Wikipedia:Reference desk/Archives/Science/2007 October 30

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October 30

Protein domain

Two different protein domains can have a same function why or why not?

If I consider two amino acid sequences of a protein with same domains but changes in 2 or 4 amino acids in the chains. Could it have the same function?

Respected teacher

My problem is that I considered 2 chains of the same protein

Chain A ---> n l i i l a n n s l s s " n g n v" t e s g c k e c e e l e e k n i k e f l q s f v h i v q m f i n " t s "

Chain B ---> n l i i l a n n s l s s " n g n " v t e s g c k e c e e l e e k n i k e f l q s f v h i v q m f i n t s

Those in double Inverted commas are excluded from the domain chain but they are considered in the same domain why? —Preceding unsigned comment added by Biomedicalpersonal (talk • contribs) 05:12, 30 October 2007 (UTC)

I do not understand what you are trying to ask in the second part of your question but I may be able to help you with the first part. A few amino acid changes in non-critical regions or mutations resulting in similar amino acids (see Neutral mutation) in critical regions may not cause measurable effect on the functioning or the interactions of the protein domain. It would help if you clarify the second part of your question about protein chains. By the way, these appear to be homework questions. The users on the reference desk are not supposed answer your homework questions, but if you have do not understand a concept or need help getting pointed in the right direction by all means ask away. 71.226.56.79 04:22, 31 October 2007 (UTC)

food poisoning ???

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

This question was removed for a reason. We cannot offer medical advice on either poisoning or allergies. If you are worried about the state of your friends health you should consult a medical professional immediately, especially if you believe she has been poisoned. Discussing it on the internet first should not be your immediate priority. Lanfear's Bane | t 21:41, 30 October 2007 (UTC)

production of particles by pair production method .

in the wikipedia article "pair production" only example of electron-positrion pair production is given . is it possible to produce particles like proton , neutron and neutrino by pair production method ? —Preceding unsigned comment added by Shamiul (talk • contribs) 12:30, 30 October 2007 (UTC)

Neutrinos and antineutrinos can be produced from a photon.[1] Like electron-positron pair production needing other particles involved in order to conserve energy and momentum, neutrino-antineutrino production from a photon needs other particles involved in order to conserve spin, which is a form of angular momentum.

Protons and neutrons aren’t elementary particles, but instead bound states of quarks. So in quantum chromodynamics, low-order particle interactions would include pair production of quarks, not of protons or neutrons. A quark and its antiquark can be produced from a gluon.[2] MrRedact 21:02, 30 October 2007 (UTC)

While these predictions from theory are very likely correct, we are currently far from being able to experimentally confirm pair production of neutrinos (because our neutrino detectors are not very sensitive). Icek 01:08, 31 October 2007 (UTC)

Somehow my previous answer to this question has been removed? However there is no neutrino pair production. They are electrically neutral and as such do not couple to photons. The nearest equivalent would be production of a neutrino/anti-neutrino and corresponding anti-lepton/lepton from a w particle. MrRedact is right about quarks being pairproduced, but note they can also be produced from photons as well as gluons (they are charged). Pair production of protons/neutrons is nigh on impossible, when quarks are pair produced they hadronise into two jets of particles and protons/neutrons maybe included in the jets. Cyta 08:56, 1 November 2007 (UTC)

Actually I may have been hasty to dismiss the original answer I didn't spot a link had been provided. The pair production of neutrinos seems only to happen in dense matter, which seems to me a different effect. There is no direct neutrino-photon coupling in the standard model. I suspect the matter is required as there is an intermediate stage in the reaction. Cyta 09:00, 1 November 2007 (UTC)

Anomalous hair

REMOVED. —Preceding unsigned comment added by 193.188.46.61 (talk) 13:23, 30 October 2007 (UTC)

(EC) Do not request regulated professional advice. If you want to ask advice that "offline" would only be given by a member of a licensed and regulated profession (medical, legal, veterinary, etc.), do not ask it here. Any such questions may be removed. See Wikipedia:Medical disclaimer and/or Wikipedia:Legal disclaimer. Ask a doctor, dentist, veterinarian or lawyer instead. Sorry, even a query that sounds innocuous should be addressed to a professional. Lanfear's Bane | t 13:32, 30 October 2007 (UTC)

REMOVED. --JWSchmidt 14:55, 30 October 2007 (UTC)

The original question did not ask for medical advice. My original comment made this point. There was no reason to delete my original comment. --JWSchmidt 18:23, 30 October 2007 (UTC)

REMOVED. --M@rēino 15:03, 30 October 2007 (UTC)

Per Lanfear's Bane's comment, we cannot offer medical advice. In this case, the original poster was seeking a diagnosis--the identification of the cause of a particular symptom. If someone would like to discuss in more detail why this constitutes a request for medical advice, please bring it to the Ref Desk talk page: WT:RD. [hidden unsigned comment by User:TenOfAllTrades made public for clarity]

I am appalled at this continuing deletionism by people who are apparently incapable of telling the difference between a request for an explanation of a biological phenomenon and a request for medical advice. To take this behaviour to its logical conclusion would result in the prohibition of any question relating to human biology (or animal biology for that matter). What causes blue eyes? What causes grey hair? Why does alcohol abuse cause liver damage? All are questions relating to biological phenomena - just as is "What causes an observed variation in human body hair types in humans?" Hiding comments about the removal of questions is also profoundly unhelpful. DuncanHill 15:20, 30 October 2007 (UTC)

One clear sign of a question that we aren't allowed to answer is one that starts off "I have some symptom..." or "A friend has some symptom...". This is quite clearly one of those - and we aren't allowed to answer it - period. The questions you put up as strawmen are not the problem here. I would like to turn this around and ask DuncanHill: "What kinds of question do you think the ban on giving medical advice is intended to cover?" - clearly it covers something or it wouldn't be there. What? Give me some examples. SteveBaker 16:38, 30 October 2007 (UTC)

Why don't we stop wasting energy here now and instead just send the questioner to where he asked the same question a week ago (8 times in fact). DMacks 15:16, 30 October 2007 (UTC)

Hey, can everyone confine metadiscussion to the talk page of the Ref Desk? This sort of debate about what questions are appropriate doesn't belong out on the Desk itself. TenOfAllTrades(talk) 16:52, 30 October 2007 (UTC)

• "can everyone confine metadiscussion to the talk page" <-- If content is removed from this page because it contains descriptions of personal health matters, then say THAT, but do not say that someone asked for medical advice when they never did. --JWSchmidt 18:20, 30 October 2007 (UTC)

• Hey, why was my comment removed? All I said was that the original question did not seek medical advice. And that continues to be my opinion. The question was not describing a symptom -- "a sensation or change in health function experienced by a patient" -- because there was no implication that the questioner's health was affected. They were just curious about Hair follicles, a subject on which the Wikipedia article is B-class at best. --M@rēino 04:23, 31 October 2007 (UTC)

This is plainly ridiculous! The sense of this regulation is to avoid unqualified suggestions to be accepted and considered professional by the user. How should this do any type of damage what so ever? If you apply that definition about a symptom it can be eligible to all sorts of things, to nausea due to boat movements for ezample. Aren't you allowed to explain the processes that occur in that event?! Laws and regulations should be implemented only when they make some type of logical sense. You're just tking it to the extreeme here.193.188.46.254 13:56, 31 October 2007 (UTC)

Membrane Potentials

What is the difference between membrane potentials, diffusion potentials and nernst potentials. I understand membrane pot. = diffusion pot. and nernst pot. to be when the electrical force opposes the concentration force.?

In biology, a membrane potential is the electric potential difference across a membrane of a cell or an organelle such as a mitochondrion. For charged ions there can be a balance between movement across a membrane due to diffusion and movement due to the electric potential across the membrane: see reversal potential. If you had a membrane and only one ion was able to cross it by passive diffusion then at equilibrium the membrane potential would be equal to the diffusion potential of that ion: Nernst Potential. --JWSchmidt 14:29, 30 October 2007 (UTC)

Thanks for the quick reply. I have a slightly better understanding now but still wich to clear some issues [this is in the context of the establishment of an RMP]. 1) Does the term diffusion potential apply to an ion or membrane? 2) Could the Nernst potential (equilibrium potential) be described as the potential difference required to prevent net diffusion of that ionic species? (and how is Nernst potential related to diffusion potential?) 3) What is the purpose of the Na/K ATP'ase (it contributes slightly by reducing RMP; is its primary function to repolarise?). Thanks.

[ATP'ase] I thought a bit more and reasoned that the purpose may be to create the diffusion potential? or allow the tissue to become excited (function)? i.e. to maintain concentration gradient thereby preventing the Nernst potentials for each ion (Na/K) being reached (a scenario where membrane potential- or is that diffusion potential- is a result of only Na and K)

Did you find Resting potential? For most cells, the Na+/K+-ATPase is not thought to make a major contribution to the resting membrane potential. The resting potential of many cells is close to the equilibrium potential of potassium ions (K⁺). Many cells have potassium "leak" channels that control the resting potential. --JWSchmidt 18:13, 30 October 2007 (UTC)

When will oil run out?

Based on world wide consumption trends, and ignoring that it takes millions of years to produce more oil. 64.236.121.129 16:04, 30 October 2007 (UTC)

It will never "run out" - but it will become far too expensive to use as fuel. When? See Peak oil. Cheers Geologyguy 16:06, 30 October 2007 (UTC)

I did some calculations in response to an earlier question - the answer is that if we were to carry on consuming it at the present rate, it would run out in about 500 to 600 years. However, if we actually did that, the CO2 levels in the atmosphere would be far beyond "mere" global warming problems - they'd be at a point where humans (and most animals) couldn't breathe. However, the assumption that we'll carry on using it at present levels is flawed. I don't think that running out is a practical proposition. Even if we somehow managed to 'sequester' the CO2, we would only have to halve our consumption every 250 years in order to make the stuff last forever. Another issue is that these numbers for oil reserves are always accompanied by a caveat that says "economically retrievable" - in other words, the only things the oil companies care about is the stuff they can dig up for less than they can sell it for. There are reserves of stuff like "oil shale" that contain a lot of oil - but which are so expensive to dig up and refine that it's not worth doing it. If the oil were ever seriously likely to run out, then the price would go through the roof and suddenly oil shale (or whatever) would be worth exploiting and our reserves would increase (although the price would still be astronomical by today's standards). However, we must stress that with what we know about global warming, it's all completely irrelevent. We must not ever come even close to running out - because even a tenth of that amount of oil - when converted to CO2 - would kill the planet. SteveBaker 16:28, 30 October 2007 (UTC)

Our article on world energy resources and consumption says that the world's oil reserves are 5.7x10²² J, and annual oil consumption in 2005 was 1.8 x 10²⁰ J, so this gives a ratio of reserves to consumption of over 300 years. However, as Geologyguy and SteveBaker have pointed out, this is a rather meaningless figure. In reality oil prices will rise, and oil consumption will fall as alternative energy sources become more economically attractive, and global warming imposes a shorter deadline on us anyway. Gandalf61 16:44, 30 October 2007 (UTC)

Perhaps by then we will have made advances in scrubber technology, and have them on every car, big ones atop every building, and just generally all over the place. I mean, once it comes down to economy vs. survival... Arakunem^Talk 17:18, 30 October 2007 (UTC)

The chemistry of scrubber technology is not very promising - the kinds that merely absorb CO2 will give the gas up again fairly easily and the substances that react with CO2 to actually get rid of it require lots of energy to make in their own right - so you end up needing more scrubbers to scrub the output of the factory that makes the scrubbers (or the power station that drives it) than the factory itself can make. It's really a bad idea to pin one's hopes on such things because it distracts from the very critical thing of cutting CO2 production in the first place. The whole "Clean Coal" campaign (which has to rely on science-fiction "carbon sequestration" techniques) is a particularly bad example of this kind of wishful thinking. SteveBaker 03:40, 31 October 2007 (UTC)

Are you saying that collecting and burying CO2 from a coal plant won't work and will use more energy than you get from the coal?--Dacium 05:47, 31 October 2007 (UTC)

Yes and no. I'm saying that on small scales, it takes more energy than you get - and on large scales there isn't a viable technology for doing it at all. Not one single large scale CO2 removal/sequestration plant exists anywhere in the world - not even experimentally. (Which hasn't stopped the US from licensing the building of "Clean Coal" power stations - which is a scandal just waiting to get media attention!) Our article on Carbon capture and storage explains that what we're likely to have will remove 80 to 90% of the CO2 from the gasses and consume 10% to 40% more energy. But the biggest problem is what you do with the stuff once you've captured it. Sequestering it into limestone requires 180% more energy - so that isn't going to fly. If you try to sequester the CO2 without chemically converting it to something else then you've still got to find a place to store millions of tons of something that's a gas at normal temperatures and pressures. That's no easy task. You can't store it underground or underwater because there isn't enough space at normal temperatures and pressures (If you burn a cubic meter of oil or coal - you get a LOT more than a cubic meter of CO2 as a result! So pumping it into disused coal mines and oil wells isn't going to work for very long.) If you compress the CO2 so it takes up less space (eg storing it as dry ice), then that requires either very high pressure storage or very low temperatures. Either of those technologies will require yet more energy - and worse still, will be vulnerable to long term corrosion and other damage - so you're just building up more trouble for the future. There is talk of dissolving the stuff into saline aquifers or deep oceans - but those are not permenant solutions (eventually, the CO2 would get out again) and the resulting carbonic acids would likely do untold amounts of damage to the environment. Dealing with radioactive waste from a nuclear power plant is EASY by comparison because so little material is involved. So, no, we aren't going to be doing this if we want to save the planet. We have to cut down our consumption (probably the easiest thing to do in the short term) and switch rapidly over to nuclear and (where possible) wind/solar/tidal power until we figure out how to make fusion reactors that actually work. SteveBaker 18:00, 31 October 2007 (UTC)

On the scales you are talking about, I would imagine there would be nowhere near enough suitable locations to bury CO2 and be reasonably sure that it won't escape at some point in the future. Hopefully within 300 years we will have managed to develop alternatives to fossil fuels, otherwise our pathetic species probably doesn't deserve to survive. Bistromathic 16:41, 31 October 2007 (UTC)

Quantum foam

I was thinking about Quantum foam last night. Since particle/antiparticle pairs emerge out of the vacuum - and since there is no "rest frame" - it seems like the particle pairs must be travelling at random velocities relative to my motion. This implies that they have random kinetic energy relative to my motion - which means some of them must be arbitarily energetic. How come we don't measure them? Even though they only last for a spectacularly short amount of time in their own frame of reference - in mine, they'd spend an eternity recombining. Our article briefly sketches over that. SteveBaker 16:45, 30 October 2007 (UTC)

You are taking the idea of virtual particle pairs too literally. Quantum foam is a broad term for the fluctuating nature of space-time at a quantum level that theory demands. Those fluctuations are abstractly described as virtual particles, but from the practical point of there are no particles. Imagine a tablecloth with marbles on it. The marbles may move because they are hit by other marbles, or they may move because the tablecloth shakes. If all you could ever see were the motions of marbles, you might try to explain the motions caused by shaking in the tablecloth as being caused by invisible "virtual" marbles. What is going on in physics is similar. The ways that real particles are affected by the quirks of the vacuum can be usefully described by replacing the vacuum with infinite numbers of virtual particles constantly bombarding matter. However, those particles don't really come from anywhere or go anywhere. They don't have an existence that one could isolate and interact with individually. Really, they are collectively just a way of describing the manifestations of the complicated quantum mechanics intrinsic to space-time. Dragons flight 19:55, 30 October 2007 (UTC)

Steve, "quantum foam" does not refer to the virtual particle/antiparticle pairs in the quantum vacuum in general, but specifically to what happens around the Planck scale, where spacetime becomes quantum mechanical. The short answer to any question about quantum foam is that we don't know anything about it at all. But I think you're asking about the quantum vacuum in general, so let's step back from solving quantum gravity and consider something more manageable. Take QED or Klein-Gordon theory. You asked "How come we don't measure them?", referring to virtual pairs with arbitrarily large energies. OK, how do you want to measure them? You would have to interact with them somehow. That means that instead of a vacuum-bubble diagram, you have to consider diagrams with external vertices, and virtual particle loops inside. One way to think about these diagrams is that your real external particles are encountering the virtual particles from the vacuum; and they can indeed have arbitrarily large momentum and energy. In many quantum field theories, these loop contributions cause all calculations to come out infinite. Similarly, the vacuum diagrams can cause the vacuum energy to come out infinite. To get something physically sensible, you have to renormalize the theory, and "renormalize" the vacuum energy by zeroing out the infinite offset. So even if you never observe the virtual particles as discrete events, they are hugely significant in every interaction between particles! In some theories, like supergravity, the case is even worse than that, and renormalization doesn't work. Because all of this is not very intellectually satisfactory, we hope that there is some real, underlying physics that doesn't have these problems. Supersymmetry takes care of the infinite vacuum energy, but still needs renormalization. Superstring theory attempts to avoid the need for renormalization at all. But now we're back in the realm of speculations about quantum gravity. --Reuben 21:49, 30 October 2007 (UTC)

Why don't they put some kind of grating over jet engine intakes to prevent birds from getting sucked in?

Why not? 64.236.121.129 16:57, 30 October 2007 (UTC)

It probably doesn't happen all that often and may actually cause too much disruption to the air intake on the engines. Also, birds would still (I imagine) be sucked and stuck to the grating over the intake. -- MacAddct1984 17:05, 30 October 2007 (UTC)

Per MacAddct, a grating would seriously disrupt the airflow into the engine, creating a tremendous amount of drag. (Remember that air is flowing through the engine at several hundred kilometers per hour.) Plus, what if the bird strike actually damages the grating? In addition to having a bird in the turbine, you'd get all those jagged metal bits of broken grating.... TenOfAllTrades(talk) 17:12, 30 October 2007 (UTC)

No - there is no grating - but there is a requirement to test engines for bird strike damage. They actually have an air-powered cannon to shoot birds into running jet engines in order to test them. However if you fly at high speeds and lower altitudes (where birds tend to be) - and if you hit a big one - you can certainly throw a turbine blade and utterly trash the engine in the process. If you have a strong stomach - read Bird strike which has some exceptionally grisley photographs of the effects of birds on airplanes and airplane engines in particular. SteveBaker 17:35, 30 October 2007 (UTC)

Yep. Even with a no-drag indestructible grating, you're still talking about smashing a bird into something at several hundred miles per hour. It's not that the engine is sucking in birds from all directions, just that the plane and bird are hitting -- and even with a grating, the engine still has to generate the same suction. But as SteveBaker said, there's a bird strike test, so a grating is superfluous. — Lomn 18:18, 30 October 2007 (UTC)

A bird running into a turbine is usually not dangerous. The bird will be ripped apart. If the turbine does throw a peice and destroy itself, all that happens is that fuel will continue to be pumped in and a massive flame will come out the back because the fuel is being burned. Obviously you get no thrust from the engine, but the plane can still fly. I don't think any commercial airliners have been brought down, many have had engines taken out.--Dacium 05:43, 31 October 2007 (UTC)

According to Bird strike: according to the FAA only 15% of strikes (ICAO 11%) actually result in damage to the aircraft. But you're wrong about commercial airliners - there is at least one instance: Eastern Air Lines Flight 375 flew into a a flock of small birds that took out three out of the four engines at once - at the critical moment just after take-off when the engines were at full power - they also splattered over the windshield - blocking the pilot's view and clogged the pitot tubes, preventing them from knowing their airspeed. They didn't stand a chance - the plane rolled over and smashed into the ocean - there were 62 fatalities out of 72 people aboard. Our article on bird strikes also says: the problem costs US aviation 600 million dollars annually and has resulted in over 200 worldwide deaths since 1988. We have a brief article about Birdstrike simulators too! SteveBaker 17:31, 31 October 2007 (UTC)

Having a grating over the fan intake can introduce another problem. When engines are being tested, they have what they call a debris guard which fits over the front of the engine, but it means that the engine cannot be run in all conditions. To fully test the engine, at some point the guard needs to be removed.

This is because, at the speed the air enters the front of the engine, well over 300 miles an hour, it creates a huge cooling effect on the debris guard. That combined with the right (or wrong) level of humidity can cause ice to form on the guard. It has been known that enough ice has formed for the fan to create a vacuum behind the guard, and the result is, the entire guard is pulled through the engine, which will utterly destroy the engine, no question about that. On the other hand, with a bird strike, it's quite possible for an engine to keep running without any problems, especially if the bird is passed straight through the cold stream ducts and out the back. —Preceding unsigned comment added by 132.244.246.25 (talk) 08:33, 1 November 2007 (UTC)

Taste bud abnormality

I was wondering if there is a name for the painful bumps that crop up on tongues from time to time. It seems as though a single taste bud turns white, enlarges, and becomes very sore to the touch. I can't seem to find a name for it anywhere (and no, it's not herpes or canker sores) -- MacAddct1984 17:10, 30 October 2007 (UTC)

Sorry, but this question is basically asking for a diagnosis, which we aren’t allowed to do here. As it says at the top of the page:

Do not request regulated professional advice. If you want to ask advice that "offline" would only be given by a member of a licensed and regulated profession (medical, legal, veterinary, etc.), do not ask it here. Any such questions may be removed. See Wikipedia:Medical disclaimer and/or Wikipedia:Legal disclaimer. Ask a doctor, dentist, veterinarian or lawyer instead. MrRedact 17:33, 30 October 2007 (UTC)

While MrRedact is correct that we can't diagnose, you might nevertheless be interested in the brief stub on lie bumps. It could stand to be filled out if you want to do some source research. --Trovatore 17:36, 30 October 2007 (UTC)

Ah, thank you very much Trov! While I wasn't really looking for medical advice, I do realize there is a very fine line between "diagnosing" and what I was asking. But that is what I was looking for, I remember my mother always saying the old wife's tale was that you get them when you lie. -- MacAddct1984 17:53, 30 October 2007 (UTC)

I can't say what this is in your case, but it also happens to me when I accidently scrape the area with a sharp piece of food or bite the tongue. Here's an article that discusses lie bumps a bit more: [3]. Again, this may not be what you have though. Sancho 17:47, 30 October 2007 (UTC)

they are basically caused by cuts in the tongue by food or your own teeth. If they are on the edge of a tongue it almost defiantly is caused by you biting your tongue accidentally. usually a mouth full of food pushes the tongue over the teeth and people bite without realising.--Dacium 05:38, 31 October 2007 (UTC)

how do i make my dog smart

please thank you —Preceding unsigned comment added by 77.234.83.173 (talk) 17:19, 30 October 2007 (UTC)

See dog training. Sancho 17:38, 30 October 2007 (UTC)

I don't think you can change your dog's intelligence - as with humans, it's pretty much something that you're born with - but you can certainly enroll in a training course for you and your dog. Sadly, it generally turns out that your dog is plenty smart and it's you that gets trained - but that works too! We also have an article on Dog training. I have two dogs - one smart (female), the other dumber than a bag of hammers (male). The smart dog has learned to bark at the front door when she wants to be let in. The stupid dog has not. He just stares at the door hopefully. However, the smart dog has realised this and when she sees him standing there looking puzzled, she runs up to the door, barks until we open it and let him in - then she goes back to whatever she was doing before. SteveBaker 17:43, 30 October 2007 (UTC)

Intelligence can most certainly be changed in humans. And it's important that people are aware of that. There was a study recently that took two classes of high-school students, gave one a lecture about something boring and irrelevant (just to have a control), and gave the other a lecture on the nature of intelligence, and how intelligence and problem solving skills can be improved through training. After about half a year the second group showed a significant increase in grades and the first didn't. Of course there is always the criticism that training intelligence is just training for intelligence tests, but I believe strongly that intelligence by any reasonable definition can be consciously improved. I see no reason why dogs couldn't do the same, except that they probably won't have the mental capacity for defining the concept of intelligence, so they can't set it as a goal for themselves explicitly. Still, if you set out a wide range problem solving exercises with rewards that the dogs can understand (like the 'stack boxes to get to a banana'-kind of exercises they give monkeys, only simpler), they may generalize over all exercises and improve their problem solving intelligence instead of just learning specific tricks. risk 18:16, 30 October 2007 (UTC)

thats a lot of reading, what's something simple ic an do like some toy i can buy or music to play. i cant afford obedience school. —Preceding unsigned comment added by 77.234.83.173 (talk) 18:09, 30 October 2007 (UTC)

There are no magical shortcuts. If you can't afford obedience school - read our Dog training article carefully and do what it says - it's pretty much what the obedience schools teach. Set aside an hour a day for training. Make sure your dog knows that this is something special - "Now is training time - later will be play time" - so have a special routine you go through at the start and end so your dog will come to recognise that. SteveBaker 00:08, 31 October 2007 (UTC)

I have an instinctive negative reaction to the idea that learning to obey demonstrates intelligence. I've always sort of felt that cats are smarter than dogs, precisely because they don't obey you. --Trovatore 01:33, 31 October 2007 (UTC)

Dog training is more about learning inter-species communication than obeying orders. I prefer to think of it as unlocking the intelligence that was always there - and in a way that we humans can understand. SteveBaker 03:25, 31 October 2007 (UTC)

I don't know about smart but I made my dog smarter with this and this and this. All three are essential. --DHeyward 05:40, 31 October 2007 (UTC)

Get involved with Dog agility or Flyball. You and the dog have fun; you and the dog get to socialize; you and the dog get good outside exercise; and the dog's intelligence is developed. It's mostly just run by volunteers, so there's little cost.--Eriastrum 17:06, 31 October 2007 (UTC)

When you here about plane crashes on the news

They usually manage to find the Black Box flight recorder thing even in the worst crashes, when the rest of the plane has been completely destroyed by explosion and fire. So, why don't they make the planes out of the same material they make the black boxes out of? --84.68.112.172 17:50, 30 October 2007 (UTC)

While black boxes are of durable construction, I think they benefit a great deal by being inside the aircraft. By analogy, I could get into a car wreck that's bad enough to total my car, but it's likely that my CD player would survive. It's not that it's made of some magic substance—it's just protected by the body of the car, which can deform and break up, absorbing a lot of impact energy. -- Coneslayer 17:57, 30 October 2007 (UTC)

In short, the black box is so heavily armored so as to survive the worst impact, that if the airplane was made similarly, it would be more like a tank than an airplane, and would be too heavy to fly. Planes are made to fly, CVR's are made to crash, as "they" say. :) Arakunem^Talk 18:03, 30 October 2007 (UTC)

Check out this classic Cecil Adams column. "If aircraft "black boxes" are indestructible, why can't the whole plane be made from the same material?" 69.95.50.15 18:01, 30 October 2007 (UTC)

It's also worth noting that an indestructible airplane would provide little extra protection to all-too-destructible passengers, who are still independently subject to the laws of inertia. Crash casualties are not so much the product of a deforming airframe as they are of a sudden stop. In fact, the deformation is good -- it absorbs crash energy that would otherwise injure passengers even more. Modern cars are constructed with this same theory in mind. — Lomn 18:12, 30 October 2007 (UTC)

I wonder if the querent is looking for material for a stand up comedy routine? According to our article, Flight data recorders tend to be "double wrapped, in strong corrosion-resistant stainless steel or titanium, with high-temperature insulation inside." We don't make jetliners out of titanium for the same reason we don't make windows out of diamonds, its not cost effective (though, as an aside, while the SR-71 Blackbird was made out of titanium, its windows were not diamond), and if we packed it full of high-temperature insulation, where we would put the passengers? Rockpocket 18:14, 30 October 2007 (UTC)

Also, black boxes aren't black - they're orange. SteveBaker 00:04, 31 October 2007 (UTC)

Depends on how hot the fire is. --DHeyward 05:09, 31 October 2007 (UTC)

Even if the plane were made to survive a crash, it doesn't help people inside. Say the plane can survive 1000G of force, your body cant and you would be squished to death on impact, regardless of if the plane body deformed or didn't. The best solution for safety would have to be a plane that deforms enough so that a +100G impact is reduce to say 10G.--Dacium 05:50, 31 October 2007 (UTC)

Digitap imaging & printing

perfect on screen but when i printed it on my Epson stylus Photo RX620 it looked nothing like what it did on screen. I was truely gutted. It was duller, darker, more saturated & lost a lot of fine detail. I am using the correct paper & my ink channels settings are set to default. This is happening with all of my images.

Why is this happening & how can i resolve it so that what i create on screen prints as it looks on screen? Also what is the difference between a jpeg, tiff, Esp, btmap etc?

Thanks kindly

Nay —Preceding unsigned comment added by 86.145.223.206 (talk) 19:33, 30 October 2007 (UTC)

For the latter, articles such as JPEG, TIFF, and BMP file format may be of use. For the former, I have no suggestion apart from experimenting with configuration settings (as this is not so much a case of correctness as one of preference). — Lomn 20:05, 30 October 2007 (UTC)

You may find this is better answered on the computing reference desk however I'll have a quick stab. Computer screens use additive colour. They add red, blue and green colours together to make white. Printers OTOH use ink which substracts colour. They use cyan, yellow and magenta and mixing them together makes black :-( So the screen will never look the same as a printer.

Also ink jet printers use wet ink thqat runs a bit and the colours bleed together making it dull. Having a good quality laser printer and using top quality paper will definately produce crisper and brighter prints. Fortuately the cost of colours lasers has been plummeting in recent years Theresa Knott | The otter sank 20:10, 30 October 2007 (UTC)

There are many problems here. Additive versus subtractive, impure inks and toners, the fact that you are printing in four colours (Cyan, Magenta, Yellow and Black) instead of three, that the printer needs to use dithering and bleeding of inks to do what it does, that the brightness of your screen is independent of the room lighting - but the brightness and hue of your print is entirely dependent on the colour of the ambient lighting - that the software that does the conversion is rarely correctly set up for the kind of paper you are using - that the gamma of cameras and screens are NEVER correctly set up, that not all programs take notice of the gamma values that the camera put into the file header - and if you save the picture out in another format, that information is almost certainly lost, that our eyes respond differently to a pigment that reflects yellow (meaning a true yellow) versus a seemingly identical pigment that reflects both red and green, that your CRT probably has several different colour temperature settings and you have no clue which one you picked...there are a million reasons. The bottom line is that you're doomed and you just have to tweak the available settings until you get it "how you like it". (There is no "Right"). SteveBaker 23:50, 30 October 2007 (UTC)

Oh - and the difference between various file formats (for the purposes of this discussion) are that JPEG and GIF both compromise the true colours of your photos in order to save a lot of memory. 24 bit TIFF and PNG can store colours in their original perfection with no losses whatever. BMP (urgh) can go either way - and it's a horrid format anyway so don't use it. The various 'raw' formats that cameras sometimes use are better still - IF you have the right software to handle them. There are some esoteric formats that do even better - but I doubt you'll ever come across them. On balance:

• Use PNG for original artwork and photos stored on your computer at home - where (presumably) you have plenty of disk space.
• Use RAW images for original photo archives if your camera and software supports them - but convert to PNG for day-to-day use.
• Use JPEG for photographic types of pictures on the Internet - it's compact - which means it downloads quickly - and the losses due to it's compression tricks are not noticable on a typical browser at the default screen resolutions we have these days. As broadband starts to conquer the world - I'm going more and more towards using PNG even in these situations.
• Use GIF only on really high usage web pages for cartoony stuff or (if you absolutely must) for animated images.
• Don't use TIFF or BMP if you can possibly avoid it - they are both only patchily supported in areas like gamma that truly matter.

SteveBaker 00:01, 31 October 2007 (UTC)

Mom Haircut

Okay, this is a stretch, but I'm going to try it anyways... just bear with me, okay?

Is there a condition or an illness (for lack of a better word, I don't mean to imply bad health) that would describe the tendency for new mothers to get a drastic haircut? I don't mean the "mom haircut" but, just even like dying it a different color, something that makes a dramatic change. I know this could just be associated with going through major changes in their life or, more dangerously, depression, but I was wondering if there was a name for it specifically. Thanks, and I apologize if this question is just too dumb for words. Beekone 20:18, 30 October 2007 (UTC)

You might find more information under the mid-life crisis article -- MacAddct1984 20:43, 30 October 2007 (UTC)

One could argue it is an evolutionary successful strategy: long hair is an energy intensive characteristic adopted by females to attract a mate. After pair bonding and generating offspring, the female no longer considers the energy invested in maintaining long hair is no longer required, hence they cut it. Or it could be that they don't want to get nits from all the little brats they interact with. Or it could be to reinvent themselves for the next stage in their lives, or it could be part of an effort to "look good" again after the physical changes associated with child birth. Interestingly (or not) there does seem to be some recognition of "mom hair" in the mommy blogosphere, but its extremely unlikely that it has a specific biomedical name. Rockpocket 20:45, 30 October 2007 (UTC)

I'm not even sure what you are describibg is a real phenomenom. Is there any data to suggest that on average new mums get more dreastic haircuts than women of that age who are not new mums? Theresa Knott | The otter sank 20:52, 30 October 2007 (UTC)

No, I'm not sure such research exists... I guess that's why I asked. It seemed like a funny quirk that I'd noticed in some friends and acquaintances. I agree that the likelihood of this activity having a specific medical name is extremely un, but you never know until you ask, right? Beekone 21:05, 30 October 2007 (UTC)

Googling "mom haircut" at least provides evidence that the "mom haircut" is culturally believed to be a real phenomenon. From reading the various pages, it sounds like a "mom haircut" is either quite short, or long and tied back. In either case, it sounds like the point is to have a low-maintenance, no-nonsense haircut that isn’t going to get in the way of the harried new mother, who suddenly has less time for dealing with such frivolities as hair. MrRedact 21:30, 30 October 2007 (UTC)

Don't think anyone has mentioned the obvious answer (well, obvious to anyone with practical experience of babies), which is that babies of a few weeks and older love to practise their hand-eye co-ordination by grabbing and pulling long hair. Gandalf61 10:39, 31 October 2007 (UTC)

"I don't mean the "mom haircut" but, just even like dying it a different color, something that makes a dramatic change. " signed, the very first post! Read, think, reread, comprehend... maybe Beekone 13:04, 31 October 2007 (UTC)

You start off with: "Is there a condition or an illness ... that would describe the tendency for new mothers to get a drastic haircut?" If you are going to ask contradictory questions, you are going to get contradictory answers. Rockpocket 17:14, 31 October 2007 (UTC)

How does "drastic haircut" translate into "mom haircut"? I mean I know I called the topic that, but I state repeatedly that that's not what it's about. To be technical I start off with this: "Okay, this is a stretch, but I'm going to try it anyways... just bear with me, okay? " 'Clearly the message is going to be muddled so I should pay close attention,' thought the reader. Beekone 17:18, 31 October 2007 (UTC)

Additionally, I liked your answer, Rockpocket. You seem to get what I was asking, and correctly stated that such a condition is unlikely to have an actual label. But at least you got what I was asking, even if you're answer was basically "I don't know." The other answers are "I don't know" plus a hint of "I obviously didn't try to get what you were asking" which i frustrating because if you don't know why even answer? Just pass it by. I obviously asked in the case that someone with knowledge of the topic might answer. It's sort of what the Help Desk is all about... in my understanding anyways. Beekone 17:23, 31 October 2007 (UTC)

Thats a fair point, well taken. Rockpocket 04:10, 2 November 2007 (UTC)

Why don't they use water jets on very large ships?

The largest they used it on was a frigget I think. Why not larger ships? 64.236.121.129 20:26, 30 October 2007 (UTC)

Our article on pump-jets notes some of their advantages, contrasted with a decrease in efficiency versus propellor-based designs. In particular, the note about power density may be relevant, as frigates don't have as much hull volume to fill with engines as do destroyers or cruisers. The shallow-draft advantages provide additional merit for new littoral combat ships. At some level, though, the lack of adoption may simply be industrial inertia. Propellors are well-understood and consequently are considered to inherit less risk than a relatively new technology like pump-jets. In the absence of a compelling advantage for the latter, then, the former is likely to remain in widespread use. — Lomn 20:36, 30 October 2007 (UTC)

Many very large ships still have bow thruster jets.--Dacium 23:54, 30 October 2007 (UTC)

Sugar in Soda

I've decided to eliminate soda from my diet. While shopping at a local grocery store, I came across a powder lemonade product that one mixes with water. The lemonade’s packaging said it "contained 40% less sugar than soda." So with everything being equal between the soda and the lemonade (calories, fat, etc), what would be the benefits of 40% less sugar? I would assume that there would be some benefits…or is this a fancy marketing ploy?

Thanks 64.85.199.27 20:41, 30 October 2007 (UTC)

It's precisely a marketing ploy. Whether it actually benefits you depends entirely on your diet. People hear that carbs are bad, carbs make you fat, so they advertise that they have fewer carbs. Sugars/carbs are the normal person's primary source of energy, and it is the first form of energy (calories) the body will burn in order to operate (fats it prefers to store away). Now, if the food in your diet contains all the calories you need in a day, and you just want something to quench your thirst, there's really no need to drink something laced with sugar that will just get converted into fat for long term storage, so you may as well go for that low-sugar lemonade. Someguy1221 20:47, 30 October 2007 (UTC)

(ec)Soda contains a lot of sugar! 40% less means 60% still remaining which is still very bad for your teeth. Having said that soda contains not fat, protein etc. It's water and sugar, so 40% less sugar will be 40% less calories. Those calories that remain are junk food calories though. Much better to drink water or tea. Theresa Knott | The otter sank 20:49, 30 October 2007 (UTC)

Also, the drink may have had that 60% of sugar boosted by an artificial sweetener, and if you read sugar substitute you'll see that all the common ones have some kind of controversy about potential health risks attached. Confusing Manifestation 21:39, 30 October 2007 (UTC)

Just drink diet or zero soda's (diet coke, coke zero, pepsi max etc). These contain zero suger. Also other things that are high in suger are sauces like ketchup, alcohol etc. Personally I would try to ditch soda all together and drink water. Try drinking two classes of water before you eat.--Dacium 23:27, 30 October 2007 (UTC)

There are two very different things being talked about here. Diet Coke/Pepsi/whatever contains almost zero carbs. Giving up Diet coke and drinking this stuff will increase your carbs by a large percentage because their claim to have less carbs than "Soda" is a poorly worded and highly misleading statement. WHICH soda do they have 40% less than? If has 40% less than one of those insane "energy drinks" (Mountain Dew MDX for example) then it probably has more sugar than Classic Coke too! Different kinds of soda have everything from zero sugar up to (probably) the maximum amount that'll stay dissolved in water without crystalizing out! It's nothing to do with whether it's carbonated or not. So if you need to reduce your sugar intake, switch to a diet soda. If you are concerned about the CO2 in the soda - then switch to a non-carbonated beverage. But don't give up either "just because". Read the ingredient list and compare the actual numbers - forget the silly marketting percentages. Think about what you are really doing! As others have mentioned, if you get your total carbohydrate intake down to zero - you'll get seriously ill amazingly quickly of something called "protein poisoning" (aka Rabbit starvation). SteveBaker 23:39, 30 October 2007 (UTC)

Actually sugar will dissove in huge amounts in water without crystalising out. I suppose the max would be something like golden syrup but you would't drink that. Theresa Knott | The otter sank 00:35, 31 October 2007 (UTC)

Lemonade mix is almost all sugar. 16 of a 17 gram Country Time serving, for example, and it may be even worse than that, when round off is considered (16.4 of 16.6 grams, perhaps ?). I'd avoid both sugar and sugar substitutes and drink water with lemon juice. StuRat 16:45, 3 November 2007 (UTC)

Will it fly?

I say yes, and so does straightdope, but what is the answer????--Goon Noot 23:08, 30 October 2007 (UTC)

Yes it will. Airplanes move due to thrust from the engines, not torque from the wheels. The plane's wheels will just be spinning at 2x the takeoff speed when it leaves the ground. Arakunem^Talk 23:11, 30 October 2007 (UTC)

I say nay. There is no lift because the plane isn't moving forward.

It is moving, but it is on the treadmill, and the treadmill isn't moving forward.

strap that whole shebang on top of a car... then we're talking —Preceding unsigned comment added by 128.175.187.238 (talk) 05:59, 31 October 2007 (UTC)

-Stephen Hawking —Preceding unsigned comment added by 74.196.103.230 (talk) 23:15, 30 October 2007 (UTC)

It's an enormous treadmill, but the aeroplane's wings will be ripped off as it starts to fly. DuncanHill 23:17, 30 October 2007 (UTC)

In the original formulation of the question, the treadmill was infinitely long and the wheels completely free-running. The photo just confuses the question. The plane doesn't give a damn what happens to its wheels - they are free-running. Moreover, once it's engines are running with enough power to overcome the tiny amount of rolling friction in the wheels, the plane will take the same distance to take off no matter what speed the treadmill is running (forwards, backwards, who cares?). This one has been done-to-death and the answer is as clear and obvious now as it was at the beginning. I don't believe Stephen Hawking (or at least "The" Stephen Hawkin) said that. SteveBaker 23:21, 30 October 2007 (UTC)

It 100% will not take off. There is no way for it go gain lift. The plan engines thrust forth, pulling the wing, with the idea that the wing is pulled fast through the air, air goes over the wing and creates lift. There is no way for the plain to gain lift. People who think it could take off must also believe that a plane with no wheels could simply turn on its engines and hover up in the air.--Dacium 23:22, 30 October 2007 (UTC)

If you think about it, any plane is already on a giant moving treadmill. It's called the Earth. Remember that all motion is relative, so putting a plane on a treadmill moving with constant velocity is really no different from having a wind coming up from behind the plane. From the plane's perspective, it has to go a little faster to take off because of this wind. From your perspective, it takes off at normal speed, but it takes a little longer to reach it (since it started moving backwards with the treadmill) and the wheels will be turning faster. Now, you could also have the treadmill accelerating backwards at the same rate the airplane accelerates while taking off. In this case, the plane sits where it is, the wheels constantly speeding up, and the engines working to keep the plane exactly where it is (although, in that case, you could just turn the plane around and use the treadmill to launch it). Simply put, all motion is relative, being a treadmill won't have any greater effect on the plane than wind. Someguy1221 23:24, 30 October 2007 (UTC)

A plane moves forward by air entering the engines to create thrust. A plane has to build up it speed because there is only little thrust to begin with. As the plane gets faster, more air is entering the engine and the thrust increases. It is the air speed relative to the plane that is the only thing that matters. A plane could hover straight up in the air if the air speed was great enough. The treadmill stops the plane gaining speed relative to the air and stops it taking off.--Dacium 23:44, 30 October 2007 (UTC)

The plane still moves. Unless the treadmill is accelerating, the plane will eventually beat it and take off. Imagine the treadmill is massive, say, the Earth. Would the plane notice or care if the treadmill were moving? Not unless it's accelerating. So this is why I say, if the treadmill is moving backwards at 30mph, this is no different than a tailwind of 30mph. The plane has to speed up a little more (from its own perspective) to generate sufficient lift. But it is by no means prevented from moving. Someguy1221 23:49, 30 October 2007 (UTC)

Sorry I thought we were assuming the treadmill was accelerating to match the speed of the plain. Obviously if it doesn't the plain will still be able to gain speed relative to the air, and take off. So we are all in agreement then. Non accelerating treadmill - plain takes off. Accelerating treadmill - plane does not take off.--Dacium 23:52, 30 October 2007 (UTC)

The treadmill would have to have tremendous acceleration to slow the plane below its takeoff speed. (Remember, the wheels are free-wheeling. The only thing slowing the plane is double the normal amount of friction in the axles. The situation is nearly the same as if the plane had hovercraft instead of wheels. ) I'm pretty sure that a treadmill constructed to put out that sort of ridiculous acceleration would reach near-C speeds in a minute or two then the plane could still take off normally. 69.95.50.15 18:42, 31 October 2007 (UTC)

So I have this funny feeling I may have my relativity backwards on the accelerating part, someone please check me on that. Someguy1221 23:57, 30 October 2007 (UTC)

The wheels play zero part in generating forward speed. The engines react against the air to generate forward thrust. The treadmill could be going faster in "reverse" than the plane is moving forwards, and it will still move forward. The wheels would be spinning reeealy fast backwards but thats irrelevant to this. Arakunem^Talk 23:33, 30 October 2007 (UTC)

It all depends on how you define the question. If the airplane's wheel bearings are frictionless and the wheels themselves are inertialess, then it doesn't matter what the treadmill does: the airplane's engines will move the airplane forward and it will take off. If the wheels have rotational inertia, or the wheel bearings have friction, and the treadmill is allowed to adjust its speed without limit, then it is possible to use the friction or rotational inertia of the wheels to counter the thrust of the engines, and the airplane won't take off. --Carnildo 00:03, 31 October 2007 (UTC)

I think it's best to assume the plane is just a normal plane, with normal wheels. Someguy1221 00:08, 31 October 2007 (UTC)

Say a big plane like in the picture takes off at about 150mph, do you think it could take off with a 150mph tail wind? I don't think so. So imagine the treadmill is already travelling with the plane on it at 150mph backwards, can the plane take off? I don't think so. Now imagine the plane and the treadmill both start at 0mph, can the treadmill accelerate the plane backwards as fast as the plane accelerates forwards? I don't think so. At the very start of the plane's acceleration as the engines spool up a considerable amount of the thrust would be used to overcome the friction in the wheels, but very quickly as the thrust increases, I think the treadmill would have to travel MUCH MUCH faster backwards then the plane accelerates forward for the friction of the wheels to act as a break on the plane's forward acceleration, otherwise the plane will come to speed and take off, just with very fast spinning wheels. Vespine 00:54, 31 October 2007 (UTC)

Yes, if the treadmill is allowed to transfer enough net force through friction in the wheels it could hypothetically keep the plane stationary. If the plane is stationary with respect to the air, it will not take off, since lift depends only on the plane's speed with respect to the air. Dragons flight 00:57, 31 October 2007 (UTC)

Just to straighten things out hopefully. Assume still air (no headwind or tailwind). If the conveyor belt/plane contraption is set up so that the plane remains motionless relative to the air (whether or not the conveyor belt, wheels, or engines are going) the plane will not take off as no air is moving over the wing generating no lift. If the plane is moving forward relative to the air, it could take off. Another way to think about this problem is to envision a plane on a conveyor belt that pushes the plane forward while the plane's engines are off and the wheels not rolling at all. Will the plane take off? Yes, because air is moving past the wings generating lift. (Of course to maintain flight it needs the engines, but that is besides the point) Or you can envision it this way: with a strong enough headwind, a plane perfectly at rest could take off although to a stationary observer on the ground, the plane would be moving backwards while acquiring altitude (i.e. moving in the direction of the wind). I hope this helps. Sifaka ^talk 03:59, 31 October 2007 (UTC)

No, it will hit the handrails of the treadmill. (Darn, DuncanHill beat me to that answer :P)-- Diletante 01:10, 31 October 2007 (UTC)

It's worth noting (belatedly) that we did this question to death back on May 21. —Steve Summit (talk) 01:31, 31 October 2007 (UTC)

More importantly, would a bird flying in front of the treadmill get sucked into the plane's engine? Rockpocket 01:39, 31 October 2007 (UTC)

Yes because the engines are drawing in air. 71.226.56.79 04:02, 31 October 2007 (UTC)

If the treadmill matches whatever the speed the plane can do, then surely it would stir up a huge surface headwind wouldn't it? Voilà, there's your moving air. --antilived^{T | C | G} 07:09, 31 October 2007 (UTC)

A treadmill moving at 100 or 150 mph wouldn't stir up that much of a headwind. (And stop calling me Shirley.) —Steve Summit (talk) 12:01, 31 October 2007 (UTC)

It doesn't have to limited to 100 or 150mph. Assuming it's a perfect treadmill it and the plane will simply accelerate until there's enough induced wind from the treadmill for the plane to take off. --antilived^{T | C | G} 05:13, 1 November 2007 (UTC)

It won't take off because there's no airflow around the wings! That's the whole point of why you need a runway for an airplane. You could say the Earth is a giant treadmill, but the air moves with the earth, and so do we. Air does not move with the treadmill. I'm surprised some of the people here thinks it will take off. It really makes me doubt how credible they were to answer my question about the ducted fans aircraft. Maybe it will take off if you have a powerful fan in front of the plane, but then you don't need a treadmill in the first place. Just thrust against the wind. 64.236.121.129 13:23, 31 October 2007 (UTC)

Aww you're mad *pats your head. You're also thinking of it wrong. I'm not going to bother explaining it because your last few posts prove that you aren't interested in listening. *pats your head*. Just because you don't understand it, doesnt mean it isnt so. Now you run on back to Starcraft lil guy —Preceding unsigned comment added by 207.67.148.212 (talk) 15:49, 31 October 2007 (UTC)

As I thought I made clear in my Earth/treadmill analogy, the only point of that is to dispel any belief that frame of reference is important. The only difference the plane cares about is the relative wind speed. Someguy1221 17:11, 31 October 2007 (UTC)

Actually, this is quite backwards. It takes off fine from a treadmill under the generally stated conditions (the treadmill moves at the same speed as the aircraft). Carnildo raises a good point that wheels aren't frictionless, and if you allow the treadmill to run so fast that the airplane is stationary, then it won't lift off (probably -- you're left with a weird feedback cycle). Thus, the key point of properly stating your constraints and assumptions is illustrated. On the other hand, a stationary aircraft in front of a fan can lift off, but as soon as it's no longer in front of the fan, it crashes due to the rapid change in airspeed over the wings (as opposed to the treadmill liftoff, in which the aircraft flies away normally).

In a related question, A friend once suggested to me that the real issue in this situation would be that the wheels would be turning at double their normal RPM (obviously). He suggested that the tires on many jets are not rated for those RPMs and would destroy themselves before the plane went airborne. Is this true? Stated more clearly, if a 747 was placed on a treadmill like the one described so that its wheels were always turning at double the normally expected rate, would the plane survive takeoff? 69.95.50.15 18:36, 31 October 2007 (UTC)

With no true evidence, I'll say "probably". The wheels undergo significantly more stress at landing (going from no speed to 150 MPH or so very quickly) and have a sizeable engineering margin above that. Simply spinning on takeoff should be no big deal. — Lomn 19:13, 31 October 2007 (UTC)

For the consequences of a tyre failure on takeoff, see Air France Flight 4590. Admittedly, the tyre failed due to debris on the runway, but airplane tyres were subsequently redesigned. -Arch dude 22:25, 31 October 2007 (UTC)

As i stated in my post, the "initial" resistance of the wheel would be very quickly overcome by the acceleration of the jet engine and I belive the wheels would have to spin MUCH MUCH more then twice as fast. Think of this, scale down the plane so it fits on a piece of paper on a desk, move the paper slowly and the plane will move with it, move the paper fast and the plane won't move, the wheels will just spin faster, i think the same thing will happen with a jet. Once the engines are at full thrust i think moving the treadmill backwards WON'T be able to stop the plane from accelerating, it will just make the wheels spin faster backwards, unless you start spinning then SO fast as to act as a break, in which case I think probably eventually fast enough to fail. Vespine 06:04, 1 November 2007 (UTC)

I was referring to the most commonly stated version of this problem where the treadmill goes backwards at the plane's take-off speed. In this case the plane takes off almost normally except for the tires which spin double their normal speed. 69.95.50.15 16:32, 1 November 2007 (UTC)

I think the main point here is that the air will not move with the treadmill. People seem to be thinking here that somehow either the treadmill can move the air, or the plane's engines drive the wheels. Either way you need air movement over the wings to generate lift. The treadmill's movement, forward, backward, whatever has no bearing on the air. The plane still needs to be pulled (by its engines) through the air forward to generate lift. The force from the engines act on the air, not the ground, so how the ground is moving has no bearing. The plane in that picture absolutely would not leave the ground. It's like having someone holding a hang-glider and running on a treadmill. They're not going to suddenly zoom up into the air, because the wing isn't travelling through the air. That's the whole point of a treadmill, so you don't move anywhere. —Preceding unsigned comment added by 132.244.246.25 (talk) 08:45, 1 November 2007 (UTC)

Hey, let's put this a couple of different ways:

• You've got a 3 km runway, well and truly long enough for about any plane. But some tricky person has replaced the surface with a conveyor belt loop. The belt runs at 100km/h (~60mph). Can a Cessna 152 take off?

Plane is dropped onto the runway at the North end, facing north, and starts accelerating south (backwards). The engine's running and is throttled up to maximum, it starts moving forwards, engine slowed so it progresses backwards at walking pace (5km/h), that's groundspeed (relative to treadmill) +95km/h, airspeed -5km/h, groundspeed relative to control tower -5km/h. The Cessna gets half way down the runway, pilot decides to stop stuffing around, and throttles up to max, speed increases, at 120km/h airspeed it takes off, that's airspeed=120km/h, groundspeed relative to tower=120km/h (it's using up runway at 120km/h and getting rapidly closer towards the end), groundspeed relative to treadmill = 220km/h - well within design limits of the plane. Yep. It flies.

Of course, you can make the situation work or not work as you please by tweaking the setup. Sure you can find a treadmill speed where the plane's wheels are wrecked, sure you can make the plane too large or the treadmill runway too short for the plane to take off - but was that the question?

If the original question was "We have a cessna 152, with a flying speed of 120km/h, on a treadmill as long as the plane. The treadmill is run up to 120km/h, will the plane fly?" the answer to that is an emphatic "no", groundspeed is irrelevant to whether a plane flies. --Psud 10:00, 1 November 2007 (UTC)

You mean an emphatic "yes", right? Because the Cessna will have the same airspeed it always has. It's 'groundspeed' would be double if you're counting the treadmill as the ground, but like you said, the groundspeed is irrelevant. (The wheels are free-spinning, Imagine them as hovercraft if that helps you.) 69.95.50.15 16:38, 1 November 2007 (UTC)

Relative to the surrounding air this plane is motionless. Ergo the lift = 0. Ergo it won´t take off.
The tradmill is totally irrelevant.
--Cookatoo.ergo.ZooM 23:12, 1 November 2007 (UTC)

PS: It is identical to a normal plane on a "normal" runway taking off at a tailwind which inceases parallel to the speed of the accelerating plane. The Cessna / Jumbo / whatever could travel at the speed of Mach x or even v=c. As long as the velocity of the tail wind is identical, there are no aerodynamics to create a counter-gravitational force.
QED. --Cookatoo.ergo.ZooM 23:27, 1 November 2007 (UTC)

ZOMG, people are still not getting it.... but the plane is accelerating with JET THRUST not with the wheels, the plane, at full throttle, WILL accelerate through the air, regardless whether the wheels are spinning forward or backwards, the ground and wheel resistance is negligible to the thrust of the engines. there is a clip on youtube of a thrust test where a bus behind a jumbo jet, not RIGHT behind either, some way behind, is blown clean over and away by the blast from the engines. Put it this way, people agreed that the treadmill will NOT be able to move a significant amount of air with it, right? So it MUST also work in reverse, is the treadmill, even going super fast enough to counteract ONE HUNDRED THOUSAND LBF of thrust?? NO WAY! The plane WILL accelerate and WILL take off. Actually using that example, I've changed my mind from my previous post, I think it will accelerate and take off even if it starts at "going backwards" on the treadmill at whatever speed, it will just take longer for it to gather the airspeed... the people who think it will not take off are essentially making the assumption that a treadmill under the plane can counteract the acceleration of 100000 lbf of thrusting air, no way no how. Vespine 00:51, 2 November 2007 (UTC)

It's becoming clear that this is, in effect, a troll question. It is specifically designed to fuck with your head. The more you think about it, the more confused you get. Or, even if you don't overtly confuse yourself, you find yourself compelled to come up with ever-more bizarre theories to explain how the plane might not be able to take off.

And if you stop and really think about it, coming up with those ever-more bizarre theories is a pretty stupid thing to do. Remember, the primary purpose of the question is to fuck with your head and spark meaningless but prolonged debate. When the people who aren't thinking clearly say "Oh, right, of course the plane won't take off", the sadistic person who thought up the question in the first place calls them stupid and has a good laugh at their expense. But seriously: you think he's not also laughing at you when you get all "clever" and come up with some exotic and barely-plausible (well, even less plausible than a runway-sized treadmill, that is) theory under which you get exactly the same answer as the stupid people!?

As we all hopefully know by now, the proper response to trolls is to ignore them, to not feed them, to wait patiently for them to get bored and go away. And I think we had best apply the same remedy to this dorky airplane-on-a-treadmill question, too. (And soon, before this thread achieves critical mass and collapses into a black hole, or something...) —Steve Summit (talk) 04:57, 2 November 2007 (UTC)

Oops. I recant my above statements. The devil made me do it!
Due to a brief attack of fallibilty, causing delusions of omnisciensce, I uttered what may be classified as pure and unadulerated bovine faeces.
Thank God I am not a pope or president, but just a humble wheel on a treadmill, attempting to soar into the heavens of perpetual knowledge and eternal bliss...
I promise to take my prescibed medicine in future !--Cookatoo.ergo.ZooM 13:00, 2 November 2007 (UTC)