Wikipedia:Reference desk/Archives/Science/2010 February 1

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Science desk
< January 31 << Jan | February | Mar >> February 2 >
Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

February 1[edit]

Earth gear[edit]

When I was younger I said to my mom that we could create a good energy source using the earth's rotation. All I need was a gear which the earth could spin using its rotation much like the gears in clock work. This spinning gear would then be used to generate electricity. My mom said it was impossible. Why?-- (talk) 02:09, 1 February 2010 (UTC)

The difficulty of finding something to mount this gear to, such that the earth will spin it. --Tagishsimon (talk) 02:11, 1 February 2010 (UTC)
You could probably find a way to extract energy from a foucault pendulum. It's unlikely that you'd be able to extract much. Essentially, you'd be tapping off the reservoir of angular momentum (or rather, rotational kinetic energy, and slowing the earth's rotation. Nimur (talk) 02:36, 1 February 2010 (UTC)
You can only do that once. After that the pendulum is spinning at the same rate as the earth, and you can no longer extract any energy. It would be a violation of conservation of angular momentum if you could constantly extract energy from the rotation of the earth by slowing it down. Ariel. (talk) 08:31, 1 February 2010 (UTC)
I guess tidal energy is sort of that. (talk) 02:39, 1 February 2010 (UTC)

Perhaps a gyroscope in a vacuum cylinder spinning on frictionless magnetic bearings at one of the earth poles would stay still as the Earth turned, allowing the difference in rotation to turn gears to speed up the rotation and turn a dynamo?Trevor Loughlin (talk) 03:33, 1 February 2010 (UTC)

See what I wrote above. You can only do that once, because you need to conserve angular momentum. Ariel. (talk) 08:31, 1 February 2010 (UTC)
If I understand you correctly, the maximum energy you'd get out of that would be somewhat less than you had to put in to it to get the gyroscope spinning in the first place. --Tagishsimon (talk) 03:40, 1 February 2010 (UTC)
Well, I'm not quite clear on Trevor Loughlin's idea. But, it's possible to harness energy that's stored in the form of Earth's rotation - actually netting more energy than you expend to collect it. You aren't creating any energy - you're just harnessing kinetic energy of Earth's rotation. Presumably, that energy is left over from the formation of the solar system (and by extension, from the Big Bang and cosmogenesis... whether the energy was created or has always been there is irrelevant for this discussion). Presently, that energy takes the form of rotational kinetic energy in the planetary rotation of the Earth. If you could actually build a device that could be spun by the Earth, you would be ever-so-slightly slowing down the enormous planetary-sized flywheel; and you could extract energy from it. It's not perpetual motion - there's a finite (but really, really huge) amount of energy to extract. However, the impracticality of building such a device makes it less attractive than harnessing other natural energy reservoirs (tidal motions have already been brought up). Nimur (talk) 03:58, 1 February 2010 (UTC)
No, i's not impractical. It's impossible unless you can transfer the momentum somewhere. With tides the momentum goes to the moon. Ariel. (talk) 08:31, 1 February 2010 (UTC)

The gyro would not be spinning horizontally like a top, it would be at right angles to the Earth-dynamo axis. Would this make a difference?Trevor Loughlin (talk) 03:58, 1 February 2010 (UTC)

No. How does this differ from spinning a bike wheel then putting the bike down? --Tagishsimon (talk) 03:59, 1 February 2010 (UTC)

Oh come on! It's easy! Buy a simple electrical generator with a large wheel welded to it's input shaft. Take it to the South Pole and bolt it firmly though the ice and into the bedrock beneath with the input shaft pointing straight up and the wheel laying horizontally. Tie a long rope to one side of the wheel. Tie the other end of the rope to a nice strong nail hammered into the south pole of the moon. As the earth spins, so the generator turns at roughly one revolution per day (actually, not quite that because the moon orbits the earth once a month). You'll keep generating power until the earth eventually stops spinning - an event that would be very slightly hastened by doing this. (Actually, since the moon does set below the horizon even at the south pole, you might need to erect a very tall tower and mount your generator on top of that to ensure you have a continual path for the rope.) There are of course some trivial engineering issues to deal with! SteveBaker (talk) 08:09, 1 February 2010 (UTC)

Now this could work. It would do rather interesting things to the orbit of the moon. Especially if you don't lengthen the rope. (But you could never actually make the earth stop spinning, the best you could do would be to have it spin at the same rate as the orbit of the moon. But I think you could get that to any desired slowness you want (very far away moon), just not zero.) Ariel. (talk) 08:31, 1 February 2010 (UTC)
I think it would be hard to get the rope really tight enough that the elliptical orbit of the moon would be a problem, and the rope doesn't need to be tight for this to work. But to assuage your concerns, I'd be prepared to spend the extra to buy bungee cord. (In truth - if you could do this at all, you might be better off to forget the generator and use a conductive wire instead of rope - generating electricity directly from the motion of the wire through the magnetic field. You'd need two wires - one from the north pole and one from the south with a wire running across the lunar surface to complete the circuit.) SteveBaker (talk) 19:19, 1 February 2010 (UTC)
SteveBaker, you've solved the energy problems of the earth. Except that people who like eclipses and use a lunar calendar would object since as you transfer momentum to the moon it will get farther and farther away. (You are lucky the moon and earth rotate in the same direction, otherwise you might just bring the moon crashing down on us.) Ariel. (talk) 19:28, 1 February 2010 (UTC)
That won't be a problem because, sadly, eclipse-lovers and anyone who even knows where to find a lunar calendar will have died during the three centuries of enforced labor required to hand-make half a million kilometers of bungee cord and an antarctic generator tower several hundred miles tall. The lunar antipodeal nail could be purchased at Home Depot for approximately 50 cents and I was planning to repurpose the spare generator out of my 1963 Mini Cooper - so relatively little loss of life would be entailed in those phases of the construction project. Rewiring the major world-wide power grids to run off 12 volts with a positive ground will have to be someone else's problem because I have to talk NASA into lending me one of those million dollar space-hammers. :-)
Steve, have you taken into account the tensile strength of the bungee cord involved? (talk) 01:00, 3 February 2010 (UTC)

A vaguely related topic is the use of Gravity assist to "steal" energy from other planets orbital momentum, rather than their rotational energy. The energy is not free - it causes the planet's orbit to slow. Mitch Ames (talk) 12:13, 1 February 2010 (UTC)

The Foucault pendulum suggestion was correct, the objection to it was wrong. The only problem is that to get a significant amount of energy the pendulum would have to be miles high. The winds in winter storms, it might be worth noting, are powered by the same mechanism -- that is, they draw their energy mainly from the Earth's rotation. Looie496 (talk) 17:11, 1 February 2010 (UTC)
You object to conservation of angular momentum? The winds are not powered by the rotation of the earth, they are powered by the sun. The rotation just effects what direction they will go in. Ariel. (talk) 19:24, 1 February 2010 (UTC)
Hmmm - so we could build a vast, elliptical train track - with the major axis of the ellipse running north-south. The train would be loaded with bowling balls which we'd release from the side of the train on the southern leg of the journey - picking them up again on the northern leg after the coriolis effect had moved them across the width of the track. Recovering the kinetic energy from the bowling balls and using this to power the train itself is a mere engineering detail that will be left as an exercise for the reader. SteveBaker (talk) 19:19, 1 February 2010 (UTC)

I assume this is a joke in reply to Looie496 :) (Since this will not work.) Ariel. (talk) 19:24, 1 February 2010 (UTC)

Why not? SteveBaker (talk) 19:46, 1 February 2010 (UTC)
Because to move the balls north on the return trip you would have to spend energy in the train to speed them up against the (reverse) coriolis effect. And conservation of angular momentum also says no, since you have nowhere to transfer the momentum of the rotating earth. Ariel. (talk) 20:06, 1 February 2010 (UTC)
Oh, yeah - conservation of angular momentum...duh. SteveBaker (talk) 20:21, 1 February 2010 (UTC)
All joking aside, I don't see any reason a gyroscope running perpendicular to the earth's axis wouldn't feel some force from the earth's turn. The force would be incredibly weak, so actually constructing a device so frictionless that it would turn is probably impossible, but I don't think there are any theoretical problems with the idea. APL (talk) 19:41, 1 February 2010 (UTC)
It would feel a force. But you can only collect the energy once, after that the force would move (accelerate) the gyroscope, and there would no longer be a force. The only reason a foucault pendulum turns is that they work really hard to make sure there is no force at the joint (frictionless). Ariel. (talk) 20:06, 1 February 2010 (UTC)
Angular momentum would be conserved. The object you accelerated would now have angular momentum. Earth would have less angular momentum. Energy and momentum are both conserved, but the process of the transfer can be used to do productive work (accelerating something you want accelerated, like a turbine). Why can you transfer angular momentum to the moon, but not to a bowling ball or a turbine? Ariel's objection doesn't seem valid. Again, the engineering details of how to couple a turbine to Earth's rotation are left to the reader; but I think it's definitely feasible. Nimur (talk) 21:58, 1 February 2010 (UTC)
You can do it once. The reason you can transfer to the moon is that it's in orbit around the earth, not on the earth. I guess technically you are also transferring just once to the moon, but you can collect almost all the rotational momentum of the earth, by giving the moon a huge orbit with lots of momentum. With a gyroscope or pendulum you can't give that much - they are not able to hold that much momentum. Ariel. (talk) 22:24, 1 February 2010 (UTC)
If you used the moon as an anchor you would of course decelerate the moon and consequently lower the orbit, and probably also slow the earth's rotation, which is something we probably don't want to do. You might be able to get an arbitrarily large amount of energy before we had cataclysmic side effects but ultimately you would crash the moon into the earth. Vespine (talk) 03:17, 2 February 2010 (UTC)
That's true in theory - but if you are really concerned about it as a practical matter then you should be out there protesting tidal power stations because those are having the exact same effect. For an identical amount of power generated, my "generator + rope + nail" approach would cause exactly the same amount of slowing of spin and lunar orbit degradation as tidal power stations are actually doing in practice TODAY! (Trust me: the effect of extracting power this way would be negligable.) SteveBaker (talk) 14:30, 2 February 2010 (UTC)
You would actually accelerate the moon, not decelerate it. The earth and the moon both rotate/orbit in the same direction. So if you slow one down, you must speed the other up. So you would raise the orbit of the moon. This is why eclipse lovers are so mad at SteveBaker, with the moon farther away you don't have a good eclipse. Ariel. (talk) 20:54, 2 February 2010 (UTC)
I don't know if I agree with that Steve. Aren't you extracting power that is there either way, except that when you don't harvest it, the waves just crash and dissipate as "heat" and noise and what not. I can't see how it would effect the moon. I would think it would be similar to saying that collecting solar energy has some sort of effect of depleting the sun, the energy is already there either way, either you collect it and use it or you don't and it just goes to waste. As for your second point, I thought that if you go to the trouble of attaching a gear to the earth you'd want to get a little more then megawatts.
As for ariel's point, that's extremely counter intuitive, I'm really struggling to model in my head how that would work, it's like a plane taking off on a conveyor belt:) If you are "extracting" energy, how can you be accelerating the moon? I get that the earth is rotating a lot faster then the moon is orbiting, but isn't the whole point "not" to accelerate anything but instead extract that force as "energy"? Vespine (talk) 03:55, 4 February 2010 (UTC)
Ok, I think I got it, it's much easier to visualize if you place yourself on the moon and if the initial condition is that the moon starts as a stationary object. ignoring the gravity that would cause it to crash into the earth of course. But that makes it easy to see why the moon will be accelerating. Vespine (talk) 04:22, 4 February 2010 (UTC)

linear permanent magnet bearing?[edit]

I have heard about rotational magnetic bearings. But has anyone invented an (unpowered) linear magnetic bearing, which could do away with wheels without the costs of electromagnetic levitation? And don't cheat by using high temperature superconductors floating above liquid nitrogen-this has its costs-I'm talking about ordinary magnets. Is it theoretically possible? There is no violation of thermodynamics or conservation of energy laws to make it impossible(?)Trevor Loughlin (talk) 03:52, 1 February 2010 (UTC)

See Earnshaw's theorem. It's not possible. Rotational ones don't work either. Ariel. (talk) 06:55, 1 February 2010 (UTC)
See [1]. Wikipedia has a short article on the Barnett effect. Cuddlyable3 (talk) 11:45, 1 February 2010 (UTC)
It seems it could be done with Diamegnetic Levetation, or at least our WP article would have you believe so. CoolMike (talk) 01:34, 4 February 2010 (UTC)

Thermal Gravimetric Analysis[edit]

Is it possible to determine the composition of a mixture of CaC2O4 and CaCO3 using Thermal Gravimetric Analysis? If so, how? —Preceding unsigned comment added by (talk) 04:04, 1 February 2010 (UTC)

Thermogravimetric analysis, for those interested. --Tagishsimon (talk) 04:07, 1 February 2010 (UTC)
Welcome to Wikipedia. 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. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. TenOfAllTrades(talk) 04:17, 1 February 2010 (UTC)

Contracting diseases via intercourse with cells?[edit]

If an individual has sexual intercourse with a cancerous cell (e.g. a mutated cell cluster or cancerous tissue as detected in a biopsy), will they contract cancer? Does it matter if the disease that the cell carries is a sexually transmitted disease (e.g. gonorrhea); that is, is it more viable or likely that the person will become infected as a result of intercourse? Further, why or why not would this happen? As much as this may seem like a facetious question, I am genuinely curious and would appreciate any insight that can be offered, whether it is theoretical or concrete. Thank you, Arcendet (talk) 06:00, 1 February 2010 (UTC)

You will not 'catch cancer' by having sex with someone who has cancer. If the cancer was generated by an underlying sexually transmitted disease (e.g. gonorrhea or HPV) you might catch that particular disease, and that disease might (eventually) induce cancer in you as well, but there is no necessary, direct, or causal relationship implied there. relax, you're relatively safe. next time use a condom. --Ludwigs2 06:18, 1 February 2010 (UTC)
Actually we don't know that. See Devil facial tumour disease which is a transmissible cancer (we actually have a page on that). There is no reason to assume it could not happen to humans too - and in fact the page lists one case where it happened. Especially if the lag/incubation period is very long it would be very hard to figure out the correlation. Ariel. (talk) 07:01, 1 February 2010 (UTC)
Uh... those refer to dogs and tasmanian devils... and (excuse me) apparently to Syrian hamsters as well. There is no known pattern of a transmissible cancers in humans, or even in primates. assuming that the OP is not a tasmanian devil, canid, or Syrian hamster (and has not been using Syrian hamsters in some fairly perverted way) I see no reason to alarm him/her over the risk of transmissible cancers. --Ludwigs2 07:20, 1 February 2010 (UTC)
And a human too, did you miss that part? It's not just theoretically possible, it's actually happened. I never said it was common, I said we don't know. He did ask for even theoretical information. Ariel. (talk) 07:43, 1 February 2010 (UTC)
I missed any mention of Devil facial tumour disease being transmissible to humans and I would think the amount of research that has been done on it is a reason to assume that would have been noticed if it were possible. However research into dog to human STD's is as yet only in its infancy puppyhood. Cuddlyable3 (talk) 11:33, 1 February 2010 (UTC)
I don't think Ariel is referring to Devil facial tumour disease being transmissible to humans. Rather some surgeons have had tumours that have been transmitted via accidential implantation on an injury site with the article linking to this specific reference [2]. This clearly is very uncommon and requires a specific set of circumstances (i.e. isn't something that occurs in the 'wild' if that has any meaning for humans) and tumour types and isn't associated with sexual intercourse nor blood transmission but Ariel never said it was. Transplanted organs can of course also effectively transmit cancer although I don't know if you'd call that a transmittable cancer. Nil Einne (talk) 14:16, 1 February 2010 (UTC)
It would have to be a mighty big cell to have sexual intercourse with it! As for human transmissible cancers, see HPV which is responsible for transmitting cervical cancer. However, as I assume the questioner is a man, he won't actually catch cervical cancer (not having a cervix), but apparently can get cancer of the penis. You're at most risk of catching an STD if you don't use a condom. It's possible cervical cancer could be classified as an STD. --TammyMoet (talk) 09:09, 1 February 2010 (UTC)
As an aside, HPV infection is also associated with oropharyngeal cancers – cancers of the mouth and throat – which again are of concern to both women and men. TenOfAllTrades(talk) 14:28, 1 February 2010 (UTC)
File:Cases of HPV cancers graph.png is perhaps of interest here.
However as explained by Ludwings, this isn't really a transmittable cancer at least by the definition used in both of the earlier linked articles. Rather the virus is transmittable which when it infects a human can eventually (along with a whole host of other changes) lead to cancer in a small number of people. This compares to a transmittable cancer where the cancerous cells themselves infect the other host. A more complicated case which perhaps illustrates the complexity is HIV which usually compromises the immune system can also greatly increase the risk of cancers [3]. This includes for example Kaposi's sarcoma itself caused by Kaposi's sarcoma-associated herpesvirus [4]
Nil Einne (talk) 14:43, 1 February 2010 (UTC)

Scientific Film Association[edit]

The Scientific Film Association was constituted on 20 November 1943 to promote the use of the scientific film in order to achieve the widest possible understanding and appreciation of scientific method and outlook. Active members included eminent film makers such as Sir Arthur Elton and Edgar Anstey. Several standing committees were set up and the Medical Committee became a leading authority on medical films in the UK and published several catalogues of appraisals of films on specialist medical topics. The SFA, together with the French Institut de Cinematographie Scientifique, established the International Scientific Film Association in October 1947.

There is no mention of the SFA in Wikipedia but one note of an Italian who was an ISFA member. Do you think that I should prepare a possible entry? Michaelsthgate (talk) 10:35, 1 February 2010 (UTC)

First look at WP:N. Have you citations that verify the SFA is a leading authority? Cuddlyable3 (talk) 11:19, 1 February 2010 (UTC)
Leading or not, if it existed and produced lasting artefacts like catalogues, then I would go ahead and include it. But, as Cuddlyable said, you must provide citations for every claim. --Heron (talk) 12:43, 1 February 2010 (UTC)
Googling the name produces articles about the association in Nature and several other significant references. I don't think you'd have a hard time establishing notability. So yeah - I think Wikipedia needs an article about this. As others have pointed out - you need to be sure that there are a good number of references for the article in general - and in particular that all potentially controversial statements are individually tagged with a specific reference. I look forward to reading it! SteveBaker (talk) 18:59, 1 February 2010 (UTC)


IS THERE ANY INFORMATION ON ZERO HALOGEN FLAME RETARDANT CABLES? —Preceding unsigned comment added by (talk) 13:15, 1 February 2010 (UTC)

You can find references to them in our articles on Trirated cables and Low smoke zero halogen. Does that help? Gonzonoir (talk) 14:21, 1 February 2010 (UTC)

Do wires carrying DC get corroded more or less easily than those carrying AC?[edit]

Do wires carrying DC get corroded more or less easily than those carrying AC, or are they the same? -- (talk) 13:32, 1 February 2010 (UTC)

Yes where dissimilar metals are in contact e.g. aluminium cable to brass or copper connectors. This [5] reports "5% of total corrosion costs in USA, [mostly arise] from electrified DC transit system operations". Cuddlyable3 (talk) 14:40, 1 February 2010 (UTC)
Otherwise, there should be NO difference between AC and DC that I know of. See Electrolysis and Electrolytic cell for relevant info. See the related Sacrificial anode for corrosion prevention. Also Galvanic corrosion-- (talk) 15:29, 1 February 2010 (UTC)

Wires get corroded by heating-up. They heat-up since they have a typical resistance per unit length (depending on the material), so when current flows through them, it disspates power in them given by P=I²•R (where I is the current). Note that AC current must have a larger amplitude than the DC current, to generate the same power. The result of integrating the square of the current over time, to find the mean of the power-contribution, is called [Root mean square] (or RMS). So an ac current of the same RMS as a dc current will dissipate the same amount of power along thw wire, and will generate the same amount of heating-up. The result of the RMS integral is dependant upon the waveform of the ac current. For sine (cosine) waves, the RMS value is sqrt(2)/2 (=~0.7071...) of the amplitude. For example, in incandescent light-bulbs, you need an ac amplitude of current, which is larger (times the inverse RMS amount) than a constant dc current, to produce the same amount of heat (and light). --Shimon Yanowitz (talk) 16:39, 1 February 2010 (UTC)

I would expect more electrolytic effects from wires carrying DC than AC, unless the insulation is perfect. With AC, the metal removed in one half cycle might be returned in the other half cycle, but with DC there should be a continuous deposition of metal, provided there is leakage current, as when wires are underground and there are small cracks in the insulation. There is also electrolytic action causing ferrous metal underground to lose metal when copper is nearby, but that should not depend on AC versus DC current in the copper, as long as the circuit has a return path and is not just unipolar. Edison (talk) 20:43, 1 February 2010 (UTC)

Advice on modelling a flood[edit]

For a creative project I'm imagining a scenario in which unprecedented rainfall causes disastrous flooding in (inter alia) Cambridge, UK. The premise is unrealistic, but I want what follows from it to be as plausible as possible. So I'm seeking tips on how I could model what flooding would look like in this town: I'd like to be able to produce a map showing which parts of the city are still above the flood level.

I guess I would need to find values for variables, including:

  1. rate of precipitation (how much rainfall per time period)
  2. topography of the area
  3. effect of rainfall upstream
  4.  ?season (drains clogged with leaves in autumn? Water table higher at certain times of year?)

Can anyone give me pointers on how I could realistically model the flooding of the town, if I had set values for these variables? If I wanted to say "it has rained solidly for x days at a rate of y centimetres per day", how can I figure out what effect that would have on the ground? I'd be very grateful for tips on ways to get started, or on factors I'm missing from my list. Gonzonoir (talk) 13:44, 1 February 2010 (UTC)

You will want a relief map of the area such as the maps with contour lines published for the U.K. by the Ordnance Survey. Without effective measures of Flood control, floodwaters will settle within a given elevation contour line. Cuddlyable3 (talk) 14:27, 1 February 2010 (UTC)
Further, you'd need to estimate flood points and try to work out a flow pattern. rising water does not create floods; floods are created when water passes the lowest point on the river bank, and how it flows from there will determine damage patterns (damage will be more extensive, for instance, where water can pick up momentum or build up pressure). You'l also want to consider whether you're talking about natural flooding (where water passes a bank and more or less gradually fills the surrounding region) or catastrophic flooding (where the failure of a natural or man-made containment wall releases huge quantities of water rapidly). --Ludwigs2 15:46, 1 February 2010 (UTC)
Historical information about previous floods in the city may be helpful (perhaps to confirm whether your model has validity). A google search throws up links to photographs of previous floods. You may be able to estimate how high the water was at the stated locations but I didn't find an aerial photograph. Museums and pubs often seem to have photos of floods :-) --Frumpo (talk) 16:33, 1 February 2010 (UTC)
Another variable you need is the percolation/drainage capability of any area - and that's complex since drainage capabilities of any area will be affcted by the drainage capability of another area (e.g. if both discharge into a common and limited drainage channel). --Tagishsimon (talk) 17:37, 1 February 2010 (UTC)

Many thanks all - this is exactly the sort of thing I was after. Some follow-up questions:

  1. The OS 1:25 000-scale map for the city has contour intervals of 5 metres. Cambridge is as rugged and mountainous as a pancake, so there ain't that many of them. Does anyone know of a resource showing contours at a finer level of detail?
  2. The point about percolation is well taken. Can I make the blanket assumption that the broader the scale of the storm (i.e., the greater the size of the area that's getting rained on), the worse drainage at any one point will be?
  3. Ludwigs2, just to clarify, by "flood point" you mean the spot(s) at which the river breaks its banks? That seems like an area where Frumpo's suggestion of gathering data on earlier floods would be helpful. Gonzonoir (talk) 20:15, 1 February 2010 (UTC)
The Environment Agency has maps of areas likely to flood. AndrewWTaylor (talk) 14:00, 2 February 2010 (UTC)
Cheers AndrewWTaylor. Gonzonoir (talk) 09:19, 3 February 2010 (UTC)

Speed of heat transfer[edit]

Can we say that heat is transferred at the speed of electromagnetic waves throughout a medium? I understood it is transferred by conduction, for instance at the speed of sound, but isn't there a radiation contributing factor through this medium?--Email4mobile (talk) 16:53, 1 February 2010 (UTC)

There are three important ways heat is transferred: radiation, which goes at the speed of light; diffusion, which does not have a definite speed; and convection, which depends on bulk movements of the medium. In many situations radiation does not play a significant role and diffusion is the main factor. "Conduction" is the same thing as diffusion here, and it does not go at the speed of sound -- its speed drops off with distance. Looie496 (talk) 17:01, 1 February 2010 (UTC)
I'm afraid I couldn't get it. Let me rephrase the question: What is the time required to cause an infinitesimal or tiny change in temperature provided that a significant change has taken place at a given distance of known medium (with its characteristics involving heat transfer)?--Email4mobile (talk) 17:21, 1 February 2010 (UTC)
It depends on what your medium is. If it is transparent to infra-red radiation then a solid object immersed in the medium will be heated most rapidly by electromagnetic radiation (although the medium itself is not heated this way becqause it does not absorb the e.m. radiation). If the medium is opaque to infra-red radiation then a thin layer near its surface is heated rapidly by e.m. radiation but the bulk of the medium has to be heated more slowly by convection in a liquid or gas or by conduction in a solid. Gandalf61 (talk) 17:37, 1 February 2010 (UTC)
Then at what (slowly) speed will the heat transfer by conduction and convection occur? This question will help me save the time asking another question about a maximum theoretical possible speed for sound if it will be the same, thanks in advance.--Email4mobile (talk) 18:04, 1 February 2010 (UTC)
The question you phrased is probably not the question you want to be answered. As any (as far as I know) medium is transparent to some kind of electromagnetic radiation, and as any material will radiate on any frequency (albeit and notably not at the same intensity) any change in temperature will reach any other body at the speed of light. The energy exchanged in this way will in most cases be negligible compared to the energy flow by slower convection and conduction. (talk) 18:28, 1 February 2010 (UTC)
Let's try to break this down a bit.
  • Radiation: If you had a hot body and a thermometer separated by some distance in a hard vacuum - then such heat as would be transferred from one to the other would happen via infrared radiation (mostly) and that travels at the speed of light (because it is light).
  • Conduction: If you had a steel bar and heated up one end with the same thermometer at the other end, then because steel is opaque to infrared light, the heat would have to travel from one end to the other by conduction...a much slower process in which the jiggling of a hot atom at one end knocks into another atom next door and sets that jiggling too - and atom-by-atom, the jiggling spreads from the heat source to the thermometer. The speed at which that happens varies dramatically from one material to another. At one extreme, metals like steel conduct heat fairly quickly (although nothing like as fast as the speed of light). At the other extreme, materials such as aerogel or the stuff they make space-shuttle heat tiles out of conduct heat incredibly slowly. Everything depends on the structure and constituents of the material. The speed of conduction is nothing like the speed of sound. Sound travels through steel bar at hundreds of miles per hour - but when you stick a metal teaspoon into a near-boiling cup of coffee - it might take several seconds for the heat from one end of a six foot chunk of steel to be noticable at the other end.
  • Convection: If you put a hot body into a room that's full of air - and put one thermometer six feet to the left of it and a second thermometer six feet above it - then the first thermometer will take a lot longer to register the temperature rise than the second one. That's because as the air around your heat source warms up, it expands. It's density gets lower...the air becomes "lighter". This lighter, warmer air tries to float on top of the denser air - just like a piece of wood floats on water. As the air rises upwards, it reaches the thermometer above the heat source quite soon - but that warm air has to be replaced by cool air from around the sides - so the conduction of heat through the air is messed up by that air flow and the thermometer off to the side may never show a temperature increase at all! This convection effect relies on the materials being free to move around - so you don't see convection in a steel bar - but you do see it in water, mercury, air, etc. Even within liquids, the runnier the liquid, the faster the convection currents can move. The amount of convection in (say) treacle is far less than (say) in water. I suppose that the rate of convection might be limited by the speed of sound...but I don't think so. At any rate, it's not usually that fast.
So the answer to your question is fairly complex. In many situations, the transfer of heat from one place to another depends on all three of these mechanisms. If you light a fire in your fireplace, you are immediately warmed by the thermal radiation - but as the hot air produced by the fire goes up the chimney, you feel a cool draft from the colder air in the rest of the room. However, heat from the fire is also warming up the walls and floor of your house by conduction - and you get some warmth that way too. Figuring out the results of those three things complicates the answer to the point where we can't give you any kind of measure of speed without knowing precisely what materials and distances are involved. SteveBaker (talk) 18:44, 1 February 2010 (UTC)
Just to add to Steve's reply, in a thin column of air (or other fluids), the descending cool air can't move to the side of the ascending warm air, and thus inhibits free convection. This is one of the methods in double-glazing. CS Miller (talk) 20:26, 1 February 2010 (UTC)
Steve, your description of the conduction microphysics is incomplete. Thermal conduction in most solids is mediated by phonon diffusion. Phonons do travel at the speed of sound in the material, but most materials are opaque to thermal phonons. As a result the thermal diffusivity in most solids can be estimated as the speed of sound in the material (typically a few km/s) times the phonon mean free path (typically several angstroms). I assume the original poster knew something about this or else he wouldn't have mentioned the speed of sound. So, in principle the information about a new thermal contact could transfer as fast as the phonons do, i.e. at the speed of sound, but in practice most materials are limited by the internal scattering of phonons and measurable diffusion takes much longer. The other issue with your discussion was the choice to use a steel bar. Heat conduction in steel, like all metals, is totally dominated by the propagation of conduction band electrons. So the idea of atoms bumping into each other, though an appropriate image for phonons in insulators, is not the right image to use for metals at all where essentially all the work is done by electrons bumping into each other. This difference is also why thermal conductivity of metals is so much higher than for insulators. Dragons flight (talk) 23:15, 1 February 2010 (UTC)

Europa (moon)[edit]

When Europa warms up I thouhgt this is possible Europa can end up back to watery globe. The surface is made of white ice which is thick layers of oxygen. If scinetist think Europa is once cover with oceans when gravity is too low how can they keep a substantial atmosphere? Isn't Europa even smaller than Pluto so outgassing should be even likely-- (talk) 17:29, 1 February 2010 (UTC)

I don't know about "when" Europa warms up - that seems unlikely to happen before the sun turns into a red giant...and even then, not for long. Anyway - what prevents all of the oceans from boiling off into space is precisely because there is all of that ice there. If the planet warmed up enough for the ice to melt, it would start to boil. On a larger body, the water vapor would form an atmosphere, the pressure of which would gradually increase until there was an equilibrium between liquid water and water vapor. But Europa has insufficient gravity to keep that water vapor as an atmosphere - so rather than the pressure building up to maintain that equilibrium, the oceans would keep on boiling until they were all gone. If there are liquid oceans there - they are locked below a thick layer of ice which (being a solid) is only sublimating away very slowly. Outgassing (of a sort) is one of two proposed mechanisms to explain the cracked appearance - yet super-smooth surface of the moon. It is thought that the surface ice may occasionally crack due to tidal forces from nearby Jupiter. The pressure in the oceans beneath the ice would force geyser's of water to be forced up through the crack - only to freeze as soon as it reached the surface. This mechanism would continually force water from the liquid oceans, up through cracks - across the surface. Because warm water from the ocean is likely to slowly melt the underside of the ice - undermining it and causing more cracks - there would be a slow recycling of water through the ice sheets. This seems to be the most likely explanation for the observations of Europa - but there is another plausible theory that there is no liquid water - but merely slowly flowing ice beneath a brittle surface layer. SteveBaker (talk) 18:28, 1 February 2010 (UTC)
Hang on. Europa was once thought to have watery surface in the history billion of years ago [6]. It must be said somewhere in our article if somebody could find it. That's what solarview website said.-- (talk) 20:40, 2 February 2010 (UTC)
See oceans of Europa. Also, the end of the Sun would cause many parts of the solar system to be destroyed, including (according to one documentary) all of the gases of Jupiter, leaving only its core, which it erroneously claims will be smaller than Europa (which is not possible, given the size of Jupiter's core). The shedding of the sun's outer layers would be sufficient to disrupt the ice if the expansion does not do it first, but it's possible that its entire orbit around Jupiter would be disrupted, sending it into the planet or being swept out to space–we don't know. ~AH1(TCU) 02:53, 2 February 2010 (UTC)

is melvin manhoef okay?[edit]

? —Preceding unsigned comment added by (talk) 17:53, 1 February 2010 (UTC)

Does this question has any scientific aspect? (Mind you, you're asking this on the Science Reference desk, not on a news desk.) (talk) 18:08, 1 February 2010 (UTC)
Our Melvin Manhoef page doesn't list any current injuries, and I went to Google News and typed "Melvin Manhoef", and 25 stories were found about this weekend's fight. I only read one of them, which didn't mention any lasting injuries. For future reference, 95 is correct, this would probably belong better on the Entertainment desk; and also for future reference I do recommend a news site like Google News for "what happened yesterday" questions like this; it's faster than coming here to Wikipedia, asking, and then waiting several hours for someone like me to go Google it for you. Comet Tuttle (talk) 18:27, 1 February 2010 (UTC)
Ah, this is our world today and I don't have much capacity to complain about but, please all of you think twice, is the state of health or injury of any human being really a matter of entertainment? I think, yes, in the world as it is, it is, but it should not. (talk) 18:39, 1 February 2010 (UTC) (And sorry if this violates Wikipedia:NPOV and current political correctness.)
Good one! I suggested the Entertainment desk not because injuries are hilarious, but because Melvin is the Light Heavyweight World Champion of Cage Rage, which is a form of entertainment. Questions about injured boxers or wrestlers belong there too, unless, I suppose the questioner is asking about the details of the fighter's subdural hematomas. Comet Tuttle (talk) 19:18, 1 February 2010 (UTC)
So isn't it illegal to inflict such injuries to anyone, or to promote or endorse such doings? Why aren't all those rubbernecks paying attention and money to see such incidents simply going to prison? (talk) 19:55, 1 February 2010 (UTC)
Presumably these actions are between consenting adults? Googlemeister (talk) 21:03, 1 February 2010 (UTC)
If so, why then is there any fuss about any injuries consented? (And if in any countries with national health care, is there any compensation for the non-consent-forced-contributors?) (talk) 21:53, 1 February 2010 (UTC)
This is not really the place to soapbox about the morality or moral hazard of boxing. Please do it elsewhere. Rckrone (talk) 22:57, 1 February 2010 (UTC)
I'm surprised that there is no boxing license article. (talk) 21:40, 1 February 2010 (UTC)

Can I eat my father's popcorn?[edit]

For the longest time I didn't know it was there. It was in the back of a cabinet. I've never bought popcorn, so it must be his.

My father moved out 11 years ago.Vchimpanzee · talk · contributions · 18:48, 1 February 2010 (UTC)

Are you asking if it has gone bad? Popcorn will basically not go bad IF it has not been exposed to moisture or bugs. But you should be able to tell by looking at it if it has gone bad—with over a decade of time, it has either probably gone reeeeeaallly bad (it will be able to carry out a conversation with you), or it is just fine to eat. Note that this may vary depending on any flavoring or coating on the popcorn—if it has all sorts of synthetic butter stuff on it, I don't know whether that stuff goes bad, stale, whatever. I would be a bit wary of that stuff. --Mr.98 (talk) 18:58, 1 February 2010 (UTC)
I found a bunch of other stuff too. Sugar, cocoa, pancake syrup ...Vchimpanzee · talk · contributions · 19:07, 1 February 2010 (UTC)
Assuming this is a commercial product, it probably has a relatively long shelf life. at any rate, or popcorn to go bad it needs to absorb moisture, and if it absorbs any significant amount of moisture is won't pop.
That being said, popcorn costs a dollar or two (US currency) per pound. Unless you're talking about a huge quantity (e.g., your father stockpiled shelves of the stuff), it's probably wiser just to toss it and buy a new package. --Ludwigs2 19:08, 1 February 2010 (UTC)
It's a very small amount. That's why I never saw it. Vchimpanzee · talk · contributions · 19:11, 1 February 2010 (UTC)
(after ec) Answering quite formally, we are not to give legal (that stuff is owned by your father, ain't it?) nor medical advice (no one would like to be liable if you get stomach cramps or worse) I have to tell you that we cannot answer your question. But I can tell you what I did in a similar situation (which is not even original research, I did not research, I just did it). I used the sugar, threw away the cocoa (it tastes bitter when rotten, but it also tastes bitter when fresh), and I had a taste on the syrup before deciding it didn't taste of and was sticky enough that it would have not enough free water for any bacteria to live in it. If you are not in really dire need of food, throw away whatever you're in doubt of being harmful. (talk) 19:23, 1 February 2010 (UTC)
This is why we have "use before..." dates - are there any of those on these products? I would be surprised if any of the things you mentioned would be a problem - providing no moisture got into them - and no rodent chewing/droppings are evident. SteveBaker (talk) 19:30, 1 February 2010 (UTC)
"Best before" dates are set very restrictive, to protect the selling company from lawsuit. It's not a Median lethal dose test. (Which is well, that is is not.) (talk) 19:38, 1 February 2010 (UTC)
The popcorn is not in its original container. Neither is the sugar. I could check the cocoa.Vchimpanzee · talk · contributions · 20:24, 1 February 2010 (UTC)
Old popcorn loses the internal moisture needed to explode into steam and make it pop, so the size of the popped kernals should decrease and the number of unpopped kernals should increase in very old popcorn. We cannot predict other harmful effects such as fungus or insect infestation. Edison (talk) 20:36, 1 February 2010 (UTC)
I missed one the responses. As executor of my father's estate and the only one who inherited from him after his wife agreed to a certain amount, the food is mine.Vchimpanzee · talk · contributions · 20:39, 1 February 2010 (UTC)
So I assume it has some kind of personal, memorable value. I encountered this from personal experience, in a time when Germans socialists where on top and I didn't know if I'll ever get a job again, thus valuing any left food twice as high (not wanting to be in need to beg the apparatchniki for sustenance). My personal advice is: throw away what is clearly rotten, use what can safely be eaten, and await a time where the rest of it clears out to be on one or the other side. (talk) 21:15, 1 February 2010 (UTC)
None of the things you mentioned will spoil, but you might have bugs in them, and the taste might be bad. But from a safety point of view, I would be comfortable eating them. The popcorn will almost certainly not pop, and the cocoa might taste bad. The sugar and corn syrup will be fine. But please check for bugs (look for webs). It's a rare airborne fungus that would be harmful to eat (as opposed to breathe). And bacteria can not live in those things (too dry). Ariel. (talk) 21:11, 1 February 2010 (UTC)
Good advice from Ariel and Mr.98 (among others). As an aside to re " 'Best before' dates are set very restrictive". The meaning of these terms may be different between jurisdictions, meaning countries. In Australia 'Use by' means it should be used by and NOT eaten after. 'Best before' is a much more rubbery figure. Many foods are perfectly good to eat well after that date, ie. Fruit cake comes to mind, but probably not (depending on food and storage) 11 years (I have some cake 5 months past best before, still very yummy). Shelf life covers both terms. -- (talk) 22:58, 1 February 2010 (UTC)
Some dangerous microbes also live in anaerobic environments. That's why canned foods can be dangerous. (talk) 02:18, 2 February 2010 (UTC)

to get to orbit, is the weight of the rocket fuel you need linear with the weight of the payload you get up?[edit]

if a trillionaire was inspired by a successful government rocket launch and decided, I wanna get a payload that's ten thousand times heavier up into orbit, would they need a rocket system that is ten thousand times as massive? (ie a linear relationship). Or would it be more/less?

In general, how massive a rocket system (rocket system including fuel) do you need to get x pounds of weight up into orbit? (ie what is the formula).

neitehr is homework question, thanks. (talk) 19:13, 1 February 2010 (UTC)

  • Depending on the distance you want to go and the time you have (if a trillonnaire, plenty or none ?), fuel may put you off terrestrial gravity and then you just have to let solar winds or ionic propulsion take the relay with very much less load costs. -- (talk) 19:25, 1 February 2010 (UTC)
No. See Rocket equation. The reason is that you need to lift (part of) the fuel, too. (talk) 19:30, 1 February 2010 (UTC)
You are wrong. It IS linear with the amount of stuff you want to lift. Here is a thought experiment: Imagine you have a launch vehicle that can get 1 ton up to the required orbit with a certain amount of fuel. Now you want to launch a 1000 ton object. Well, you could cut it up into 1000 one ton pieces and launch each piece using a 1 ton launcher and the cost in fuel and motors would be exactly 1000 times as much as for launching 1 ton. Then, because all of the 1000 rockets are identical and with identical payloads - they would go up at the same speed/acceleration. That means that you could launch them all simultaneously and they would stay together. So you can bolt them all together and pretend that they were just one large rocket - and now you don't have to cut your payload into bits. In reality, there would be some parts such as control circuitry and many redundant systems that would not need to be duplicated 1000 times - so in practice, it's a little better than linear. SteveBaker (talk) 19:58, 1 February 2010 (UTC)
You are right, it is linear from the equation. I got it wrong in memory and was too convinced to read the article I've linked for a check. It probably is not linear with very small weights as the hull weight is not linear (so I think). (talk) 20:23, 1 February 2010 (UTC)
No doubt that below the size of an effective present-day launch vehicle, things might get unlinearly worse - but above the present size shouldn't be a problem in principle. Of course, the practical issues are a problem. If you have 1000 rockets, the probability of them all working perfectly is close to zero - so you need lots of redundancy. A one in one hundred chance of a 1 ton launch vehicle getting off the ground would translate into a near certainty of failure for a 1000 ton launcher made up of 1000 one ton launchers. Hence you need more thrust to take account of that expected failure rate. But in theory, it's a linear thing. SteveBaker (talk) 14:25, 2 February 2010 (UTC)
Agreed. If my math is correct, if your rockets were 99.93% reliable, you would have just under a 50/50 shot at success. Googlemeister (talk) 17:35, 2 February 2010 (UTC)
But I would like to hitch-hike the question and add my own: how small (weight and dimensions) can a rocket be to enter near earth orbit from earth? (talk) 19:30, 1 February 2010 (UTC)
Well, our comparison of heavy lift launch systems provides a good starting point. Considering low earth orbit only, here's some common systems and their efficiency (payload over launch mass):
Now, of those, the Titan (the least efficient) is also the largest. The Atlas (most efficient) is also the smallest. It's also got a large payload range specified, so I'm more suspicious of that estimate being high. Anyway, we can finally consider the Saturn V, with 3.9% efficiency to LEO, and it's many times larger than any of the above. So basically, economy of scale doesn't apply from a size standpoint. As such, you're probably not going to make one ten-thousand class launcher; instead, you'll launch ten thousand generic ones (or one thousand ten-class launchers, or something else that really will let you use economies of scale). — Lomn 19:32, 1 February 2010 (UTC)
Addressing the rider question: Given the above, you could expect to launch a 1 kg payload to LEO with about 50 kg of rocket, if everything scaled well. 500 kg of rocket should work out fine as a theoretical minimum launch vehicle. Poking through our comparison of small lift launch systems, the British Black Arrow was the smallest actual launch vehicle I saw at 18000kg and 13 m tall. — Lomn 19:40, 1 February 2010 (UTC)
So if you wanted to send something really high, best to use a ballon. Beach drifter (talk) 19:44, 1 February 2010 (UTC)
No - a balloon won't get you above the top of the atmosphere - and it won't get you the orbital speed you need so even if you could get up to the right altitude, the payload would just fall back to earth again. So you still need a rocket or something similar to get you up to orbit. However, a balloon is a great way to get really high without orbiting. SteveBaker (talk) 20:03, 1 February 2010 (UTC)
Er, well, thats why I said really high, and said nothing about orbit. Beach drifter (talk) 20:18, 1 February 2010 (UTC)
Uh me bad for original thinking! I imagine a pipe of glass carbon (what, no article on that? Did I get the spelling wrong?) filled with oxidizing rocket fuel and using the flopping effcet (what, no article???) to throw off burnt parts of the pipe as to emulate multiple stages of a rocket thrown off. And, of course, set off in a high altitude reached using a hydrogen balloon. (talk) 20:07, 1 February 2010 (UTC)
Rockets that use the airframe as part of the fuel do exist. They usually explode on impact, too. (Not commonly a design goal for orbital launchers and certainly not for manned rockets!) Generally, if you want to guarantee safety of the payload, it's considered a bad idea to burn through your structural elements. I've never heard of "glass carbon", at least not in the context of a rocket fuel. It's worth noting that graphite is used in nozzles because it's reluctant to combust and/or ablate, even in the presence of extraordinarily strong oxidizers and extreme heat. As for the OP, you can cut down on your mass ratio in a lot of ways. The easiest way is to cut down on your safety factor. This is rarely desirable. Ultimately, as has been pointed out, you want to see rocket equation - and remember that "inert mass" includes all kinds of structural things like pipes, tubes, aerodynamic control surfaces, and more "connective tissue" than you probably expect. (Every part of the rocket has to be held in place). Extremely small rockets can't ammortize this overhead mass very well. Extremely large rockets suffer from an excessive requirement for structural support. The result is a "sweet spot" in terms of total rocket size, as evidenced above. This is more about engineering details than pure physics - but there's a theoretical limit too. Even an infinitely staged rocket can't beat certain physics, based on the efficiency of your rocket motor's combustion (in particular, the energy-per-mass of propellant, which is related by the effective exhaust velocity). Nimur (talk) 22:10, 1 February 2010 (UTC)
I have to admit that I am a bit startled that I can't find neither the (an??) article about glass carbon nor on flopping. From my memory, glass carbon is a from of carbon (supposedly) based on fullerenes that is "glassy" (none-crystalline), gaining its optimal strength at somewhat over 3000°C. Flopping is a mostly undesirable effect of uncontentious burning of rocket fuel leading to yet undesirable pressure fluctuations that could (warning: original thinking!) be used to throw off burnt stages of the rocket. (talk) 22:36, 1 February 2010 (UTC)
Combustion instability goes by many names. I've never heard it called "flopping" but I've heard "chugging", "luffing", "chuffing", "burn instability," "oscillation", and "parametric decay instability." I don't think anybody wants this to happen, it's generally an undesirable effect that can lead to poor performance and even damage. Nimur (talk) 02:20, 2 February 2010 (UTC)
Yes, it's Combustion instability and I can't find "flopping" any more but it's what I remember as name for it when I first heard of that effect. The other thing is spelled glassy carbon. (talk) 21:22, 3 February 2010 (UTC)
Your trillionaire would be better thinking outside the box and coming up with an innovative launch method that does deliver economies of scale - such as Project Orion or a space elevator. Gandalf61 (talk) 14:46, 2 February 2010 (UTC)
Space elevators have got a few mentions recently, so this [7] may be of interest to help deskers. (talk) 11:17, 3 February 2010 (UTC)

mRNA and secondary structure...[edit]

What causes mRNA secondary structure? What impact did the presence of secondary structure in the mRNA have on the scanning and initiation steps of translation? —Preceding unsigned comment added by (talk) 21:12, 1 February 2010 (UTC)

RNA structure and mRNA might be a good start. Rckrone (talk) 23:40, 1 February 2010 (UTC)

Black Arrow awakened[edit]

Is there any reason why, if the engineering plans and other details survive, that a Black Arrow could not simply be built, giving a working launch vehicle with zero development costs? Obviously a launch site would be needed too. (talk) 21:33, 1 February 2010 (UTC)

Are you counting the cost of the engineers needed to build it? Rocket scientists aren't cheap. Nimur (talk) 22:18, 1 February 2010 (UTC)
That program had 2 successful launches and 2 failures, according to the infobox. It would be possible to take the plans and go and make one and launch it, yes; but there would be the cost of building whatever ground control facilities are necessary to communicate with the thing. You might consider that a development cost. Upon launch, if there is a launch failure, you're going to want to fix the problem on future rockets, so there will be development costs there for incremental improvements. There will also be the inevitable engineer's burning desire to improve this 40-year-old design, with all the improvements in materials science and rocket engineering that have transpired. If I know engineers, they're going to say "start from scratch" when this is proposed. Comet Tuttle (talk) 22:18, 1 February 2010 (UTC)
I think the OP is underestimating the difficulty of looking at a rocket schematic, and actually building a rocket. It's not exactly like a Lego set. Material costs are high. Rockets are built from weird stuff (exotic metal alloys, dangerous chemicals, toxic fuels and oxidizers). Many of the things you need to acquire to build one, including the metals, chemicals, electronics, and software, are controlled by the government (ITAR). A huge amount of hassle and red tape goes into this to make sure you aren't building anti-aircraft systems or weapons. (Let me clarify - the cost of this red-tape comes out of your budget!) The actual costs of design are much lower than the total project cost. Testing is often dangerous and/or destructive. (If you had a re-usable rocket, you'd be in great shape!) But a huge number of elements - even things you wouldn't expect - are "consumable". This means you need one item per test, (not even counting catastrophic failures!) Even if you have a perfect schematic, what about assembly? You need dozens, if not hundreds, of skilled engineers, technicians, machinists, and a huge variety of hard-to-find, specialized skill-sets. Hiring those people, either full-time or contractually, is not free. Are these enough reasons why a Black Arrow, or indeed any rocket, can't be built with "zero development cost"? Nimur (talk) 22:25, 1 February 2010 (UTC)

It's 1960's technology. Can't be that difficult. (talk) 00:38, 2 February 2010 (UTC)

Well, there was a bunch of stuff commonly manufactured fifty years ago which is not manufactured now. And if your rockets happens to need any of that stuff - which is fairly likely - then you do have to rediscover how to make it. And I agree that all things being equal, that is well possible. But it is a damned site harder than simply being able to put in an order at your nearest supplier. And that is one of the reasons that "can't be that difficult" is not very well observed. --Tagishsimon (talk) 00:45, 2 February 2010 (UTC)
I'm sure if "1960's technology" equated with "trivial to acquire", then classic car enthusiasts would be a lot richer. "Classic aerospace engineering" is a little more expensive than repairing an original Mini-Cooper! You could start with that, and once you've totally mastered it, start working your way up the ladder of vehicle complexity. Nimur (talk) 02:23, 2 February 2010 (UTC)
It's incredibly difficult to take someone else's plans and turn it into a workable thing. There will always be ambiguities - and situations where you really need to ask the designer "why did you do it like that?" - and in this case (as User:Comet Tuttle points out) the rocket only had a 50% success rate - so you already know that there's going to have to be a certain amount of redesign. But without being able to talk with the original designers, it would be an uphill struggle to turn these things to a solid launch vehicle. SteveBaker (talk) 03:00, 2 February 2010 (UTC)
See ths story about another program having trouble following some blueprints. To refurb some not so very old nuclear warheads: "The component, known by the code word "fogbank," is thought to be made of an exotic material and is crucial...When it came time to make new batches of fogbank for the refurbishment program, the current workforce was unable to duplicate the characteristics of the batches made in the 1970s and 1980s, according to a March report by the Government Accountability Office. 'I don't know how this happened that we forgot how to make fogbank,' Coyle said. 'It should not have happened, but it did.'" Rockets have similar national security and technical issues. (talk) 06:31, 2 February 2010 (UTC)
Nice story! And we have an article on this: FOGBANK. Comet Tuttle (talk) 18:29, 2 February 2010 (UTC)

The unused latest rocket is in a museum somewhere for inspection - pity it wasnt/isnt filled up with juice and fired off. (talk) 12:33, 2 February 2010 (UTC)

horse distance[edit]

How far can a horse travel in one day over flat terrain such as the American Midwest without wearing it out (it must be able to travel roughly the same distance for many days in a row) presuming it has 300 lbs or rider and equipment? I am sure that various breeds would have different results, so am just looking for a ballpark estimate. Googlemeister (talk) 22:11, 1 February 2010 (UTC)

You're talking about draft horse work. I googled on the phrase "typical speed of a draft horse" and there was exactly one hit, which said that at one time many cities set their speed limit to 6 mph because that was the typical speed of a draft horse. I don't know how many hours a day a horse could walk under the specific conditions you're talking about, but I imagine it would be most of the daylight hours, so 60 miles (100 km) would be my ballpark estimate.
At Oregon Trail it says wagon trains took 4-6 months to cover 2,000 miles, and that's only 11 to 17 miles a day; but the wagons were heavy enough that they used slower animals than horses. Plus the logistics of operating a wagon train must have been more difficult than a single animal. --Anonymous, 00:00:00:00:00:00:00:00... :-) UTC, February 2, 2010.
Anonymous, why did you link to a movie in your signature? ~AH1(TCU) 02:35, 2 February 2010 (UTC)
As a hint explaining the joke just before that. --Anon, 11:20 UTC, February 2, 2010.
It is Groundhog Day today, so I guess it's appropriate. (I'm not the original Anonymous, BTW.) (talk) 03:45, 2 February 2010 (UTC)
I think 60/day is pretty generous -- 6 mph is a trotting pace, not sustainable indefinitely, plus the horse will need several hours each day to graze. I would guess 30-50/day is a more reasonable range. Looie496 (talk) 00:21, 2 February 2010 (UTC)
I was under the impression that the Roman Legions could easily march 20 miles along the Roman roads in a day, so I would imagine a rider on horseback could manage much further, even without the benefit of a road. Astronaut (talk) 06:22, 2 February 2010 (UTC)
You might find Horses in the Middle Ages#Transportation useful (it provides some typical daily distances). Astronaut (talk) 06:31, 2 February 2010 (UTC)
As a tangent, to this day the fastest army in history, over long distances, is likely still the all-cavalry Mongol armies of Genghis Khan. They pretty much pushed the horse to its limit, and by some calculations they still covered more ground per day than even a modern mechanized army can. Mongol military tactics and organization notes that they covered up to 100 miles per day. --Jayron32 02:14, 2 February 2010 (UTC)
Why not look at Endurance riding, not draft horse (speed not power): 300 lbs, 100 miles, rough terrain in one day. (talk) 06:18, 2 February 2010 (UTC)
Looks like a good ballpark guess then would be between 20 and 40 miles a day. Not sure if it can be done for 10+ days in a row, but it seems like this might be one of the areas of human knowledge that has been reduced in the last 100+ years. Googlemeister (talk) 15:03, 2 February 2010 (UTC)
See Yahoo Answers: [8] which says 8 mph, 100 miles per day. Another says that a horse might go 100 miles in a day in a grueling endurance ride, but would need rest and care afterward.That writer says he did a distance ride and let the horse set the pace and decide when to stop for the night. The load was 190 pounds on an 1100 pound horse, and he covered 24 miles per day for 58 days out of a 5.5 month period. After a 40 mile day, he rested for two days. Another answer was 10-15 miles carrying 200 pounds. They say the load must not be more than 20% of the horse's weight. How much did you say your horse weighs that has to carry 300 pounds? Other answers there say 25 miles per day over several days. Other accounts I have read say the horse will break down or go lame after a few days at such a pace. In wartime, a messenger might ride a horse literally to death to get a message through, so extreme values of milage covered might not be sustainable. Keeping the weight carried to a minimum would be important, and a 150 pound rider with 50 pounds of tack and cargo would be more successful than your 300 pound load. See also the Long Distance Riders' Guild website. Its "Hall of Shame" exposes many lies about speed and distance, and cases of horse abuse. Edison (talk) 16:48, 2 February 2010 (UTC)
The hundred-miles-per-day number for the Mongol armies was actually due to their wise use of their horses. They would often have 3-4 horses per rider, so each rider could change rides multiple times in the journey; an individual horse may ride 100 miles with a rider on one day, and then the horse may have spent a day resting, and a few days catching up without a rider, and at a more leisurely pace. Besides being good riders and horsemen, the Mongols were also master logisticians, able to get the most out of their horses without ruining them. --Jayron32 17:45, 2 February 2010 (UTC)
The same was true of the Comanche, also known for their expert horsemanship. Comanche war parties would have several times as many horses as people. Pfly (talk) 05:54, 4 February 2010 (UTC)

Drug expiration dates[edit]

Inspired by the "best by XXX date" discussion above: I've been told the US military purchases prescription and/or over-the-counter drugs in bulk that have expired, because the prices are at rock bottom (believable) and because the Army's doctor-accountants have a table of dates and drugs telling them the real expiration dates — or, at least, the dates past which soldiers will start to keel over if they take the drugs. (Less believable.) The theory is that the drug companies are incentivized to label drugs with the nearest possible palatable expiration date not for product effectiveness reasons or liability reasons, but because consumers and pharmacies will throw out the old Tylenol to go buy more Tylenol. (I'm pretty sure the expiration date is not something consumers really look at when comparing Tylenol v. Advil.) True about the Army? False? Lunacy? Comet Tuttle (talk) 23:21, 1 February 2010 (UTC)

There has been some research done by a number of organizations into extending the permissible shelf life of some pharmaceuticals. This paper offers a summary of some recent work in the area.
The Shelf Life Extension Program (still a redlink, unfortunately) is a joint program of the U.S. Department of Defense and the Food and Drug Administration (FDA); it may be the basis for the rumors you heard. Here's the website: [9]. Here's a detailed program description (Word .doc file): [10]. Briefly, the DoD maintains large stockpiles of certain drugs (particularly antidotes for chemical or biological weapons) which have limited peacetime use. As it would be extremely costly to replace these drugs upon their nominal expiry dates, SLEP was established to determine if properly-stored drugs might be safely and effectively retained for longer periods. From the outline document:
It is important to note that products tested under this program are maintained under tightly managed, controlled conditions at a limited number of locations. Extrapolation of these data to drugs stored by others would be inappropriate. Storage conditions may vary widely across the population and SLEP data are not generalizable unless storage conditions are identical and verifiable. Even within the SLEP, products known to have been stored under adverse conditions (i.e., high temperature or low temperatures) by SLEP Participates are excluded from the program, unless they are marked and tested separately from “normal” stocks."
In other words, the information that the DOD has collected may not be applicable to pharmaceuticals stored and handled outside the military. There's also no program for purchase of expired drugs, as the military cannot rely on outside organizations to have stored and handled the drugs properly. TenOfAllTrades(talk) 23:57, 1 February 2010 (UTC)
It's also worth noting that an "emergency stockpile" needs to satisfy a different set of practical conditions than a normal supply - whether it's food, medication, or anything else. In the event of cataclysmic chemical warfare, I think most people would be willing to make exceptions about antidote potency, side-effect hazard, and other potential pitfalls of extended shelf-life. During non-emergency situations, the level of concern for those issues is much higher. Nimur (talk) 16:37, 2 February 2010 (UTC)