Wikipedia:Reference desk/Archives/Science/2010 June 4

= June 4 =

How does a battery-less moisture-meter work?
How would a moisture meter such as this work, bearing in mind that it uses no batteries? When inserting into soil, the needle flicks to the right before slowly moving a distance to the left and settling. Which of the readings can be considered the proper moisture level of the soil, based on how the device supposedly works? Would it be likely to harm the meter, to leave it sitting in soil, rather than removing and cleaning it every time? --92.25.237.15 (talk) 01:18, 4 June 2010 (UTC)
 * The picture clearly shows the two electrodes are made of different metals, so I would imagine it works in a similar way to a lemon battery. In the normal use of the device, the electrodes will be eroded (that's how it works - see the article I linked to), so leaving it in the soil will drastically reduce its working lifetime. --Tango (talk) 01:34, 4 June 2010 (UTC)


 * Have you tried covering the light sensor of the light meter? If the device stops working it might mean it uses the light as a source of energy. Either way, leaving it in the soil might not be a good idea. Have you tried asking the manufacturer? Dauto (talk) 02:45, 4 June 2010 (UTC)


 * That's a quote from the link provided by the OP "To avoid damaging the electrode, please clean the electrode after each use". I guess that answers the question. Dauto (talk) 02:50, 4 June 2010 (UTC)

Does Synthetic Vanillin / Vanilla contain Alcohol
Does synthetic Vanillin or synthetic Vanilla contain alcohol? Or is alcohol used in the process of making synthetic vanillin/vanilla? If yes which alcohols are used? —Preceding unsigned comment added by 212.22.185.11 (talk) 06:30, 4 June 2010 (UTC)


 * I think that vanillin is often dissolved in ethanol - pure vanillin would not contain any alcohol but if you were to buy a bottle of vanilla extract then it will contain 35% alcohol. 86.7.19.159 (talk) 12:21, 4 June 2010 (UTC)


 * I have a bottle of synthetic vanilla which contains: water, caramel color (to make it dark like real vanilla), flavors, potassium sorbate. No alcohol. --Chemicalinterest (talk) 12:42, 4 June 2010 (UTC)


 * Guys, vanillin is not water-soluble. It has to be dissolved in some sort of (edible) organic solvent or be stabilised with surfactants. John Riemann Soong (talk) 17:27, 4 June 2010 (UTC)
 * The "alcohol-free" vanilla flavorings I've seen use glycerol or other "not ethanol but similar-structure" solvent. DMacks (talk) 17:41, 4 June 2010 (UTC)
 * Vanillin is water soluble. Not highly soluble, admittedly, but I've regularly made 100mM solutions in water without it crashing out. Rockpock  e  t  18:04, 4 June 2010 (UTC)
 * "Solubility in water 	1 g/100 ml (25°C)" if we're to believe our own article. DMacks (talk) 18:10, 4 June 2010 (UTC)

JRS: "Guys, vanillin is not water-soluble. It has to be dissolved in some sort of (edible) organic solvent." Apparently, it's slightly soluble in water.

Page 3-292 of the CRC Handbook contains the following data on vanillin:

The solubility abbreviations are as follows:


 * i = insoluble
 * sl = slightly soluble
 * s = soluble
 * vs = very soluble
 * msc = miscible
 * dec = decomposes

Other abbreviations:


 * tetr = tetragonal
 * w = water
 * lig = ligroin

I have three different bottles of vanilla flavouring in front of me:

Ben (talk) 14:12, 5 June 2010 (UTC)
 * Hey, you must like your vanilla! ;) As for the artificial vanilla mentioned above, potassium sorbate is a mild surfactant, which would help keep vanillin in emulsion (if necessary). Also, depending on the country, it's not always necessary to include ethanol in the ingredients below a certain level, or in certain preparations. In the UK, for example, drinks with less than 1.2% ethanol do not have to be labelled. Physchim62 (talk) 15:43, 8 June 2010 (UTC)

Mercury and Dental Fillings
Let me preface this question with two things: this is not a request for medical advice, and I do not put any stock in amalgam fillings causing mercury poisoning. However, my question is related to the second point; supposing you took a normal sized amalgam filling and ate it, what would the effects be? What if you inhaled the equivalent ammount of mercury present? Finally, instead of ingesting/inhaling it all at once, what if you stretched out the time span to taking 1/500th of the filling every day, what would be the effects after 500 days (any number can be put in place of 500, I'm really just curious about how dangerous amaglam fillings would be, were the people opposing them correct.) 66.202.66.78 (talk) 10:43, 4 June 2010 (UTC)
 * Have you looked at Dental amalgam controversy which while not addressing your hypotheticals would seem the obvious starting point. Nil Einne (talk) 11:12, 4 June 2010 (UTC)
 * Mercury poisoning also has a lot of useful information. Between the fact that the mercury is in an amalgam with silver and is thus carried out of the body fairly easily - and the fact that the uptake of mercury through the digestive system is so low (0.01%), this is a really small problem.  Mercury is exceedingly dangerous when it's reacted with other stuff - but the pure metal is much less nasty. The amount of mercury you absorb from a tunafish sandwich is likely to be greater than from accidentally swallowing a tooth filling. SteveBaker (talk) 13:06, 4 June 2010 (UTC)
 * Mercury is a rather inert metal, so its rate of absorption is low. Mercury compounds are reactive and toxic, and some of them are easily absorbed, making them extremely toxic. Improperly made dental fillings may be at more risk of mercury poisoning. --Chemicalinterest (talk) 14:38, 4 June 2010 (UTC)
 * I had a filling like this when I was a kid. I remember nausea and a lot of vomiting. --Ouro (blah blah) 15:56, 4 June 2010 (UTC)\


 * That may be better explained by stress or side effects of the anaesthetic, Ouro. The studies I've read show zero history of actual mercury poisoning effects in post-1950s dental fillings. SamuelRiv (talk) 17:33, 4 June 2010 (UTC)
 * As I recollect, I got this filling in communist Poland. I surmise that the quality might not have been that high. Or I was young, or stressed. No way to check it out. Just volunteering information, SamuelRiv. But thanks though. --Ouro (blah blah) 19:42, 4 June 2010 (UTC)
 * Plus, those really aren't the symptoms you'd expect with mercury poisoning. - Running On Brains (talk) 16:31, 6 June 2010 (UTC)
 * I swallowed a fresh amalgam filling at the dentists while a teenager. I subsequently got a Master's degree so I hope and assume it had no effect on me. I do not recall felling ill or sick. 92.24.185.225 (talk) 13:26, 6 June 2010 (UTC)

In case you were interested, no ill effects have ever been shown to be associated with dental amalgam statistically significant; it has been shown, however, that the bis-GMA in composite restorations ("white fillings") is associated with a higher risk of breast cancer in rats.  DRosenbach  ( Talk 23:50, 7 June 2010 (UTC)

Technological family tree.
Partly a follow on from an earlier disscusion...

Has anyone here come across (in published sources) the idea of a technological family tree?

This being a diagram illustrating which technologies or discoveries are required for a particular technological development to occur.

Technology trees are used in the computer game Civilization and it's sequels and was wondering if these had been used in the academic world as well?

Sfan00 IMG (talk) 13:43, 4 June 2010 (UTC)
 * It's not really academic, nor does it involve a formal graphical "tree", but I'm reminded of James Burke's interesting series Connections and its sequels, which traced (some of) the developments that were necessary for particular bits of modern technology to arise. Deor (talk) 14:13, 4 June 2010 (UTC)
 * Burke's website here may also be of interest. Ghmyrtle (talk) 15:11, 4 June 2010 (UTC)
 * As you can see from his website, though, Burke would be the last person to describe technological advancement in that way as he's spent his professional life illustrating that technology in fact gets developed through all kinds of weird happenstances. He would (and is trying to) make a web, not a tree. Matt Deres (talk) 16:28, 4 June 2010 (UTC)
 * Well, the technology trees in Civilization are actually more complicated webs, as I recall. They are greatly simplified from real life, of course. --Tango (talk) 17:03, 4 June 2010 (UTC)
 * General histories of technology commonly note breakthrough technology which is the key to some later invention. A powerful compound electromagnet with many layers of insulated wire (Joseph Henry, 1827)) was essential to a practical electric telegraph relay and sounder(one which would function over miles of wire under all conditions), so Morse could not have introduced the practical telegraph before 1827. The phonograph (able to record and play back intelligible speech and music) was invented in 1877, but no breakthrough technology came along just in time as was the case for the Morse telegraph. It could have been built many decades earlier, or as early as good machine tools were available, perhaps in the 1770's, had someone chosen to mechanically impress concentrated sound vibrations on a medium such as wax, tinfoil, lacquer or even soft wood or clay. Edison (talk) 18:30, 4 June 2010 (UTC)
 * I think instead of a tree, it would be a directed acyclic graph with all edges pointing in the direction time is flowing. --Rajah (talk) 01:07, 5 June 2010 (UTC)

RESOLVED! -- Houseplant identification please... -- RESOLVED!
Unfortunately, I haven't a picture. In several stores around China I've seen a small houseplant for sale. It has one very large seed - almost as big as a golf ball - that is dark green and split down the middle from which a stem and a few leaves grow. I can't describe it better than that, but if you've ever seen one that should be enough. I've tried all manner of google searches and haven't hit on a picture. Can anyone out there help me? 91.216.105.31 (talk) 13:50, 4 June 2010 (UTC)


 * Are you sure it's a seed, and not some form of bulb? Sfan00 IMG (talk) 13:59, 4 June 2010 (UTC)
 * If the seed was red, then it could be a lychee which is a fruit, but I doubt if they are grown as house-plants. CS Miller (talk) 14:15, 4 June 2010 (UTC)
 * I've grown avocado seeds before, and the description of the seed fits the bill here. --TammyMoet (talk) 14:48, 4 June 2010 (UTC)


 * OP here, on a different IP. I'm sure it's not avocado (I've got one of those growing right now) - this seed is a dark forest green color and smaller than that. It has 2 clear hemispheres. I'm also sure it's not a bulb. If all else fails, I'll try and get a picture on Sunday for you all to look at... no chance before then though. 61.189.63.191 (talk) 15:40, 4 June 2010 (UTC)


 * Ok, I went and bought one. http://www.drewsjournal.com/JUNK/mystery-plant.jpg Now someone please help me figure out what it is! My original description stands - golfball-sized seed dark green in color, clear hemispheres. The pot pictured fits in the palm of your hand, so maybe 3" across. Too small and wrong color for an avocado, though it certainly share similarities with that plant. Anyone? 91.216.105.21 (talk) 13:33, 5 June 2010 (UTC)


 * It looks to me like some kind of nut, see if this page helps any. Ariel. (talk) 03:32, 6 June 2010 (UTC)


 * Yay! One of my coworkers was able to identify it! It's Castanospermum australe, native to the rainforests of eastern Australia! 218.25.32.210 (talk) 05:09, 7 June 2010 (UTC)

Oil floating under water
News reports say there are "huge plumes" of crude oil from the leak in the Gulf of Mexico which are floating around below the ocean surface. lists densities of various forms of crude ranging from 790 to 973 kg/cubic meter. compared to 1021.98 for "ocean water at 77 F." Tony Hayward of BP claims that"oil has a specific gravity that's about half that of water" per that news story, quite different from the s.g. values cited from the online source. In either case, what force would prevent the less dense crude oil from rising to the surface, or is it uniquely dense, or is the water in the Gulf uniquely less dense? Consider how much force would be exerted by 1 cubic meter of crude at the weakest assumption of 973 density for crude, when it was submerged in seawater at density 1022 kg/cubic meter? Would it be simply the mass difference of one cubic meter (49 kg) times 9.81 m/sec2 or 480.7 Newtons (108 pounds force)? Does the density of the water change more than the density of crude with depth or temperature? Each barrel of oil (.159 cubic meter) should require about 17.1 pounds force to hold it below the surface. If it were in 1 ml droplets or smaller would it somehow not tend to rise? Is it supposed to float under heavier liquid from surface tension/force of habit/? Edison (talk) 16:32, 4 June 2010 (UTC)
 * My understanding is that the oil is mixed with gas, which blows it apart into droplets after it escapes. Just as tiny droplets of water may remain suspended in air for a long time, tiny droplets of oil may remain suspended in water for a long time.  It's basically what happens when you mix the vinegar and oil to make salad dressing. Looie496 (talk) 16:53, 4 June 2010 (UTC)
 * I tried as an experiment releasing 0.1 down to 0.01 ml droplets of motor oil (density about 888 kg/m3 below the surface of a basin of  (fresh) water (density about 998 kg/m3. The tiny drops tended to stick to the hypodermic needle, but when I shook it a bit they darted rapidly up to the surface of the water. How small are the "plume" droplets supposed to be, and what principle of physics or chemistry would keep them from rising? So far it sounds like "force of habit." Edison (talk) 16:56, 4 June 2010 (UTC)
 * I think it's a result of the dispersant they've been adding to the oil. It causes the oil to form droplets rather than a layer, and those droplets end up suspended in the water. I don't know the details. --Tango (talk) 17:01, 4 June 2010 (UTC)
 * If the droplets are down in the "few micron diameter" size then maybe they are in fact rising but some frictional effect of moving the water apart impedes the rise to a slow rate and some surface tension effect impedes their coalescing into larger drops with a greater terminal velocity of rise. Edison (talk) 17:06, 4 June 2010 (UTC)
 * Yes - upward force is proportional to cube, 'drag' proportional to square - so smaller drops should accelerate faster slower - though I expect there's a peak velocity in water as there is in air. Also viscosity
 * Don't think any surface tension effect would prevent coalescing though - unless when as a micelle
 * Perhaps there are down currents in that area that keep the drops underwater for longer ???87.102.32.39 (talk) 19:18, 4 June 2010 (UTC)
 * Keep in mind too that the crude is coming out pretty hot so it may also be partly fractionating, so the light ends will separate and head more quickly to the surface. The s.g. of vacuum tower bottoms is 0.97 to 1.03. Admittedly, that is the very heaviest fraction. Franamax (talk) 17:19, 4 June 2010 (UTC)
 * If it so hot that it is "self refining" in a fractionating or cracking process, then why is it simultaneously so cold that it freezes up and clogged the removal dome? And the sludge left in a refinery (if that's what "vacuum tower bottoms " is) is still far lighter than seawater. For the stuff to stay in an emulsified blob below the surface, the blob would have to have a higher density than the water, or the entire column of water would have to be part of the emulsion. Edison (talk) 17:29, 4 June 2010 (UTC)
 * First of all, the crude is what's hot, it's the ocean water that is very cold, it is mixing with the gas portion of the outflow to form gas hydrates, that is what is clogging the containment domes. Second, the MSDS I linked for bottoms (it's only sludge when it's really hot, it's asphalt when it cools) says the specific gravity is 0.97-1.03, this shows seawater wirh a s.g. of 1.025, so are you saying 1.025 >> 1.03? Or have you done all the lookups for temperature and pressure and you have a derivation for "far lighter than"? Lastly, all crude oil is "self-refining", that's why it stinks. The lighter fractions are separating preferentially and the benzene is making you dizzy. Crude oil is not one "thing", it is a mixture of many different compounds, each with a different partial pressure. There is certainly no cracking process at work, but the light ends will definitely get to the surface (and evaporate) faster than the heavies. That's why they've been discussing the problem with burning-off once the slick has been floating around more than a few days. Franamax (talk) 03:56, 5 June 2010 (UTC)
 * Press reports, such as one from the New York Times say one plume is "3 miles by 10 miles by 300 feet," which would be 7.5 x 10 11  cubic feet, which would be 133 x 109 barrels of oil. The max leak rate estimate is 80,000 barrels a day, or about 3.5 million barrels total so far. Thus there appears to be a gross overstatement of the actual mass of oil involved in the plumes.  A scientist states it might have the "consistency of thin salad dressing" in places, fostering the impression that far more mass of oil is in the plumes than seems likely.  Edison (talk) 17:44, 4 June 2010 (UTC)
 * The media can also be quick to jump on a sensational story and slow to admit error. The laws of physics are hinting to me that this is what is going on.  Googlemeister (talk) 18:26, 4 June 2010 (UTC)
 * Two things - when the Times gives the size of a plume, they're likely to be describing the volume in which the concentration of oil is appreciably higher than zero &mdash; not the volume of pure oil. Compare with coverage of the 2010 eruptions of Eyjafjallajökull, where our article discusses an ash plume more than 8 km high.  The ash is there, it's visible, it's definitely occupying that volume &mdash; but no one assumes that there's a solid inverted cone of ash more massive than the volcano beneath; there's air mixed in.  Indeed, the vast majority of the ash plume is air, just as the vast bulk of these oil plumes is seawater.
 * A second point that the ash also illustrates nicely is how long it takes for fine particles to settle. Air and volcanic ash particles have a much greater difference in density than oil and water, and air is a far, far less viscous medium than water &mdash; but volcanic ash still managed to stay suspended in the atmosphere for days and travel for hundreds of miles.  I applaud your experimental spirit in your motor oil and water test, but if the oil is being forced out of the borehole and is undergoing turbulent mixing, then the droplets produced – at least some fraction of them – are apt to be significantly smaller than the 10-100 microliter volumes you tested.  Using the creeping flow approximation to calculate terminal velocity, and assuming a density difference of 200 kg/m3 between oil and water one can estimate the rate at which oil droplets will rise to the surface.  A sphere 1 mm in diameter (which is quite distinctly visible, though it only has a volume of about 0.5 microliters) would have a terminal velocity of just 3 millimeters per minute; the effect of its bouyancy would in most cases be dwarfed by the effect of rising or falling ocean currents.  At that speed, droplets deposited at the borehole depth of 1500 meters would take about a year to reach the surface. TenOfAllTrades(talk) 20:11, 4 June 2010 (UTC)
 * One of the biggest sources of error here is accurately estimating the density of the oil that is coming from the reservoir. It is at least plausible that some of the oil in the Gulf of Mexico is on the order of 10° API - in other words, heavy oil - in which case it is not less dense than water.  Deep below the sea surface, there is not much turbulence, but as the plume jets its way out of the bore-hole (or some other place where it is leaking), it is probably spraying out in a very turbulent way.  This may complicate its path to the surface.  If the pressure were low, the plume would rise as a laminar flow to the sea surface (where wave action would turbulently mix it in the top few feet of water).  But since the borehole pressure was very high (enough to cause a blowout), it is hard to predict exactly what happens as the oil contacts the open ocean at the sea bottom (or other leak location).  As has been pointed out above, the situation is further complicated because the fluid that is leaking from the reservoir is a mixture of crude oil, natural gas, sediments, brine, drilling mud, drilling crud, and other impurities.  Nimur (talk) 19:17, 4 June 2010 (UTC)
 * Heavy crude oil describes that product as bitumen or oil sand. Is there any evidence that was in the deposit they drilled into, or that it is found in that area of the Gulf? It sounds like heavy crude does not flow well in general. Edison (talk) 20:20, 4 June 2010 (UTC)
 * "What we're doing is we're taking a highly pressurized solution, and we're exploding it out of the sea floor under high pressure and high velocity."
 * expand assuming the oil is tar+oil+gas then at lower pressures the gas will boil off .. pressure increases with depth - it's possible therefor - that as the mixture rises further de-gassing (of methane/ethane etc) happens. It's possible again that this degassing is sufficiently violent (especially if it becomes supersaturate with gas before boiling) that this loss of gas causes the droplets to become yet smaller, again reducing the speed at which they rise. It's also possible that this doesn't happen or the effect is negligable.
 * I didn't actually see anywhere a claim that the liquid is heavier than water though. Density of 0.8 - 0.9 cc takes quite a long time to rise hundreds of feet - and there may be strong lateral currents.
 * Did you misread the CEO ? :"Mr. TONY HAYWARD (Chief Executive Officer, BP): There's no evidence of (that) .. (the) oil has a specific gravity that's about half that of water. It's very difficult for oil to stay in the column. It wants to go to the surface because of the difference in specific gravity."


 * As regards the density vs. depth question compressibility is the thing you want this compares toleune and water (tolune is ~twice as compressibile at 8.94 x 10-4 MPa-1) - so maybe there is something in this idea.. but it's a very small figure (no idea what the pressure is down there) There should be better tables somewhere on the internet.87.102.32.39 (talk) 19:56, 4 June 2010 (UTC)

87.102.32.39 (talk) 19:27, 4 June 2010 (UTC)
 * Hayward seemed to be trying to say that the oil has a low specific gravity and that there was no evidence of plumes (despite the fact that he was speaking in a nonsentence which could be taken to mean the opposite). Edison (talk) 20:22, 4 June 2010 (UTC)
 * Uh - yes - I think they mistyped in the link is used (corrected it) - looks like they've joined two sentences together - but it does look like he was saying oil has half the density of water. (The english have acquired the bad habit of lying/stretching the truth in the last decade  - I know . live there.)..87.102.32.39 (talk) 20:48, 4 June 2010 (UTC)


 * Several news sources have used the terms "heavy crude" and "tarballs".  It is not clear whether this terminology is scientifically accurate or media hype.  Heavy oil is definitely known to exist in the gulf, and indeed is the primary constituent of the geologically similar Orinoco Belt.  Biological activity in the deep subsurface and the origin of heavy oil (Nature, 2003), states: "Biodegraded oils also represent a significant fraction of the petroleum in conventional oil reserves and will be common among future oil discoveries likely to be made in deep-water areas of the world (for example, the Atlantic margin basins of Africa, South America, Canada and the Gulf of Mexico)."  Reservoir geochemistry of South Pass 61 Field, Gulf of Mexico: compositional heterogeneities reflecting filling history and biodegradation (Organic Geochemistry, 1996) has tables of geochemical analysis.  A quick look through some of my Oil & Gas Journal archive has a bunch of market report stories on "heavy" crude in Gulf of Mexico - I'm looking at a February 2010 issue talking about 14 and 17° oil production in Louisiana.  Those would still be lighter than water, though.   Unfortunately, the exact chemical makeup of the Macondo is pretty intensely "company confidential" and I'm sure only privileged members of BP's production team know what's coming out of the reservoir.  Nimur (talk) 20:56, 4 June 2010 (UTC)


 * John Ebdon, an Emeritus Professor and chemist at Sheffield University said in a letter in Friday's Guardian (can't find a link): "...True, seawater has a specific gravity of about 1.03g/cubic cm whereas that of crude oil is about 0.8g/cubic cm ... but significant fractions of crude oil consist of asphaltenes and other complex substances with specific gravities around 1.4g/cubic cm ... these heavier fractions will almost certainly separate and so be retained at depth." --Tagishsimon (talk) 04:11, 5 June 2010 (UTC)
 * The improvised refinery which fractionates the oil to create the asphalt/bitmen submarine is of dubious plausibility. Asphalt of dubious 1.4 density "retained at depth" would not wash up on Pensacola Beach and would not be much more of an issue than if it had not been brought up by drilling. The media creates spectres of "plumes" of oil many orders of magnitude greater in mass than could possibly exist.  Edison (talk) 04:41, 5 June 2010 (UTC)
 * Scientists now say that microscopic drops of oil are a natural part of ocean water, and that bacteria digest it and eventually are feed for fish. Edison (talk) 01:51, 8 June 2010 (UTC)

Doorbell Continually Hums or Buzzes
the button is stuck in the contact position. how long till  the electromagnet will burn out and the bell unit won't work  —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 17:30, 4 June 2010 (UTC)
 * Why not just disconnect and repair it, rather than go through the discomfort of waiting for it to burn out. which I suspect you've already read as it's linked to from a page almost identical to your question, gives you a description of how to dissemble a doorbell. Regards, --— Cyclonenim | Chat  17:37, 4 June 2010 (UTC)

can you just tell me how long till it burns out? i dont have the tools right now. —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 17:50, 4 June 2010 (UTC)
 * It depends, but "long" is a good estimate. Think weeks or months, or even years. There is no particular reason why anything should "burn out". --Stephan Schulz (talk) 17:57, 4 June 2010 (UTC)
 * A defective doorbell circuit is likely to cause radio, television and celphone interference, which is one good reason to get it fixed. Some doorbell transformers have a thermal protection element which heats up and opens the current, then resloses, providen a spark each time which interferes with electronic communication. The thermal protector often burns out and just arcs continuously, provide ongoing interference. In the US, it is a violation of the FCC rules to create "harmful interference". A shorted transformer could also start a fire, . (Paradoxically, in a great many instances over the years, doorbell wires shorted by a house fire have alerted the family and saved their lives).How long would it take to burn out? I once read an account of a person growing up in an apartment with a defective doorbell circuit. The transformer or chime hummed all the time, 24/7, except when someone pressed the doorbell, at which time it quit humming momentarily, and they knew someone was at the door. Edison (talk) 18:00, 4 June 2010 (UTC)
 * Doorbells are often very high-current devices - you may be burning two or five amps if the electromagnet is constantly activated. (Some are lower-power - here's a 30 watt bell).  Most bells are not intended to be "energy-efficient", because you want the bell to be loud and momentary - so effectively, they are designed to consume on the order of 50 or 100 watts, (but quickly shut off).  If the switch is stuck in contact-position, and you are burning a steady 50 or 100 watts, over a month that will add up) and will cost you in the neighborhood of $5, depending on your electricity price.  Nimur (talk) 19:08, 4 June 2010 (UTC)
 * That makes me wonder, is there a danger that it was installed with wiring that can't handle constant use? APL (talk) 20:45, 4 June 2010 (UTC)
 * Actually, since you mention it - that's certainly possible in older houses. In the UK, there is stuff called "bell wire" that used to be used specifially for wiring up doorbells and those bell systems in big houses that let the lady or gentleman of the house summon servants from the kitchen from any room in the house.  That wire was very thin indeed, single-core with enamel paint insulation.  Bell wire was the home-experimenters wire-of-choice back when I was a kid because it was cheap and you could get it in any electrical repair store.  So it wouldn't surprise me at all if it overheated and burned out in an old property...and that's a fire risk.  But I'd expect chunkier wiring in modern doorbells - so it's probably not a problem for a house that's less than maybe 50 or 60 years old.  SteveBaker (talk) 04:25, 5 June 2010 (UTC)

can any of these radio frequencies harm me?
 * No. APL (talk) 20:45, 4 June 2010 (UTC)


 * Really - you can trivially repair this with no more tools than a screwdriver - or (if desperate) a kitchen knife - or maybe even a thin coin! Waiting - on the offchance that it'll just blow up and "fix itself" - is pretty pathetic.  Turn off the power, unscrew the bell button or pop open the cover, if the contacts inside look corroded then just scrape off the surface corrosion with your knife/screwdriver - then bend them so they don't quite touch when the button isn't pressed, and do touch when it is pressed.  Reassemble the button and turn the power back on - and you're done.  It couldn't possibly take 10 minutes to fix. SteveBaker (talk) 23:12, 4 June 2010 (UTC)
 * Curiously enough, there was "bell wire" before electricity was in use. Great houses in the 18th century, including the White House in John Adams' Presidency had "bell pulls" to signal servants that someone in a certain room wanted a servant to come. The "bell wire" was uninsulated copper, brass, or iron running to the kitchen or "Servant Central" where a pull on it rang a bell. Edison (talk) 04:31, 5 June 2010 (UTC)
 * Yes - I noticed that when I searched Wikipedia for bell wire and found it mentioned in Bell pull. It did surprise me to see the term used that way.  I wonder whether these old houses went from physically pulling the wires to passing electicity down them when they converted to new-fangled electrical systems (maybe using an earth as the return path).  That would save ripping out the walls to put in the new wires.  But the stuff I remember having as a kid in the late 1950's was single-core copper, very brittle and coated with what looks like a brown enamel paint or maybe a dark varnish...that was called "bell wire" too.  The electrical projects in "Boy's Own" style books always specified either "Bell wire" for battery-powered things or "Lamp wire" where higher current was required. This definition on Answers.com confirms my memory. SteveBaker (talk) 04:56, 5 June 2010 (UTC)

The difference between fire and plasma
Take this image for example, it's a projectile fired from a railgun. But of course, there are no explosives involved so that trail behind the projectile is plasma and not fire correct? So is it fair to say that plasma and fire can look the same sometimes, but are two different things? ScienceApe (talk) 18:06, 4 June 2010 (UTC)
 * You don't need explosives for flame; just heat, oxygen, and something to burn. --Sean 18:53, 4 June 2010 (UTC)


 * (ec) Most of the time, ("day-to-day" interpretation), when you think of fire, you are thinking about two things: (1) an oxidation reaction between oxygen in the air and carbon (or something else) in the fuel; and (2) a gaseous semi-ionized plume of hot air that is incandescent - glowing reddish yellow because it is so hot. The chemical reaction (1) provides the energy and heat, and contributes some chemical constituents to the flame plume, but mostly the glowy part is just the ambient air getting heated up (and indeed, somewhat ionized).  It would be fair to call that flame plume a "plasma" - but more specifically, it would be a dense weakly-ionized plasma.  In other words, it is more "gas-like" than "plasma-like", in that thermal interactions dominate the behavior, rather than electromagnetic interactions.  Typically, in plasma physics, we like to think about "sparse" (i.e., nearly a vacuum) plasmas where the collisions between molecules and ions are very rare.  But plasmas can be created in many ways - anything which provides enough energy to ionize a gas sufficiently that its electromagnetic effects are non-negligible.  That can be a chemical flame, or any other energy source.
 * All this being said, let's analyze the railgun photo you linked. Unfortunately, the caption/description is not really very explanatory - it says the gun is "electromagnetic," but that doesn't necessarily mean that there was no explosive (a lot of railguns use a primer charge to create a super-compressed gas in preparation for additional energy).  It's also possible that at 2000 m/s, the hypersonic projectile is tearing up its surrounding air so much that the thermal energy imparted to the shock cone is enough to incandesce or even ionize.  To what extent is the shock cone ionizing?  To what extent does the electromagnetic propulsion system ionize the surrounding air?  To what extent does the primer-charge interact with the muzzle blast?  How do these parameters affect the muzzle ballistics, kinetics, trajectory, and the energy balance for the projectile?  All of these things would be interesting research questions, and I would bet that the NSWC guys are instrumenting the heck out of this apparatus to answer exactly those kinds of questions.  But we only have the image caption - without further information, it's not easy to answer definitively.  But keep in mind - a plasma is just a gas that has been ionized so much that the electromagnetic effects are dominant, whether it's ionized by energy from a chemical fire, thermal collisions, electromagnetic radiation, nuclear energy, hypersonic shock, or other energy source.  Nimur (talk) 18:57, 4 June 2010 (UTC)
 * chemisty I've always understood most flame/fire to be primarily a radical reaction - also high energy but not a "full" plasma since many of the entities are neutral. If the flame is hot enough though gas will be ionised.. answer? it's a borderline case depending on T and gases burnt as well.87.102.32.39 (talk) 19:38, 4 June 2010 (UTC)
 * (EC)Plasma and a fire can look alike. Both can involve very hot gases. See Plasma (physics), which says that a plasma is electrically conductive because of ionization. But flame and smoke can also be conductive, depending on what the chemical composition is. Edison (talk) 19:01, 4 June 2010 (UTC)
 * If you look at the video that this shot was taken from, I think that it appears to be flame, not plasma. J.delanoy gabs adds  19:05, 4 June 2010 (UTC)
 * I can't tell - but yellow air plasma isn't usual. A plasma should decay without any soot etc. Maybe there was some coating on the 'bullet' that caused the plasma to go yellow?87.102.32.39 (talk) 19:45, 4 June 2010 (UTC)
 * You're right, for it to glow that brightly there must be something more than just incandescent air. With a flame, there are tiny particles of soot glowing (if you have complete combustion with no soot then you don't get a yellow flame, you get a dim blue flame that isn't caused by incandescence). There must be something similar in that plume. --Tango (talk) 19:54, 4 June 2010 (UTC)
 * This sounds 'clu-ey' "Particle debris ignites as a test slug exits the Office of Naval Research (ONR) 32 MJ (megajoules) Electromagnetic Railgun (EMRG) laboratory launcher located at the Naval Surface Warfare Center Dahlgren Division (NSWCDD)." 87.102.32.39 (talk) 20:04, 4 June 2010 (UTC)


 * Also, we have no way of knowing whether the photo is a true-color or false color image. I'm leaning towards a Schlieren photography, Rapatronic camera, polarizing filters, or some other "weird" photographic trickery (not even counting post-production digital color rescaling!) Note that the timestamp has microsecond precision.  Such high-speed cameras often are monochromatic.  Note how you can see the shock cone - that's a dead giveaway for a shadowgraph or Schlieren system.  So, we can't say for sure whether the yellow and green in this photograph are "meaningful" for analysis.  Nimur (talk) 21:11, 4 June 2010 (UTC)
 * There's an even more clear image of the shock cone at this link (scroll down) 87.102.32.39 (talk) 21:30, 4 June 2010 (UTC)
 * Horse's mouth "The flames are from pieces of the projectile disintegrating; the 7-pound slug is jammed so firmly between the rails that when it’s fired, pieces shear off and ignite in the air."
 * one commenter says "...but the video is slightly out of order... the first shot is of the impact. If you pause the video around 6-7 seconds you can see the projectile only has a plasma trail until it strikes the target." (same link) this isn't quite right the image above is earlier in time than that in which the projectile flys between gun and target.
 * The linked video has time count in the lower right . so if doubtful you can check for yourself. 87.102.32.39 (talk) 21:49, 4 June 2010 (UTC)
 * This image is confusing File:EMRG 070128-N-0000X-001.jpg - apparently showing a very similar moment in time - but a different colour - since the slug is aluminium and the fire is supposed to be from particles from the slug I would assume that the photo is a better colour representation. So why is the video footage (and the frame above) yellow?87.102.32.39 (talk) 22:12, 4 June 2010 (UTC)

Archimedes principle???
if a body is immersed in a fluid,is the volume of the displaced fluid equal to the volume of the body???......... —Preceding unsigned comment added by Researcher02 (talk • contribs) 19:38, 4 June 2010 (UTC)
 * Only if it sinks - this can be demonstrated with a full bathtub, large amounts of polystyrene foam, and some lead shot..
 * The density of the body must be more than the density of the fluid.87.102.32.39 (talk) 19:42, 4 June 2010 (UTC)


 * (e/c) under conventional assumptions (non-viscous fluid, unconstrained and not otherwise subject to compression, non-bouyant, non-dissolvable object, etc), yes. The fluid will conform to the shape of the object (so displacement will not be greater than the volume of the object).  note that for hollow objects, displacement will differ according to whether the interior spaces are open or sealed - open spaces will fill, making the displacement equal to the volume of the solid material; sealed spaces will displace both the volume of the solid mass and the volume of the sealed space.  -- Ludwigs 2  19:48, 4 June 2010 (UTC)
 * (ec) The volume of the displaced fluid is equal to the volume of that part of the body that is in the fluid. If the object sinks, that will be the whole body. If the object is floating then it will only be part of the body (a part with volume equal to the volume of the fluid that has the same mass as the object). --Tango (talk) 19:49, 4 June 2010 (UTC)
 * That assumes that the fluid displaces all the air in the body - if air is trapped (closed-top, open-bottom area or by hairs, etc), then the trapped air has to be counted as part of the body (after compression). CS Miller (talk) 13:33, 5 June 2010 (UTC)


 * The article section about this is Buoyancy. Comet Tuttle (talk) 21:09, 4 June 2010 (UTC)
 * The OP's question does not concern Archimedes' principle. The OP did not ask about a floating body. Cuddlyable3 (talk) 22:41, 4 June 2010 (UTC)

Why did my bonfire burn 'blue'?
Last summer, I used a bonfire to dispose of a large quantity of waste wood (mainly laurel branches) in my garden..

I noted that, when started the fire was rather yellow and produced a lot of smoke, but as it got going it smoked a lot less and changed from a yellow flame to a more blueish and less visible one...

What might be the cause of this?

In addition, a previous bonfire in a previous year apparently managed to make a small quantity of charcoal, although I'm not entirely sure how... The same bonfire for whatever reason was also able to be 'relit' merely by placing suitably dry fuel on the ashes the following morning, which came as a quite a suprise...

Anyone care to suggest a possible explanation for the charcoal production? or for the 're-light' capability? 62.56.112.251 (talk) 20:19, 4 June 2010 (UTC)
 * It's very common for a wood fire to create coals that stay burning hot overnight, in some cases they can continue to burn for days. That article describes them better, but briefly: after the outside of the wood burns, and the more volatile componants of the wood have escaped and burned, the heavier carbon based solids in the innermost parts of the wood stick around because they haven't been properly exposed to the air, but at the same time they're not volatile to evaporate through the hot wood. Usually these componants burn very slowly making hot coals. (These are good for cooking over, because of their even heat.) If they go out before they're entirely spent I suppose you'd have charcoal.  (Which does not come from true coal. A lot of people are confused on this point.)
 * Hot coals can stay hot for a suprisingly long time because they're covered in a layer of light, fluffy ash that both insulates them and prevents very much oxygen from reaching them. That way they don't cool off, but they also don't burn up very quickly. APL (talk) 20:39, 4 June 2010 (UTC)
 * Indeed - a fairly large bonfire will usually have hot embers left for several days. --Tango (talk) 21:12, 4 June 2010 (UTC)


 * Follow on question, Would this 'coals' method be exploitable for low-level metalworking? Sfan00 IMG (talk) 21:55, 4 June 2010 (UTC)
 * Did you mean could the charcoal you made be used for metalworking? I see no reason why not - it was used in the past,as the article charcoal says. 87.102.32.39 (talk) 03:21, 5 June 2010 (UTC)

Hmm. Have you seen She? --Trovatore (talk) 20:42, 4 June 2010 (UTC)


 * I would think that at first the oxygen supply was limited. After a while it started burning more completely, producing the hotter blue flame and less smoke. --Chemicalinterest (talk) 20:54, 4 June 2010 (UTC)
 * The yellow flames are incomplete combustion. The blue flames are complete combustion. If everything burns cleanly then there are no soot particles to glow red-hot, which is what gives the flame its colour. --Tango (talk) 21:12, 4 June 2010 (UTC)