Wikipedia:Reference desk/Archives/Science/2007 October 3

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October 3

First missile guidance system

After reading the article on missile guidance I started wondering what guidance method the first guided missile had. I have tried searching a bit, but so far I haven't been able to find it. - Dammit 00:23, 3 October 2007 (UTC)

As I recall, and as Anti-ship missile suggests (but does not source!), these first appeared in WW2. I think they were radio guided, as certainly some "plane bombs" were (haven't uncovered the link for that one yet). Someguy1221 00:30, 3 October 2007 (UTC)

Ah, Operation Aphrodite. Someguy1221 00:33, 3 October 2007 (UTC)

Maybe the Henschel Hs 293 radio-controlled anti-ship missle? --Milkbreath 00:37, 3 October 2007 (UTC)

IMO the V1 was the first guided missile. —Preceding unsigned comment added by 88.111.81.231 (talk) 01:02, 3 October 2007 (UTC)

I wouldn't call the V-1 flying bomb "guided." It could only be guided to the extent that the operators could control roughly how far it travelled before it landed, and you can do the same with an artillery shell. Someguy1221 01:55, 3 October 2007 (UTC)

The definition of "guided" in this case is whether the projectile's path can be changed in flight. Which you can't do with an artillery shell. The V-1 could do this in about the bare minimum sense of the word, since its "autopilot" would make adjustments based on the conditions the V-1 encountered. --24.147.86.187 02:31, 3 October 2007 (UTC)

The V1 was more of an unmanned airplane than a missile. It flew at a controlled altitude in a selected direction until the fuel ran out, then it fell and exploded. The V2 was a ballistic missile with a guidance system which operated during the boost phase. —Preceding unsigned comment added by Edison (talk •

contribs) 05:05, 3 October 2007 (UTC)

Come on, the very 1st paragraph of the V1 article contradicts precisely what you are saying. It was NOT simply an unmanned airplane, it was the 1st guided missile as it did have a dedicated albeit rudimentary guidance mechanism. The engine cutting out for lack of fuel was a design flaw and was rectified, the control mechanism caused a powered dive onto the selected target area, it was not simply a "run out of fuel" process. Vespine 05:47, 3 October 2007 (UTC)

My mother was living in London throughout the time of the V1 attacks (and twice came close to being a victim of them). She told me many, many times that her most vivid memory of the V1 (she calls them 'doodlebugs') was that the distinctive sound of their pulse-jet engines going overhead was actually rather comforting because it was only when the engine stopped that the weapon would glide down and explode. She told me this often and explained the terror that everyone felt when the engine sound cut off and there was that awful silence that would end in an explosion - I simply do not believe that they were ever powered into the ground. They may not have run out of fuel - but the engine was definitely not running when the things actually smacked into the ground. SteveBaker 12:50, 3 October 2007 (UTC)

There are details on it in the article. The early ones did not have powered dives but later ones did. And they certainly did not just run out of fuel—they had their distance "programmed" into them and that would make it dive at a steep angle. I mean, we all could just talk about stuff without checking, but it seems so easy to just check, right?)--24.147.86.187 13:10, 3 October 2007 (UTC)

While I also first thought of the V1, as the first one I've found that there already were some before the V1, but I have no idea if one of these is considered the first:

• The US Navy's N-9 Curtis-Sperry Flying Bomb, might not even be considered a missile although NASA states it to be the "Navy's first guided misile effort" (1917)
• The German A3, test rocket with inertial guidance (1937)

As I've said, I've already consulted a few sources, but none that claims to describe the first. - Dammit 10:37, 3 October 2007 (UTC)

If it has to, like, work, I'm pretty sure the Henschel was the first, unless you count the falcon with its biological navigation, acquisition, and terminal homing. --Milkbreath 16:14, 3 October 2007 (UTC)

The dictionary definition of a "missile" is "something that is thrown." A V2 clearly is a missile. It is loose terminology to call any "cruise missile" a missile, when they are sustained in flight by their engine, like the V1. The V1 was a pilotless jet, but it also had a kamikaze style piloted version which the Germans may not have actually deployed. If a WW2 B17 bomber had an autopilot to fly it as an unmanned drone into a populated area of Germany, would that have made it a "guided missile?" I think not. Sure the V1 is a guided missile, like a whale is a fish. Edison 04:24, 4 October 2007 (UTC)

Yeah but a V1 weighs a lot less than whale, doesnt it? —Preceding unsigned comment added by 88.109.121.209 (talk) 20:06, 5 October 2007 (UTC)

"Missile" = "something that is thrown." Hmm... okay, the guidance method for the first guided missile would be tugging on the rope.  :-) 152.16.59.190 08:51, 6 October 2007 (UTC)

joints in the human body

What is a joint in the cranium? —Preceding unsigned comment added by 68.248.145.158 (talk) 01:28, 3 October 2007 (UTC)

From Human skull: "Except for the mandible, all of the bones of the skull are joined together by sutures, synarthrodial (immovable) joints formed by bony ossification, with Sharpey's fibres permitting some flexibility." The term you're probably looking for is suture. --Ybbor^Talk 02:04, 3 October 2007 (UTC)

Household electroplating

I have some small objects that I would like to coat in copper. They are very small, and I believe they are zinc. What would be an effective way to plate them? HYENASTE 02:03, 3 October 2007 (UTC)

Spray the surface with small balls of copper, when the balls hit they heat up and melt forming a thin layer.

In theory, just stick them in a copper sulfate solution. In practice, that will produce a mess of little flakes or feathers, which will be oxidized, so it will be reddish brown and not shiny. If you want a nice and even, permanent, shiny coating, it will take a lot more effort. This classroom lab manual seems reasonable. —Keenan Pepper 03:02, 3 October 2007 (UTC)

Thanks for providing an easy setup. I assume a lantern battery and some wire will work for electrodes. Now, where do I find sulphuric acid, soda lye, and copper (II) sulphate? HYENASTE 01:56, 4 October 2007 (UTC)

Copper sulphate can be found in garden supply stores - it's an old-fashioned herbicide, fungicide and pesticide. I believe tropical fish fanatics use the stuff too - so you could try a pet store if you don't need much of the stuff. If you only need rough-and-ready plating, you can skip the acid and lye. "Soda Lye" is an old-fashioned name for Sodium Hydroxide - it's also called "caustic soda". I've seen it in swimming pool supply stores. You might maybe find it sold as a drain cleaner - but probably it would be mixed with a bunch of other junk. Sulphuric acid used to be easily available for topping up car batteries - but with the advent of sealed-for-life batteries, it may be hard to find. Maybe a car parts store might stock it...I suppose you could get some out of an old car battery - but it's about 30% concentrated in a car battery - so please be VERY careful! Wear gloves, mask, goggles...also, remember - always add acid to water - NEVER add water to acid. SteveBaker 02:19, 4 October 2007 (UTC)

Why so much effort? There's many simpler ways. Here's one that I've personally used. It recommended for home plating enthusiasts by a professional metalworker on finishing.com (an answers forum for the industry).

• Strip the insulation from about 2 feet of copper wire. Clean with toothpaste and a sponge or brush. Coil this up and place in a beaker or bowl. Wear gloves so you don't recontaminate the wire with oil from your fingers.
• Add 100 cc of white vinegar
• Add 1 heaping teaspoon of salt or preferably baking soda. (baking soda is safer, as using salt will produce chlorine gas)
• Add 3-6 cc of ethylene glycol antifreeze, if you have it. It'll still work without.
• Use a spare copper coin or piece of copper wire for a temporary cathode. This is to dissolve enough copper into solution so it can be available for plating. The temporary cathode also keeps you from dirtying the item you want to plate.
• Give the temporary cathode a quick rinse with alcohol and water to remove surface dirt & oil.
• Next, rig a 1.5 volt battery, optionally with a 30 to 200 ohm resistor in series.
• Attach the positive terminal to the anode (your copper wire).
• Attach the negative terminal to the cathode (the temporary copper object).
• If using alligator clips, make sure they grip the very edge. The less space covered, the better.
• Electrolyze the plating solution for 10-15 minutes.
• Replace your original cathode with the item you want to plate. A faint copper color should appear after 60-120 seconds. Occasionally jiggle the cathode a bit during plating.
• Move the clip around the coin a few times while plating to plate the bare spots where the clip was.

Plating brightness, depth and coverage will steadily improve over 20-90 minutes. You can plate pieces for longer periods to get a thicker plate. The color will eventually turn black after plating more than an hour or so. You can wipe this off with a damp cloth, or gently polish to an antique copper finish using toothpaste when you finish. This method of plating will produce a reasonably durable and attractive, but not quite as good as a pro job. Simple as that, and no lye or sulfuric acid needed. Kel - Ex-web.god 02:44, 4 October 2007 (UTC)

Hominin evolution

What is the most recent common ancestor of humans and bonobos? Would it be Australopithecus, or not necessarily?--Sonjaaa 02:30, 3 October 2007 (UTC)

I've only seen the term "Australopithecus" applied to bipedal Hominina. See: Image:Hominintree4.gif. According to Hominini, "both Orrorin and Sahelanthropus existed around the time of the split, and so may be ancestral to both humans and chimpanzees". --JWSchmidt 04:03, 3 October 2007 (UTC)

Building 140 decibel or higher system at 25KHZ (ultrasonic)

I'm wanting to build a 140 decibel or higher system at 25KHZ (ultrasonic). Amazing1.com has something like it, but it's huge. I'm looking for something that'll do it but be really tiny. Anyone have any ideas where I can start? William Ortiz 03:33, 3 October 2007 (UTC)

140dB is a horribly high noise level, which could harm the listener. What is the goal? Deafening mice? Edison 04:50, 3 October 2007 (UTC)

Driving certain animals away. I have something at 130DB and in the most obvious example, birds will still hang out all the time 20 centimeters (less than a foot) away so clearly more decibels are needed. William Ortiz 05:44, 3 October 2007 (UTC)

This seems like a really bad idea - 25kHz isn't much above the level of human hearing (lots of people can hear 20kHz - and young people may hear 22kHz and higher) - and 130dB is quite capable of damaging your ears - 140dB is above the pain threshold! I would certainly not want to be around this thing when it's turned on. If you really need such high amplitudes you should certainly be using a higher frequency to be really sure that humans aren't going to be harmed. Are you even sure that the species of bird you are trying to repel can hear 25kHz? If they could, there is no doubt that 130dB would be enough to scare them off. SteveBaker 12:36, 3 October 2007 (UTC)

Look into hydrophones. These are bidirectional transducers (speakers AND microphones) and are most often used for underwater applications. Next you'll need a signal generator (any standard electronics lab will have a function generator suitable for 25 kHz, or you can build your own oscillator). Finally, you need a power amplifier of a considerable size (unfortunately, there are physical limitations on power densities, and 140 dB is a lot of power). Also, it is more difficult to miniaturize components for such low frequencies (in the electromagnetic spectrum sense). Are you building a sonar or are you trying to make a sonic weapon? Please do not use the reference desk for destructive purposes. Nimur 16:50, 3 October 2007 (UTC)

Reaction to frankincense?

Whenever I smell frankincense resin (in essential oil blends), especially if I am exposed to the scent for a longer period of time, I get a dry, scratchy feeling in the back of my throat. It's like a need to cough that is not satisfied by coughing. It is slightly irritating but doesn't feel like a serious or life-threatening reaction; it never occurred to me before to wonder what it was. I know I can't ask for medical advice here, and I'm sure that my doctor would only tell me to stop exposing myself to frankincense, which I've already figured out. I am really more curious about whether anyone else experiences the same thing, or whether there is a name for that symptom. --Grace 05:31, 3 October 2007 (UTC)

It's possible you are slightly allergic to it, or something else in the oil. Stick go gold and myrrh. Lanfear's Bane 09:42, 3 October 2007 (UTC)

Perhaps you went to too many requiem masses as a kid, and developed a sub-conscious aversion to the stuff?

Atlant 12:05, 3 October 2007 (UTC)

It's the sort of thing that's definitely worth asking a doctor about, as they are going to know about this sort of thing. They might have rather more to tell you than just avoiding frankincense, which may not always be possible; since nobody with medical training will answer this question in this sort of forum, it's really rather hard to tell. On another note, I tend to find many people's throats are irritated by various incenses. —Preceding unsigned comment added by 79.65.119.193 (talk) 22:51, 3 October 2007 (UTC)

Couple of Questions on Acids

pH of HCl, Citric and Acetic Acid

I've read over their articles, but I only have a basic understanding of chemistry so I don't get the kP_a1 things, is someone able to give me the pH and % dissociation of hydrogen molecules of:

• HCl
• Acetic acid (CH₃COOH)
• Citric acid

under standard conditions. Thankyou

Have you taken a look at Acid dissociation constant yet. The first two are monoprotic acids, whereas citric acid is triprotic. Graeme Bartlett 12:55, 3 October 2007 (UTC)

Acidity of Salts

I'm sort of having a little bit of trouble understanding this, so would someone be able to tell me if this is correct:

Some salts are acidic/basic as their ions are derrived from weak bases/acids. They can undergo a hydrolysis reaction with water to reform the original base/acid

For example consider ammonia chloride (NH₄Cl). When it dissolves it dissociates to form NH₄⁺ and Cl^-. The chloride is the conjugate base of a strong acid (HCl), and hence is neutral and will not react with water. The ammonia is the conjugate acid of a weak base (NH₃) and hence will react with water such that NH₄⁺ + H₂O -> NH₃ + H₃⁺. Hence it is an acidic salt derrived from a weak base.

Similarly consider sodium acetate (NaCH₃COO^2-). When it dissolves it dissociates to form Na^- and CH₃COO^-. The sodium ion is derrived from a strong base and hence is neutral and will not react with water. The acetate ion is the conjugate base of a weak acid, and hence will react with water to reform the original acid, such that CH₃COO^- + H₂O -> CH₃COOH + OH^-. Hence it is a basic salt derrived from a weak acid.

On the other hand, consider sodium chloride (NaCl). When it dissolves it dissociates to form Na⁺ and Cl^-. The sodium ion is derrived from a strong base (NaOH), and hence is neutral and won't react with the water. Similarly the chloride ion is derrived from a strong acid (HCl) and hence is neutral and won't react with the water. Therefore it is a neutral salt derrived from a strong base and a strong acid.

That's the pinnacle of my understanding so far, I just have three big biffs with it

• Why don't the ions from strong acids/bases react with water to reform the original acid/base (someone said this was something to do with the conjugate of a strong thing being weak and vice versa but I'm not sure)

The ions such as Cl^- does not react much with water, and the same with Na⁺, so their presence does not alter the pH. You need something that will react with H⁺ or OH^- to change pH. So if you dissolved a salt of a strong acid and a strong base in the water you just get the ions from the salt hydrated in solution. Any H⁺ or OH^- reacts with each other to leave a very small remainder, with the product of their concentrations being about 10^-14. Graeme Bartlett 12:41, 3 October 2007 (UTC)

• What about Fe(OH)₂, it's a weak base but then how does the ionic component of the salt derrived from it act as an acid in water (it has no proton to give up)? This sorta follows for a lot of other weak bases.

The weak acid is actually Fe²⁺ it reacts with water taking away OH^- to form FeOH⁺, and a H⁺ ion in solution. Graeme Bartlett 12:41, 3 October 2007 (UTC)

• Is the reaction between HCl and NH₃ even a proper neutralisation reaction? I thought the formula was acid + base = salt + water, but there's no water involved

Yes - water does not have to be formed. A base can also work by removing H⁺ instead of supplying OH^-. Graeme Bartlett 12:41, 3 October 2007 (UTC)

I have a test on this coming up, and this is the only thing I don't understand. If the question was say, explain the acidic, basic and neutral nature of salts do you think my explanation would be adequate, and if not what can I add in to complete it?

Thankyou very much in advance 124.183.13.48 09:29, 3 October 2007 (UTC)

Balancing equations

--Mostargue 18:05, 3 October 2007 (UTC)

Hi all, thanks in advance.

1. When the question below is balanced correctly, what is the co-efficient for O₂

C₄H₁₀ + O₂→ CO₂ + H₂0

Is the answer:

A: 9

B: 13

C: 18

D: 24

2. Consider the composition of the particle, W, X, Y and Z below.

W: Protons: 11, Neutrons: 12, Electons: 10

X: protons: 12, Neutrons: 12, Electrons: 12

Y: Protons: 12, Neutrons: 13, Electrons: 12

Z: Protons: 13, Neutrons: 14, Electrons: 10

Which two particles are isotopes of the same element.

Once again thanks guys. --Andrew Hadland 2007 07:55, 3 October 2007 (UTC)

1) b - 2C₄H₁₀ + 13O₂→ 8CO₂ + 10H₂0

2) W and Y, they both contain the same number of protons, hence have the same atomic number hence are the same element —Preceding unsigned comment added by 121.217.13.71 (talk) 08:02, 3 October 2007 (UTC)

This looks an awful lot like homework - I don't think we should be answering with exact answers - broad brush explanations please! SteveBaker 12:26, 3 October 2007 (UTC)

And multiple choice, at that! Nimur 16:46, 3 October 2007 (UTC)

For the first problem, put coefficients in front of the CO₂ and H₂0 first, making sure that each side of the equation has the same number of carbon and hydrogen atoms. Once you have the carbon and hydrogen balanced then you move on to the oxygen, count the number of O atoms taking account of the coefficients you already added. For the second question, the article on Isotopes answers your question in the first paragraph. Man It's So Loud In Here 16:43, 3 October 2007 (UTC)

Another way to do the first one is to put coefficients in front of the substances with Hydrogen in them, because on each side there is exactly one substance containing hydrogen.--Mostargue 18:05, 3 October 2007 (UTC)

Electron arrangement

Sorry for the sloppy formatting, the 16 and the eight are supposed to be directly above and underneath each other. What is the electron arrangement of the ion ^16₈O2-. Is it:

A: 2, 6

B: 2, 8

C: 2, 8, 6

D: 2, 8, 8

Thanks --Hadseys 08:42, 3 October 2007 (UTC)

Uh, you've asked for the electron configuration of an ion of oxygen, and then the electron configuration for the diatomic oxygen gas molecule. What I think you're after is the electron configuration of a single oxygen atom which is 2.6 or 1s²2s²2p⁴ (the easy way to see this is that the number of protons in oxygen is 8, and 2+6=8 since the charge is (I think) neutral). So the answer is a UNLESS you are after the electron configuration of the O^2- ion which would be 2,8 which would be b. 124.183.13.48 09:06, 3 October 2007 (UTC) Nevermind, I misread the question (it should be O^2-, not O_2-). In this case the atom has a charge of 2-, so it has two more electrons than protons (10 electrons). The only answer which fits this is b, 2.8 124.183.13.48 09:09, 3 October 2007 (UTC)

HCl vapor from Na2CO3 + H2SO4?!

A friend's sister was working on her upcoming science project, part of which required producing (I think) sodium sulfate by neutralizing sodium carbonate with 97% sulfuric acid. She didn't have any Na2CO3 available, so made some with Arm & Hammer baking soda, which, according to their literature is 99.995% pure. She did this by heating the NaHCO3 at ~200 °C until it (presumably) thoroughly dehydrated into Na2CO3, which she then let cool. However, when she later pipetted H2SO4 onto the Na2CO3, she noticed a bit of white, sharp-smelling fumes being produced which she said smelled "just like HCl fumes". She didn't think this should be possible, so she freaked out and dumped the experiment. She wants to know what this vapor was. She's still too embarrassed about making such a huge mess in the lab that she won't ask her chem teacher. :) My guess was that Arm & Hammer's purity claims aren't as accurate as they'd like to believe, and the product contains small amounts of one or more chloride salts -which would explain HCl vapor. But I could be wrong, and I'm pretty curious myself about what could have caused this. Any ideas? Thanks in advance. Kel - Ex-web.god 08:53, 3 October 2007 (UTC)

Is it possible that she used hydrochloric acid instead of sulphuric? Or that the acid was labeled incorrectly? Lanfear's Bane 09:36, 3 October 2007 (UTC)

Well she would have produced CO₂ gas and some spray consisting of sulphuric acid. A fair bit of heat would be released also. It is quite likely that this would smell like hydrochloric acid. 97% sulphuric acid is pretty nasty, so it is not a good idea to sniff it. One test is to see if it really is sulphuric is if it carbonizes sugar. HCl would not do this. Food products should be quite pure. But I could imagine that NaCl could be a contaminant. Graeme Bartlett 12:30, 3 October 2007 (UTC)

Well, I've seen the lab, and it's definitely reagent-grade sulfuric acid (still in the original dispenser from the supplier). To further clarify, she noticed the fumes from 2-3 feet away, so she didn't exactly stuff her nose into her Erlenmeyer flask. Also, the vapor was wispy and white, just like fuming HCl. It wasn't a spray. Again, I may be wrong, but I'd assume a mist of H2SO4 being released from bubbles of bursting CO2 wouldn't form a visible wispy strand that rises out of the flask. :)

Also, assuming she did somehow accidentally use HCl, (see above, she didn't.) That still doesn't explain the fumes, as if I'm not mistaken: 2HCl + Na2CO3 ---> CO2 +H2O +2NaCl. I also thought there might have been a little carbonic acid that hadn't completely broken down yet, but she says an indicator strip placed at the top of the flask showed a pH of around 1, which that acid wouldn't do. So, any other ideas? Kel - Ex-web.god 21:28, 3 October 2007 (UTC)

• I'm rather nonplussed about her being ashamed to tell her teacher. I think a student with her sort of curiosity about an unexpected result would delight most teachers. As they say, the productive moment in science is not "eureka!", but "that's funny ...". --Sean 21:58, 3 October 2007 (UTC)

I agree, but it's a teenage girl, so what do you expect? :) She apparently made a pretty big mess when she knocked over her entire apparatus. Kel - Ex-web.god 23:50, 3 October 2007 (UTC)

Wonder if she got exothermic and vaporization enough to create substantial H₂SO₄ vapor. Lots of acids smell similarly "sharp" to me, not sure what specific part of "the HCl smell" was noticed. That's a pretty hydroscopic acid, maybe the visible vapor trail was from it absorbing humidity? Or maybe she drove off some SO₃, which would be another sharp/acid-smelling thing, and would maybe also leave a visible vapor trail as it absorbed humidity to become or H₂SO₄ droplets (a la "fuming sulfuric acid"). DMacks 01:56, 4 October 2007 (UTC)

Possibly, but according to her, she had only combined ~100mg of sodium carbonate and 5-6 drops of sulfuric acid when she noticed the fumes. As for the "HCL smell", I can tell a slight difference between HCl and SO₃. Not sure if she can, but that was what seemed the most familiar to her, I guess. Given that she was freaked out about getting an unexpected result, it's possible she was mistaken, hence the question. :) Kel - Ex-web.god 02:49, 4 October 2007 (UTC)

Basically you don't mix 97& sulphuric acid with any base - it is too concentrated and will give out so much it it will volatalise. 10% acid would be safer - usually at school all experiments need to be supervised - for safety - in most places it's the law - however this dosen't seem to have been the case here - this was a dangerous and stupid experiment.87.102.94.194 15:09, 4 October 2007 (UTC)

That answer was incredibly presumptuous and generally unhelpful, not to mention the part about never mixing concentrated acid with any base. I guess the all those college labs that required I do exactly that (on countless occasions) was also stupid? I think not. For the record, the experiment she attempted was taken directly from her textbook, was pre-approved by her teacher, used less than 10 drops of acid, and of course there was an adult supervisor present. She also wore appropriate lab gear. No, stupid are those kids that somehow managed to steal 70% HNO3 and used it to dissolve pennies in the bathroom sink while standing around gloveless in short-sleeve shirts giggling and poking their fingers in that cool cloud of brown smoke. Kel - Ex-web.god 00:59, 5 October 2007 (UTC)

Where exactly does a text book say to mix conc acid with base - maybe america hey - fuck you I cant wait for the next fucking 9/1183.100.250.154 13:14, 5 October 2007 (UTC)

Um, how about any reaction where excess water isn't wanted? Normally, I'd remind you of the minuscule scale of the experiment in an attempt to appeal to your sense of reason, but your last post proves that would be a colossal waste of time. If you can't be helpful, kindly spew your venom elsewhere. Not only does it discourage potentially useful and rational responses, it gives those people with a rational anti-American sentiment a bad name. Kel - Ex-web.god 20:32, 5 October 2007 (UTC)

Marfan Syndrome

How is Marfan Syndrome diagnosed? Is it done solely by physical examination, or is there more to it than that? --MKnight9989 12:09, 3 October 2007 (UTC)

Our article on Marfan syndrome says There are no signs or symptoms that are unique to Marfan syndrome. It is usually a single apparent sign or symptom that leads doctors to look for others and eventually to diagnose the syndrome. So evidently each symptom has to be tested for separately since no single test would be conclusive. From what the article describes, some of the symptoms might require X-ray or MRI exams - there is also an eye test. Since the disease is genetic and the defective gene is dominant, a detailed family history might be a useful aid to diagnosis. SteveBaker 12:23, 3 October 2007 (UTC)

The British Medical Association Complete Family Health Encyclopedia, 2nd ed., 1995, states "There are no specific diagnostic tests for Marfan's syndrome. Echocardiography may be used to investigate heart abnormalities, and an eye exam may be performed." DuncanHill 13:34, 3 October 2007 (UTC)

• I can tell you from experience that many American doctors are eager to diagnose Marfan's when a patient with the usual connective tissue symptoms also has a high palate. In the case of one hapless patient that I know of, though, each of the doctors ultimately found that the diagnosis was non-productive. --M@rēino 17:53, 5 October 2007 (UTC)

Possible to create an aircraft supported by magnetic levitation alone?

Is it possible? 64.236.121.129 15:59, 3 October 2007 (UTC)

Did you read Magnetic levitation? An airplane flies anywhere- magnetic levitation requires that you are directly above the other part of the system. Also, the distances between the objects are typically quite small, whereas an airplane flies pretty high. Friday (talk) 16:02, 3 October 2007 (UTC)

I guess I should have clarified the idea, and yes I did read it obviously, but I don't think you understand what I'm asking. If the aircraft is generating the magnetic field, can it repel the ground with it. 64.236.121.129 16:58, 3 October 2007 (UTC)

In general, the ground is uncharged/unpolarised, and thus won't be affected by a magnetic field. Also, given the relative masses of the Earth and the aircraft, it'd be a tad silly to say that the Earth is being repelled. GeeJo ^(t)⁄_(c) • 17:23, 3 October 2007 (UTC)

The ground is still diamagnetic I believe. I guess this question is directed towards people who are familar with how things can be levitated with diamagnetism. With sufficient energy in the magnetic field generated (by the aircraft), is it possible? Btw, as for your last point, the object of less mass would be the one which is "repelled", in other words, ideally the aircraft would be floating due to it's magnetic repullsion from the ground. 64.236.121.129 17:35, 3 October 2007 (UTC)

Only if the ground was also made of something magnetic. But the problem with using magnetism (Magnetic levitation) is that the force it exerts drops off with the square of the range. So if there was enough force to lift to the aircraft a foot off the ground, it would take a magnet 100 million times more powerful to fly at 10,000 feet. (10,000 squared is 100 million) If you think of the size of magnet you'd need to lift an entire airplane...then imagine one 100,000,000 times bigger! We do use magnetic levitation for trains (Maglev train) - they move on special tracks (unlike a plane - which you'd like to fly everywhere in!) - and they only hover a 15 millimeters above the track! (Remember - the SQUARE of the range!) —Preceding unsigned comment added by SteveBaker (talk • contribs) 17:26, 3 October 2007 (UTC)

Technically you could run a very powerful current through an aircraft, parallel to the Earth's surface and perpendicular to its magnetic field to generate magnetic lift. However, you would need current in one direction to not be going through the aircraft, or else this would generate a counterforce that would exactly cancel out your lift. You could theoretically accomplish this by ionizing a region of air outside the aircraft and sending the current through that (and have the aircraft appropriately insulated so that the current only goes through that. However, needing to constantly ionize the air around the aircraft, as well as needing some rediculous current to levitate on the Earth's oh so weak magnetic field would be quite energy consuming. Disclaimer: This idea I have just described is certifiably rediculous and will probably never work except as an amusement. Someguy1221 17:40, 3 October 2007 (UTC)

Yeah but then you might as well build an Ionocraft - at least those things actually work. SteveBaker 19:19, 3 October 2007 (UTC)

• My magnetic hovercraft is full of electric eels. --M@rēino 17:55, 5 October 2007 (UTC)

• A version of a maglev train could be created with wings, however, to create something similar to a ground effects airplane. This would, though, mean it could only travel a few feet above the ground and only on top of energized tracks. Such a vehicle might be useful for low cost (lower than normal aircraft), high speed transport, along a few busy routes, over flat terrain. StuRat 18:10, 5 October 2007 (UTC)

• The earth's magnetic field is about .06milliTesla. At various locations, the field lines go vertically downward, vertically upward, or parallel to the ground. If our magnetic aeronaut had a magnetic monpole, how powerful would it have to be to support, say, 1000 kilograms at a point where the field lines were vertical? If magnetic monopoles do not exist (no one has ever found one), then aren't there stable configuration of normal magnets or solenoids producing a magnetic field which could in principle hover in a magnetic field with vertical field lines, and with field lines horizontal or at any arbitrary intermediate angle? (Talking theory, not practicality here). Edison 18:32, 5 October 2007 (UTC)

Human Spine

Do all the bones move?

What is the function of the discs?

In which area of the spine do most people get back ache?

This is not for homework, as some of you might think. - 81.158.75.136 16:05, 3 October 2007 (UTC)

Nothing triggers my "homework" RADAR like an assertion that questions are "not homework." In any case, here's some links which will help:

• Vertebral column
• Intervertebral disc
• Back pain

Many of the bones are fused; so these bones do not articulate with respect to each other.

The discs are part of the joint, and serve as a soft cartilaginous material to allow for slight movement.

Of course you can have an ache in any part of your back, depending on the source of the pain. Poor posture may result in lumbar pain. Nervous system problems, such as a pinched nerve, can be very serious. If you are seeking medical advice, see a doctor.

Hope this helps, Nimur 16:43, 3 October 2007 (UTC)

Quantum physics (I think). Confused. Deuterium is a wave?

According to deuterium, deuterium is a boson and according to boson, this makes it a "force carrier" particle like a photon? Does this mean that deuterium is as intangible as light? --Seans Potato Business 16:54, 3 October 2007 (UTC)

Deuterium is a "composite boson" (it's a boson because its spin is an integer: +1), but it acts as a boson only at long distances. In high energy interactions it acts as an assemble of two fermions (a proton and a neutron). Thus it is in a sense as "solid" as any fermion. See under the heading "Composite bosons" in our article boson.--Eriastrum 17:17, 3 October 2007 (UTC)

It's an isotope of hydrogen - one proton, one neutron. In bulk, it's a gas...just like hydrogen - but heavier. SteveBaker 17:18, 3 October 2007 (UTC)

However, at very low temperatures composite bosons can do wierd things, or yet wierder things. Someguy1221 17:34, 3 October 2007 (UTC)

All matter have waves. See matter wave.--Mostargue 17:36, 3 October 2007 (UTC) Oh dear, Wikipedia has no article on that??--Mostargue 17:38, 3 October 2007 (UTC)

There, redirected to de Broglie hypothesis.--Mostargue 17:40, 3 October 2007 (UTC)

Confirm vs define

Mendeleev's_predicted_elements says, in the last paragraph, that hydrogen was confirmed to be the first element. I don't understand what that means. Wouldn't it be better to say that hydrogen was defined to be the first element? How has the definition of "element" changed over time? Of course, the classical elements are no longer considered elements, but I mean from Mendeleev to now.--Mostargue 18:24, 3 October 2007 (UTC)

Mendeleev sorted elements in terms of weight. Therefore, to say that hydrogen is the "first" element is to say that it is the lightest, which can certainly be confirmed. The modern periodic table sorts elements by atomic number, and it can again be confirmed that hydrogen has the lowest atomic number (one), making it first. So, what we are truly saying here is that hydrogen can be scientifically "confirmed" to be the first element, within the confines of a particular definition of "element." Someguy1221 18:30, 3 October 2007 (UTC)

Since Mendeleevs time we have come to understand that the atom is composed of electrons, neutrons and protons, with the number of protons being equal to the number of electrons and corresponding to the ordering of the periodic table. By ionizing hydrogen, one can find that the remaining core has positive charge +1 and it must therefore be the first element. Mendeleev I believe, to say that Hydrogen was the lightest, may have needed the concept of the Avogadro constant. You can't say that element A is heavier than element B just because a litre of A is heavier than a litre of B, you need to know how many atoms goes into a litre of each element. This was easiest with gases, then I believe other regularities in the table allow you to sort the non-gas elements in the right order. EverGreg 20:00, 8 October 2007 (UTC)

Well I've heard of a single Neutron be called the element neutronium, with atomic number zero.--Mostargue 19:02, 3 October 2007 (UTC)

An isotope of which would be neutronium⁰ I suppose? SteveBaker 19:24, 3 October 2007 (UTC)

I've also heard of positronium, which only has an electron and a positron. — Daniel 22:17, 3 October 2007 (UTC)

speed

Does a car speedometer measure speed,velocity or both? —Preceding unsigned comment added by Ekumak (talk • contribs) 19:21, 3 October 2007 (UTC)

Only speed. Velocity is a measure of speed AND direction. So "20mph, heading North" is a velocity, "20mph" by itself is a speed. SteveBaker 19:26, 3 October 2007 (UTC)

Though I wouldn't be surprised if there were a dashboard out there with a built-in compass. GeeJo ^(t)⁄_(c) • 20:40, 3 October 2007 (UTC)

Maybe if it had an inclinometer too... SteveBaker 18:26, 4 October 2007 (UTC)

The surface of a sphere can be treated as a two-dimensional geometry, in which case a compass and speed indicator are enough to give you the velocity. --Carnildo 21:56, 4 October 2007 (UTC)

Well, this "velocity is a vector; speed is a scalar" stuff is convenient for high school physics teachers, but it doesn't necessarily reflect real-world usage. Plenty of times "velocity" is used to mean just the magnitude, and this usage isn't wrong. Similar considerations apply to "weight" and "mass" -- historically, there are lots of contexts in which "weight" means "quantity of matter" rather than "gravitational force". When teaching the subject to students who aren't used to making the distinction, it no doubt helps to have different words, even if you have to be a bit arbitrary about which word to use for which concept. Unfortunately sometimes the students don't realize that the particular semantic assignments made to these terms in a scholastic context don't necessarily apply outside that context. --Trovatore 21:20, 3 October 2007 (UTC)

Well, yes, but the questioner specifically asked about the two as separate terms, so e is clearly aware that there's a difference between the two. It'd be silly to pretend there's another difference between them other than the scalar/vector "stuff" when answering. GeeJo ^(t)⁄_(c) • 22:15, 3 October 2007 (UTC)

My point was precisely that, depending on context, there may not be a difference between the two. Some people have so rigidly internalized what they were taught in freshman physics that they're not aware of that. --Trovatore 22:29, 3 October 2007 (UTC)

Nonsense - there is always a difference between the two words. In some contexts the difference may not matter - but that's not the same thing. A lot of people mis-use these two words - but their meanings are clear and quite distinct. If someone misuses the terms - then please correct them - and if (as in this case) someone asks about the distinction - then we should explain it clearly and without cluttering up the explanation with this kind of misdirection. Some serious errors can be made by people misusing words - so let's not condone it. When we say "The velocity of an object remains constant unless an external force is applied to it" - we mean that neither the speed NOR the direction of motion changed. When we say that "an object cannot exceed the speed of light" - we mean that the direction doesn't matter. It's an exceedingly precise distinction and you make life harder by screwing the terms up. Ditto mass and weight. They are as different as "time" and "thyme". SteveBaker 02:01, 4 October 2007 (UTC)

No, Steve, you're making the mistake I outlined; over-rigidly internalizing a distinction that someone found convenient to make. "Velocity" is simply the Latinate word for "speed" (must be late Latin; I think classical Latin for "fast" is celerus, not velox). Somewhere along the line someone got the bright idea to use the fancier word distinctively for the vector quantity, and that's fine in context, but it's not wrong not to.

For the mass/weight thing, do a "Google Groups" search on Garry Vass's Gene Nygaard's postings on the subject in alt.usage.english; he makes the point quite convincingly. --Trovatore 02:24, 4 October 2007 (UTC)

The word "velocity" has two meanings- a more precise one, used within certain fields (science and engineering) and also a less precise common meaning. When in doubt, consult a dictionary- mine shows both meanings, so I'd say this means they're both considered correct. Yes, unfortunate confusion can happen (the word "theory" is notorious for this), but I don't see that it's terribly bad in this case. If someone uses "velocity" to mean "speed" in physic class, yes they should be corrected, but I don't think it's fair to say the usage is always wrong. Friday (talk) 02:31, 4 October 2007 (UTC)

Exactly -- in physics class, not in physics generally. In class, the assignment speed/scalar, velocity/vector, is observed scrupulously, not at all for linguistic reasons, but as an aid to help students remember that the scalar quantity and the vector quantity are not the same thing (whatever you call them). Once you're past the point where you might confuse the two concepts, there's no longer any great necessity to follow this rather arbitrary naming convention (how would you do a similar thing in Italian, where there's only one word, velocità?). I imagine you wouldn't have to look very hard to find plenty of formal research papers in physics using the word "velocity" for the scalar quantity -- it's hard to imagine a context where this would result in confusion among trained physicists; it will generally be obvious whether the scalar or the vector is intended. --Trovatore 03:09, 4 October 2007 (UTC)

From our Muzzle velocity article: A gun's muzzle velocity is the speed at which the projectile leaves the muzzle ... (emphasis added) - hydnjo talk 03:49, 4 October 2007 (UTC)

But surely that is a vector? The muzzle velocity is the speed in the direction out of the muzzle. The distinction still seems apparent :) I'm not saying people don't use one for the other, just that this is perhaps not an example of it. 79.65.119.193 10:01, 4 October 2007 (UTC)

Maybe the distinction seems apparent because you just happen to know that when a bullet leaves a gun, it travels in the same direction as the muzzle. And, I must say, that would seem pretty obvious to most people, I imagine. I think the purpose of that definition was to talk about the speed/velocity of the bullet without regard to whatever direction it happens to be travelling in relative to the muzzle. Which would explain why the direction isn't referred to. -- JackofOz 10:24, 4 October 2007 (UTC)

Toe Nail

What might make a human toe nail discolor, like to an ugly brown or black? I was assuming that the toe nail was "dead" -- but, on second thought, isn't every toe nail already "dead" (that is, some form of dead skin)? If a toe nail were to become dead/discolored, would it just remain there or would it fall off? And, what type of doctor handles this? Would it be a dermotologist ... or something else? Thanks. (Joseph A. Spadaro 19:41, 3 October 2007 (UTC))

We aren't allowed to offer medical diagnoses. See a doctor...a podiatrist perhaps. SteveBaker 19:48, 3 October 2007 (UTC)

He's asking a question. What makes a toe nail discolor. That's not a medical diagnoses. 64.236.121.129 20:42, 3 October 2007 (UTC)

It can go black when there is blood underneath it. This could happen if a bruise happens to the nail - eg hit with a hammer. If the nail bed is damaged then a new nail may grow out. Eventually the black will disappear. The nail itself is not living cells, but underneath the skin is alive. Graeme Bartlett 21:06, 3 October 2007 (UTC)

I agree. It's a question, not a diagnosis. With that said: The toenail is "dead", but there is a living layer of cells underneath called the nail bed. The most common causes are damage to the nail bed, which can occur from dropping something heavy on your toe or kicking something (or someone!). Also very common are dermatophytic fungal infections of the nail bed. Minor damage from blunt-force trauma will usually heals naturally over a few weeks, however, fungal infections usually persist and may worsen over time. This can result in the nail completely falling off, and even spreading to other toes. Any licensed general/family practice doctor is able to diagnose and treat the problem. If it's a fungal infection, there are prescriptions available (Lamisil). If the problem is due to a less-common problem (skin condition, immunological problem, adverse drug reaction, diabetes, gangrene) or the toe is damaged to the extent that it requires surgery, the family doctor will usually refer the patient out to an appropriate specialist, which may be a dermatologist or even a podiatrist. Kel - Ex-web.god 21:04, 3 October 2007 (UTC)

Apropos of nothing, bruises under nails are subungual hæmatomae GeeJo ^(t)⁄_(c) • 22:00, 3 October 2007 (UTC)

• Another common source of blackened and/or falling-off nails is running marathon distances, as I can currently -- and grotesquely -- attest. --Sean 22:05, 3 October 2007 (UTC)

• Another couple causes of this are frostbite and lead poisoning. StuRat 06:23, 5 October 2007 (UTC)

Tattoos, Moles and Fat

I'm wondering whether moles can have an impact on tattoos. For instance, is it at all possible to tattoo a mole? What happens if you get a tattoo, and some time later you develop a mole where the tattoo is?

And while I'm at it, what happens to a tattoo if you get fatter/more muscular?

Thanks, 81.165.126.252 20:17, 3 October 2007 (UTC)

The Tattoo FAQ on About.com may be of some use. In short: moles, acne, and other skin blemishes while you are getting a tattoo aren't going to make the artist's job any easier, and if the mole(s) are particularly prominent, you'd probably be better off getting them removed. As for weight change, provided it's fairly slow, you should be alright. Pregnancy or other rapid changes to the area the tattoo is covering are less forgiving, though. GeeJo ^(t)⁄_(c) • 20:56, 3 October 2007 (UTC)

No reputable tattooist will tattoo over a mole because occasionally they can develop into skin cancer and a possible warning sign is changes in shape & size of the mole. Covering one with a tattoo would make it harder or impossible to spot changes in the mole. Exxolon 01:05, 4 October 2007 (UTC)

Doppler Effect

If there were two torches, one stationary and one moving towards a stationary observer, the photons from the torch moving towards the observer would have a higher frequency than the other torch. This means that they have a higher energy. Where does this energy come from? (I think I have a basic misunderstanding of the doppler effect, as applied to electromagnetism, but I couldn't decipher most of the article on the Relativistic Doppler effect ). Thanks a lot for your time.86.150.251.208 21:59, 3 October 2007 (UTC)

Before the moving torch is moving fast enough for this effect to be noticeable, the wind will blow out the flame.

But if you had something other than a torch, say a flashlight for example, then to trace where the extra energy was coming from in your frame of reference, you'd have to trace back to the battery, consider time dilation, consider the changes to the electromagnetic fields within the battery, etc. It would be a tricky accounting problem, but all the books balance in the end. Maybe someone else can break it into a manageable number of accounting steps. --Trovatore 22:42, 3 October 2007 (UTC)

A torch can mean a flash light in some parts of the world. --antilived^{T | C | G} 00:57, 4 October 2007 (UTC)

UK IP address generally means UK terms. Torch = electric torch. I hope someone with a better knowledge of relativity than me can answer this question. In my ignorance, I would assume that the energy came from the movement, or something. Hmm, that doesn't really make sense. Skittle 01:00, 4 October 2007 (UTC)

It's ordinary kinetic energy. In the rest frame of the observer, the moving torch has more kinetic energy than the stationary one, and it also loses more due to radiation pressure (it slows down more than the stationary torch accelerates backwards). —Keenan Pepper 01:10, 4 October 2007 (UTC)

Don't say I am spoiling all the fun but since Kinetic energy is half mass times velocity squared, where will you fit this extra energy in the equation? A photon has no mass and it has a specific velocity. Oh, I am falling into my own trap ... --Kushal^{Click me!} write to me 03:18, 4 October 2007 (UTC)

A photon doesn´t have rest mass, but it still has relativistic mass. But does that formula actually work in special relativity? --antilived^{T | C | G} 04:01, 4 October 2007 (UTC)

Of course the kinetic energy of the source (the flashlight, not the photons!) can be non-relativistic. This effectively provides more energy to the photons, even if the total Doppler effect is treated non-relativistically. Nimur 16:22, 4 October 2007 (UTC)

Kinetic energy is the difference between rest mass and relativistic mass. If that formula is applied to photons, the result is that they are pure kinetic energy. — Daniel 23:40, 4 October 2007 (UTC)

OK I am not good at Physics. I always thought the mass of the torch or the apeed of the torch made no impact on the kinetic energy of the <strikethrough>light particles</strikethrough> photons. What am I missing? --Kushal^{Click me!} write to me 02:53, 7 October 2007 (UTC)

normal variation sample #

I've heard more than one stats person say that you need 30 samples to be able to describe a normal variation. Why is this? How do they get 30? I think I once heard 34 too, why would this be? Thanks . —Preceding unsigned comment added by 12.217.195.89 (talk) 22:30, 3 October 2007 (UTC)

Start by reading Sample size and the links within. --Cody Pope 23:47, 3 October 2007 (UTC)

In elementary statistics (professional statisticians look away now !) 30 is traditionally given as a heuristic minimum sample size for applying the central limit theorem - see this Yahoo!Answers link. Gandalf61 08:59, 4 October 2007 (UTC)