Wikipedia:Reference desk/Archives/Science/2008 June 2

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June 2

Battery Life in Hybrid Vehicles

Just how long can and do these batteries last? I know that all rechargeable batteries loose the ability to hold a charge over time, so this make me wonder how long the batteries that are used in hybrid vehicles can last. I've read some where that NiMH batteries have a lifespan of 400-600 charge cycles with Li-ion being around that number also, but I have no idea how true those numbers are. Any help would be appreciated. Deltacom1515 (talk) 00:19, 2 June 2008 (UTC)

Anything good here? Fribbler (talk) 00:44, 2 June 2008 (UTC)

I would surely hate to have to replace the batteries every year and a half, since they are a major part of the price of the car. Edison (talk) 00:32, 3 June 2008 (UTC)

The "hybrid drive" battery in the Toyota Prius is warranted for 100,000 miles. It's capable of this very long life because the drive management controller only cycles it over a very narrow range. IIRC, the battery cycles between 40% and 60% of its full-charge capability. The battery also has forced-air cooling so that it never faces extreme heat. I believe you can find back-up references for this information at some of the sites describing plug-in hybrid conversions for the Prius.

Atlant (talk)

100,000 miles is a lot, but my truck has close to 200,000 miles on it. I wonder how much it would cost to replace the batteries in a hybrid after they've "died."RedStateV (talk) 21:05, 3 June 2008 (UTC)

When I bought my Prius I asked about that, and they said about as much as a new transmission would in a non-hybrid, so, there you go. dcole (talk) 18:11, 5 June 2008 (UTC)

what is the three intrinsic property of a pure substance?

--24.78.51.208 (talk) 00:33, 2 June 2008 (UTC)

I'm not sure that you could say that there are exactly three intrinsic properties of a "pure substance", so this sounds like it's probably a homework question that expects you to look at your textbook, or your previous notes, to where you've been told three properties. However, a look at chemical substance may offer a little assistance. Confusing Manifestation(Say hi!) 00:41, 2 June 2008 (UTC)

infact that's in review booklet and the question is which isn't a intrinsic property..a)densiy.b)color.c)Melting point.d)boilling point

i cant find answer for it--24.78.51.208 (talk) 02:17, 2 June 2008 (UTC)

Ask yourself this; which of those properties are you able to change? That's the one that isn't intrinsic. Also, don't think about it too deep - it's not that kind of question. SpinningSpark 02:29, 2 June 2008 (UTC)

See Intensive_and_extensive_properties). --Bowlhover (talk) 03:34, 2 June 2008 (UTC)

I think you may have confused him more Spinningspark.. (you confused me more). This appears to be a very poor question as all four of these can be changed by simple modifications of the system, but maybe, as you said, I am thinking about it too hard. So...I think it is Density as you just need to change the temperature to change this...that being said the other three properties can be easily modified.--Shniken1 (talk) 04:09, 2 June 2008 (UTC)

No, it's not density. You are right though, it is a rubbish question and my answer was possibly not much better, my excuse is I was trying not to directly answer a homework question. The article found by Bowlover explains it better. An intrinsic property does not depend on the amount of the substance so it is not density - that remains the same however much there is of it. SpinningSpark 04:39, 2 June 2008 (UTC)

I don't think an "intensive property" is the same as an "intrinsic property". If you think about it, even the boiling and freezing points require a certain quantity to measure, as those terms are rather undefined for a single molecule. I'd say the answer they are fishing for is indeed density, as that can be changed easily for materials in a gaseous form, simply by adding or subtracting some from the container, or by changing the temperature for a liquid or a solid. Changing the pressure will also change the boiling and melting temps, but those can't be the answer as the same logic would apply to both, and we're only looking for one answer. StuRat (talk) 16:36, 2 June 2008 (UTC)

Yes, density is easily changed with temperature. However, color can also change, e.g. sulfur, which turns red when heated above 200 C; there are probably special cases, but density is easily changed in any element that undergoes thermal expansion. Nimur (talk) 16:44, 2 June 2008 (UTC)

I agree that the question is total crap (can we give the teacher a failing grade ?), but I still think they are going for density. StuRat (talk) 20:46, 2 June 2008 (UTC)

? [1]--76.111.32.200 (talk) 15:29, 3 June 2008 (UTC)

Going back to the question, it states for a pure substance. A well known quick and easy test to find out the purity of a substance is to measure the melting temperature and perhaps this is where the question was leading to? Jdrewitt (talk) 15:40, 3 June 2008 (UTC)

I'm going to go out on a limb, and say that the correct answer is whatever three properties the book or lecturer listed when the topic was presented. -- Coneslayer (talk) 15:48, 3 June 2008 (UTC)

—Of the four properties mentioned (density, color, melting point, and boiling point), color stands out as the most likely intended answer. The apparent color of a substance depends on the illuminant. Two substances displaying the same color under one illuminant may look very different under a different illuminant.

This question looks like it is from some high school/secondary school level study material. Unfortunately, it happens all too often that the person attempting to answer the question has more insight than the person writing the question had or expected. When dealing with questions like that, it's often helpful to think about fact/principle the question writer is trying to test the student on, and scale back the level of analysis appropriately. --71.162.249.251 (talk) 14:46, 7 June 2008 (UTC)

If stars can't fuse past iron...

How did we get heavier elements than iron in our universe? 24.46.50.159 (talk) 01:39, 2 June 2008 (UTC)

They get generated in supernovae, if I remember correctly. -mattbuck (Talk) 01:51, 2 June 2008 (UTC)

(ec) See Supernova#Source_of_heavy_elements. --Milkbreath (talk) 01:52, 2 June 2008 (UTC)

So it means that the solar system was created out of an earlier supernova due to the number of heavy metals found here?--Lenticel ^(talk) 01:57, 2 June 2008 (UTC)

At least one. The common opinion is that at least some of the material on earth must have gone through more than one supernova to account for the relative abundances of elements. SpinningSpark 02:23, 2 June 2008 (UTC)

Note, however, that planets, and terrestrial planets in particular, manage to filter out most of the lighter elements and leave a highly disproportional amount of heavy elements. So, while our solar system is 99% hydrogen and helium, most of the hydrogen and helium on Earth and the other terrestrial planets has bled off into space, by rising to the upper atmosphere and being blown away by the solar wind. StuRat (talk) 16:26, 2 June 2008 (UTC)

liquid water versus water

I was watching a history channel documentary on the universe and a scientist kept talking about "liquid water". My family was mocking him for not just saying "water", but as the documentary went on we discovered all the scientists in it used the term. Why? What is different between water and liquid water? thanks experts. 64.231.202.9 (talk) 01:42, 2 June 2008 (UTC)

Well, it's about being precise. In scientific terms, water refers to the molecule H₂O. In common terms, water refers to the stuff that comes out of your tap. To a scientist, this is liquid water. This distinguishes it from ice (solid water), as ice can be the solid form of many different compounds (dry ice for example); and also from steam (water vapour) as steam can again refer to the gaseous state of many different compounds. -mattbuck (Talk) 01:50, 2 June 2008 (UTC)

Also, since the documentary was on the Universe, the scientists may have been referring to environments in which water won't necessarily be liquid. Zain Ebrahim (talk) 01:56, 2 June 2008 (UTC)

Yes, we scientists (I rather like saying that) use the term "liquid water" to distinguish between liquid water, solid water, and gaseous water. – ClockworkSoul 02:51, 2 June 2008 (UTC)

I use the scientific terms as well, but often get laughed at by those who simply call them "water", "ice", and "steam". StuRat (talk) 16:21, 2 June 2008 (UTC)

Just as an additional point gaseous water or water vapor may be preferable to steam due to popular confusion with mist formed by the condensation of water vapor formed by boiling. Thomashauk (talk) 19:39, 8 June 2008 (UTC)

Very strange pigeon picture....

WTF?

Just discovered this odd pigeon image whilst browsing. Does it look like a photoshop job to anyone else here? The position of the head looks completely anatomically impossible, to the extent that I was unable to even parse the content at first... --Kurt Shaped Box (talk) 01:48, 2 June 2008 (UTC)

Unless these two pictures and others from google images are all shopped, I think they might actually be real. The necks of these pigeons do seem pretty long, even though it still looks anatomically wrong to me with that knowledge. Guess their necks are just really flexible. (addendum) Found this and this image too, the latter makes me think that it's all the more likely it's possible, but maybe the patterns on the grey ones make it look like it's in a weirder position than it really is. --Wirbelwindヴィルヴェルヴィント (talk) 02:15, 2 June 2008 (UTC)

I suppose it's the pigeon equivalent of a human being able to touch his buttocks and the back of his head together. That said, some humans *can* do that. Maybe these birds were selectively bred - specifically so they could pose like that? Can't see the point myself, but those selective breeders do seem to like the weird and wonderful... --Kurt Shaped Box (talk) 02:32, 2 June 2008 (UTC)

Well, from what I can gather, "modern" fantail pigeons are the ones featured in these pictures, so I would guess also that it's selective breeding. --Wirbelwindヴィルヴェルヴィント (talk) 02:37, 2 June 2008 (UTC)

Yep. A lot of people just don't seem satisfied with normal pigeons. [2] --Allen (talk) 04:07, 2 June 2008 (UTC)

Given the taste of Bride of Wildenstein it's not surprising, since people often aren't satisfied with normal people either. Julia Rossi (talk)

It was quite popular in England in the 19th century to breed all sorts of bizarre and strange looking pigeons (it still is today, to a much lesser extent). Pigeon fancy was one of the many inspirations for Charles Darwin when thinking about the plasticity of heredity. That particular one just has a huge tail, and a ridiculously huge, puffed-up chest. It is "not natural" in the sense that the appearance did not evolve that way in the wild, it is a human intervention to make funny looking birds. --98.217.8.46 (talk) 15:52, 2 June 2008 (UTC)

This does not look at all strange to me. Many birds have a great range of motion in the neck. The pictured posture would be a typical mating display for a number of species, e.g. grouse. 67.131.66.162 (talk) 22:40, 2 June 2008 (UTC)

It might just be the angle of the picture and/or this bird's particular markings but it looks to me as though the head is sat at 90 degrees to the neck in that image. Are they really *that* flexible? --Kurt Shaped Box (talk) 17:57, 3 June 2008 (UTC)

redox

Okay, so I'm having a bit of trouble understanding the whole redox thing. Here's the question I'm supposed to be answering:

If copper wire is placed in AgNO₃(aq).

a. Which element is going to try to lose electrons?

Copper

b. Write the redox equation between copper and silver

Cu + AgNO₃ → Ag⁺ + CuNO₃

c. What is the net voltage for this reaction?

.28V

d. Is copper wire the anode or cathode?

anode

So I'm wondering how well I did, thanks for the help! --71.117.35.118 (talk) 04:39, 2 June 2008 (UTC)

Now, I'll have to say that this definitely smacks of a homework question. Wisdom89 _{(T / ^C)} 04:57, 2 June 2008 (UTC)

Well at least he made an effort in answering the questions.--Lenticel ^(talk) 05:07, 2 June 2008 (UTC)

It could be just a typo, but in part b., your equation violates charge conservation. —Keenan Pepper 05:18, 2 June 2008 (UTC)

Who cares if this is a homework question? They've made an effort and they're struggling so they want some help, that's absolutely fine. At least they made the effort. As Keenan said, your second part violates charge conservation but I think you just missed the + off the initial Cu. Regards, CycloneNimrod ^talk?_contribs? 10:45, 2 June 2008 (UTC)

Nope, changing Cu to Cu⁺ does not make the equation correct. That's solid Cu in that wire, with no other elements involved, so it must be neutral. Something else must be involved to balance the charge... —Keenan Pepper 18:41, 2 June 2008 (UTC)

So if I took out the positive charge of the silver so it would just be neutral would I have gotten all of the problems right? --71.98.15.188 (talk) 03:32, 3 June 2008 (UTC)

measuring fecundity

This line appears in Niall of the Nine Hostages:

In January 2006, scientists suggested that Niall may have been the most fecund male in Irish history, and second only to Genghis Khan worldwide.

They get this distinction not so much by fathering numerous children themselves (Niall is said to have had at least eight sons, which is remarkable but hardly record-setting) as through their later descendants. But then what about their fathers? Is there a way of weighting generations such that one can meaningfully say "This guy, this is the one who gets most of the credit for founding a proliferative lineage"? —Tamfang (talk) 05:29, 2 June 2008 (UTC)

I believe he's called Y-chromosomal Adam. 67.68.34.26 (talk) 09:41, 2 June 2008 (UTC)

...who lived long before Niall and Genghis. Thank you for playing. —Tamfang (talk) 19:30, 2 June 2008 (UTC)

Could it be that Niall and his father have the same amount of living descendants but Niall is a generation more recent? The only alternative that makes any logical sense to me is that Niall's father isn't a "male in Irish History". Stanstaple (talk) 12:50, 2 June 2008 (UTC)

Compressed hydrogen car

A disadvantage of hydrogen is that transportation requires compression/cooling, resulting in low efficiency. But can't this energy be won back? For example, like in a compressed air car, the pressure could be used to drive the pistons or a quasiturbine or whatever (or the wheels directly, as done by K'airmobiles). I don't know how risky it would be to use hydrogen in such a mechanical manner. (Such as sparks. Maybe use plastic parts for the mechanism?) Alternatively, instead of the pressure-difference with the surroundings, the temperature-difference could be used to generate energy, although I believe that can't be done very efficiently. What is the name for that technology again? DirkvdM (talk) 07:21, 2 June 2008 (UTC)

You could possibly get something back from those methods, but the question is whether hauling around the weight of the equipment to do so incurs more of a cost than the benefit. I would guess that it would. The one exception that comes to mind is using cooled liquid hydrogen to air condition the car. The advantage here would be that this method would replace the mechanical compressor and Freon system used currently, and quite possibly reduce the car's weight rather than increase it. Compressed hydrogen could also be used, as it provides quite a bit of cooling when decompressed. StuRat (talk) 16:15, 2 June 2008 (UTC)

It is true that there is mechanical energy which could be extracted from compressed Hydrogen. However, I think it would be a bad idea to use hydrogen for any sort of pneumatic system. It is highly flammable, and the probability of disaster would be significant. It's not a matter of "how risky" in absolute terms, it's "how risky relative to the alternative" (which would be, use any other thing except hydrogen in these systems). Putting flammable materials into a pneumatic system is tantamount to confining an explosive charge - should anything go wrong, the contained gases would pressurize the chamber, and firey metal fragments would fly everywhere - it would not be a good idea. Imagine using gasoline as brake fluid! It can be done, but it's far more dangerous than any alternative. Nimur (talk) 16:52, 2 June 2008 (UTC)

Yeah, I already mentioned the risk, but any risk can be dealt with (hell, nuclear energy is even being used all around the world and millions of people die in car accidents, and that doesn't stop us from driving cars). If the advantage is big enough, that is, and that is what I am asking this for. One of the main (principal) advantages of hydrogen is transportation, which requires compression/cooling and thus causes energy loss. So solving that could have big enough advantages that someone else will come up with a safer system. Let's take this one step at a time. :) DirkvdM (talk) 17:12, 2 June 2008 (UTC)

I agree with Dirk here. Sure "confining an explosive charge" is potentially dangerous, but that's the basic concept behind the internal combustion engine, after all, so it certainly can be done safely. Also note that hydrogen is only explosive once mixed with oxygen, before then it could absorb a lightning strike and not combust. StuRat (talk) 20:34, 2 June 2008 (UTC)

StuRat, I'm not talking about an add-on to existing cars, which would increase the weight. The original idea is to have a hydrogen powered car and then adapt that to use the cold/pressure, but you could also look at it the other way around. A compressed air car is so light that that is actually named as one of the disadvantages in the article. So the question then becomes if adding the hydrogen sytem would not negatively affect the car's performance through weight. But of course if either system works, then the combination should too.

But the main thing that is bugging me is what method might be used to make use of the cold. Or rather the heat difference between the tank and its surroundings. That represents energy, but I have no idea how to make use of that (other than for airco). Something that uses a heat pump would probably be way to heavy for a car. DirkvdM (talk) 17:12, 2 June 2008 (UTC)

I don't quite understand. If a car has weight X and only has equipment to utilize the burning of hydrogen, and you then add components to allow it to also take advantage of the pressure and/or cold of the hydrogen gas, then you're adding weight to the vehicle (unless you can remove something as heavy or heavier, like the A/C compressor and refrigerant storage system). This same logic applies whether the additional equipment is added after-market or at the factory. StuRat (talk) 20:30, 2 June 2008 (UTC)

No I'm sorry, I was thinking you meant adding something to an already designed car. I'm talking about a completely new design. But yeah, unless the two technologies share some part(s), the combination will mean an increase in weight. DirkvdM (talk) 06:32, 3 June 2008 (UTC)

Are you thinking of a Stirling engine? This would efficiently exploit a temperature differential to do work; but as the article notes, there are some disadvantages including the weight of heat exchangers. I imagine a Stirling engine which used liquid hydrogen to chill the cold section of the engine, then burned the hydrogen to warm the hot section, would be very efficient. For pressurized hydrogen, the tank pressure would seem to eliminate the need for a separate fuel pump; further, if the pressure is much higher than is needed to admit fuel to the prime mover, perhaps it could power a turbine or piston in series with the prime mover? And that in turn could compress the incoming air to the engine, a tank powered supercharger, if you will. I agree with other comments that using compressed hydrogen as a sort of general purpose pneumatic system would be too dangerous; you would want the system to be closely integrated with the engine casing for safety, either having the prime mover directly exploit a pressure/temperature differential, or having an auxillary unit closely attached, as a supercharger or turbocharger would be on a conventional engine. Fletcher (talk) 14:04, 5 June 2008 (UTC)

Number one exporter of potassium

Now, we all know that according to Borat, Kazakhstan was the "number one potassium exporter in the world". But that isn't, I believe, true. Nor is it true that "all other countries have inferior potassium". So here is my question, as I cannot find the answer in the potassium article. Which country is the number one potassium exporter in the world? Based on potash (potassium carbonate), the biggest company is the Potash Corporation of Saskatchewan, so that would be Canada. But is potash the primary source of potassium? What about potassium chloride, potassium oxide or potassium hydroxide, all of which are used in fertilizers? A bit random, but I even thought of bananas - they have a very high potassium content. I did the math, and India (#1 producer of bananas - 16.8 million tons of bananas produced in 2005, at 358mg of potassium per 100g) produces 60,200 tons of potassium per year via bananas. I'm not sure if this is even close to the weight of potassium in fertilizers. Anyone know the answer? Who is number one potassium exporter in the world? Neıl 龱 15:38, 2 June 2008 (UTC)

I would be quite surprised if bananas are worth more for their extracted potassium than as food. Are you asking who produces the most potassium sold as such, or are you including potassium found in other products ? StuRat (talk) 16:02, 2 June 2008 (UTC)

(after edcon)I'd say if you want to include potassium inside plants and animals it gets rather extensive. Potassium is an electrolyte essential for both plants and animals. So if you count bananas you'd have to look at all the other foods, too. e.g. [3] Just an example: although soybean only contain 149 mg potassium /100g, the US reported exports of 4.36 million tonnes [4] for just one week. Add to that exports in meat, rice and other foods. You'd then have to do that for all major exporters. Next you'd have to add compounds [Category:Potassium compounds] and again products that contain those, like e.g. toothpaste and softdrinks. Good luck.Lisa4edit (talk) 16:32, 2 June 2008 (UTC)

As a matter of interest, how exactly would you go about extracting potassium in elemental form from bananas? --Kurt Shaped Box (talk) 17:52, 2 June 2008 (UTC)

The traditional way, I think, would be to burn them to make potash (potassium carbonate), boil that with slaked lime (calcium hydroxide) to make potash lye (potassium hydroxide), then electrolyse that to get potassium metal. But there probably isn't a huge demand for potassium metal, so you might be better off leaving it at the potash stage to make fertiliser. --Heron (talk) 18:49, 2 June 2008 (UTC)

I think sales of potassium metal itself are very low, given it's highly reactive with water (so that wouldn't be the answer - it's almost always sold as a compound). I also have a feeling I've taken on too much if I include foodstuffs etc. I'm going to make my life easier, and stick with potash, and Canada. Thank you for your help, though, guys. Neıl 龱 08:39, 3 June 2008 (UTC)

DREAMS

why do we dream? I have read that dreams occur due to the memories that had been stored in our brain during sleep. but i need a clear cut idea —Preceding unsigned comment added by Pinni smart (talk • contribs) 16:00, 2 June 2008 (UTC)

I don't think we know for sure. There have been many theories:

1) They are "random firings of nerve cells" while we're asleep.

2) They are a method for us to review what we've done and come up with better strategies for dealing with similar situations in the future. (I like this idea.)

3) They are attempts by our subconcious to communicate with our concious minds. (Sigmund Fraud loved this idea.)

4) They are attempts by God/the gods to communicate with us. StuRat (talk) 16:07, 2 June 2008 (UTC)

Check out Dream#Dream_theories. --98.217.8.46 (talk) 16:15, 2 June 2008 (UTC)

Maybe because 'directed thinking' (as described by Carl Jung) is tiring. Somehow dreaming recharges our batteries, so to speak. Em3ryguy (talk) 17:53, 2 June 2008 (UTC)

Yeah, this question has caused people problems for ages. Although REM sleep has been identified as "recharging" as Em3ryguy put it, it's just as likely that dreams are jsut a werid side effect of REM-sleep. We have no way of knowing for sure if the dreams themselves have a recuperative effect. One theory that hasn't been posted yet is the behaviorist answer: "Dreams are just a propensity to tel funny stories immediately after waking." --Shaggorama (talk) 05:09, 4 June 2008 (UTC)

Here is a document on the importance of rem sleep http://www.psychlotron.org.uk/resources/sleep/AQA_A2_sleep_deprivationstudies.pdf

Here is the same article in html http://209.85.173.104/search?q=cache:93gvQl7J9qkJ:www.psychlotron.org.uk/resources/sleep/AQA_A2_sleep_deprivationstudies.pdf Em3ryguy (talk) 13:03, 4 June 2008 (UTC)

Burr oak

I posted a question concerning burr oaks last week and it is no longer posted. What happened???129.112.109.252 (talk) 16:33, 2 June 2008 (UTC)

What's your question? If it asked for medical or other advice it might have been deleted.Lisa4edit (talk) 16:37, 2 June 2008 (UTC)

After a week, questions are moved to the Archives. -- Coneslayer (talk) 16:44, 2 June 2008 (UTC)

Your edit history shows no such question, although you might have a varying ISP number. By all means ask again.--Shantavira|^{feed me} 16:49, 2 June 2008 (UTC)

Might want to look at burr wood. Ziggy Sawdust 18:55, 2 June 2008 (UTC)

Bur oak?--Lisa4edit (talk) 19:03, 2 June 2008 (UTC)

thin film book

i need book about thin film, how can i find thin film book? —Preceding unsigned comment added by More55 (talk • contribs) 17:26, 2 June 2008 (UTC)

Have you tried an on-line bookshop? Amazon has plenty of titles with "thin film".--Shantavira|^{feed me} 07:11, 3 June 2008 (UTC)

You did not by any chance mean books captured on microfilm or microfiche? The article has some links at the bottom, but I don't know if they'd be helpful to you. --76.111.32.200 (talk) 21:22, 3 June 2008 (UTC)

Nutritional information Aquafina Alive Satisfy water - specifically, what substance is the fiber?

This product states it has 3 grams of dietary fiber per 8 ounce serving. Reading the ingredients on the Pepsi website states exactly what the label on the bottle states....nothing that I can identify as being the substance that is the "fiber" in this water. I know that there are some types of seed husks that are used in Metamucil and the like.

What is in this water that is considered to be fiber?

--Dbacksfanbrian (talk) 17:53, 2 June 2008 (UTC)

Looking at the ingredients list from this site, the only ingredient listed that might contain dietary fiber is the NATURAL FLAVOR. Everything else is water, sugar, and assorted small-molecule chemicals. I'd say it's likely that those 'natural flavors' include some sort of pureed fiber source. I couldn't tell you what that was, however. TenOfAllTrades(talk) 18:56, 2 June 2008 (UTC)

Maltodextrin is considered a "dietary fiber" apparently. Lisa4edit (talk) 18:59, 2 June 2008 (UTC)

I did review the ingredient list from the PepsiCo website. I never imagined that maltodextrin could be considered "fiber". I know it's used in a lot of candy, likely for the same purpose as it serves in pharmaceuticals...as a binder. I guess I struggle with calling something "fiber" just because it isn't digestible. Thank you for answering the question. I wonder if the FDA considers it to be fiber! Thanks again! --Dbacksfanbrian (talk) 13:18, 3 June 2008 (UTC)

Propeller aeroplane under water

If a propeller aeroplane is made waterproof, will it work under water? What are the issues involved? --Masatran (talk) 18:20, 2 June 2008 (UTC)

Submarine what would be the difference? What changes do you propose? Lisa4edit (talk) 18:48, 2 June 2008 (UTC)

Do the gear ratio of the motor of the propeller, etc. have to be adjusted? If yes, how? --Masatran (talk) 18:55, 2 June 2008 (UTC)

Water is a heck of a lot thicker (more viscous) than air. If you start trying to spin an airplane prop at its normal speed, it will cavitate for a little while – if you're very lucky – and then snap off. TenOfAllTrades(talk) 18:58, 2 June 2008 (UTC)

Yea, it wouldn't work well. For water you need a shorter, thicker, slower prop than for air. I suppose you could run an airplane prop extremely slowly (less than one rev per second), and get some propulsion under water, but you would do better to have a separate prop for underwater use. Another issue is cooling, as airplane engines will commonly be air-cooled and won't tolerate being submerged in water. The wings will also provide a lot of drag under water. Finally, an airplane is way too light to submerge in water, it would float until it fills with water, then it would sink. So, this idea really won't work. However, an airplane that would operate on (or just above) the surface of the water could work well, as a ground effects aircraft. StuRat (talk) 20:17, 2 June 2008 (UTC)

Normal airplane engines work by burning fuel and therefore require an oxygen supply, which is in the form of air. See Submarine#Propulsion for discussion of underwater power supplies. --Anon, 16:50 UTC, June 2, 2008.

If the pitch of the propellor were adjusted (many modern planes have adjustable pitch) and the speed of rotation were reduced, to compensate for the higher density of water, and the wings were folded in somewhat for similar reasons, and compartments were flooded to decrease bouyancy, and the craft had a passenger compartment which could withstand the pressure of the water, and the propulsion system could switch over to battery (or other non air breathing technology) then it should be do-able, at least sufficiently for plausibility in a Jules Verne or Saturday Morning Cartoon type of fiction. Fluid is fluid. I'm relatively sure I saw something like this in a movie in the last ten years. Edison (talk) 00:29, 3 June 2008 (UTC)

Probably Sky Captain and the World of Tomorrow. 24.2.176.64 (talk) 01:16, 3 June 2008 (UTC)

Mercury poisoning

If there were a liquid metal other than Mercury, would it also be poisonous? --Masatran (talk) 18:31, 2 June 2008 (UTC)

No, that's not a logical conclusion. For example, Gallium melts in the hand and it is non-toxic. Mercury has a low melting point, and it also happens to be toxic, but those two facts are independent and not logically connected. —Keenan Pepper 18:44, 2 June 2008 (UTC)

Does Gallium conduct electricity? If not: Are all liquids that conduct electricity poisonous? --Masatran (talk) 18:50, 2 June 2008 (UTC)

Salt water conducts reasonably well. It depends on your application. How conductive do you need it to be? APL (talk) 19:34, 2 June 2008 (UTC)

I'm not sure where you got this idea that liquid metals relate to toxicity but it's not the case. Toxicity depends on what your body does with it (or often doesn't do with it). For example, water is a liquid and it conducts electricity, but it is not poisonous. As for metals, there are several metallic ions there which are not poisonous (at least in the correct quantities). Regards, CycloneNimrod ^talk?_contribs? 19:36, 2 June 2008 (UTC)

Ahem. Water is an excellent insulator. --Milkbreath (talk) 21:46, 2 June 2008 (UTC)

I know. That's why I said salt water. -- APL —Preceding unsigned comment added by 24.2.176.64 (talk) 01:15, 3 June 2008 (UTC)

I know you know. That's why I appended to Cyclonenim's thing. Now we all know. --Milkbreath (talk) 01:37, 3 June 2008 (UTC)

Oh yea, I didn't notice that Cylconenim mentioned water. Sorry. -- APL —Preceding unsigned comment added by 24.2.176.64 (talk) 02:59, 3 June 2008 (UTC)

No prob, Bob. --Milkbreath (talk) 03:03, 3 June 2008 (UTC)

The OP seems to be committing the illicit minor fallacy. All A is B, all A is C, therefore all C is B - where A = mercury, B = toxic and C = liquid metal (or conductive liquids in his/hers second post). --Mark PEA (talk) 19:47, 2 June 2008 (UTC)

(ec) I don't know about gallium specifically, but most metals do conduct electricity. (Because they are held together with metallic bonds, where electrons are only loosely-held.) To get to the real meat of your question, though, you want to know "Why is mercury toxic?" I'm sorry I don't have a reference, but as I understand it, mercury poisoning is due mainly to the fact that mercury is not readily excreted (it bioaccumulates). This causes problems because mercury likes to bind to sulfur atoms, and sulfur atoms are a vital component to the activity of a number of proteins (e.g cysteine proteases). -- 128.104.112.147 (talk) 19:47, 2 June 2008 (UTC)

OK, I'll be the bad guy this time. Both "poisonous" and "conductive" are relative terms. Everything is poisonous at a certain dosage, and everything is conductive given enough voltage. I know that sounds like I'm just trying to be a jerk, but if you want good answers on the Science Desk, you've got to ask good questions. To try to answer, no, not all liquids that are good conductors of electricity are dangerous poisons, and neither are all metals that are liquid at temeratures that the human body can tolerate well. --Milkbreath (talk) 19:51, 2 June 2008 (UTC)

Liquid mercury is not very toxic at all. Liquid mecury is not readily absorbed into the body. From Mercury poisoning:

”Cases of systemic toxicity from accidental swallowing are rare, and attempted suicide via intravenous injection does not appear to result in systemic toxicity“

...

In humans, approximately 80% of inhaled mercury vapour is absorbed via the respiratory tract where it enters the circulatory system and is distributed throughout the body.[17] Chronic exposure by inhalation, even at low concentrations in the range 0.7–42 μg/m3, has been shown in case control studies to cause effects such as tremors, impaired cognitive skills, and sleep disturbance in workers

The vapour is toxic but not the liquid, this is essentially because of the relative reactivities of the two.Shniken1 (talk) 04:45, 3 June 2008 (UTC)

Keep in mind that organometallic, or other liquid/solvable forms of mercury, can be extremely toxic (see dimethylmercury). Someguy1221 (talk) 04:48, 3 June 2008 (UTC)

Toy helicopter

I want to buy a toy helicopter to get an understanding of aircraft. Is there any inexpensive model that has a control to fly forward? I am looking at Apache Havoc but I don't think it can fly forward. --Masatran (talk) 18:46, 2 June 2008 (UTC)

If you're looking for an understanding of aircraft broadly, then a helicopter isn't really a good choice -- that's a much more specific form of aircraft based on different principles. I'm afraid I can't advise regarding selection of an r/c copter if that's what you want to continue with. I will note that weighting the nose of a very cheap rc copter will tend to cause it to fly forward, though I doubt this constitutes the control you want. — Lomn 19:09, 2 June 2008 (UTC)

Here, for example, is a r/c copter with forward flight control -- but said forward flight is accomplished by pusher propellors, not the standard means of helicopter propulsion (again falling afoul of your "understanding of aircraft" criteria). — Lomn 19:16, 2 June 2008 (UTC) —Preceding unsigned comment added by Lomn (talk • contribs)

journal article without subscription

I am trying to access an article from a journal to which my university (u of oregon) does not subscribe. Our library also does not stock the print edition of this journal for any newer dates than 1988, so my only option is an inter-library loan and this usually takes over a week. I need the article sooner than that for a presentation, so I was hoping that someone here might be able to access it and provide it somehow.

The article is titled "The Redfield equation in condensed-phase quantum dynamics" by Pollard and Friesner, Adv. Chem. Phys. 1996

The article is cited by every other article I've been reading so I'd like to go directly to the source. My apologies if this request is a breach of wikipedia guidelines. Man It's So Loud In Here (talk) 19:17, 2 June 2008 (UTC)

I think it would probably breach copyright in some way to comply with your request, so I'd advise you to buy the article instead. Regards, CycloneNimrod ^talk?_contribs? 19:33, 2 June 2008 (UTC)

As helpful as the above suggestion is, I'd like to think there is some site on the web where people do fulfill requests such as this one. Does anyone know of such a site? Man It's So Loud In Here (talk) 19:57, 2 June 2008 (UTC)

A helpful hint would not be posting such requests on very public boards such as this one. I'd consider asking elsewhere. Sorry I could not be more illegalhelpful. Regards, CycloneNimrod ^talk?_contribs? 20:51, 2 June 2008 (UTC)

Perhaps if you were to write the author(s) directly, they could get a slave post-doc to send you a copy? Here's one of them. --Sean 22:01, 2 June 2008 (UTC)

Thank you very much for your help, I think that that will work very well. I just didn't see paying $30 as a viable option. If someone would like to delete this section, that would be fine with me. Man It's So Loud In Here (talk) 22:14, 2 June 2008 (UTC)

You can also try Wikipedia:WikiProject Resource Exchange, either posting to the requests page or asking one of the members. You can count me out though, as I don't have a subscription to that series. Someguy1221 (talk) 22:15, 2 June 2008 (UTC)

It is not illegal to distribute single copies of articles for academic purposes—it easily falls under fair use (even if might be a breach of user policies for the journals, but even then, most journals are pretty lenient when you are talking about very small-scale, not-for-profit, one-off stuff). My university doesn't carry e-copies of that one either (which surprises me), otherwise I'd be happy to send you a copy. Your best bet might be e-mailing one of the authors, if you want it quickly. It seems like a pretty rare journal. --Captain Ref Desk (talk) 22:15, 2 June 2008 (UTC)

My university's library claims to have a paper copy, though the online catalog says that particular issue is shelved at the physical chemistry laboratory rather than at the main library. I can try to find it tomorrow, though at 58 pages(!) according to BL Direct it sounds like a pain to scan. —Ilmari Karonen (talk) 23:21, 2 June 2008 (UTC)

Thanks for your offer but I would hate for you to scan in the 58 pages, that sounds like a real pain in the rear. I emailed the author and put in a request for an inter-library loan, patience is a virtue right? Man It's So Loud In Here (talk) 04:44, 3 June 2008 (UTC)

Liquid state of water

Why is water a liquid and hydrogen sulphide a gas, when hydrogen sulphide's Mr is nearly twice as much as that of water's? —Preceding unsigned comment added by 195.158.94.171 (talk) 19:28, 2 June 2008 (UTC)

The conventional answer is hydrogen bonding. The hydrogens from one water molecule really like to bind to the lone pair electrons of an oxygen from a different water molecule. They can't do this in the gas phase, so the boiling point is much higher that it would be otherwise, as you have to add in enough energy to break all of those hydrogen bonds before the water will boil. Sulfur, for various reasons, doesn't participate all that well in hydrogen bonding, so hydrogen sulfide doesn't get the boiling point boost. -- 128.104.112.147 (talk) 19:33, 2 June 2008 (UTC)

The reason for H₂S not having hydrogen bonds is due to the small difference in electronegativity of S and H atoms, where as O and H atoms have a much larger difference in electronegativity. --Mark PEA (talk) 19:52, 2 June 2008 (UTC)

Interesting. The density of water is almost the same as the density of liquid oxygen but the density of hydrogen sulfide is much less than the density of sulfer (which is approximately 2 g/cc. At least I think it is. Something else I read said it was 5.4 g/cc). Em3ryguy (talk) 20:43, 2 June 2008 (UTC)

In liquid sulfur the atoms are held together tightly with short covalent bonds, which is not the case in hydrogen sulfide liquid. Graeme Bartlett (talk) 21:58, 2 June 2008 (UTC)

Benzodiazepines and barbiturates at the GABAa receptor

GABAA_receptor#Agonists only vaguely describes the difference between the action of benzodiazepines and barbiturates at the GABAa receptor. Normally I would simply edit the section; however, I'm afraid that I don't understand the difference all that well myself. I apologize for the somewhat vague question, but can anyone explain exactly what the difference is in the way these two classes of drugs generally bind to and modulate this receptor? If anyone knows of reliable external sources that explain this well, a link or two would be greatly appreciated; if not, an explanation would be greatly appreciated. CrazyChemGuy (talk) 22:50, 2 June 2008 (UTC)

Benzodiazepines bind to the aptly named "benzodiazepine binding site" located at the outer intersection of α and γ subunits of GABA_a receptors, while barbiturates bind inside the Cl^- pore on the α and β subunits (see this diagram, from Purves et al's Neuroscience). Benzodiazepines increase the probability that the channel will open, while barbiturates cause the channel to remain open longer once triggered (see the section entitled "The GABAA receptor is the major molecular target for the action of many drugs in the brain" here from Siegel et al's Basic Neurochemistry). Hope that helps! St3vo (talk) 01:51, 4 June 2008 (UTC)

strobe lights

how can i make a strobe light with a the flash lights found in cameras? do i need a different capacitator?wat is the amount of electricity needed to run it? —Preceding unsigned comment added by 76.14.124.175 (talk) 23:11, 2 June 2008 (UTC)

I strongly advise you not to make the attemp[t. The reason is that the capacitor which powers a photographer's electronic flash store a large amount of energy at a high voltage. It is sufficient to stop your heart if you accidentally get a jolt while experimenting. This is not for the amateur or novice to experiment with. Edison (talk) 00:23, 3 June 2008 (UTC)

u didn't answer my question.....how do i make a strobelight using the flash on a camera......i wasn't asuming i needed that big of a capacitator....i was thinking of using a smaller one..... —Preceding unsigned comment added by 76.14.124.175 (talk) 00:51, 3 June 2008 (UTC)

I suggest an alternate method: Shine a flashlight thru a fan. You can vary the fan speed to control the strobe speed. You can also use paper and tape to block all but one of the openings between the blades to slow the strobe down further. Black paper would be best to absorb light. StuRat (talk) 02:41, 3 June 2008 (UTC)

Edison was right. Our Edison, not Thomas Alva. I googled and found a site that gives a schematic and all, but it carries a warning that you're looking at 350 volts across a big electrolytic, saying that "it won't kill you" but will give you a "nasty shock". They are wrong, it will kill you. Get 350 volts hand-to-hand and it's sayonara muchachos, maybe. Arcking and sparking at those levels is a serious hazard, and you'd better be wearing a helmet too if you get a big filter cap in backwards. What you want to do is way not safe. --Milkbreath (talk) 03:18, 3 June 2008 (UTC)

None of the above are really helpful replies. There's a big difference between a xenon tube flash and StuRat's suggestion of using a flashlight+fan, which doesn't give you adequate flash brightness with short enough duration to freeze an image, if that's what the OP wants.

Examples of do-it-yourself strobe light circuits can be found here, even an example of an adjustable one.

Milkbreath is right about capacitors being dangerous, but also wrong in that voltage doesn't kill you, current does. Electrostatic generators such as a Van de Graaff generator generate thousands of volts and are safe to touch because they don't actually store enough charge to generate much of a current. Generally when a spark arcs from your fingertips, that's about 30,000 volts per centimeter required to make the arc. =Axlq 04:39, 3 June 2008 (UTC)

One could just as well point out that a roomful of 12-volt lead-acid batteries in series-parallel like they have down at the phone company can deliver thousands of amps, but at 48 volts they are harmless to humans. Of course it's the current that kills you, but that pat statement both belies the complexity of the relationship among the factors involved in producing electric shock, and reveals a simplistic conception of it in the one mouthing it. Static electricity is a whole nother aminal and is not pertinent here. If I get across a few hundred volts as my final act, please put the following on my tombstone: "It was the voltage that killed him." --Milkbreath (talk) 11:11, 3 June 2008 (UTC)

I think the unhelpfulness was well-placed, since it's non-intuitive that anything in a camera flash could kill you and the poster's writing style suggests youth. If someone asked "how do u fit a knife in2 an electric sokket?", I'd also hesitate to answer, the gene pool be damned. --Sean 09:55, 3 June 2008 (UTC)

An electronics magazine I subscribed to decades ago had an editorial specifically warning electronics experimenters not to try to repair, modify, or in general experiment with the electronic flashes used by photographers, and cited a friend, an experienced electronic worker, who was killed by one. A charged capacitor at several hundred volts has eneough energy to cause death, far beyond the energy or available current from a typical high voltage static shock. At the same time, the source of the danger does not look as intimidating as what's up on a utility pole or inside a glass tube TV set. It is the type of device that may not give a second chance. The questioner did not give the impression of having the training or experience or knowledge of necessary safety measures to work with high voltages. Edison (talk) 13:57, 3 June 2008 (UTC)

I recently got a nice shock from a flash from a camera that had been off for at least half an hour. Stupidly, I forgot completely about the flash capacitor. I put my thumb across the terminals, got a shock and threw the camera across the room. My whole arm was all pins-and-needles tingly for hours. I'm imagine that if I'd somehow managed to touch it with both hands it would have been even more uncomfortable. APL (talk) 20:02, 3 June 2008 (UTC)

A bit more on the mechanical (fan) system I started to describe. You can mask out all but a small circle on the fan and use a laser pointer aimed at that hole. StuRat (talk) 00:49, 4 June 2008 (UTC)