Wikipedia:Reference desk/Archives/Science/2009 March 4

Science desk
< March 3	<< Feb | March | Apr >>	March 5 >

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.

March 4

Creation (and use) of mass alternative fuel based cars would solve the petroleum Environmental effects?

So much has been talked nowadays about electric cars, hydrogen cars.... Because of petroleum problems and other things... My question is, would the used of alternative fuel only (or almost only) cars would solve the Environmental effects of petroleum?? I mean, petroleum is used to another things also. 201.79.81.7 (talk) 01:41, 4 March 2009 (UTC)

Hidrogen and electricity are means of distribution of energy. They are not sources of energy and cannot in themselves be a solution to the energy problem. But they can be important links in the distribution of other sources of energy. Dauto (talk) 02:23, 4 March 2009 (UTC)

No - without doubt. Solving the car problem completely with some kind of magical 100% renewable-energy, non-CO2-producing fuel would not be enough to fix the global warming or energy shortage crises. But on the other hand - neither would solving any one of the other problems either. In order for us and our planet to get through the mess we've created, we have to agressively attack all sources of greenhouse gas emission and all source of energy consumption. In truth, the "energy crisis" isn't a problem at all because if we burned all of the oil, coal and gas we know that we have - we'd have made the planet unlivable long before we ran out. Whatever solution we come up with for fixing global warming will (by necessity) result in us not having a shortage of coal, oil or gas.

As you can see from the diagram, transportations (which includes trucks, trains, planes and shipping) is only 28% of our energy consumption. To limit global warming to 2 degrees C worldwide (which is a HELL of a lot of temperature increase), we need to get back to 1990 consumption levels by 2020 and to between 40% and 95% BELOW 1990 levels by 2050...clearly cutting 28% off our consumption won't do that.

I think we could fairly easily halve our domestic energy consumption - using better insulation and energy-efficient appliances, I've managed to get my house down to about one third of my neighbours...and I paid for it using the electricity savings I made amortized over about 5 years. With fairly modest government help - all new homes could EASILY do that with the government paying the difference in price for us and collecting that back from fuel taxation equal to the savings you'd make over those 5 years. The result would be that for new home owners, there would be no cost to building an energy efficient home - and after 5 years, they'd make a huge profit on the savings when the fuel tax would go away. For the government/tax payer, it would be a zero-sum game. For energy producers, they'd win because they'd need fewer new power plants. I would assume that commercial users (office buildings, stores, etc) could make similar savings. The two tough ones are industry and transport. Personally, I drive a 40mpg car (a MINI Cooper'S) - the average fuel consumption of a car in the USA is 19mpg - so without electric/hydrogen/hybrid technology - we could probably halve our consumption in the USA...in Europe it's going to be tougher because everyone is already driving tiny cars...but there are other ways to squeeze more out of less.

I'd like to telecommute - that would cut the energy consumed by my 'commercial' contribution to zero at work. I think we could do more shopping online and such like to cut the need for so many 'big box' stores...but for that we need a more efficient delivery system...electric postal delivery vehicles would make a TON of sense for that.

So it's basically do-able (at some cost) for everything EXCEPT industry...hence the pressure for 'cap and trade' systems to put pressure on the big energy consumers in factories. If more people recycled - and if the recycling system were more streamlined, we could make some significant savings there...but it's tough.

Some of the savings can be had without cutting consumption by using windmills (which seem very popular right now) and solar power (less so)...and I'd really hope to see more nuclear power - but there is no way to get the nuclear industry back up and running in as little as 10 years. It takes longer than that to get through the regulatory hurdles - let alone building the darned things.

However, to hit that 2020 target (WORLDWIDE!!) we have to start now. Houses last a lot longer than 10 years - we're still building energy inefficient homes! Even if a super-efficient-home law were to pass today, we wouldn't have more than maybe a quarter of our houses replaced by the deadline. Cars also last 5 to 10 years - getting the old gas-guzzlers off the streets would be very hard - even if we sold no cars that did less than 40mpg starting today! The longer we leave it - the tougher it becomes. We wasted 8 years with that idiot Bush...let's hope we can kick things into high gear now.

There are also huge problems in the developing world. It's going to be very hard indeed to get China and India to follow the 40% to 95% cut by 2050...especially if the cost of oil and gas drop precipitously as the western world starts to use less of it.

SteveBaker (talk) 03:30, 4 March 2009 (UTC)

The major reason why transport is considered a particular problem is because most moving vehicles are inherently "off the grid". Solar, wind, water, tides, nuclear (fission or fusion) can be used to generate electricity, and electricity is extremely versatile, i.e. it can easily be used for most stationary energy needs. So solving this is a problem of scale, economics, and policy. But Hydrocarbons are extremely attractive as energy sources for mobile needs - they have comparatively high energy density, and they have reasonably benevolent handling properties. And we have the infrastructure for their use in place. So changing transportation to other energy sources is much harder - its an unsolved research problem. Cars can go electric, but with reduced range and/or performance. I don't know of any serious attempts for ship or aircraft that do not involve hydrocarbons in some form (although possibly as biofuels). Well, ships can sail - not quite a stupid idea for bulk goods with modern weather satellites and predictions supporting route planning. --Stephan Schulz (talk) 10:12, 4 March 2009 (UTC)

SteveBaker and Stephan Schulz already covered that one pretty well. I would like to point out that Global Warming may make lieving on earth more unpleasant, but it will not be "unlievable". Even with full blown Global Warming humans will survive to see another day (and do some more enviromental damage). Dauto (talk) 14:04, 4 March 2009 (UTC)

One question for Steve Baker here. Does the average of 19 MPG only cover passenger cars, or does it also include tractor trailers? Because it would appear to me that a significant percentage of the transportation energy would originate from them, and there is absolutely no way that you can get one of those as a hybrid without major sacrifices to pulling power using current technology. 65.167.146.130 (talk) 15:08, 4 March 2009 (UTC)

Yeah - that figure is for passenger vehicles - I'm not sure where the cutoff is for trucks and pickups and such. Also, that's the figure for what vehicles are actually achieving in practice - not the EPA numbers (which tend to be pessimistic for new gasoline vehicles but wildly optimistic for hybrids and old, poorly-maintained vehicles) which I vaguely recall says that the average mpg for passenger vehicles is something like 25 mpg. I agree that work is also needed on tractor-trailers...but there is no reason in principle why a similar application of high-technology shouldn't help them too. You can absolutely build a hybrid-technology truck and it would make perfect sense because truck engines are even more sensitive to the RPM you drive them at than car engines (that's why trucks have so many gears!). The single biggest reason that true hybrids like the Prius produce the benefits they do is that they run the engine ONLY at it's most fuel-efficient RPM level.

But in case you doubt the degree to which these things are being agressively pursued - check out Big-Rig trucks, this...um...hybrid truck, er, pusher, Hybrid-engine tug-boats, of course most submarines and diesel/electric railroad locomotives have been using 'hybrid' technologies since before the name was invented. SteveBaker (talk) 04:17, 5 March 2009 (UTC)

You might want to visit here (http://withouthotair.com/) - it's a very interesting book and is available to be read online for free. The section on cars is here (http://www.inference.phy.cam.ac.uk/withouthotair/c3/page_29.shtml) - the book explores simplified calculations to consider whether or not we can maintain our current way of life and reduce our energy consumption as required based on using different technology etc. It's really rather an interesting read, made me much more appreciative of the scale of the issue at hand. ny156uk (talk) 21:01, 4 March 2009 (UTC)

Density

What are the primary factors that make substances as dense as they are? Say, at STP, why is hydrogen less dense than Iron? Does this correlate at all with Atomic size? Is there any pattern in the density of the elements in the table? 99.226.138.202 (talk) 01:49, 4 March 2009 (UTC)

It really is "how much mass is crammed in a certain volume", just like the definition says:) What are the things that compose a substance? "How much they weigh" and "how close they are together" is what gives density. What gives an atom its weight? What controls how closely you can pack atoms together? What pattern(s) do these properties follow? DMacks (talk) 02:15, 4 March 2009 (UTC)

So I understand that Atomic weight is determined by the number of protons and neutrons in an atom, but what determines how closely they can be packed together? Does this have to do how easily atoms are excited? If so, what determines how easily atoms are excited? If the answer to the previous question was atomic mass, why do noble gases stay gases? —Preceding unsigned comment added by 99.226.138.202 (talk) 02:24, 4 March 2009 (UTC) Well, I was going to sign that, but signbot got there ahead of me. XD 99.226.138.202 (talk) 02:26, 4 March 2009 (UTC)

Well, for gases, the controling factor is simply pressure and temperature, as explained by the Ideal Gas Law. Density of different gases at the same set of pressure and temperature conditions is controled entirely by the atomic mass of the gases. (Well, a real gas differs slightly from an ideal gas due mostly to Van der Waals forces, but these effects are negligible at room conditions). In condensed phases (solids and liquids), the volume is controlled by such things as atomic radius and ionic radius and Intermolecular forces which are all a function of the electrostatics going on at the atomic level. --Jayron32.talk.contribs 02:39, 4 March 2009 (UTC)

edit conflict

Mass is pretty well understood at the atomic level - roughly speaking, "count the number of protons and neutrons and ignore everything else." Volume is a lot more complicated, and it depends entirely on packing density. Atomic packing density is an extremely complicated field and an active area of research. While some simple atomic and molecule packing arrangements (particularly, gases and solid-state crystal structures) can be derived from fundamental atomic physics, most of the more complex substances are too complicated to describe their molecular packing analytically (with equations) at present. (Note that "density" is less useful than "pressure" for a gas, although they will be related by the ideal gas law and its experimental variants. Those variants are exactly meant to account for the "unexpected" volume errors due to atomic spacing, atomic bonding, etc.). For most substances, the density is measured macroscopically as the mass per volume at a large scale. Scientists are developing new techniques, and already have a repertoire of long-existing techniques like x-ray diffraction to probe atomic arrangements at the molecular scale. Nimur (talk) 02:40, 4 March 2009 (UTC)

It's a tricky subject - as others have pointed out, the packing of complex compounds is too complex to easily explain. But broadly speaking - the atomic radius of atoms increases fairly slowly as they go up the periodic table. That's because all of the mass is in protons and neutrons the very center of the atom - packed into 1/100,000th of its total size. Adding more neutrons to an atom doesn't change it's size - adding more protons only increases the size because more electrons are required to neutralize the atom - and the number of electrons alters the size of the entire atom. But if you look at Atomic radius#Empirically measured atomic radius - you'll see a table of atomic radii plotted onto the periodic table. Compare some of the lighter elements: eg Lithium with a radius of 145pm - that's picometers - and an atomic mass of around 7...to and the some of the heavier: eg Lead at 180pm and an atomic mass of 207) only differ by a small factor in radius - but the atomic masses are different by a factor of around 30! Now, admittedly, the 'atomic radius' is a slippery term - and it doesn't directly predict density - but you can see that the size of the atom doesn't get much bigger when you add protons and neutrons to it's nucleus. So the higher numbers in the periodic table tend to be the most dense. SteveBaker (talk) 03:00, 4 March 2009 (UTC)

That's just wrong. The size and weight of the nucleus is wholly irrelevant to the atomic radius, which is entirely dependent on the nuclear charge. Comparing Lithium to Lead is ridiculous. Lithium has a relatively large radius due to its 1s¹ configuration and Lead has a relatively small radius due to the lanthanide contraction and relativistic effects which are entirely insignificant in Lithium's case. It's actually fairly predictable that the densest elements will be the heaviest non-lanthanide/actinide ones. --Pykk (talk) 05:35, 4 March 2009 (UTC)

No, Pykk, you just missed entirely what Steve was saying. First: Steve gives effective atomic radii, not nuclear radii; so he is right. And he clearly says that nucleus size is much smaller, hence irrelevant. Second: Lithium atom has ground state configuration 1s² 2s and not 1s¹. That, however, is again entirely beyond the point, as solid Li is a metal and 2s electron is free (what used to be the 2s orbital becomes a part of the conductivity band). Third, it is quite fair to compare Lithium to Lead; differences in electronic structure don't make them any less comparable. Now, to the original question. H, F, Cl, N, O, and noble gases are in gaseous state at STP. All the other elements are solid or liquid. Now, if you are asking "why H₂ is a gas and Fe is a metal", the answer is "because H₂ molecules don't attract each other strongly enough to keep them together at STP; but Fe atoms do". If you are asking "why all noble gases (Group 18) are gases, but all alkali metals (Group 1) are metals", the answer is "because noble gases have an electronic structure such that makes the attraction between their atoms very weak, and the atoms do not stay together; but alkali metals have electronic structure such that atoms attract more strongly, and furthermore one electron per atom is collectivized, which makes them metals". You surely know that the periodic table arrangement into groups mirrors the regularities of the electronic structure of the atoms of chemical elements. Finally, if you are asking "what determines how closely the atoms are packed in a solid" - that was answered already. --Dr Dima (talk) 06:45, 4 March 2009 (UTC)

A chart of density versus atomic number. Actually I'm a little disappointed that Wikipedia does not appear to already have such a graph. Dragons flight (talk) 03:06, 4 March 2009 (UTC)

Aha! Thanks to all the people who helped. 99.226.138.202 (talk) 23:23, 4 March 2009 (UTC)

Length of one second in meters

As is well know, time is the fourth dimension of the space-time continuum. This means that, fundamentally, duration and physical length are simply two forms of the same thing. What then is the equivalent of one second in meters? If this is not a valid question, why not? —WikiMarshall (talk) 01:50, 4 March 2009 (UTC)

299,792,458 meters? :) Arakunem^Talk 01:54, 4 March 2009 (UTC)

Arakunem's got it right. for some reason he worded it as a question? Dauto (talk) 02:15, 4 March 2009 (UTC)

It is not useful in all physical contexts to treat time duration and spatial extent as equivalent or interchangeable quantities. "One second" and "2.99e8 meters" are not as interchangeable as, for example, one gram and 1000 milligrams. Nimur (talk) 02:22, 4 March 2009 (UTC)

I don't think this is a valid question - we casually talk about time as "the fourth dimension" - and lots of really annoying high school text books say it - but time is so different from spatial distances that this really doesn't make much sense. To the extent you can express something I suppose it's most natural to use the speed of light as the 'conversion factor'...so one nanosecond is a foot...but I really don't think that works. Time is SO different from the three spatial dimensions that it hardly bears comparison - why would we arbitrarily lump them all together? So I'd prefer to answer: "Time is NOT the fourth dimension" and "The space-time continuum comprises three spatial and one temporal dimension". It really goes deeper than that - there are "three spatial dimensions"...OK - so point to one of them! The fact is that you can pick any three 'axes' in space to use as your three dimensions - or you can pick an angle and two distances or two angles and one distance. Certainly it's OK to say that "space is three dimensional"...but there aren't three specific dimensions out there. On the other hand, time just "is" - we can't really swap it with the other axes...and it behaves differently from them too. There are lots of equations where you can't use spatial dimensions instead of temporal ones and vice-versa. SteveBaker (talk) 02:43, 4 March 2009 (UTC)

Time isn't just time, you can change your coordinates to combine space dimensions and time dimensions. When you do so you will always end up with one timelike dimension and three spacelike dimensions, but they can be completely different from the one timelike and three spacelike dimensions you started with. Time dilation and related concepts can be viewed as a change in coordinates. For example, if your coordinates start off as (t,x,y,z) you could change that to (t-x,t+x,y,z) and still have a perfectly valid description of spacetime, just with two of your axes "rotated" 45 degrees. In general relativity, spacetime is modelled as a four-dimensional pseudo-Riemannian manifold, it really is four-dimensional and "time" can be considered as one of those dimensions (for varying definitions of "time").--Tango (talk) 13:24, 4 March 2009 (UTC)

Yes - but that's just a mathematical convenience. I often (in computer graphics) treat (X,Y,Z)-space and (R,G,B)-color as a uniform six-dimensional (X,Y,Z,R,G,B)-space. It doesn't mean that space-color is a meaningful concept - it's just easier to do some math operations that way. Some of the things I do have extended up to 14-dimensional "spaces" - but I certainly don't "see the world" as a 14-dimensional place. Doubtless some calculations could usefully be done with three spatial coordinates and one 'mass' coordinate - that would make things like 'density' fall out with greater elegance - just as 'c' falls out when you consider space and time together. We shouldn't confuse a mathematical convenience for "how things are". SteveBaker (talk) 15:08, 4 March 2009 (UTC)

SteveBaker, what universal constant do you suggest we should use to convert color to distance? Or to convert mass to distance. (Hint:there there is an right answer to the second question). Dauto (talk) 16:10, 4 March 2009 (UTC)

You couldn't meaningfully change your (X,Y,Z,R,G,B) coordinates to anything else (at least, not anything that would mix locations and colours in one coordinate), though. (You could do it, mathematically, but it wouldn't have a real world interpretation. Coordinate transforms of space-time do have real world interpretations.) --Tango (talk) 19:39, 4 March 2009 (UTC)

Why the need for a 'universal' constant? As it happens, we typically scale colors either 0..1 and distances at some points in the 3D calculations are scaled 0..1 in screen X/Y and in depth into the screen (Z) - but in other places we have X,Y,Z in meters or something and R,G,B on a 0..255 scale...and in high dynamic range rendering situations, we may toss in another constant ('S') to allow brighter colors than the 0..255 or 0..1 scale would allow. But we're not arrogant enough to claim that there is "one true way" - it's all just a matter of convenience. It's the same in physics - for some fields, using so-called natural units in which 'c' is 1.0 - and in other fields that's a crazy choice and meters per second makes more sense. It's ridiculous arrogance to claim that there is "one true way". If I have to use a conversion constant of e or pi or c or 7 - then that's what I'll use. So long as you make it clear - everything works out just fine. For example, I've used 14-dimensional math to determine whether a particular pair of triangles with a shared edge form a quadrilateral that is "convex" and "planar" in 14-space...if it is then I can dissect the quadrilateral along the opposite diagonal to form two different triangles without messing up the appearance when I draw them. The fourteen (or so) "dimensions" are things like color, translucency, gloss, lighting and shading 'pseudo-curvatures' (normal, tangent and binormal), texture 'grain'...as well as the traditional (x,y,z). Now - in practical work, the precision of the computer isn't infinite - so hardly any quadrilaterals actually turn out to be perfectly planar - so I need to assess the amount of non-planarity and decide whether it's small enough that we don't care. Now I'm measuring this non-planarity in 14-space and coming out with a 'distance' that's in 14 dimensions. Now - the relative scaling of all of these bizarro 'dimensions' suddenly matters. So the 'natural' units for things like color and texture grain are chosen such that a minimally acceptable visual error is the same amount in all 14 dimensions. Are these now in "natural" units? Well, yes...no...who knows?! The fact is that this is what makes things work. In this application, scaling gloss from 0..0.1 while color goes from 0..1 turns out to make pragmatic sense. Would I claim some 'fundamental' connection between color and gloss and distance? Certainly not! It's merely a notational and computational convenience. What physicists do when they drop out 'c' is exactly the same deal. SteveBaker (talk) 03:53, 5 March 2009 (UTC)

Spacetime is not about saying time = length. It's about saying that time and length are deeply connected. So there isn't "one second in meters"—you don't convert time into length. Spacetime, as Einstein formulated it, is about saying that you can't make a length measurement without a time measurement, and you can't make a time measurement without a length measurement. So instead of saying, "this bus is one meter long," you recognize that what you are really saying is, "I measured the position of the front of the bus at time t, and I measured the position of the back of the bus at time t', and now I can express the length of the bus as the difference between these two points." Which in most cases is pretty trivial and it hardly matters, but when the bus as the person measuring it are moving at different speeds, it becomes more problematic, ergo special relativity. --98.217.14.211 (talk) 02:58, 4 March 2009 (UTC)

WikiMarshall, don't pay attention to the nay sayers. Time is indeed the fourth dimension of spacetime and c=299,792,458 m/s is indeed the conversion factor. This is as much true as, for instance, the conversion factor between calories and joules is 1 cal = 4.18 J (approximately). Dauto (talk) 03:35, 4 March 2009 (UTC)

Okay, so if a car is driving at 60 miles per hour, it is moving at 8.97x10^-8? Your assertion of absolute interchangeability of time and space holds no water in virtually all standard physics contexts. Nimur (talk) 08:45, 4 March 2009 (UTC)

Actually, special relativity tells us that all world lines have a four-velocity whose magnitude is fixed at the speed of light. If you are locally at rest, one could say you are moving through time at the speed of light. As your velocity in purely spatial coordinates increases, then your velocity in time coordinate must decrease by a compensating amount. This is another way of looking at the result that highly relativistic objects experience an apparent decrease in the flow of time (i.e. their velocity in the time dimension is decreased). Also, contrary to what Steve says above, there is not one fixed time dimension, but rather the "direction of time" is also a property of the local reference frame. Lorentz transformations are formally coordinate rotations that partially interchange spatial and time dimensions. In order to fully interchange space and time dimensions (so that the time dimensions behaved in a space-like manner, and vice versa) would require traveling faster than the speed of light and so as a practical matter this is forbidden under our existing understanding. Nonetheless, the perception of the spatial distance and time difference between events will vary significantly depending on the local reference frame of the observer, and one can add apparent distance by subtracting apparent time, and vice versa. Dragons flight (talk) 09:19, 4 March 2009 (UTC)

To Nimur, Yes! a speed of 60 miles per hour is (approximately) equivalent to a speed of 8.947x10^-8 (no units). No problem there. Dauto (talk) 13:42, 4 March 2009 (UTC)

While we're throwing caution to the wind, and canceling units for no good reason, I also found the speed of the 60 mph car to be equal to 3.99x10^-4 ... (no units).

(60 miles per hour)/ sqrt(Boltzmann constant * room temperature/electron mass).

But, in real physics..., there has to be a better reason to multiply a quantity by a physical constant. "Just because" doesn't cut it, even if the units work. Nimur (talk) 14:46, 4 March 2009 (UTC)

Nimur, "room temperature" ain't a physical constant. Dauto (talk) 15:05, 4 March 2009 (UTC)

Yes - exactly. As I said above - don't confuse a mathematical convenience with "how things are". SteveBaker (talk) 15:08, 4 March 2009 (UTC)

Lets make things a little more clear. 'c' is indeed a universal physical constant that can be used to convert distance units into time units. The Boltzmann constant is indeed a universal physical constant that can be used convert temperature units into Energy units. Electron mass is a physical constant but it is not a universal physical constant (You had to specify a particle, making it non-universal) so it cannot be used to convert units. Room temperature isn't a physical constant at all. SteveBaker, that is "how things are". Dauto (talk) 15:59, 4 March 2009 (UTC)

My point was that canceling units is not acceptable justification for a physical operation. Pick the mass of the car and the temperature of the car, and you will get a different value, and the units will still cancel, but it has no physical meaning. Why would you be willing to multiply by the speed of an electromagnetic wave, but unwilling to multiply by the temperature of an electron? Why would either of those operations ever make physical sense when calculating a car's speed? Nimur (talk) 16:04, 4 March 2009 (UTC)

And if I wanted to play with fundamental constants long enough, I can create a "universal mass", let's say (ħ/c^2)/t_planck; and a temperature constant... Still, random changing of variables and units does not make physical sense. Nimur (talk) 16:09, 4 March 2009 (UTC)

The car temperature and mass are not universal physical constants. Yes!! use Plank's mass and Plank's temperature in your expression (those are universal constants). See what you get. It won't be random, I promiss. Dauto (talk) 16:23, 4 March 2009 (UTC)

Clearly you are missing my point; maybe my example is distracting from the main issue here. Take a look at The Application of Dimensional Analysis to Cosmology, by Prof. P.S. Wesson of Harvard. He's got a whole book on the subject! Regarding dimensional transformations resulting in unit cancellation: "Physically, it represents a loss of information and can lead to confusion, as a little thought will reveal." Nimur (talk) 16:31, 4 March 2009 (UTC)

The 3+1 dimensions of space and time are not euclidean. If they were, distance would be ${\sqrt {x^{2}+y^{2}+z^{2}+t^{2}}}$. In special relativity, it's ${\sqrt {x^{2}+y^{2}+z^{2}-t^{2}}}$. This makes rotation work different. For the specifics, see Lorentz transformation. Rotations involving time are really just changing to a moving point of reference. Where in euclidean geometry, you could just rotate <0,0,0,1> (one second) by 90 degrees to get <1,0,0,0> (one light-second), in special relativity, rotating it would increase the time component. You could say that one second is two seconds and, I'm not sure, ${\sqrt {2}}$ light-seconds? Anyway, there's no way to rotate it to get zero seconds, or for that matter, anything less than one second, for the time component. — DanielLC 16:32, 4 March 2009 (UTC) [edit] Come to think of it, you could say that one second is i light-seconds, because if you put them both in that equation for distance I mentioned, they would get the same value. — DanielLC 22:03, 4 March 2009 (UTC)

Nimur, I've seen Paul Wesson's quotation before. He is simply wrong. There's no loss of information. We would still be able to apply dimensional analysis even if we use plank's units.

See the last section of dimensional analysis article. Dauto (talk) 17:39, 4 March 2009 (UTC)

There is a loss of information - you don't know how many factors of pi are floating around. You can deal with all the dimensionfull (is that a word?) constants, but once you introduce dimensionless constants it starts to get confusing. That section talks about using h-bar as a conversion factor, it could just as well talk about using h as the conversion factor, it's an arbitrary choice. --Tango (talk) 19:46, 4 March 2009 (UTC)

Tango, some people use degrees to measure angles, some people use radians. It's an arbitrary choice. Both units are adimensional. Yet there is no loss of information (as long as you tell people what units you are using). What was your point again? Dauto (talk) 20:52, 4 March 2009 (UTC)

Mathematicians always use radians, anything else is just radians multiplied by an arbitrary number. An angle is defined as the ratio of the radius and the arc length, there is no reason to multiply that by anything. But that's beside the point - as you say, you need to tell people what units you are using. If you were working dimensionlessly, then there aren't any units, so it doesn't work. --Tango (talk) 21:16, 4 March 2009 (UTC)

Tango, you are right. angles are defined as the ratio between an arc and an radius which comes out naturally in radians but some people chose to arbitrarily multiply that by a constant for tradition's sake and use degrees instead. hence it is necessary to specify which units you are using (radians or degrees) in order to avoid confusion. Notice that angles are dimensionless but it is still possible to use different units, contrary to your point that when working dimensiolessly there aren't any units, so it doesn't work. You just didn't think it through. The same thing is true about the definition of the speed of an object. it is defined as the ratio between two components of the quadrivector $ds^{\mu }\,$ along the direction of the particle's trajectory (world line) through spacetime. These components must have the same units, since they are components of a single object. Therefore velocity is an adimensional quantity. c=1 comes out of this definition naturally but some people chose to arbitrarily mutiply that by a constant for tradition's sake and use m/s instead. hence it is necessary to specify which units you are using (m/s or natural units) in order to avoid confusion. No loss of information as long as you tell people which units you are using. Dauto (talk) 22:26, 4 March 2009 (UTC)

Mathematicians never use degrees (in any real work, anyway - they might come up in casual conversation) and very rarely use the word "radian". Angles are dimensionless, there are no units, we don't use units. A right angle is "pi-by-2" not "pi-by-2 radians". Using degrees is simply wrong from a mathematical perspective. Any comparison between radians vs degrees and ft/ns vs m/s is misconceived. The four vector you mention is defined in terms of c, you need the c in there otherwise it is wrong (you can, of course, define c=1 and then not worry about it until you get to the end of your calculation and plug in the appropriate constants to get the units to balance). When you work out the velocity as you were doing, you do get a dimensionless quantity, but that quantity isn't velocity, it's velocity/c. c has dimensions, so so does velocity. --Tango (talk) 22:41, 4 March 2009 (UTC)

Mathematicians can get away with skipping mentioning the fact that they are using radians because they know that their audience knows that they are using radians. It goes without saying because, as you said, radians come naturally and any other units would in a sense be wrong. Guess what, quantum field theorist and relativists also get away with skipping mentioning the fact that they are using natural units because they know that their audience knows that they are using natural units. It goes without saying because natural units come naturally (hence the name) and any other units would in a sense be wrong (to use your words). c=1(no units) is more than a mathematical convenience. It is the right way to think about it. In fact, Those physicists I talked about never (to use another of your words) use 'c' in their equations. Think about it. Why should two different components of a single physical object (a quadrivector) be measured using different units? You said I have to stick a 'c' in there in order to make it right. I say you are the one sticking 'c' in there when you arbitrarily chose to use different units to measure time and space. Dauto (talk) 23:50, 4 March 2009 (UTC)

It's not even true that radians are somehow 'natural' units for angles. There are engineering applications where 'grads' are used (100 grads = 90 degrees). There are plenty of situations where a full 360 degrees is more usefully and 'naturally' scaled to a 0..1 or -1..1 scale. There are times in computer-based applications when it's more natural to use 1/256th of a circle. If you ever played a computer game that used the "Unreal Engine", all of your angles are in 1/65536ths of a circle. Math isn't just for mathematicians - we normal people get to use and adapt it too! SteveBaker (talk) 03:27, 5 March 2009 (UTC)

SteveBaker, radians are the natural units for angles. But you are free to introduce arbitrary constants in your choice of units if that is somehow convenient. As you said yourself, "don't confuse a mathematical convenience with 'how things are'". Dauto (talk) 03:54, 5 March 2009 (UTC)

No! That's bullshit. Having 2.pi units in a full circle is undoubtedly convenient in situations where pi is involved for some other reasons (eg when working with sines and cosines) but in other situations where pi is NOT involved, a 0..1 scale is vastly more 'natural'. You have a prediliction for having 2.pi units because that's the kind of field you happen to be working in - but in areas I happen to work in (some of the time), having an irrational number of angle units in a full rotation is not merely inconvenient - it's utterly untenable! There are things you literally cannot do with radians. For example - I have two objects that are spinning - adding some amount of rotation per time-step...and I want to know on any given time-step whether they are pointing in the same direction. Using radians I have to divide their total accumulated rotation by 2.pi and take the remainder and compare the two results. However because pi is irrational - I can't make such a comparison in finite precision. In that case using radians is not only unnatural - its downright useless! So - I store rotations such that a full rotation is 1 unit. This is beautifully natural - I simply compare the fractional parts of the numbers and I'm done...what could be more natural? Radians are also useless for people who have to do actual numerical calculations rapidly in their heads - using degrees is incredibly useful in that situation because you can do exact division by 2,3,4,5,6,8,9,10,12...and so on...jut try calculating the numerical value of a third of two-pi in your head so you can mark it using your (non-existant) radians-scale-protractor!!! One man's "natural" is another man's "completely and utterly impractical". So your 'natural' units are only natural for your applications - and this pigheaded insistence that your way is right and everything else is somehow wrong is just phreaking crazy! We can do calculations using angles using any damned units we like. Get out here in the real world where math is actually used for practical purposes and you'll soon find that what is 'natural' or 'convenient' changes from one day to the next. The sooner you get your head out of the clouds (or wherever it's currently stuck) and into the real world the sooner your contribution to the world will be of practical relevance. SteveBaker (talk) 05:22, 5 March 2009 (UTC)

"Natural" has a very precise meaning in this context, it doesn't just mean "the most obvious/useful". There are plenty of situation where it is best to use unnatural units and conventions, but that doesn't make them natural. --Tango (talk) 15:41, 5 March 2009 (UTC)

SteveBaker, I don't dispute that other angle units can be more useful or practical then radians. I myself find it more practical to use degrees in many situations, and I understand why a computer programmer would prefer to use some power of 2 such as 256 for 360 degrees. That does not change the fact that an angle is defined as the ratio between two lengths (a radius and an arch) and the natural thing to do is to use the same units to measure both lengths. Guess what angle units turn up when you do that? Dauto (talk) 19:27, 5 March 2009 (UTC)

No! You choose to define an angle as the ratio between the length of a radius and an arc...which results in you deciding that radians are "natural". But in many applications, defining an angle as a fraction of a complete planar rotation makes much more sense - especially if you don't give a damn about the lengths of arcs or the areas of pie-wedges. When you work in applications where you're more interested in objects rotating - there is no "ratio of distances - one being an arc", the incredibly ugly use of an irrational number for useful concepts like 'right angle', 'identity rotation', 'reversing direction' simply goes away and the result is a much more natural 'fraction of a full rotation' definition for an angle...in some applications. I'm not claiming that radians are bad - they have their place - I'm just saying that which units seem most 'natural' is in the eye of the beholder and it's extreme arrogance to claim that your application - your definition of 'angle' - is somehow more fundamental than the others. There is no one definition of 'angle' that we somehow all have to assert to be "The One True Definition" - and hence there is no one representation for angular units that is somehow more natural than the others. I use radians sometimes, degrees at other times, 0..1 other times, -1..1 in others and even 0..65536 (urgh!) when I work with the god-awful UnrealEngine. All are perfectly 'natural' in the environment in which they are used. SteveBaker (talk) 20:33, 5 March 2009 (UTC)

It may not be the only definition, but it is the standard definition. I suppose you could define angles as "points in the natural parametrisation of orientation preserving linear isometries of the Euclidean plane by the unit interval" (rather a mouthful!), which would give you angles ranging from 0 to 1. I can't think of any natural definition that yields anything other than radians or 0 to 1, though. Any other units would require a definition that introduces arbitrary elements with no justification in elementary geometry. --Tango (talk) 21:02, 5 March 2009 (UTC)

SteveBaker, I agree with Tango that there is also some naturalness for the definition where 1 = 360 degrees. Instead of defining an angle as a ratio of two lengths it seems equally reasonable to define it as a fraction of a full turn. The other definitions are somewhat more arbitrary. But I don't care about that since naturalness is not definable anyways. I'm actually glad you said that because you are kind of making my original point for me. My point was that despite angles being adimentional quantities, there is still the possibility of choosing different units without any loss of information (what do you know, we're actually agreeing here despite the appearances). Interestingly enough, the factor of 2pi between the radian definition and the 0 to 1 definition is the same factor o 2pi that relates frequency $\nu \,$ and angular frequency $\omega \,$ which is the same factor of 2pi which relates $h\,$ and $\hbar \,$ which started this whole discussion to begin with. Thanks for helping me make my point, Dauto (talk) 21:48, 5 March 2009 (UTC)

So what we've concluded is that there are multiple natural unit systems and you can use whichever you like, you just have to make sure you keep track of the pi's. Did anyone think otherwise to start with? Have we just had a big long debate only to conclude that we didn't really disagree on anything substantial to start with? --Tango (talk) 21:59, 5 March 2009 (UTC)

I don't know, Tango. Do we all agree that 1 second = 299,792,458 meters? if we do, then you may be right that there is no substantial disagreement. Dauto (talk) 23:17, 5 March 2009 (UTC)

Physicists never use c in their equations? I can't tell if you're just making stuff up here or are somehow totally confused. Show me some of this physics that somehow never uses natural units and implies multiplying things by c but doesn't say it. I call foul—you're spouting nonsense. --98.217.14.211 (talk) 01:00, 5 March 2009 (UTC)

May be I didn't make my self clear enough. What I meant to say was that whenever using natural units $(c=\hbar =1\,)$ 'c' or '$\hbar \,$' don't appear in the equations. What would be the point of multiplying by powers of c=1(no units)? That's why c never apears in the equations when natural units are being used. Dauto (talk) 03:29, 5 March 2009 (UTC)

Look at the rightmost column of the table atPlanck units#Planck units simplify key equations. See any physical constants there? That's what I'm talking about. Dauto (talk) 03:47, 5 March 2009 (UTC)

Maybe, but those haven't any special sense, at least, until we find a real correlation between them all (as temperature is medium kinetic energy). Would be i*t, a spacial magnitud, or i*x a time magnitude? I'm intersted in that problem.

Plumbide

I just created an article called Plumbide and was told to come here for help expanding it. Chlorine Trifluoride (talk) 02:07, 4 March 2009 (UTC)

It would help if your footnotes actually explained the reference - WP:CITATIONS will help you with the formatting. From what I see at present, it is not possible for a reader to track your sources down. I've done one as an example for you... (it's not a perfect cite template, but it's at least possible to track down the article without a lot of effort). Nimur (talk) 02:25, 4 March 2009 (UTC)

Well, there are quite a few things here:

• Your 'references' aren't references, they're footnotes. References are links to documents outside of Wikipedia that specifically back up what you are saying - scientific journals, chemistry books for example. You could start by doing a Google search on your subject and see what decent articles have been written about it.
• Your link to rare earth links to a 'disambiguation' page - that's bad because the poor person who follows your link doesn't know which meaning of the term you are referring to. Link instead to rare earth element.
• The article is very short - it'll definitely need some expansion. I recommend you look at other articles on similar topics - phosphite for example. It has diagrams of the structures it's talking about, a 'See Also' section - which you should use to link to other Wikipedia articles that talk about related topics.
• You should do a 'search' on the word 'plumbide' using the regular Wiki search box and see what other articles mention the word - this may give you more ideas for things to write about - and you can edit those articles to link to yours on the first occasion they mention the word.
• If you have a copywrite-free photo of some samples of these materials - add it into your article.
• There are lots of other categories you could add your article to - there are categories "Inorganic compound stubs" and "Lead compounds" that seem reasonable.
• You could try joining the Wikipedia:WikiProject Chemistry - they have MANY resources for people writing on chemistry-related subjects. There are entire specialised manuals-of-style for writing these kinds of article.

I hope that helps! SteveBaker (talk) 02:29, 4 March 2009 (UTC)

Damn, I saw the link to Rare Earth and thought I was gonna get a 22 minute version of Get Ready... --Jayron32.talk.contribs 02:42, 4 March 2009 (UTC)

Well you've definately got a good name for this type of work CF₃.

For some reason you put the page in the category 'plumbates', I changed that to 'lead compounds' - as phosphide is not a phospate etc.

Beyond that I can't see so much wrong with it. Why not go and make another article. It's perfectly acceptable to me after I made tiny changes to it. Keep up the good work, wikipedia needs more articles like this.FengRail (talk) 04:23, 4 March 2009 (UTC)

Right now this article is an ophan, meaning that no other articles link to it. If you can think of some articles that should link to it, you should correct this. ike9898 (talk) 19:59, 6 March 2009 (UTC)

medium oil

what is the composition of medium oil? —Preceding unsigned comment added by 119.154.9.144 (talk) 03:42, 4 March 2009 (UTC)

It depends on the brand and where you bought it. Megilp is a painting medium consisting of a mixture of mastic varnish and linseed oil. Most will be similar, combining a thickener with linseed or synthetic oil. Nimur (talk) 08:48, 4 March 2009 (UTC)

Legal "uppers"

Caffeine and sugar are legal "uppers": something you can take that gives you some more energy for some hours. Are there more "things" a normal healthy person can take to get some more energy? I'm not interested to read about illegal drugs or about stuff that is detrimental for your body, just something comparable to coffee (but that I don't know of). Lova Falk (talk) 07:27, 4 March 2009 (UTC)

Some people find coffee or tea stimulating even if it is decaffeinated. This may be a psychological response, but it's possible there are other compounds in the drink that are also categorically stimulants. Nimur (talk) 08:50, 4 March 2009 (UTC)

Indeed, I am one of those people. —Cyclonenim (talk · contribs · email) 23:22, 4 March 2009 (UTC)

See energy drink and energy bar. Those articles contain a number of links to other compounds people ingest to get some "energy", ranging from outright stimulants like ephedra to Calorie rich food products like starches. Dragons flight (talk) 08:56, 4 March 2009 (UTC)

Starches are converted to sugar by the saliva in your mouth...(try chewing a piece of bread and notice how it gets sweeter as you chew)...so for our purposes, starches ARE sugars. SteveBaker (talk) 14:59, 4 March 2009 (UTC)

If you chew long enough, yes. Saliva isn't the only source of amylase, some starch is broken down later, so it does take longer to get energy from starch than sugar. See glycemic index. --Tango (talk) 19:36, 4 March 2009 (UTC)

Laws vary from country to country. Kava seems to be legal in most places, although perhaps hard to come by other than in the South Pacific. It's also not very pleasant to drink - like mud, but perhaps it's an aquired taste.-gadfium 09:17, 4 March 2009 (UTC)

Hmm, Kava as an "upper"?

Kava is a tranquilizer primarily consumed to relax without disrupting mental clarity. Its active ingredients are called kavalactones. In some parts of the Western World, kava extract is marketed as herbal medicine against stress, insomnia, and anxiety.

— Kava

I have never tried Kava, but its mechanism of action appears similar to benzodiazepines, and they sure don't make me feel "up" (since I take them for sleep!). -- Aeluwas (talk) 11:27, 4 March 2009 (UTC)

Beware of Kava, I don't have a reference right now, but remember reading that one particular part of the plant contains some hepatotoxic compounds. --Mark PEA (talk) 12:41, 4 March 2009 (UTC)

If this piece is to be believed, consuming bicarbonate of soda before exertion leads to amazing increases in performance.[ http://ironpower.biz/sup/sup_energy2.htm] --TammyMoet (talk) 11:57, 4 March 2009 (UTC)

I was expecting that to be a typical pseudoscience piece by some uninformed layperson, but was pleasantly surprised. However, it still isn't peer reviewed (I can't access full studies of 30+ years ago) and if the OP is asking for an alternative to caffeine for mental stimulation, sodium bicarbonate is not going to help. --Mark PEA (talk) 12:41, 4 March 2009 (UTC)

Contrary to popular belief, increased concentration of lactate does not directly cause acidosis, nor is it responsible for delayed onset muscle soreness. Noodle snacks (talk) 06:09, 5 March 2009 (UTC)

Native peoples in Bolivia and similar places chew coca leaves for energy, and it's legal for them to do so. I personally take pseudoephedrine for chronic sinus headaches, and I've noticed that it gives me a big energy and concentration boost. Other stimulants, such as Ritalin, have a similar effect. --Sean 14:00, 4 March 2009 (UTC)

In Brazil it is common to use guarana as an energy boost. It contais more caffaine then coffe as well as Theophylline plus other components. Dauto (talk) 14:49, 4 March 2009 (UTC)

I've seen guarana listed in some energy 'uppers' commonly sold in gas stations in the USA. SteveBaker (talk) 15:00, 4 March 2009 (UTC)

I used to have a friend who ate supari, but the taste is pretty awful (at least to my taste buds). You can check out our articles under the Herbal and fungal stimulants category [1]. If you consult a doctor, there's Adderall. A Quest For Knowledge (talk) 16:03, 4 March 2009 (UTC)

Khat may or may not be legal depending on where you are (legal in UK, not in USA); it contains the stimulant cathinone. --Maltelauridsbrigge (talk) 18:37, 4 March 2009 (UTC)

Something else that hasn't been mentioned: modafinil, piracetam and the various other racetams. Please also see this template: Template:Psychostimulants, agents used for ADHD and nootropics. --Mark PEA (talk) 21:07, 4 March 2009 (UTC)

Abstinence from sexual activity will allow you more energy than its opposite. Cuddlyable3 (talk) 14:17, 5 March 2009 (UTC)

Thank you all for answering! I'll check everyone of them, to see if I'll use it, but the side effects scare me.Lova Falk (talk) 17:18, 5 March 2009 (UTC)

Fluid therapy

Explain the difference between "maintenance" volume, "replacement" volume and "ongoing losses" in fluid therapy? —Preceding unsigned comment added by 124.178.147.147 (talk) 09:10, 4 March 2009 (UTC)

Or article on fluid balance may provide some useful background information for you. As for your questions:
Maintenance = the volume of intravenous fluid required to maintain a neutral (no net loss or gain) fluid balance (so input matches output).
Replacement = the amount of fluid required to correct a negative fluid balance to neutral (so input = fluid volume deficit + ongoing losses).
Ongoing losses = fluid losses through all means, both sensible ( or quantifiable, including urinary output, faecal/diarrhoeal, wound drainage, bleeding) and insensible (or non-quantifiable, including evaporative losses to respiration, perspiration and open wounds, especially burns and other large surface area wounds). Hope that helps. Mattopaedia ^{Have a yarn} 13:17, 4 March 2009 (UTC)

The Rust Process

I need a few minutes of the right person's time and his/her expert opinion on how fast rust can appear on newly exposed steel following removal of paint on a car part - the frame of a door open to the weather. (I'm in dispute with a body shop as to how some damage was caused.) The car was parked outside for ten days in cold, wet conditions. How quickly would a visible layer of rust appear? A few days? A week? Would much more than ten days be needed?

Many thanks

FrancisMacFrancisMac (talk) 09:23, 4 March 2009 (UTC)

This is original research so not actually permissible in the World of Wikipedia, but steel body work can rust in a couple of days in wet conditions, a couple of years ago I was making a steel framed table and this rusted within 36 hours after a shower of rain. Richard Avery (talk) 10:12, 4 March 2009 (UTC)

Original research is not allowed in articles. I don't see how knowledge of rust constitutes original research

However we are not here to give legal advice, and any information given here can't be relied on in a legal dispute at all.

It also depends on the depth of rust. Exposed steel can get a thin layer of rust in seconds213.249.232.187 (talk) 12:13, 4 March 2009 (UTC)

Sorry 187 I missed out a ;-) Richard Avery (talk) 15:03, 4 March 2009 (UTC)

Indeed. High quality knives, such as Honyaki and other Japanese cutlery require constant vigilant maintenance. They must be wiped dry immediately after use, lest moisture rust the blade and ruin the edge. Visible rust and pitting can occur within minutes if the blade is left damp. --Jayron32.talk.contribs 14:43, 4 March 2009 (UTC)

I also agree that exposed steel will start to rust immediately. In my case, I polished steel samples for microscopic viewing, and it was necessary to repolish them the next day because of surface rust. However, the serious type of rust that causes pieces of the metal to flake off will take longer. Also note that the car steel may have had some protective coating underneath the paint. Whether this coating was also stripped off with the paint, I do not know. Salt will greatly speed up the rusting process, so, if they splashed saltwater on it while moving it through an icy lot, that would also have an effect. StuRat (talk) 14:50, 4 March 2009 (UTC)

It's vastly variable.

When I lived on the south coast of the UK, my wife reversed one of our cars into the other (doh!) scraping a 6" swath of metal on one car down to the bare metal. Two days later, it had a patina of rust on it - the metal was no longer shiney and it had little orange splotches. By the time we got it to the body shop, maybe a week later, it was orange-colored all over, rough to the touch and there was no shiney metal visible anywhere.

Here in central Texas, I was rear-ended in my old pickup truck and lost about the same amount of paint in roughly the same area. Since the truck was old and crappy - I pocketed the insurance money and didn't bother to get it repaired and I never did get around to painting the 'ding'. Four years later, when I sold the truck, that patch of metal was still as shiney as the day the accident happened.

The difference was:

• The car in the UK was a Morris Marina - notorious for being built from low-grade steel. The truck in Texas was a Ford Explorer. Made from pretty decent steel.
• The weather in the UK is damp and rainy - the humidity is often high. The weather in Texas is hot and dry - and in central Texas, the humidity is typically close to zero.
• In the UK, it snows and gets icy in the winter and they used to spread a lot of salt onto the roads to melt it. Here in Texas, it only rarely gets icy - and when it does they use grit from inland quarries - not salty beach sand. When the ice melts and the road dries out - the salt stays there. UK roads are salty even in the summertime - and it's well known that salt+water+steel=rust.
• In the UK, we lived in Brighton - close to the sea - lots of salt is in the air. Here in Texas, we're 300 miles inland...so not.
• Although the annual rainfall in this part of Texas is comparable to the southern counties of the UK, the rain happens in a few torrential downpours a few times a year. Cars get wet - but they dry out pretty quickly. In the UK, it drizzles just enough rain to get things wet - then stops for a while - then does it again - and it does that through most of the year. It often doesn't get dry enough or warm enough for things to properly dry out for weeks or even months at a time.
• Even in the winter, in Texas there are cold days (below freezing sometimes) - but they are mixed in with hot days - so again, things don't stay wet for long. (There is a saying here that in the winter: "If you don't like the weather today - wait until tomorrow - it'll be different.")...sometimes we have snow on Xmas day - but other times we can eat our Xmas dinner out in the open air...it's random.

I also have a 1973 VW Bug that spent most of it's life in Arizona (hot, dry, no humidity) and the rest in Texas - despite its age and a total lack of rustproofing, it has zero rust.

Somewhere between two days and 35 years is where your answer lies!

SteveBaker (talk) 14:56, 4 March 2009 (UTC)

(Are very expensive cars ever made of stainless steel?)FengRail (talk) 17:42, 4 March 2009 (UTC)

The added cost and difficulty of working with stainless steel mean that it is seldom used unless absolutely necessary. (Stainless steel is harder than most other steels, and it's a bloody nuisance to work with.) The DeLorean DMC-12 – the car featured in the Back to the Future films – is a famous exception, being equipped with stainless steel body panels. DeLoreans were left unpainted, as their fiberglass and stainless-steel bodies were not vulnerable to rust. A few other vehicles have also been built with stainless steel finish, usually for promotional or demonstration purposes: [2]. TenOfAllTrades(talk) 22:39, 4 March 2009 (UTC)

Thanks.FengRail (talk) 22:52, 4 March 2009 (UTC)

I believe that the DeLorean was the only mass-production car ever to use stainless steel. They don't make regular cars out of the stuff because it doesn't take paint very well - you can have it any color you want so long as it's dull-silver. (Hence the "natural metal" finish on the Deloreans). Sure, DeLorean's don't rust (and because the stainless steel body panels are essentially just decorative - it would still work just fine if it did). But it was far from an easy car to maintain - there were problems with hard-to-remove marks from fingerprints and bird poop and such. You had to clean it with some fairly exotic cleaning agents that you had to get from the DeLorean factory. Without a protective paint finish, fine scratches were more noticable because you couldn't just wax the car to get rid of them - and because you can't use paint and bondo and the body has a 'brushed' finish - you can't either hammer out or fill and paint a ding. SO any kind of minor body damage pretty much requires replacing the entire body panel. SteveBaker (talk) 03:01, 5 March 2009 (UTC)

It would be a lot easier? to make them out of normal steel, polished and then clear lacquered. (by the sounds of it) Such as is found on many shiny steel tools.FengRail (talk) 13:52, 5 March 2009 (UTC)

Birds and sex

Sorry if this is a bit of a vulgar question, but I saw two pigeons having sex outside my window this morning and it got me thinking. How exactly does the male bird manage to get his cum into the female and avoid getting it plastered all over her rump feathers, or his own feathers when he ejacultates, seeing as though he doesn't actually have anything he can 'stick inside'? There seems to be an awful lot of feathers to get in the way of a successfull mating. --81.77.40.134 (talk) 14:19, 4 March 2009 (UTC)

Well, they must work it out somehow, since there do seem to be an awful lot of little pigeons running around. Seriously though, you should read Cloaca, and especially the paragraph on the "Cloacal kiss". It's enlightening. --Jayron32.talk.contribs 14:40, 4 March 2009 (UTC)

I would guess that a lot does miss the target, but enough hits to cause pregnancy, and that's what's important. StuRat (talk) 14:44, 4 March 2009 (UTC)

The cloaca is colloquially known as a "vent", presumably because "cloaca" sounds vulgar. Nimur (talk) 14:56, 4 March 2009 (UTC)

I seem to remember someone mentioning something on here once about how the mating method used by birds is not particularly efficient, compared to the way that most mammals go about it. As someone who's bred birds, I suppose the fact that sometimes you'll get a hen laying an entire clutch of unfertilized eggs, despite being 'serviced' repeatedly by her mate (or only ending up with one or two eggs that develop - out of six) is testament to its (literally!) hit-and-miss nature. As Jayron32 said, I suppose that it works as well as the species needs it to work in order to keep the numbers up. --Kurt Shaped Box (talk) 19:29, 4 March 2009 (UTC)

Ask the quelea how it works, they seem to have got the hang of it! Richard Avery (talk) 07:23, 5 March 2009 (UTC)

There must be more chickens than quelea? Kittybrewster ☎ 07:39, 5 March 2009 (UTC)

Expected decline of the Earth biosphere

Hello. I'm looking for an article about this subject. But I cant find one. Is there one? (Specifically, an article which describes the predicted decay of the biosphere due to the growth of the sun. How and when different aspects of the biosphere would be expected to decline and dissappear. When would the oceans become shallow seas? When would the disappear altogether? When would life begin to decline? When would it dissappear? And so on). Thanks in advance for pointing me in the right direction! —Preceding unsigned comment added by 81.233.212.12 (talk) 15:19, 4 March 2009 (UTC)

According to our article on the Sun, we have about a billion years. A Quest For Knowledge (talk) 16:34, 4 March 2009 (UTC)

I see it. I've no plans to still be here by then, so I should be OK. But is there a full article on the subject? If not, can I request the creation of one? 81.233.212.12 (talk) 16:38, 4 March 2009 (UTC)

Be bold and make it yourself. Just make sure you follow all notability and referral guidelines or you risk having your article deleted. Livewireo (talk) 16:55, 4 March 2009 (UTC)

We have an article, Risks to civilization, humans and planet Earth, if that helps. --Tango (talk) 00:01, 5 March 2009 (UTC)

There is no way to realistically predict that. We have no clue how life would evolve in the presence of gradually increasing heat - and we really don't know precisely what will happen to the sun and when. This would be approximation layered on guesswork layered on wild supposition. SteveBaker (talk) 02:33, 5 March 2009 (UTC)

We can put upper bounds on it, though. Once the average temperature gets above the boiling point of water, life as we know it is going to struggle. That's where the 1 billion years prediction comes from. --Tango (talk) 13:47, 5 March 2009 (UTC)

That's a bold supposition. Evolution has produced some rather impressive extremophiles. It's not beyond the realms of possibility for a creature to be able to operate at those temperatures. Hyperthermophiles are around today that can survive well above boiling point (see Methanopyrus Strain 116...happily living their boring, hot little lives at 122 degrees centigrade...well beyond boiling point. As temperatures rise - those critters will become more prevalent as their competitors are wiped out - evolution will allow some of them to survive at higher and higher temperatures and in increasing salinity...perhaps multicelled hyperthermophiles will evolve? As the oceans boil, the cloud cover over the planet will increase - pushing up our Albedo and reflecting more sunlight away - that'll slow things down somewhat...but precisely how much is a relative unknown because we don't know the geography of that future era. Will the oceans be deep or shallow when they start to boil? Will ocean current mix up the cold, deep layers and the hot top layers or not? We can't predict ocean currents a billion years from now! Heck we can't even predict the effects of global warming to that kind of degree over even 50 to 100 years! But until the oceans are literally boiled dry - I think we'll see life clinging on in some niche environments - because that's what evolution does. However, once all the water has gone - it's certainly gonna be tough. But predicting that with the kind of specificity and precision that our OP demands does not seem likely. Will we have extremophiles above the size of a bacterium? Will there be extremophile Lions and Giraffes? Will they learn to live in the air like birds and insects in clouds of live steam? Due to the random nature of evolution - we can't know - we can't even sensibly speculate. SteveBaker (talk) 14:09, 5 March 2009 (UTC)

Those examples you mention live at above 100C, they don't live at above the boiling point of water, since they are deep underwater where the high pressure increases the boiling point. The Earth may have to heat to somewhere above 100C in order for all the water to boil (especially since the atmospheric pressure would presumably increase will all the extra water vapour), but sooner or later the temperature will reach the boiling point of water even at the bottom of the oceans. Some life may be able to survive after that, but it wouldn't be life as we know it. --Tango (talk) 15:36, 5 March 2009 (UTC)

Does anyone happen to know how warm Mars will be and how habitable it will be by then? A Quest For Knowledge (talk) 17:08, 5 March 2009 (UTC)

While it is possible Mars would warm up to a habitable temperature for a time (probably a fairly short time, geologically speaking), it still wouldn't have much of an atmosphere. The ice caps would sublime, providing some more atmosphere, but probably not enough to support humans without protect (and there certainly wouldn't be any free oxygen without active terraforming). It might make terraforming an easier job, but it would still take a lot of work. --Tango (talk) 18:02, 5 March 2009 (UTC)

looking for a photo

I am looking for a photo of the earth from space at night, however there is a catch. I want one during a large widespread power outage, so I can see how much light there is on emergency power only. Anyone able to help? 65.167.146.130 (talk) 16:31, 4 March 2009 (UTC)

List of power outages is a first place to look. You should be very careful that you are comparing "apples-to-apples" images - with modern processing techniques like image compositing, multispectral cameras, gain adjustment and auto-leveling of brightness and intensity in both acquisition and post-production, it may be hard to tell exactly how much light you are actually receiving (typically, I think Earth at night as viewed from orbit looks pretty dark when viewed with the naked eye). Next, take a look at NASA's Science on a Sphere Night Lights data sets. They specifically mention techniques to display power outages by comparing average data to single-night data. Again, note that these are false-color (enhanced) images. Alternatively, you can look at this Columbia University Earth Institute press release, which has a few low-resolution images, and references further research. Here's a blog which makes a vague citation to "NASA" but no real information on the image processing techniques. Nimur (talk) 16:38, 4 March 2009 (UTC)

After a major outage in the northeast USA a few years back, such a picture made the rounds, but was said to be phony. —Tamfang (talk) 18:37, 4 March 2009 (UTC)

Here are the real images of the 2003 blackout. They're not as impressive as the fake ones, but still pretty neat. APL (talk) 18:55, 4 March 2009 (UTC)

Surely there has never been a world-wide outage? Kittybrewster ☎ 07:36, 5 March 2009 (UTC)

no. an outage can only go as far as the power systems are linked. --98.217.14.211 (talk) 12:55, 5 March 2009 (UTC)

I'm tempted to say that the original questioner, being American, thinks that America makes up 99% of the world. A very common idea, apparantly. 78.146.195.92 (talk) 00:47, 7 March 2009 (UTC)

Hypothetically speaking, an external event (like an extraordinarily strong geomagnetic storm) could affect multiple power grids simultaneously. It would take a heck of a solar storm to bring down all the electric grids in the world (or even in just one hemisphere), though. TenOfAllTrades(talk) 18:09, 5 March 2009 (UTC)

Being American, I'm blind to the bias mentioned, so: What? —Tamfang (talk) 04:41, 8 March 2009 (UTC)

Comparing the nightime views from space of the North and South Koreas supports the contention that the South may suffer an occasional power outage but the North never enjoys a power inage. Cuddlyable3 (talk) 14:25, 5 March 2009 (UTC)