Wikipedia:Reference desk/Archives/Science/2007 July 13

Science desk
< July 12	<< Jun | July | Aug >>	July 14 >

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.

July 13

Holdridge life zones

Picture of the day

The Holdridge life zone climate classification system is named after its creator Professor Leslie Holdridge. The relative simplicity of the model, and ease of determining life zones from climate data, has led to its use in modelling climate change impact.Image credit: Peter Halasz

My diagram of Holdridge's life zones is going to featured picture of the day in less than 48 hours, and I feel embarrassed that the caption is so dull and that there's not much text in the associated article. So I've just started Holdridge life zones (maybe that should be renamed to something singular). I created the diagram to get a grip on it all, but I still don't know many of the details, so the text is still sketchy.

(Questions moved to Talk:Holdridge life zones)

Most natural shape ?

Which is the most natural closed figure? When I say natural, I mean the figure found most often in nature/universe. I tend to see circles most of the times (the shape of the planets, shape of liquid drops, cross section of tree trunks, waves originating from a point etc). I rarely see squares and rectangles. -- WikiCheng | Talk 03:55, 13 July 2007 (UTC)

Spheres are the most perfect, but most structures (at least on astronomic and atomic scales) look more like oblate spheroids. Similarly, circular orbits would be perfect, but ellipses are far more common. Batmanand | Talk 07:12, 13 July 2007 (UTC)

Fractals? Nimur 07:13, 13 July 2007 (UTC)

I agree that we don't see perfect spheres and circles in nature but to a good approximation, the things I mentioned in the question are circles. A cross section of a tree trunk is more of a circle than an ellipse. Coming to fractals, there are so many varieties and hence they don't qualify. We can also generalise saying that polygons are most common but that would include too large a number of shapes. -- WikiCheng | Talk 09:56, 13 July 2007 (UTC)

A "nearly perfect circle" in nature is almost always an ellipse, even if it has very small eccentricity. Batmanand | Talk 10:23, 13 July 2007 (UTC)

Sinusoids show up a lot, but usually as a function of time. This is because a lot of natural phenomena are well-modeled by second order differential equations (the solution to which is a sinusoid). A circle (like an orbit) is two orthogonal sinusoids with a perfect 90 degree phase shift; an ellipse is two orthogonal sinusoids with some other phase shift. Nimur 15:24, 13 July 2007 (UTC)

What about the humble egg (chicken, duck, or whatever you like). These are usually ovoid, I believe. A beautiful shape. -- JackofOz 23:16, 13 July 2007 (UTC)

Undoubtedly the most common 3D shape is the raindrop or teardrop shape, which is not a sphere. Everytime it rains there must be a huge number of them, and it rains a lot on earth. Even other planets may have 'rain' of other chemicals rather than water. If you want the most common 2D shape then its going to be a circle. 80.0.106.3 14:29, 14 July 2007 (UTC)

It's not a matter of some abstract notion of "perfection" - it's good hard mathematics. The ratio of surface area to volume is smaller in the case of a sphere than any other shape. So in something like a raindrop - the surface tension is pulling inwards trying to minimise the surface area - while the intermolecular forces are forcing the raindrop to maintain a constant volume. The minimum energy configuration is therefore a perfect sphere - and a stationary drop of liquid in zero-g will indeed form a perfect sphere. In the case of real raindrops, gravity and air resistance get involved and reshape the drop into something more aerodynamic. But there is no mysticism here - it's just math. With eggs - it's the same deal. To enclose the most nutrients for the young animal using the least amount of wasted shell material - eggs should be spherical. But getting a large egg out of that small hole at the end of the momma bird means that ellipsoidal eggs are better in some other species. Also, a spherical egg would very easily roll out of the nest - and in bird species where this is a particular problem, they lay eggs that are slightly smaller at one end than the other. This makes the egg roll in a circle - so they can't roll far from where where they were laid. To pick another example, our skulls are roughly circular - maximising brain volume while minimising the amount of heavy bone needed to enclose it. In every case where there is a competition between maximum volume and minimal surface area - you get a sphere - possibly modified by other considerations.

But it's not true that everything in nature is like that. In other circumstances, nature is trying to MAXIMISE surface area while MINIMISING volume - then you get something furry or knobbly or very convoluted.

Cubes are also surprisingly common in nature. The kinds of things that make cubes be optimal are considerations of packing lots of things into a small space. Hence with crystal growth - you have a lot of atoms to cram into a small space - and packing them into a regular grid works best. Look at sugar or salt through a hand-lense and you'll see that every grain is an almost perfect cube. Stick a bunch of pingpong balls into a box and gently shake them so they pack down and you'll see a hexagonal structure emerging.

Geometric rules apply to nature - they aren't just something humans invented! SteveBaker 15:39, 14 July 2007 (UTC)

SteveBaker - yours was a very interesting reply. You stated: "In other circumstances, nature is trying to MAXIMISE surface area while MINIMISING volume - then you get something furry or knobbly or very convoluted." Can you give a concrete example or two of this, so I can better understand the abstract concept ...? Thanks. (JosephASpadaro 18:40, 14 July 2007 (UTC))

The lining of your intestine, and the insides of your lungs spring to mind. Unfortunately the articles don't have pictures that do much to illustrate the point. —Pengo 23:26, 14 July 2007 (UTC)

Thanks - I get the picture now. Thank you. (JosephASpadaro 00:46, 15 July 2007 (UTC))

A thought experiment: Take six square sheets of paper - tape them together to form a cube. Now try to minimise the volume of the resulting object whilst keeping the surface area the same...for example by jumping on it! Observe how crinkly the paper has become! But there are lots of biological examples - lungs and intestines are great examples because in this case the body is trying to absorb something (air, food) and the bigger the area exposed to the stuff being absorbed, the better. However, we don't want a big volume of our bodies given over to this function - so they are intricate, convoluted, folded shapes. Coral reefs, trees - these are all things where maximum area/minimum volume is best - and they are about the least spherical things you could imagine! SteveBaker 01:15, 15 July 2007 (UTC)

the last bathtub

A classic method of suicide is to slit one's wrists while sitting in a warm bath. Why? Does the water encourage bleeding, reduce pain, or what? (I hope this is not construed as seeking medical advice.) —Tamfang 04:29, 13 July 2007 (UTC)

In light of a cryptic message of concern I received, I should mention that I have no bathtub to call my own. (I'd rather use a bullet anyway.) —Tamfang 05:59, 18 July 2007 (UTC)

I believe the idea is simply that the mess will be easier for ones relatives to clean up. There is of course also the added fascination of dying like Marat. I really don't think that warm water alone is going to diminish the considerable pain of cutting into ones wrists. --S.dedalus 06:24, 13 July 2007 (UTC)

Actually, I believe the reason is to encourage vasodilation and thus increase the speed you will bleed out (the added bonus being the bath will collect the blood and it would be quite a relaxing environment to end it all.) Rockpocket 06:53, 13 July 2007 (UTC)

I think there are serious ethical problems with using Wikipedia to discuss the effectiveness/painlessness etc of methods of committing suicide. I do not know if there is a policy about this, but I do find it very disturbing to see a suicide method described as "relaxing". DuncanHill 12:17, 13 July 2007 (UTC)

There's absolutely nothing unethical about rational discussion of things like this. Wikipedia is not censored on this or any other topic (it has a very large article on suicide, as well as a well-filled category — where I found the intriguing idea of quantum suicide!). I have never heard of a case where someone who was not already planning to commit suicide decided to do so after reading a straightforward discussion of it, and I think that it takes an overwhelming argument (and probably an empirical base) to justify censorship on an "ethical" basis. --24.147.86.187 13:09, 13 July 2007 (UTC)

It is quite well known that people at danger of committing suicide can be greatly affected by what they read, hear and see. People can be 'triggered' or 'pushed over the edge' or however you want to put it. This is why after a prominent suicide there is usually a string of copycats. That is why charities try to reduce the media exposure suicides are given. That was the main concern charities had with that film that showed people jumping from the Golden Gate Bridge. Describing any suicide as 'relaxing', 'painless', etc is dangerous and dishonest. Also, it is important to avoid implying that the fallout for loved ones would be restricted to 'cleaning up'. We definately should not discuss which methods work best. If someone is actually interested purely from an academic point of view, they would do better to learn enough about human anatomy to be able to answer this question, among many others, themself. Sorry if this seems restrictive, but there are the things you can say and the things you should say. Wikipedia is not censored, but we do not allow anything that even looks like child pornography. Skittle 16:31, 13 July 2007 (UTC)

In the US child pornography is illegal. Talking about suicide is not. --S.dedalus 19:35, 13 July 2007 (UTC)

Yes, child pornography is illegal in the US. Things that look like child pornography are not. Yet, I do not think you will find anything that looks like child pornography on Wikipedia. In addition, isn't assisting suicide a crime in many jurisdictions? Not that I think this is the reason we shouldn't do it, just that if people are pushing to the legal limits... Skittle 21:28, 13 July 2007 (UTC)

Lolicon. --Carnildo 22:03, 13 July 2007 (UTC)

However, given the people who edit Wikipedia, there is a definite possibility that we will discourage some of them from bathing. Gzuckier 14:50, 13 July 2007 (UTC)

What is the most effective way of removing the "bathtub ring" afterwards? And by the way many articles are deleted in WP:AFD if they amount to "how-to" manuals. "Fascination" and "relaxing" are not appropriate words to associate with suicide in this reference desk. As for the claim that Wikipedia is not ensored, that is pretty laughable, given how fast "inappropriate" or "disgusting" illustrations are removed form some articles, and how many bio articles are deleted by admins on the grounds that they are embarrasing to the subjects, even when well referenced. Edison 15:13, 13 July 2007 (UTC)

Actually, before everyone gets too wound up in moral indiganation, "relaxing" was used to describe the bath, not the suicide. That is hardly controversial and a perfectly appropriate adjective to describe a warm bath. If frank answers on controversial subjects offend you, I suggest you don't read them, rather than attempt to silence them. Rockpocket 16:47, 13 July 2007 (UTC)

"...it would be quite a relaxing environment to end it all" This is not a frank comment on a controversial subject, it is an attempt to describe a particular way of committing suicide as 'relaxing'. If you had restricted yourself to facts, such as 'it keeps the cuts open and is easier to clean up', then, with the existing comment emphasising that it will still be extremely painful, I would just have added that cleaning up any mess would not be the most upsetting part of the act for the suicider's family and friends, and then left it at that. While I would rather people weren't unnecessarily spreading 'tips' on suicide, it was the use of triggering language that I consider dangerous and thoughtless. Skittle 21:52, 13 July 2007 (UTC)

Please everybody. Wikipedia is not censored, not a soapbox, etc. The original question was answered competently and neutrally. If anyone has disagreements about whether suicide is off-limits on the reference desk, please contribute to the Guideline Discussion, instead of getting off-topic here. Finally, per usual Medical Advice disclaimer, if the original poster is considering suicide, please see a licensed psychiatrist who will be able to help you - as a group of unlicensed internet volunteers we are neither qualified nor able to dissuade a suicide attempt. Nimur 16:59, 13 July 2007 (UTC)

Actually there have been several proposed and (rejected policies) concerning how suicide should be handled on Wikipedia. No one to my knowledge has proposed that we should refuse to answer abstract questions ABOUT suicide however. This question is a not a request for suicide advice, it is a scientific question about suicide. --S.dedalus 19:24, 13 July 2007 (UTC)

None the less, people should take care not to use potentially triggering language when discussing suicide. This is not because the community might not like it, nor because it might be illegal, but because someone might commit suicide who otherwise wouldn't have. I fail to see what is gained by describing a set-up for suicide as 'relaxing', but I can see a lot of loss. Skittle 21:28, 13 July 2007 (UTC)

I have replied on your talk page. --S.dedalus 01:15, 14 July 2007 (UTC)

I agree that Rockpocket's comment "it would be quite a relaxing environment to end it all" was misleading and would tend to encourage suicidal individuals to use this method. However, rather than censoring him and removing that comment, I feel clarifying remarks are in order, so will include them myself. I don't feel that dying with one's wrists slashed would be at all relaxing, but rather quite painful. And, while certain suicidal individuals do put a lot of thought into "making it easier" on the survivors (neatly folded clothes are often found near the body, for example), the other responders are correct that the cleanup effort pales in comparison with the emotional pain of having a loved one who committed suicide. Would-be suicidal individuals should consider this deeper, and permanent, pain they will inflict on their loved ones. StuRat 15:11, 15 July 2007 (UTC)

Are we important for this world!!?

Every species of animal and plant in this world has got a role to play in the ecosystem. And removal or addition of one, might adversely affect the delicate ecosytem balance. But I wonder if one day all human beings are wiped out of this world (lets say it happens...) will the whole ecosystem come to a stand still!!? or will it improve a lot since the very reason which has been destroying the balance is out of the stage!?202.54.176.11 11:24, 13 July 2007 (UTC)M.M.

I think you're suffering from the preconception that everything in the ecosystem was precisely arranged like a house of cards, and that if you pulled one card out, it'd all collapse. Evolution would continue to occur even if humanity was wiped away, and other organisms would fill in empty ecological niches. It's certainly possible that a lot would change, because of the abrupt change in use of resources by humans. However, if you've ever seen what an abandoned house looks like even after 6 months of neglect, imagine what a decade would do? -- JSBillings 11:47, 13 July 2007 (UTC)

As JSBillings said, "delicate ecosystem balance" is a false conception. People who use the phrase conveniently ignore ecosystems such as Krakatoa. It was altered heavily and still flourished over time. -- Kainaw^(what?) 12:06, 13 July 2007 (UTC)

I think the phrase "delicate ecosystem balance" is correct from one POV, that if we wipe out one component of the ecosystem, let's say algae, the effects on other species (possibly including humans) could be disastrous. However, over time the ecosystem would adapt, some species would go extinct and others would arise, and on a geological time scale it would just be a "blip". If humans went extinct, this would be worst for those species dependent on us, including pets, parasites, and species we have specially bred as food. Many of those might go extinct or evolve into something able to survive independently. StuRat 22:58, 13 July 2007 (UTC)

To answer the Original Post, I would have to say offhand that if humanity disappeard in a single day, the worst thing to happen for the ecology would be all of the unattended nuclear powerplants. Some may automatically shutdown, some may not. To A lesser extent failures at chemical plants / refineries would also be a problem. Czmtzc 13:44, 13 July 2007 (UTC)

In the words of George Carlin, "The earth wanted plastic, didn't know how to make it, needed us. That might be the answer to the age-old question "Why are we here?" Plastic!" -- MacAddct1984 13:52, 13 July 2007 (UTC)

If an alien were to view earth, his main impression would be the titanic struggle between plants and insects. Gzuckier 14:49, 13 July 2007 (UTC)

Carl Sagan wrote in his book Pale Blue Dot that it would be extremely difficult for an extra-terrestrial to identify us as "the" intelligent life on earth. He even goes so far as to suggest that our automobiles might be identified as the primary species on the planet, since they have large, strong exoskeletons, are efficient converters of chemical energy, and have elaborate electronic and mechanical control systems for decision-making. Nimur 15:30, 13 July 2007 (UTC)

Didn't New Scientist do a competition on this in their feedback column? Imagining what the SMS message an ET would send home when they discovered Earth? Ah yes I found it: "Arr. Earth. Dominant species "car". Colourful exoskeleton and bizarre reproduction via slave biped species. Aggressive but predictable. Intelligence uncertain.". Brilliant stuff. More here. - Capuchin 16:01, 13 July 2007 (UTC)

I know the idea goes back further than that. I remember seeing a pretty funny TV cartoon (it had a 1950s feel/style of drawing) on this very thing. Clarityfiend 16:05, 13 July 2007 (UTC)

Could it be Destination Earth? This 1956 film is entirely available at Archive.org, and details Martian attempts to... overthrow communism after observing the plethora of automobiles running on a free-market, petroleum-fueled Earth. Nimur 17:05, 13 July 2007 (UTC)

Nope, that wasn't the one. It had an alien observer watching the life cycle of cars, starting from their "birth" in a factory and I think, remarking on the "parasites" they seemed to pick up. Clarityfiend 20:46, 13 July 2007 (UTC)

I think I've heard of this too, but I don't have a title. I can, however, mention a textual version, a research report on "Life on Earth" by a Martian. This appeared in the book A Random Walk in Science, 1972, compiled by R.L. Weber, edited by E. Mendoza. --Anonymous, Friday the 13th, 21:50 (UTC).

I'm pretty sure I've seen the cartoon you're thinking of. No idea where, though. --Reuben 01:37, 14 July 2007 (UTC)

Got it: "What on Earth!" (imdb) --Reuben 01:49, 14 July 2007 (UTC)

And, it is the source of the name Ford Prefect. -- Kainaw^(what?) 16:30, 13 July 2007 (UTC)

Really? Is there any evidence that Douglas Adams was aware of "What on Earth!" prior to writing the first H2G2 radio series? Skittle 21:01, 15 July 2007 (UTC)

There is an long interesting article in the current edition of Scientific American which gives a lot of detail about what would happen if humans suddenly all died off. I've just found that you can read the article "A Future Without People" online for free at the Sciam website, although you lose the nice pictures. 80.0.106.3 14:18, 14 July 2007 (UTC)

We don't have to speculate. We have an example where exactly this scenario took place. Look at the abandoned areas around the Chernobyl nuclear plant. That's just about the worst possible scenario. Humans blow up a power plant - irradiate the area and run away. What's happened to the "abandoned" wildlife around the old (and still very radioactive) plant? According to Zone of alienation, it's thriving! Rare species of Lynx are living there. The power of nature to recover in that one small spot is spreading out - actually causing nature to do better in human inhabited areas immediately outside of that zone. But bear in mind that this is the WORST that could happen if we all just vanished - imagine the improvement in areas where humans just vanish and this kind of disaster doesn't happen - you'd still get the natural 'bounce back' of nature - but without any of the downsides. Not only would our departure not be noticed - it would be a huge win for the majority of species. Cows...maybe not so good...Shih Tzu...very bad indeed. SteveBaker 15:14, 14 July 2007 (UTC)

Three phase electric motor - braking motor speed using motor windings when current disconnected.

I have a three phase electrical radial arm saw which is not electrically braked when the current is switched off. This means that the inertia of the motor and blade keep the machine turning for a few minutes after switching off making it dangerous to work nearby. I have another single phase machine which does have electric braking and this stops within 5 seconds. Can the three phase machine be modified to electrically brake itself at switchoff?Primexco 12:50, 13 July 2007 (UTC)≠

I think so, by short circuiting the windings (connecting them to each other). Just avoid short circuiting the incoming wires (i.e., from the wall outlet). There might be practical difficulties, like sparks wearing down the circuit breakers that short circuits the windings. That problem would be the same for a single phase machine, of course. —Bromskloss 13:08, 13 July 2007 (UTC)

Simply shorting an induction motor isn't especially effective because there aren't any remnant fields to induce generation.

Atlant 13:10, 13 July 2007 (UTC)

Ah, the rotor needs to have a permanent magnet. —Bromskloss 15:54, 13 July 2007 (UTC)

(edit conflict)

There are two ways to stop an electric motor. For the first, you might want to see our dynamic brake article. The key is twofold: 1) somehow, cause the motor to become a generator, and 2) provide a place to dump the energy that is beng generated by the motor-turned-generator. I have an electrically-braked chop saw but I believe it is a universal motor rather than a pure induction machine so it's easier to rig for dynamic braking. For an induction machine, it should be possible to do the deed by briefly applying a modest amount of direct current to the field windings; electricity will be generated and dissipated in the rotor. The timing has to be correct, though, or you'll overheat the motor.

The second way you can stop an electric motor is by plugging; this means to rig the electrical connections to apply power that would run the motor in the reverse direction. Usually, you need a pretty sophisticated controller to accomplish this without burning up the controls, the motor, or blowing the line/mains over-current protection device. Again, it has to be timed accurately as well or the motor will decelerate past the stopping point and begin accelerating in reverse. The variable frequency drive article might provide some hints.

Atlant 13:09, 13 July 2007 (UTC)

Child rearing/ sleeping habbits

Why should children sleep in their own bed and what age should they begin regularly sleeping in their own room?

I don't know what scientific research has been done, but there is probably a huge variance across cultures. Nimur 15:31, 13 July 2007 (UTC)

My son slept in his own bed from birth, which was next to our bed. At three months, he moved to a crib in his own room. It is unwise to have an infant in bed with an adult. The adult can easily roll onto the infant. The infant does not have the strength to push the adult or wake the adult, so he or she will suffocate. It is a very bad way to learn that babies do not belong in bed with adults. -- Kainaw^(what?) 18:48, 13 July 2007 (UTC)

"It is unwise to have an infant in bed with an adult." - well, our co-sleeping article cites some significant support for the practice, as well as the dangers you cite, and equipment to facilitate the practice with more safety. Gosh, I hate child-rearing articles (in the real world, it's not Wikipedia's fault) - they all sound a bit like protection rackets : "buy our book and do exactly what we say, or your child will die and it'll be all your fault"). Creepy. -- Finlay McWalter | Talk 22:37, 13 July 2007 (UTC)

I believe this article from the NY Times does a better job as stating what I was saying. In a nutshell, a "normal unmodified" adult bed with an adult in it is as statistically dangerous to an infant as one of those old cribs that allowed the child to get his or her head stuck in the rails. Statistically, the study found 64 deaths a year in adult beds compared to 50 deaths a year in a crib (mostly due to the old known unsafe design). This does not mean that there are no benefits to having an infant in the bed. I stated that I kept my son next to our bed in a bassinet for the first three months - within arms reach but away from the risks of the bed. In fact, I slept days and my wife slept nights, so one of us was always awake and alert when he woke up. Of course, anyone can google and come up with a thousand links that claim babies are more save in an adult bed. I'm sure there's at least one site that claims they should sleep in the tub or the sink. -- Kainaw^(what?) 22:57, 13 July 2007 (UTC)

There are books and books and books of advice - and they all contradict each other. Do what works for you - go with the flow. SteveBaker 14:55, 14 July 2007 (UTC)

Carbon sequestering

Is it not a good idea to grow more trees and then cut and regrow them in an controlled manner in an effort to sequester excess CO2 from the planet??Also we already have cars giving 60-80 km to the gallon.Is it not easy for the gas guzzling automotive nations to adopt??or is it plain ego coming in the Way??59.92.243.13859.92.243.138

You mean for fuel? I think so, but replacing petroleum with wood would be hard as liquid fuels are the most versatile and it's hard to liquidise wood, mainly because of the lignin, which is what makes wood wood and not paper. Various oil seed plants are being looked into. As a method of sequestering carbon emissions from fossil fuels at today's rates, it's far too slow. To meet today's demands, we don't have the technology to sequester carbon, or produce energy, biologically. Bendž|Ť 17:36, 13 July 2007 (UTC)

No, it's a terrible idea. In Australia they cut down old growth forest and pretend they're doing the environment a favour. The problem is that only a tiny percentage of the carbon in that forest is in the logs that they take away. About half is in the soil, and the rest in other parts of the tree and undergrowth. Then from that tiny fraction (found in a large tree trunk), a large amount of carbon is lost again in the processing. Few logs make into furniture or anything solid, and a large amount is lost again in the woodchipping and paper mills that turn it into paper. Then the forest trees may take over 400 years to recover and hold as much carbon as they did in the first place, and meanwhile the birds and animals which called those trees their living room have been wiped out and possibly set on a trend towards extinction.

Plantations are different in that you don't have all that carbon locked away in the first place. But the best thing you could do would be to leave the trees to grow and retain the carbon, becoming a stronger, denser forest, rather than releasing large amounts of it by cutting it down.

Deforestation is the second largest contributor to global warming on the planet, so the best thing we could do along these lines is simply to leave existing forests alone. —Pengo 23:58, 13 July 2007 (UTC)

There is a big difference here between old-growth hardwood forests and fast-growing pine forests.

• If you cut down a tree - then immediately plant another to replace it that's going to grow to the same size as the original one - then the amount of carbon locked up in the forest remains exactly the same over the long term because the number of trees stays the same. Whatever you do with the tree you cut down is therefore carbon neutral - you can burn it - it doesn't matter in the grand scheme of things. If you dumped the logs from that tree into (say) a disused mine - and somehow walled it off to stop them from producing CO2 as they decomposed - then you would indeed be sequestering carbon. However, the amount of carbon in a tree is nowhere close to the amount in a similar volume of coal or oil - most of what makes up a tree is water. So you'd have to sequester a VAST number of trees in order to counter our present rate of fossil fuel consumption.
• Old growth hardwood forests are a different prospect. They take hundreds of years to grow - so if you play the same game (cut down a tree - plant a replacement) then it will take hundreds of years for the carbon you liberated by cutting down that tree to get re-absorbed by the slow-growing replacement. So over hundreds of years you might balance out the equation - but that's nowhere near fast enough to solve our present problems. So yeah - it's fluffy thinking to imagine that old growth forests are a sustainable source of energy or whatever. But for faster growing plants - pine trees, grasses, corn - then a carbon-neutral energy production system is very do-able.

Yes, there is a problem with the energy required to produce fuel from corn or whatever - but so long as you get more energy out than you put in, you can run your production plant from the fuel it's generating - and you are still carbon-neutral. What you can't do is cheat and use 1 ton of carbon from coal to produce 10 tons of carbon from corn/grass/trees which you sell on the open market. You have to use 1 ton of fuel from last weeks production to produce 9 tons of fuel for the open market and 1 ton to power the factory next week. But even if it takes 9 tons to power the factory to produce 10 tons of fuel - then so long as you sell 1 ton of fuel and put 9 tons back to run the factory, you have carbon-neutral nirvanah. The trouble with that latter scenario is that sales from 1 ton of fuel doesn't cover the cost of running the factory and repayment of the loan you took out to build it. That's why fuel costs MUST increase in order to make these factories viable. Since we don't want to spend more money on fuel - we'll STILL need fuel efficient vehicles in order to keep our economy on the rails. So carbon-neutral fuels are not the ONLY answer - we still need vastly more efficient vehicles, power plants, etc. SteveBaker 14:39, 14 July 2007 (UTC)

Nuclear power is more than carbon neutral. --Tbeatty 05:21, 17 July 2007 (UTC)

Why 'more than' ? It consumes no CO₂ and produces none - as far as I can tell, it's precisely carbon neutral. SteveBaker 14:20, 17 July 2007 (UTC)

if the presumption of carbon neutral is energy is extracted and then requestered through plant growth, then Nuclear power allows plant growth without extraction. The corn field can be replaced with forest since it's no longer necessary for energy. IT can be repurposed into providing more sequestered form of carbon such as composites material or forest that is used to provide lumber. --Tbeatty 15:21, 17 July 2007 (UTC)

Solar powered lifting wing Remote Controlled RC plane

Any idea where I can get suggestive plans and efficient solar panels???

I believe there was a research plane that used solar power both to heat it's single balloon wing and to power it's props. However, this wing was rather large, as smaller wings would be more subject to effects from winds, so I don't think a small-scale version is likely to work for long. StuRat 22:45, 13 July 2007 (UTC)

See the "Solar Challenger" section of our Gossamer Albatross article.

Atlant

I agree. Most of the weight of this thing would be in the solar panels. The weight of a solar panel is proportional to it's volume. The power it generates is proportional to it's area. But you can't make thinner panels for a model plane - so if you made a half-scale model of that plane, you would have one quarter the amount of electricity - but also one quarter the weight of solar panels. But the thermally heated 'balloon' wing would only displace one eighth the amount of air - so your lift budget is severely compromised - but you can't make it up from your engine because the engine power is being reduced at the same rate as the mass of the solar panels. Smaller isn't better in this case. SteveBaker 14:18, 14 July 2007 (UTC)

Tidally locked at geosynchronous orbit?

Is there any reason a natural satellite couldn't become tidally locked at a geostationary orbit? I know our Moon is a special case because it's so large compared to the planet, but without having gone through all of the equations yet, it seems possible, if improbable, that a natural satellite could land at this orbit by accident (or design, of course). Or is g-synch orbit too far out for tidal forces to act efficiently? 64.126.24.11 17:43, 13 July 2007 (UTC)

Even if it were placed in a geostationary orbit, it'd degrade for the same reason it was tidally locked, so it wouldn't stay in that orbit for long. -- JSBillings 18:04, 13 July 2007 (UTC)

In fact tidal drag creates a tendency toward a geostationary situation. This is why the Earth's rotation is slowing, thus causing the geostationary orbit to move higher, toward where the Moon is. The angular momentum is transferred to the Moon, which absorbs it by moving into a higher orbit itself. Without interference from other bodies (i.e. if the Sun doesn't go red giant first and destroy the Earth), the ultimate outcome would be that the day would be about 40 times its present length (ths number from memory) and the Moon enough farther out that its orbit would be geostationary. A similar situation has already been reached by Pluto and Charon. --Anonymous, July 13, 2007, 21:57 (UTC).

Red AntHive Invasion

Here's a good one If I dig out a red ant hive so the hive is in a panic and then get a scoop/shoveful of another hive(not necessarily red ants) will they attack?or continue to pursue their quest for their eggs?-shredder0288

Ants from different hives/nests will attack each other even if they are the same species. Chances are the ants will probably continue to move their offspring and attack the "invaders." (and get attacked back) It would be cruel to do it though. Sifaka ^talk

If you have a bunch of fire-ant nests - this might be a better way of disposing of them than poison - I'm not sure whether it's "cruel" - compared to poison at least. Certainly better for the environment in general. Interesting. SteveBaker 14:10, 14 July 2007 (UTC)

There are multiple-queen and single queen colonies. The difference between them is mentioned at www.extension.org/pages/Fire_Ant_Biology_and_Identification . I've read elsewhere also that the multiple-queen colonies dont aggressively compete with each other, so the ant has an advantage over native ants when invading. So multiple-queen colonies might not fight under the conditions mentioned in the question.Polypipe Wrangler 07:19, 17 July 2007 (UTC)

Slutty bugs

Just getting your attention... Anyway, are there any insects which reproduce more than once in their life cycle? Other arthropods? Thanks Gzuckier 20:53, 13 July 2007 (UTC)

It is rather common, isn't it? Bees and ants have the "queen-drone" structure. The queen reproduces many times. The praying mantis female usually kills the male, reproduces, and then finds another mate. I'm sure there are many other examples. -- Kainaw^(what?) 21:21, 13 July 2007 (UTC)

Social insects in Hymenoptera have a queen that reproduces many many times. But there are many insects, such as the Mayfly that spends very little of its life as an adult, before it mates and dies. -- JSBillings 00:01, 14 July 2007 (UTC)

Not sure about that. Our article on Queen bee implies that, while they spend most of their laying eggs, the actual fertilization is a semi-singular event (multiple drones with a single queen over a short period of time). Several insects lay their eggs over a period of time, it's just that bee queens live fairly long. My impression was that the questioner was asking about insects having multiple instances of mating/reproduction, not just a singular (though extended) period. If that's the case, tarantulas may fit the bill; the article doesn't explicitly say it, but it is somewhat implied. Matt Deres 02:54, 14 July 2007 (UTC)

Thermos Mechanisms

Vacuum flasks use both vacuum insulation and reflective coatings to minimize heat loss due to conduction and radiation, respectively. Can anyone tell me which is the primary mechanism of heat-trapping? Supposing Thermos decided to go all-out on the best materials (I've read above that the most efficient telescope mirrors are ~90% reflective, and 10^-9 Torr counts as a rather beefy man-made vacuum), which mechanism would more efficiently isolate its respective form of heat loss?

Once you have pulled a sufficiently high vacuum that radiation totally dominates the rate of heat transfer, what you want to do is to slow down the radiative heat transfer by making it have to make several jumps to bridge the gap. This is done by "superinsulation" (no Wikipedia page yet – the link only goes to an unrelated house-building meaning of the word – and even our Dewar flask page is rather minimal). Superinsulation simply consists of many layers of thin, crinkly, mirrorized mylar foil stuffed into the vacuum space. Heat radiation has to jump the first gap and heat up the first foil, then that foil has to radiate heat toward the next foil, heat it, etc., and this process creates a much higher thermal resistance than a single gap does. This scheme is typically used when the inner vessel contains liquid helium, which by itself creates a very good vacuum, by freezing out any residual gas that might have been present in the gap, so that radiation is indeed the dominant source of heat leakage. Yes, mechanical contact between neighboring foil layers does in principle allow some conductive heat transfer, but with many layers, thin foils, and very small contact areas between randomly crinkled foils, that transfer rate can be very low. --mglg_(talk) 22:02, 13 July 2007 (UTC)

Fish Hooks

Unfortunately, sometimes fish swallow the hook. If its not worth pulling it out, I've always just cut the line and let the fish go; I read somewhere that the fish dissolves the line and hook somehow. Is this true, or will the hook be stuck in the fish until it rusts long after the fish is dead? Does this cause the fish a slow, painful death? Or can the fish live a relatively "normal" existence? Thanks for the help. --71.98.15.170 22:44, 13 July 2007 (UTC)

I'm betting on a slow painful death. THe plastic line certainly won't dissolve - and I very much doubt that the stomach acids of a fish could dissolve stainless steel in anything under a few years - the barb of the hook is eventually going to embed itself in the stomach and every move from that point would be agony. So no - I don't think there is a way to rationalise your way out of this one. It would be better to kill the fish under those circumstances. SteveBaker 14:06, 14 July 2007 (UTC)

Non-stainless steel hooks dissolve within a few weeks due to a fish's stomach acid (much more powerful than ours - rememeber most game fish are predators that swallow prey bones and all). Stainless steel hooks may not dissolve, but still won't necessarily be fatal or hampering. If it gets torn up inside, it might die - but just having a hook stuck in its stomach won't kill it. Vultur 21:21, 15 July 2007 (UTC)

As I suspected, this stuff about hooks dissolving is simply not true (it certainly didn't sound believable). It's something someone somewhere is spreading to make fisherman feel less bad about the harm they do to the fish they throw back. Here is a decent study: http://www.dnr.sc.gov/marine/mrri/insh_fish/reddrum/gonefishin.htm - yes, the fish suffer - most of them die. SteveBaker 19:17, 17 July 2007 (UTC)

Amazon parrots - which is the best breed to get?

There are so many different breeds to choose from. Which is the best type of Amazon parrot to own as a pet? --84.64.89.222 23:14, 13 July 2007 (UTC)

I think you need more guidance than we can give you, but let me start off with a question: Have you really already settled on some species of Amazon, or are you using the term more-generically to refer to anything from an African Grey Parrot to small conures and parakeets and parrotlets? FYI: We adopted a Sun Conure; we'd have liked a 'Grey but any Grey would likely have long outlived my wife and me so that affected our decision.

Atlant 23:59, 14 July 2007 (UTC)

Jumping off a speeding train - the physics involved

Over the years I've seen lots of actors in movies jumping off moving trains. I realised recently that they invariably jump off onto the sloping surface of an embankement, rather than when the ground near the train is flat.

Does anyone know why they choose a slope? It might be that rolling away makes them less likely to get limbs under a wheel, but are there any other reasons such as the energy from the speed and the fall being better disapaited by spinning rather than just falling flat? Or is it just because it looks better and takes longer? 80.2.220.179 23:58, 13 July 2007 (UTC)

There is at least some basis in fact for this. In any sort of incident like this, you want to decelerate as gradually as possible to reduce the forces on your body. It would be ideal if you could hit the ground running as fast as the train is moving and then slow down as if from a normal run, but you can't run that fast, so what will probably happen is that you fall over and stop abruptly. The next best would be to land on something like a dense layer of shrubbery with many small branches, but that has to exist first. On sloping ground it would at least be easier to go into a roll and you might at least be able to roll a few times before stopping. (And, yes, this is more visually interesting, which filmmakers love.) On the other hand, jumping onto lower ground means you fall a few feet more, so you have additional speed to dissipate. I can't say what the comparative effect would be in practice, and I certainly don't advocate doing any experiments to find out! --Anonymous, July 14, 2007, 00:20 (UTC).

We should have an article on impulse. Hitting the ground at a given speed, you're going to need a certain ammount of impulse to stop tumbling. Spreading this over a greater time interval will allow you to stop with less force applied to your body, breaking your fall. Bendž|Ť 09:03, 14 July 2007 (UTC)