Wikipedia:Reference desk/Science

May 18

heat to elrctricity

what is the best known way to transfer heat to electricity?

A steam turbine driving an electric generator. Those articles should help you out. 161.222.160.8 02:16, 18 May 2007 (UTC)

How much heat? At what temperature? How much electricity? how do you define "best"? in some situations, the aforementioned turbine/generator is best. in other situations a thermocouple is best. There are a very large number of alternatives depending on the particular conditions. -Arch dude 02:28, 18 May 2007 (UTC)

thermocouple are used to mesure heat but can it be used to make large quantity of electricity? and how afficient are steam powered turbines in % of convertion?

No, but they are the "best" way to generate small amounts of electricity in specific applications, which was my original point. Your question did not specify "large" amounts. See the thermocouple article for the use of "thermopiles" (arrays of thermocouples to generate enough electricity from the pilot light of a gas-fired furnace to run the the gas valve. This scheme lets the furnace operate with no external electrical power. -Arch dude 22:01, 18 May 2007 (UTC)

also ive been wondering if surounding a container with a heat source in it with aerogel would keep all the heat inside or if it would absorb it?

"All" and other such superlatives are usually tricky words in the engineering world. Aerogels are extremely good insulators, but not perfect ones. There's always some non-ideality that makes "all" untrue. As Arch dude pointed out, scale has a LOT to do with efficiency. Schemes that are fairly efficient on a large scale (like the steam turbine) are often very ineffective at smaller scales (such as micro power generation for MEMS and self-powered ICs) and vice versa. There's rarely a "best" solution to any problem, especially one so broadly phrased. -- mattb 04:16, 18 May 2007 (UTC)

what would you propose for extremely high heat , im trying to think of the best way to turn to electricity a solar furnace and im trying to figure out if there would be a way to achieve higer % of energy convertion or more cost eficient way to turn sunlight to heat

How high, like thousands of degrees (using mirrors to focus light on a small volume) ? A steam turbine would still work if you have a nice free supply of water, like a river. If you need to reuse the fluid, perhaps instead of water you should use some fluid with a higher boiling point. StuRat 05:04, 18 May 2007 (UTC)

You also need to define your goals a bit more precisely. Do you want to produce the maximum amount of electricity per dollar of install price, per dollar over the projected life of the solar collector, per square foot of surface area, etc. ? These different cases may lead to using very different technologies. Your choice would also depend on the sunlight patterns in each particular location and other factors like tax incentives. Also, if you need to supply energy when the Sun is down, this necessitates more expensive equipment. StuRat 05:04, 18 May 2007 (UTC)

See also: Pyroelectricity, Thermoelectricity. I entered an international science fair with a project on the thermoelectric effect but miserably died. [Mac Δαvιs] ❖ 21:30, 18 May 2007 (UTC)

You were electrocuted and now edit Wikipedia as a ghost ? StuRat 22:56, 18 May 2007 (UTC)

Look at this article: http://www.technologyreview.com/Energy/18211/ --Joe 21:29, 19 May 2007 (UTC)

Price of chemical type stuff and stuff

Where can I find the prices for stuff like liquid nitrogen or uranium or potassium permanganate or sodium chloride? Also, where can I buy this stuff? Thanks.--71.175.125.135 02:17, 18 May 2007 (UTC)

Well, liquid nitrogen probably requires a permit of some kind, but once that's covered I'm told it's cheaper than milk by volume (and with the price of milk these days I'm not surprised). Potassium permanganate is, according to the article, available over the counter from pharmacies in the former Soviet Union, and I suspect would be available from maybe hardware stores. Sodium chloride ... ARE YOU MAD?!?!? That stuff's as dangerous as DHMO!

But in general, if you were looking for high quality, pure supplies of chemicals in general, ie. suitable for lab work, and especially if you were looking to buy in bulk, there seem to be a lot of companies selling this kind of stuff according to a quick Google search. You'd probably also want to check the Yellow Pages (or local equivalent) for "Chemical supplies". A good supplier would, I believe, take fairly heavy steps to make sure that you're aware of any safety issues involved, and also keep a track of what you were buying to make sure there was no nefarious purpose involved. Confusing Manifestation 02:29, 18 May 2007 (UTC)

I don't believe liquid nitrogen requires a permit, and is indeed fairly inexpensive. However, the containers to store it in can get pretty expensive, depending on how much you want to store. I seem to remember a previous discussion here saying that a normal thermos wouldn't work for storage. --Bennybp 02:54, 18 May 2007 (UTC)

Thanks guys. Is there any website that I could look at that would list prices for stuff like this?--71.175.125.135 03:05, 18 May 2007 (UTC)

By the way, you didn't mention uranium. :) --71.175.125.135 03:05, 18 May 2007 (UTC)

Well, like I said, the Google search brings up a large list of suppliers. Just going to the first one, http://www.alfa.com, you can search their catalogue and get prices. For example, 99.99% pure NaCl will cost you about $40/50g, or $150/250g (and apparently you can get a quote for a bulk order, presumably giving you a discount). Which is quite an expensive way to flavour your food ;) They also have some KMnO4 in stock, but no LN2 or U - you'd probably have to look elsewhere for them (perhaps a more specific Google search, although I'd point out that amassing quantities of radioactive substances can get you into trouble sometimes, as David Hahn would attest). Confusing Manifestation 04:29, 18 May 2007 (UTC)

You should also be aware that there is a hidden cost to chemicals: disposal. When it comes time to get rid of whatever you have, many if not most lab chemicals can not be poured down the drain or buried in your back yard. Be sure to ask your chemical supplier and/or hazardous waste disposal outfit where and how you can rid yourself of the stuff (or anything you make with it). You may have paid for it, but you may have to pay even more to get rid of it. --TeaDrinker 06:24, 18 May 2007 (UTC)

http://unitednuclear.com/ has some pretty cool stuff for sale. 69.244.213.58 17:26, 18 May 2007 (UTC)

Can Elephants Really Paint?

I know they can hold a brush and can be interested in smearing a canvas with paint, but can they see color? Do you guys know of any study where it's shown that elephants can appreciate color and lines? Because if they can, then that would mean that their paintings can be an expression of what they think or whatever is going on in their head. Moonwalkerwiz 02:53, 18 May 2007 (UTC)

Most mammals have dichromatic color vision: they see color but not as well as us trichromatic primates. This includes elephants, as I found out with a simple Google search on "elephant", "color", and "vision". Whether elephants are capable of forming the concept that marks on paper can represent the appearance of something, I don't know. --Anonymous, May 18, 03:07 (UTC).

Thanks. So at least I know now that they see the colors they paint differently than people see them.Moonwalkerwiz 03:53, 18 May 2007 (UTC)

There have been color blind human painters. Anyway, who says appreciation of color and lines is required to "paint".. or even to produce "art", whatever "art" is. It may be that elephants don't understand their paintings very well, but then, I'm skeptical that human painters actually have a halfway decent understanding of their own work. Pfly 03:09, 18 May 2007 (UTC)

I know that. I'm not talking about the author's death here. Anything can be art if we're talking about perspective. But it's different if elephants can actually associate something in colors and lines. Like, if they know they paint orange, that they like orange, or if they paint the orange horizontally, it's better than if they paint it vertically.Because if they could, then their work is not merely accidental, but has some degree of intention in it. That means that if you bought an elephant painting, that the elephant, in some degree, however small, intended the painting to be that way. Moonwalkerwiz 03:53, 18 May 2007 (UTC)

I'm sure elephants make paintings which you'll never forget. 04:50, 18 May 2007 (UTC)

You asked if the elephants work "has some degree of intention in it." I was recently reading an essay by Daniel Dennett about the intentional stance, which is the stance we adopt to predict the behavior of a system by assuming that it has beliefs and goals, and it will take actions to meet its goals based on its beliefs. To your question about whether the elephants really have beliefs about how to create paintings, I think dennet would say that's the wrong question , what matters is whether their behavior forms a pattern which can be described by the intentional stance. I know this answer doesn't explain alot, I just happened to be doing some reading on this issue. -- Diletante 17:06, 21 May 2007 (UTC)

is there any secure website where anyone can submit their new scientific idea for worldwide response having all the rights of the invention ?

ur answer should include external links .

If you can demonstrate the idea and it is fairly novel, peer reviewed journals might be an option. What kind of response in particular are you looking for? In most countries you must apply for a patent (I assume this is what you are getting at) before public disclosure. The U.S. is an exception, in which you may still apply for a patent up to a year after you disclose the idea. -- mattb 04:26, 18 May 2007 (UTC)

Halfbakery, although if you don't have a patent, I doubt anything will protect you -- Phoeba Wright^OBJECTION! 04:35, 18 May 2007 (UTC)

In fact even a patent is essentially worthless unless you have the financial resources to bring lawsuits against companies you think are infringing on your patented intellectual property. --mglg_(talk) 18:20, 18 May 2007 (UTC)

Electrical Current

Hello. In a series circuit with multiple loads, does the current stay the same? Thanks. --Mayfare 03:45, 18 May 2007 (UTC)

See charge conservation. Basically, yes, assuming that there are no other paths for current to flow out of the circuit (that is, the components are truly in series). -- mattb 04:22, 18 May 2007 (UTC)

Are you talking about AC or DC circuit? If you measure the instantaneous current in an AC circuit, you will find that the current goes up and down, positive and negative as times goes on. Hence the term Alternate Current or AC. 202.168.50.40 04:33, 18 May 2007 (UTC)

I am talking about a DC circuit. --Mayfare 21:29, 18 May 2007 (UTC)

Egg yolks

In egg yolk:

The yolk makes up about 33% of the liquid weight of the egg;

Which one has more yolk by weight? A small egg or a large egg? -- Toytoy 03:53, 18 May 2007 (UTC)

Well, unless this is a trick question, 33% of a large egg would weigh more then 33% of a small egg, right? Vespine 04:22, 18 May 2007 (UTC)

Shouldn't that be 33% of the mass of the egg? The use of "liquid weight" rather than "solid weight" suggests that some sort of weight transference takes place upon cooking, which I don't imagine it does.--Shantavira 07:09, 18 May 2007 (UTC)

Is it not just discounting the mass of the shell? And I would assume it was talking about an uncooked egg; the percent could be different in a cooked egg, I suppose. Skittle 10:07, 18 May 2007 (UTC)

Liquid weight vs. the shell weight perhaps? Dismas|^(talk) 10:12, 18 May 2007 (UTC)

The question is a good one. The quote given is an estimate based on an overall average; it says nothing about how the actual percentage varies for different kinds of eggs. So, let's see. I'll assume we are only talking about chicken eggs; otherwise the question is far too complex. Poultry raising is a huge business, with lots of associated research going on, so the data ought to be available. A quick Google search for "percentage yolk" "egg weight" turns up hundreds of hits. This one says that there is generally a negative correlation between egg weight and pertcentage yolk, although some studies have reported exceptions to this.

Summary: bigger eggs tend to have less yolk by weight, at least for chickens, although there are exceptions. --Tugbug 17:58, 18 May 2007 (UTC)

A friend of mine wants to make ice cream. I mean LOTS of ice cream for all of us gangs. We are thinking about how to make use of the unused egg white. I think it's better that we buy smaller eggs or a bottle of soybean lecithin. -- Toytoy 01:02, 20 May 2007 (UTC)

Make Meringues! They are awesome with a blob of icecream and all you need is egg white and caster sugar. There are lots of other recipies that call for meringue - our article links to several of them. SteveBaker 15:17, 20 May 2007 (UTC)

Left shoe squeaking more than right

I have noticed that my left shoe squeaks more than the right. Now that I think of it, the last 3 pairs of shoes I have bought (different brands, medium prize) started squeaking on the left shoe before the right. It seems I am not the only one who have noticed this phenomenon: http://www.cs.utexas.edu/~arao/writings/squeaky.html

I think my feet are pretty much the same size, and I don't think that I often go counterclockwise around in circles.

"Coincidence is God's way of remaining anonymous" -A. Einstein

130.225.96.2 09:20, 18 May 2007 (UTC)

Not sure whether there is a question in there, or a request for a straw poll, but "left shoe squeaks" gets about the same number of G-hits as "right shoe squeaks", and I can't think of any reason why one shoe should sqeak more than another, although since most people lead with their right foot, the forces applied to each shoe might be differently distributed...--Shantavira 10:10, 18 May 2007 (UTC)

If it were random chance, the odds of three pairs of shoes starting to squeak with the same foot is only one in four - it seems likely that it's just chance at this point. SteveBaker 11:02, 18 May 2007 (UTC)

Maybe it's not the shoes that are squeaking ;) 213.48.15.234 11:18, 18 May 2007 (UTC)

If you're an average person, you use your right hand more often then the left, and you'll jump more often starting with your left foot. With what hand to use, we are often forced by society to do it the way everyone does it. For the legs, society is less sensitive and thus more tolerant. 84.160.252.186 20:00, 18 May 2007 (UTC)

Have someone watch while you walk normally (good luck not walking self-consciously while they do) to see if your stride is uneven - I know mine is. If you live somewhere snowy of sufficiently dusty, you could also check stride length and how you apply the force as you step - do you apply your weight more evenly to your right, or twist more on push-off with your left or somesuch. Also, if you regularly carry a heavy bag over one shoulder or some other unevenly distributed weight, that might account for it. Eldereft 08:41, 19 May 2007 (UTC)

I think Ice Skiing might also help. Thats how I found out my tendency to push-off more with my right leg. And in Ice Skiing you need to use both legs equally. I think. I went Ice Skiing only several times >.< Shinhan 15:42, 19 May 2007 (UTC)

One of my hips is crooked enough to make my stance and tracks asymmetrical; nobody noticed until I was about 16 and Mom asked "Why does one foot turn out when you walk?" (though it later occurred to me that an embarrassing incident at age 9~10 could be blamed on it). Perhaps the questioner has some similar subtle asymmetry. —Tamfang 19:16, 19 May 2007 (UTC)

using various nimh batteries togather

hi, I sometimes charge and use 2 AA batteries that have different currents (600mah and 1800 mah ). Will this damage the charger or the device (pocket radio)?. The charger is a wall socket type that could charge a maximum of 4 batteries, 2 on the top side and 2 on the other side (please look at www.onlybatteries.com/webimages/images/10965.jpg). I read that one must charge either 2 or 4 batteries at a time but not 1 or 3 batteries as this will damage the charger. Is this true?. Please pardon my bad english.

131.220.149.185 10:37, 18 May 2007 (UTC) charger

Yes, it could catch fire, and yes, you should always charge batteries in matched pairs. 213.48.15.234 11:14, 18 May 2007 (UTC)

Is our NiMH article of any use ? StuRat 22:50, 18 May 2007 (UTC)

The problem you'll run into is that the smaller-capacity battery will discharge first. With just two batteries, this isn't too much of a problem because the device you're powering will probably shut down when the first cell goes dead and the voltage (roughly) drops in half. But with a larger number of batteries in series, you could find that one cell can become fully discharged and still there might be enough voltage to keep the device operating. But the fully-discharged cell will now try to charge "in reverse", and this will likely cause permanent damage to the cell and might cause leakage.

Because of this, you chould always use cells that are approximately matched in capacity and age (so they all fully discharge in about the same runtime).

Atlant 12:35, 21 May 2007 (UTC)

Mineral Hardness

I am doing a bible study on Rev. 21: 9-27, in this scripture a wall of new Jerusalem is described. The wall consist of twelve stones, as follows:

Jasper Sapphire Chalcedony emerald sardonyx sardius chrysolyte beryl topaz chrysoprasus jacinth amethyst

I am trying to find the hardnes of each stone to show the strength of this wall in Heaven. I have found some of the comparison charts showing the stones in relation to other stones but not the hardness, or how many pounds before stone will collapase or be crushed. Can you give me direction to where to search or a scale that reveals all the stones.

Monty

Um, that's an unusual way of reading the Scriptures. Don't you think you are missing out on the real message of it? —Bromskloss 11:19, 18 May 2007 (UTC)

Hardness is very hard to quantify. The Mohs scale of mineral hardness is a good start. 213.48.15.234 11:20, 18 May 2007 (UTC)

You would also need to know the value of g in Heaven. Presumably it is somewhat less than on Earth.--Shantavira 11:44, 18 May 2007 (UTC)

Haha! :-) —Bromskloss 12:01, 18 May 2007 (UTC)

Why would he need to know g? :/ 213.48.15.234 13:19, 18 May 2007 (UTC)

OP wanted to know "how many pounds before stone will collapase or be crushed". This is (partially) dependent on their weight, which is a function of gravity. Judging by the relatively small size of angels' wings, gravity is much less of an issue in Heaven, and the stones will not be as liable to crushing as they would be on Earth, though of course it would still help if the lower courses were made of the stronger varieties of stones. Don't forget some of the above stones are quite brittle, i.e. hardness is not necessarily a measure of their strength.--Shantavira 13:46, 18 May 2007 (UTC)

Quick question. Is the OP Satan or one of his agents? --Kurt Shaped Box 18:06, 18 May 2007 (UTC)

You could find this in wikipedia anyway. From the first one Jasper, it says it's a variety of quartz, and on the mohs scale it has an Absolute Hardness of 100 found using a sclerometer. I'm sure you could find the relative strengths using the Absolute Hardness scale. Sandman30s 12:18, 18 May 2007 (UTC)

Actually, Monty, the parameter you are looking for is not the hardness but the compressive strength of the materials. --mglg_(talk) 16:19, 18 May 2007 (UTC)

Actually, the translation of the precious and semiprecious stones of the wall is somewhat of a guess. And come to think of it, how many angels can on a wall of semiprecious stones? bibliomaniac15 04:35, 19 May 2007 (UTC)

aircraft engine

what are the similarity between turbo fan and turbo prop engine-—Preceding unsigned comment added by 219.64.90.156 (talk • contribs)

Try Turbofan and Turboprop, or Jet engine. The notes for whatever course this is the homework of might also be of use. --YFB ¿ 14:43, 18 May 2007 (UTC)

They both have a turbine at their core. In the turboprop, the jet engine/turbine is geared or otherwise interfaced with a propeller, so the propeller is spinning because a jet engine is giving it power. A turbofan also has a turbine/jet engine at its core, but instead of driving a propeller, it runs a large fan in the front that provides air for the engine and also blows the extra air past it. It's also typically called a 'high bypass jet engine', what people usually are talking about when they say 'turbofan'. This is the kind of engine that a modern jet liner would have. - CHAIRBOY (☎) 14:45, 18 May 2007 (UTC)

Identifying Identical Twins' DNA...How Can One Tell Which Identical Twin May Have Committed A Crime?

--69.124.86.198 15:49, 18 May 2007 (UTC)Identifying Identical Twins

Identical twins have the same genetic material, as the article explains. Friday (talk) 15:52, 18 May 2007 (UTC)

How about good old fashioned fingerprints? You might get lucky and find a SNP (Single nucleotide polymorphism) that is different between the twins but DNA fingerprinting would be useless with the current genetic markers. David D. (Talk) 15:54, 18 May 2007 (UTC)

They come from the same egg and sperm so there will not be SNPs between them. Now let me qualify that by saying that if spontanious mutation did arise during the development of one of them, it would not be in all their cells, only the cells that are descendant of that cell. You cannot tell them apart by genetic means. How can you tell which one committed a crime? It could be very tricky indeed. Even with other evidence like alibis, a defense lawyer could definately put together a case where you couldn't tell which twin was which. Tattoos, scars etc would be very useful. I'm sure there are some interesting case studies out there... Another interesting point - total bone marrow transplants (eg. for leukaemia) mean that the patient's blood has the same DNA as the donor. But there would likely be other markers in the blood - antirejection drugs maybe? Aaadddaaammm 22:58, 18 May 2007 (UTC)

"Somatic mosaicism" for SNP's is not uncommon but finding one that occured early enough in development would be very difficult (if not impossible). Hence my disclaimer, you might get lucky. The important observation is that it is wrong to assume that identical twins have identical DNA. David D. (Talk) 04:54, 20 May 2007 (UTC)

Some genes undergo somatic hypermutation and other types of modifications that make the DNA sequences in some somatic cells of each individual unique. Also, DNA modifications such as DNA methylation can be different between monozygotic twins. --JWSchmidt 04:17, 19 May 2007 (UTC)

Drilling for Oil

I'm working on a project about oil drilling at ANWR and there's what appears to be an industry specific word I don't understand. In learning about the different studies on the potential for oil at ANWR, the word "play" often appears. It seems to be a reference to a location or possibly some way of categorizing a hierarchy for differing levels of oil field size. I can't find a thorough description of what a "play" is anywhere. Your help is greatly appreciated. Thanks! 161.28.144.36 16:12, 18 May 2007 (UTC)Paul

According to this USGS report, "a play is a volume of rock that contains similar geological parameters (such as petroleum charge, reservoir, and trap) that determine petroleum potential." There's a bunch of stuff that may help clarify if you do a Google search for petroleum play. — Matt Eason ^{(Talk &#149; Contribs)} 16:23, 18 May 2007 (UTC)

Petroleum...duh. I was typing in "oil play" into google and not getting anything worthwhile. Thanks a bundle :) 161.28.144.36 16:31, 18 May 2007 (UTC)Paul

You know what would be cool? Someone should create the article petroleum play. --Kainaw ^(talk) 17:35, 18 May 2007 (UTC)

Is this related to the term "played out", as in "that oil field is played out" ? StuRat 22:46, 18 May 2007 (UTC)

My first thought was that it came from play as in free range of movement ('there is too much play in the steering, I need to get my car's alignment checked), but the OED relates it to play as in manoeuvre or venture (Richard III makes a briefly successful play for the throne through murder and treachery).

forgot to sign. Eldereft 09:16, 19 May 2007 (UTC)

question about multinertia

Hello,i have a question for you guys:

what's a better situation?

driving at 100 M/H against a concrete wall,or driving at 100 M/H against a car,which is driving directly towards your path.

better situation,meaning,which one is least deadly?

thanks for answering

oh and i know that it has to do something with inertia,and the difference of V over the diff of A

see you —Preceding unsigned comment added by 84.192.49.154 (talk • contribs)

One factor is the total speed of the collision. When hitting a wall, the speed is your speed. In a head-on collision, the total speed is the sum of the speed of both vehicles assuming nearly-equal mass and a direct hit. However, that is rarely the case. Going back to the wall, your collision will be rather survivable if you are travelling below 45mph. I don't know of a single vehicle (not including motorcycles) that cannot survive a 45mph impact. As the speed increases, the strength of the cage inside the body and length of the crumple zones plays a major role. The goal is to slow you down over time rather than go from 100mph to 0mph instantly. So, cars are designed to crumple everywhere except where the people sit.

Now, back to the head-on collision. There are many factors involved. Just last weekend, I saw an SUV that hit a little VW Rabbit on the interstate. It wasn't a head-on, but the result was not as most people expect. The back of the rabbit was smashed in and the driver was standing next to it talking on the cell phone. The SUV was on its side, all beat up (obviously rolled). There was a lot of blood coming out of it and two bodies covered in sheets by it. The fire department was cutting as least one other person out of the SUV. The problem is that the SUV is too high and top-heavy. When hitting the little car, it just lifted one tire and flipped. The small car that was low to the ground just crumpled where it was supposed to and skidded to a stop. --Kainaw ^(talk) 17:26, 18 May 2007 (UTC)

Kainaw, I'm not sure I agree that all vehicles are safe in a head-on collision at 45 mph. This propagandized crash test video seems to demonstrate fatal results for a certain brand of vans. Nimur 06:29, 19 May 2007 (UTC)

It really depends on too much that any gross simplification can be made here. You can argue that in a car versus car scenario, there is twice as much engine to crush when the cars meet. However, car-car scenario also has twice the energy involved. Potential structural differences would force more energy to dissipate/spread into the unlucky car, but basically this question can't be answered in the simple way you might be seeking. Not from where I stand, at least. :) (Rabbit? That's GOLF to non-yanks :)) 81.93.102.185 18:11, 18 May 2007 (UTC)

What matters most in terms of survivability is the maximum acceleration your body undergoes. If we treat the wall as an infinitely strong, uncrushable, unbendable thing - then at 100mph, you have to go from 100mph to zero in the distance over which the car can crush. A foot or two. In a head-on crash between two identical cars, both going at 100mph - you can look at it in several ways:

• You could 'pretend' that the other car was stationary and you were going 200mph, and the crush zone was twice as long because both your car and the other one will crumple up equally. So you have to go from 200mph to zero in TWICE the distance it took you when you hit the brick wall. Theory says that the accelleration you'll undergo will be the same either way.

• ...Or you can notice that if there is perfect symmetry between the two cars then when they finally come to a stop, each one will have crumpled up and stopped with their bumpers at the precise point of impact - so from your car's point of view, you might just have well have hit an immovable object. So you still have to go from 100mph to zero in that same distance.
• ...Or you can say that the energy has to be dissipated by bending and snapping metal. In the head-on case, there is twice as much kinetic energy (mass x velocity) to be dissipated - but twice as much metal to bend and break to dissipate it.

This says (counterintuitively) that if both cars are going the same speed - and all else is equal and if the wall is truly an immobile object that doesn't break or anything - then it doesn't make any difference at all whether you hit the wall or the oncoming car.

However, if the other car was parked - or even just going a bit slower than you - then you are much better off hitting the car than the wall because the your car will absorb half of the combined energy - and if the other guy is going slower than you then half of the combined energy is less than all of your energy. Of course if the other car is going faster than you - then the reverse is true.

But in truth it's VASTLY more complex than this. For a kick off, walls do break - so it's going to take out some of the energy of the collision. There are also complicated matters of whether your car is going to wind up running over the other car - or under it - or flipping over. This is all very complicated and hard to predict. The best we can say is that lacking that knowledge, our best guess is that it doesn't matter whether you hit another car head on at identical speeds or hit a wall.

SteveBaker 19:30, 18 May 2007 (UTC)

One factor that hasn't yet been mentioned is the relative masses of the two vehicles. If one vehicles weighs 10 times less than the other, it will decelerate about 10 times as fast, and end up going backwards at maybe 80 miles an hour, while the heavier vehicle will only decelerate from 100 mph to 80 mph. Thus, you might survive in the larger vehicle. Of course, as noted previously, this is just in theory (a perfectly inelastic collision), while, in reality, the bigger vehicle might roll over, etc. StuRat 22:42, 18 May 2007 (UTC)

But the short answer is as Steve says. Assuming the wall is massive enough to be undamaged, it makes no difference whether you collide with that or collide symmetrically with an identical car coming the other way. Of course, neither example is really realistic. --Anonymous, May 18, 2007, 22:54 (UTC).

Do snakes have eye lids?

My daughter was curious, seriously. Thanks! --Tom 17:20, 18 May 2007 (UTC)

See snakes (search for "eyelids" - it is under Evolution). --Kainaw ^(talk) 17:27, 18 May 2007 (UTC)

Interesting. Philosophically-speaking, is an eyelid still an 'eyelid' when it ceases to function as an eyelid? --Kurt Shaped Box 17:34, 18 May 2007 (UTC)

They may have fused eyelids, but they don't blink, and the covering of the eye comes right off when they shed. --Zeizmic 17:35, 18 May 2007 (UTC)

Although snake says "yes", snake scales says "no"... Looks like some folks choose to call the brille eyelids, some don't. Weregerbil 17:37, 18 May 2007 (UTC)

I was just about to thank you folks for the yes answer, but now I am not so sure :) --Tom 17:40, 18 May 2007 (UTC)

Reading the 2nd article, I would say NO, snakes do not have eye lids?? Anyways :) --Tom 17:44, 18 May 2007 (UTC)

I edited the second article. Brille is the term for an eyelid that is fused shut (so it cannot open). There is no need for it to open since it is transparent. --Kainaw ^(talk) 17:47, 18 May 2007 (UTC)

So the answer is yes? Now I am really confused. More than normal :) --Tom 17:50, 18 May 2007 (UTC)

I would NOW answer "yes, they have eye lids that are fused and transparent." Done. --Tom 17:55, 18 May 2007 (UTC)

Non-linear voltage amplifier

I would like to build an electronic device using only analog components that will allow me to replicate the behavior of the curve in this image. Ideally, I would be able to adjust the rise-time (Adj. 1) and the proportions of the three slopes (Adj. 2 & 3). Could you suggest any circuits that would help me design this device?

--Jcmaco 17:32, 18 May 2007 (UTC)

Is this AC or DC? You apparently intend this to be a controller, limiting voltage on another line, or a transformer that changed A or W to turn 1V into 5V. --Kainaw ^(talk) 17:40, 18 May 2007 (UTC)

What do you want the output to be when the input is less than 1 V? —Bromskloss 18:34, 18 May 2007 (UTC)

The output should stay at 5V, if the input exceeds 5V, the output should stay at 10V. --Jcmaco 21:43, 18 May 2007 (UTC)

Any design will surely involve Zener diodes and at least one Operational amplifier, and resistors, of cours. I imagine something like R1 serial ((Zener serial Rz) parallel R2) serial R3 would provide the flatend middle part of the curve. 84.160.252.186 19:45, 18 May 2007 (UTC)

I don't know if this is incredibly stupid or not, but given that you seem to have 4 segments with 3 different slopes you may use some comparator circuit to decide when to switch from a "slope" to another. Since the segments are linear, you can create them with resistors, the switching would be triggered by the comparators using relays, triacs, or something like that. Of course, with any modern digital microcontroller you would be able to accomplish that much easily. 84.90.24.136 19:59, 18 May 2007 (UTC)

Is that curve intended to be three linear segments? If not, I built such an amplifier by adapting the design of a logrithmic amplifier. A classical logrithmic amp uses a matched pair of bipolar transisters (which have a logrithmic current response) in the feedback loop of an op amp. The classical log amp takes positive voltage input only and as the inout goes to zero the output goes to "negative infinity" (i.e., to the negative rail.) You can build a second type of lograthmic amp that takes nagative inputs, simply by reversing the transistors. The output of this type goes to "positive infinity" as the input approaches zero from the negative side. I built my amplifier by using two matched pairs of transistors with each half-pair connected in anti-parallel with the other in the feedback loop. The resulting curve is similar to the one you show. -Arch dude 21:01, 18 May 2007 (UTC)

Do you have schematics of your circuit that I could use? --Jcmaco 21:43, 18 May 2007 (UTC)

Thanks for all the responses, finally, I think that I will use a microcontroller (PICAXE-18X) to do this, although I will have to limit my input to 0-5V and my output to 0-5V. This should be feasible, but I still have to test a few things before. Any other suggestions are welcome. --Jcmaco 21:43, 18 May 2007 (UTC)

Yes, the vast majority of the microcontrollers have a Vdd limit of about 5V, however, that would only limit your input range, because you can create a similar curve with a half of the amplitude and then amplify the signal. You may also search for special applications microcontrollers. I think there are some PIC's (by Microchip Technology) that work with higher Vdd, but, for your purposes, you will need the IC to contain a DAC and a ADC as peripherals and that may not be available. 84.90.24.136 21:54, 18 May 2007 (UTC)

By using the pwmout function and a low pass filter, I'll be able to generate a 10bit analog output from 0 to 5V. It is true that I could use an op-amp to get a 0-10V range, but the device I wish to control can operate in either the 0-5V range or the 5-10V range. A look-up table will provide the correlation between the input voltage and the output voltage.--Jcmaco 22:36, 18 May 2007 (UTC)

It's a class B push-pull output. What you see in the middle of the graph is a crossover dead spot that is non-linear. You can build it with npn/pnp bipolar transistors with their emitters tied together. The dead spot is 2*Vbe and is the minimum gain. You can add resistors between the xtors to increase the dead spot. --Tbeatty 06:24, 19 May 2007 (UTC)

The circuit wouldn't necessarily involve zener diodes; ordinary diodes (silicon or Schottky) will do if they are connected to appropriate Thévenin circuit voltage sources. What you're trying to do is very similar to what is done in the sine wave shaping circuit of a function generator.

Atlant 12:39, 21 May 2007 (UTC)

Amplifying 6 different signals in a breadboard using the least space possible.

What method would you choose to amplify 6 different signals in a breadboard using the least space possible? For "least space" I mean about 15 rows in a breadboard just like this one. I would appreciate your help, thanks. 84.90.24.136 19:50, 18 May 2007 (UTC)

Use an array of Operational amplifier, I know there are chips that pack several on them in one case, with common pin for ground and voltage supply. 84.160.252.186 20:13, 18 May 2007 (UTC)

That's a good solution. If such IC exists, it would be probably packaged in a DIP-10DIP-20. It's not a lot of space. Of course I would need additional space to place the feedback circuitry. I'll search for that. 84.90.24.136 20:25, 18 May 2007 (UTC)

There are plenty of dual op-amps in 8-pin DIP packages, and quad op-amps in 14-pin packages, available, some for less than a dollar. One of each would give you 6 channels and use up 4+7=11 rows for the ICs themselves. There's even a hex op-amp from JNR, but AFAICT they only sell it in surface-mount packages, which won't fit directly into your breadboard. Of the external components, I think only the input resistors will require any more space: a half-row per channel, which would add up to 14 rows. If you are willing to solder, you could solder each input resistor in line with its input wire, saving those extra 3 rows. --mglg_(talk) 20:59, 18 May 2007 (UTC)

Yeah, thanks, I have easy access to TL082's and TL084's, I'll try to fit those in my breadboard. Given that one in each pair of the feedback resistors is connected between the output and the inverting input, I'll only need six different additional nodes, making a total of 17 rows. 84.90.24.136 21:13, 18 May 2007 (UTC)

Six nodes needs only 3 rows, since each row of your breadboard has two unconnected halves. If that weren't so, you'd short out the pins of any IC pairwise... --mglg_(talk) 21:28, 18 May 2007 (UTC)

Yes, of course, my mistake, and given that each side of the IC contains the pins of half of the amplifiers, the shortest and "cleanest" way is to connect three resistors in each side of the breadboard.

manta rays

Hi, I'm a manta ray fanatic, and i've noticed that in most of the pictures of manta rays, they have a wingspan of 6-10 feet. I know that their "wings" can get up to 29.5 feet wide, so is this another species of manta ray? If so, what is it called? Thanks!Gbgg89 22:45, 18 May 2007 (UTC)

It's the same species, Manta Birostris. Straight out of manta ray. Someguy1221 22:50, 18 May 2007 (UTC)

You're a manta ray fanatic? So am I! Have you ever read the Peter Benchley book The Girl of the Sea of Cortez? It features a monstrously huge manta ray. Anchoress 00:04, 19 May 2007 (UTC)

i'll make a note to try that! thanks!Gbgg89 03:11, 19 May 2007 (UTC)

Problem (punching Marines in the head)

This is something I heard some time ago: There are 6 Marines in a line with their head touching. One of them punches a person on the end on the line. Who gets knocked out? All of them?

Newton's cradle, one of the most well-known examples of conservation of momentum

Assuming their skulls are sufficiently elastic, only the last one. Personally though, I wouldn't want to be any of them. Someguy1221 23:30, 18 May 2007 (UTC)

That might be true if by "knocked out" you mean "knocked out of line". However, if you mean rendered unconscious, the first one hit would take the most injury, and absorb some of the force. The second one would take less of an impact, etc., and the 6th would probably not feel much impact at all. Incidentally, this is an interesting way to jar the heads of jarheads. StuRat 02:45, 19 May 2007 (UTC)

The Newton's Cradle example makes certain assumptions about the strength of skulls which I beieve you'll find don't hold. A sufficiently-strong blow will simply fracture the skull of the first marine in line while not transferring much momentum to the next one (and so on). Steel balls are much tougher than human skulls.

Atlant 12:43, 21 May 2007 (UTC)

Pressure on ears while scuba diving?

How do deep-sea scuba divers cope with the immense water pressure on their ears? Do they have some sort of ear-plug? Thanks. Jamesino 21:20, 18 May 2007 (UTC)

You pinch your nose (scuba divers generally have their nose clipped anyway, I think) and blow air into your eustachian tube - that equalises the pressure on the interior of the eardrum. -- Finlay McWalter | Talk 21:45, 18 May 2007 (UTC)

No scuba divers should not have their noses clipped. Instead it is open inside the diving mask and allows equalisation of the pressure within the mask's airspace on descending (one breathes out into the mask to stop it being compressed against the face - the "squeeze"). Also if a mask floods with water, a quick exhalation through the nose will displace out the water. David Ruben ^Talk 01:17, 19 May 2007 (UTC)

and consequently if you have a head cold, which blocks the eustachian tube, you can't dive. -- Finlay McWalter | Talk 21:48, 18 May 2007 (UTC)

This is called the Valsalva maneuver. -- Finlay McWalter | Talk 22:15, 18 May 2007 (UTC)

Deep-sea scuba divers do not have immense unmatched water pressure on their ears, instead the slow pressurisation allows time to equalise the presure through the eustachian tubes; so as to maintain equal pressures on the inside and outside surfaces of the ear drums. Whilst the pressure compared to land-based normal atmospheric dwellers is high, the deep-sea diver has no pressure differential across their ears. See Saturation diving. David Ruben ^Talk 01:13, 19 May 2007 (UTC)

May 19

Where can I buy a spaceship

Where can I buy a spaceship

The first Google result for "buy a spaceship" says that the Spaceship Company will sell spaceships. A.Z. 01:40, 19 May 2007 (UTC)

Oh come on. Ebay. Duh! -- Phoeba Wright^OBJECTION! 02:21, 19 May 2007 (UTC)

You might also be able to buy used spaceships (test ones or re-entry modules), say from Russia, who might appreciate the extra cash more than the memorabilia. StuRat 02:32, 19 May 2007 (UTC)

Russia may also sell a functional Soyuz stack. The full-up cost would probably range between $25-50 million USD, based on most some educated guesses by folks like James Oberg. - CHAIRBOY (☎) 02:37, 19 May 2007 (UTC)

Hmmmm. I wonder if you'd run into legal problems if you attempted to set it up and launch it unannounced from your own property (say, if you owned a large area of land in a remote-ish area of the US)? --Kurt Shaped Box 04:52, 19 May 2007 (UTC)

In the US, it would probably be classified as a flight vehicle, so you'd need to get FAA approval. They made a movie about this lately, didn't they? Astronaut Farmer or something -- Phoeba Wright^OBJECTION! 06:08, 19 May 2007 (UTC)

You will probably have some problems with weapon regulations as you basically set up a launch platform for an ICBM.

... If only your father was Anakin Skywalker ... -- Toytoy 02:55, 19 May 2007 (UTC)

You could probably make your own, it would be cheaper...

MASA. anonymous6494 02:23, 22 May 2007 (UTC)

Evolution vs Cars

Will roadkill eventually be a thing of the past because animals who are not afraid of cars get hit? I am guessing yes, but I am surprised google doesn't turn anything up. -Ravedave 03:38, 19 May 2007 (UTC)

I did once read somewhere (I think it was in New Scientist magazine several years ago) that natural selection is starting to favour the hedgehogs that run instead of rolling into a ball when faced with a predator (i.e. car). --Kurt Shaped Box 04:58, 19 May 2007 (UTC)

Eventually, yes, but it may take thousands of years, and cars may not be used for that long. StuRat 05:20, 19 May 2007 (UTC)

I've noticed that gulls (or at least my local urban gulls) seem to have a strong concept of 'car'. If they're feeding in the road, they are constantly looking back and forth for oncoming traffic as they stand there. Come to think of it, the only roadkilled gulls I've ever seen have been young ones. The street pigeons, on the other hand don't seem to pay as much attention and do get hit quite frequently. --Kurt Shaped Box 05:30, 19 May 2007 (UTC)

Yes, I've noticed I need to swerve much more severely to hit a gull than a pigeon or person. :-) StuRat 06:03, 19 May 2007 (UTC)

The gull's reactions will probably be faster than yours (try it sometime and watch some real aerial skill). It's not unknown round here for chav jackasses to see birds on the road and deliberately speed up or swerve to hit them. --Kurt Shaped Box 06:28, 19 May 2007 (UTC)

"Chav" ? StuRat 22:50, 19 May 2007 (UTC)

http://en.wiktionary.org/wiki/chav. —Steve Summit (talk) 23:33, 19 May 2007 (UTC)

I take umbrage to that definition. Referring to chavs as 'working class' is pretty insulting to decent, working class people who don't feel the need to be antisocial petty criminals who overindulge in booze and smack. It's a state of mind - not a class/money thing. --Kurt Shaped Box 07:17, 20 May 2007 (UTC)

wiktionary:umbrage —Bromskloss 16:44, 21 May 2007 (UTC)

There is a precedent of an evolutional change of the type discussed here, long before Homo sapiens or Toyota Avensis. Indeed, some spiders, most notably Argiope, have evolved to add a stabilimentum to their web. The stabilimentum is thought to be a "don't run into me please" sign for rabbits and low-flying birds. A spider hit by a bird or a rabbit/hare is essentially roadkill, so an added conspicuousness is definitely beneficial rather than detrimental. (Note that Argiope sp. tend to be quite large, and webs over two feet across are not uncommon. So they are rather conspicuous anyway, at least wor a slow-walking human; but probably not conspicuous enough for a fast running hare). It is therefore not unthinkable that, instead of developing "car phobia", cats / skunks / hedgehogs will develop conspicuous "please don't squash me" markings; perhaps like these. Cheers, Dr_Dima

If natural selection works, then the result you posit should in time eventuate. I have read somewhere that rattlesnakes in the U.S. are far less noisy than they were when the country was thinly populated, because the noisiest snakes were most likely to get shot. Edison 16:41, 19 May 2007 (UTC)

I've heard that too. It used to be that a loud rattle kept them from being stepped on, while now it just gets them shot. StuRat 22:53, 19 May 2007 (UTC)

See also this thread from two days ago. —Steve Summit (talk) 23:37, 19 May 2007 (UTC)

I would think so, I would be surprised if urban pigeons have not learned to avoid cars. Some will always still be hit though. The amount of time it would take is more questionable. If every autophillic pigeon was hit and all autophobic pigeon survived, then the evolution could occur in months but I expect the time it would take to have a significant effect is more like 100 years. Ozone 02:54, 21 May 2007 (UTC)

A/C efficency

Currently the weather is hot during the day and cool at night. However I have a problem getting the cool air into my house. My house's ventilation system has a heat exchanger on it, so running the furnace fan doesn't do much good. It is a town house surrounded by townhouses, opening windows doesn't do much. So I run the A/C and worry about my elec bills. My question is, if it is 60F outside and 75F in my house will the A/C be almost as efficient as just running the fan? Coefficient of performance is the closest thing I could find. Another Q that is more of a gripe, and probably not answerable: Why the heck aren't new houses better designed to take advantage of outside weather conditions? -Ravedave 03:55, 19 May 2007 (UTC)

Sorry to ask another question rather than give an answer, but how does having a heat exchanger keep the furnace fan from doing what you would want? (I looked at the article you linked to, but I still can't figure it out.) --Allen 04:24, 19 May 2007 (UTC)

Hrm I used the wrong name for it, thats why. Energy recovery ventilation, better shown here http://www.fantech.net/hrv_erv.htm. Air from the outside goes past air from the inside going out. The heat is exchanged resulting in fresh air in the house, but little temperature change. -Ravedave 14:07, 19 May 2007 (UTC)

What you need are some window fans. Put fans on one side blowing in and on the other side blowing out. Make sure all doors between are open. Also, make sure all windows without fans are closed (counter-intuitively, this improves air flow). This will give you a nice flow. If you time the fans properly, you can save lots of money over A/C. Also, be sure to close the windows when it might rain. StuRat 05:17, 19 May 2007 (UTC)

That's exactly what I do. But when he said he's in "a town house surrounded by townhouses", I took that to mean he's in the middle of a hot little microclimate, surrounded by glass and metal and concrete, and the hot side of all his neighbors' heat exchangers, such that there's rarely any cool air just outside to let or blow in. --Steve Summit (talk) 13:55, 21 May 2007 (UTC)

So no idea on how efficient A/C is when there is a large temperature differential? -Ravedave 14:07, 19 May 2007 (UTC)

No easy way to quantify this. A test you could do yourself is spray the garden hose on the unit to keep it the temperature of the water as opposed to the hot air outside, (make sure you dont run more water on/in the unit than would normally occur in a heavy downpour). I doubt there would be an appreciable difference in temperature and efficiency is impossible to determine without a more isolated system(not a house). I think greater cooling would be sought by increasing duct flow by using more fans than just the central fan.

Thermogenerator efficiencie

theoricaly if a Thermogenerator wich as a 10% efficienci rating was in a box of aerogel with x quantity of heat , would the thermoganerator eventualy turn (almost) all the heat to electity or would something else happen?

In any thermodynamic system, one must first consider if the system is closed. In a standard system the container or 'box' can exchange enthalpy with the external environment, but not mass. Next, the enthalpy exchange is dependent on the material of the system. In this case the aerogel seems to indicate the insulative properties are ideal and the thermal conductivity is low. This would mean the enthalpy that is in the system stays there. The last question is to consider how the generator would be set up in the system. We need a temperature differential between a bimetalic or p-n doped silicon molecule. Thus, the generator would have to be set up inside and outside of the box. If this is some ideal aerogel system, the easy answer is that yes, most of the enthalpy would be converted to an electric potential difference(electricity). This would continue to happen until there was no temperature differential which is when the system reaches equilibrium. However, in a non-ideal system that any engineer would deal with, they would soon realize the box would be at equilibrium with the outside air and X heat would have to be added continuously to keep generating electricity with a Thermogenerator. Theoretically, if one uses an ideal generator that perhaps is a p-n type silicon junction which has no heat loss across it, I would expect efficiency to approach 100%. The article quotes typically 10% efficiency which is basically due to the conversion of a suitable fuel into enthalpy that will have a lot of loss before it is "put in the box". Compare this to a typical heat engine that has no more than 35% efficiency.

69.241.236.12 06:41, 19 May 2007 (UTC)Adam

what's are the processes that an electron emit and gain energy in form of photon ?

when electron collide with a photon, the electron gain energy leaving the photon weaker . when neutron, proton and other particles collide with electron what happen then ? electron emit photon when it is accelerated . so in an particle accelaratir when electrin is accelerated it radiates energy in form of photon as a result it's energy should be decreased . but the reverse happens how ?

Not sure if I quite understand all the questions. For the last question: I think when you are referring to the energy decrease from an accelerated particle emitting photons, you are correct in that it does decrease in energy. However, it is still accelerated at high velocities with large voltages and the overall change in energy is increased from the initial ground state of that quantum particle, proton or electron.69.241.236.12 07:09, 19 May 2007 (UTC)Adam

temperature question !

consider a fully thermal insulated box which contain a mixture of oxygen and fuel(gasoline). if the mixture is ignited then the resulting chemical reaction release energy(photon)that's why temperature inside the box increases and pressure inside the box increases . after a certain period of time temperature peaks at maximum and is stable . does pressure changes same way ?

If I understand your question properly, in a word the answer is 'yes'. Temperature is basically a measure of the motion of the particles in the system, in your case in the box. Following the release of energy from the chemical reaction the particles move faster, so the temperature rises. The faster moving particles bang into each other and the walls of the box harder and more often - this is the increase in pressure. So when temperature peaks and becomes stable, so will pressure (assuming everything else remains constant). Of course this ideal situation where the box is fully insulated and allows the temp to stabilise does not exist in reality. --jjron 17:28, 19 May 2007 (UTC)

Be sure to see this excellent illustration of the particles pinging the walls as Jjron described. The cumulative tiny pushes of those trillions of impacts is what creates pressure. --TotoBaggins 02:29, 22 May 2007 (UTC)

Submarine pens and air pressure.

A few TV shows and films I've seen feature completely-submerged buildings with a submarine pen -- a floor open to the ocean where submarines can rise and dive. (Image: http://img241.imageshack.us/img241/8343/vlcsnap2225370nx4.jpg) What sorceror's magic do these mermaid-architects use to avoid flooding the building? Would the room need to be pressurised, only enterable via an airlock? Froglars the frog 07:43, 19 May 2007 (UTC)

TV magic. In theory, you probably could pressurize it, but far easier would be to use a waterlock, or just have the actual building be above ground, so the water will, naturally, not try to come up... although that would give you problems with low-tide, unless you raised the building itself. -- Phoeba Wright^OBJECTION! 07:52, 19 May 2007 (UTC)

I thought that those actually existed? Pressurized rooms inside a larger structure - e.g. deep sea exploration vessels? --Kurt Shaped Box 09:13, 19 May 2007 (UTC)

I don't think it makes sense. The building was slowly flooded, without waterlocking mechanisms built in. This was evidenced as we saw someone swim from the surface of the ocean to the inside without meeting any waterlock/porous membrane/whatever. The entire building is around 50-100 feet underwater.

Instead of pressurizing the room, a way to do it would be to pressurize the entire building. This also allows the building to be relatively lightly built, as the air pressure holds back the sea, instead of requiring a pressure hull like a submarine or bathysphere. Of course you then have the issue that people in the building will have to breathe the pressurized air (or a suitable breathing gas), just as scuba divers do, which limits the depth where this technique can be used. It would also mean that when a submarine was going to visit the place, its interior air pressure would have to be turned up to match the pressure in the building, and decreased again (slowly enough to avoid decompression sickness) after leaving the building. --Anonymous, May 19, 09:00 (UTC).

An equivalent analogy would be underwater caves with air pockets below sea-level. Such things occur naturally, but I'm not sure how stable they are in the long term, as air can slowly escape upwards and/or dissolve into the water (I think??). However, they do exist at least at shallow depths (and I think in some James Bond-type movies). --Cody.Pope 10:06, 19 May 2007 (UTC)

PS when I read the title I thought it was about the other kind of submarine pens. --Cody.Pope 10:18, 19 May 2007 (UTC)

See SEALAB. This link[1] has a diagram at the bottom. The SEALABs were pressurized to the ambient sea pressure, and divers entered and exited via a simple door in the bottom. -Arch dude 18:10, 19 May 2007 (UTC)

Oh man Arch dude, genius diagram, especially the shark cage around the port, that would have prevented Samuel Jackson from being eaten in Deep Blue Sea.

See Caisson (engineering).

Atlant 12:48, 21 May 2007 (UTC)

Eucalpytus balls

What are the spiked balls that fall off of eucalyptus trees called? Wiwaxia 08:30, 19 May 2007 (UTC)

From our eucalyptus article:

The woody fruits or capsules, known as gumnuts, are roughly cone-shaped and have valves at the end which open to release the seeds. Most species do not flower until adult foliage starts to appear; Eucalyptus cinerea and Eucalyptus perriniana are notable exceptions.

So I guess that means, gumnuts is the answer? --Cody.Pope 10:31, 19 May 2007 (UTC)

Thanks! I searched for "ball" and "spike" in the eucalyptus article and couldn't find the words. Wiwaxia 23:05, 19 May 2007 (UTC)

automobiles

Why do tractors have their rear wheels larger than their front ones?125.63.107.129 13:01, 19 May 2007 (UTC)

For more torque I believe. I apologize for the off the cuff answer. --Cody.Pope 13:18, 19 May 2007 (UTC)

Nope. all other things being equal, the bigger wheels would provide a less powerful pull, not more. But other things are not equal: The tractor's gear ratios are much lower than on a car to compensate for the large wheels. The wheels are large to provide a large surface area of contact with the ground so that they will not simply dig themselves into a muddy field. When a farm worker misjudges the situation, then whatever the tractor is hauling will begin to sink into the mud, increasing the required traction. The driver will try to compensate by adding power, and the tractor wheels will begin to dig in. If the driver persists, the tractor can sink all the way to the axle, and you generally then need to haul it out with a bulldozer. Instead, the driver should stop immediately. You can then detach the tractor from the equipment it's hauling and reposition the tractor to haul the equipment out backwards. The front wheels are small because they are not motorized and therefore do not dig themselves in. They also do not carry much weight relative to the rear wheels: it's relatively easy to do a "wheelie" with a tractor, and farmers regularly used to kill themselves by flipping the tractor over as the front came up past the vertical. Tractors now generally have roll bars.-Arch dude 17:56, 19 May 2007 (UTC)

Many tractors are also weighted so they are more stable (by placing mechanized parts low to the ground or adding ballast. This lowered center of gravity might make a wheelie impossible on some tractors. Nimur 00:34, 21 May 2007 (UTC)

A larger wheel will reduce torque at the ground, not increase it. A larger wheel will however give better traction and improve your ability to travel over uneven ground. Friday (talk) 17:38, 19 May 2007 (UTC)

which torque? since shaft is connected to engine through gear box it gets constant torque and rpm.MAY BE it is something related to mechanical advantage.125.63.107.131 12:12, 21 May 2007 (UTC)

And tractor "wheelies" are famously parodied in Cars.

Atlant 21:35, 21 May 2007 (UTC)

i.c.engines

I.C.ENGINES will be more efficient in winter or in summers & why?125.63.107.129 13:05, 19 May 2007 (UTC)

See Heat engine for guidance on this

In the winter, the air is colder and hence denser - so your engine gets more oxygen than it normally would - this allows it to burn more fuel and get more horsepower. But more horsepower doesn't mean better fuel economy. The engine runs inefficiently until it gets up to it's ideal operating temperature - which takes longer in the winter. So in all likelyhood, you'll get worse fuel consumption but more peak power. SteveBaker 18:08, 19 May 2007 (UTC)

We also have to consider that in the winter molecules are moving more slowly and the metal is smaller and more tightly compacted in the metallic crystal. Therefore not only would the viscosity of the oil increase adding to friction, but less clearance between machined metal parts may also add to friction. This should decrease power and fuel consumption which wouldn't make it more or less efficient, I think (right?).

That's all true for the first minute when you turn the engine on - but it's all pretty hot within a minute or so. Starting your engine in cold weather uses more gas and wears out engine and oil faster - but unless you are doing a lot of really short trips with long waits for the engine to cool down between them, this isn't a huge factor. SteveBaker 02:32, 20 May 2007 (UTC)

I once had a car that ran on 10-11 liters of gasoline per 100km in winter but needed only 6-7 in summer. What puzzeld me was that this even held for long traveling times when the motors temperature souldn't depend much on the outside temperature. 84.160.200.170 22:19, 19 May 2007 (UTC)

Cold weather makes the lubrication less effective in every part of the vehicle (even non-motorized wheels / axles). This may play a large factor in fuel efficiency. Nimur 00:36, 21 May 2007 (UTC)

so plz tell me gentlemen what is the final conclusion?125.63.107.131 12:05, 21 May 2007 (UTC)

effexor xr

i am trying to find out some info on the pescription drug effexor i have recently been given this drug and i have to submit to randon urine drug screening for methamphetamine will effexor make my ua,s test positive for amphetamine or methamphetamines

effexor™ also known by the common chemical name Venlafaxine is an antidepressent in a class known as SNRI. The difference between this drug and other antidepressents is that effexor acts on norepinephrine (nor-adrenalin) neurotransmitters as well as serotonin. This norephinephrine reuptake blocking may be similar to a low dose of cocaine. To answer your question, effexor, to my knowledge, will not turn into an amphetamine metabolite. I tried to research amphetamine metabolites and effexor metabolites but I couldn't find anything. However, just by analyzing the two structures of amphetamine and Venlafaxine, one can clearly see that amphetamine will be deaminated by the liver into a ethyl benzene while it looks like the liver may have problems deaminating the tertiary amine of Venlaxfaxine. Furthermore, even if it was deaminated there is still dimethyl ether group in a para position making it distinctly different. Therefore effexor will not produce amphetamine metabolites and will not make a common NIDA-5 show positive for amphetamine. —69.241.236.12 13:57, 19 May 2007 (UTC)Adam

planes in air

Can you tell me how many planes are in the air around the world at any one time or how many flights there are each day on earth please?

okay first we define plane. Fixed wing commercial jet aircraft? Then remember that in any commercial airport, many planes are flying in circles waiting for clearance to land and others waiting to take off. This means commercial airport throughput is the limiting factor here. This would be fairly simple to calculate if one did exhaustive research on every commercial airport's flight capacity. This is the only way to figure out the world's commercial air traffic, in my opinion, because some countries dont have centralized FAA like the United States. However, if your question includes non-commercial flights, I think your question is impossible to calculate unless you have access to huge RADAR arrays or imaging satellites.

69.241.236.12 14:18, 19 May 2007 (UTC)Adam

Or you can go here for U.S. flights. [2] At this instant, there are about 4,400 planes with flight plans in the air (doesn't include non-flight plan flights such as VFR flights). 45,000 arrivals in the last 24 hours. --Tbeatty 19:48, 19 May 2007 (UTC)

Here is a video showing air traffic on a map. Click "more info" to go to the site that created this. 71.237.51.41 (talk) 20:16, 14 October 2008 (UTC)

Purely Hypothetical

Lipids in the body are made up of fatty acids and glycerol. Acids and bases neutralize to form salt and water. This being said, what would happen to someone who consumed many bases? Would the bases somehow react with the acids and allow this person to trim fat? In essence, the question is: Is consuming large amounts of basic foods e.g. drinking tea beneficial to those who wish to lose weight? Conversely, does consuming large amounts of acid foods e.g. Coca Cola contribute to lipid stores in the body?

Thanks a lot 208.96.96.207 14:19, 19 May 2007 (UTC)

First of all remember the pH in the stomach is about 1 because of all the HCL, meanwhile the intestine is buffered by the pancreas. Second, the pH of the blood is kept constant by our various buffering systems to between 7.35 and 7.45. Dietary acids and bases are not going to effect the acid base chemistry of a human unless it is in a toxic dose. If the dose was toxic, yes, but not beneficial; acid base reactions would occur locally in the tissues of the alimentary canal and will cause tissue damage. However, lipid tissues that we call fat, is subcutaneous fat that resides between the muscle and skin. Therefore, there would be no way to react acid or bases with this tissue unless you had gross metabolic pathologies resulting from excess dietary intake. Basically, acid-base is biochemically regulated and in a healthy system will not be the deciding factor in any tissue formation or loss. Coca-Cola® with over 40 grams of high fructose corn syrup in a 12oz can will contribute to lipids stored in the body, but not with acid base chemistry that you describe. The insulin will spike and when the muscles and liver are full of glycogen (glucose and water) the extra simple sugars from fructose will be stored as lipids. Furthermore, remember that our body has many nucleic acids as well, so just by looking for the word acid in a bio-molecule isnt a really good indicator of what happens in situ. However, there are diets that do describe the corresponding weight gain and loss with respective acid and base foods, but for me the mechanism and evidence is not well understood.--InitialMan(adam) 02:14, 20 May 2007 (UTC)

How does Diabetes cause damage to blood vessels

Diabetes mellitus often results in longterm damage to blood vessels. How and why does this happen? AxelBoldt 16:18, 19 May 2007 (UTC)

Long term damage of small and large blood vessels known as micro and macroangiopathy, is a chronic complication of hyperglycemia. Histiochemically the lesions in the vessels are characterized by increased accumulation of glycoprotein. In addition, because the chemical components of the basement membrane in the blood vessel lumen can be derived from glucose, it causes an increased rate of formation and thickening of basement membrane. These cells do not require insulin for glucose use.--InitialMan(adam) 02:14, 20 May 2007 (UTC)

Area Moment of Inertia with Multiple Materials

I have a beam made of a layer of silicon and a layer of gold on top. I want to find the area moment of inertia (I) of the beam. I know that I have to use the ratio of the Young's Moduli to scale the widths to find the neutral axis, but must I also scale the widths when calculating the moment of inertia? --Joe 16:44, 19 May 2007 (UTC)

If you've calculated the moment of inertia of each material about it's own neutral axis, you can then combine that info using the parallel axis theorem to calculate the moment of inertia of each material about the resultant neutral axis (which you've already found), and then just total the two translated moments of inertia. Also, you can test that you have calculated the neutral axis correctly, by seeing if the beam will balance about that axis. If you have access to a lathe, place the beam on the lathe such that the neutral axis is the axis of rotation. If you are correct, it should spin nicely. If not, it should vibrate the lathe as it spins, from the imbalance. Start the lathe slowly, in case you were way off in your calcs, and always wear goggles and use the lathe guard. StuRat 17:17, 19 May 2007 (UTC)

But when I am calculating the individual section's inertia, should I still scale the base according to the Young's Moduli ratio? The total inertia is different if I scale the first material to the second or vice-versa. I can't really put it on a lathe as the total thickness of the beam is only 2 micrometers.--Joe 17:49, 19 May 2007 (UTC)

Isotretinoin / Roaccutane

About four years ago I went on two courses of "low dosage" roaccutane (isotretinoin) - and 4 years later my life has been extremely affected by it in a very detrimental way...

• I have very dry eyes,
• a very dry nose (where occasionally I have to remove the dry skin inside, sorry),
• a reoccuring mild nasal infection,
• my facial skin is dry and irritated (whereas at once stage after Roaccutane it was good),
• as well as a generally dry mouth

all at the age of 20.
I am going to be scheduling appointments with an ENT (for my nose and mouth),
a dermatologist for my skin,
and I've seen several opthalmologists about my eyes.
I am seeking one of two outcomes: Either I must cure my symptoms or I must seek retribution.
I am even keen to try find a forensic dermatologist and possibly taking legal action against the manufacturer and/or my dermatologist.
Questions:

1. Who is the best doctor(s) to see about reversing the long-term affects of Isotretinoin/Roaccutane?
   
2. How should I go about proving isotretinoin as the cause of my problems?
   

Any advice on reversing the damage done by isotretinoin is greatly appreciated (I have scoured the Roaccutane survivor forums many times)
Thank you in advance...

We can't offer legal or medical advice, but I can offer some dietary advice. A low fat diet will lead to dry skin, and a high fat diet tends to lead to oily skin. Of course, you also need to keep in mind that some fats are unhealthy in other ways. Particularly avoid trans-fats, saturated fats, and animals fats. Vegetable fats, as in avocados and most salad dressings (but not mayo) are healthy for you, as are nuts and cold water fish, like salmon, which are high in omega-3 fatty acids. Learn to read labels to figure out which foods are high in good fats and low in bad fats. Also, avoid drying shampoos, soaps, and detergents, and instead use moisturizing products, like Dove (soap). You may need to regularly use a nasal spray to keep the inside of your nose moist. StuRat 22:31, 19 May 2007 (UTC)

Why no animal fats, other than for avoiding saturated fats (which seem to be less causative for cardiovascular disease than non-conjugated trans-fats)? A fish is not an animal? See also essential fatty acid interactions for information about omega-3 and omega-6 fatty acids. Unfortunately, I cannot offer any advice on the original question. Icek 22:20, 21 May 2007 (UTC)

Fish certainly are animals from a scientific POV, but dietitians tend to differentiate between "animals" and "fish". Cold water fish tend to have fats that are better for you than other animals. StuRat 07:49, 22 May 2007 (UTC)

purely hypothetical

What is the chemical structure of dithetamine, and is it toxic? Also, is it illegal to possess the substance in Maryland?

I searched PubMed and found nothing. Google only points to fictitious references to it, not the actual chemical. 69.140.164.142

is it even a real compound? Coolotter88 22:58, 19 May 2007 (UTC)

never heard of it InitialMan(adam) 01:57, 20 May 2007 (UTC)

Dithetamine is a fictional creation of Connie Willis in her novel Passage about chemically induced near-death experiences. I suspect it is intended as a reference to N,N-dimethyltryptamine (DMT), as research has been done on the role of DMT in near-death experiences, and the names are similar. DMT is not immediately lethal in low doses in most people, but the long-term effects of use are unknown. It is a Schedule 1 substance and would be illegal to possess in Maryland, unless you are a member of a religious organization that has Supreme Court permission to use DMT. However, 5-methoxy-DMT (5-MeO-DMT), a very similar substance that is found in toad venom, is not a federally controlled substance (I don't know about Maryland, and there are other laws, such as the analog act, that might apply.) See the Wikipedia pages on DMT and 5-MeO-DMT for more information on this fascinating molecule. 98.210.158.239 (talk) 01:40, 28 October 2009 (UTC)

green eyes

Hi there, I want to know that which haircolour heads mostly have green eyes: Red heads or Black heads? The reason I asked this question is that most of the time, blondes have blue eyes while brunettes have brown eyes and what blackheads? which eyecolour do they mostly have?

Wouldn't black-haireds most commonly have black eyes? I should imagine that Red-haireds most-commonly have green eyes. But this is all a guess. 138.130.23.133

A majority of humanity (at a guess) has black or brown hair and brown eyes. Most of the redheads I've known (including grandma and my ex-wife) had/have blue eyes. Most of the green-eyed people I've known had brown hair. I don't know where you'd look for solid statistics; there may be none because hair color varies continuously and thus there may be no consistent classification. —Tamfang 18:53, 19 May 2007 (UTC)

Comparing Template:Light hair coloration map and Template:Light eye coloration map, we can see that people with blue eyes have the lightest hair, and then people with green eyes have slightly darker (but still very light) hair. I would say brown would be most likely (red is a rare hair color). --Spoon! 22:11, 19 May 2007 (UTC)

How do you distinguish green eyes from blue eyes on that map? —Tamfang 19:39, 21 May 2007 (UTC)

ASTROPHYSICS

if an object is kept between 2 black holes having the same gravitational pull and everything thing is same ,where will the object go?

I don't study cosmology, but do we need to know if the object is past the event horizon. If I understand this correctly, two blackholes with over-lapping event horizons would be one black hole. Therefore, if an object is placed between two black holes (which would have to be outside the event horizon), then wouldn't it just have a gravitational pull such that it was between two stars of equal mass. Thus it would be stationary. Anyone else have anything to add?69.241.236.12 19:21, 19 May 2007 (UTC)Adam

woodn't it be torn in half?

If the two black holes were close enough and it was at the proper point, then it would, yes. Otherwise, the object would stay where it is, assuming no other force is acting upon it. This type of Lagrange point exists between every pair of objects, such as the Earth and Moon and Earth and Sun (there are also some other stranger types of Lagrange points). However, note that the two black holes would pull on each other, as well, and they would eventually merge, unless they were in orbit about each other as a dual black hole system. StuRat 19:44, 19 May 2007 (UTC)

Now I know what sucks more than getting sucked (no pun intended) into a black hole, getting sucked into two black holes at the same time...Someguy1221 22:15, 19 May 2007 (UTC)

Does a black hole get sent into orbit without merging because of Kinetic energy. Are two a black holes in orbit exhibiting rotational energy as well as translational energy(centripetal) which balance to create the orbit?

Any two objects can orbit one another, due to rotational kinetic energy. However, if there were material being sucked into the two black holes from outside the system, this would tend to drive them together. StuRat 06:08, 20 May 2007 (UTC)

Sometimes black holes collide. Here's a story about such an event. Here's a computer simulation of it occurring, with nifty video. I don't think it's true that two black holes with intersecting event horizons are automatically one black hole. Big black holes have event horizons on the order of the size of our solar system, so it would take at least some number of light-hours for the singularities to merge. --TotoBaggins 22:33, 19 May 2007 (UTC)

It's not really important that these are black holes - being at the mid-point of two equal mass stars or planets or anything else produces the same effect - the gravity fields are equal and opposite and cancel out. This happens somewhere between the Earth and the Moon - but this isn't a stable position - if your object moves even a little bit away from that precise mid-point, it'll be attracted fractionally more by the nearest black hole (or whatever) and fractionally less by the other - so it'll start to move towards that one - increasing the effect. Between two planets or even stars at a reasonable separation, the gravity field changes very gently and it might take a long time for the object to drift away from this 'zero g' midpoint - but with two black holes (especially if they are very close), moving even a tiny amount away from that midpoint would cause this instability to become evident. Keeping the object at the precise position where the fields cancel would be like balancing a coin on it's edge. It's an inherently unstable situation and even the slightest vibration would cause rapid motion away from the centerpoint. If the object is relatively large - compared to the rate of change of the gravitational field - then it might well be torn in half because each side of the object is closer to one or other of the black holes - so each side will be pulled in opposite directions - and if the black holes are big and close then getting ripped in two is possible I suppose. In reality, your two black holes would accellerate rapidly towards each other and 'kersplatt!' in the middle - right where your object is sitting. In order for this careful balance to exist, the black holes would have to be orbiting each other. When things with nice large gravity fields orbit each other (like the Earth and the Moon) - there are places called Lagrange Points that offer zero gravity and stability. An object in one of those places would stay firmly put - if it drifted a bit out of place, it would be pulled back into that perfect spot. Read Lagrange points for more information. SteveBaker 02:10, 20 May 2007 (UTC)

It's not my interpretation that all Lagrange points are stable. I believe the diagram at that article shows that points L1, L2, and L3 are stable in one direction, but not another, while L4 and L5 are stable in all directions. See Lagrange_Points#Stability. StuRat 08:00, 22 May 2007 (UTC)

Hygrometer animals?

In the 1950s and '60s weather barometer animal figurines were popular. They usually changed color when the weather was going to change from sunshine to rain or snow. After a period of time they stop working (changing color). I am curious as to what chemicals they were coated/painted with that made them work and if it would be possible to recoat one and have it work again. At the very least, anyone know where i can find out more information about them? I've had a quick search and come up blank. 80.229.228.229 20:11, 19 May 2007 (UTC)

Yeah - I know exactly what you mean. When I was a kid in the late 1950's and early 1960's we had animals made of a soft soap-like or perhaps waxy stuff that changed colour like that. I think the pigment was absorbing water from the air and changing colour as a result. When rain is due, humidity goes up - so the animal absorbed water - when the weather is turning sunnier, the humidity drops and the animal dries out - causing the colour to change back again. My recollection was that they went from red to blue. Desiccant#Coloured saturation indicators suggests this may have been Cobalt(II) chloride (See also Cobalt chloride paper). SteveBaker 02:22, 20 May 2007 (UTC)

Oh - and by the way - Cobalt Chloride is toxic. Back in the 1950's it was enough to print "WARNING - TOXIC" on the packaging and then to sell it to little kids...these days...I don't think so! If you are planning to rejuvinate these toy animals - please don't let your kids near them! SteveBaker 02:25, 20 May 2007 (UTC)

So these were hygrometers, not barometers. I've changed the header to match this.

Atlant 12:54, 21 May 2007 (UTC)

That's my belief - yes - but I don't have proof. It's hard to imagine a simple chemical change that would come about as a result of air pressure and which would have been commercially exploited in the 1950's - but since humidity is also some kind of a weather predictor - it might well be that. People claim to be able to predict the weather with pine-cones (for example) - and those open and close due to humidity - not air pressure. (Hmmm - neither pine cone nor weather lore mentions this yet it's a really common thing in the UK to see people keeping an old pine cone to predict the weather?!). Cobalt Chloride is also a guess - but it fits with my memory of the colour change from blue to pinkish red - and the stuff was well known for changing colour in the presence of moisture even back in the 1950's. Of course these days, so many people have air conditioning - which removes the humidity from the air - that this kind of trick isn't going to work anymore and a barometer makes more sense for indoor use. Also, the toxicity of Cobalt Chloride means that there is no way anyone is still going to be using the stuff in children's toys - but back in the '50s, you could get away with killing a few of your customers now and then. SteveBaker 23:08, 21 May 2007 (UTC)

Plants water purification

These are biologic questions.It would be nice if I take useful references and links: 1.How plants can purify the solutions and water in the ground and attract necessary substances? 2.how they can discern the particles of substances and elements , with what special characteristic of them? 3.Is the attraction according to the requirement or instinctive?Flakture 20:49, 19 May 2007 (UTC)

Venom

Hi, could anyone tell me which animal is the most venimous in the world? I've been wondering for a while. Gbgg89 21:09, 19 May 2007 (UTC)

According to this source [3] the worlds most venomous animal is the box jellyfish (the most venomous snake is the inland taipan and the most venomous fish, the stonefish.) Other animals are more poisonous - such as types of poison arrow frog - but do not "deliver their toxins by stinging, stabbing, or biting." Rockpocket 21:29, 19 May 2007 (UTC)

Terrific timing! anonymous6494 01:58, 20 May 2007 (UTC)

Pt as Hydrogen Catalyst

I am trying to find a source that describes how Pt acts as a catalyst for hydrogen combustion. I am trying to find the temperature range that it acts at. If anyone knows of an academic paper or website, please post. --Joe 21:21, 19 May 2007 (UTC)

It seems to varying considerable according to this 1995 journal article and can be controlled by varying the helium concentration in the gas stream. -- MarcoTolo 04:09, 20 May 2007 (UTC)

The hole truth

Are superlarge black holes less dense as Fred Pohl writes (i.e. we could be inside one right now)? If so, how are they created? I mean, if infinitely dense small black holes accrete enough mass to grow that big, what is the transition process? Clarityfiend 21:51, 19 May 2007 (UTC)

The singularity at the center is, in theory, infinitely dense for all black holes. If you mean the volume within the event horizon, the density there might very well vary, but I'm not sure in which direction. StuRat 22:06, 19 May 2007 (UTC)

He might also be referring to the fact that supermassive black holes have a larger event horizon, which is less gravitationally severe to enter than that of a small black hole. You would certainly survive entering the event horizon of such a black hole (though I wouldn't buy any green bananas), but the gravitational gradient at the event horizon of a small black hole would lead to spaghettification. Black holes are fascinating enough without having to insert any balderdash about us being inside one; I suggest you stick with reliable sources. --TotoBaggins 22:56, 19 May 2007 (UTC)

Reliable sources? Well, the article Schwarzschild radius says: "The Schwarzschild radius of a sphere with a uniform density equal to the critical density is equal to the radius of the visible universe." But I don't understand what value this critical density has. To me, it reads like the visible universe might have a density and radius such that the Schwarzschild radius is even bigger. In other words, we are inside of an universial black hole. 84.160.200.170 23:12, 19 May 2007 (UTC)

Hmm. I don't understand what critical density is, so I can't comment. I assumed the "we might be in a black hole" notion from a sci-fi author was a variation on the sort of "what if the whole universe is just an atom in a bigger universe" Gedankenexperiment that keeps frat boys in states of wonder. My apologies if we are indeed situated in a black hole. :) --TotoBaggins 00:55, 20 May 2007 (UTC)

Well, if the numbers for the universe agree to it, we are in a black hole. I see not much room for a "might". It is a precondition that the universe must be in a process of implosion to be a black hole. If the universe has less than critical density it expands forever and is not in a process of implosion and not a black hole. See Hoop Conjecture.

About the first question: Large black holes are less dense than small black holes in a certain sense, yes. The schwarzschild radius grows linear with the mass and the volume of a sphere grows with the third power of its radius, so the density = mass/volume falls with growing size. Please remember that the schwarzschild radius is a theoretical radius that the hole would have, if it's diameter to circumference ratio would be pi. Measured from the inside the volume will be something very strage, maybe even infinite.

Evolutionary purpose of eye colour

Surprisingly, neither our articles on eye colour nor iris answer this; is there any reason humans have evolved to produce such a wide range of eye colours? The eye is only part of the body which isn't always just some shade of pink or brown, yet it seems to play no role in life (a person with green eyes can't see any better than one with brown or blue eyes). Laïka 21:51, 19 May 2007 (UTC)

actually the article History of eye colors might help you Coolotter88 22:11, 19 May 2007 (UTC)

The obvious reason is that it's used for identification of specific individuals, and, at some point in the past, membership in an ethnic groups (by now eye color genes are so intermixed that it's no longer useful for that purpose). StuRat 22:15, 19 May 2007 (UTC)

That's an example of a question that sometimes bugs me: can variability itself be selected for? —Tamfang 19:47, 21 May 2007 (UTC)

That's a very good question. You might want to read chapter 8 of Mérő László, Moral Calculations for a good discussion of this. (I won't give a definite yes or no answer.) – b_jonas 12:55, 22 May 2007 (UTC)

Mutation of genes involved in melanogenesis, followed by genetic drift is the most likely reason. There is no statistical evidence of positive selection driving the spread of mutant alleles in pigmentary genes in humans, despite what the history of eye colors article suggests. (see PMID 10733465). Rockpocket 23:37, 19 May 2007 (UTC)

Surely the wide variation in human eye colour is actually a demonstration that eye colour isn't very important genetically. Things we (almost) all have in common - like having exactly ten fingers are likely to have evolved that way for really important reasons - things that are wildly different between us can't have a lot of importance from an evolutionary standpoint or one or other of the variations would come out clearly on top and we'd all be the same. So I would assume that the wide variety of eye colours indicates that there is so little evolutionary benefit to one colour versus another that no single eye colour has come to dominate our society whilst polydactylism (having more than 10 fingers or toes) is quite rare - even though it too is genetically linked. We may suppose that there have been strong evolutionary pressures to maintain a ten fingered population whilst there has been little or no pressure to allow blue-eyed people to take over the world. SteveBaker 22:54, 21 May 2007 (UTC)

I have to disagree partially on this. There's been talk about the extinction of non-black (or dark brown, whatever) colored eyes because of "interracial" breeding, because it's a dominant gene. Although it's been argued that the other colors won't go extinct, because they're still recessive and can occur, even if it's much rarer. But then this begs the question: Why is dark brown eyes a dominant gene if it has no evolutionary benefit? --Wirbelwindヴィルヴェルヴィント (talk) 08:03, 22 May 2007 (UTC)

A brown-eye gene says "produce brown pigment" where a blue-eye gene says "do nothing". If both are expressed, the brown pigment is produced. That's what dominance typically means: the action of one allele masks the non-action of the other. Are you asking why dark-eye genes are so much more common than pale-eye genes? —Tamfang 18:20, 22 May 2007 (UTC)

No, I'm asking why brown eyes is dominant compared to other colors. Is there a evolutionary benefit that causes it not to be an equally dominant gene as the other colors? --Wirbelwindヴィルヴェルヴィント (talk) 06:41, 23 May 2007 (UTC)

I just told you why brown eyes is dominant (perhaps someone else can paraphrase more clearly). I don't understand the other question. —Tamfang 21:01, 23 May 2007 (UTC)

Globular Clusters

Why is it that globular clusters are unlikely to support life? --Kitty ^who? 22:37, 19 May 2007 (UTC)

For one, the globular cluster article states that globular clusters are groups of tightly packed old stars which IIRC, the radiation kind of kills off life. The article also states that most of the stars are "population II" which means they have low metal content (I guess it would therefore mean a less likely chance of terrestrial planets like Earth forming).Coolotter88 22:45, 19 May 2007 (UTC)

Note that this is the astronomers' usage of "metal", which means "anything other than hydrogen or helium". So indeed a low "metal" content means that terrestrial planets are unlikely. Also, I think the closely spaced stars means that planetary orbits are more likely to be perturbed over time by other nearby stars and will not remain stable for the billions of years we see in our solar system. --Anonymous, May 20'07, 03:38 (UTC).

Volcanoes- Mount Krakatoa in Indonesia

When was Mount Krakatoa first created and what boundary was it created over ( divergent, convergent or hotspot) ?209.247.23.85 23:03, 19 May 2007 (UTC)

Is our Krakatoa article of any help ? StuRat 05:56, 20 May 2007 (UTC)

Plate tectonics is also useful. Krakatoa, like much of the Indonesian archipelago, is located at the convergent plate boundary where the Australian plate is subducting under the Eurasian plate. --mglg_(talk) 00:07, 21 May 2007 (UTC)

Mount Everest

I'm not sure this is the right reference desk for my question. The article Mount Everest says "Radhanath Sikdar, an Indian mathematician and surveyor from Bengal, was the first to identify Everest as the world's highest peak in 1852, using trigonometric calculations based on measurements of "Peak XV" (as it was then known) made with theodolites from 240 km (150 miles) away in India." Can Mount Everest really be viewed from that far away? Or is it still visible even further away? (Provided ofcourse other physical features don't block the view) Aecis^Brievenbus 23:10, 19 May 2007 (UTC)

If we assume the earth to be a perfect sphere of radius 4000 miles, and Mount Everest to be six miles tall, then by the pythagorean theorem it is viewable from up to 219 miles away (did I get my math right?). You do this by constructing a triangle in that connects the peak of Everest, the person viewing it, and the center of the earth. As long as the leg from the viewer to the peak doesn't pass through the surface of the Earth, Everest can be viewed from that position. Someguy1221 23:22, 19 May 2007 (UTC)

Just as an aside, this math assumes your eyeballs are pretty much laying on the ground, standing on top of something tall will allow you to see quite further. Someguy1221 23:25, 19 May 2007 (UTC)

The computed value is correct according to Horizon, but it assumes that your viewpoint is at sea level. I don't know how rapidly the land drops off as you move away from Everest (and I don't have time to look now), but I don't think there's anything implausible about a sighting from 150 miles. --Anon, May 20'07, 03:44 (UTC).

Another issue is that you would need to have 240 km (150 miles) of visibility, which is rare just about anywhere, but especially in the mountains, which are prone to poor weather. StuRat 05:48, 20 May 2007 (UTC)

Visibility says "clean air in Arctic or mountainous areas, the visibility can be up to 70 to 100 km". But I personally have seen a mountain from ~150 miles (Nelson to Mt Taranaki in New Zealand). It wasn't a particularly clear day. Aaadddaaammm 08:54, 20 May 2007 (UTC)

In case anyone cares, you dont need pythagoras. The length is simply given by 4000*arccos(4000/4006)Zain Ebrahim 14:47, 21 May 2007 (UTC)

The practical problem when using that formulation is that when you plug in the numbers for the real radius of the earth, then the result of the inner division is a number very close to 1.0 - and because most pocket calculators and simulations of pocket calculators on computers use floating point arithmetic - you get a really inaccurate answer. Then taking the arc-cos of a number very close to 1.0 stresses the series expansion that the calculator uses and generates an even worse answer...which you proceed to multiply by the radius of the earth which magnifies the error still more. So whilst that equation is true, it's really poor for numerical reasons. Formulations that don't rely on that method work better in practice. SteveBaker 22:45, 21 May 2007 (UTC)

Ok Thanks. Just two questions. If you didn't use a series expansion to solve arccos (some sort of iteration perhaps) then would that significantly improve the method? What other formulations are there? Zain Ebrahim 08:28, 22 May 2007 (UTC)

Northern bluefin tuna

Is the Northern bluefin tuna really on the verge of extinction? Because I just saw an abc news story on the subject, and it suggested that they are practically an endangered species. However, our article on Northern bluefin tuna suggests that while the population has declined steadily, it's no where near as dire as the new story suggests. What's the best possible answer? No fish stories please--69.118.235.97 23:11, 19 May 2007 (UTC)

According to the IUCN page on the Northern Bluefin (which is in the references section of the wikipedia article), we don't know ("data deficient")... However, it also says the Eastern Atlantic stock is endangered and the Western Atlantic stock is critically endangered, so they're in a pretty bad way. The assessment by the IUCN is only from 1996 though. So I'd say they're pretty badly off, especially with high demand for quality sushi. ADW says "Many are concerned that bluefin tuna could easily become endangered due to high demand as a food source and resultant overfishing." —Pengo 02:29, 20 May 2007 (UTC)

Note, however, that being "endangered" isn't the same as being on "the brink of extinction". Many endangered species have recovered after action was taken to protect them. StuRat 05:35, 20 May 2007 (UTC)

"On the brink of extinction" is journalist talk, and could mean anything. Though I'd think it would be fair to say "critically endangered" (CR) species or stocks are on the brink of extinction. —Pengo 00:51, 21 May 2007 (UTC)

need help with birds

A few weeks ago, a bird set up a nest above my front doorway. (what a rare occurrence!) There were two eggs, and now they both hatched. (they look so cute, btw) Can anyone tell me what I should be feeding them? So far, my dad put in raw rice, but I don't know if they actually ate it yet. Am I supposed to give the two birds water?--Ed ^{¿Cómo estás?} 23:55, 19 May 2007 (UTC)

Could someone please help me??? The birds might get hungry...--Ed ^{¿Cómo estás?} 00:35, 20 May 2007 (UTC)

If the parents are still there, I'm sure they can take care of feeding their babies themselves. Coolotter88 00:41, 20 May 2007 (UTC)

It looks like the parents flew away...but they might come back--Ed ^{¿Cómo estás?} 00:55, 20 May 2007 (UTC)

Put in rice? Did you put rice in the nest!?

There is Bird#Diet and Feeding, but I think the parents will come back, for evolutionary reasons: little birds whose parents didn't come back have died, and didn't pass on their genes that told them not to come back to feed their children. A.Z. 01:02, 20 May 2007 (UTC)

Parents who have been disturbed in their hatching will leave their children to die and breed new ones next summer instead of being eaten along their current ones this summer.

I kinda had to put the birds in a separate basket because they fell from the nest. Should I put them back in their original nest?--Ed ^{¿Cómo estás?} 02:35, 20 May 2007 (UTC)

Yes, and try not to touch them, as they will then acquire your scent and the parents won't recognize them. I would watch for if the parents return. If they don't, then you can try to take care of the birds yourself. You will need to know what kind of birds they are, as some eat berries, some eat bugs, some eat seeds. I suppose you can offer them a selection of foods and they will likely take whatever they like. They will also need water, of course, if you are taking care of them. You'd better get a cage for when they start to fly. Chances are, they won't survive "in captivity", but you can still give it a try. If you take some pics and post them here or show them to a bird expert, we can try to identify the species and what they eat. StuRat 05:30, 20 May 2007 (UTC)

I heard that most species if not all of birds didn't reject young based on olfactory contamination. Has anyone else heard this was a fallacy? --InitialMan(adam) 13:31, 20 May 2007 (UTC)

Yes, that's true; most birds have a poor sense of smell. Snopes has a piece on it [4] here. I'm assuming the baby birds aren't turkey vultures! Matt Deres 01:49, 21 May 2007 (UTC)

What sort of birds are they? Did you muck around with the nest, put food in, etc, before the parents 'flew away'? When did you last see the parents visit the nest? If you do have to feed them (ie, the parents never come back), you'll have to do it very carefully. I imagine you'll have to pipette/syringe it into their beaks. Skittle 16:23, 20 May 2007 (UTC)

Some species of birds seem to abandon their young in the nest without actually doing so. We've often had nesting hummingbirds on our property. After the first few days, the babies are able to regulate their own temperature, so don't need Mom sitting on them all the time; after that, Mom is hardly ever around - she's spending the bulk of her time flitting around catching insects to feed the little poop-generators. (Amazing how much guano a pair of baby hummingbirds can generate.) So don't assume abandonment; it could easily be "oh crap, those annoying humans are there, let's wait until they leave so we can come back and feed the kids." (Currently, we've got Black Phoebe and House Finch nests at our summer place, and Black-chinned Hummingbirds at our regular home. The phoebes couldn't care less whether we're around, nor could the hummers; on the other hand, the finches fly off if we so much as look at them.) --jpgordon^∇∆∇∆ 17:29, 20 May 2007 (UTC)

Ed, it looks like you are in the Chicago area. There should be a chapter of the Audobon Society in your area. They should be able to advise you on how to best care for the hatchlings, though they may ask you to give the birds to them. 161.222.160.8 23:14, 21 May 2007 (UTC)

May 20

Evolutionary purpose of anal sex

Surprisingly, neither our articles on anal sex nor anus answer this; is there any reason humans have evolved to gain pleasure from anal sex? Besides the fact that the anus does play a role in life (people actually need it), it's function in anal sex is different from the "main" function. Did evolution cause the second function to appear, because it was an advantage to gain pleasure from anal sex, or is it actually a coincidence that we are able to have anal sex? Also, did the penis also evolve to be able to be inserted into the rectum or is it, again, a mere coincidence that it is? A.Z. 00:06, 20 May 2007 (UTC)

That's a really disturbing question, but I'll try to answer it. Anal sex might be practiced by gay couples, probably because men don't have vaginas (unless their transgender). Now I'm not a biologist, but I would probably think that an organ in the excretory/reproductive system (the penis) might have evolved separately from an organ in the digestive system (the anus)--Ed ^{¿Cómo estás?} 00:14, 20 May 2007 (UTC)

It's not just a gay thing, btw. Plenty of heterosexuals practice it too, silly people. What's the evolutionary reason for sneezing feeling good? It's gonna happen no matter whether you want it to or not. What's the evolutionary reason for inedible flowers smelling nice to humans? What's the evolutionary reason for any number of things? Like the law, the rule is not "that which is not explicitly designed must be painful". - CHAIRBOY (☎) 00:18, 20 May 2007 (UTC)

In evolutionary terms, there are often happy accidents. It is an accident that the lumen of the colon is separated by a relatively thin membrane from reproductive organs that contain tissues lined with many nerve-endings. There is also a problem with this anatomy, this small separation can lead to what is referred in medicine as a vaginal-anal fistula if there is necrosis in this area.--InitialMan(adam) 02:11, 20 May 2007 (UTC)

Did the nose evolve to wear spectacles for the eyes? Just because the anatomy is in close proximity and has beneficial relationship, doesn't mean it evolved that that way. There is no selective processes by which would afford an evolutionary edge to the scenarios in your question.

I admit that, before I read the answers above, I was more inclined to believe that there was an evolutionary cause for anal sex feeling good, but I guess I can cope, after all, with the idea that it was just an accident. However, I think an at least credible theory could be devised to explain how the apparently accidental anatomical particularity could give us an edge. A.Z. 00:52, 20 May 2007 (UTC)

Um, see Occam's_Razor.--InitialMan(adam) 02:11, 20 May 2007 (UTC)

Not everything has an evolutionary benefit - in this case it seems counter-productive from a reproductive point of view - so one might expect it ought to be selected against. But genetics and evolution isn't everything. We didn't evolve the ability to make digital watches...humans do many things that our genes didn't prepare us for. SteveBaker 01:53, 20 May 2007 (UTC)

So far, everyone had merely said that there is no evidence that the development of the ability to derive pleasure from anal sex had an evolutionary purpose, but no-one had argued that it could actually be counter-productive. Why would you say that the said ability would be counter-productive from a reproductive point of view? And, by that, do you mean that the development of such an ability during the course of evolution would be counter-productive to passing on our genes? If yes, how so? A.Z. 02:21, 20 May 2007 (UTC)

Okay this isnt a debate, but... the problem with that logic is you haven't considered that chordata which mammals are a part of, have evolved from a long line of proto organisms. See mesoderm and remember that the ectoderm and mesoderm are important in blastogenesis(fetal development). These are evolutionary reasons for why they are located in close proximity.--InitialMan(adam) 02:25, 20 May 2007 (UTC)

That seems to be a good point. I don't know a lot about proto organisms, unfortunately, but, if I understand it correctly, what you're saying is that our anuses and sex organs have been close to one another since ever, for some reason that I don't understand (that they are important in blastogenesis), since we were proto organisms, and still proto organisms did not have anal sex. A.Z. 02:58, 20 May 2007 (UTC)

Ok, the thing is that you really can't produce a child through anal sex unless the semen somehow enters the vagina via the perineum. True, performing anal sex is counterproductive towards procreation, probably because it's a waste of the male's sperm. Since the sperm can't do anything in the anus, it's probably best for the male to actually make use of his sperm by having regular sex.--Ed ^{¿Cómo estás?} 02:32, 20 May 2007 (UTC)

A consequence of your logic is that every specimen that can't reproduce for one reason or the other is bad for the species and therefore the genes that made that specimen have the feature that made them not be able to reproduce would not be passed on. Therefore, there would be no reason for female human beings to live for more than 40 years, since they cannot reproduce after that age, and they would just eat everyone's food, and produce less food since they're old, living a life devoid of purpose (from an evolutionary perspective).

However, grandmothers are necessary to take care of their grandchildren, and therefore people that didn't die just after having children survived and passed on their genes, and people that just had their children and died right after that didn't pass on their genes, because the children (and the genes) would die without anyone to take care of them.

Having white or black skin also doesn't directly help you making kids, but it allows you to survive in Europe and in Africa, so you can actually live and then have the kids. Some thing like that can be true with anal sex. A.Z. 02:40, 20 May 2007 (UTC)

I haven't read what other people have said about it, but here's my two cents:

1. Freud described the different great pleasures of different ages. There is an "anal" stage. I've seen "taking a really good shit" as sometimes being quite pleasureful. There must be a pleasure in doing it, otherwise, some people would be inclined not to do it at all!
2. It's a coincidence of people taking advantage of their bodies. While anal sex almost never feels as good as say, vaginal sex, manual, or oral for the recipient, man or woman, the nerves are there so that you don't mess around in there. If there was something acidic, something puncturing, or something too hot touching your intestinal walls, that probably isn't good. The more sensitive something is, normally the better you need to take care of it, really.

There you go, rectal pleasure and pain, and people just are smart enough to take advantage of their bodies, as in masturbation. I forgot what else I was going to say. [Mac Δαvιs] ❖ 02:59, 20 May 2007 (UTC)

Interesting. I guess people are also smart enought to take advantage of opposable thumbs to get food, in many different ways. Yet, getting food is not something nearly as unimportant to our survival as you seem to be implying that anal sex and masturbation are. Could we have survived at all without masturbation? A.Z. 03:10, 20 May 2007 (UTC)

Well, maybe we could. But the article on non-human animal sexual behavior states that "Georgetown University professor Janet Mann has specifically theorised that homosexual behaviour, at least in dolphins, is an evolutionary advantage that minimises intraspecies aggression, especially among males." We are not talking about homosexuality here; we are talking about anal sex, but that is one example of an apparently unimportant behavior of an animal that one could say to be derived from the fact that the animals are just smart enough to take advantage of their bodies (by having sex even though it's not for procreation). Nonetheless, it could give dolphins an evolutionary advantage, for the reason stated above. Maybe we took advantage of anal sex in a way that it gave us an evolutionary advantage as well, and people who felt more pleasure with anal sex survived more, and people that felt less pleasure died instead... A.Z. 04:49, 20 May 2007 (UTC)

I believe if you go back far enough in the evolutionary timeline, the cloaca served as the anus, bladder outlet, and reproductive canal. Once they separated, the "pleasure nerves" apparently split up, as well, with some going to the anus. As for why they remained there after millions of years, I guess you'd need to go with the theory that nonreproductive sex serves to reduce aggression within a population, as in the dolphin example above and the somewhat closer to home bonobo example. StuRat 05:05, 20 May 2007 (UTC)

Well, finally! Someone saying that there could be an evolutionary purpose after all! So, once the anus and reproductive canal split up, evolution would have made the nerves in the anus just disappear, because they were devoid of purpose. However, they remained there, and those nerves don't necessarily participate in vaginal intercourse at all. So, the reason why they remained there could be because engaging in anal sex gave us an evolutionary advantage!

But, aren't there any other reasons why it would be an advantage, besides reducing aggression within a population? Not that that's not a good reason. I'm just wondering. A.Z. 05:21, 20 May 2007 (UTC)

Evolution doesn't make anything "just disappear, because they were devoid of purpose." Firstly, there may be plenty of purposes for something, we may just not appreciate them fully. Even if if there isn't a purpose, there may be a very good reason they are there (for example, as a consequence of a developmental mechanism that is essential for something else). Finally, even if there isn't a purpose or reason for something anymore, for it to be lost by evolution it would most likely require selection against it. Rockpocket 07:17, 20 May 2007 (UTC)

Agree with most of what you say here, but not quite with the final sentence. If there's no longer a selection pressure 'for' something, it can be lost randomly without necessarily being selected 'against'. See for example genetic drift. --jjron 07:49, 20 May 2007 (UTC)

Incidently, putting pressure on the ventral wall of the rectum will stimulate the (male) prostate gland, this happens during anal sex. The prostate plays an essential role in male orgasm, therefore part of the pleasure from anal sex (in males) may simply be an artifact of prostate stimulation. Secondly, there appears to be an element of pleasure derived from having a full bowel (just as there is from having a full stomach). Therefore the feeling of pressue during anal sex may be pleasureable for that reason. Rockpocket 07:40, 20 May 2007 (UTC)

"There is no evidence that same-sex sexual acts per se are under direct [evolutionary] selective pressure any more than is masturbation, anal sex, bestiality, pedophilia, vaginal entry from the front or rear, or any other sexual practice. Sexual desire, arousal, orgasm (especially in men), and male ejaculation, all basic human capacities, are selectively maintained through production of offspring. But these capacities are not specific to reproduction . . . [The strong human] sex drive, maintained by its guarantee of reproduction, is available for elaboration in socially condoned, prohibited, or ignored forms for social, emotional, and physiological satisfaction. . . . It is a common "Darwinian" fallacy to assume that all components of a behavioral act are under equal selective pressure. This leads to treating behavioral acts as discrete adaptive units when in fact they usually have both adaptive and nonadaptive or neutral components. Language, for example, aids in survival and reproduction, but not all linguistic acts provide direct reproductive gain. There is no direct selection for, nor are there genes for, the creation of poetry. The direct, genetically inherited components of homosexuality are those listed above, common to all sex acts."

—Jeffrey M. Dickemann, commentary on "The Evolution of Human Homosexual Behavior" by R. C. Kirkpatrick, from Current Anthropology, Vol. 41 No. 3, June 2000. From "Gay Gene" Critique Quotes, echoing some of the statements made above. ---Sluzzelin talk 08:07, 20 May 2007 (UTC)

Excellent answer, Sluzzelin, and bonus points for the childish amusement to be drawn from finding a Mr Dickemann commenting on homosexual behavior. Rockpocket 08:21, 20 May 2007 (UTC)

I find it astonishing that someone dismisses so easily the possibility that there is a genetic component of homosexuality besides those common to all sex acts, and that this component could have given animals an evolutionary advantage and could have been selected to stay with us. I don't think there is any proven explanation of how psychological development could lead an otherwise straight male (as the author says that we are when we are born) to feel no attraction for females at all and to start directing all that strong sex drive towards other men. Having anal sex and masturbating do not require that one shifts one's entire idea of what is attractive the way that becoming homosexual as one grows up would.

Anyway, Sluzzelin, we are not talking about whether homosexuality has a genetic component in the first place. The question is about anal sex. We all seem to agree with the author that the desire to have anal sex wasn't selected through evolution: this desire is the same primitive sexual desire that we all have. As Mac Davis said, animals are smart enough to take advantage of their bodies, and so they took advantage of the fact that they could have anal sex. What I did want to find out is whether the physiological characteristics that make anal sex feel good (not that make us want to have anal sex) remained with us because having anal sex gives us an evolutionary advantage or are with us because of other reasons unrelated to the fact that we have anal sex. A.Z. 16:51, 20 May 2007 (UTC)

A couple more comments:

1) I don't agree that there must be selection against a feature for it to disappear over time, the mere absence of selection for it will eventually lead the trait to disappear due to genetic drift. A common example is that formerly sighted animals which live in complete darkness appear to lose their eyesight. There is no reason why eyesight would be harmful to them, it simply isn't necessary any more.

2) A more general explanation for nonreproductive sex is that it serves a social bonding purpose. Thus, like grooming each other or eating together, it helps to ensure to cohesion of a group. As mentioned previously, this tends to be used more in some species than others. StuRat 00:59, 21 May 2007 (UTC)

While it is true that many men and women, whatever their sexuality, do find receptive penetrative anal sex pleasurable, a person reading the above thread might gain the impression that this is true for all homosexual men. It is not. Many gay men refrain from receptive anal sex; there are numerous reasons, one of which is that they find being penetrated intensely uncomfortable, even painful. It is possible to train oneself to relax so that it becomes less uncomfortable, but for many men it never leaves the discomfort zone even if they are happy to accommodate their partner's wishes. I'm sure this is true for many women as well. For some uncircumcised men, even being the penetrator can cause pain when the foreskin is forced backwards during sex. The majority of gay men who engage in anal sex on a regular basis like to be either the "top" (penetrator) or the "bottom" (penetratee). Relatively few are "versatile" (like it both ways). JackofOz 01:28, 21 May 2007 (UTC)

Identification

I found this in the upper track of the sliding door when I moved into my apartment. It is on the southside of the building, in Houston, TX. Anybody have any idea what it is? I have no clue...

anonymous6494 02:22, 20 May 2007 (UTC)

Guess: A dry rot fungus ? ---Sluzzelin talk 02:51, 20 May 2007 (UTC)

I think some paper wasp nests look something like that (they are better disguised when on the side of a tree). I would guess, if it is a wasp nest, that the openings are between the two layers. See this pic of a paper wasp nest built on top of bird house (halfway down the page), it looks a lot like yours: [5]. (I wouldn't want to be the bird that flew into that nest !) StuRat 04:48, 20 May 2007 (UTC)

Looks a bit like a very untidy house martin nest. Not sure if you get those in Texas, but it could be an old bird's nest of some sort. It seems to be made of mud and twigs, although that could be just me misinterpreting the photo. How big is it? --YFB ¿ 05:04, 20 May 2007 (UTC)

You can get an idea of the size by the screen mesh in the lower right. It's about two inches long, and maybe an inch wide and an inch deep. anonymous6494 05:25, 20 May 2007 (UTC)

Since I didn't know what the pitch of the mesh was, I couldn't tell much from that! :-) But at 2 inches that seems far too small to be a bird's nest. No idea what it is. --YFB ¿ 05:27, 20 May 2007 (UTC)

I agree with StuRat, it looks like a wasp nest to me too. I live a long way from Houston (in Australia), but have found wasp nests around my place that look very similar. Pretty sure the ones around my place are European wasps nests. (BTW, re Sluzzelin, I don't think it would be a fungus growing on metal). --jjron 06:01, 20 May 2007 (UTC)

Question: have you tried breaking it open to see what it looks like inside? That could give you the answer. If it has a cellular/honeycomb type structure, it'd almost certainly be a wasp nest. --jjron 06:16, 20 May 2007 (UTC)

If you get stung on the nose by a wasp when breaking it open, you can be reasonably sure it was a wasp nest. If you want to avoid that, try breaking it off on a cold day when they will be dormant, or soak it with wasp spray first. StuRat 00:40, 21 May 2007 (UTC)

Re-re: yep, seems a bit unlikely now. :-) ---Sluzzelin talk 08:14, 20 May 2007 (UTC)

Mud dauber wasp?

Atlant 13:01, 21 May 2007 (UTC)

Red something syndrome

There's this syndrome I'm trying to think of. It has red in it and has to do with... something? It's a hereditary syndrome and very rare. Red rag or red fiber or red strings or somethings syndrome. What is it? People that have it tend to be short I think because... I don't remember. Help? [Mac Δαvιs] ❖ 04:00, 20 May 2007 (UTC)

Red man syndrome? — Kieff | Talk 04:10, 20 May 2007 (UTC)

Are you thinking of the mitochondrial myopathies - maybe myoclonus epilepsy (which is associated with ragged-red muscle fibers)? -- MarcoTolo 04:14, 20 May 2007 (UTC)

Whoops - here's a link. -- MarcoTolo 04:15, 20 May 2007 (UTC)

How about Rett syndrome? People with it can be short. --Joelmills 04:16, 20 May 2007 (UTC)

What about redshirt syndrome? --Cody.Pope 11:15, 20 May 2007 (UTC)

It was ragged-red fibers that I was thinking of, thanks :) MERRF syndrome. [Mac Δαvιs] ❖ 04:24, 21 May 2007 (UTC)

energy loss = mass loss

Hi,
We're doing Einstein's special relativity in Physics at school now, and we watched a film called "E=mc^2 Einstein's Big Idea" (something like that anyway). And one of the things that was said was that if for example Paris was burnt to the ground and you had a dome over it and retained all the gases etc - if you measured all the mass it would identical to what Paris was before you burnt it. Seem logical enough. But then, taking the example perhaps too far, I thought that this wasn't true since heat and light energy would be lost, and hence because of the interchangeability between mass and energy according to e=mc^2 then a small amount of the matter will be lost. My physics teacher disagrees because it is only chemical reactions which are taking place and hence no mass is lost. Which is true? Thanks, --Fir0002 09:55, 20 May 2007 (UTC)

I'm not entirely positive, but I believe you are right. Though the conservation of mass rule does generally apply, I think that bond energy makes compounds lighter than the sum of their parts. When the bonds are broken this mass is expressed as energy in the form of light/heat. So if the this dome retained all the "energy" as well, then you'd still have a balanced equation, but if the dome let out heat/light then there would be mass loss. It depends on how closed the system really is. In the end though, this mas loss is so minimal it doesn't matter. --Cody.Pope 10:28, 20 May 2007 (UTC)

If any energy is radiated away from the system e.g. heat and light, as the above poster says, then mass will be lost. But the amount of mass lost is likely to be only a small proportion of the total mass of the system, as is E=mc^2, then m = E/c^2. With E in Joules, c in meters per second, then you need ~9 x 10¹³ Joules of energy radiated to lose just 1 gram - that's approximately the same as the energy released in the Hiroshima and Nagasaki atomic bombs - equivalent to around 20 kilotons of TNT. So yes, burning an entire large city will end up releasing mass if there is energy lost from the system, but you need to release a lot of energy to get measurable mass loss. Compared to the overall mass of Paris, the mass lost would be negligible.Richard B 10:50, 20 May 2007 (UTC)

Thanks for that! Yeah I understand about the miniscule amounts we'd be talking about - but it was just a Gedanken experiment where it was just a question of whether mass could be lost even in a chemical reaction. Yay I was right! --Fir0002 12:55, 20 May 2007 (UTC)

Einstein was able to show mass and energy were related with Special_relativity using an absolute velocity ~3x10ˆ8 which is independent of inertial reference frame relative to any observer. One consequence shows an equivalent between mass and energy. A fire is an oxidation reduction reaction which is exothermic in nature. Regardless of infra red electromagnetic radiation, other wavelengths of visible and lower wavelength radiation undoubtedly was produced in this reaction. Electromagnetic radiation can get transferred through convection, conduction and irradiation. Therefore, if the surface was an ideal insulator and had a surface that reflected all wavelengths of electromagnetic radiation, this would demonstrate special relativity fairly well.--InitialMan(adam) 13:04, 20 May 2007 (UTC)

How about a flashlight in a dome with those properties going the speed of light? According to your science teacher's logic, a chemical half cell is a chemical reaction as well, yet it is producing visible light EMR. The battery is losing some mass on a small scale, I believe. Yet the mass/energy would still stay in the dome while the light would be going no faster than 3x10ˆ8m/s

In an educational film? Was it old? Maybe that film is the root cause for this stupid myth.

No, I know the film he's talking about. Here [6] is a link to it. It's 2005. BTW the part he's talking about is in the part of the film about Antoine Lavoisier and his original statement of the law of conservation of mass. --jjron 04:38, 21 May 2007 (UTC)

Siphon

Does a siphon work in a vacuum? Actually that's just an excuse to ask someone who knows about these things to take a look at the article, as I'm sure it needs work but I don't think I'm up to it. It seems to me that a simple siphon will still work in a vacuum as it is more dependent on gravity than air pressure. (Surely someone has tried it.) Also soda-siphon bottles aren't really siphons, are they? And is a sink trap an inverted siphon? I don't think so...--Shantavira|^{feed me} 13:13, 20 May 2007 (UTC)

Siphon

No, it wouldn't work. The air pressure is what makes the fluid in the upper reservoir flow upward through the tube. —Bromskloss 13:36, 20 May 2007 (UTC)

Siphon cannot work in vacuum because no material remains liquid in vacuum (except possibly Helium; but liquid Helium is a different story anyway). Any material at zero pressure is either solid, or gas, or a mixture of solid and gas; the gas being (formally speaking) infinitely dilute in absence of containing wall, which is the case here. The solid-liquid-gas triple point pressure is the minimal pressure at which liquid can exist in thermodynamic equilibrium. Lower the pressure, and the liquid will boil out. At atmospheric pressure the proximity of the triple point is not an issue, since most "siphonable" liquids have triple-point pressure orders of magnitude below 1 atm. However, at sufficiently low pressure the weight of the liquid in the "down" part of tube will produce a certain pressure drop, causing the liquid to boil in the upper part of the tube and thus breaking the flow. Now, as far as fixing our siphon article is concerned, I have no books here, and I would really hate to add stuff with no refs. I may get to it later (no promise) , but definitely not before the next weekend. Best regards, Dr_Dima.

So if we imagine a really big tank of liquid - so while the surface of it is boiling off into the vacuum, the rest is still comfortably liquid a foot or two beneath the surface - and presuming that the siphon tube is full of liquid and immersed deeply enough - then the air pressure that would have been pressing down on the upper container is absent - but so is the air pressure on the bottom container (or the end of the siphon tube if it's not submerged). So the lack of air pressure should completely cancel out - and so long as there is enough liquid that it can siphon before it boils away - I can't see any reason why it would matter that it's happening in a vacuum. SteveBaker 15:06, 20 May 2007 (UTC)

If at no point the siphon is above the surface of the liquid in the big tank then - yes - it will work. However, that would be a simple pipe, not a true siphon. In other words, when the surface pressure (in the upper vessel) equals to the triple-point pressure, the pressure of the liquid in the siphon above that level would be lower than the triple-point pressure, and liquid in that part of the siphon will boil. What can save the day, however, is a phenomenon called metastability. That is, even when the gas phase (or solid-gas mixture) has lower Helmholtz free energy than the liquid phase, which is exactly the case below the triple-point pressure, the boiling may be delayed somewhat, see superheating. Relying on metastability is basically the same as taking chances: it may boil or it may not. So it is not a good idea for space applications ... Best regards, Dr_Dima.

Let's eliminate the gas boiling problem by adding a plate to cover the liquid on each cylinder. The plates in the two cylinders are of exactly equal weight and (since this is a thought experiment) the plates can move without friction and float in contact with the liquid.Now what happens? My guess is that liquid flows from the top cylinder tot he bottom one, but I don't know the mechanism. -Arch dude 20:31, 20 May 2007 (UTC)

Ah - OK. I think I've got it. I've changed my mind - it won't work in a vacuum. The maximum height of the siphon tube above the surface of the upper container is determined by the air pressure - for water, on a normal day at sea level, your siphon tube can't rise more than about 32 feet above the tank. The reason for that is that the air pressing down on the surface of the water weighs as much as water that's 32 feet deep. The water in the siphon tube can't tell whether it's immersed in 32 feet of water - or an equivelent weight of air. As the air pressure drops - the height of the pipe above the surface of the liquid decreases until in a perfect vacuum, the siphon tube has to be level with the surface of the liquid - at which point it's not a siphon anymore - it's just a hose sticking out of the side of the container. SteveBaker 21:01, 20 May 2007 (UTC)

If you do this experiment under low pressure conditions (which eliminates the problem of boiling), the fluid will just run out of the siphon at both ends and leave the top part evacuated.

Almost. Under reduced pressure (but not a hard vacuum), the siphon would still work so long as the siphon tube doesn't rise too high above the two containers. But if it is too high and if both ends of the siphon tube are submerged - then the liquid would be some way up the tube with the top part of the loop being full of vapor from the liquid. In effect, the siphon tube is behaving like a Barometer tube. SteveBaker 12:31, 21 May 2007 (UTC)

identifying a bird

Due to the likelihood that my previous post might not be seen anymore (earlier post), I'm beginning a new thread here. This is the bird that I'm talking about. The parental bird has come back (thank god) and has resumed feeding it. Can someone help me to identify this bird?--Ed ^{¿Cómo estás?} 15:00, 20 May 2007 (UTC)

looks like a dove. What part of the world do you live in? Dr_Dima

Chicago suburbs--Ed ^{¿Cómo estás?} 15:54, 20 May 2007 (UTC)

It's a mourning dove. --YFB ¿ 16:01, 20 May 2007 (UTC)

Yep. Dr_Dima

Doves grow up really quickly. A.Z. 16:27, 20 May 2007 (UTC)

Why is it mourning? Who died?

According to the article: "The "mourning" part of its common name comes from its call." SteveBaker 20:13, 20 May 2007 (UTC)

Template:Spoiler

Civility? Clarityfiend 18:23, 20 May 2007 (UTC)

Template:Endspoiler

Should there also be Tailfin warnings, or do too few cars have them to justify a template? Edison 15:14, 21 May 2007 (UTC)

Absolute Error

If one has two values, a=30±0.5 and b=28±0.5, and calculates a value z=a-b, what is the absolute error in z?

As I understand it, there are two avenues of approach.

(1) One could first find the percentage error of a and b, and add them, then convert this back to an absolute error? So error in a=1.67% and error in b=1.79%, thus error in z=3.46% Hence one can find absolute error in z as being .0346 × 2 = ±0.0692. Thus z=2±0.0692.

(2) Or is it true to say that one could simply add the absolute errors of a and b to get the absolute error in z? If absolute error is defined as maximum deviation from a value, is it true to say that z=2±1?

I think that (1) seems to be too much of a small error, and (2) seems better, but surely there is only 1 right answer-which is it?

Thanks! --Fadders 15:13, 20 May 2007 (UTC)

I was going to refer you to our Error analysis article, but it doesn't say much.

But it does refer to our Errors and residuals in statistics article, which... also doesn't say much.

But it does refer to our Propagation of uncertainty article, which says quite a bit, although it's heavy on the math.

But between the three of those, you might find some pointers to your answer.

(One thing I do know is that the proper method for combining the two errors will depend on whether the values are independent or not. So there's not "one right answer".) —Steve Summit (talk) 16:23, 20 May 2007 (UTC)

Well, just think about it - if the true values for your variables are a=30+0.5 and b=28-0.5 - then your estimate for z would be off by +1, if a=30-0.5 and b=28+0.5 then z would be off -1.0 - so adding your errors will give you the worst case. But if you are measuring a and b with the same instrument and the error is because it's mis-calibrated or something (so the actual errors in a and b are not independent) then the expected error in z might actually be zero because the error in a and b neatly cancel out. In the real world, some part of the error will likely be independent and some part not. Basically - you've got to know more about the nature of the sources of your errors. SteveBaker 20:50, 20 May 2007 (UTC)

Last question (not about starch)

All I need now is a link to a websight where I can find a list of beta sources. I would particularly like a list of sources of just beta radiation, and with a long halflife. I tried searching the internet and found a lot of adverts and junk. Can anyone here give me some advice as to what I should do?

Also can a beta partical be said to have an electrostatic charge or have I accidentally borrowed this word from another sort of physics?

Yet another last question- how could I go about making an electron travel in a certain direction using magnets?

I think this is basically what a Cathode ray tube does :) I'm not sure exactly how, but if you read the article you may find it somewhere in there :( HS7 16:30, 20 May 2007 (UTC)

Red article, not got a clue. Would just having the source in a solenoid work? It doesn't have to be too accurate.

Hello. Really need help here

Answer to question regarding moving an electron in a certain direction with magnets. A magnet has magnetic_field lines, B^→ that originate at south poles and terminate at the north pole of the permanent magnet. These ferrous magnets will repel an electron with the N-pole and attract it with the S-Pole depending on the orientation the magnet is held toward a beam. With other electromagnets, the right hand rule comes into effect when predicting the direction of the field related to the polarity of current. ferrous magnets are simple. An electron gun can be used to fire a beam of electrons at a phosphorescently coated screen, however unlike a CRT, the device in my physics lab had an open area which when exposed to magnets, let us demonstrate this phenomena you describe. (Anyone know what this setup is called specifically?)--InitialMan(adam) 18:40, 20 May 2007 (UTC)

Re. the two first questions: our article Common beta emitters might be a reasonable place to start. For more information, try the links at the end of the article Radioactivity. The word 'electrostatic' implies electrical charge that is static, i.e. not moving, such as static electricity. A beta particle carries electrical charge, not electrostatic charge. --NorwegianBlue ^talk 18:48, 20 May 2007 (UTC)

Very last question. If I wanted to measure how much radiation passed through something would I be measuring its permeability or permittivity? Or something else?

That's it now, I've finished. Thanks for all the help with my homework, if it wasn't for you, I might have had to do some work. ;)172.189.71.94 09:41, 21 May 2007 (UTC)

Electrical source

Hi. I've been wondering about many possible sources of electricity, and I have ideas that may work. However, I want to know which do work and which don't. Please indicate if they have already been used as a source of electricity, if they have already been planned as a source, if it is already being used in a different way, if it has been used in many different ways, if it is likely, unlikely, near impossible, too hard to control, too rare to harness, too expensive, too unpredictable, generates too little power, requires more power than it produces, etc. Here is the list:

• lightning
• aurorae
• heat from combustion
• energy from explosives
• human power
• animal power
• chemical reactions
• electrons from matter
• recycled electricity
• continuously rotating magnets
• supercompressed superheated water
• supercompressed air
• energy from pressurised air leaking into a vaccuum
• short wavelength radiation to strip off electrons
• bacteria
• concentrated radio waves
• controlled nuclear explosion
• controlled antimatter annilation
• energy from meteoroids
• moonlight
• gravity
• the strong and weak forces
• colliding atomic particles

So, which are possible? Thanks. -- AstroHurricane001^(T+C+U) 19:10, 20 May 2007 (UTC)

One creates difference in electric potential in a conductor through electromagnetic induction. This process turns mechanical energy into electric energy. Therefore, anything you can attach two magnets to and have them spin near a wire is capable of creating AC electricity suitable for transmission down long lengths of copper wire.--InitialMan(adam) 19:24, 20 May 2007 (UTC)

The trouble with moonlight is that it is almost entirely visible light - solar panels require either the high energy of ultraviolet or the radiant heat of infrared. Also, attempting to extract energy from particles colliding seems to violate the Second law of thermodynamics, unless you are constantly adding more heat to the mixture, in which case it simply becomes an inefficient generator (it would be easier to heat those particles, cause them to enter the gas-phase, and use them to drive a turbine). Laïka 19:37, 20 May 2007 (UTC)

In theory, you could power something with bacteria, provided bacteria were only part of the process: pump sugar solution into a tank of bacteria, and ferment it to ethanol/methanol, which are both good fuels for vehicles. Laïka 19:39, 20 May 2007 (UTC)

He clearly asked about electricity and then referred to power as a measure of electrical output, I think. Could run generator with the ethanol. There are also ways to use photoelectric effect as was mentioned earlier.InitialMan(adam) 19:45, 20 May 2007 (UTC)

Here's your list (slightly rearranged) with my comments:

• lightning

Suggested, but never implemented.[7] —Keenan Pepper 20:45, 20 May 2007 (UTC)

• aurorae

Same deal.[8] —Keenan Pepper 20:45, 20 May 2007 (UTC)

• energy from meteoroids

Not steady or reliable (and not very big energy sources at that).

• heat from combustion

We use it all the time, of course.

Can you give me a few examples (not too many) of how we use combustion for electricity? Thanks. -- AstroHurricane001^(T+C+U) 22:01, 20 May 2007 (UTC)

I'm sure you can think of some examples (not too many) yourself! How many methods of electrical generation do you know of? How many of them involve burning something? --Steve Summit (talk) 02:06, 21 May 2007 (UTC)

• energy from explosives

Not so different from "heat from combustion" (remembering, though, that in either case, you need a source of fuel/explosives).

• controlled nuclear explosion

Not so different from the nuclear power we already use today. (Again, though, you need a source of nuclear fuel.)

• human power

Works great on small scales; here's a radio with a crank: [9] —Keenan Pepper 20:45, 20 May 2007 (UTC)

Yes, but what if people volunteered to get a paid job where they use their energy to generate electricity for a town, etc? Thanks. -- AstroHurricane001^(T+C+U) 22:01, 20 May 2007 (UTC)

As I said below, humans can't provide the vast quantities of power we need for modern industrial society.

In fact, let's ignore "industrial" society, and look for a moment at the power required by just an ordinary house. According to this web page, the average household in the United States consumes power at the rate of about 1000 watts. (Stated another way, the average household uses 1 kilowatt-hour of energy per hour. Stated another way, this is like having 10 hundred-watt light bulbs burning.)

But according to our article on Horsepower, an average human can only do about 0.1 horsepower of work for sustained periods. There are 746 watts in a horsepower, so an average human can only put out about 75 watts -- not even enough to keep one of those hundred-watt lightbulbs lit. So this average household would have to have 1000 ÷ 75 = 13 (and a bit) people in it, working all the time, just to provide that one household's electricity needs. And there wouldn't be any left over for streetlights, or for the electricity used by city hall, or the electricity used to pump the city's water, or the electricity used to run the steel mills to make metal things out of, etc.

(Now, my analysis here isn't really fair, because you didn't say you wanted to generate all the electricity we need from people, but rather just some, from as many people as volunteer. But I think you can see that a few people, generating electricity just some of the time, aren't going to put much of a dent in a large city's electricity needs. And if you're thinking of paying these people, you have to compare what you'd pay them to the amount you'd spend on other sources of energy. I think electricity tends to cost 10-15¢/kWh these days, at least in the U.S. It'll take 1000 ÷ 75 = 13.3 hours for one person to generate 1 kWh of energy, so if you don't want to pay them more than conventioanlly-generated electricity would cost, you can't pay them more than about 1¢/hour. And you also have to think about the cost of the food they're eating, and the energy cost of transporting the food to them, and the energy cost of transporting water to them to replace the water they'll lose due to perspiration while generating electricity, and...) --Steve Summit (talk) 02:03, 21 May 2007 (UTC)

• animal power

Both work fine and have been used historically, but don't provide the vast quantities of power we need for modern industrial processes. Also, they require food.

Further to Keenan's comment: part of me desperately wants every stairmaster, treadmill, elliptical trainer, and rowing ergometer in every gym and health club connected to a generator feeding back into the electrical grid, instead of dissipating the "excess" energy as heat (which, if in the summertime, we may well have to expend extra real energy on air conditioning to remove). But it's not clear it'd make any significant difference... --Steve Summit (talk) 21:20, 20 May 2007 (UTC)

• chemical reactions

Combustion is of course a chemical reaction. There are plenty of chemical reactions that can be used to produce electricity -- but once again, the problem (if you want to make the process economical) is finding the reactants in quantity and for less money than the generated electricity is worth.

• recycled electricity

There's no such thing.

Really? Isn't it possible to use the leftover electricity (because appliances also send electricity back to the socket) from home use, then combining this energy from many homes, to be stepped back up to powerline voltage, then sent back into homes? Thanks. -- AstroHurricane001^(T+C+U) 22:01, 20 May 2007 (UTC)

Yes, really, there is no such thing as "recycled" electricity.

You can think of a flow of electricity as a flow of water, but what's interesting is not the water itself, it's the water pressure. Electrons aren't valuable in and of themselves; there are billions of them in every gram of matter you own. Electricity isn't just a bunch of electrons; it's a flow of electrons (a current) under pressure (a voltage).

Imagine that in your house you used pressurized water for energy, instead of electricity. Whenever you wanted to do something, you'd turn on a faucet, and the water would run a little waterwheel and do a little work. Then the water would run down the drain. (This would obviously be better for running motors than creating light or heat, or making your television or computer work.)

Now, you could say, the sewer in the street contains all the "leftover" water from all the houses on the street, so can't we recycle it somehow? Well, no, because it's not under pressure any more. Unless you pressurize it again, you can't get any more useful work out of it. But pressurizing it would require more energy. You could recycle it right away as plain water for washing or making cement or something, but not as pressurized water for powering machines with.

When you turn on an electric appliance, yes, the electrons flow into your house, through the appliance, and back out of your house. But the energy flow is one-way: from the power company, to your house. (And actually, since it's alternating current, the electrons aren't even really flowing into, through, and back out of your house, they're basically just sitting there vibrating back and forth. But this doesn't change the fact that the energy flow is one-way.) --Steve Summit (talk) 22:42, 20 May 2007 (UTC)

Just a side comment here. You might imagine that when Steve writes "Imagine that in your house you used pressurized water for energy, instead of electricity", he's describing an imaginary system of power transmission. Not so; hydraulic networks were available in some cities, notably in London, as an alternative to electricity 100+ years ago. However, the power was intended for big industrial-type machines, not for household appliances. And of course it couldn't provide light; but people could burn gas for that. --Anonymous, May 21, 2007, 03:15 (UTC).

• continuously rotating magnets

What rotates the magnets? If a turbine, then this is in effect how our generators (either water- or steam-powered) already work. Otherwise, you might be talking about perpetual motion, which of course doesn't work at all.

I was thinking if the magnets were given a little "push" (which would be quite big since they would have to be quite large) to make the magnets rotate. I was thinking of a hollow cylindrical magnet with alternating polarities across its length, with NSNSNS consecutively, etc, fixed to a kind of axle, but still able to rotate, around another non-hollow cylindrical magnet, with similar consecutively alternating poles all around, also fixed to an axle and able to rotate, and the "push" should send the magnets into motion, with poles constantly attacting and repelling, pushing the magnets around, to generate magnetoelectricity (aka electromagnetism), quite similar to the way bullet trains work, so is it possible? Thanks. -- AstroHurricane001^(T+C+U) 22:01, 20 May 2007 (UTC)

No. You are basically talking about a perpetual motion machine, and as I said, those don't work. --Steve Summit (talk) 22:50, 20 May 2007 (UTC)

• supercompressed superheated water
• supercompressed air

Sure -- but what energy do you use to do the supercompressing and superheating?

Other electricity, of course, which is why I wanted to know whether it will generate more power than it uses or not. Thanks. -- AstroHurricane001^(T+C+U) 22:01, 20 May 2007 (UTC)

It never generates more power than it uses. No matter what "it" is. Besides TANSTAAFL and the perpetual motion article, you might want to read our articles on the second law of thermodynamics (specifically, the Perpetual motion of the second kind section) and conservation of energy. --Steve Summit (talk) 22:50, 20 May 2007 (UTC)

• concentrated radio waves

Sure -- but what energy do you use to generate and concentrate those radio waves?

I was thinking about using background radio waves (eg, from radios or satellites or astronomical objects) concentrated in the same manner as a radio telescope, using radiowavemirrors to concentrate the energy. Thanks. -- AstroHurricane001^(T+C+U) 22:01, 20 May 2007 (UTC)

• energy from pressurised air leaking into a vacuum

Sure -- but how long will your vacuum last?

• electrons from matter
• short wavelength radiation to strip off electrons

What do these mean?

Sounds a little like betavoltaics... —Keenan Pepper 20:45, 20 May 2007 (UTC)

I was thinking about, since electricity is partially made of electrons, to use those electrons from normal matter, and send them into the powerlines, for electricity, and unlike betavoltaics, should probably not require dangerous radioactive material.

The problem, as I mentioned above, is getting those electrons to move.

Hold an unconnected piece of wire in your hand. Make it a bare piece of wire, no problem. It contains billions of electrons, but they're not going anywhere. They're not under any "electrical pressure" (voltage), so you don't get shocked. But you can't get any useful work out of the electrons in that wire, either, because they're just sitting there.

Now, there are lots of ways of imparting energy to those electrons, to give them some voltage so that a current can flow and do some useful work. The easiest way to get the electrons moving is to wave the wire around in a magnetic field. Presto! A current is generated; the electrons move. If you now connect the wire to a light or motor, you can make the light light up or the motor move. You've generated electricity! But: you had to do work, with your arm, waving the wire in the magnetic field. You had to do exactly as much work as the light bulb dissipated, or the motor did. In fact, you had to do a little more work than that, because no generator, no wire, no light bulb, and no motor is 100% efficient. And although you generated this energy, you did not create it; you just transferred some energy from the breakfast you ate this morning. --Steve Summit (talk) 23:03, 20 May 2007 (UTC)

• bacteria

Probably possible, if there's an untapped food source.

• controlled antimatter annihilation

Sure -- but only if we find some hitherto-unsuspected but readily-available cache of antimatter. Otherwise, you've got to create the antimatter, and that'll take at least as much energy as you'd get back out.

• moonlight

is just sunlight reflecting off a rock, and it's all we can do to extract electrical energy economically from bright, daytime sunlight.

• gravity
• the strong and weak forces

These are just forces, they're not energy sources.

Yes, but I was thinking, for example (and only as an example, there are many other possible alternatives), that maybe you could use gravity to pull down a supply of fluid, etc, quite similar to hydroelectricity, to rotate and generate the generators' power. Thanks. -- AstroHurricane001^(T+C+U) 22:01, 20 May 2007 (UTC)

No, not "Yes, but I was thinking". The point here is "No, force is not energy".

It's very easy to generate electricity from gravity -- sort of. Be at the top of a tall tower (or a steep mountaintop cliff) with a rope, a rock, a capstan, and a generator. Wrap the rope around the capstan, so that if the rope is pulled, the capstan will turn. Connect the capstan to the generator. Tie the rope to the rock. Drop the rock into space. Gravity pulls the rock, the rock pulls the rope, the rope turns the capstan, the capstan turns the generator, presto, you've got electricity.

Until the rock hits bottom. Then, no more electricity.

If there happen to be a lot of rocks on the top of the mountain, you can keep this up for a little while. But eventually, when you run out of rocks to drop, you're stuck. You can haul some of the rocks you dropped back up, but of course to do that you're going to have to expend just as much of your own energy as you got out of the rock as it fell. You might as well have turned the capstan by hand yourself, and eliminated the middleman.

For purposes of producing energy (or, rather, attempting to produce energy, that is), gravity is just like a spring. You can get energy out of a compressed spring, but you had to expend energy to compress it in the first place. You can get energy by dropping something from a height, but somebody had to expend energy to raise the object to that height.

Hydroelectric dams don't extract energy from gravity. They extract energy from the weather systems that lifted the water vapor that fell as rain to feed the streams and rivers that filled the reservoir behind the hydroelectric dam. Since those weather systems are all powered by the sun, in a sense, hydroelectric energy is "just" another form of solar energy. --Steve Summit (talk) 00:59, 21 May 2007 (UTC)

• colliding atomic particles

Not sure what you mean here. Those collisions (by some definition) happen in all chemical and nuclear reactions, including the ones we already use for generating electricity. But they aren't energy sources in and of themselves.

Pardon me if I'm wrong, but I suspect you may not have a solid grasp of the concepts of force and energy, and the law of conservation of energy. Electricity is a very, very convenient medium for transmitting energy around, but it doesn't just spring into existence magically. Every kilowatthour of electricity we generate -- by any means possible, including those we haven't invented yet -- requires an input of at least 3.6 million joules of energy. That energy has to come from somewhere -- either from the sun, or from fuels (biological, chemical, or nuclear) which tend to be expensive and in limited supply. TANSTAAFL. —Steve Summit (talk) 20:27, 20 May 2007 (UTC)

In fact, scratch the "tend to be". All fuels are expensive, and this is due to a perfect collision of the laws of economics and physics. It's like this: 1. Energy can neither be created nor destroyed. 2. Energy is valuable. 3. Ergo, any fuel that can be converted to energy is, economically, just about as valuable as the energy you can get from it.

[Now, it's true, before someone corrects me; ever since Einstein my lemma #1 has not quite been true; energy can be created, and in fact you can get c² of it for each unit of mass you manage to convert directly to energy. If we ever succeed in creating controlled, self-sustaining nuclear fission, the energy landscape will be very, very different. (However, IMO we'll then have a new kind of global warming problem, but that's OR on my part so I'll stop now.] --Steve Summit (talk) 21:36, 20 May 2007 (UTC)

Hi. Thanks for solving my question, although I've but a few replies to your questions. Also, your mention of global warming has spawned three new ideas: How about using greenhouse gases to produce heat and electricity, or using a greenhouse-like structure to trap heat, and use it to make electricity, or using photosynthesis for electricity? Thanks. -- AstroHurricane001^(T+C+U) 22:01, 20 May 2007 (UTC)

In order:

How are you going to make electricity from (say) carbon dioxide? I can't see an obvious way.

Trapping heat is all very well, but you need an energy source: where's the heat going to come from? If from the sun, then there are (probably much better) ways of converting sunlight into electricity already.

Using photosynthesis for electricity is what you're doing already when you burn fossil fuels and so on. Or are you thinking of a more direct method? Algebraist 22:24, 20 May 2007 (UTC)

The confusion of forces with energy sources by the questioner smacks of the 1830's era when Thomas Davenport, a blacksmith, saw a strong electromagnet invented by Joseph Henry, which could lift a ton. He thought that a strong magnet equalled a powerful energy source, ignoring the counsel of Henry and others that electricity at that time was generated by batteries, that force was not energy, and that the cost of zinc meant that the motors Davenport invented and patented were then uneconomical no matter how cleverly he applied them to railroads or printing presses. Davenport eventually died insane and impoverished, and the electric motor was re-descovered by others. He didn't even get credit for his priority of invention, when years later dynamos could generate electricity economicalyy from coal or oil fireed steam engines. Edison 15:09, 21 May 2007 (UTC)

Hi. Thanks for all your answers, and even though I don't have time to respond to all of them, I appreciate your help. Thanks. -- AstroHurricane001^(T+C+U) 15:50, 21 May 2007 (UTC)

Varenicline and dreaming

One of the listed side effects for varenicline (Chantix) is changes in dreaming. In my experience over the last two weeks that has included increased vividness and improved recall afterwards. What would be the mechanism for this? --Joelmills 19:30, 20 May 2007 (UTC)

I know that the brain has two main phases of neurotransmitter activity. During waking hours, dopamine and acetylcholine are most active within the CNS. When the mind is unconscious, serotonin and melatonin predominate. Dreaming is most vivid during Rapid Eye Movement sleep, often psychoactive drugs will effect these sleeping patterns indicated by delta waves.

Arctic Waters - Why so prolific?

I've been watching the (amazing!) "Life on Earth" series - and was struck by what seems an anomalous thing. Why is it that the arctic oceans are teeming with life and nutrients - the place to be if you are a whale or a seal or something - when the tropical waters have minimal amounts of nutrients - little plankton, krill, etc?

This seems like the complete opposite of what you'd expect - life is ultimately powered by the sun - and there is a heck of a lot more sunlight in tropical waters than in the arctic.

What's going on here? SteveBaker 20:08, 20 May 2007 (UTC)

I think your point is valid, but ocean currents, especially the thermohaline circulation, tend to flow from warmer to colder waters due largely to convection, thus carrying the nutrients to the poles. Sorry, don't have time to elaborate further. An interesting article I read last week was talking about new findings showing the amazing richness of the deep Antarctic waters, and made a similar point about how you would expect them to be low in life being so far away from the sun, with so little light penetrating to the depths. --jjron 01:04, 21 May 2007 (UTC)

The book which accompanies the Planet Earth TV series says:

"In the oceans, the variety and quantity of life is also determined mainly by the availability of energy from the Sun. The top 100m or so of sunlit, shallow waters contains 90 per cent of life in the oceans. Here it is the availability not of water but of vital nutrients, especially phosphorus and nitrogen, that has shaped marine communities. Though tropical seas receive the largest amounts of sunlight, they are, with the exception of the coral reefs and seagrass beds, largely deserts. This is because these waters are calm, allowing most of the the nutrients to sink to the depths. The ocean's greatest riches tend to be found in rough temperate seas or where upwelling currents provide a good supply of nutrients."

and

"The vast blue desert of the tropical oceans receives ample supplies of sunshine, but once again, lack of nutrients limits phytoplankton growth - the algae at the base of most marine food chains. Tropical oceans are the famously calm seas of the doldrums, and there is little surface mixing to bring nutrients up from deeper water. Neither do these waters benefit from the regular supply of nutrients that rivers bring to shallower waters on the continental shelf."

So that explains why the tropical seas are pretty short of life. The northern and southern oceans, which are subjected to a mighty battering from storms for more than half of the year, undergo much greater mixing so that nutrients are brought up from as far down as 200 m. This fuels the phytoplankton bloom in spring, which feeds the copepods (Arctic) and krill (Antarctic) which drive the marine food chains. --YFB ¿ 03:25, 21 May 2007 (UTC)

Lightning safety

Hi. I wanted to know what activities are safe and which aren't to do during an electrical storm inside a building if lightning stikes nearby. Here is the list:

• turning on a light
• urinating
• inserting a lightbulb into an electric light
• using magnets
• walking
• going to the basement
• opening a window or keeping one open
• touching a doorknob
• swimming
• editting wikipedia
• using an elevator
• putting on or taking off staticy clothes
• touching a washing machine
• lighting a fireplace
• turning on a gas powered furnace
• touching an appliance
• opening a door
• touching a metalic or wet object
• combing hair
• throwing something outside
• lighting a candle
• skating on an ice rink
• going to the top of a building

So, which are safe and which are not? Thanks. -- AstroHurricane001^(T+C+U) 20:14, 20 May 2007 (UTC)

Here's an idea: Read http://www.lightningsafety.noaa.gov/indoors.htm to get a general idea, remove any of these that are obvious, and leave the ones you're still curious about. You'll get better answers with a shorter list. —Keenan Pepper 20:49, 20 May 2007 (UTC)

editing wikipedia - never safe, electrical storm or not. --88.110.39.243 22:24, 20 May 2007 (UTC)

LOL! Well, it's not like some random wikipedian will emerge through the computer and eat your brains, right? Thanks. PS. if it's not safe, then why are you editting it ;-) ? Hehe. -- AstroHurricane001^(T+C+U) 22:32, 20 May 2007 (UTC)

Actually, editing Wikipedia is the most risky one, though if Astro had included using a telephone (landline) or watching television that would also be risky. This is because those devices probably have electrical connections outside the house, to the telephone line or an aerial. If a lightning strike is possible, switch off your computer and don't use the phone. I once had a answering-machine melt because of a lightning strike. I was using my PC at the time, but although it went dead at the time, it fortunately survived. (I now have a surge protector of course.)--Shantavira|^{feed me} 08:23, 21 May 2007 (UTC)

Mythbusters tested quite a few of these: they found that having a shower was very dangerous (current passed from the shower, through the person, to the plug hole). Swimming could be dangerous; it depends where the lightning is relative to the drains of the pool (lightning always wants to flow to ground, and the metal drain pipes are the best route, so it will try to find a route to these drains, through people if necessary). Opening a wooden door is unlikely to be dangerous, as electricity will not want to flow through the door, but touching a metal door while standing on a metal surface (such as a metal fire-escape) could be very dangerous. Taking off clothes which produce static shouldn't attract lightning towards you at all; nor should lighting a candle or using magnets. Standing on top of a tall building would be incredibly dangerous though; you'd become a human lightning rod! Urinating would probably be safe, as although electricity can travel through urine, the stream tends to break up into individual droplets which cannot transmit 'leccy (as shown again by Mythbusters). Laïka 08:35, 21 May 2007 (UTC)

merging of storms

Hi. Is it possible for a very low-pressure storm, say, a tornado or hurricane, to merge with another one, if the two or more came really close? Would their low pressure centres cause them to come closer and merge, or would the speed at which they spin past each other cause them to fling each other away? Has this ever happened before? I know about an effect where hurricanes come close to each other and swirl around each other, and when a storm absorbs another, but I'm talking about when two storms like hurricanes or tornadoes or galaxies come very close together and of similar intensity collide nearly head-on at a steady, but not too rapid pace. Is it possible for them to merge and for their centres to collide? Also, if the Andromeda Galaxy collided with ours, wouldn't all the mass from the supermassive black holes, dark matter, orbiting satellite galaxies, and even M33 cause their centres to come together and merge, possibly exploding, and while it heads toward the Virgo cluster and the great attractor, could it cause other galaxies to fluctuate and merge, causing the supercluster to merge into itself? Thanks. -- AstroHurricane001^(T+C+U) 20:24, 20 May 2007 (UTC)

Yes - see 1991 Halloween Nor'easter (aka "The Perfect Storm") for example. SteveBaker 20:35, 20 May 2007 (UTC)

Why do magpies like metallic objects?

My grandma was telling me today about how a magpie stole her wedding ring, many years ago. She'd taken the it off to do the washing up and the bird flew down, put its head through an open window and boldly grabbed the ring from the windowsill.

What exactly is the deal with magpies and their obsession with shiny metal (the European Magpie article only touches on the subject briefly)? Why do they need it? What do they do with the stuff after they've collected it? --Kurt Shaped Box 21:21, 20 May 2007 (UTC)

I've heard they use shiny things to attract or look good in front of potential mates. "Hey look at all the shiny things I got, will you marry me?" Not so different from humans really. —Pengo 00:38, 21 May 2007 (UTC)

I don't think they need it as such, but (like a lot people) are just attracted by shiny things. Some birds, the bowerbird is a notable example, use brightly coloured objects to decorate their bowers and attempt to attract mates. I don't really know, but perhaps magpies put this shiny stuff in their nests and hope to attract mates - if it attracts one bird to take it, perhaps it could attract another bird, a potential mate, to the nest. --jjron 00:42, 21 May 2007 (UTC)

The concept of Bling may be effective across species. Why do humans need necklaces and earrings and various other bejewelled piercings? Edison 14:58, 21 May 2007 (UTC)

derivation for the moment of inertia of a sphere

Hi. I need a derivation using calculus of the moment of inertia for a solid sphere of uniform density (which is 2/5 MR^2). Only I need it so that the derivation doesn't require the knowledge of any other moments of inertia(such as a disk's or hollow sphere's). I'm in high school and understand math through BC calculus, so if you need to use more advanced stuff (which I think you do), try to quickly explain it please. Thanks. --71.185.134.107 21:30, 20 May 2007 (UTC)

I (a pure mathematician by inclination) have sufficiently forgotten physics that I can't readily do this. However, I can point you to this website, which looks ok, where the MoI of a sphere is derived from that of a disk (also explained on the site). If there's anything there you don't understand (BC calculus means nothing to me I'm afraid) then come back here and I'll try to help. Algebraist 22:07, 20 May 2007 (UTC)

Thanks, but what I meant by without knowldge of any other moments of inertia is that you don't even calculate other moments of inertia within the proof and this proof uses the MoI of a disk.

By the way, BC Calculus is basically the first year of calculus in college, except it's in high school.--71.185.134.107 22:28, 20 May 2007 (UTC)

Still lost, I'm afraid, you're talking to a parochial Englishman. So you aren't allowed to use other MoIs, even if proved. Why is that, anyway? I'll think about it (and try to find a pen :P); I suppose your best bet is just to bash out the integral. Algebraist 22:37, 20 May 2007 (UTC)

If I change co-ordinates to cylindrical polar co-ordinates and use the word Jacobian, will you understand that? Algebraist 22:54, 20 May 2007 (UTC)

I have solved the problem using cartesian co-ords alone. Due to the ghastliness of the expressions, I'm putting them on your talk page, not here. Algebraist 23:13, 20 May 2007 (UTC)

Hi. There's nothing on my talk page. As to what I understand, I understand the coordinates but I dont know the word Jacobian, but I supppose I'll click on that link.--71.185.134.107 23:17, 20 May 2007 (UTC)

After much texing, there is now. That (unless I've made a mistake) is a direct calculation of I in cartesian co-ords. It would be more sensible to transform into cylindrical co-ords (the integrals are somewhat nicer), which is more-or-less equivalent to using the moment of inertia of a thin disk. Algebraist 23:44, 20 May 2007 (UTC)

Thank you very much.--71.185.134.107 00:08, 21 May 2007 (UTC)

Alex Chiu - "Better living through the power of magnets"...

I'm fully aware that Alex Chiu and his magnetic healing theory is a laughing stock amongst the scientific community - but reading some of his stuff has left me a teeny bit curious. Has anyone ever actually tested his devices with an open mind and documented their findings in an unbiased, scientific manner? I can easily find lots of writings online, basically taking the piss out of the guy and calling him names - but little in the way of hard science. --Kurt Shaped Box 22:36, 20 May 2007 (UTC)

Nobody wants to waste their precious time or money in constructing a proper scientific test of the "magnetic healing theory". You, Kurt, can take the honor of being the first to do so. When you have done the experiment, do come back and report to us. Thank you. 202.168.50.40 22:59, 20 May 2007 (UTC)

I said I was curious - not that I was born yesterday... ;) --Kurt Shaped Box 23:10, 20 May 2007 (UTC)

I'd be interested to see a photo of him, since he claims his "gorgeouspil" (which he takes) makes people more beautiful than supermodels. He also claims to be able to reverse aging, cure herpes and cancer, and predict the future. Next thing you know, he'll claim he can win the war in Iraq. Clarityfiend 23:04, 20 May 2007 (UTC)

There's an interview with him here. I'm straight but I don't think he's necessarily a bad-looking looking bloke... :) According to this, he also apparently sleeps with his head beside an electromagnetic coil and has experimented with passing electrical currents through his bathwater. --Kurt Shaped Box 23:10, 20 May 2007 (UTC)

Apparently sleeping with your head next to an electromagnetic coil causes a particular type of brain damage which makes you think you can cure anything. :-) StuRat 23:45, 20 May 2007 (UTC)

Yeah, but is he more fab than Fabio? (too lazy to download) Clarityfiend 23:23, 20 May 2007 (UTC)

Since it's rather expensive to do legitimate scientific tests, I'd prefer that we spend that money on things with a higher probability of being legit, like herbs that have been used for generations for healing. I don't think all such herbs work, but I bet that some do. StuRat 23:49, 20 May 2007 (UTC)

We all know that's total malarky. Next think you know Stu will be telling us that mold extract can cure infections. Someguy1221 00:06, 21 May 2007 (UTC)

...or that willow tree bark can cure a headache. StuRat 00:23, 21 May 2007 (UTC)

Science isn't about taking a vast number of random, untested theories from people with no training and no scientific approach - and one-by-one disproving them (or perhaps once in a million times - finding they are true). Just read this help desk - we regularly get two or three perpetual motion machine ideas every week - despite the impossibility of perpetual motion being one of the most well proven things we have in science. That's a total waste of time and money for trained scientists. A far more productive use of time is to find things that are well known to actually work - which we don't understand - and to ask "Why?" - or to extrapolate from known knowledge into the unknown by probing the outer edges of our understanding. It's really, really well documented that magnets have almost zero effect on the human body. Millions of people have had CAT scans - the magnets on those things are insanely powerful - and they have absolutely zero documented effect on humans. We live in the earth's magnetic field 24:7 - no effect. We've had people live on the Moon for several days - far away from the Earth's magnetic field...no effect. It's simply a waste of everyone's time to investigate every crackpot idiot - especially since neither they nor their 'believers' are going be swayed by what your careful investigations prove. SteveBaker 00:12, 21 May 2007 (UTC)

If Chiu had an electromagnetic coil similar the ring around Uranus it might be easier for him to sleep with his head up it. Asking for research grant to replicate or refute his claims would do little to advance the career of a medical scientist. It might be worked into studies of the claimed detrimental effects of electromagnetic fields on human health. Maglev railways and even subways/elevated trains with a 600 volt DC third rail have large magnetic fields, so effects should be obvious on the conductors/motormen. I have seen offices where there was a large enough DC magnetic field to cause the image on a computer monitor to move halfway off the screen, due to a battery backup system on the other side of a concrete wall. Health effects on the workers? They did not know there even was a magnetic field at theor work location until they got a computer in the 1980's. Edison 14:52, 21 May 2007 (UTC)

My head's spinning...

What is a propeller spinner? Spinner says it's a propeller, but in Albatros D.III, it says "Austrian pilots often removed the propeller spinner from their planes, since it was prone to falling off." Clarityfiend 22:45, 20 May 2007 (UTC)

According to [10] it is A cone-shaped piece of an airplane, mounted on a propeller, which reduces air resistance, or drag. Here is an image of a propeller spinner for model airplanes: [11]. --mglg_(talk) 23:18, 20 May 2007 (UTC)

Looks like our Spinner page was wrong. Fixed. --Steve Summit (talk) 00:42, 21 May 2007 (UTC)

Perhaps the person who originally wrote that spent too much time under a Beanie, where one might actually refer to the entire propeller as a "spinner".

Atlant 13:06, 21 May 2007 (UTC)

Not to be confused with Spinner (porn industry), a term once applied to the tv character Ally McBeal on the eponymous show. Edison 14:43, 21 May 2007 (UTC)

When someone is cold = liquid snot. When someone is warm = solid boogers

Why??????? That makes no sense???--0rrAvenger 23:55, 20 May 2007 (UTC)

Just an educated guess really - if it's warm the warmer air being constantly inhaled and exhaled will evaporate more moisture out of the snot thus leaving it dryer and more solid. If it's cold, less evaporation, watery snot. --jjron 00:46, 21 May 2007 (UTC)

I don't agree, I've definitely had a runny nose in hot weather, and especially when eating hot soup I almost always get a runny nose, even if I don't have a cold. Vespine 01:21, 21 May 2007 (UTC)

If you're cold (and especially if you have a cold), your nose runs. No mystery there. The mucus is excreted in a runny state, and since it's being excreted voluminously, it runs right out of your nose. I think this is one component of the defense mechanism: as it runs out of your nose, it takes viruses and other pathogens with it.

But if (for whatever reason, like because it's a warm sunny day, and you're healthy) your nose isn't running very much, what little residual mucus it does contain has plenty of time to lose moisture and congeal. This is especially true when it isn't raining such that there's more dust in the air to get mixed in with the snot to form a nice conglomerate. (But I'm speculating, too; I don't know if this is the right answer.) --Steve Summit (talk) 01:21, 21 May 2007 (UTC)

I think we'd need to take some control over this 'experiment'. We need to take a person with the same runny nose, say with a cold, and put them somewhere warm and somewhere cold, then compare the composition of their snot. What Steve and Vespine are saying is fine, but lacks this control. Now, I seem to remember that my nose runs less when I have a cold if I go into a warm environment. I think that's what OrrAvenger was originally asking, why this was so. --jjron 02:54, 21 May 2007 (UTC)

Don't just mean to be contrary but actually, what I was trying to do is point out the fact that what OrrAvanger was saying lacks this control. Vespine 05:18, 21 May 2007 (UTC)

It doesn't necessarily lack the control, but exactly what he was asking is open to interpretation. As you interpret it, you are right that you can't just make a blanket statement about it. It seems a bit pointless to me to answer it like that though, which is why I say you need the controlled experiment. OrrAvenger could clarify the question a bit. --jjron 06:48, 21 May 2007 (UTC)

When I'm cold, my nose is runny. When I'm warm, my nose is stuffy. I don't know what else to say.--0rrAvenger 14:50, 21 May 2007 (UTC)

Rage Virus

Seeing as some chemicals (like in chocolate, which makes you feel good) can affect your emotions, is something like a Rage Virus as seen in 28 Days Later and 28 Weeks Later possible? --81.179.110.37 22:34, 20 May 2007 (UTC)

Rabies can make animals crazy, so I suppose it doesn't sound impossible. Vespine 00:06, 21 May 2007 (UTC)

Toxoplasmosis is a nasty disease, carried by a quarter of the population, which causes the infected to take risky behaviour; infected mice will become attracted to cat urine, while humans drive less responsibly[12], develop a lower IQ and become more promiscuous. Infected men become anti-social and angry, while women become outgoing and friendly. That's a huge change in a person's personality just from a common disease. Laïka 08:43, 21 May 2007 (UTC)

Ice cream in hospitals

Why do hospitals give out ice cream? Yes, it's particularly ice cream that patients get "as much as they want". Where does this come from? --88.193.241.224 19:08, 20 May 2007 (UTC)

[disclaimer: this is speculation on my part]

Why wouldn't they? Because it's "unhealthy"? But if hospitals served only (one definition of) the "healthiest" food, it might be boring and/or unpalatable to lots of patients. But patients need to be happy to get better, and they can't be happy if they're eating gruel. (I'm oversimplifying here, but I hope you get my point.) There's a tradeoff to be made between "healthy food" and comfort food, and it could be that someone decided that ice cream was comfortable enough, and not so unhealthy, that it could be provided. (Also, besides being a comfort food, ice cream is of course soothing to sore throats, which lots of hospital patients have for various reasons.) —Steve Summit (talk) 19:55, 20 May 2007 (UTC)

[P.S. With that said, a lot of hospitals serve pretty crappy food, not because it's healthy or unhealthy or comforting or grueling, but rather because they contract with the same sorts of food-service companies as other large institutions do, and with an institutional food-service company... well, you get what you get.]

One advantage of ice cream and a few other foods, like Jello, is that it quickly melts and becomes a liquid, making it far easier on a digestive system that may be impaired. Healthy food, with lots of roughage, is not so easy to digest. So, while healing, it makes sense to eat ice cream. Just make sure there isn't any Olestra in that ice cream. StuRat 23:17, 20 May 2007 (UTC)

I got as much ice cream as I wanted when my tonsils were removed. It was supposed to help the healing process. I have no idea, if this is a myth, but I was 6 and couldn't care less. ^^

Ice cream can also possibly numb pain, and is no way unhealthy. Just like Jello, patients need quickly metabolizable sugar, and ice cream has plenty. Also, everybody likes it! [Mac Δαvιs] ❖ 04:16, 21 May 2007 (UTC)

May 21

Resilience of light polarization

Does polarized light stay polarized when viewed through things? Specifically, I'm wondering about windows - both normal and frosted glass - and clouds. (I don't know if this question was answered in the polarization article or not -- it was too technical for me to understand.) CameoAppearance ^orate 00:08, 21 May 2007 (UTC)

Polarized light will rotate its polarization when passing through anything that qualifies as a wave plate due to birefringence. Also, when light passes through a transparent material, only some of the light will pass through and some will be reflected. How much is reflected/transmitted is dependent on the polarization of the light. At a certain angle (See Brewster's angle for more) this will actually result in only a single polarization passing through the material. So yes, if the sun and window are at the correct relative angle, only one polarization will actually reach your eyes (ignoring light that reflected off of other sources and then through the window). Someguy1221 00:14, 21 May 2007 (UTC)

Actually, this is also ignoring scattering in the atmosphere, the fact that the sun is not infinitely far away...You can see these effects very nicely if you're playing with a laser. Someguy1221 00:26, 21 May 2007 (UTC)

Or just a pair of polarized sunglasses. I've seen car windshields that look positively psychedelic, with rainbow colors and patterns from how the glass was prepared. —Keenan Pepper 05:18, 21 May 2007 (UTC)

I'm not sure if the above responses fully answer your question, CA. You wanted to know whether polarized light stays polarized after being reflected, scattered, transmitted, etc. The answer is, as usual, it depends. Firstly, some terminology. Polarized light includes the two extremes of linear polarization (where the electric field is fixed in direction but oscillates in magnitude) and circular polarization (where the field is fixed in magnitude but spins in direction), and all the cases of elliptical polarization in between. Any beam of light, polarized or unpolarized, can be considered as the combination of two components, linearly polarized in perpendicular directions (or equally validly, two circularly polarized components, left handed and right handed, but that may be a little harder to visualise). The distinction between polarized light and unpolarized light is that in polarized light, the two components are coherent with each other: their oscillations are correlated, and they have a constant phase difference. The actual value of the phase difference, in combination with the average magnitudes of the two components, determines the type of polarization and its orientation. In unpolarized light, the two components are independent, uncorrelated, randomly related.

If a beam of polarized light is reflected from or refracted through a smooth surface (smooth on the scale of a wavelength) then in general its components remain coherent, therefore it remains polarized, although its state of polarization may change, e.g. from linear to elliptical. If it is scattered from a rough surface or by a turbid medium, like clouds, then its components can be randomly altered in phase, making the beam unpolarized. So normal glass will not cause depolarization, but frosted glass may, depending on how dense or thick the frosting is. Clouds will depolarize the light if the droplets are large enough. Scattering from very small particles (Rayleigh scattering) will generally alter the state of polarization, but won't destroy it. Polarized light scattered from an ordinary cinema screen becomes depolarized, so to get 3-D movies to work, you have to use a silver screen. Sometimes the change in state of polarization depends on wavelength, which gives the startling colours and patterns seen in plastics between crossed polarizers (see photoelasticity), or car windscreens illuminated by partially polarized skylight and viewed through polarizing sunglasses. It's a fascinating and rich subject, which is why the polarization article may look a bit impenetrable. --Prophys 13:44, 21 May 2007 (UTC)

Energy and mass - Binding energy

This question is in relation to the earlier question energy loss = mass loss.

The first reply from Cody Pope says "...bond energy makes compounds lighter than the sum of their parts. When the bonds are broken this mass is expressed as energy in the form of light/heat...". The binding energy article does appear to say the same thing. I can see how this may be the case where the compound is formed in an exothermic reaction, but it doesn't seem to make sense when formed in an endothermic reaction.

If there is energy stored in the bonds, according to E = mc² shouldn't the mass be greater in the compound than the component parts, not less? If it was less, when the bonds are broken and energy is released (as stated earlier), further mass would be lost, and the component parts would have less mass than when they first formed the compound, ultimately meaning the elementary particles would have to lose rest mass.

Can someone explain this apparent anomaly please? --jjron 03:17, 21 May 2007 (UTC)

If you do a really accurate analysis of the energy levels of a molecule, there are no such things as bonds and it gets horribly, horribly difficult. Try to work with this premise: Every molecule (or atom, just any object) has a specific ground level energy. That energy includes everything, bounds, rest mass, internal stress, everything. It is a natural constant that can in principle be measured for any type of molecule by putting one molecule in the ground state on a scale and take the reading.

For any chemical reaction, take the sum of the energies for the old parts and compare it to the sum of the energies of the new parts. If the new parts are heavier, you have to add some form of energy to make the reaction happen. If the new parts are lighter, some form of energy needs to be removed.

Thanks for your answer, but it's not answering the question (or if it is, it's agreeing with what I said, which indicates a problem with the binding energy article and the answers to the earlier question). My quandary is that the binding energy article says:

• "A bound system has a lower potential energy than its constituent parts; this is what keeps the system together.", and
• "Because a bound system is at a lower energy level than its unbound constituents, its mass must be less than the total mass of its unbound constituents."

In other words, according to this, the mass of the bound system will always be less. That doesn't seem right to me (and also disagrees with what you're saying, which is that sometimes the products will be lighter and sometimes heavier). Can this be clarified? --jjron 04:55, 21 May 2007 (UTC)

The article seems correct to me. All bond breaking is endothermic. Give an example of a compound that you think has a positive-energy bond. —Keenan Pepper 05:16, 21 May 2007 (UTC)

Dihelium. Atoms bond to each other so they can sit in a nice potential well. You can smush two atoms together (not very technical, I know), and if they physically can't exist in a potential well (like two helium atoms) they'll never actually "bind." Molecules often break apart spontaneously and reform in a new form, with even less potential energy, but breaking the initial bonds always takes energy for any remotely stable compound. Someguy1221 06:32, 21 May 2007 (UTC)

Re Keenan. Take an exothermic reaction, such as regular combustion. Yes, you may need to add some energy to break the initial bonds, but overall the energy released is greater than that which you add to break the bonds. Now, energy (overall) has been released, which I would think according to E = mc² would suggest mass has been lost, but according to the statements above, mass will have been gained by the now unbound constituents. Can you explain where this is wrong? Am I misinterpreting terms like bound systems/unbound constituents? --jjron 07:27, 21 May 2007 (UTC)

Okay, let's look at combustion. You start with oxygen molecules (O2) and a hydrocarbon. You break the bonds between the carbon and hydrogen atoms in whatever you're burning, and you break the bonds between the oxygen atoms in the oxygen molecules. This is what takes energy, this is the activation energy. But wait, combustion isn't finished yet! These unbound oxygen and carbon and hydrogen atoms shuffle about and new bonds are created, giving you water (H2O) and carbon dioxide (CO2). Creating these new bonds gives out energy. In this case, creating these new bonds gives off more energy than was needed to break the old bonds, making this reaction exothermic. So you go from oxygen and a hydrocarbon, to oxygen atoms, carbon atoms and hydrogen atoms, to water and carbon dioxide. Both the reactants and the products have bonds. For an exothermic reastion, the products will have less energy in their bonds than the reactants. Skittle 15:51, 21 May 2007 (UTC)

Seeing imaginary colors

I just wrote Imaginary color, and I was going to add a section on the possibility of seeing them, but didn't because it would be nothing but OR. Is there some substance you can inject into your eye that chemically stimulates one kind of cone pigment much more than the other two? Or, for a less dangerous way of seeing imaginary colors, you could stare at a bright purple light to bleach out your red and blue pigments, and then immediately switch to a green light to see greener-than-green. Is there any literature on this subject? —Keenan Pepper 05:13, 21 May 2007 (UTC)

There is tetrachromacy. And you could always be missing a color receptor or two. Someguy1221 06:51, 21 May 2007 (UTC)

[ec] Yep, that's just what I was gonna say. --Cody.Pope 07:10, 21 May 2007 (UTC)

Some kinds of colorblindness is caused by the absence (or non-functioning) of red or blue detectors - those people would see these colors. SteveBaker 12:16, 21 May 2007 (UTC)

I have proposed merging the new article Imaginary color into Color vision. Please discuss the merger on the talk page of Color vision if you have interest in the matter. There does not appear to be a need to have a standalone article on imaginary colors. Imaginary supersaturated colors outside the CIE chromaticity diagram can be seen by staring at a saturated color until the receptors are fatigued, then staring at the complementary color. Do not inject anything into your eye. "Human Information Processing" by Peter Lindsay and Donald Norman, Academic Press, 1972 has a long section on this. Edison 14:35, 21 May 2007 (UTC)

I agree with Edison's suggestions. This material would fit well at color vision as a section. We can create a redirect. Nimur 14:52, 21 May 2007 (UTC)

Filter standard

To whom it may concerns I want to learn about Classification or Standard of dust filter media Would you please let me know Thanks in advance Quang TuanQuang Tuan 07:27, 21 May 2007 (UTC)

You might check the HEPA article... it discusses what qualifications are required to be labeled "high efficiency." [13] appears to be the official government regulatory and information website.Nimur 14:54, 21 May 2007 (UTC)

AUTOMOBILES...................HELP

I am asking again bcz i am not satisfied with earlier answers.

why the tractors have their rear wheels lager than front ones? if the answers are in terms of torque plz clearly state driving or resisting torque.(the engine gives constant torque and rpm)125.63.107.131 11:49, 21 May 2007 (UTC)

Also I.C. Engines will have more efficiency in winter or in summers?125.63.107.131 11:49, 21 May 2007 (UTC)

So far the helpdesk said:

• Tractors have big rear wheels so that the tractor doesn't get bogged down in deep mud and to avoid over-compacting the soil - the front wheels can be smaller because they aren't powered and most of the weight is on the rears anyway.
• Car engines burn more gas but are able to produce more horsepower in the winter than in the summer.

Those answers were both good - what else do you need to know - or what didn't you understand? SteveBaker 12:12, 21 May 2007 (UTC)

i don't know exactly, but it is related anyhow to torque? but no body is telling abt that(formatting fixed)

They clearly stated, it reduces torque. Please read the answers to questions you ask. -- Phoeba Wright^OBJECTION! 13:02, 21 May 2007 (UTC)

I think the confusion is about the meaning of torque. The "traction" of a tractor is the amount of force it can apply on the ground, at the area where its tyres contact the ground. This force, multiplied by the radius of the tractor wheel, equals the torque. So even though the engine has a constant torque and RPM, the force that it exerts on the ground depends on the radius of the driving wheel: the bigger the radius, the less force for the same torque. Yes, it is related to mechanical advantage. --Prophys 14:02, 21 May 2007 (UTC)

Expanding on Prophys' point, I think the key to the traction of a tractor is the use of lugged tyres. Those large ribs on the tyres provide a concentration of the normal (downward) force of the tractor's weight and allow the transference of a very large traction force (front-to-back force) to the earth without heaving large clods of dirt out and back behind the tractor. Smaller lugs (on smaller tyre) wouldn't work as well because there'd be less volume of soil over which to distribute the tractive force.

By comparison, the front tyres are smaller because they don't have any need to be big; they only have to be so big as to adequately support the weight of the front of the tractor and, has already been pointed out, the weight of the tractor is mostly on the driving wheels, not the steering wheels. This is no different than for over-the-road tractors which commonly have 8 driven wheels and only two steering wheels.

Atlant 15:43, 21 May 2007 (UTC)

Bucklling

what is the reason of buckling of structures?125.63.107.131 13:33, 21 May 2007 (UTC)

The article on Buckling explains it. -- Diletante 15:09, 21 May 2007 (UTC)

Others might say it was the illuminati, but I think such conspiracy theories are out of the mainstream (not to mention, riddled with factual inaccuracy and POV). Nimur 15:31, 21 May 2007 (UTC)

Moments

Can anyone explaing the concept of moments in physics and mathematics. Like second moment of area, third moment of mass etc? Thanks. And why are they called moments?

Have you checked moment (physics) and moment (mathematics)? --Kainaw ^(talk) 15:07, 21 May 2007 (UTC)

"The n-th moment of a distribution is the expected value of the n-th power of the deviations from a fixed value."[14].

It's an obscure etymology; a lot of words in physics, such as Action (physics), have evolved from historical meanings and are now fairly different from the modern meaning of the word. "Moment" has more to do (linguistically) with "momentum," though you shouldn't let this word-quibbling be any issue. From the physical standpoint, each moment is just a mathematical operation to describe an object.

The various moments are merely a way of constructing a more complete description of a function. Mathematicians have come up with many ways to approximate an entire description of an object (such as its density, which is a continuous function) into one or more numbers (such as its total mass, and its moment of inertia). This saves the headache of using large integrals at later stages of the problem by creating descriptive "constants" (which are the results of simpler integrals). Put another way - a continuous function has an infinite number of values ("density is defined for every point in space", while most problems are easily solved with simplifications ("total mass is 5 kilograms"). Computing higher-order moments allows as much complexity as you are willing to compute, without resorting to the continuous-function approach.

The definition of a moment is given at Moment (mathematics); a specific case of first-order moments is available at Moment (physics). Each of these can be thought of as a specific case of the more general kernel integral.

Hopefully this math has not scared you off... the purpose of computing such integrals is to reduce the amount of work in harder problems by defining continuous functions in terms of their moments. Nimur 15:08, 21 May 2007 (UTC)

Carbonic acid & stomach acid

Does drinking carbonated drinks lower the pH of stomach acid/bile?--69.118.235.97 14:52, 21 May 2007 (UTC)

Probably not much; if anything, it most likely dilutes the stomach acid. Of course, the system is not static - as soon as you ingest anything, the digestive system may begin to deliver additional digestive chemicals as a result of the stimulus. This would change the results dramatically as external reactants are added. I think you were probably asking about the restricted case, where no new stomach-acid is created. If you have access to a chemistry lab, you could easily perform a controlled experiment - simulate the gastric acid with a small amount of hydrochloric acid and add a small amount of carbonated beverage, and measure the pH change. Be sure to follow safe lab procedures and obtain permission if necessary. Nimur 15:13, 21 May 2007 (UTC)

This page gives the pH of several soft drinks. Coke, Pepsi, and a generic store brand cola are all reported at about 2.5; the remaining non-cola beverages range upward from there, though none have a pH higher than about 4. Our article on gastric acid ('stomach acid') puts the normal pH in the stomach at between 2 and 3. (Acid secreted by parietal cells in the stomach can be as concentrated as pH 0.8, but this is quickly diluted by liquid present even in the 'empty' stomach.)

So, cola beverages are at about the same pH as gastric juice. Adding cola to the stomach will leave the pH relatively unchanged, as it has the same hydrogen ion concentration. Other soft drinks may temporarily raise the pH, as they are less acidic than the colas. The stomach will compensate for this dilution by secreting more acid to restore the 'normal' low pH. TenOfAllTrades(talk) 15:35, 21 May 2007 (UTC)

Tension

Every once in a while I get a pulling feeling on the top of my head? ???Nick 15:55, 21 May 2007 (UTC)