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March 23

Ideal gas

My roommate and I cannot agree on the solution to the following problem:

A sealed and flexible container of gas has its pressure doubled, and then its temperature doubled. What is the new volume?

My roommate believes it to be 'remains constant' (halved, then doubled), while I claim that the answer needs more information (not automatically clear what the doubled temperature has on V, only on PV). Which one of us is correct, and why?

(geez, this is like one of those retarded 'discussion' questions, heh)

137.99.77.171 00:27, 23 March 2007 (UTC)[reply]

How flexible is the container? Since PV = nRT, if you double the pressure, and double the temperature... Yea, I think the new volume should be the same as the original volume. --Wirbelwindヴィルヴェルヴィント (talk) 00:45, 23 March 2007 (UTC)[reply]

Consider the equation V = nRT/P → What happens to this equation when you double both the temperature and the pressure? − Twas Now ( talk • contribs • e-mail ) 03:21, 23 March 2007 (UTC)[reply]

I think the confusion arises from the vagueness in the question. How, exactly, did you double the pressure of the gas? The only way would be to either: double the amount of gas (that is, add more gas), to double the temperature, or halve the volume. So you're right; more information is needed. — Knowledge Seeker দ 03:49, 23 March 2007 (UTC)[reply]

Doubling the amount of gas in a flexible container will usually not double the pressure. That depends entirely on the container and the surrounding pressure. —The preceding unsigned comment was added by 84.187.7.58 (talk) 06:20, 23 March 2007 (UTC).[reply]

Yes, the problem is ill-posed unless you make some additional assumptions which are not stated as part of the problem. The first step is to double the pressure of the gas in the container. The assumption that your roommate and Wirbelwind are making is that this step is performed as an isothermal process, i.e., performed such that the temperature of the gas is the same at the end of this step as at the beginning. Note that doubling the pressure on the gas will cause the gas to heat up, even though no heat source has been applied to the gas, so for this step to be an isothermal process, you’d need to wait for the gas to cool back down to its original temperature (possibly applying refrigeration for a while to speed up the process), before considering this step to be completed.

The second step of the experiment is to double the gas’ temperature. The assumption that your roommate and Wirbelwind are making about this step is that this is done as an isobaric process, i.e., performed such that the gas’ pressure during this step remains constant. This step, too, could be tricky, depending on the nature of the “flexible container”. For example, if the “flexible container” is a balloon, assuming the external pressure on the balloon is held constant, doubling the temperature of the gas in the balloon will cause a combination of increasing the gas’ volume and increasing the gas’ pressure, so the volume of the gas will less than double during this step.

If you make the above two assumptions, then yes, the volume at the end of the experiment will be the same as at the beginning. MrRedact 04:12, 23 March 2007 (UTC)[reply]

If you cannot make those two assumptions, it would be better to assume the process is adiabatic; since the ideal gas law is an approximation anyway, we may as well approach the problem as an adiabatic and internally-reversible process - that is, an isentropic process. From there, you can use

{PV}^{\gamma }=constant

, and go from there. Titoxd^{(?!? - cool stuff)} 04:47, 23 March 2007 (UTC)[reply]

But if you assume that both steps of the experiment are adiabatic, then the final volume is less than the initial volume. In particular, the only way to double the gas' temperature in the second step adiabatically would be to double the gas' pressure (again) without use of an external heat source, which would shrink the volume even further than it was already shrunk to in the first step. MrRedact 13:50, 23 March 2007 (UTC)[reply]

Snakeboards and non-holonomic locomotion

So I have been honing my snakeboard skills and I am wondering, how does the blasted thing work? I don't mean how does one make it go, I have that figured out, I just cannot for the life of me understand how my feet moving translates into the board taking off in a somewhat straight line. The snakeboard article describes it as non-holonomic locomotion. I read the pertinent article and if I understand correctly the system in non-holonomic because the board moves forward even though there is no "control" that directly allows for it, unlike a regular skateboard. All of the info I have found off-wiki is more technical/mathematical than I am presently able to grasp. I guess what I am looking for is a description of the force vectors that I can visualize. Thank you in advance for any help you can provide. 161.222.160.8 01:36, 23 March 2007 (UTC)[reply]

Bottle Rockets

A friend of mine is planning a competition in which teams would design and launch bottle rockets which are powered by a chemical reaction. My question is this: what kind of reaction would give enough thrust and impulse to allow a rocket a modest flight (~30ft), while still remaining marginally safe. Are there safe reactants that could produce this result? Would the bottles stand up to the pressure stresses? (I'm assuming the thrust would largely be a product of pressure) —The preceding unsigned comment was added by 138.29.51.251 (talk) 02:35, 23 March 2007 (UTC).[reply]

For such a short distance you could launch a cork from a bottle of carbonated water shaken vigorously. An ultrasonic device can provide the shaking. This would eliminate the possibility of causing a fire, which is perhaps the greatest risk of bottle rockets. StuRat 02:58, 23 March 2007 (UTC)[reply]

Or, instead of shaking you do the Mentos and Diet Coke reaction with a cork as the projectile. I do not know if sufficient pressure would build fast enough though. Sounds like a project for this weekend! 161.222.160.8 03:03, 23 March 2007 (UTC)[reply]

With a small nozzle, the Mythbusters were able to get Diet Coke to shoot up over 30'. But the altitude depends on the initial powered accelleration - and the amount of time for which it is applied. The accelleration is determined by the Force divided by the Mass. So the trick to getting something to go high SAFELY is to shoot something of very small mass using relatively less force - presumably requiring a less dangerous energy source. SteveBaker 03:53, 23 March 2007 (UTC)[reply]

StuRat I think the OP is using an alternate meaning of bottle rocket disambiguation) as in a water rocket which is made out of a bottle, as opposed to what you are reffering to as supposedly the more common use of the term bottle rocket.. No fire hazard with a water rocket. Rereading the post, I could still be wrong, it could be taken either way. Vespine 05:26, 23 March 2007 (UTC)[reply]

Could be, can we get a clarification from the original poster please ? StuRat 00:42, 24 March 2007 (UTC)[reply]

Sinus tachycardia

Apart from stress, trauma etc, are there any other causes of this condition?

I have linked the title for you, there is a list there that should answer your question.161.222.160.8 03:06, 23 March 2007 (UTC)[reply]

Verizon credit approval

i have been attempting to get a two year contract with verizon wireless however it asks for for my SSN for credit approval. the next day i get an email saying i have to do a $400 security deposit. I have good credit i am wondering why that is happening. are there any ways to bypass that.--logger 04:34, 23 March 2007 (UTC)[reply]

1) wrong place to ask. 2) get a prepaid phone or try another provider161.222.160.8 04:37, 23 March 2007 (UTC)[reply]

Where are you located? In the states, a security deposit is almost unheard for cell phone contracts. Are you dealing exclusively with email, because you may have gotten involved in a scam (never email your SSN to anyone). I would suggest going to a Verizon store in your area, and try setting up the contract in person. --Cody.Pope 04:37, 23 March 2007 (UTC)[reply]

i am in the states i got the order VIA wirefly. and i get only email for the order confirmation--logger 04:42, 23 March 2007 (UTC)[reply]

I agree with Cody. It's almost certainly a scam. What reputable company asks for $400 by email? Contact Verizon directly. Clarityfiend 04:45, 23 March 2007 (UTC)[reply]

And even if it isn't a scam, who needs to do business with a company that requires a $400 deposit ? Get a prepaid phone, like TracFone, they don't stick their noses into your credit report. In fact, you never have to give them your name (if you buy with cash). StuRat 05:46, 23 March 2007 (UTC)[reply]

I think phone companies give back the deposit after a few months though. --Wirbelwindヴィルヴェルヴィント (talk) 06:46, 23 March 2007 (UTC)[reply]

You should think of the money as gone once you give it as a deposit. You would have to sue to get it back if they decide to keep it for whatever reason, and it might very well cost you more in time off work, etc., to get your money back than you actually get. They know this, so will feel free to keep it. StuRat 15:07, 23 March 2007 (UTC)[reply]

I'm not so sure about this. You might want to find out if the security deposit is returned without any other conditions as long as you make the first few months' payments on time. At least, I think that's how cellphone deposits work. --Wirbelwindヴィルヴェルヴィント (talk) 19:13, 23 March 2007 (UTC)[reply]

Maybe your credit is no longer good because of identity theft. Get a copy of your credit reports from the credit reporting agencies. Qaz 19:43, 23 March 2007 (UTC)[reply]

Dream recall and masturbation

Ok, I know there are probably quite a few people here that have differing opinions on Lucid dreaming, but while this question does have something to do with LD, it isn't part of the question itself so give me a break, OK : ).

I am one of those people who has a lot of difficulty remembering dreams (at least since I was 16), and I've recently been making attempts to increase my dream recall (my ability to remember dreams), with some success.

Though I myself initially passed off any connection as mere coincidence, there are many antecdotes on increasing dream recall that hint that masturbation may inhibit the process, and if I trace back my most vivid dreams in the last 5 years (which is about 3 or 4 dreams), they just happen to be smack in the middle (or end) of my longest bouts of celibacy (reasons vary), so I instinctively start to wonder "why?".

Could there be any explanation for this? The Wikipedia is vehement on pushing the fact that masturbation has no known psychiological side-effects, but due to the large amounts of hormonal release involved in ejaculation, I find that surprising, almost hard to believe. 222.158.162.242 05:45, 23 March 2007 (UTC)[reply]

I've personally done plenty of experiments on masturbation and checking for correlations with things and found none. With dream recall, which is my only problem with lucid dreaming, I have found no correlation. Dream recall I have found works best for me if I wake up many times. When I wake up I try and remember (absolutely best thing to do is write them down) and then I fall asleep, have another dream, wake up, and remember. [Mαc Δαvιs] (How's my driving?) ❖ 05:57, 23 March 2007 (UTC)[reply]

Plenty of experiments, eh? =P --Wirbelwindヴィルヴェルヴィント (talk) 06:46, 23 March 2007 (UTC)[reply]

Can't help with the original question, but I'm fascinated at why one would choose to see of masturbation correlated with anything. Would you mind telling what sort of things did you checked and on what basis you hypothesized there might be a correlation? Rockpocket 07:31, 23 March 2007 (UTC)[reply]

Think of it like this: We have things like candy, money, fast food, and video games. Human beings in general are pleasured by such commodities, but bad effects emerge when large amounts of the said commodities are involved. A sceptic is driven to assume the same must be possible for something like masturbation, and a good sceptic will do his best to prove or disprove the notion. 222.158.162.242 08:47, 23 March 2007 (UTC)[reply]

I'm curious if the correlation is meant to be just for masturbation or if it is the same for sex as well? —Pengo 13:33, 23 March 2007 (UTC)[reply]

That's one of the flaws in the theory I guess. Does the body know the difference between real sex and sex a la manus? 222.159.65.25 05:51, 24 March 2007 (UTC)[reply]

Back to Mac Davis's observation: you dream while you are in REM sleep. If you wake up during the middle of REM, you will literally "come out of the dream", and will have a much higher chance of remembering the dream. Non-REM sleep will erase some of the details in the dream. Now, if you wake up more frequently, you have a higher chance of waking up during the middle of REM. Titoxd^{(?!? - cool stuff)} 07:13, 24 March 2007 (UTC)[reply]

On that, note the wake-back-to-bed technique. From personal experience it works wonders with dream recall, and naturally lucid dreaming.

And going into pure (pure) speculation mode: I would take a guess that your celibacy increased your chances of sleep disturbances due to, well, wet dreams and general sexual dreaming. If that type of thing even somewhat arouses you, it might affect your dreaming. -- Consumed Crustacean (talk) 07:32, 24 March 2007 (UTC)[reply]

Question on the chemical composition of "crocodile" tears

Just caught an airing of an episode of CSI:NY, and one of the CSIs checked the chemical composition of the tears shed by one of the suspects and determined that they were not true "emotional" tears because they did not have certain levels of chemicals found in those kind of tears.

Presuming that you are not introducing an irritant into the eye to induce crying, aren't "crocodile tears" basically just emotional ones? What I'm thinking is that when an actor is actually able to make themselves cry, most, I believe, are inducing the emotions in themselves that would cause them to weep, and thence, the tears would be emotional tears, and not basal or reflex.

That is assuming, of course, that the person is not simply squeezing their eyes a great deal to produce more basal tears, but I wonder if enough basal tears could be produced that way for one to actually have the tears leave the eye as when one is weeping.Lkusz 08:35, 23 March 2007 (UTC)lkusz[reply]

I'm not sure, but the only thing I can think of is that real tears would secrete certain hormones that aren't present in fake ones. But to be honest, I agree with you. It sounds like the writers took some artistic license with it. - Mgm|^(talk) 09:28, 23 March 2007 (UTC)[reply]

- In fact, there is a difference, if the tears were artificially induced. According to the paper Effect of stimulus on the chemical composition of human tears, the protein concentration of emotional tears from women exceeded that of irritant-induced tears by 24%. If there were tears brought about by fake emotion though, it would be impossible to tell the difference (the process works by artificially inducing the same hormonal channels that normal tears do). Laïka 09:58, 23 March 2007 (UTC)[reply]

Also, I'd expect there to be an overlap. That is, while on average "emotional tears" might contain 24% more protein, some people's "emotional tears" probably contain less protein than some people's "crocodile tears". One of the biggest failings of CSI-like shows is that they portray all evidence as 100% certain, when almost nothing is. Even a DNA test is not 100%, as the samples are often contaminated. The murderers rarely draw blood samples of themselves with a sterile needle and leave the syringe for the CSI team. The funniest one I saw was where they found a human hair in the room of the murder, so concluded the person who matched that hair must be the murderer. There are probably hairs and skin flakes from every person who has ever been in your house still there, no matter how meticulously you clean your house. StuRat 15:01, 23 March 2007 (UTC)[reply]

A new reward!

Yep! I said I'd place more, so here I am again letting you know that there is a task for you here. It involves some simple formatting, but don't attempt it if you are not familiar with footnotes. As per the reward specifications, you'll recieve an award if you can complete the task. Not much more I can say really - go forth & footnote! :) Thanks, Spawn Man 11:02, 23 March 2007 (UTC)[reply]

All done! SteveBaker 17:09, 23 March 2007 (UTC)[reply]

Hydraulic transformer

We know that pistons convert hydraulic pressure into linear motion. Any idea how conversion of hydraulic pressure to rotational motion is done?59.92.240.176

One way is to have a piston connected, via an articulated rod, to a bearing on the circumference of a wheel. You pump the cylinder and the rod pushes the wheel around, which turns its axle. We have a great animation at Steam engine which shows just this method. Darryl Revok 12:46, 23 March 2007 (UTC)[reply]

Or you can use a turbine of some kind. SteveBaker 12:52, 23 March 2007 (UTC)[reply]

Well in RoadRollers the drive does not look like it has an articulated piston, it is quite compact.So was just wondering what sort of gadget could that be..210.212.194.209

An Automatic transmission is probably the best practical example seen everyday but there are lots of other examples. Automatic transissions are a hydraulic fluid coupling. See Transmission (mechanics) --Tbeatty 06:56, 24 March 2007 (UTC)[reply]

CO2 recovery method

Why can we mutate a gene in any particular species of plant that causes the leaves to grow to a bigger size and photosynthesize at a faster rate so as to control gobal warming???59.92.240.176

Plants are pretty much doing the best they can already. They have evolved leaf patterns, branch angles and trunk rotation so as to optimise the surface area facing the prevailing sunlight. If plants had bigger leaves (but no other structural changes), all that would happen would be that more of the leaves would be in shadow from other leaves - and since photosynthesis is driven by sunlight, that could be strongly counterproductive. At night (and when in deep shadow), plants actually produce CO2 - so plants with larger leaves than they need could actually add to global warming - not remediate it. For this approach to work, we would need more of the earth's surface covered in natural plants - not genetically modified plants. So if (for example) we could somehow turn the Sahara desert into a rain forest - that would have a major effect. But all of these kinds of solutions are too long-term - and they are risky - they might well have unforseen consequences for the environment that we do not yet understand. Maybe the Sahara forms an important part of the world's weather systems and covering it with trees might do something terrible to the oceanic heat cycles or something. What we do know is that reversing the production of CO2 gets us back to a more natural situation that we know works. It also reduces our dependancy on fossil fuels - which we have long known are being consumed at a rate that is perhaps a million times faster than they are being renewed - and must therefore run out some day. We need to do something fairly drastic and have it take effect in a couple of decades at most. There are a bunch of things we KNOW we can do - we just have to do them. My car does 35miles per (US) gallon. It's a great car - it's not even a hybrid - it'll go 140mph and does 0-60 in 7 seconds...yeah it's a fast car too. This year's model does over 40 mpg. Why is the average US car's gas consumption 12 miles per gallon? If everyone switched from their present monsterous gas guzzler to a fuel efficient car we would produce ONE THIRD the amount of CO2 from cars. No new technology, no serious 'quality of life' issues. The fact that people aren't doing that means that there is insufficient incentive. We need a gasoline tax that BY LAW starts at 50 cents per gallon and goes up by 25 cents per gallon every year until the average US fuel consumption is over 30mpg. That money should go into research and development in the car industry. Do the same thing with commercial vehicles...but adjust the slowly ratchetting tax increases to better fit economic needs - which probably means starting with a lower tax rate - but increasing it more rapidly to give them more time to adapt. 12:51, 23 March 2007 (UTC)

Average fuel economy in the US is about 21 miles/gallon, not 12: [1]. I agree with the need for a fuel tax, but it shouldn't go up so quickly as to cause people to junk their current vehicles before they wear out, that would be even worse for the environment (and our wallets). I'd increase gasoline taxes a cent a month, for 50 years. That would be $1.20 in 10 years, $2.40 in 20 years, $3.60 in 30 years, $4.80 in 40 years, and $6.00 in 50 years. Knowing that the rate will continue to climb would convince people to buy fuel efficient vehicles the next time they buy a new car. StuRat 14:36, 23 March 2007 (UTC)[reply]

That figure of 21 mpg is the average mpg rating of US cars - ie if they were all new and well-maintained and driven as per EPA test track rules - then they would get 21 mpg. But the average of actual running cars is 12 mpg...because older cars use steeply more gas than they did when they were new, many are poorly maintained, and almost everyone drives more agressively than the EPA tests assume they do - and the EPA run cars with the A/C turned off. SteveBaker 17:45, 23 March 2007 (UTC)[reply]

I disagree. If you look at the subpage [2], it states that "...fuel economy values in this report are based on ‘real world’ estimates provided by the Federal government to consumers and are about 15 percent lower than the values used by manufacturers and the Department of Transportation...". You are correct in saying that those are values for new cars only. However, fuel economy has been relatively constant, and even a bit higher, over the past 20 years, in the US, so it would seem unlikely that older cars would bring the average down that far. If you have a source for the 12 mpg figure, I'd like to take a look. StuRat 00:23, 24 March 2007 (UTC)[reply]

As for increasing the amount of photosynthesis to convert CO₂ into oxygen and carbon, the oceans have the most potential for this. While we could increase the amount of algae or other sea plants in some areas by providing missing nutrients, like iron, there could be side-effects, as described above. For example, there was a concerted effort a generation ago to create artificial reefs by sinking used tires, but many of those tires broke loose and damaged natural reefs and the project was a disaster. We don't want to repeat mistakes like that. StuRat 14:47, 23 March 2007 (UTC)[reply]

Many would argue we don't want to repeat the mistakes of trying to manage an environment far more complex than we can comprehend. [Mαc Δαvιs] (How's my driving?) ❖ 16:03, 23 March 2007 (UTC)[reply]

I agree that we don't want to repeat those mistakes, but would argue they could be avoided by carefully testing methods before we put them into widespread use. The tires as artificial reefs could have been tested in a small area for 50 years before this method was used everywhere, for example. Similarly, the idea of seeding an area of ocean water with nutrients could be tested on a small scale and gradually increased if it seems to be doing more good than harm. StuRat 00:38, 24 March 2007 (UTC)[reply]

Actually, since we use stomata density on fossilized plant leaves as a proxy for CO₂ ppm reconstruction, the best way to do this would be to put out a higher CO₂ ppm. Right now I recall it as being around 435 for the Earth, but when it is 1000 ppm plants are known to grow about 50% faster, with photosynthesis also working on turbo. Plant's aren't doing the best they can do, they just adapt to the parameters of the moment the best they can.

I think one of the most pernicious aspects of the modern environmental movement is the romanticization of peasant life and the idea that western society is the destroyer of the world. The environmental movement has evolved into the strongest force there is for preventing development in the developing countries. I think it is legitimate for me to call them anti-human. Ok you don't have to think that humans are better than whales or owls, but I think it is not ok to think of humans as scum. That's it's ok to have millions of them go blind or die. I just can't relate to that"
— Patrick Moore, Co-founder, Greenpace

The Sahara Desert used to be a much more luscious land. The region's desiccation is thought to be a major force in the forward movement of humans as a species—it forced humans to migrate to the Nile riverbanks and Northward they moved up to the Fertile Crescent. [Mαc Δαvιs] (How's my driving?) ❖ 15:58, 23 March 2007 (UTC)[reply]

de broglie's wavelength

assuming we have aparticle have charge (q) and mass of (m) moving with speed according to potintial diffreance (Δv) what its de broglie wave length exprission? —The preceding unsigned comment was added by 196.20.48.41 (talk) 16:34, 23 March 2007 (UTC).[reply]

It's unclear to me what you mean by "moving with speed according to potential difference Δv". For example, perhaps you're talking about a one-dimensional scattering problem, where the potential function is a step function with height Δv? If not, please describe in more detail the experiment you have a question about. MrRedact 19:09, 23 March 2007 (UTC)[reply]

MINALK GASOLINE SWEETENING

in the MINALK gasoline sweetening reactor what happens to the hydrogen di-sulphide in the gasoline, and why do we vent the reactor. and whiles venting what do we vent? —The preceding unsigned comment was added by 41.204.33.199 (talk) 17:09, 23 March 2007 (UTC).[reply]

There doesn't appear to be a Minalk article, but there is one on Merox which is relevant. It links to this[3] external PDF, which has more details of Minalk. I think the venting is excess air, probably containing hydrogen sulfide, mercaptans, and other waste product. Nimur 17:32, 23 March 2007 (UTC)[reply]

Juvenile gulls

I can understand that the mottled brown colouration of gull chicks and newly-fledged birds helps to camouflage them when in and about the nest in their natural cliff/beach/coastal scrubland habitats. I'm curious however as to why juvenile gulls maintain this plumage for so long, once independent of their parents (it can take four years for the bird to fully attain its adult plumage) and fully versed in the ways of the gull. Is there any real advantage to be had for (for example) a 2-y.o. gull to still be a predominantly dull dirty-brown bird? As far as I've seen when watching them, adult birds don't treat the juveniles any differently to any other gull in their general, daily interactions and once past the fledgeling stage, juveniles are in no way submissive to adults. --Kurt Shaped Box 17:47, 23 March 2007 (UTC)[reply]

Cracking open my animal behavior textbook, it says that not all current traits are adaptations, in other words it is not possible to explain all traits as beneficial in the evolutionary sense. Maladaptive or benign traits can develop as side-effects of otherwise beneficial adaptations. Apparently Stephen_Jay_Gould is a major critic of explaining every characterstic of living things as a beneficial adaptation. Who knows, in a few thousand years, juveniles may be white.-- Diletante

Interesting answer, thanks a lot. :) --Kurt Shaped Box 22:18, 23 March 2007 (UTC)[reply]

I'm going to speculate that it's used as an age marker, and they don't gain their adult plumage until of mating age. This serves to keep adult gulls from wasting time and energy courting immature gulls, and this helps the species. StuRat 00:10, 24 March 2007 (UTC)[reply]

Yes, it's true that gulls don't attain their adult plumage until sexually mature (for the great black backs, this can be up to six years - they're long-lived birds). Wouldn't a gull be able to tell that another bird was sexually immature just by its behaviour when spring came around though? I mean, I'm sure that gulls know more about their own species' behaviour than we do and are certainly capable of 'reading' their own kind better than we can. Or am I just anthropomorphizing? --Kurt Shaped Box 00:30, 24 March 2007 (UTC)[reply]

I'm sure they could, at close range, after some observation. But it's better if they can tell adults from a distance, so they don't have to go and investigate every gull they encounter to determine their age. Incidentally, people have similar age markers, such as beards on men (before razors) and breasts on women. StuRat 13:25, 24 March 2007 (UTC)[reply]

I don't think it is safe or accurate to claim that breasts on women are age markers to facilitate mating. The development of mammary glands is largely to be able to provide milk for offspring. Oradwan 13:28, 26 March 2007

I think you misunderstood me. Breasts (large, fat-filled protrusions) are not the same as mammary glands (which produce milk). Permanent fat-filled breasts are completely unnecessary for providing milk to the young. The evidence for this is that most other mammals don't have them. Instead, most have quite minimal breasts (when not actually lactating), with a possible exception for cows. StuRat 00:13, 27 March 2007 (UTC)[reply]

How little sodium intake is too little?

I calculated the mineral content in my diet the other day and found, to my great joy, that it contained only 431mg of sodium. This seemed so little that I thought maybe it's little enough to cause hyponatremia, yet there's no mention of hyponatremia from inadequate sodium intake at eMedicine. Anyone who knows how little is too little? Thanks in advance, Jack Daw 19:02, 23 March 2007 (UTC)[reply]

It depends on who you are (do you run marathons regularly?), and who you listen to. The lowest Adequate Intake level that I've seen for sodium is New Zealand's, which recommends at least 460 mg/day. See Edible salt. MrRedact 19:37, 23 March 2007 (UTC)[reply]

My anaerobic exercise is highly limited ;) I might do well in sipping some Gatorade during the day. Thanks for the info, Jack Daw 20:33, 23 March 2007 (UTC)[reply]

The answer is that sodium conservation by the kidneys for a healthy adult is so efficient that urinary excretion can go down to as little as 100 mg per day. Expiration and fecal losses are negligible. Except in a hot climate, sweat losses are much smaller as well. The major circumstances in which someone can become Na depleted are unusual: prolonged intravenous or oral replacement with no food and fluids with no Na; or many types of "salt-wasting" renal or adrenal disease. There have been at least one reported case of Na depletion in a normal breastfed newborn infant due to too low Na content of mother's milk. alteripse 11:36, 24 March 2007 (UTC)[reply]

The TwinTowers Collapse

I want to determine how much water was being pumped into the buildings after they were struck by the planes from the plumbing that was broken,damaged, or sprinkler systems ect. I need to know the amount of water and how much it would weigh to prove my theory that the weight of all the accumulated water was great enough to cause the building to implode, just from the weight of the water. I think water weights ~~3.785 pounds per gallon~~, I know that because of the 110 story height of the bldg. Special plumbing had to be used to withstand the high pressure required to pump water up that high. If It can be determined the exact pressure the plumbing was under, then a rate of flow can be arrived at, at least a good approximation depending on the amount of damage done to the plumbing. The Tower with the T.V. Tower on it stood for 105 minutes before it collapsed and I believe that many many tons of water would have been pumped into the bldg in 105 minutes especially at high pressure and from multipal sources.

The building plans should show the exact plumbing that was broken or damaged
The fire sprinkler systems that were activated- a person on the 76 floor said" the Fire Sprinklers were broken and just gushing water onto the floor.
A person escaping from one tower said they were walking up to their knees in water.
The building had pumps that used the water from the Hudson river for their source of water. How can the amount of pressure be determined?
Were the Towers water cooled, would that cause even more water to pump into the bldg when broken or damaged?

I really wish someone could find out exactly how much water was poured into the bldgs in 105 min. and how much that much water weighed. Because I think that added weight from all that water is what caused the towers to collapsed the way they did and as fast as they did

According to this University of Wisconsin page, the total mass of one of the towers was approximately 600 000 metric tons (1 ton = 2204 pounds). That's about 5500 tons per floor. So the amount of water that would have been in the building would be minimal compared to that figure. - Akamad 21:39, 23 March 2007 (UTC)[reply]

To test the hypothesis that the mass of the building was increased nontrivially by water, suppose that enough water entered into the building to increase the mass of the building by just 1%. The 13,224,000 pounds of water that represents has a volume of about 3.5 million gallons. For that much to enter the building in 105 minutes would require a flow rate of about 33,333 gallons per minute. In comparison, a large bore, high pressure fire hose, that takes about 3 or 4 firefighters just to handle one hose, puts out about 300 gallons per minute.[4]. So increasing the mass of the building by just 1% with water would require the equivalent of about 111 high-end fire hoses pumping water into the building in those 105 minutes. It's safe to assume that the actual amount of water that entered the building during those 105 minutes was a lot less. MrRedact 22:29, 23 March 2007 (UTC)[reply]

Oops. I was using your water density figure of 3.785 pounds per gallon. The actual density is about 8 pounds per gallon. So it would "only" take in the ballpark of 50 high-end fire hoses to increase the mass of the building by 1%. But the actual mass of water that may have entered the building is still trivial compared to the mass of the building, either way. MrRedact 22:36, 23 March 2007 (UTC)[reply]

The density of 3.785 is actually in kilograms per US gallon, a unit that we don't see very often! --Anon, March 24, 03:25 (UTC).

Also note that most of the water sprayed on the building would evaporate, flow out of the building, or at least flow to lower stories which were structurally intact. Only a small portion of the water would remain above the impact areas for any length of time. StuRat 00:05, 24 March 2007 (UTC)[reply]

I have wondered if there was a large water storage tank in the upper stories like in The Towering Inferno movie. If there had been the equivalent of one high pressure fire hose per floor, or even one giant deluge as in the movie, it would have gone a long way toward extinguishing the fires and would have cooled the steel somewhat. How to justify the cost of reinforcing to place such a mass at the top of a building? A Mass damper can stabilize a high rise during earthquakes or wind gusts. Why not a tank full of water (full means no sloshing) instead of a hunk of concrete (which is not so good for extinguishing fires, but would only contribute to pancaking). Edison 18:42, 24 March 2007 (UTC)[reply]

While you would need a larger volume to have the same mass in water, I think your idea is a good one. You wouldn't want to cool the steel too quickly, though, or the thermal stress would cause it to rupture. Ironically, solid wooden doors often withstand fire longer than steel, for this reason. StuRat 06:49, 25 March 2007 (UTC)[reply]

Methodological naturalism's acceptance among scientists

Hello. Just how well established is the convention that science should not use supernatural causes as explanations? Do almost all scientists think this? A majority? Just a lot? What about philosophers of science? Is this convention more of a firm philosophical statement, or just a rule of thumb? Is it the same as "methodological naturalism?" Thank you. 69.223.174.232 22:05, 23 March 2007 (UTC)[reply]

Supernatural causes as explanations of scientific fact is definitely agreed on as junk science. However, using science to explain supernatural causes, writing off events' causes as unknowable at the present (Richard Dawkins writes a humorous passage noting that gravity did not mysteriously stop between Newton and Einstein just because the cause and mechanism via general relativity was not immediately apparent), or using science to disprove supernaturalism are not - they are 'mainstream'. Supernaturalism can't override science - that's generally accepted. Can science override supernaturalism? Perhaps, but that's controversial in areas such as the existence of God. -Wo o ty Woot? contribs 22:40, 23 March 2007 (UTC)[reply]

The answer depends to some extent on your definitions of "science" and "supernatural". But if your definition of "science" is "a systematic attempt to understand natural phenomena", and if your definition of "supernatural" is "something that exists or behaves above or outside of nature", then science can by definition neither explain supernatural phenomena, nor accept supernatural explanations for anything. —Steve Summit (talk) 13:25, 24 March 2007 (UTC)[reply]

Certainly if you accept the Wiktionary definition of 'supernatural': "Something for which there is neither ocular proof nor is measurable." -- then this is something that (by definition) science cannot ever either prove or disprove. That is an unfalsifiable theory and most scientists will reject it for that reason. The guiding principle here is Occams Razor - when there are two possible explanations for something, one's initial hypothesis should be the simpler of the two - the one that makes the least addition to what we have to assume. That's only a principle though - it's not a cast iron rule. Hence, when you wonder how the universe was formed, you can either use all of the physics we already know to postulate the big bang - or you can say that the invisible pink unicorn (Blessed Be Her Holy Hooves) created the earth from left-over ham and pinapple pizza crusts 5000 years ago. The former explanation requires no new science to be invented and comes about naturally from what we already know. The latter explanation requires a new and untestable (and unfalsifiable) theory about a supernatural being - and will be rejected until/unless more evidence for that approach can be found. The problem with supernatural theories is that there are an infinite number of them. If it wasn't the invisible pink unicorn (BBHHH) then perhaps it was Amon-Ra or the Raven of the Haida myth or Gaia or... But since every single one of those 'explanations' is unfalsifiable, we can't pick just one of them and label it as 'true' - and there is no conceivable way to disprove any of them - so we're left with a big empty "Dunno?!". Employing Occams Razor gets us down to a theory that we could (in principle) disprove if it were not true - or prove to a satisfactory degree. This approach does have it's problems - if it truely was that the world was created by the invisible pink unicorn (May Her Hooves Never Be Shod), then science would be wrong - and that's a definite possibility. The question is: Does the scientific method have any merit at all? An the answer is a resounding "Yes". By consistently denying supernatural answers (and other unfalsifiable theories), in just a few hundred years we have cracked quantum theory (which is why the memory in your computer works) and understood how inheritable diseases come about and how to send a man to the moon and...well, you get the idea. Over a much longer period of time, belief in the supernatural has produced zero progress - and that's not surprising. If you firmly believe that there is a literally omnipotent being out there somewhere who messes with our very existance - then no experimental results can be believed. You measure the swing of a pendulum and discover that the period of the swing depends only on the length of the pendulum - and you are just about to rush off and make a reliable pendulum-based clock - when you have to say to yourself: "Perhaps the invisible pink unicorn decided to make the results come out this way to punish me for putting anchovies on my Pizza last week?" (a not entirely unlikely thing if you believe in Her Holy Pinkness) - so now you can't know for sure how pendulums actually work - so there isn't a whole lot of point in building a clock because you have no clue about whether it'll work or not. Science can only progress if the ground on which each idea is built is solid - supernatural entities make literally everything unknown and unknowable. SteveBaker 14:52, 24 March 2007 (UTC)[reply]

Also, if science was to explain something 'supernatural' it would become natural, wouldn't it? —The preceding unsigned comment was added by 137.138.46.155 (talk) 07:34, 26 March 2007 (UTC).[reply]

Methodological naturalism (which is indeed the idea that you presume there are no supernatural causes) became pretty much predominant by the end of the 19th century. Even during the earlier 19th century it was extremely common, though. It is often forgotten by various opponents to it that the people who initially proposed it were as pious as could be — they just weren't worried about the possibility of disproving the Bible. (Fundamentalism in general, per se, is actually a relatively recent concern. None of the scientists attacking Darwin on religious grounds were anything like what we would find in a modern Young Earth Creationist; all were quite outside of Mosaic cosmology.) I would expect that almost all Western scientists today are methodological naturalists — it is part of the Western definition of "science" by this point. Most philosophers of science probably fall into this category as well though if they are clever they will realize that the line between one man's naturalism and another man's occult is a pretty fine one (e.g. Newton's "Gravity" was initially dismissed as occult, but later triumphed as one of the great accomplishments of naturalism, even though of course Newton believed in a very directly active God). --24.147.86.187 14:22, 26 March 2007 (UTC)[reply]

Coins and Bomb like things

Hello,

I herd somewhere that if you drop a coin on the top of a tall skyscraper, say 300m+, that it would travel fast enough to kill, by means of a bang on the head, anyone who it hit when it got to the ground. Is this true? If so then wouldnt a great cheap way of bombing somewhere be getting something, a bit bigger such as snooker ball sized metal balls, and dropping them over somewhere. They will be quite heavy and be dropped from alot higher. They should just destroy everything below?

thanks, --12345 wiki 22:12, 23 March 2007 (UTC)[reply]

Nope, not true. That was busted on Mythbusters a while back. I'm sure we have an article about this somewhere.. -Wo o ty Woot? contribs 22:40, 23 March 2007 (UTC)[reply]

Snooker balls can work as they are quite heavy and will be enough to give someone a concussion, but that's still not a bomb per se. --antilived^{T | C | G} 22:52, 23 March 2007 (UTC)[reply]

The all-knowing Cecil Adams of Straight Dope fame also debunked it. Unless of course you use one of these coins. Clarityfiend 22:54, 23 March 2007 (UTC)[reply]

One of these coins would also do the job. But you might be able to find something cheaper! --Anonymous, March 24, 2007, 03:29 (UTC).

Can't get much cheaper than a nickel. 222.159.65.25 05:43, 24 March 2007 (UTC)[reply]

As a serious comment (well, more serious than most of these), the largest easily portable coin I can find are Spanish 50Reales coins from 1628, but they can cost £1500 each now :) The 1797 english 2d coin (only costing a few £s) weighs 2oz, so it might have a considerable impact on anyone below it :) HS7 15:30, 25 March 2007 (UTC)[reply]

The myth about a coin tossed from a skyscraper being able to kill someone is false. It's true that the Newtonian Equations for a falling body predict very high speeds for a coin dropped from the height of a skyscraper in a vacuum, like 193.4 mph from the top of the Empire State Building.[5] However, in the real world, skyscrapers are not surrounded by a vacuum. For a fall from a skyscraper in air, the speed of a coin is limited by its terminal velocity, which is only somewhere around 20 to 45 mph.[6] So it would be just like someone throwing a coin at you hard. It might sting, but it wouldn't kill you. The TV program Mythbusters examined this, by firing coins from a modified staple gun at speeds up to 64 mph at Adam's rear end. The coins stung a bit, but didn't cause any damage. MrRedact 23:11, 23 March 2007 (UTC)[reply]

A variant on this idea has been considered for military use. Kinetic bombardment techniques (studied by the United States in Project Thor, and more informally described as "rods from God") involve dropping a metal pole – typically tungsten, for its high melting point – from orbit. Striking the surface of the Earth at speeds up to several kilometers per second, such an object would pack more wallop at impact (as kinetic energy) than would a conventional explosive bomb of the same weight dropped normally (as chemical energy). There have been no confirmed tests of such a system, however there have been rumours. No government is believed to have such a system operational. TenOfAllTrades(talk) 12:44, 24 March 2007 (UTC)[reply]

Hmm. My question is, would it be easier and cheaper to build (and fuel!) a device which could expend enough energy to get these masses into orbit, versus building a device (i.e. a bomb) to expend the same amount of energy just sitting on the ground? TANSTAAFL, when it comes to conservation of energy. —Steve Summit (talk) 18:18, 25 March 2007 (UTC)[reply]

Well, speak of the devil. This suggests the Pentagon has not been idle, with not one, but two hyperkinetic weapon systems on the drawing board under the Prompt Global Strike moniker, one using modified Trident missiles and reaching a speed of up to 13,000 mph, and the X-51 cruise missile (if you consider Mach 5 to be cruising). Clarityfiend 00:51, 26 March 2007 (UTC)[reply]

As for dropping small, heavy objects as an antipersonnel method, it could work, but would be less effective than explosives, napalm, fuel-air bombs, etc. Perhaps this could be used as a last resort once all other munitions had been exhausted. StuRat 23:56, 23 March 2007 (UTC)[reply]

What BS. I put my comment up before MrRedact but it was removed by the person who posted the question below. See here. --Wirbelwindヴィルヴェルヴィント (talk) 01:32, 24 March 2007 (UTC)[reply]

It just looks to me like your comment was lost due to an edit conflict, so I included it below:

The theories came up I think because they assume that the object will accelerate forever. But terminal velocity generally keeps things like coins not as dangerous. --Wirbelwindヴィルヴェルヴィント (talk) 23:05, 23 March 2007 (UTC)[reply]

StuRat 13:21, 24 March 2007 (UTC)[reply]

Hehe, thanks, but I wasn't actually that upset over it, except that I did say it first! =P Thus I only linked to the history. --Wirbelwindヴィルヴェルヴィント (talk) 21:30, 24 March 2007 (UTC)[reply]

The article Terminal velocity provides an equation that says that the speed that such an object would hit the ground is proportional to the square root of its mass and inversely proportional to its cross-sectional area. Since our coin is made of a pretty dense material, anything else thrown in this way needs to be heavier - and also bigger. When you double the size of something, it's area quadruples and its mass octuples - which means that the terminal velocity goes up by a factor of 1.4 every time you double the size of the object. However, the damage you do is proportional to the mass times the velocity - so doubling the size of the object probably makes it about 2.8 times more dangerous. You'd have to be dropping something pretty big to do much damage. The probability of actually hitting someone (at random) would be small too - so you'd need to drop an awful lot of these things to have much chance of hurting someone. SteveBaker 14:24, 24 March 2007 (UTC)[reply]

That's phrased a little awkwardly. If I talk about doubling the size of something, I don't normally mean doubling in every dimension. Two nickels are double the size of one nickel - the mass doubles and the area increases by no more than 100%, depending on the shape. Matt Deres 16:01, 24 March 2007 (UTC)[reply]

SteveBaker, I guess that depends on what you mean by "pretty big". Certainly a bowling ball would kill someone, and I suspect something considerably smaller, if sufficiently dense, could kill you, as well. The shape is also important, with a teardrop shape perhaps limiting turbulence and allowing the maximum speed for a given mass and volume. Maybe 3 tail fins might help, too. You're quite correct on the low probability of a direct hit, however, no matter what objects are dropped. StuRat 16:16, 24 March 2007 (UTC)[reply]

(Non-serious) see [7] – b_jonas 18:05, 24 March 2007 (UTC)[reply]

In a World War 2 movie, a cargo plane crew had to fly over Germany, getting shot at by strong antiaircraft fire, just to drop propaganda leaflets telling the German citizens that resistance to the allies was futile. The airman dropping the leaflets was pushing 200 pound bundles of them out the door. His companion said "Hey, you are supposed to cut the rope around the bundles before you drop them!" He said "The leaflets have more impact this way." Edison 18:30, 24 March 2007 (UTC)[reply]

Energy obeys the superposition principle. A "snooker ball" has some destructive energy due to its mass and height. a bomb of equal size also has that energy. In addition, the bomb also has a huge stored chemical (nuclear, ... etc) energy reservoir, probably orders of magnitude larger. Nimur 06:51, 25 March 2007 (UTC)[reply]

Music Enjoyment

Why do we enjoy music? I looked through the Music article, but I didn't see anything. Imaninjapirate^{talk to me} 23:05, 23 March 2007 (UTC)[reply]

I guess its similar to the other sensory inputs that we enjoy (taste, touch, sight). --Seans Potato Business 23:53, 23 March 2007 (UTC)[reply]

I've heard that we enjoy music so much because it's rhythm is close to our own heart rate. Whether this is true or just pseudoscience, I have no idea, I don't have an reliable source to point you at. →Ollie (talk • contribs) 00:59, 24 March 2007 (UTC)[reply]

I doubt that. I like trance, which is "generally characterized by a tempo of between 130 and 160 bpm". My heart doesn't go to 130 bpm if I run for a few miles. --Wirbelwindヴィルヴェルヴィント (talk) 01:14, 24 March 2007 (UTC)[reply]

You must have an amazingly slow pulserate then, my heart would excede 130 just thinking of running a few miles :( HS7 13:28, 25 March 2007 (UTC)[reply]

Ask yourself why you are repulsed by a chalk screeeeeeech on a blackboard and then take a peek at the article on Harmony. Nebraska bob 02:48, 24 March 2007 (UTC)[reply]

Aesthetics and Aesthetics of music has some info (but not alot). -- Diletante 04:06, 24 March 2007 (UTC)[reply]

The evolutionary biologists have thought about this question. I think I read about it in one of Richard Dawkins's books, but I can't remember which one, or exactly what the theories were. I think part of it had to do with an extension, or an overgeneralization, or an unexpected consequence, of the songs and rhythms that other animals use to communicate. —Steve Summit (talk) 13:33, 24 March 2007 (UTC)[reply]

Of course we are putting the cart before the horse here. Music pleases us because...well because we made sounds that made us happy and called them 'music'. By definition, music is that set of sounds that pleases us - otherwise we wouldn't call it music - we'd call it "cacophany". So it's not at though music suddenly came along and we liked it. As an evolutionary thing - it could be that we started off bashing on things to make a noise that could be heard at a longer distance than our voices to communicate with other tribe members - then we found that it was easier to distinguish those sounds from natural sounds if they were somehow distinctive - maybe with a set rhythmn. At this point those of us genetically able to make and hear and take note of un-natural rhythems and perhaps pitch changes would have an evolutionary advantage over those that do not - this allows evolution to kick in - and before you know it, we all love music. Perhaps then we evolved to be better at making complicated sounds for the same reason peacocks evolved their beautiful tails - it's attractive to the opposite sex to show that you excel at something impractical because it proves that you have the survival skills to allow you to have free time and to waste energy on things that aren't strictly necessary. We enjoy all of the things that primitive man needed to do - our brains are wired like that. Eating, hunting, sex, making things with our hands, playing with small children...all of those things give people pleasure - and that's because we have evolved brains that compel us to do them. I think it's likely that our musical sense comes about the saem way - but we've lost sight of the original purpose of it all. SteveBaker 21:01, 24 March 2007 (UTC)[reply]

If you like this topic, you may be interested in a research paper I was involved with. It discusses the "pleasing" quality of music and the mathematical basis for it. It is here. --Kainaw ^(talk) 21:14, 24 March 2007 (UTC)[reply]

One clue is that animals generally don't care for music,

Don't they? You think those songbirds are all singing to us? :-) —Steve Summit (talk) 12:06, 25 March 2007 (UTC)[reply]

so music enjoyment is something (mostly) human-centric. One hypothesis is that music appreciation is related to having the capacity for (human/complex) language. —Pengo 01:07, 25 March 2007 (UTC)[reply]

I'm going to have to disagree--I know I read about a study in which rats which were brought up surrounded by the music of a certain composer generally preferred that composer. No time to dig up the link now (I should be working) but worth doing some googling for. Meelar (talk) 00:08, 26 March 2007 (UTC)[reply]