Wikipedia:Reference desk/Archives/Science/2009 February 23

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February 23

Red Hot Ice Cube

Here is an interesting found on the internet. Since there are lots of people smarter than me here, I'd like your thoughts. It is supposedly a video of an ice cube glowing red hot due to induction heating. For now I will withhold my thoughts, since I'm not particularly familiar with inductive heating. Thanks :) --Bennybp (talk) 03:56, 23 February 2009 (UTC)

Induction heating affects metal objects - not ice. I've seen demo's of inductive kitchen ranges where someone can put their hand on the range top with it turned on - and a pot held an inch or so above the hand would still heat up. So I'm not even slightly surprised that the ice doesn't melt. However, the red glow and the flames must be coming from something ELSE inside the inductive loop. SteveBaker (talk) 04:24, 23 February 2009 (UTC)

I'm surprised the ice didn't melt - if something in the system is getting hot enough to glow bright red and flame, there should be enough heat around to melt the ice. Ice on its own wouldn't melt, but that looks like ice in contact with (or, at least, very close to) metal - the metal would be heated by induction and it would then heat the ice. --Tango (talk) 13:24, 23 February 2009 (UTC)

Ice doesn't conduct heat very well - so the surface of the block is obviously going to melt - but s-l-o-w-l-y because it's a big block. This is why it's so important to defrost your thanksgiving turkey before you cook it - even though the oven is set at hundreds of degrees the ice inside won't melt quickly enough. In this case, little or none of the induction heaters' energy will be transferred into the ice because induction cookers rely on heating up the metal pot rather than heating the food directly as a microwave oven would. So the ice obviously does melt - but (evidently) slowly enough to not be noticeable over the few seconds it takes an induction heater to get red hot in the video clip. At any rate - production of light due to heat follows a fairly simple relationship between temperature and color. For the ice to be glowing red hot, it would have to be up at several hundred degrees - which would (of course) mean that it would have to be steam. Since it's clearly still ice, it is DEFINITELY not glowing. It's simply refracting the red light from whatever is glowing beneath and off to the sides. There is nothing weird or special going on here - it's just another typical bullshit-faked-science fraud that you see on YouTube all the time. Please - everyone - IGNORE "SCIENCE" VIDEOS ON YOU-TUBE - they are almost all stupid people out to trick you and spread disinformation. SteveBaker (talk) 13:56, 23 February 2009 (UTC)

Yes, of course the ice isn't glowing red hot, but if it is that close to something that is growing red hot I would expect it to melt faster than that. That kind of bright red hot corresponds to about 1500C, if memory serves - far hotter than an oven (unless you were right up close to the heating element). Is it possible the whole thing is faked and there is just a red LED under there? --Tango (talk) 15:58, 23 February 2009 (UTC)

I think Steve is being unfair. There are lots of good and very legit physics and chemistry demonstration videos on Youtube. There is junk too, so Steve is right about keeping your sceptic hat on. Besides content, things that tip me off to potentially suspicious "science" videos are handheld camera work (versus a steady tripod mounted camera), non-lab equipment (ex: using kitchen measuring cups instead of beakers), lack of expected safety equipment such as goggles, lab coats, gloves or plexiglas shields (whatever is relevant), "at home" filming versus in lab filming, youthful age of the commentator (not a very reliable predictor), and the maturity and "scientificness" of the dialogue. There is a very real chemistry demo superficially similar in appearance only to this which is the combustion of dry ice (carbon dioxide) by magnesium. You can see it here The ice though in this "ice induction video" evidenced by the liquid around it and the transparency is most likely H₂O. If the ice itself is being heated to what the black body color suggests, then part of it should have flash boiled and there would be steam everywhere (not just a little). There may very well be some metal under the ice and the ice is put on top of it for aesthetic purposes. If that's the case it's a very poor design because it conveys the wrong idea.152.16.253.109 (talk) 22:46, 25 February 2009 (UTC)

Cheap trickery. Easy to do. I am most certain it is a metal object inside the ice, below the rim of the induction ring. Once the metal object heats up and starts to glow, the whole ice cube glows. It can take several seconds before the ice starts to melt fast enough not to be noticable, but it was on for mere seconds in this video anyway. My conclusion is it was simply modern day smoke and mirrors: camera angles and deliberate cuts.

Microwave ovens heat by induction, don't they? And they heat nonmetallic objects. Maybe the difference is a matter of frequency. There is a freuency allocation in the rf spectrum for microwave ovens.-—Preceding unsigned comment added by 98.21.104.187 (talk • contribs)

Yes, but the point is, an ice cube would not glow when heated. It would melt. Then boil. Then maybe, if the conditions were right, glow.-RunningOnBrains 14:41, 23 February 2009 (UTC)

No - microwave ovens use the dielectric effect to heat water - not induction. The dielectric effect doesn't work well on ice either - although it's highly effective on liquid water...which is why 'defrost' mode on your microwave turns the oven on and off repeatedly so it can heat the surface layer of water WITHOUT boiling it - then let that heat melt some of the ice into cold water - then it turns on again to heat that water and thereby slowly melt the ice. So no - that doesn't help the case for this crappy video (Also - where do the flames come from? Water doesn't/cannot-possibly burn!! There MUST be something else in there doing that). SteveBaker (talk) 14:55, 23 February 2009 (UTC)

I noticed the "burning" too, but thought it might just be a little bit of steam being colored by the red hot "ice." Of course, where does the steam come from? I agree that it is likely some metal in the ice. A one point, it seems like maybe the ice cracked somewhere, letting the steam out.

The demonstration might have been honest enough (showing how inductive heating can heat metal, even through ice) with some cool effect in the ice. But likely the person uploading the video misinterpreted. I agree about the science videos on YouTube - The only thing worse than the videos are the comments on science videos, but I digress --Bennybp (talk) 15:59, 23 February 2009 (UTC)

There are also videos on "Hot Ice", where a substance is added to hot water to make it freeze when poured. ~AH1^(TCU) 00:12, 24 February 2009 (UTC)

"Freeze" or "solidify"? --Tango (talk) 14:59, 24 February 2009 (UTC)

I bet by hot ice you mean the supersaturated sodium acetate solution demo seen here. There are lots of great science videos on Youtube. There are more good ones than bad ones, and half the bad ones are just poorly or wrongly explained rather than flat out fabrications. You just have to watch out for the bad ones. I have to agree with you on the comments though. The ratio of stupid to useful/intellectual comments is too high for me to tolerate. 152.16.253.109 (talk) 23:02, 25 February 2009 (UTC)

http://www.huettinger.com/en/about-us/multimedia.html <--- this. 2secs on google

Although having a metal ball in the middle of the ice cube is more plausible, could the frequency of the AC current in the inducting coil not be set to the resonant frequency of a certain electron state in the H2O molecule, exciting them more than the electrons in the hydrogen bonds that hold the lattice together? Then these electrons drop down energy levels again, releasing photons, before the electrons in the H-bonds get excited enough to start the melting process.

Oil Platforms

The platforms are structures which including one or more systems. Oil platforms are used for processing the crude oil

I've put links in your statement to help your search. Do you have a question about your homework? Julia Rossi (talk) 10:59, 23 February 2009 (UTC)

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Collapsed content not directly related to the question

(Julia: Please don't edit the OP's question - even to add links because it might imply a particular meaning of some terms that the OP did not intend...or suggest to some respondants that the OP already understood those terms or read the articles. Just place the links in your own reply. Thanks! SteveBaker (talk) 13:42, 23 February 2009 (UTC)) Thanks for your pov Steve, but I did it in good faith, after much consideration as someone who doesn't make a habit of it. It has been done by others and also seemed gentler than something like the reprimands people go in for when homework questions are treated like some kind of affront to the desks. If the links were lost on the OP or totally misleading, then it's my mistake. Julia Rossi (talk) 22:24, 23 February 2009 (UTC) I didn't mean to suggest a lack of good faith...just that it's generally better just to say something like: "Have you read Oil platform and crude oil?" than to edit someone else's post. SteveBaker (talk) 22:40, 23 February 2009 (UTC) I agree it's good to do that and mostly I do, but this time I wanted to vary it. I'm not comfortable with "might imply" which sounds speculative, and prefer not to be corrected on a speculation. Julia Rossi (talk) 22:55, 24 February 2009 (UTC)

--Scray (talk) 16:56, 21 February 2009 (UTC)

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battery life in laptops

Hello Wikipedia.

I got told by a stranger in the library today that if my laptop was plugged in, it is better for the battery if it is taken out. Anyway, for those who know more about these things than i do, is this likely to be true? My battery is a recharable Li-Ion (for a samsung Q310) if it makes any difference... thanks81.140.37.58 (talk) 11:23, 23 February 2009 (UTC)

Essentially the answer is...no. Modern Lithium-ion battery batteries don't have to have the full-drain-recharge cycle that older batteries do, so you don't need to worry about your laptop battery being connected when you are using the mains-supply. Someone will explain the science behind why i'm sure. Maybe try Lithium-ion battery for starters. 194.221.133.226 (talk) 11:58, 23 February 2009 (UTC)

update: though a link in the article suggests that by removing the battery when using the power-supply it can help keep the battery cool which will reduce the degredation of the battery. 194.221.133.226 (talk) 12:02, 23 February 2009 (UTC)

My laptop manual similarly suggests that it is better not to leave it on continuous charge. I have ignored this advice, but I notice that the battery capacity has reduced by 70% over 18 months. Could I have extended the battery life by fitting it only when I needed to either use or recharge it? Dbfirs 13:18, 23 February 2009 (UTC)

If you have a MacBook, you actually have to leave the battery in or processing speed drops quite a bit. No idea why. arimareiji (talk) 13:51, 23 February 2009 (UTC)

(That's probably using a SpeedStep technology to slow the processor based on a reading of "low battery voltage" - but if the battery is removed, it is not clear why the sensor would be active, nor why the measured voltage would be isolated from the AC-DC power-supply's standard voltage. Complex systems fail in complex ways. Nimur (talk) 15:58, 23 February 2009 (UTC)

Edison,Tesla spat cost them a Nobel !!!

Isaac Asimov has calimed that bioth Edison and Tesla were supposed to share the Nobel in 1915 but niether was willing to shar the award with teh other hence it was awarded to Braggs -father and son duo who never came close to the two in terms of their acievement.Is this true?(Ramanathan)

Likely not true. The nobel is usually awarded for novel discoveries, and neither was much of a scientist. True, they both improved existing technologies, but that isn't what the Nobel is normally awarded for. They were successful entrepreneurs and "inventors," but scientists they were not. --Jayron32.talk.contribs 12:29, 23 February 2009 (UTC)

Actually, the physics prize is also awarded for technical work, and was in particular during the early years (e.g. Gustaf Dalén). And Tesla did in fact do important theoretical work. --Pykk (talk) 12:36, 23 February 2009 (UTC)

This is mentioned in Nobel Prize controversies. However, I spot several issues here. Number one is that the prize winners are simply never consulted about sharing an award, or indeed consulted at all, before they win the Nobel. The second issue is that sources seem to be contemporary rumors in the press. That's a bad source. The Nobel committee work is kept secret for 30 years (IIRC), so if Tesla and Edison were under real consideration, it'd be relatively easy to come up with real documentation of it. Also, it's worth noting that Tesla and Edison were big celebrities in the USA - whereas the Nobel committee in Sweden would be more aware of European innovators in the area, such as Mikhail Dolivo-Dobrovolsky and their own Jonas Wenström, both of whom independently developed three-phase AC systems within months of Tesla's work. Finally, Bragg was indeed deserving of the prize. --Pykk (talk) 12:34, 23 February 2009 (UTC)

Lest you underestimate the value of the Braggs' prize, note that it was for a technique that has been of immense value for physics, chemistry, and biology since then (the discovery of the structure of DNA hinged on it as well). Whether you think Tesla/Edison should have gotten a prize does not distract from the importance of the Braggs' work. --98.217.14.211 (talk) 13:52, 23 February 2009 (UTC)

The 1915 Nobel prize being offered to Tesla and Edison claim has been debunked by someone with access to all the Nobel Committee files. The talk page archives for the Nikola Tesla article say: Talk:Nikola Tesla/Archive 6#Nobel claims

"Another verifiable site for the initial incorrect report is the New York Times, Nov 6, 1915, p1: "Edison and Tesla to get Nobel Prizes" which based their statement on the Copenhagen correspondent of the Daily Telegraph. Also see Nov 7, 1915, p12, "Tesla's discovery Nobel prize winner". The article said "Nikola Tesla, who, with Thomas Edison is to share the Nobel Prize in physics, according to a dispatch from London, said last night he had not yet been officially notified of the honor. His only information on the matter was the dispatch in the New York Times." Tesla thought the honor was for the transmission of energy without wires. He said he thought Edison was worthy of a dozen Nobel Prizes. He had often expressed his friendship with and admiration for Edison, and gave no hint he would refuse the honor if Edison was also getting it. The reported antipathy toward Edison only showed up when he was elderly. Finally Dec 28, 1915, p83 the NY Times reported that the initial report was incorrect. It had also given an incorrect report for the person to receive the chemistry award, further disproving the claim that Tesal refused the prize because Edison was also getting one. Also disproof of any great antipathy between them causing them to refuse the 1915 Nobel Prize is that in 1916 Tesla accepted the Edison Medal'For meritorious achievement in his early original work in polyphase and high-frequency electrical currents.' This often repeated claim that Tesla refused a Nobel prize needs something like a rejection letter from the Nobel files, or a memoir by someone involved with the Nobel award, or papers from Tesla's files. In other words, something more than someone writing a book or creating a webpage and stating it is so without a good source. Edison 23:48, 17 July 2006 (UTC) There is not much room for controversy. Seifer in "Wizard" pp378-380 has obtained detailed info from the Nobel people. Tesla never received a Nobel nomination in 1915, so he did not refuse it. Neither did Edison. Out of 38 nominations for the prize in physics, Edison received one and Tesla zero. The winners were the Braggs, father and son. There was an erroneous press report as listed above. Tesla also received one bid out of 38 in 1937, again not enough for him to win the prize. No nomination, no controversy, other than perhaps that he might have deserved one.I am removing refrence to the 1915 Nobel Prize and Tesla.Edison 22:56, 22 July 2006 (UTC).

. Edison (talk) 20:31, 23 February 2009 (UTC)

Better luck next year, Edison DMacks (talk) 20:48, 23 February 2009 (UTC)

Yuh just haveta wait. And hope. Edison (talk)

To the original poster: I would be very surprised if Isaac Asimov made any such claim. Where did you see this? --Anonymous, 05:29 UTC, February 24, 2009.

Manual gear

I drive amanual gear car ,,, it's annoying how you should reach that balance

between the clutch and fuel at start of movment , specially at crowded streets,

i'am wondering , was it to difficult for them to make a medium gear which can

transfer the power from the engine to the gear to the tires smoothly at movement

starting without that precious driving actions ... its Twinty-one century ,,,  ???

Smooth transfer of power by manual gear-change improves with practice. Perhaps you would prefer a car with automatic gear change, where twenty-first century technology helps you to transfer power smoothly. I recall a continuous gear on some Daf vehicles in the mid-twentieth century which achieved the smooth transfer using a belt drive without separate gears, but I presume it had significant disadvantages. Does anyone know what happened to that technology? Dbfirs 13:14, 23 February 2009 (UTC)

That would be the Variomatic transmission, a type of Continuously variable transmission. DuncanHill (talk) 16:10, 23 February 2009 (UTC)

There is such a thing as a Semi-automatic transmission, where you control the gear changes as in a manual, but the clutch is handled for you - you just pull on a paddle on the steering wheel to change gear, usually. --Tango (talk) 13:19, 23 February 2009 (UTC)

The problem with what the OP is requesting is that a 'clutch-less' transmission relies on a kind of 'sloppy' coupling between engine and gears or between gears and drive-shaft. In an automatic (or semi-auto) gearbox, that's typically handled with a 'fluid clutch'. The problem with fluid clutches is that they are the precisely the reason you didn't want a fully automatic in the first place - they take a while to 'catch up' and that means that you have less acceleration and you waste fuel compared to a manual transmission being driven by a competent human.

Going to semi-automatic doesn't help. Essentially, a semi-automatic transmission is just a fully automatic transmission where you give hints to the on-board computer about when you'd like it to shift. My wife's MINI Cooper has that and if you try to over-rev the engine or stall out or lug the engine due to too few revs, the computer just quietly takes back control from the driver and sneaks back into fully-automatic until you get it right! Semi-automatic is the worst of both worlds in that a poor human driver can persuade the car to be in the wrong gear for much of the time - yet you still suffer all of the losses of a fluid clutch.

The idea that I love is currently (I believe) only available on the MINI Cooper - but for some entirely arbitrary and stupid legal reason - not in the USA. The UK version of the MINI turns off the engine when you come to a stop. When you start to move off the line, it uses the starter motor to get the car rolling again - and doesn't restart the engine unless you stomp on the gas - or until you are going faster than about 10mph (or if the battery voltage starts to get low). This means in annoyingly slow stop-start traffic, the car almost becomes an electric car - turning back into a gas-powered vehicle only once you need the speed and/or acceleration. That's such a simple trick - requiring almost zero additional parts in the car (it's mostly a software trick in the engine management computer) - I can't believe that all modern small cars don't have that.

Sadly - in other cases - the alternatives are to become better 'in tune' with your car so that you can get the clutch control just right - or to give up and drive an automatic.

SteveBaker (talk) 13:36, 23 February 2009 (UTC)

A semi-automatic does have some advantages over a fully-automatic - in particular, you can anticipate the need to change gear (just before you pull out to overtake, say). You don't get the fuel savings, though, you're right. --Tango (talk) 13:53, 23 February 2009 (UTC)

Yes - I agree. And in really top-notch cars the paddle-shifters can shift gears faster than you could in a stick-shift car, so there are some benefits to be had there in terms of not using engine power to uselessly spin the engine in the brief moment when you have the clutch pedal on the floor. I haven't driven semi-automatics much - but in playing around with my wife's new MINI over the weekend, I found that putting it in full automatic mode and just hitting the paddle shifter to drop a gear when you want to overtake or something was a pretty neat compromise. It has three modes - full automatic (with paddle shifter 'override'), semi-automatic-for-morons (where you shift with the paddles - but if you try to push the revs too high or too low it takes over and shifts for you) and semi-automatic-for-real-men (where you shift with the paddles and the car does what you tell it no matter what). But I'm a stick-shift enthusiast - my car is manual. SteveBaker (talk) 14:47, 23 February 2009 (UTC)

On my first driving lesson the instructor took me to an up-going hill. He made me hold the car stationary on the hill without using brakes, just sliding the clutch. At first I was clumsy, either over-revving the engine or stalling it. Finally I mastered the "feel" of the clutch and could even drift the car up or down at will. After that practice, smooth start-ups become instinctive and you have better control than any automatic transmission. But start a different car, such as a hired car, and it takes a little while to feel out the unfamiliar clutch.

Yes - you are quite likely to wear out the clutch while you're learning. If you can find a driving instructor with a stick-shift car who'll give you a couple of lessons - that's the best way to learn. I haven't seen stick-shift rental cars for a very long time - but if you can find one - that's better still. SteveBaker (talk) 22:36, 23 February 2009 (UTC)

The reason few cars have SteveBaker's electric start aid is that it would quickly wear out a conventional starter coupling gear and motor. The starting cycle is predetermined so I wonder how well it works in all conditions of hills and battery charge. These problems are worse for heavier cars and/or larger engines that need more torque to crank.Cuddlyable3 (talk) 19:06, 23 February 2009 (UTC)

It's not 'mine' - it's BMW's - and it's not hypothetical - it actually exists in real production cars. Of course the MINI is indeed one of the smaller/lighter cars available in the USA - but it's pretty normal by European standards. But bigger cars have bigger engines and therefore bigger startermotors and bigger gears - so there need not be a problem for larger vehicles. I suspect the reason most other cars don't have it is that without the MINI's Gasoline direct injection gizmo there is a risk of flooding the engine or something. The amount of gas you save on in-town driving by doing this is pretty spectacular - so even if a slightly meatier starter and coupling gear is required - it's still a pretty good deal. I presume the car can measure whether it's on a slope and whether the battery is getting low - and in those cases, it can simply start the engine as a number of cars that turn the engine off while idling do. I'm pretty sure the MINI knows when it's stationary on a hill because it knows to hold the foot-brake on for three seconds after you take your foot off of it so you can do easy hill starts without messing around with the hand-brake. Sensors for things like tilt and rotation are becoming very cheap these days - compared to tens of thousands of dollars for the car - a $5 sensor is nothing. The MINI already has yaw rate sensors and all manner of other stuff for figuring out what's going on. SteveBaker (talk) 22:36, 23 February 2009 (UTC)

I'm wondering why nearly every car in the USA has automatic gear, while in Europe most of the cars have manual gear. --131.188.3.20 (talk) 12:05, 24 February 2009 (UTC)

I don't know if (or why) that's true in Europe in general - but there is a REALLY good reason why it is so in the UK. In the UK, there are two different drivers licenses - one that permits you to drive any kind of car - and a lesser license that only allows you to drive automatics. In order to get the 'any-car' license, you have to pass your driver's test in a stick-shift car. Since hardly anyone wants to be limited as to what they could drive in the future - or to have to take a second drivers test later in life, nearly everyone learns to drive stick and passes their test in a stick-shift car. Almost the only people who have the automatic-only license are disabled people who for whatever reason are physically incapable of driving stick. I don't think I know anyone in the UK who has the automatic-only license. Since new drivers are generally a little nervous, the first car they buy tends to be a stick-shift car because that's what they are used to. This then becomes the habit of a lifetime. That in turn means that there is a much higher demand to manual transmission cars - there are more manual transmission cars on the used car market and so forth. Because car manufacturers have to go to some extra trouble to make cars with the steering wheel on the right hand side for the UK market - they make relatively few automatics - and the price of automatics is generally considerably higher than manuals. This feeds back still more because now you have a community of drivers who almost all are quite happy driving stick - and a car market where automatics are a lot more costly. Another factor is that gasoline prices in the UK have always been VASTLY higher than in (say) the USA - since automatics get worse MPG than a properly driven manual gearbox car, this is further pressure to drive stick. SteveBaker (talk) 13:14, 24 February 2009 (UTC)

Not in Europe obviously but NZ also has quite a lot of manuals. In NZ you can only drive an automatic if you pass the test under one while you have your probationary license. But once you have a full license you can drive either car no matter what you pass your full license test under. A bigger factor may be that NZ's car fleet is very old with an extensive used car market (many coming from Japan, Singapore and other countries with strict regulations and probably left hand drive where people don't keep their cars long). Manual cars tend to last longer and are cheap to maintain with fewer things that can go wrong. Of course we're ultimately also somewhat limited by what is available on the world market. Nil Einne (talk) 14:20, 24 February 2009 (UTC)

increase of relative mass

I have understood the time dilation and length contraction in special relativity. But i don't understand the mass increase.can someone explain why the mass of a body increases relatively when it is moving and why only by the formula in special theory of relativity? i am a ninth grade student. please explain accordingly.--harish (talk) 15:34, 23 February 2009 (UTC)

Short answer: When an object is moving it has kinetic energy, energy and mass are just different ways of looking at the same thing (E=mc²), so when you increase the energy you increase the mass. (It's worth noting, most of time when we talk about mass we mean "rest mass", which is the mass when the object isn't moving - that is constant. The concept of "relativistic mass" isn't actually very useful when doing calculations, etc., so it isn't used much.) --Tango (talk) 15:53, 23 February 2009 (UTC)

I have a feeling that you are referring to the common note that a person cannot reach the speed of light because as energy is added to increase speed, the mass increases. More energy is needed to make it go faster because there is more mass. If that is what you are referring to, the energy itself is adding to the mass based on e=mc², which can be rewritten as m=e/c². The mass increase for a little energy is very small, but when you are talking about the amount of energy required to get something up to the speed of light, the mass increase becomes huge. -- kainaw™ 15:57, 23 February 2009 (UTC)

There really isn't much special to say - if you have gotten your head around time and length changes due to fast motion with respect to some observer - then just apply the exact same principles to the object's mass...the equations are the same, the cause is the same, the sheer cosmic wierdness of it all is exactly the same. When an object moves rapidly past some observer, that observer judges the mass of the object to have increased. The closer the object gets to the speed of light, the more its' mass increases...just as time and length change when that happens. If you have your head around length and time changing - mass should be easy to imagine! SteveBaker (talk) 16:34, 23 February 2009 (UTC)

As Tango said, physicists do not like the concept of a varying mass. That is because it does not add anything to our understanding. Length and time changing is enough to explain everything, including the speed limit of the speed of light. You do not actually need a varying mass to explain that! Essentially, "relativistic mass" is just short-hand for E/c². The really important concept of mass is rest mass, which is E/c² for a particle that is at rest. Still, for a lay person it is apparently easier to accept a varying mass, and it's probably easier to "understand" the speed limit as being due to increasing inertia than to the structure of Minkowski space-time, and therefore it is probably okay to use the concept in popular presentations. --Wrongfilter (talk) 17:55, 23 February 2009 (UTC)

wood - properties

is wood an isotropic solid. please qualify your answer.

Sathyanarayanan.d (talk) 15:50, 23 February 2009 (UTC)

"please qualify your answer" sounds like something from a homework question, we won't do your homework for you. Do you have a textbook that you can look up what "isotropic" means? I think once you understand the definition the answer should be fairly obvious (if you've ever done any woodwork, at least!) --Tango (talk) 15:53, 23 February 2009 (UTC)

Maybe lumber and wood grain will give you some insights. Isotropy means that the properties, like strength, hardness, and even color are the same in all directions. Nimur (talk) 16:02, 23 February 2009 (UTC)

And the opposite of 'isotropy' is 'anisotropy' - which (oddly) has it's own article. SteveBaker (talk) 16:27, 23 February 2009 (UTC)

Please do your own homework. Welcome to the Wikipedia Help desk. Your question appears to be a homework question. I apologize if this is a misevaluation, but it is our policy here to not do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn how to solve such problems.
Please attempt to solve the problem yourself first. You can search Wikipedia or search the Web.
If you need help with a specific part of your homework, the Reference desk can help you grasp the concept. Do not ask knowledge questions here, just those about using Wikipedia. —Scheinwerfermann ^T·_C16:24, 23 February 2009 (UTC)

{{dyoh}} might be better for the refdesk. Zain Ebrahim (talk) 18:39, 23 February 2009 (UTC)

Spread of Disease from America to the Old World

Which Pre-Columbian diseases spread from America to the Old World, from the 15th Century and on? I know Syphilis is assumed to have spread from America to Europe ([1]), but other subspecies of Treponema pallidum already existed in Asia and Africa. Which pathogens were endemic to America before they spread to the rest of the world? Thanks, ליאור (talk) 17:39, 23 February 2009 (UTC)

The Spanish Flu is supposed to have originated in America.--217.84.62.226 (talk) 18:57, 23 February 2009 (UTC)PS But alas its a Past Columbian one.

Potato blight.Cuddlyable3 (talk) 19:29, 23 February 2009 (UTC)

Well, the H1N1 strain causing the Spanish Flu is just a subtype of a globally common virus, that happenned to mutate in Kansas. And potatoes were cultivated in the Andes, so one clearly needs potatoes to have potato blight. Is there a pathogen that was once only found in America and is now also found in Europe\Africa\Asia\Australia, affecting local hosts? ליאור (talk) 20:11, 23 February 2009 (UTC)

Tobacco smoking originated in the Americas and has probably killed more Europeans than all the other health risks originating there. Edison (talk) 20:15, 23 February 2009 (UTC)

Cocaine addiction? 76.97.245.5 (talk) 00:01, 24 February 2009 (UTC)

Nicotine and Cocaine are lethally addictive indeed, but these are alkaloids, not pathogens. Any more ideas? ליאור (talk) 05:59, 24 February 2009 (UTC)

There is also always the option of Argentine hemorrhagic fever or one of its relatives, though again I dont really know how old that one is. Coccidioidomycosis is also endemic in America.--91.6.42.166 (talk) 08:40, 24 February 2009 (UTC)

Chagas disease is also endemic to America, but neither disease spread to the Old World. Which ones did spread? ליאור (talk) 08:53, 24 February 2009 (UTC)

It seems that the Great French Wine Blight matches my request. Will it be safe to say that Borrelia burgdorferi, Trichomonas vaginalis, Francisella tularensis and Bartonella bacilliformis all originated from America? Was Xylella fastidiosa detected outside of America as yet? Thanks, ליאור (talk) 10:13, 24 February 2009 (UTC)

"... Irradiated the world's supply of steel"? Clarify?

I was reading the article on the Scuttling of the German fleet in Scapa Flow, and came across this line: "Minor salvage is still carried out to recover small pieces of steel that can be used in radiation sensitive devices, such as Geiger counters, as the ships sank before nuclear weapons and tests irradiated the world's supply of steel." Now, I can understand that atmospheric tests would leave residual radiation, even very small amounts, but wouldn't steel that has yet to be mined be similarly clean? Or is it that the steel in the ground has been irradiated, but the steel under Scapa Flow is somehow radiation free? Can someone elaborate on the meaning of the above quote? Thanks —Preceding unsigned comment added by 38.118.48.5 (talk • contribs)

That seems odd to me. Being irradiated shouldn't make the steel radioactive. It might have radioactive substances on the surface that need to be cleaned off, but that isn't too difficult. Even if it has been, all steel is going to be slightly radioactive since it contains carbon, some of which will be carbon-14, which is radioactive (only slightly, but still). That means a Geiger counter is always going to need to be calibrated to take into account the radiation of the counter itself, so you just have to calibrated it differently if it is made with irradiated steel. And even that seems pointless since background radiation from everything from uranium in the bedrock to people's smoke detectors probably results in a significantly higher order of error. --Tango (talk) 19:37, 23 February 2009 (UTC)

This question was raised and discussed last month on this reference desk: See World steel supply irradiated ? Abecedare (talk) 19:47, 23 February 2009 (UTC)

Iron ore mining does not take place in a "clean room," so any surface or subsurface dust naturally gets mixed in and is tin the resulting steel. Back in the late 1950's and early 1960's there was atmospheric nuke weapon testing by the various nuclear powers, and children were warned not to eat snow because of the Strontium 90. There was also concern about radioactivity in milk. There was no atomic bomb detonation before 1945, so the older steel has less radiation in it than post 1945 steel. When scientists want to use steel to shield nuclear testing instruments, there is apparently a meaningful difference in the radiation levels of the two vintages of steel. In i=other words, the modern level may be low so far as health risks are concerned, but they want the lowest possible level. Edison (talk) 20:13, 23 February 2009 (UTC)

Couldn't they just clean pre-1945 above water steel? The radioactivity will only be on the surface. --Tango (talk) 21:14, 23 February 2009 (UTC)

In the production of steel, oxygen produced from air is bubbled through molten iron. That removes impurities by oxidizing them. The oxides appear as slag on the surface of the molten metal, or are passed off as a gas. It is possible that strontium 90 left in the oxygen, and other nuclear-explosion products from the air, remain in the molten metal. One of the chief materials removed from the iron ore is carbon. But perhaps some of the carbon 14 from the air also remains in the molten metal. The OP will get a good homework grade for this. – GlowWorm.

Disagree - first the OP will have to separate out the slag, as it were. arimareiji (talk) 22:30, 23 February 2009 (UTC)

There's no need to do expensive diving to get old steel. Structural steel (I beans, channel iron) from old buildings and bridges will do as well. – GlowWorm.

One would think if that were the case then nobody would bother with the diving. Either the divers and their customers are idiots or it's harder than RefDeskers think. --98.217.14.211 (talk) 00:28, 24 February 2009 (UTC)

If anyone finds out, let me know (I'm personally curious). T'only ref I saw supporting this contention was an offline one. arimareiji (talk)

Huh. Found it through Google books, and it's legit - but heaven only knows how well the author sourced it. arimareiji (talk) 00:38, 24 February 2009 (UTC)

Is it not possible that steel present on the surface of the earth (structural) collects enough residual radiation over time to make it less useful, and that old steel wouldn't have been subject to such levels of residual radiation at the time, and is thus "cleaner"? Diving for steel is certainly more cost effective than mining, so there must be something less desirable about modern scrap (used) steel. Perhaps the problem with , say steel columns and rebar from 1944 skyscrapers its that the steel cannot be machined down to make the required shielding members for nuclear instruments, while 16 inch thich armor can be used as raw materials and cut to shape and used more economically. Still, one would think that pre 1945 steel columns and beams from demolished buildings could be ground free of surface contamination, then melted and used to cast the required shielding members. Edison (talk) 02:38, 24 February 2009 (UTC)

Perhaps induced radioactivity is involved. This might be produced in the iron in the steel, or in some other element in the steel. (There are various kinds of steel, produced by adding other elements to it.) The induced radioactivity may be produced by nuclear-explosion products in the air, and the radioactivity may not be able to penetrate depths of the ocean. (How deep is Scapa Flow? The German ships there are popular diving sites, which would indicate the depth.) But if the induced radioactivity is only at the surface of old structural steel, it could be ground off, sandblasted off, or milled off. – GlowWorm. —Preceding unsigned comment added by 98.21.104.187 (talk) 06:00, 24 February 2009 (UTC)

How can I depigment hair extensions??

I am looking for a way to depigment my hair extensions without harmful bleaching. Is there some agent I could soak the hair in for a period of time (even days) to slowly remove pigment from the hair extensions?? —Preceding unsigned comment added by 76.110.2.85 (talk • contribs) 19:34, 23 February 2009

I have no clue how to answer this - but I bet whoever does will need to know what the hair extensions are made of. SteveBaker (talk) 22:17, 23 February 2009 (UTC)

Not only that. See Artificial hair integrations. We'd also need to know how the extensions were attached. Your hairdresser is probably the better source for information. They should have the manufacturer's directions for your product. Your goal of lightening your extensions while protecting them may not be realistic though. AFAIK most/all decolorizing agents are oxidative. That damages hair by definition. The best you could probably hope for is to find a product with a conditioner that will coat some of the damage. Google coughed up this patent [2]. 76.97.245.5 (talk) 22:55, 23 February 2009 (UTC)