Wikipedia:Reference desk/Archives/Science/2010 March 10

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March 10

crazy raccoon

http://www.youtube.com/watch?v=El_m4iitN5k&feature=related

i saw this with a bird too when i was a kid is that why they go in the middle of the street so they can get killed because there suffering to much and want to die i know its weard how i have said it —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 00:04, 10 March 2010 (UTC)

It is not very likely that the animal in the video is attempting suicide-by-car. The consensus in the youtube discussion is that it was rabid, the symptoms of which include malaise, headache and fever, progressing to acute pain, violent movements, uncontrolled excitement, depression, and hydrophobia. I hazard they are more cogent reasons for the sort of behaviour seen on the video. --Tagishsimon (talk) 00:14, 10 March 2010 (UTC)

yes it could be rapid and mabye thats why its suicidal? like iv said iv seen this before in nature, with the bird i moved it out of the road and it just walked back into the road and waiting patiently til it got run over. which it did. —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 01:39, 10 March 2010 (UTC)

See anthropomorphism. You are projecting human traits onto an animal. There is zero evidence that animals commit suicide in this way. There are any number of plausible reasons why an animal would be stupid enough to hang around in the middle of the road. I have to dodge stupid pheasants and grouse pretty much every time I drive my car, as they saunter into the middle of the road. I find it most easy to believe that they just have not got an understanding of the threat represented by my car. Quite why you reach for a suicide motivation is beyond me. --Tagishsimon (talk) 01:54, 10 March 2010 (UTC)

Is there a question here? Dismas|^(talk) 05:15, 10 March 2010 (UTC)

Arguably yes: "is that why they go in the middle of the street so they can get killed". More succinctly, do animals commit suicide? At least, that's the one I've been answering. --Tagishsimon (talk) 05:21, 10 March 2010 (UTC)

And oops, sorry, that's with the exception of Bubbles the chimpanzee owned by Michael Jackson, who was alleged, according to our article, to have tried to commit suicide. And now we're on to something: Bubbles (chimpanzee)#cite_note-40 provides a bunch of references for a discussion of animal suicide. Who knew? --Tagishsimon (talk) 05:27, 10 March 2010 (UTC)

did you people read what i wrote im not talking about dodging pheasants or squirrels im talking about moving it out of the road and it just walked back into the road and waiting patiently til it got run over. which it did. —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 05:32, 10 March 2010 (UTC)

That contradicts the description of the video, which says: "Just so you know...HE DID NOT GET HIT...A few people actually got him out of the road and back in the woods." --99.237.234.104 (talk) 06:47, 10 March 2010 (UTC)

He's now talking about the bird he mentioned later, which did indeed get run over. Vimescarrot (talk) 11:28, 10 March 2010 (UTC)

I'm talking about the general principle. Animals have little appreciation of the risks of the road. Find one on the road, shoo it off the road, and like as not it will wander back on the road. Maybe settle down in the middle of the road for a nice long sleep if it's warm. None of this is a suicide intent. I don't know how many times and in how many different ways I can say, just because an animal did something which if human would be taken as a conscious and premeditated suicide bid does not mean that it is the same for the animal. But whatever. If you want to live in some sort of manevolent Beatrix Potter world, be my guest; I'm done with this. --Tagishsimon (talk) 11:54, 10 March 2010 (UTC)

Also note that few, if any, animals are likely to fully understand death (that is, that they will cease to exist), therefore "suicide" isn't likely to have the same meaning for them. There may be animals that have instincts which cause them to do things which result in their death (like whales that beach themselves), but that doesn't necessarily mean they know that doing so will result in their death. (Although whales may be one of the few species that really do understand death, as we do.) StuRat (talk) 14:13, 10 March 2010 (UTC)

I have seen dogs and cats which appeared to be cognizant of the danger from cars. They cross the street in the middle of the block so they can be sure a car is not about to turn the corner and hit them. They time their crossing so avoid cars. Animals get old and sick and in pain, or perhaps they just get depressed. "Suicide by car" or "suicide by hunter" is not something I would rule out. It would be quicker and arguable less unpleasant than "suicide by not eating or drinking" which an elderly cat with cancer once did. Edison (talk) 17:44, 10 March 2010 (UTC)

They know that getting hit by a car would hurt, but understanding the possibility or meaning of their own death is probably beyond a dog or cat. As for not eating when sick, it's likely just a loss of appetite. StuRat (talk) 18:04, 10 March 2010 (UTC)

I'm with StuRat, much more likely the loss of abilities due to illness or old age would acount for death on the road. any number of illnesses of older animals could lead to loss of appetite. Richard Avery (talk) 19:33, 10 March 2010 (UTC)

The "few species that really do understand death" can't include humans. Just look at all the religious stories of the afterlife and you'll see that humans, as a whole, don't understand what death is about. Until relatively recently (a few thousand years ago), people didn't even know that consciousness rests entirely in the brain and that damaging the brain would end all thought processes. An animal would have no chance of knowing this. --99.237.234.104 (talk) 19:17, 10 March 2010 (UTC)

Well, perhaps some are intelligent enough to know that something more than just pain will occur, and that they will cease to exist (at least in the way they have existed). This requires a leap from seeing other dead animals and thinking that the same thing could happen to them. StuRat (talk) 19:45, 10 March 2010 (UTC)

Dolphins are commonly described as one of the few non-human animals that appears to actively commit suicide. Of course it is not (yet?) possible for us to know what they are really thinking, but they can at various times choose to do things that in other contexts they appear to know would kill them. --Mr.98 (talk) 18:52, 10 March 2010 (UTC)

I read in Encyclopedia Brown that iguanas are capable of ending their own life. ~AH1^(TCU) 01:40, 14 March 2010 (UTC)

slouching

When I'm at the office I slouch and sometimes walk in a slouched position and I feel that it is a pain to adjust into a straight position. However, when I have to do moderate exercise (jogging, sprinting, abdominal exercises etc.) I noticed that after a while I'm involuntarily standing straight and its hard to slouch. Why is so? --121.54.2.188 (talk) 01:53, 10 March 2010 (UTC)

Slouching is a result of very relaxed muscles. Exercise tends to result in the opposite of relaxed muscles. --Tagishsimon (talk) 01:56, 10 March 2010 (UTC)

Could be you find your job boring. One is more alert and clear thinking when properly erect. The Alexander techniqueis about practising good posture and movement until it feels natural again.--Aspro (talk) 09:28, 10 March 2010 (UTC)

It could also be due to sitting in a bad position due to poor workplace ergonomics. Here is some more information:[1][2] --Normansmithy (talk) 15:52, 11 March 2010 (UTC)

Also see slouching. ~AH1^(TCU) 01:35, 14 March 2010 (UTC)

Minkowski Diagram

In Newtonian physics for both observers the event at A is assigned to the same point in time.

This image comes from Wikipedia's article on Minkowski diagrams, and shows what such a diagram would look like in Newtonian physics. In the accompanying text, it says that the time coordinate in the ct and ct' are the same (as one would expect), but from the text it would appear that ct' is a little greater than ct. Help? 173.179.59.66 (talk) 04:54, 10 March 2010 (UTC)

I took the liberty to fix your red link. I'm not sure I understand your question. Dauto (talk) 05:12, 10 March 2010 (UTC)

OK, I think I understand it now. t and t' are the same coordinate, that is t=t' but they use different scales in the diagram. I other words, a unit of time t and is represented by a shorter segment than a unit of time t'. Dauto (talk) 05:42, 10 March 2010 (UTC)

Okay great, thanks. PS the article should be clearer. 173.179.59.66 (talk) 13:43, 10 March 2010 (UTC)

chrome sink

i unscrewed my handles from my bathroom sink today for cleaning and theirs a long brown metal rod attaching them. what is that metal its a dull dark brown? i at first thought it was brass but its darker and not shiny almost like lead. what is it?

Chrome plating is porous to moisture (and too expensive to be fashioned out of solid sheet) so not very good for sinks unlike stainless steel. Are you sure its chrome? They could be just cheap Ferritic Stainless Steel which has oxidised -after all their out of sight, so you just after durability. [3]--Aspro (talk) 09:33, 10 March 2010 (UTC)

Almost certainly brass that has just oxidised to be darker than "fresh" brass. --Phil Holmes (talk) 15:08, 10 March 2010 (UTC)

is brass what they plate chrome? —Preceding unsigned comment added by 67.246.254.35 (talk) 20:25, 10 March 2010 (UTC)

hello? —Preceding unsigned comment added by 67.246.254.35 (talk) 06:12, 11 March 2010 (UTC)

Chrome is what they use to make chrome. Brass (and bronze and copper) is another metal commonly used in sinks - especially for things like water connections. The last three oxidize to give green to greenish black to black. However if you have a bit of emery cloth (sandpaper), you can try rubbing off some of the oxidation. If it was brass/bronze/copper, you'll see the copper-colored unoxidized metal below the layer of oxidation. By the way, it may take us a while to get to your question - lag times of several hours are not unknown - we're all volunteers here. -- 174.21.235.250 (talk) 16:05, 11 March 2010 (UTC)

Inorganic Reaction Mechanisms

How could one tell whether a substitution reaction is proceeding via an associative rather than a dissociative reaction pathway? Is there a standard test? 188.221.55.165 (talk) 10:37, 10 March 2010 (UTC)

Yep. Just look at the entropy of activation.

From Dissociative substitution: "The entropy of activation is characteristically positive for these reactions, which indicates that the disorder of the reacting system increases in the rate determining step."

From Associative substitution: "The first step is typically rate determining. Thus, the entropy of activation is negative, which indicates an increase in order in the system."

Variations are also possible, notably the Sn1CB mechanism.

See User:Benjah-bmm27/degree/2/transition metal mechanisms and Eyring equation for more details.

Ben (talk) 13:48, 10 March 2010 (UTC)

weather

hOW —Preceding unsigned comment added by 216.178.90.202 (talk) 12:12, 10 March 2010 (UTC)

What you mean to ask? -- Extra999 (talk) 18:00, 10 March 2010 (UTC)

How to turn of the caps lock key? Richard Avery (talk) 19:26, 10 March 2010 (UTC)

I suppose he was to write "How to stop an hurricane?", but the hurricane was so fast... --Aushulz (talk) 19:45, 10 March 2010 (UTC)

We may never NOAA what the real question is. 10draftsdeep (talk) 20:16, 10 March 2010 (UTC)

If you want to know how weather works, I suggest you start by reading weather. If you have any specific questions after reading that article, we would be happy to help. --Tango (talk) 23:18, 10 March 2010 (UTC)

Also take a look at atmospheric dynamics, climate and Coriolis force. ~AH1^(TCU) 01:34, 14 March 2010 (UTC)

Bubbles

When a soft drink is under high pressure, as in an unopened can, bubbles don't form. When the pressure is released, bubbles emerge from liquid. Why does high pressure prevent the CO₂ from forming? 173.179.59.66 (talk) 14:06, 10 March 2010 (UTC)

The Bubbles ocupy a volume V and require an energy WORK=PV in order to form. At high pressure that energy is just to high and the bubbles won't form. Dauto (talk) 14:13, 10 March 2010 (UTC)

(ec) The CO2 doesn't "form" - there isn't a chemical change going on. The CO2 is already there, it's just dissolved in the liquid. However, the amount of a substance that can remain dissolved in a liquid depends on pressure and temperature. When you reduce the pressure by opening the container, the liquid can't keep so much of the CO2 dissolved - so it comes out of the solution as bubbles. You can see the same effect with (for example) salt dissolved in water. If you get some really hot water and dissolve salt into it until no more will dissolve - then let it cool - you'll see a lot of salt crystals form as the cooler water can't keep so much salt in solution. In that case it's heat that does it - but pressure works the same way. SteveBaker (talk) 14:16, 10 March 2010 (UTC)

Yeah, I had meant CO₂ bubbles from forming...but my question is why higher pressure prevents gas from nucleating. I guess that there's some sort of equilibrium between the gas entering and the gas leaving, but I would have expected that you would just get bubbles going in and out, with no net gas difference. —Preceding unsigned comment added by 173.179.59.66 (talk) 15:53, 10 March 2010 (UTC)

I believe the reason for what you describe not happening is that the smaller a bubble of gas in liquid is, the greater the relative surface tension trying to shrink it is. Consequently, a tiny bubble has a hard time forming but, once formed, an easier time growing. This means that, ignoring temperature for the moment, above a certain pressure a potential bubble forming from dissolved gas would have insufficient internal pressure to overcome both external pressure and surface tension, so it cannot get started. If however the pressure drops sufficiently, and aided by nucleation sites if present, the bubbles once started will tend to grow further. A related phenomenon is the knocking sometimes heard in not-quite-boiling water caused by bubbles trying to grow but, due to turbulence, being deprived of steady-enough heat supply and collapsing again. I'm sure someone will be along soon to improve on or correct this hasty lay approach with all of that good stuff like proper physics an' maths an' graphs an' reference links. 87.81.230.195 (talk) 17:37, 10 March 2010 (UTC)

Well yes, that's pretty much what happens, although the bubbles never get large enough to see. StuRat (talk) 17:27, 10 March 2010 (UTC)

Are you talking about the surface tension of the liquid or of the gas?173.179.59.66 (talk) 14:53, 11 March 2010 (UTC)

The reason you don't see bubbles forming in a closed container, but you do in an open container is due to LeChatelier's Principle. Basically, when the system is closed, there is an equilibrium established such that the CO₂ concentration in the headspace over the liquid and in the liquid itself stop changing. On a molecular level, individual CO₂ molecules are both entering and leaving the soda in a closed bottle, but in bulk, the CO₂ is basically not leaving or entering, the entire system is in balance. Because CO₂ is a gas, when you open the container, the CO₂ concentration drops, which throws off the equilibrium. Via LeChatelier's Principle, when you remove a substance from a stable equilibrium, the system will work to replace it. So the CO₂ begins coming out of the solution to replace the lost CO₂ gas. However, as long as it is open, equilibrium is never established, so the gas keeps coming out in bulk until the soda goes "flat". --Jayron32 21:56, 10 March 2010 (UTC)

Yes I understand that, but I would have expected that there would be bubbles going both way, as gas goes in and out of the fluid (as I mentioned above). To make sure I understood 87.81.230.195's explanation, does the increased pressure make the pressure inside the liquid increase as well, preventing bubbles from forming? Or is it the incoming gas molecules knocking the nascent bubbles and preventing them from fully developing? 173.179.59.66 (talk) 00:02, 11 March 2010 (UTC)

At equilibrium, the bubbles don't aggregate. There's no impetus to, as the flow happens as single molecules of CO2 move in and out at a dynamic steady state. Imagine it this way. If you picture a school building when class is in session. Occasionally, there's someone walking down the halls; like a kid leaving class to go to the bathroom, or another kid going back to class from the bathroom. The kids will tend to walk down the halls one at a time; there are always kids in the halls, but only a few, because the kids are pretty much staying where they are, and those in transit aren't likely to clump together. This is like the situation with the bottle closed. There is some movement of CO2, but the rate at which it is happening is relatively gentle, and counterbalanced by CO2 moving in the other direction. When the bell rings at the end of the day, well, that's like opening the bottle of soda. The kids ALL pile into the halls, and now their movement is very different than the occasional kid going to or coming back from the restroom. Now the kids all cram together and rush, in big clumps, out the nearest door. That's the same thing with the soda. Once there isn't an equilibrium, the CO2 in the soda is rushing out of the soda to reestablish that equilibrium. In that rush, they tend to aggregate and form bubbles because of the increased rate of "getting out" of the solution. --Jayron32 02:35, 11 March 2010 (UTC)

at equilibrium under pressure, the rate of exchange of CO2 molecules is slow and even - hence no bubbles. when the pressure is released from the top of the can, however, the CO2 comes out of suspension in the liquid at rate faster than can be transpired across the surface of the liquid; consequently you get pockets of gas forming inside the body of the liquid (aka bubbles). You can think of it as the liquid increasing its available surface area for transpiration - the surface of each bubble becomes a release area for dissolved gasses. it's basically the same process that causes the bends in diving (nitrogen in the air tanks is absorbed in the bloodstream under the pressure of the ocean, and turns into bubbles in the blood if the diver comes up too quickly), and why champagne is served in tall, thin flutes (decreased surface area at the top increases the number and life of bubbles formed). --Ludwigs2 03:14, 11 March 2010 (UTC)

@Jayron32: If the carbonated liquid were to be put under pressure by Nitrogen gas, then, by LeChat's principle, there would be an outflux of carbon dioxide and an influx of nitrogen. But there wouldn't be any bubbles. I don't think LeChatelier's principle is sufficient to describe the formation of bubbles; it's a statistical phenomena, but the carbon dioxide molecules themselves don't have any individual desire to re-establish the equilibrium. So the question becomes why does the outflux of carbon dioxide increase once the pressure above decreases?

@Ludwigs2: Why does the CO₂ come out of suspension so fast when the pressure decreases? 173.179.59.66 (talk) 14:44, 11 March 2010 (UTC)

In other words, why is the nucleation of bubbles pressure dependent? 173.179.59.66 (talk) 16:26, 11 March 2010 (UTC)

In the case of pressure, a high pressure cooker similarly does not explode but at a sufficient pressure the water vapor contained inside needs to escape through a vent. ~AH1^(TCU) 01:31, 14 March 2010 (UTC)

Structure of the earth

In this chapter of Journey into the Interior of the Earth one of the protagonists argues that a liquid layer in the interior of the earth will experience tides. (He presents this as an argument against the existance of a liquid layer as the displcements due to tides would cause daily quakes, which are not observed)

I know this is fiction, but does the outer core or mantel really experience tides? If it does, how much would the displacement due to tides be?

Would the model described in the chapter have sounded plausible to geologists in 1864(when the book was written)?

Brief summary of model:

-The earth is hollow.

-The heat in the interior is caused by water reacting with alkali metals.

-Since the heat source is located inbetween the surface and the centre, temprature would go up as we go down but then reduce as we go deeper than the heat source.

Also this model of a hollow earth:Structure of the Earth#Historical development of alternative conceptions, based on the flawed caluclations of the masses of the earth and the moon, assumes that the density of earth material will be the same as that of moon material. Was there any historical reason for this asumption?

Diwakark86 (talk) 14:36, 10 March 2010 (UTC)

Yes, the whole Earth experiences a tidal deformation due to the Moon's gravity; this note in Scientific American puts the tidal range at 25cm. That article also points to two presentations given by the operators of two particle accelerators, really the only people whose structures are large enough, and sensitive enough, to care. -- Finlay McWalter • Talk 16:52, 10 March 2010 (UTC)

At the time you're talking about, scientists seem to be settled that the Earth isn't hollow - the calculations done before and around that time mentioned in the Age of the Earth article all assume the Earth isn't hollow. The Hollow Earth article is somewhat disappointing, in that it doesn't give any idea as to what general credence these ideas were given - it would appear that, as soon as people started seriously thinking about the interior of the Earth (in a scientific fashion) they thought of it as not being hollow. By the time of Murchison it was clear that the Earth was stratified to at least a nontrivial depth, but I don't think it was until large scale seismic studies were carried out (e.g. by Mohorovičić) a few decades later that the gross structure of the Earth became, to a limited extent, observable. As to the source of heat, Kelvin's calculations trying to age the Earth assumed it didn't generate its own heat, but that its warmth was a fossil of its creation (and thus put the Earth as being rather young) - but at that time no-one was at all clear as to how old the Earth was, and it wasn't until later that the mounting evidence of the great age of the Earth made it necessary that it contain source generating heat. I don't think anyone by that time would believe the third element of the model you discuss, as by that time physicists had a sufficient grasp of thermodynamics. So, all in all, I doubt that any scientist who seriously studied the known results about the Earth's interior would believe the model you discuss, but geology was a very young science with very few real practitioners, and with very limited means of finding things out. -- Finlay McWalter • Talk 16:52, 10 March 2010 (UTC)

As for the Moon having the same density as the Earth, that depends on the model you use to explain their formation. If you believe they formed together from a dust cloud, then they should have a similar composition, although the heavier materials might have found their way down to the Earth and the lighter materials formed the Moon, so the Moon might be expected to be somewhat less dense (which it is). If you believe the Moon was captured from some other source, then it could be made from completely different material and thus have a completely different density. A more recent theory is that during the Earth's formation, or shortly after, a giant meteor hit that ejected the material which formed the Moon. In this case, the Moon might be a mix of the Earth's material and the meteor's, while the Earth would also have some of the material from the meteor, again leading to somewhat similar densities. You might think that the higher mass and hence gravitational attraction on Earth would lead to a greater density. It's actually the opposite, since most terrestrial material isn't very compressible in that range of g, and objects with less gravity tend to lose their lighter gasses and liquids to space. StuRat (talk) 17:23, 10 March 2010 (UTC)

As to the "Was there any historical reason for this asumption?" part of Diwakark86's question, there really wasn't much evidence to distinguish which of these theories of Lunar origin might be true (there's not nearly enough evidence now, alas). All they had to go on was the appearance of the Moon - it's vagely Earthlike, in that it has flat bits and mountainy bits, so one might as well assume, absent any better evidence, that its composition is vaguely Earthlike too. It wasn't until the examination of the Allan Hills meteorite in 1982 that science began to realise that actual physical samples of moonrock were already available on Earth (as Lunar meteorites). So, with what little evidence they had, it's a reasonable assumption for the geologists of 1864 to make. -- 87.114.240.222 (talk) 17:52, 10 March 2010 (UTC)

Even lunar meteorites, like the samples returned by astronauts, provide samples only from the outermost part of the Moon. If you only had samples from the surface of the Earth, they wouldn't tell you that the core is largely iron, or how big it is; likewise with the Moon's internal structure. --Anonymous, 21:52 UTC, March 10, 2010.

Also, plenty of earthquakes (some as deep as 500 km) occur in the mantle, as their depths indicate that they are below the crust yet they are still felt on land. ~AH1^(TCU) 01:27, 14 March 2010 (UTC)

Biogas from plant and animal waste

Copied this from article space, where I am going to request deletion. I have let the page author know I have moved the question to here Gonzonoir (talk) 15:09, 10 March 2010 (UTC): I'm a boy from Botswana and i'm thinking of compiling a project on the comparisons of producing biogas between using rotten plant materials and cow-dung, so if you have got any piece of information which i can use be free to help me out and the god lord will bless you, i just want to make things better in my country and make my parents proud of my achievements. Originally posted by Ofentse mmereki (talk) 15:03, 10 March 2010 (UTC)

Optimum gas production per cubic metre requires a mix of both dung AND plant matter. The ratio is usually discovered by trial and error based on what is most available. See this section for more info:Anaerobic_digestion#Feedstock--Aspro (talk) 16:03, 10 March 2010 (UTC)

Back in the 1970's some third world country had a project to install a zipper in old truck inner tubes, to allow the insertion of dung. Methane would be produced in the tube and eventually it would be inflated to a pressure sufficient to allow the gas to be transmitted via a rubber tube to a gas ring on which the family could cook. The next day, open the zipper, clean it out, repeat the process. Surely someone has worked on this since the 1970's to improve it and make it larger scale. A larger scale version of the same plan might work like the gas producing plant in my great-grandfather's house from the late 19th century, but using dung and plant material to produce methane in place of the carbide he used to produce acetylene gas. A metal tank outside the house had a suspended or floating dome to maintain pressure containing the gas over a water reservoir into which the carbide was dropped whenever the pressure dropped below a setpoint. Metal pipe carried the gas into the house, wherein it went to gaslight fixtures and a cookstove in the kitchen. Please observe safety precautions with methane, since it is explosive, and the gas or its combustion products can cause asphyxiation. Commercial gas plants add an odorant so that leaks are detected, since methane has no odor of its own. I wonder if the dung and rotting plant material would provide their own odor when the gas was used? In a place where dung is commonly used for fuel, the odor should not be that novel. One important consideration is avoiding an explosive mixture of oxygen with the methane in a reservoir or in pipes. Some results at Google Book Search include (which discusses an improved methane generator), (which says the leftover slurry can be sold as fertilizer),(which says 5-6 bovines can provide 40 cubic meters of gas per day), (which has some simple designs), as well as [4], [5], [6], [7], and [8]. Edison (talk) 17:38, 10 March 2010 (UTC)

For Wikipedia articles, see biogas and methane#Uses. ~AH1^(TCU) 01:24, 14 March 2010 (UTC)

Oh my god i never thought that things would get this complicated but i think it is for the betterment of my knowledge, can anyone please tell me how you can compile a project with two tanks, one containing cowdung and one containng rotten plant materials and then they must state the comparisons and diferences of the two like each's effectivesness, the amount of gas produced in each and how i can start compiling it.... i know it is too much but please i need serious help because it is a project. thnks.--168.167.134.115 (talk) 14:06, 15 March 2010 (UTC)

Heating through air resistance

I ride a motor-cycle to work, around 30 miles on freeways. Last few mornings it has been cold. This got me to thinking about heating through air resistance. Re-entering spacecraft experience extremely high temperatures, and even jet aircraft wing leading edges heat enough to make them a viable target for IR-based air-to-air missiles to lock on. So, my question is, how fast would I have to drive to heat up my hands to 37 degrees Celsius? Assume I'm at sea level and the airflow to my hands is completely unobstructed. --John (talk) 16:57, 10 March 2010 (UTC)

Aerodynamic heating is generally due to the air being compressed as an object passes through it. Per compressible flow, there is little compression (thus little heating) until Mach .3, about 230 MPH. Keep in mind also that moving air will speed up heat transfer away from your hands, making them feel colder. So I would expect your hands would be colder while moving for any speed that you're able to ride (solely considering aerodynamic effects). anonymous6494 17:13, 10 March 2010 (UTC)

When I pump up the tyres of my bicycle, the end of the pump gets hot. 78.151.126.97 (talk) 17:22, 10 March 2010 (UTC)

From memory the ‘frictional’ coefficient is 0.007 deg C per knot of wind speed. Small but is useful in meteorology.--Aspro (talk) 17:47, 10 March 2010 (UTC)

That seems too low. Based on that, and a knot (unit) being 1.151 mph, a plane going 1151 mph would only be heated 7°C. I suspect it's nonlinear, with more of an effect at higher speeds. StuRat (talk) 18:21, 10 March 2010 (UTC)

Right Stu, that coefficient is useful until the speed gets to be high enough for compressibility to start playing a greater roll. As anon said above, that speed is usually considered to start in the neighborhood of mach 0.3 or so. Googlemeister (talk) 19:14, 10 March 2010 (UTC)

Meteorology it is at sea level. (Motor cyckles not much higher). Otherwise it does go non linear (log ‘e’ I suppose). The batteries in my slide rule have gone flat, but there is a bit about this for those smarty pants who are good at mental arithmetic.[9]] Now lets see: carry one and add it to the first number you thought of... Foreseeable problems: High pressure turbulence will cause sevier bruising (Try skying behind a jet-ski in the wash of the water jet!) . Fighter pilots ejecting (or even bailing out) at high speed get bruised from air blast. The expanding air (after being compressed on the leading edges) will under go adiabatic cooling thus freezing the local tissue towards leeward side of the flesh. The local police forces will see an opportunity for issuing a months worth of speeding tickets on one night that this motorcyclist driveS though. Inquirer is obviously on a higher plane than the rest of us and would be better off in a Buddest monetary where he could write a squeal to the Zen and the Art of Motorcycle Maintenance.--Aspro (talk) 20:40, 10 March 2010 (UTC)

Also the NASA article points out that it is British Thermal Units (or Joules, Ergs, Watts etcs) that is the energy units to consider first and full most. The Temperature rise of air molecules in themselves does not contribute much to the question asked, which is about positive heat balance via increased linear speed.--Aspro (talk) 21:00, 10 March 2010 (UTC)

This is a tough one. Gut feel says that the answer is clearly going to be much faster than a motorbike could go - because the wind-chill effect of removing the 37 degC heat from your hand has to be overwhelmed. But we don't want 'gut feel' - so that won't do!

But we're not going to come up with a good number. Perhaps the best way to think about this would be from a thermodynamic angle. I guess we could figure out the coefficient of drag of the bike+rider, then we can calculate the drag force - and from that the amount of energy from the engine of the bike that's going into overcoming drag. That energy has to go somewhere - so we could consider what fraction might go into heating the air that the bike leaves behind in it's wake and what fraction is heating the skin of the bike and the rider - and make a stab at what fraction of that would be warming your hands. Knowing the energy input we should be able to figure a temperature rise. My big problem is that there could be three orders of magnitude of estimation in all of those guesses - so the answer might come out to be "Somewhere between 10mph and 1000mph." - which isn't really much use.

Another angle would be to consider things that actually do move very fast through the air. We know that at the speed of an airliner (400 to 600mph maybe), the skin heating is overwhelmed by the cooling effect of the cold air blasting past. Airliners might "ice up" but they don't get hot from the friction. On the other hand, aircraft that fly at Mach 3 and up have to be made of exotic metals and have active cooling on their leading edges to avoid melting. Similarly, spacecraft slowing down from orbit get incredibly hot when they are moving fast - but wind up being only slightly warm by the time they slow down and touch down. Meteors that people have found within minutes of hitting the ground as meteorites are reported to be merely warm, or even chilly to the touch. That strongly suggests that you're going to need to be moving considerably faster than Mach I...but again, so much depends on the air density and the shape of the object that we can't easily extrapolate from that to what you'd need on a bike.

Some questions can't be answered without an experiment - and this is probably one of them.

SteveBaker (talk) 00:53, 11 March 2010 (UTC)

Steve, to address your airliner point, airliners fly where the ambient temperature is between -40 and -70 deg, and air density is about 30% that of sea level, so there would be more then 3x as much heating if the aircraft was at sea level, but you are right, massive air resistance heating occurs at supersonic speeds, mach 0.9 has some heating, but it is a lot lower then mach 1.1. Googlemeister (talk) 14:26, 11 March 2010 (UTC)

Thanks a lot for all the great responses. So, we're looking at maybe somewhere between M1.1 and say M1.5? I know M2.02 is too high because I think that was Concorde's limiting factor to produce a TAT of 127 °C, which is way too hot for my fingers; and it flew at over FL50; as Googlemeister says, the heating effect would be greatly enhanced at sea level. I half-understand the calculations in the great NASA reference Aspro found, and I think we could solve it from that end with a bit of concerted effort. I also love the thermodynamic approach that SteveBaker brought in. Would it be fun to work it from the NASA data, and from the conservation of energy angle, and see if the two answers in any way fell into concordance? Or maybe folks have better things to do? I'd love to solve it, having wondered about it for several years. I predict the answer might be around M1.3. Let's take ambient air temp as 2 degrees C, a good deal warmer than at the heights aircraft fly at, as well as denser and damper. Any takers? --John (talk) 04:14, 12 March 2010 (UTC)

If the temperature outside your hands is cold, then wind chill would be a factor and would cool your hands more than they would warm them. The speed of a space shuttle during re-entry is much faster than the speed of sound, in which case your hands would not only heat but detatch from your arms. ~AH1^(TCU) 01:20, 14 March 2010 (UTC)

Nanomaterials

what is the cause behind the invention of nanomaterials? —Preceding unsigned comment added by 118.102.186.3 (talk) 17:08, 10 March 2010 (UTC)

Bored scientists. Dauto (talk) 17:11, 10 March 2010 (UTC)

Bored scientists who had read There's Plenty of Room at the Bottom yet who (perhaps wisely) didn't pay too much attention to Engines of Creation.

Actually - it's not really "bored" scientists - it's scientists who are being paid to research things that can make the people who employ them very rich...which they are beginning to succeed at. SteveBaker (talk) 18:11, 10 March 2010 (UTC)

I suppose the reasons are similar to any other invention. That is: fame, money, to help mankind, etc. StuRat (talk) 18:14, 10 March 2010 (UTC)

What do you mean by "cause" here? Motivation of inventors? Or the scientific/technological path that led to them? --Mr.98 (talk) 22:39, 10 March 2010 (UTC)

See nanotechnology and carbon nanotubes. ~AH1^(TCU) 01:18, 14 March 2010 (UTC)

(Arabic question)

أريد تقرير علمي عن تشريح الخشب النباتي —Preceding unsigned comment added by 95.170.208.114 (talk) 18:25, 10 March 2010 (UTC)

Hi. I don't know if you will be able to read my response, but all of our responses on here are generally in English. You could ask at the language desk but I still don't know if they will be able to help you with your question (which appears to be about reports on a wood plant, according to Google Translate). If you are unable to ask your question in English, then there are probably better places to ask it than here, as this is basically an English-only resource. --Mr.98 (talk) 18:47, 10 March 2010 (UTC)

مرحبا. أنا لا أعرف إذا كنت سوف يكون قادرا على قراءة ردي ، ولكن كل ردودنا على هنا عادة في اللغة الإنجليزية. هل يمكن أن نطلب من مكتب في اللغة ولكن ما زلت لا اعرف ما اذا كانت سوف تكون قادرة على مساعدتك في سؤالك (الذي يبدو أنه حول تقارير عن مصنع الخشب ، وفقا للمترجم جوجل). إذا كنت غير قادر على طرح سؤال في اللغة الإنجليزية ، ثم ربما يكون هناك أماكن أفضل ليطلب منه من هنا ، لأن هذا هو في الأساس باللغة الإنكليزية فقط على الموارد. -- السيد.98 (نقاش) 18:47 ، 10 مارس 2010 (تعم)

The above post translated by machine from Arabic:

hello. I do not know if I will be able to read my reply, but all our responses to here usually in the English language. Can we ask of the Office of the language, but I still do not know whether it will be able to help you in your question (which appeared to be about reports of wood factory, in accordance with a translator Google). If I was unable to a question was raised in the English language, and then there may be better places to ask him from here, because this is in the Foundation in English only on resources. -- السيد.98 (debate) 18:47, 10 march 2010 (prevail) Cuddlyable3 (talk) 10:24, 11 March 2010 (UTC)

Hmm. When you translate "talk" into Arabic and then back into English it becomes "debate". Think those translators might be a bit biased? Zain Ebrahim (talk) 11:59, 11 March 2010 (UTC)

Fun with online translators: Take any national anthem - translate to the language of your choice, translate it back again - enjoy songs like "The asterisks and strips indefinitely". 13:48, 11 March 2010 (UTC)

The lyrics were inspired by the patriot who said, "I only regret that I have but one asterisk for my country." -- Coneslayer (talk) 13:52, 11 March 2010 (UTC)

That second Arabic text appears to be a machine translation of Mr.98's post into Arabic, then back into English. The original question translates as "I want a scientific report of the anatomy of wood plant". Perhaps the question is about trees, in which case the OP could start at that article or use Google Scholar? ~AH1^(TCU) 01:16, 14 March 2010 (UTC)

Prices of some raw materials

Hi all. I need to know the prices of these raw materials, that need for a case-study of a chemical plant:

• Ethylene (99,9% mol)
• Hydrogen chloride (99,8% mol)
• Chlorine (99,9% mol)
• Vynil chloride (99,9% mol)

I have another question: assuming that I'll buy more than 100000 ton/year of each one, I need to consider "spot price", "contract price" or what else? --Aushulz (talk) 19:02, 10 March 2010 (UTC)

Homework question?--Aspro (talk) 21:07, 10 March 2010 (UTC)

I am thinking that if you are buying 100000 tons per year, you should not be asking here! Issue a tender in the appropriate forum and see what the responses are. If you need a large quantity you may need a reliable supply and a contract. Check out Commodity market and spot price and futures market. Graeme Bartlett (talk) 09:01, 11 March 2010 (UTC)

Another thing that will alter the prices will be the required level of purity. 99.9999% pure materials cost much more the 99.9% pure ones. Googlemeister (talk) 15:21, 11 March 2010 (UTC)

@Googlemeister: You're right. I added requested purity.

Some other suggestion? --Aushulz (talk) 16:55, 11 March 2010 (UTC)

Dehydrated people

I seem to recall reading somewhere (don't think it was here) the percentage of dehydration needed before medics start giving intravenous fluids. Can someone help me find it please? --TammyMoet (talk) 19:10, 10 March 2010 (UTC)

Our article (Dehydration#Symptoms and prognosis) indicates that severe symptoms start to set in around the 10% mark. The Treatment section says that IV fluids would be given in emergency situations, or when severe symptoms are manifest. I'm not sure if there is a hard and fast rule as to when to administer IV (in contrast to orally administering fluids). Coreycubed (talk) 20:22, 10 March 2010 (UTC)

Thank you. There's such a lot of crap talked about hydration, I want to find some decent evidence, and that article might have some pointers. --TammyMoet (talk) 21:21, 10 March 2010 (UTC)

is it possible to express matter in the form of sound?

I read an interesting article that there are some specific "verses" which when uttered create specific sounds which represent the embodiment of desired matter. In simple words - hypothetically speaking - if i needed to see a person or procure a desired object by repeating some specific words/ sounds it is belived that the matter you seek or the person you seek materialises in front of you.

My question is can matter be represented as sound waves? —Preceding unsigned comment added by 213.130.123.12 (talk) 20:52, 10 March 2010 (UTC)

That doesn't sound like science, more like some weird science fiction. The closest thing to representing an object with sound waves would be the reflected sound from SONAR, where all of the waves, collectively, can be used to reconstruct the shape of the object from which they reflected. StuRat (talk) 21:05, 10 March 2010 (UTC)

A few things to bring us back to the realm of reality. No, matter is not sound. Matter is energy (see mass energy equivalence and wave particle duality for more details), however sound energy isn't of the correct "type" to properly contain matter information. Well, sort of. Via mass-energy equivalence, we can find the "mass" of a particular sound, if we know the energy that it represents (in sound, intensity is directly related to energy). But that doesn't mean we could represent actual matter as sound waves; that's because matter is energy plus. What matter is, is energy confined by quantum numbers. Quantum numbers are basically the information that tells one particle to be a proton, and another to be an electron, and another to be a neutron. If we convert that matter into energy, we can, from the energy, directly calculate how much mass contributed to the energy via E=mc^2. However, when matter turns into energy, quantum numbers are lost. So there is no way to recreate the form or shape of the matter from merely the energy information. You'd be missing the quantum number information. So, even if we could convert a chunk of energy into pure sound energy (and I suppose we could, there's nothing in the theory that would prevent it), there would be no way to extract from that sound energy the form of the matter in terms of how it was organized. The quantum number information is lost completely. So, you could tell roughly how much matter was converted to a sound, again via E=mc^2, but you'd never be able to reconstruct the form of that matter. There are "quasiparticles" of sound called phonons, but these shouldn't be considered particles on par with those of the standard model; instead they are merely the consequence of applying the mathematics of wave particle duality to sound waves. Treating sound as a particle works mathematically, but you cannot isolate or deal with a real "phonon" the way you can with, say, a "photon". --Jayron32 21:44, 10 March 2010 (UTC)

Jayron, everything you said is quite accurate except the part where you say a phonon is less real than a photon. Dauto (talk) 22:15, 10 March 2010 (UTC)

Sufficiently high energy gamma rays (photons) will decay into pions (a.k.a. matter) http://en.wikipedia.org/wiki/Greisen%E2%80%93Zatsepin%E2%80%93Kuzmin_limit . Maybe (?) a similiar mechanism exists for extremely high energy phonons? (after all, the sound wave is a consequence of electromagnetic interactions between neighbouring atoms in matter, and these interactions involve photons, which can decay into pions at sufficiently high energy ...) 83.134.158.50 (talk) 07:09, 11 March 2010 (UTC)

edited to add : certainly I'm not suggesting a human voice can generate phonons of sufficiently high energy to create pions, let alone to create a macroscopic object 83.134.158.50 (talk) 07:12, 11 March 2010 (UTC)

Were the words of these "verses" printed for you to try? No? I wonder why not! This is utter nonsense. If it were possible to create physical objects by uttering magical spells - I really think the major manufacturing companies of the world would be using large teams of carefully trained poets on all of their production lines - and they aren't. SteveBaker (talk) 13:44, 11 March 2010 (UTC)

It's possible to have pictures encoded within a radio signal. See slow-scan television. So in a way, yes, you can represent matter with sound waves. I think that's the closest you're going to get though. 75.157.57.12 (talk) 22:03, 11 March 2010 (UTC)

Ceci n'est pas une pipe... The image of matter is not matter. You could encode data onto a sound wave, and then decode the data at the other end, but you would get a picture not matter. And radio waves are not sound waves... they are light. --Jayron32 04:48, 12 March 2010 (UTC)

thanks for the particcipation folks and thanks to a few who called my question utter nonsense. firstly if man thinks he knows all then thats the first sign of his downfall, the greatest inventions of today were all called nonsense in the past. about these verses being printed or not yes ofcourse they are printed and they are tried by several people, they say the manifestation of mattter is abstract and it is for you to feel it and not see it. and as a parting shot, just because you cant demonstrate something, doesnt mean, it isnt true, maybe today we are unable to do this very soon we might be. A few years ago, if people had said we might be able to look and talk to people sitting in different planets by looking at our hand held phones, we would have laughed. a few years and now we realise where we stand. thats the beauty of science. thanks to the positive inputs from many people who see the crux of my question - as in the case of slow scan television we are now able to convert sound waves into picture - which is a big leap forward. if we can generate images from sound logically speaking or shall i say illogically speaking we should be technically able to actually generate matter from sound waves... there are texts in sanskrit in India which document this to have been done in the past - though if you ask me to demonstrate it i wudnt be able to. this is a scintific forum and we analyse areas and this is for sure in my humble opinion a very important hot spot for research. there are several things which existed in the past that had been lost forever because of so many reasons. if man thought modern science can explain everything and we start fooling ourselves into beleiving the scientific advances of the present day is the be all and end all of science, then we would be living in a fools paradise. if we look at our past we will find answers for the future.