Wikipedia:Reference desk/Archives/Science/2008 February 21

= February 21 =

Environmental Effect of Al Gore
Often, in criticism of Al Gore, I hear people say something along the lines of "Oh, he's such a hypocrite. He preaches about saving the environment while he himself flies around in his private jet."

Which led me to approach this quantitatively... say Al Gore traveled in a private jet from New York to Los Angeles and back. During the trip, he spoke to 500 people and convinced them to switch the light bulbs in their household to energy efficient light bulbs. Would the positive effect of people switching their light bulbs outweigh the pollution from the trip, or vice versa?

I'd like to see someone work this out. If they do, I ask that they state any assumptions they make. (How much power the jet uses, average household power usage, the change in wattage from the switch of light bulbs, etc.) 04:57, 21 February 2008 (UTC)
 * Allow enough time and certainly the power savings win out -- you're comparing a one-time cost to an ongoing improvement. This, however, addresses a straw man.  It's not "Gore educates the world via private jet or not at all" but "Gore flies on a private jet or Gore flies a regular airliner".  &mdash; Lomn 05:03, 21 February 2008 (UTC)


 * Well vaguely, let's see. A Gulfstream jet gets ~1.2 miles per gallon, and he's traveling of order 5000 miles round trip, so he uses ~4000 gallons of fuel.  Jet fuel has an energy density of ~125 MJ / gal, so he used of order 500 GJ of energy.  Assuming he convinces 500 people to reduce their energy consumption by 150 W each (equivalent to replacing ten 60-W bulbs with CFLs, assuming each bulb is run 8 hours a day on average) then that is a net savings of 75 kW.  In which case, the energy cost of the plane trip will be recouped after 75 days.  Environmental impact is generally proportional to energy cost modulo small multiples depending on how the energy is generated, so for the scenario you suggest, Al looks okay.  Of course, it is probably pretty generous to assume Al gets 500 new converts every time he talks, and flying on a commercial airliner is still almost certainly more efficient regardless.  Dragons flight (talk) 05:29, 21 February 2008 (UTC)


 * Incidentally, the best commercial airlines, fully loaded, can get as good as 30 miles per gallon per person, and hence use only about 5% of the energy per person as transporting a single person by small private jet. Dragons flight (talk) 05:35, 21 February 2008 (UTC)

Good point. I'll change the question slightly. Lets say a person (for the sake of bringing politics out of it, but thats probably too late) flies from New York to Los Angeles and back every week, and that they manage to get 500 people a month to switch. 05:15, 21 February 2008 (UTC) —Preceding unsigned comment added by Pakiprince7135 (talk • contribs)

This question seems irrelevant in all kinds of ways. First of all, the resources actually consumed by Gore, or any other individual human being, are negligible on a planetary scale. His jet could get 0.01 miles to the gallon and it wouldn't matter per se. Secondly, a celebrity like Gore doesn't primarily influence people by talking directly to them. Everything he does is symbolic. Politicians don't talk to individual voters just to get their votes, they do it to get the votes of people who see or hear about the conversation and start to think of the politician as a man of the people. If Gore acts hypocritically, or more to the point if he seems to act hypocritically, he'll lose followers. That's why he shouldn't waste jet fuel, not because the energy usage of the world's small population of celebrities makes such a difference in the grand scheme of things.

Also, a given amount of energy in jet fuel is worth more than an equal amount of energy in burning light bulbs, because petroleum is a much more precious resource than energy sources in general. -- BenRG (talk) 13:48, 21 February 2008 (UTC)

The entire discussion above is missing the critically important point that Al Gore always buys a carbon offset every time he flies, so that the CO2 and other greenhouse gasses produced due to him flying are balanced out by CO2 reduction measures elsewhere. Al Gore is very meticulously carbon neutral. MrRedact (talk) 19:10, 21 February 2008 (UTC)


 * Except that carbon offsets are bunk when used in that way. And can even be bunk otherwise too, if not carefully handled. 79.74.0.57 (talk) 00:30, 22 February 2008 (UTC)
 * Could you please explain why you think carbon offsets are bunk when used to offset air travel? I'm not asking to start an argument; I'd genuinely like to know.  My girlfriend wants to take a trip to Machu Picchu that I'm not too keen on, but my global warming argument against going is getting shot down by the availability of carbon offsets.  The whole tree planting variety of carbon offsets does seem of dubious value, since it seems to me like forest land is pretty much a fungible commodity -- if you plant and protect trees in one part of the planet, without reducing the demand for land, forests will just be destroyed in another part of the planet, instead.  But it seems like it's hard to deny the value of more modern types of carbon offsets, like donating to a renewable energy project that wouldn't otherwise be developed, thereby not only reducing CO2 production, but also reducing the consumption of our limited supply of fossil fuels.  MrRedact (talk) 02:08, 22 February 2008 (UTC)

Dragon is pessimistic assuming that it saves only 15 watts to switch from a 60 watt incandescent to a comparable compact fluorescent. The CFL would use 13 to 15 watts, per GE for a saving of 45 to 47 watts per bulb or at least 450 watts per person if he operates 10 bulbs. Edison (talk) 20:10, 21 February 2008 (UTC)


 * This depends on the climate lived in. If you're heating your house, switching to CFLs will require you to use more heating to keep the house at the same temperature, since there will be less heating from the bulbs. Add to this that if lightbulbs are switched off when you leave a room, an incandescent bulb only heats the rooms you are using when you are using them (unlike central heating). If you live in Florida, switching to CFLs probably makes sense and could indeed save many watts. If you live in a cooler climate, it's less clear cut. 79.74.0.57 (talk) 00:30, 22 February 2008 (UTC)
 * This has been mentioned before, but so far, no one has provided evidence that the waste heat generated by incandescent light bulbs actually contributes usefully to household heating. As I say everytime this comes up, it's always a bad idea to generate heat at the top, because hot air travels up. Indeed most of the heat doesn't just stay at the top, a fair amount of it stays fairly close to the light bulbs (since light bulbs aren't the best radiators or heat). In reality, I strongly suspect (but freely admit I have no evidence, but nor do the people who bring this up) incandescent bulbs contribution to household heating is minimal and significant less in proportion to what is generated. In other words, that waste heat really is waste heat. The simple reality is, well designed heaters are almost definitely a lot more efficient (if that's the right word) at heating a house then incandescent light bulbs so you will IMHO still save significantly with CFLs. I'm sure there must be some studies of this, i.e. comparing the energy usage of households in cold climates before and after switching to CFLs. Nil Einne (talk) 12:12, 22 February 2008 (UTC)
 * how can it be that "well designed heaters are almost definitely a lot more efficient" than light bulbs, when we are constantly being advised that incandescent bulbs are so inefficient at producing light, and all the energy that goes into an incandescent bulb comes out as either light, or heat? and the light, when absorbed, ends up as heat? that's 100% efficiency. the typical furnace wastes a lot of energy up the chimney, heating up the furnace itself which is typically in an uninhabited area where the heat is all wasted, heating up the ducts, pipes, etc. which are also typically wasting heat inside the walls or to the outer walls. all items which are significant enough to be addressed in modern, ultraefficient furnaces.
 * if the argument is that the amount of heat is not enough to make a difference, then it can't be enough to make a difference worth conserving. if it is worth conserving, then it's significant in terms of your total energy usage, which is greater than your heating energy usage, so by definition has to be significant there as well. Gzuckier (talk) 18:10, 26 February 2008 (UTC)


 * As I said, I'm assumming the lighting in your home is only on about 8 hours a day. Do you run all the lights in your house when you are away at work or asleep?  Hence 450 / 3 is 150.  Dragons flight (talk) 00:38, 22 February 2008 (UTC)

Redact, if Al Gore flew on an airliner, it would cost him less and he could buy more carbon offsets. The only reason you'd be able to use carbon offsets to justify something is if you could only afford them because of the action you took. This requires the environmentally friendly action to be more expensive, but it's almost always cheaper. — Daniel 23:21, 21 February 2008 (UTC)


 * Flying around and convincing people a few hundred at a time that global warming is a real problem and a result of human actions is a retail process, in a world with billions of energy users, whereas making an Academy Award winning documentary achieves the same goal in a wholesale manner. DVDs and video downloads do not require nearly as much jet fuel as the hypothesizes private jetting. But the years of lectures on the topic helped in developing the presentation and in gaining the degree of credibility needed to get the movie made and distributed. An Inconvenient Truth is the fourth highest grossing documentary film in the U.S. The companion book reached #1 on the NY Times nonfiction list. This followed a period when many politicians denied there was any global warming, or that anything needed to be done about it. Senator Jim Inhofe said "global warming is the greatest hoax ever perpetrated on the American people." What would be the monetary effects of doing less to prevent global warning or doing more to prevent it? "Stay home and don't lecture, to save airplane fuel", might be penny wise and pound foolish. Edison (talk) 06:04, 22 February 2008 (UTC)

Explain about the working of nMOS super buffers in VLSI?
Can you help me?

I am Joshy Karanath from India. Now I am studying B-Tech [ Electronics & Communication ] at Ihrd College Of Engineering, Poonjar, Kerala.

Now I need help from you. Please give me the explanation or tell me about the link from where I can get this information. The topcs are given below.

1. "process" in VLSI. (with figures)

2. Working of "Super Buffer" in VLSI. (Inverting type nMOS super buffer)

3. Detailed Explanation in "Second Order MOS device effects in VLSI" (all the five effects with figures)

4. Fabrication Process in "BiCMOS" in VLSI (With Figures)

Thanking you,

Joshy Karanath.


 * Apologies if this is rude of me, but I have reformatted your question to make it easier to read. No content has been changed, simply formatting and capitalization. I am sorry that I cannot help with your request, but I hope someone else can TheGreatZorko (talk) 11:29, 21 February 2008 (UTC)


 * Well, here's a link to start BiCMOS and here's another [] to "Ion Implantation Process2 in VLSI, not sure about the figures.Richard Avery (talk) 12:31, 22 February 2008 (UTC)

Hope these links help, Nimur (talk) 22:02, 27 February 2008 (UTC)
 * Ion implantation is not specific to BiCMOS, although the concentrations of dopant are always going to vary on the exact process in use. Often times, a university-level class will pick one process and stick with that for the entire course.
 * A superbuffer is just a buffer with high current output (or high speed switching, which is often equivalent). The topology may consist of two nMOS inverters in series, (twice inverting preserves the original input), and the output stage may have a high drive strength with a push-pull output topology.
 * There are a lot of "second order" MOS channel effects. Take a look at channel length modulation and Drain Induced Barrier Lowering for a couple examples.
 * BiCMOS is almost always going to be used for a mixed signal ASIC, with digital and high frequency analog sharing the same die. The process will vary, but there are several established industrial and research processes.

Rabbit skeleton conservation
Which is the best way to conserve the skeleton of a dead rabbit so it does not disintegrate, while at the same time promoting flesh decay in the quickest and most hygienic manner? -- 83.56.190.69 (talk) 11:20, 21 February 2008 (UTC)


 * Would putting the corpse into a weak acid, and then transfering it to some sort of embalming fluid, such as formaldahyde work?

Out of curiosity what is this for? What is stopping you stripping the flesh and then simply preserving the skeleton? TheGreatZorko (talk) 11:32, 21 February 2008 (UTC)


 * Yes, I would be inclined to boil bunnikins if all you want are its bones. Of course you will need some way to reassemble the bones correctly and join them together. A museum might have some useful advice on how to do this.--Shantavira|feed me 13:43, 21 February 2008 (UTC)


 * Note that this will smell pretty bad. Ventilate! --98.217.18.109 (talk) 13:50, 21 February 2008 (UTC)


 * Flesh eating beatles beetles are what commercial companies that do this kind of use according to "Dirty Jobs". Zrs 12 (talk) 14:30, 21 February 2008 (UTC)


 * Flesh eating beatles? I knew rock-and-roll was evil! DJ Clayworth (talk) 15:54, 21 February 2008 (UTC)


 * What, you've never heard of flesh eating Beatles ? :-) StuRat (talk) 13:54, 22 February 2008 (UTC)


 * Haha. Sorry, it was early.  That better? Zrs 12 (talk) 23:11, 21 February 2008 (UTC)


 * Well, with AC/DC, rolling stones, and lead zepellins around, how could anyone doubt rock-and-roll was dangerous? 206.252.74.48 (talk) 16:07, 21 February 2008 (UTC)


 * 19th century anatomists wouold sometimes place a skull or skull with some flesh attached in a perforated metal cage and sink it in a pond for a year or so to deflesh it. Museums clean bones of some animals with insects. Edison (talk) 20:02, 21 February 2008 (UTC)

I don't think we should be answering this question. He could be abusing animals for all we know. Malamockq (talk) 02:52, 22 February 2008 (UTC)
 * So could you. In fact, ... what made you bring it up?  APL (talk) 05:57, 22 February 2008 (UTC)

ANTS ANTS ANTS

press machine
hi, pls tell us that which press machine(ie: 5 ton, 10 ton)should be used for cutting a CRC sheet of thickness of 0.5mm,which should not damage both tool&diePnengineers (talk) 11:34, 21 February 2008 (UTC)


 * CRC??--Shantavira|feed me 12:56, 21 February 2008 (UTC)


 * CRC in this context is probably "Cold Reduced Coil steel". Also known as "cold rolled steel" (see cold rolling). It's not on the dab page, but probably should be.  You would need more than 5 or 10 tons, maybe something like 30 tons, but it's years since I did anything like that and you really should contact a company that sells or hires such equipment; they would be able to advise you. Neıl  ☎  14:23, 21 February 2008 (UTC)

starch vs. sugar
Is there any real difference, from a nutrition or health standpoint, between consuming a given amount of calories from sugar vs. starch? ike9898 (talk) 14:58, 21 February 2008 (UTC)
 * Not really, no, not if you're talking calories. However, because starch is an enormous polysaccharide of glucose, and sugar (i'm assuming you mean table sugar) is a disaccharide of glucose and fructose, they will be digested into mono and disaccharide subunits for absorption in the small intestine in the same manner. Ultimately, the individual sugars will be metabolized differently when taken up by the cells, or the liver will end up processing them into glucose.  Wisdom89  ( T |undefined /  C ) 16:32, 21 February 2008 (UTC)
 * Probably most relevant to your question are the concepts of glycemic index and insulin index. These relate to how your body reacts to the consumption of equal amounts of different sugars (as far as changes in postprandial blood glucose/insulin levels are concerned, respectively.) Some people (including many doctors/dietitians) believe that there are important health benefits of a low glycemic/insuin index diet, including the South Beach diet and, to some extent, the Atkins diet, among others. (EhJJ)TALK 16:41, 21 February 2008 (UTC)
 * The glycation activity of fructose (50% of sugar) appears to be much greater than that of glucose (100% of starch). Frankg (talk) 16:54, 21 February 2008 (UTC)
 * Aren't starch and sucrose both converted to glucose before being used by cells? Other than the greater tooth decay due to sugar and the higher glycemic index of sugar, what is the difference between consuming 200 calories a day of sugar or 200 calories a day of starch as paret of the diet, so far as long term health, weight gain, or the ability to do work? Edison (talk) 20:01, 21 February 2008 (UTC)
 * "Other than ... the higher glycemic index of sugar..." There's your answer. Hello diabetes! And other things. What did the Romans ever do for us? 79.74.0.57 (talk) 00:25, 22 February 2008 (UTC)
 * See Diabetes mellitus and Diabetic diet, especially the section on recommendations of the American Diabetes Association. Their diabetic diets do not forbid all consumption of sugars. Fruits and desserts with sugar content are often allowed in such diets. The grams of carbohydrate is what is typically tracked, and the carbohydrates may come from sugar or from starch. The quantity of carbs at a given meal is the factor tracked. 200 calories a day would be only 50 grams of carbohydrate, and spread across three meals and two or three snacks would not be a huge amount, especially in a typical 2000 calorie diet. The blood sugar rise after a meal is related to the total carbs consumed. Typically the insulin administered to a Type 1 diabetic for a given quantity of carbohydrate grams in the form of sugar is the same as for that number of carb grams in the form of starch. The glycemic index addresses how fast the blood sugar theoretically level rises and falls. Per Glycemic index, the starches white rice, baked potatos, and white bread have high glycemic indexes, higher than sucrose (table sugar). Edison (talk) 05:47, 22 February 2008 (UTC)
 * Isn't it surprising that a baked potato has a greater GI than sucrose? ike9898 (talk) 13:13, 22 February 2008 (UTC)
 * It is highly counterintuitive that eating a baked potato, white rice, or white bread amounting to say 200 calories would raise a diabetic's blood sugar faster than eating table sugar or candy totalling 200 calories. But that's what the table appears to say. Edison (talk) 20:41, 22 February 2008 (UTC)

Is the universe 100% logical and 100% consistent 100% of the time?
Is the Universe always logical and consistent, so that anything that FOLLOWS LOGICALLY from something else is in fact going to BE THAT WAY, with no exceptions, ever, in the history of the universe??? —Preceding unsigned comment added by 79.122.42.134 (talk) 16:20, 21 February 2008 (UTC)
 * No. I think what you're asking about is called Determinism, and it's how scientists used to think the world worked, but quantum theory isn't deterministic. AlmostReadytoFly (talk) 16:24, 21 February 2008 (UTC)
 * You may also want to read Deterministic system (philosophy) (EhJJ)TALK 16:26, 21 February 2008 (UTC)
 * Surely determinism is the totally different position that everything that happens, happens because it follows logically (from earlier events and general laws) that it must happen? The answer to the OPs question is yes, but this is a property of logic, not the universe. In strict logical terms, no event's happening ever follows logically from any other set of events, and if something doesn't happen despite following from true facts and general laws, then the laws were false. Algebraist 16:39, 21 February 2008 (UTC)
 * I think the OP is looking at things a little too anthropocentrically. What seems logical and consistent to us might be very different to what is "truly" logical. While it may seem like is circular logic, everything that happens in the universe occurs due to natural laws and it is consistent because it's occurring in nature according to natural laws. If it didn't, one might assume some outside, supernatural force is acting upon it, or our own understanding of natural laws needs revision. -- MacAddct &#xF8FF; 1984 (talk &#149; contribs) 18:45, 21 February 2008 (UTC)

Can you give me an example of something that MUST follow, but nevertheless empirically at least once in the history of the universe hasn't? I'm thinking of examples like: If you put drop three apples into an empty a basket there MUST be three, the Universe would have to be illogical or inconsistent to return a basket of 2 apples for no reason... Has stuff like that ever happened? (Like in dreams). —Preceding unsigned comment added by 79.122.42.134 (talk) 17:16, 21 February 2008 (UTC)
 * We could only answer whether each of us individually has ever had this experience, but can't answer if something like this has ever happened. There aren't enough observers to check that the universe has been consistent 100% of the time. Sancho 18:40, 21 February 2008 (UTC)


 * Essentially, let's say the universe has a set of rules called R, and we have an approximation of those rules called A (also known as Science). What you're asking is if R has ever contradicted itself (if the universe has broken its own rules). The problem, is we don't even know what R is. We can only tell when R contradicts A and then we adjust A to match our observed R. There are PLENTY of examples of R contradicting our (at the time) A (think relativity, quantum mechanics, virtual particles, etc.), where we had to change A. Theoretically, however, R always applies and can not contradict itself. (EhJJ)TALK 19:04, 21 February 2008 (UTC)


 * That was a much more logical and elegant way of putting it than my ramblings! -- MacAddct &#xF8FF; 1984 (talk &#149; contribs) 19:06, 21 February 2008 (UTC)


 * Speaking of apples in baskets, it reminds me of a physics joke: "The physics department is having a party at a professors house. Initially, there is no one in the house. Two professors enter the house (it's a small party). Afterward, three professors leave the party. Finally, one returns to the party. How many professors are in the house? None!" (2-3+1) = 0 This might seem illogical and contradictory, but that's how the universe works! (That is, from what I've been told. Maybe someone with more physics background can elaborate). (EhJJ)TALK 19:15, 21 February 2008 (UTC)
 * Maybe an anti-professor entered the house. That would be logically indistinguishable from a professor leaving it. DJ Clayworth (talk) 20:12, 21 February 2008 (UTC)


 * If three walked out, then the initial observation that there was "no one in the house" was incorrect. I like the joke on the Mathematical joke page better. But this isn't about jokes, this is serious business, and the fact of the matter is that we know nothing. Who knows, maybe the universe isn't made up of quarks. Maybe everything is made up of universes, and our universe is a quark in another universe, ad infinitum. What is light is actually infinitely fast but it leaks into another dimension at a certain speed and gets instantly replaced by light from yet another dimension? What if time is actually tangible? How about liquid gravity? Multiverses! Stuff that exists only if people look at it! I'm not crazy! 206.252.74.48 (talk) 20:18, 21 February 2008 (UTC)


 * The other problem with determinism is that it isn't that something follows from something else, it's that everything follows from everything else - nothing in the universe is a truly closed system (except possibly the universe itself), and so even if you had all the rules at your disposal you would find it impossible to make 100% accurate predictions as that would require knowing the exact properties of everything in the universe at one time - even being accurate to a thousandth of a percent could become an error of a thousand percent in the long run, thanks to chaos theory. Confusing Manifestation (Say hi!) 22:24, 21 February 2008 (UTC)


 * Two problems: quantum theory is often nondeterministic. Read up if you are interested in details, but there are times that things seem to happen for no good reason and there is no way to predict exactly when they will happen. And it's not an issue with our knowledge of things; they seem to actually be indeterminate at a base physical level. Creepy, no? Einstein found the idea disgusting but it seems to be the case. Second problem: no non-trivial system of logic can be entirely complete and consistent, a priori. See Gödel's incompleteness theorems for the full proof, but it's pretty hard stuff to make sense of from the get-go. Nevertheless it seems to hold up well; to sum it up, as one webcomic artist I enjoy recently did: "Formulations of number theory: Complete, Consistent, Non-trivial. Choose two." --98.217.18.109 (talk) 22:56, 21 February 2008 (UTC)


 * Being controlled by quantum randomness is in a way worse than being controlled by predictable determinism...(to me personally) 199.76.153.227 (talk) 00:54, 22 February 2008 (UTC)
 * It's like everything is chaos so just pick the organised system or theory that comforts you best (as in the one that promises to cover the most ground of experience). Julia Rossi (talk) 09:30, 22 February 2008 (UTC)

At some point in the history of the universe you would have to agree that logic came into existence. Before the "big bang" what would be logical? There are 3 choices. 1) All of the nothing that existed prior to the introduction of space, time and matter acted verry illogical. The nothing decided to pack itself together so tight that it exploded and rearanged its nothing into hydrogen. You know the rest of the story. 2) We are a figment of the imagination of something and are not realy here. 3) We were created by God.- All of which realy go against logic. Some more than others. But as the gentleman said,"what is logical to us may be very differnt from what is truly logical." There is a day when eveyone finds out the diference. —Preceding unsigned comment added by 75.145.213.217 (talk) 23:48, 22 February 2008 (UTC)
 * I disagree that those are the only three choices. First of all, choice #1 is invalid since it refers to something that took place "before time".  Without time there is no "before".  Also, there is no really important difference between #2 and #3, and there is no evidence to support either version.  Personally, I like the idea of an eternal multiverse, periodically "big banging" out new universes every billion years or so (something like this), but I admit that that's pretty much just speculation too.  Still, there are probably dozens of other possibilities out there besides those.  However, without evidence for any of these possibilities we're stepping out of the arena of science and into philosophy, where we're simply debating how many angels can dance on the head of a pin.  Right now the best answer is simply, "We don't know."  Now, some people try to equate "we don't know" with "therefore we know God/Allah/Jehovah/Buddha/Vishnu/Odin/Zeus/The Flying Spaghetti Monster/etc... did it", but not knowing something is not evidence for any conclusion.  Don't let that keep you from trying to find out the answer though!  :-) --  Hi  Ev  11:38, 25 February 2008 (UTC)


 * Well said. Imagine Reason (talk) 23:46, 25 February 2008 (UTC)

Building a voltaic stack
I have been trying to build a voltaic stack for a science fair project. I have been using dime and pennies, all from after 2000, and blotter paper soaked in a vinegar-salt solution. I have used up to ten cells. I am connecting the stack by copper wire to an LED, but it will not light up. Does anyone know why or what I am doing wrong? —Preceding unsigned comment added by 70.253.160.19 (talk) 20:34, 21 February 2008 (UTC)


 * Do you have access to a voltmeter? The reason to ask is the following:  there are two or three kinds of problems possible here.
 * Your stack might be working, a little, but unable to put out the amount of current required by the LED.
 * Your stack might be generating no voltage at all.
 * You might be wiring the LED backwards. The "D" in LED stands for diode; it will only conduct in one direction.
 * A voltmeter would let you see which it is. Once you know what kind of failure mode you have, you can start looking for likely causes.  If it's the first kind, voltage but not enough current, you should look for high resistance in your circuit.  Start by cleaning the coins well.  If it's the second kind of problem, look for an unwanted current path.  If your electrolyte (the vinegar-salt solution) allows current to flow along any path other than the series order of the cells, then you might have a short circuit.  Finally, a voltmeter will allow you to detect which is the positive end of your stack, and confirm which way the LED will conduct. JohnAspinall (talk) 20:55, 21 February 2008 (UTC)


 * If we use D=dime, P=penny, and B=vinegar/salt blotter paper, does your stack look like this:

DBPDBPDBPDBP (4 stacked cells of Dime-Blotter-Penny each)
 * or like this:

DBPBDBPBDBPBDBPB (Dime-Blotter-Penny-Blotter-Dime etc, which will generate nothing except heat)
 * -SandyJax (talk) 21:18, 21 February 2008 (UTC)

If the voltmeter shows that you have sufficient voltage to light the LED, and you determine that the plus and minus ends of the battery are corrected to the correct terminals of the LED, then it still might not work because an LED requires a certain amount of current to light, and the tiny area of your coins may not produce sufficient current. A solution to this is to connect a capacitor across the battery (with the plus and minus terminals correctly connected) and allow a sufficient charge to build up with the LED disconnected. Then have a momentary pushbutton switch, or a knife switch, which is used to connect the battery/capacitor combination to the LED. The capacitor will be able to provide more of a surge of curent to momentarily flash the LED. Then open the switch to allow the charge to build up again. The capacitor should be an electrolytic one; I'm guessing of over 10 microfarads capacity and of a voltage rating higher than the battery can produce. The battery's current and voltage capability and the current and voltage requirements of the LED would enter into the design. If you provide more data, I'm sure folks here can provide more advice. You can leave the voltmeter connected across the battery/capacitor combination to monitor the buildup of voltage. You should not use so many pairs of metal discs in your battery that a hazardous voltage is built up: the LED might only need 3 to 4.5 volts- others may have some guideance for you here. See also LED circuit, Battery (electricity) and Capacitor. If the battery voltage with no load is much higher than the proper operating voltage of the LED, you might need to connect a current limiting resistor in series with the LED. You can avoid this by making sure the number of pairs of metal elements in the battery is high enough to light the LED but not too high. Older coins which were copper (or bronze)pennies and silver dimes may produce a higher voltage per pair. Edison (talk) 05:26, 22 February 2008 (UTC)


 * In response to the question, I built some voltaic cells with two coins separated by a double thickness of paper towel moistened with pickle juice, which contains both vinegar and salt. Note: the coins used in such experiments will be become corroded, discolord or damaged. With a modern dime and a modern penny, the open circuit voltage was .05 volts and the short circuit current was .08 milliamperes. With a 1958 wheat penny and a 1925 silver Mercury dime, the open circuit voltage was .15 volts and the short circuit current was .75 milliampere. With a new cent and the old silver Mercury dime the voltage was .14 volt and the short circuit current was 1.0 milliampere. With the 1958 wheat penny and the new dime, the open circuit voltage was .015 volt and the short circuit current was .05 milliampere. Then I tried aluminum foil and the silver dime. The open circuit voltage was .77 volt and the short circuit current was 36 milliamperes, which dropped in 30 seconds to 4 milliamperes. In later trials with new moistened paper in between, the max current was lower, around 10 milliamperes, but still promising for running an LED, if there were enough cells in the battery. With aluminum foil and a new penny, the open circuit voltage was .6 volt and the short circuit current wsa 6 milliamperes. In conclusion, a science fair project would do well to obtain adequate measuring instruments (a digital voltmeter is on the order of $30 at a hardware store) and to do some experimentation by trying metals at different places in the electromotive series, rather than just building something and voila it doesn't work. Get permission before experimenting with anything valuable. A worn coin worth little more than the value of the metal should be used rather than something with numismatic value which is in good condition. Why is the present dime so lousy in a battery with modern pennys? The modern Roosevelt dime is a copper center sandwiched between two outer layers of 75%copper, 25% nickel. The old Mercury dime is 90% silver, 10% copper. The modern cent (penny) is a 97.5% zinc center disk with 2.5% copper plating. The modern dime-modern cent battery is pretty close to copper and copper so far as what is on opposite sides of the blotter, and a Voltaic cell requires dissimilar metals. The 1958 wheat cent was an alloy of 95% copper, 5% zinc. Standard electrode potential (data page) gives electrode potentials for cells made of various metals. See Galvanic cell where it says more about how to calculate the expected voltage. See also Lemon battery. Edison (talk) 19:55, 22 February 2008 (UTC)


 * You might investigate using copper and zinc foil, plates, or sheet-metal (instead of coins). These plates are fairly cheap and available at hobby shops, metal shops, and some home-improvement warehouses.  Nimur (talk) 22:09, 27 February 2008 (UTC)

Body wastes H2O?
Does the body not waste significant amounts of water, when we exhale? If I took a walk in the desert, surely I'd fancy to not let go of all the water in my body, but rather keep it circulating. Why is it treated like a waste product? 81.93.102.185 (talk) 20:41, 21 February 2008 (UTC)


 * The values for obligate water loss in humans are fairly well established. The minimum insensible water loss is about 800 ml per day; of this, about 400 ml per day are lost via evaporation from the skin, and about 400 ml per day are lost via expired air. These minimum values would obviously be exceeded in the heat of the desert in the midst of exertion.
 * Humans are not particularly well-adapted for desert life (nor is there any particular reason we should be, as by and large we don't live in deserts). The kangaroo rat does a much better job, both in terms of concentrating its urine, and in terms of reducing water loss through the lungs. :). - Nunh-huh 21:32, 21 February 2008 (UTC)


 * Bleh, bad statement you made. Yes, we aren't well suited for deserts. Humans aren't well suited for a lot of enviroments, especially cold enviroments. But don't say there's no reason to be. Humans live all around the world. Not just in your neighborhood. 64.236.121.129 (talk) 17:12, 25 February 2008 (UTC)


 * Humans evolved in tropical Africa, which was wetter at the time than it is now. 98.199.17.94 (talk) 02:09, 22 February 2008 (UTC)


 * Camels, which are better adapted to desert life than we are, have a convoluted moisture-exchange organ in their noses to extract water from the exhaled air, and add it back to the inhaled air. --mglg(talk) 04:38, 22 February 2008 (UTC)


 * Note that water could be preserved, through something like the stillsuits featured in the book Dune (novel). They covered the skin and the wearer exhaled through a tube which led to a device that extracted the moisture.  (In the movie version the suits didn't cover the faces, simply because people don't want to watch a movie where everyone looks alike with covered faces.)  Why don't we really use such a device on Earth ?  Unlike Arrakis (the desert planet in Dune), water is plentiful on Earth, so the need hasn't arisen.  Such a suit would be expensive to make (something like the cost of a diving dry suit with full SCUBA gear), and it's less expensive to just bring enough water with you when you go into the desert.  One issue a still suit would have is that exhaled breath is full of bacteria, so the reclaimed moisture would need to be sterilized or the bacteria would grow in the collected water.  As for reclaiming moisture from urine and solid waste, the suit wouldn't need to do this, as those wastes could be collected and you could have their water extracted using a device elsewhere. StuRat (talk) 13:35, 22 February 2008 (UTC)


 * A stillsuit would be very challanging to make and probablly cost a lot more than diving gear. Liquid that comes out of the body would need to be collected, cooled (since one of the main reasons the human body sheds water is to shed heat), purified, steralised and then fed back to the body somehow and for it to be worthwhile you would need to do all this including providing a power source for it in less weight than it took to just bring water with you. Plugwash (talk) 13:44, 22 February 2008 (UTC)


 * In Dune, the suits ran off body motion. I can possibly buy this if they just removed water from breathing and sweat, but not if they processed urine and feces, too.  The sterilization for breath and sweat could be as simple as dropping the water through an activated charcoal filter, adding something like the disinfection tablets campers sometimes add to river water to make it safe, then dropping the water into storage tanks in the legs.  I wasn't including the cooling function.  There are dry, cold deserts, like the Gobi Desert, so the "moisture-retention only" model would have some use, although I agree that the expense would make it cheaper to just bring all the water you need with you, instead. StuRat (talk) 18:56, 22 February 2008 (UTC)


 * A minor quibble&mdash;normally exhaled breath isn't 'full of bacteria'. The vapour pressure of a bacterium (or of any other microorganism or pathogen) is essentially zero; bacteria can't 'evaporate' into the exhaled airstream.  The air exhaled by a healthy individual will be essentially free of bacteria, and what little there is will be normal and relatively non-toxic mouth flora.  A sick individual coughing and sneezing, or a healthy individual breathing raggedly and/or particularly violently will disturb droplets of mucous in the throat, nose, and mouth; this can aerosolize bacteria that may be present and will generate some bacterial load in exhaled air.
 * Of course, all the surfaces that come intact with the exhaled breath will be warm and moist, and thus excellent sites for bacterial growth. Even a small amount of input bacteria would very rapidly tend to become a lot of bacteria.  I agree that keeping such a system clean would represent a significant design challenge. TenOfAllTrades(talk) 19:38, 22 February 2008 (UTC)