you use peppercorn or Wasabi in a dish, you pretty much know exactly what you are getting. Chili peppers are a MUCH different sort of thing, and it is important to recognize the difference between a Poblano pepper, a Jalapeno pepper, and a Habenero pepper, lest you screw up a dish horibly... --Jayron32 19:27, 29 August 2009 (UTC)

Going off on a slight tangent here — does it strike anyone else as strange that most languages have no exact translation for hot as in spicy? In Italian, for example, the closest word is piccante, but that can also apply to spices that are definitely not hot (such as garlic).

I really don't think this is a culturally constructed category -- hot spices (the ones mentioned above, plus ginger) genuinely produce a sensation of heat, as in temperature, and non-hot ones don't. So why isn't there a word? --Trovatore (talk) 19:35, 29 August 2009 (UTC)

It's also intriguing that English doesn't have two separate words for knowledge: a word for knowledge that resulting from recognition and knowledge resulting from understanding...it's a trait that the German language has, yet English is lacking. Ks0stm ^(T•C) 19:43, 29 August 2009 (UTC)

Well, that's a little different — English is unusual in conflating kennen and wissen, conoscere and sapere. That can be seen as a quirk of English. In the hot case, though, English has a word for a natural, biologically based category, where no other language I'm aware of has such a word. So that's a "quirk" of all other languages, which is something that needs explanation. --Trovatore (talk) 19:47, 29 August 2009 (UTC)

I suppose that's like Irish where you're supposed to say if you know something from experience, from reading it in a book, or because somebody told you. But as to spices, I don't experience hot spices as hot in the sense of boiling water or burning as in the sense of a burn. So I see no reason at all why any other language should use the corresponding word for hot. Actually I think the Italian grouping is better though still not very good. In short I think it is a cultural construct. Dmcq (talk) 21:09, 29 August 2009 (UTC)

Well, I think you're just wrong on the facts here. The sensation of hot spices is not hot as in a burn, no, but it is definitely hot as in temperature. This is probably measurable — hook up some sort of sensor to the thermoreceptors in the tongue and the bucal epithelium, and you'll see a response. --Trovatore (talk) 00:50, 30 August 2009 (UTC)

Capsaicin may be of relevance hear, particularly Capsaicin#Mechanism of action. Capsaican does indeed activate one of the known temperature sensors. However I don't know whether you can say the stimulation is exact, as there are other sensors which are not activated including probably some we don't know about which are likely essential for our perception of normal temperature Nil Einne (talk) 08:51, 30 August 2009 (UTC)

One significant factor would be that spices (mild or hot) found their way to Europe rather late and people just "tweaked" exsting words to fit the novel sensation. I have no knowledge of languages on the Indian subcontinent or in SE-Asia, but I would not be surprised if "proper" terms existed for "hot" and "spicey" ingredients. --Cookatoo.ergo.ZooM (talk) 21:53, 29 August 2009 (UTC)

I think so. "Bedus" means "hot" in Javanese. I don't know how one would say spicy, but I'm fairly certain "bedus" isn't it. AlmostReadytoFly (talk) 22:31, 29 August 2009 (UTC)

In Malay wiktionary:pedas means spicy hot and wiktionary:panas means temperature hot (see also [1]). I don't think the word would be used for something like garlic, but perhaps that's partly because the effect is weak. I'm not sure you'd say it in relation to ginger either for that matter. ([2] says pedas means has a Chilli feeling/taste but I can't imagine any other word you'd use for something like Wasabi and the Malay Wikipedia article Ms:Wasabi does indeed use pedas.) I've always been intrigued by the lack of such a distinction in English and wondered how common it was and have even thought of asking it on the RD (WP:RD/L obviously) but never got around to it. As with Cookatoo, I've always expected it was because of the late introduction of hot spicy food into most English speaking cultures. This issue is always going to be complicated by the fact that most cultures lack a history of all the various foods that can be called 'hot' and for some cultures if the sensation is mild and/or overridden by other sensations and tastes that it may not be enough that it's likely to be called 'hot'. Actually personally I think a distinction between wasabi hot and chilli+pepper (or capsacain+piperine) hot is not unreasonable as their sensation is IMHO clearly different and from what I can tell from a brief glance at [3] and [4] (both need subscription) the receptors involved are different too. Interesting enough, it looks like garlic does in fact activate both the wasabi and capsacian receptors (second link) so perhaps it should be called 'hot' and the Italian usage is better then it seems. The entry at wiktionary:hot provides some clue on other languages but it's very incomplete and also could be wrong in some instances. Interesting enough Finnish appears to have a distinction but Hindi and Marathi appear to lack it. The lack of a distinction can of course be problematic e.g. when someone says their food is hot in some circumstances it's unclear what they mean. Nil Einne (talk) 08:26, 30 August 2009 (UTC)

In English, there is "to know", "to understand", and "to grok", in order of increasing understanding. We also have an article on Knowledge by acquaintance which goes over some of the kennen/wissen duality. As for the description of taste, Hebrew has distinct words for hot: "kham" for temperature and "khariff" for taste. It is the same in Russian, too: "goryachiy" is for temperature and "ostryi" or "perchennyi" are for taste. --Dr Dima (talk) 23:00, 29 August 2009 (UTC)

I'm not sure I think kennen/wissen is really about degree of understanding. You kennst a person; you weisst (or is it wisst? I've forgotten) a fact. I suspect that to wissen a person would have a Biblical meaning, the way Adam knew Eve. But I'm out of my depth here -- just speculating, really. I do think I've heard that Adam seppe Eve in Italian. --Trovatore (talk) 01:28, 30 August 2009 (UTC)

What's it mean "to grok"? I've never heard that word before. BTW, in Russian, "ostryy" literally means "sharp" (as of a knife, for instance), and "perchennyy" means "peppery" -- which would relate to spiciness on the Scoville scale. FWIW 98.234.126.251 (talk) 05:10, 30 August 2009 (UTC)

"Grok" is a word made up by Robert Heinlein and first used in the novel Stranger in a Strange Land in 1961. If you didn't grow up in the sixties doing magic 'shrooms and LSD, it's not at all surprising that it's unfamiliar. Its meaning is "to understand profoundly". - Nunh-huh 06:25, 30 August 2009 (UTC)

Incidentally — is it possible to damage one's tongue (whether you want to call it "burning" or otherwise) by eating overly spicy foods? Not a request for medical advice. Nyttend (talk) 13:41, 30 August 2009 (UTC)

I have two things to say here. Firstly, on the language issue noted above, Japanese uses 'karai' for 'hot' (as in spicy), but this can also mean 'salty' (even though there is also another more specific word for that). Secondly, I think garlic can be considered hot. Have you ever bitten into a piece of raw garlic (very common in Korean food)? I would say that is definitely hot as in the spicy sense of the word, so the Italian word definitely fits for me. --KageTora - (영호 (影虎)) (talk) 14:32, 30 August 2009 (UTC)

Ohm's law and Johnson–Nyquist_noise

I was just wondering how Ohm's law is valid given that resistance is related to the temperature of something. I mean it would be valid at any given instance but how would it work over time? Suppose you took something like a circuit with the light bulb. When the filament in the light bulb is cool its resistance is "x" ohms. However doesn't the resistance increase when you increase the temperature of the substance? When you completed the circuit and the light bulb lit up it's resistance would increase, which would make the current across the light bulb filament decrease. (EDIT:) Forgot to include that the current would then go down, causing the temperature to go down, and causing the resistance to go down, thus increasing the current and repeating the cycle. It seems like it would never reach a equilibrium. Is this fluctuation the Johnson–Nyquist_noise mentioned in the Ohm's law article? 66.133.196.152 (talk) 17:37, 29 August 2009 (UTC)

No, the filament will quickly reach an equilibrium point where the heat generated by ohmic resistance exactly matches the heat lost by radiation. Johnson-Nyquist noise, more commonly known as thermal noise does not represent any kind of oscillation by the applied current and is present even when the applied current is zero. It is, however, dependent on the resistance (as well as temperature) which is increasing with increased current. SpinningSpark 18:09, 29 August 2009 (UTC)

Lots of conductors have the resistance change when the temperature changes, or even when the current flow changes. Many conductors and semiconductors , diodes, transistors, vacuum tubes, mercury arc rectifiers, or arcs in general cannot be analyzed as simple Ohmic resistances. Edison (talk) 19:51, 29 August 2009 (UTC)

Exactly. In the case that the voltage-current relationship is not linear, the "resistance" is not constant, so generally it is said that the circuit is "non-ohmic" or that Ohm's law doesn't apply (at least, not with a constant R. Terms and definitions can be minced here). However, this is not really the cause for thermal noise; the theoretical basis for Johnson noise is usually attributable to the statistical, but non-deterministic, electron flow pathways at the atomic level. The mathematics of Brownian motion and Johnson noise discusses the necessary modeling from a pedagogical point of view. J. B. Johnson's original 1928 paper, Thermal Agitation of Electricity in Conductors, attributes the noise to thermodynamic equilibrium of the electrons and the atoms of the conductor material. Simple approximations can relate the thermal noise to the observed ohmic resistivity, but an in-depth analysis reveals that they have different causes and are separate effects. Nimur (talk) 00:50, 30 August 2009 (UTC)

Temperature dependent resistors, thermistors, sensistors etc do not obey Ohm's law. —Preceding unsigned comment added by 79.75.25.53 (talk) 00:57, 31 August 2009 (UTC)

Le Chatelier's principle

Hello. Why does the equilibrium shift in the reverse direction if the pressure increased by decreasing the volume for the following reaction: 6CO_2(g) + 6H₂O_(l) ↔ C6H12O6(s) + 6O2(g)? Thanks in advance. --Mayfare (talk) 18:20, 29 August 2009 (UTC)

Does it not follow the nitrogen hydrogen example in Le Chatelier's principle#Pressure? But I don't know in this case which is the greater volume of the two sides of the reaction. --Tagishsimon (talk) 18:27, 29 August 2009 (UTC)

I imagine H20 constributes to the vapour press, but only slightly. At very high pressures the CO2 will liquify first.

Mayfare, can you explain where you got the idea that the supposition you provided is actually true? Or at least give some other indication of the conditions?83.100.250.79 (talk) 18:47, 29 August 2009 (UTC)

According to the basic premises of LeChatelier's principle, this equilibrium should not be pressure dependent to a first approximation. The hypothetical solution to changes in pressure should be no change since there are the same number of moles of gas on both sides of the reaction (6 vs. 6) so NEITHER direction actually reduces the stress, so the reaction should favor neither direction in the case of increasing pressure. In actual practice, there are LOTS of factors that LeChatelier's Principle does not take into account, so there is a very good chance that changing pressure WILL cause an equilibrium shift, slightly, but that is largely due to a gap between the rather simplistic model that LeChatelier's Principle is based on, and the actual reality of the effects off pressure changes on all sorts of processes. --Jayron32 19:19, 29 August 2009 (UTC)

83.100.250.79, my tutor taught me this. I myself am as confused as you are. --Mayfare (talk) 02:28, 30 August 2009 (UTC)

The important thing is you understand the principle, which it seems you do. As for your tutor - do they make mistakes often - possibly the forgetful type? I hope they're not just incompetent :)

83.100.250.79 (talk) 12:25, 30 August 2009 (UTC)

This reaction is extremely unlikely to go in the forward direction unless there are some serious help involved, such as imput of energy and enzymes. In nature this would involve many other reactions that would have different rates and equilibria and competing side products. Graeme Bartlett (talk) 22:44, 30 August 2009 (UTC)

The other issue is that at a given air pressure the oxygen level partial pressure is constant, whereas the carbon dioxide partial pressure can vary a lot in the environment. So in a green house for example an enhanced carbon dioxide level can help plants grow faster. Graeme Bartlett (talk) 22:49, 30 August 2009 (UTC)

Bathroom scales inaccurate

The big disadvantage with the bathroom scales I've used are that the recorded weight varies by a large amount according to whether you lean slightly forward or slightly back. This is no good for precision weighing while dieting. Perhaps this problem has been due to always buying the cheapest bathroom scales available. Are there any types or brands of bathroom scales that do not have this problem please? Or do even the most expensive scales have this problem? 89.243.198.115 (talk) 18:54, 29 August 2009 (UTC)

If the reading is varying when you lean, that's probably because you're tilting the platform so that part of it is resting on the frame of the scale and taking some weight off the mechanism. If you want an accurate measurement you should look for the highest reading, which is probably going to be when your weight is centered. I don't have any good advice for finding a more accurate brand of scale though. Rckrone (talk) 19:08, 29 August 2009 (UTC)

This problem is easily solved with the 4-point scales. Often, they look like a glass plate on 4 rather chunky feet. Each foot is actually a miniature scale. Shifting weight off one foot will increase weight on another foot and the measured overall weight will not change. -- kainaw™ 19:12, 29 August 2009 (UTC)

Do you have any brand names for 4-point scales please? My Google search found nothing. 89.243.198.115 (talk) 19:24, 29 August 2009 (UTC)

Try this. Those are all glass, but you can see the manufacturers and locate more models. -- kainaw™ 19:33, 29 August 2009 (UTC)

The important feature is 4 load-cell technology (see this). The reason for inaccuracies (when leaning etc.) is that the weight distribution "web" for either a spring or a single load-cell scale is notoriously inaccurate particularly after exposure to a steamy bathroom for a few months (primarily due to friction at the pivot points). A four load-cell system truly applies the correct weight at each corner and sums those weights. hydnjo (talk) 20:26, 29 August 2009 (UTC)

Wikipedia as Education

Could Wikipedia and Wikiversity educate a child, without access to any other learning tools, to a university level? TheFutureAwaits (talk) 19:37, 29 August 2009 (UTC)

In the United States, you only need to score well on either the SAT or ACT to be considered "University Level". Those have a little mathematics, which is covered in both Wikipedia and Wikiversity. Mostly, they are reading comprehension problems, which is a skill that anyone can learn by reading Wikipedia and attempting to recall what was read. -- kainaw™ 19:41, 29 August 2009 (UTC)

If I had sought to educate myself with these tools, I would have studied what delighted me and avoided what I disliked. I speak mostly of Wikipedia and not Wikiversity. There would have been gaps, as is common among autodidacts. Who would enforce general distribution requirements in the curriculum? The student would have to be a glutton for punishment to learn science and math if only interested in art and music, or contrariwise. And reading an article about calculus, differential equations, matrix algebra, electrical engineering, physics or chemistry would not leave the pupil capable of solving problems in those fields. Reading the best articles that could be written about art or music would not produce a student whose performance level was high. Some subjects, like chorus, band or orchestra require a group. Group study can be very helpful in diverse fields such as math, the sciences, philosophy or law. Most self-taught scholars are weak on doing difficult homework in technical subjects. How would an autodidact do writing and learn from thoughtful criticism? Edison (talk) 19:49, 29 August 2009 (UTC)

The SAT is a test for admission to university. "University level" usually refers to things that are taught at university. --Tango (talk) 20:02, 29 August 2009 (UTC)

Starting from what level? You can't learn to read from Wikipedia. Once you've reached a reasonable level with the key skills you could learn quite a lot from Wikipedia, but generally it would just be learning facts. Wikipedia doesn't teach you how to do things. Wikiversity does, but it isn't anywhere near developed enough to be used in isolation yet. --Tango (talk) 20:02, 29 August 2009 (UTC)

Wikipedia and Wikiversity could probably be used as the only study materials as part of homeschooling. The parent or tutor would need some separate material to guide the student as to what to study in order to pass . Using Wikipedia (even the simple enghish version) as the only material to teach kindergarden and first grade would be impractical but not impossible. If you mean "to the level of a university graduate" I think you will need to allow for theuse of th erest of the internet, not just Wikipedia. A well-rounded student must also have some social interaction, of course, and sports and music are hard to do by yourself. -Arch dude (talk) 20:36, 29 August 2009 (UTC)

This case-study points out some of the flaws and limitations of web-based education. The case in question was using a web-based distance-education software (not Wikipedia), but the lack of interaction and feedback were found to be a source of frustration and impaired learning. Information-seeking strategies of novices using a full-text electronic encyclopedia, published in 1989, analyzes the case of encyclopedia-based learning. It is found that novice users have a very different strategy for learning than experienced learners. "The results demonstrated that, in general, young novice users could successfully use a full-text, electronic encyclopedia with minimal introductory training. Subjects in third or fourth grade were less successful and took more time than subjects in the sixth grade. ... Many, especially the younger searchers, used sentences or phrases as queries, reflecting an ill-defined mental model of the search-system, a kind of hybrid between a print-encyclopedia and an interactive computer program." Again, though, this assumes basic literacy as a prerequisite. Further, there is a big difference between being able to use an encyclopedia/ information database, and being a well-rounded student equipped for further academic study or career productivity. Nimur (talk) 01:04, 30 August 2009 (UTC)

You say that "there is a big difference between being able to use an encyclopedia/ information database, and being a well-rounded student." I would very much so argue that life with Wikipedia has allowed me to give myself a much more well-rounded body of knowledge than I would have gotten through traditional schooling. Mac Davis (talk) 04:30, 30 August 2009 (UTC)

That is a false dicotomy. You don't have to choose between Wikipedia and traditional schooling. I have made use of both and therefore have the problem solving skills, social skills, useful but boring skills and knowledge that come from school and the very broad body of knowledge that comes from spending far more time than is healthy on the Wikipedia reference desks. --Tango (talk) 16:00, 30 August 2009 (UTC)

I like Wikipedia just fine (and don't know Wikiversity well), but I don't really seem how they would replicate a "real" education. You need interactivity, you need assignments, you need more than lists of facts however well written. Sometimes, though it is miserable, you need drilling and route memorization. Sometimes you need someone to push you on your writing and on your performance. I don't really see how these sources can do it, any more than a giant Encyclopedia Brittannica would. Obviously such a thing could supplement an education periodically but the education is the method, not the specific tool. --98.217.14.211 (talk) 01:25, 30 August 2009 (UTC)

Education involves a lot more than a collection of facts organized for easy consumption. Wikipedia can never be more than such a collection of facts, and it and other print media can be a VERY IMPORTANT part of education, but it cannot and should not be the only tool. Lots of education, such as interpersonal feedback; which includes the ability to get questions answered AND the ability to have someone watch you learn and interpret the problems you are having and help correct those problems without you even realizing you had a problem that you needed to ask a question about. Also, the ability to practice a skill, to watch others with expertise perform a skill, to have someone watch you perform a skill wrong and provide correction; the ability to provide appropriate approximations which build your knowledge from the superficial to the deep learning, the ability to provide context to facts and to connect them to each other in ways that have meaning. All of that needs another person to do for you. Wikipedia certainly contains all of the raw facts covered in any typical university program; but it does not have any ability to provide you with any of the skills and activities that are the real core of any education. --Jayron32 01:47, 30 August 2009 (UTC)

St Augustine, in his "Confessions" from the 4th century or so, emphasized the importance to his early education of having the teacher beat the student when he preferred playing outside to learning things such as Greek and Latin grammar, which are not "fun." It is hard to get the encyclopedia to wield the cane in the form of grading or report cards or evaluations of any form, or directing the attention to things which "should" be learned rather than things which are intrinsically rewarding. Edison (talk) 03:28, 30 August 2009 (UTC)

When those argue that it is important to be beaten when you prefer to learn about some subjects and not other ones, they are arguing against freedom over your own education. They argue that each student needs a fine structure—all to often every student gets almost exactly the same structure and we definitely do not "take them seriously." Some children may need to be schooled, and some need to be unschooled. There is no specific body of knowledge that is, or should be, required of a child just as there is no one right way to live. Mac Davis (talk) 04:26, 30 August 2009 (UTC)

The flaw in your argument (actually, a great gaping chasm in your argument) is that an undeveloped brain without the necessary knowledge is ill-placed to decide which things are important and which are not - an untutored mind - given complete freedom to pick and choose what is learned - doesn't even know of all of the wonderful things they might want to learn about. Children require the guidance of someone who has already learned the material to guide them as to what needs to be learned (even if it's a pain to do that). A child is unlikely to voluntarily subject her/himself to the rigors of memorizing the multiplication tables - but without that, you're unable to perform any kind of arithmetic - and without that, most of science and mathematics would be shut out from their attention. Even a child who might otherwise grow into an adult with a passion for math would be exceedingly unlikely to simply stumble on that without guidance - and indeed some pressure to learn things that he/she seems to dislike. No matter how much the child resists - the multiplication tables have to be learned as a 'gateway' to giving that child the option to learn physics/chemistry/biology/etc in the future. There are also things that people have to learn to do despite hating to do it. People NEED to be able to read. Learning to read is not an option - it's a requirement. Your conclusions sound great - but are ludicrously over-simplistic in practice. SteveBaker (talk) 14:29, 30 August 2009 (UTC)

I agree with your main point, but I disagree with your example - I recently graduated with a 1st class MMath having never learned multiplication tables. I still don't know them. I do, however, know how to multiply. That is far more useful. I have no idea what 6x8 is, but I know that I can work it out very quickly because I know various landmarks (for example, I know my squares) and I know the rules of arithmetic, so I can do 6x8=6x(2+6)=6x2+6x6=12+36=48. I can do that in a fraction of a second, it doesn't really take any longer than it probably takes for you to recall that fact and use it (using it is generally so much slower than calculating/remembering it that is the only relevant part for the total time taken). My example (which applies to me, it won't apply to everyone - that is a key point in itself) is writing. I used to hate writing. I wasn't very good at it and I didn't enjoy it (the two are undoubtedly related, but I don't know what direction the causal link is in). I was, however, forced to do it. I can now confidently express myself in writing (although my handwriting is still terrible - just about legible, though!), which is a skill I now realise is extremely important for pretty much any application of those skills I did enjoy (maths, say). Had I been allowed to choose what I wanted to learn I would now know lots of maths but not being able to do anything with it. --Tango (talk) 16:00, 30 August 2009 (UTC)

A certain third grader I once taught the multiplication tables to could have furnished the answer faster than your claimed "fraction of a second," by learning 1x1 through 12x12, then speeding the recitation until it was as fast as the numbers could be spoken, then learning them backwards and sideways (breaking up the use of one rote order). It was something the student wanted to do, and not something externally required. The student went on in later years to far surpass my math accomplishments. Edison (talk) 18:50, 31 August 2009 (UTC)

Being able to recite them all in order is a completely useless skill. What is useful is being able to get the right answer to a specific question. I don't claim that knowing your multiplication tables by rote is useless, but I think the time would be better spent learning how to multiply. Tell me, how good was this third grader at his 13 times table? --Tango (talk) 22:50, 31 August 2009 (UTC)

Tango, I'm not sure if you, not having learned the "times tables", really appreciate how use of them works, and Edison's description is I think unclear. Once you've thoroughly learned them at age 7 or whatever (by admittedly tedious recitation practice) you don't have to recite all the way through, say, "Once six is six, two sixes are twelve . . ." to get up to 7 x 6 = 42: instead, as soon as "7 x 6" is articulated or read, "42" flashes instantly into the mind. This was and still is the case not just for myself, a far-from-brilliant 50-odd-y-o Brit, but for almost everyone else of my generation educated in Britain that I've met for whom the subject has arisen. Moreover, although the default maximum was usually 12 x 12, it was not uncommon for the 13- and 14-times tables to be learned, and of course higher numbers can be readily factorised in the manner you describe. None of this works as a substitute for "knowing how to multiply", it's merely a (significantly) time-saving aid. 87.81.230.195 (talk) 21:41, 1 September 2009 (UTC)

Yes, as long as the only thing they needed to learn about was Family Guy. DJ Clayworth (talk) 20:14, 31 August 2009 (UTC)

Fruit beginning with U

Are there any fruits (of the culinary or botanical definition) whose names start with U in English, other than the Ugli fruit? --✶♏‭ݣ 20:49, 29 August 2009 (UTC)

Did you mean Ugni molinae? --Tagishsimon (talk) 20:51, 29 August 2009 (UTC)

No, I really did mean the ugli fruit but that's another good one. :) --✶♏‭ݣ 20:53, 29 August 2009 (UTC)

Ulster cherry, Uva di Troia, Usakhelauri, Ume --Tagishsimon (talk) 20:55, 29 August 2009 (UTC)

Well, the fruit of almost any flowering plant who's name begins with a 'U' would strictly meet your need. There are about a quarter million species of flowering plants - many of which are known by several common names - so there could easily be a million possible 'fruit names' - which probably means there are tens of thousands of candidates - vastly too many for us to list or even research! (For example: The Elm tree has the scientific name Ulmus - so it's fruit is an "Ulmus fruit".) But in terms of edible fruit - we'd have to refer you to List of culinary fruits - which lists only one - the Ugniberry - the Ugni molinae, which Tagishsimon already mentioned. I bet there are lots of others - but they'll be hard to track down. SteveBaker (talk) 14:15, 30 August 2009 (UTC)

Smell after rain

What does the smell after rain consist of? Mac Davis (talk) 21:31, 29 August 2009 (UTC)

See http://science.howstuffworks.com/question479.htm Who then was a gentleman? (talk) 22:05, 29 August 2009 (UTC)

They didn't list one of the bad smells, drowned worms decaying on the sidewalks. StuRat (talk) 13:00, 30 August 2009 (UTC)

I wonder (without proof) whether this is a Neural adaptation kind of phenomena - like the illusion where you stare at a brightly colored object for 30 seconds - then look at a blank, white sheet of paper and see the same image in complementary colors. Is it possible that we've become 'adapted' to the smells of our normal environment and have stopped registering them - then the rain washes those smells away, leaving behind 'pure' air - and (like the white paper) causing us to smell the complement of the smells that we've been ignoring. Just like an optical afterimage. Hence the air might seem sweet even though there is no substance in the air producing that smell. I have no idea whether that's really the reason - but I can see no reason why it shouldn't be true - and it fits with the smell seeming to dissipate very soon after it first appears. SteveBaker (talk) 13:59, 30 August 2009 (UTC)

An example: During a cross-country drive, I once stayed in a hotel in Sterling, Colorado (I had reserved the room from out-of-town because their rates were half of the surrounding towns). When I arrived, I found a huge cattle feed lot next door, and the whole town stank of manure. I asked the desk clerk if it always smells like this, and she said "Smells like what ?". StuRat (talk) 15:31, 31 August 2009 (UTC)

An interesting idea, and we certainly do stop noticing smells after a while and notice sudden changes in smells, however I don't see how a smell can have a complement. Eyes convert stimuli to a 3D space, the nose converts stimuli to a far larger space (about 400D according to Olfactory receptor). The concept of complements doesn't really work in that context. (Interesting fact of the day that I've just learned from that article: About 3% of the mammalian genome is devoted to genes for different olfactory receptors. That's an enormous amount!) --Tango (talk) 16:09, 30 August 2009 (UTC)

Well, if you agree that we stop noticing smells after a while - and yet we still notice when that smell goes away - isn't that the exact effect I'm speculating about here? There is an analogy with sound too - you can sit in an office all day with the fan running on your PC and not notice it. You'd swear there were no noises - but notice a more profound silence when you turn it off. If it works for sound and vision - it would be surprising if it didn't work for smell also. SteveBaker (talk) 17:47, 30 August 2009 (UTC)

With vision we see the absence of red as cyan, a colour in its own right. With smell and hearing we just perceive the absence of a given smell or sound as an absence (as you say, you hear a profound silence, you don't suddenly start hearing a different sound). --Tango (talk) 23:38, 30 August 2009 (UTC)

Severed vine

I have severed a vine that leads to a nice pumpkin I am growing in my garden. Oops. Is there any way to patch together the vine and save the pumpkin? Panasonic phones (talk) 22:01, 29 August 2009 (UTC)

Grafting might have some information on effective ways to do this. Rckrone (talk) 22:56, 29 August 2009 (UTC)

Proximate the severed ends, ensure they are tightly connected, and hope for the best. Time is of the essence. Also Google "milk fed pumpkin." Maybe additional nutrients would help. Edison (talk) 00:21, 30 August 2009 (UTC)

Done, and hoping. Thanks. Panasonic phones (talk) 00:05, 31 August 2009 (UTC)

Hurricanes in Southern California

weather.com is warning that Hurricane Jimena may hit Baja California in 3 or 4 days. Has a hurricane ever hit Southern California (note - I'm talking about Southern California, not Baja) while still at hurricane strength? Who then was a gentleman? (talk) 22:04, 29 August 2009 (UTC)

List of California hurricanes. -Atmoz (talk) 22:27, 29 August 2009 (UTC)

Great, thanks. Who then was a gentleman? (talk) 22:30, 29 August 2009 (UTC)

No known TC has officially struck California at hurricane strength, though the 1858 San Diego hurricane may have done so. –Juliancolton | ^Talk 19:29, 31 August 2009 (UTC)

Engineering - 'agricultural drain"

I am looking for details on how to make an 'agricultural drain'. What I understand so far: These 2 words do not seem to appear together as a phrase on wiki - only as 2 separate words in an article. It may have a more technical name and maybe that's why I can't find it.

It involves plastic sheeting with some sort of tube or foam which is buried underground where water normally collects and doesn't drain ie. next to a wall. This 'system' channels the water away to a desired area. I believe landscapers use it. I really want all the details possible... the depth, the slope, covering.

looking forward to seeing something about this on the website soon. —Preceding unsigned comment added by 41.208.48.176 (talk) 22:58, 29 August 2009 (UTC)

Try Tile drainage and Drainage system (agriculture) and the articles they link to. This has been an important, but expensive part of U.S. farming since the early 20th century. It makes muck into productive farmland. I am not sure that plastic sheeting is part of it. Landscaping also involves ditches, swales and berms. Try Googling those terms. Edison (talk) 00:15, 30 August 2009 (UTC)

It could be a varient of a French drain, which IS a common landscaping tool for keeping water off of the surface of an area, and it matches the OP's description almost exactly. French drains are very commonly installed next to structural walls to prevent water from resting next to a wall and damaging it. Our article describes their construction and use quite well, and also contains links to external sites. There's lots of good DIY websites describing how to construct and maintain a french drain... --Jayron32 01:38, 30 August 2009 (UTC)

Another option, for those with fields which are perpetually flooded, is to just plant crops which thrive in such an environment, such as rice. StuRat (talk) 12:55, 30 August 2009 (UTC)

Assuming there is infrastructure and demand to support such crops. They would also need to have a suitable climate to grow.

That can be impractical against a foundational wall; and may lead to other problems as planting directly next to a house can produce "root pry" problems. While in the open, carefully chosen plants may be a better solution than a French drain, against the foundation of ones house, a french drain is often a very efficient means of draining away water. --Jayron32 03:41, 31 August 2009 (UTC)