Wikipedia:Reference desk/Archives/Science/2007 May 18

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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)