Wikipedia:Reference desk/Archives/Science/2009 July 24

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July 24

Mercury Biological Effects

How does mercury interact with the biology of humans? We know that mercury causes problems, and lead causes problems, because lead binds to places calcium would bind to. How about mercury?174.3.103.39 (talk) 00:05, 24 July 2009 (UTC)

I am not sure this is known. Mercury poisoning article says "much remains unknown", either. I'll see if I can find something in the literature, but it won't be right away. Sorry. --Dr Dima (talk) 00:10, 24 July 2009 (UTC)

One theory mentioned in literature is that mercury ion binds to sulfur in cysteine and interferes with activity of proteins, e.g., Thioredoxins. --Dr Dima (talk) 00:23, 24 July 2009 (UTC)

Yeah, that makes sense to me (76.21 posting from a library computer) -- mercury has a high affinity for sulfur in general, so it would tend to irreversibly bind to cysteine. And since neurons in particular have high concentrations of cysteine-containing proteins, it would tend to kill them neurons and (eventually) make you crazy. BTW, I think the reason why organic mercury compounds are so much more poisonous is because they're less polar and thus can more easily go through the blood-brain barrier. FWiW 146.74.230.113 (talk) 00:52, 24 July 2009 (UTC)

The best known example of mercury's ill effect on man is the minamata disease which first was identified in Japan.Due to mercury content in the river water,it passed on into the fish and then into man.The concentration in the rivers though low was dangerous due to phenomenon of "biomagnification".So the people who consumed it ended up accumulating higher concentration of mercury.This severly affected the limbs and the muscles.For more info refer http://en.wikipedia.org/wiki/Minamata_disease —Preceding unsigned comment added by 117.193.130.204 (talk) 13:55, 24 July 2009 (UTC)

See also http://en.wikipedia.org/wiki/Mad_Hatter#.22Mad_as_a_hatter.22 --Phil Holmes (talk) 22:25, 29 July 2009 (UTC)

Intelligence

If I excise my brain by thinking a lot, will i become more intelligent. And what would that mean for me/ —Preceding unsigned comment added by 79.75.60.53 (talk) 00:21, 24 July 2009 (UTC)

It really depends on what you mean by "intelligent". It isn't a well-defined concept. If you want to become knowledgeable, try reading a lot. If you want to become good at solving problems, practice solving problems lots. If you want to understand complicated things, take a course on them. --Tango (talk) 00:24, 24 July 2009 (UTC)

No I want to be more intelligent as in the IQ tests they give you. Also clever (is it the same?). —Preceding unsigned comment added by 79.75.60.53 (talk) 00:30, 24 July 2009 (UTC)

I suggest you start by reading Intelligence quotient and intelligence. If you want to do well on IQ tests, then practicing the sorts of questions found in IQ tests would appear to be indicated. But note that IQ is at best a very poor measure of intelligence; that clever and intelligent are probably not the same thing; and that neither is of much use except in combination with other attributes. The very shortest answer to your first question is "yes", but there's much hidden beneath that answer. As to what that would mean for you, we cannot say. In general, it's a good thing, but effects vary from person to person and from time to time. --Tagishsimon (talk) 00:40, 24 July 2009 (UTC)

Can I reiterate an earlier discussion that learning to think more critically will get you far in this world (and will cure you of your obsession with IQ tests!). If I can recommend a wonderful, fun little book: Thomas Gilovich, How We Know What Isn't So. It's a wonderful little primer on critical thinking and why the general-issue human brain is so poor at it. --98.217.14.211 (talk) 00:44, 24 July 2009 (UTC)

Is it my jeans that say how intelligent I am? —Preceding unsigned comment added by 79.75.60.53 (talk) 01:01, 24 July 2009 (UTC)

See Nature versus nurture and Heritability of IQ. --Tagishsimon (talk) 01:13, 24 July 2009 (UTC)

Please do not attempt to excise your brain at home. Only a qualified surgeon has the necessary skill and tools to perform this operation. Cuddlyable3 (talk) 12:10, 24 July 2009 (UTC)

By which s/he means, the correct word is "exercise". ("wiktionary:Excise" means cut out). Also, "genes", not "jeans". Knowing this doesn't make you any more intelligent, but people might think you are. AlmostReadytoFly (talk) 14:00, 24 July 2009 (UTC)

One might reasonably ask what garments express "I'm intelligent". —Tamfang (talk) 18:57, 2 August 2009 (UTC)

Medicinal use of "Cineraria[e] maritima"

My local museum has an old medicine bottle(I'm not sure of the exact date, but it's early 20th century) labeled "Cinerariae maritima". Apparently "Cineraria maritima" is an alternate name for the dusty miller plant, Senecio cineraria, but what medical use has this plant had? 69.224.113.202 (talk) 02:59, 24 July 2009 (UTC)

It was a old-time "patent medicine" or "herbal medicine" claimed to cure cataracts, advertised to doctors and pharmacists starting in the the 1880's [1] as "Succus cineraria maritima." An 1892 mention suggested it had been tried and rejected in the past as a remedy for something [2]. The plant was also called "Dusty Miller" and was a common ornamental border plant in the 19th century. Showing a great case of seemingly reliable sources not being so, several seemingly mainstream medical journals in the 1890's uncritically reprinted press releases from the nostrum's manufacturer, quoting little-known doctors in faraway countries who had "cured cataracts" with the medicine. Clinical testing, or at least the circa 1900 version where it is tried on a few patients without any control group and with the doctor and patient knowing it was the medicine, found it ineffective [3], [4].. In 1916 the U.S. government shut down one supplier who sold it via circulars claiming amazing cures, with testimonials. But at the time, all they U.S. government could do as a penalyt was fining the company $10. See [5], and [6]. Homeopathic publications still list it. "Toxicity of houseplants" suggests [7] that long term consumption of the plant could be toxic. Edison (talk) 04:09, 24 July 2009 (UTC)

Infections During Pregnancy. — —Preceding unsigned comment added by 117.198.243.37 (talk) 03:45, 24 July 2009 (UTC)

Venus

Hypothetically, if Venus could be moved to a different distance from the Sun, what distance from the Sun would result in Venus achieving an Earth-like temperature, assuming that its atmosphere stays the same? --Shanedidona (talk) 03:33, 24 July 2009 (UTC)

I'm not a planetary physicist (as I said before), but it's clear to me that it would have to move to a distance FARTHER than Earth to achieve the same temperature cause its atmosphere keeps the heat in more. FWiW 98.234.126.251 (talk) 07:16, 24 July 2009 (UTC)

Curiously if it was the same surface temp as the earth the atmosphere would not be the same, as the vapours would condense at the lower temperature. You may need to ask again in another way.83.100.250.79 (talk) 08:59, 24 July 2009 (UTC)

Tough question to answer. 98.234.126.251 is correct, at first guess, Venus would need to be moved further away than the Earth as it has a very thick atmosphere and a powerful greenhouse effect. Unfortunately, reducing the insolation (by moving it further away) will initiate changes in its atmosphere, with components of it precipitating out and changing its composition - therefore changing how much of a greenhouse effect it experiences. You would need to build a more detailed climate model, and considering how hard it is to build a climate model of the Earth, building one of Venus would be even harder. — QuantumEleven 12:48, 24 July 2009 (UTC)

"Unfortunately, reducing the insolation... will initiate changes in [Venus's] atmosphere"... -- I wonder what would be so "unfortunate" about that? 98.234.126.251 (talk) 23:46, 24 July 2009 (UTC)

The atmosphere of Venus is carbon dioxide and nitrogen to better than 99.9%. Neither of these would change state if reduced to Earth-like temperatures. Dragons flight (talk) 01:11, 25 July 2009 (UTC)

Early in Earth's history, its atmosphere was almost entirely CO2 and N2 as well. The rise of unicellular plants converted the CO2 to O2 and gave us an oxygen rich atmosphere. Without life, Earth would likely revert back to an atmosphere similar in composition to that of Venus as well. It is quite likely that if you hooked a tow-cable up to Venus and dragged it to Earth's orbit and gave it time to equilibrate, you would have a planet whose atmosphere would be almost identical to the pre-life Earth's. If you innoculated this relocated Venus with life, you may even be able to closely approximate Earth's modern conditions after a few billion years. The deal with Earth;s atmosphere is that O2 can ONLY exist because plants make it; it is FAR too reactive to exist for even a few thousand years without constantly being replenished. Prelife Earth likely had a greenhouse effect similar to that of Venus. --Jayron32 03:25, 25 July 2009 (UTC)

what is TDSi engine

how does a TDSi engine workSaurabhasks (talk) 06:10, 24 July 2009 (UTC)

You'll want to look at Turbocharged Direct Injection, Diesel engine and Diesel car history. I'm not sure what the 's' will signify - sometimes it means 'sports' and is a reference to the Trim level. 194.221.133.226 (talk) 10:18, 24 July 2009 (UTC)

Mosquito and HIV

Suppose a mosquito bites a person infected with HIV.In this process the mosquito inserts it proboscis into the blood stream of the person.Then again when it bites .i.e.inserts its proboscis into the blood stream of a healthy person ( consider immediately ) the person doesnt contract HIV.how???Is it not the same as two persons using the same syringes or needles where they contract HIV.i.e. comparing the proboscis of mosquito to a syringe or needle. —Preceding unsigned comment added by 117.193.131.167 (talk) 06:59, 24 July 2009 (UTC)

I think it's because the moskeeter sucks the blood out rather than putting it in. FWiW 98.234.126.251 (talk) 07:18, 24 July 2009 (UTC)

As linked from the AIDS article: Why mosquitoes cannot transmit AIDS.--Shantavira|^{feed me} 07:27, 24 July 2009 (UTC)

that website was very informative. thanks —Preceding unsigned comment added by 117.193.142.180 (talk) 10:58, 24 July 2009 (UTC)

In a country where a large percentage of the population is infected and mosquito bites are common, the transmission by squashing a blood-engorged mosquito who is completing his meal on a second victim, with the HIV infected drop of blood deposited on the skin around the bite, followed perhaps by scratching, sounds like the most likely route. A 1 in 10,000,000 chance sounds like it would not happen, but some countries in subsaharan Africa have a high incidence of Aids (over 15% per the Aids article) as well as a high incidence of mosquito bites. The Aids article says that health care workers anywhere must be very careful not to get blood on them, and to cleanse blood from their skin immediately. A drop of blood is a drop of blood, whether from a medical procedure or a splatted mosquito. This route does not require that the virus survive long in the mosquito, or that the mosquito somehow pumps it back into the second person. Edison (talk) 15:03, 24 July 2009 (UTC)

Here's a question. If mosquito enzymes digest the HIV virus, why don't we use those enzymes from mosquito samples to develop a cure for HIV? ~AH1^(TCU) 03:51, 25 July 2009 (UTC)

I think it's a good idea, but we'll have to do a lot more research on what those enzymes are and what exactly do they do. 98.234.126.251 (talk) 05:06, 25 July 2009 (UTC)

Most of the viruses are made up of RNA or DNA as the central core and surrounded by protective protein coat.When this protein coat is digested the virus gets destroyed.Therefore protein digesting enzymes digest the proteins surrounding the virus.Thats what happens to HIV in mosquitoes stomach.Also you asked above, the enzyme cant be used because it is not specific to HIV.It shouldnt end up digesting vital proteins in blood.For the HIV vaccine it needs to be specific against the HIV virus. —Preceding unsigned comment added by 117.193.139.242 (talk) 05:05, 25 July 2009 (UTC)

Well, how about we try chemically modifying the enzyme to make it specific? Or would that be inherently impossible? (I'm just a petroleum chemist, I don't really know exactly how this particular enzyme works, so forgive me if I'm wrong.) 98.234.126.251 (talk) 05:09, 25 July 2009 (UTC)

It is very possible to do that, but that would take a hell of a lot of research.174.3.103.39 (talk) 07:11, 27 July 2009 (UTC)

Plus, as 117.193 pointed out, the same enzyme might not work against different strains of the AIDS virus -- it might have to be specifically modified for each new strain that appears. (In other words, there's also a risk of making it too specific in the process of modification.) FWiW 98.234.126.251 (talk) 22:55, 27 July 2009 (UTC)

Just took it from the topic HIV cure that follows below..just for ur quick reference.here it is "the fact that the virus attacks the very immune system cells targeting it certainly makes things difficult. My understanding too is that the genius of this particular virus is the gp120 glycoproteins which "decorate" the proteins which effect entry of the virus into the cell. To "cure" something, or to make a vaccine against something, you need a target. But gp120 is highly variable, so it's difficult to target, and it hides the less variable proteins underneath that do the dirty work of infecting the T-cells. Any one successfully infecting HIV can produce a million new particles with variant gp120's, and only one of them has to work for the infection to continue. ".....so u see the specific difficulty associated with the menancing HIV.Most of the virus till today dont have a cure.When we can ourselves(I an engineering student) think of so many possibilities scientists who have been researching on HIV still havent hit upon the cure.So hope u get the point —Preceding unsigned comment added by 117.193.128.204 (talk) 04:17, 26 July 2009 (UTC)

Yeah, I see what's the problem with the strategy I suggested. Well, let's all of us keep trying to come up with new ideas till we find something that works. 98.234.126.251 (talk) 22:57, 26 July 2009 (UTC)

temps of stellar objects

hi, where might i find info of the temperatures of various stellar objects, the wiki pages related to the objects don't quote their temperatures/temp range/av temp... also i'm guessing that gas and dust clouds are cooler than debris disks? is that right? thanks! :) —Preceding unsigned comment added by 121.202.252.240 (talk) 07:52, 24 July 2009 (UTC)

Black body provides the temperature for most radiating objects. As for dust clouds vs debris disks, I'm not precisely sure of the distinction you're drawing. There shouldn't be anything inherently warm about either; each will be heated based on proximity to a star or other radiating thing. — Lomn 13:05, 24 July 2009 (UTC)

Does SIMBAD [8] meet your needs? That looks like it gives info on individual objects (Magnitudes, temperatures etc). Also see Category:Astronomical_databases. AlmostReadytoFly (talk) 13:13, 24 July 2009 (UTC)

thanks a LOOOOOOT guyz :)

Animals that eat 'meals'

Most humans will eat a variety of types of food in one sitting/meal - e.g. meat and two-veg. Beyond domestic pets (since we provide their food) is there evidence of other animals eating 'meals'? I.e. do any animals have little food-combos that they put together and eat, much like we do? I don't mean like chopping and preparing - just the idea of saving, say, some berries aside until it finds some nuts and then eating them both together. 194.221.133.226 (talk) 09:11, 24 July 2009 (UTC)

"Hmm," said the cat, "I think I'll save this mouse liver until I can find some fava beans and a nice chianti." I tried researching this but there are too many refs talking about "animal meal" i.e. "ground up animals," to make it easy to find an answer. I've seen various animals combining water and a food in close succession, but not who really collected foods to make a pleasing combination of flavors or colors. Certainly they have p[references for certain food combinations over others, which might be too salty or too sweet, or which might contain ingredients they do not like. They pretty much seem to browse and eat some of this, then later some of that. Chimpanzees eat food where they find it [9] rather than assembling a "meal." Edison (talk) 20:07, 24 July 2009 (UTC)

Availability might be the question, since storage may be difficult. If two varieties of food were available at once, and especially if both were plentiful, I think other forms of life would eat quantities of each, much as humans do, and they might move between the two (or more) items in a way similar to the way we move between types of food in the course of an eating session. Perhaps there have been experimental studies of this, but I don't know. Bus stop (talk) 20:22, 24 July 2009 (UTC)

Parrots may gather and transport food to their mate setting on the eggs, and they eat a varied diet. There is an opportunity to collect and serve a meal of several ingredients. Edison (talk) 20:07, 24 July 2009 (UTC)

Storage is one major drawback to assembling a meal. Availability is the other. Some animals store food for later, others lose what they don't eat now. So, eating various foods in succession is much more prevalent. E.g. a bear may wander away from a stream full of salmon to snack on some berries, a leopard may store a freshly caught gazelle and go off to hunt for smaller prey. Birds are known to rake lots of seeds out of bird feeders to get to some specific ones they like and then snack on the ones from the ground later on, cats or dogs with access to both dry food and wet food may switch between one and the other. Domestic cats are often observed to come in for some pet food after a life catch. Although most animals are specialized as "meateaters" or Herbivores they do consume a little bit of the other as part of their usual diets. Herbivores eat some worms and insects along with the plants they consume. Carnivores get their prey's last meals along with the meat. (They only get the roughage, they usually can't metabolize the nutrients.) Animals have individual tastes along with general preferences. The key problem with your question is that it assumes we can correctly assign purpose to animal behavior. That is dicey. Sometimes observation and analysis help, e.g. parrots were found to eat certain clays to provide needed nutrients for their diets and some birds eat certain herbs for medicinal purposes. But does that sparrow fly away from the seeds to pick up a maggot to "assemble a meal" or to evade being attacked by other birds or a predator. Is there some other reason we haven't thought of, or is there no reason at all? 71.236.26.74 (talk) 21:46, 24 July 2009 (UTC)

I certainly agree that I can't think of any animals other than humans who do this - so the obvious question is not "Why don't animals do this?" - it's "Why do humans do it?" SteveBaker (talk) 23:57, 24 July 2009 (UTC)

Hamsters collect food in their cheek pouches and store it in their larder for later consumption. If any animal collects food for later "meals" they would be a good candidate, having typically a pantry stocked with nuts, seeds, Cheerios, berries, etc. Edison (talk) 03:52, 26 July 2009 (UTC)

Cats purring

Another feline question today!

Somebody told me that female cats are much more inclined to purr than male cats - is this true?b Our article on purring doesn't mention that. —Preceding unsigned comment added by 62.25.96.244 (talk) 10:24, 24 July 2009 (UTC)

OR In my experience it's the other way round! --TammyMoet (talk) 10:44, 24 July 2009 (UTC)

Purring in cats has two sources: contentment and fear. So if you have a male that is happy a lot or a fraidycat he'll purr a lot. Females are less likely to challenge their position in a domestic family "pack". So, on average, they are more likely to be content with their lives and attention from her owners. That doesn't mean the opposite doesn't happen. Cats are individuals with a whole spectrum of personalities. (OR we had a tom that kept getting beaten up by any cat in the neighborhood and even the birds "dive bombed" him. He was the purriest furry I've ever encountered.) 71.236.26.74 (talk) 22:02, 24 July 2009 (UTC)

Electric Shock

What is the range of shock that is dangerous to man?That is the volltage range of shock and the number of amperes of current that is dangerous to man.Is there any animal resistant to electric shock??? —Preceding unsigned comment added by 117.193.142.180 (talk) 11:08, 24 July 2009 (UTC)

It isn’t the voltage per se that’s the problem, it’s the current. Currents approaching 100 mA are lethal if they pass through sensitive portions of the body. See electric shock. Red Act (talk) 11:30, 24 July 2009 (UTC)

Electric eels are presumably resistant to electric shock, since they themselves don’t get electrocuted when they electrocute their prey. Also, something like a turtle with its appendages pulled in would in a way be resistant to electric shock, since I’m pretty sure a turtle’s shell has a very high resistance, compared to flesh. Red Act (talk) 11:51, 24 July 2009 (UTC)

I disagree with the statements about turtles. They have skin which is always exposed to the surrounding water. Edison (talk) 14:38, 24 July 2009 (UTC)

Not all turtles are aquatic. Googlemeister (talk) 15:08, 24 July 2009 (UTC)

Yes, I was assuming the turtle wasn't in water. I should have said that. Red Act (talk) 17:42, 24 July 2009 (UTC)

It is the current that matters, but perhaps an appropriate question would be of the resistivity of the human body, so the OP could figure out an appropriate voltage that would send 100 mA through it. —Akrabbim^talk

The resistance of the human body varies a lot depending on which two parts of the body contact is made with, and how contact is made – touching a wire with a dry finger is a lot different from standing on a metal plate with wet feet. However, the electric shock article says that death has occurred with voltages as little as 32V. Red Act (talk) 12:47, 24 July 2009 (UTC)

Mythbusters thinks that 7mA can kill you if it goes directly through your heart. Not sure exactly where they are getting their info. Googlemeister (talk) 13:03, 24 July 2009 (UTC)

In the 19th century War of the currents experiments were done on a variety of animals, determining the minimum voltages and currents necessary for fatal electrocution. Thomas Edison argued that DC was less lethal than AC. Ultimately, several thousand volts of AC was chosen as the means of execution, first used on muyrderer William Kemmler. Electrocution was widely used from the 1890's through the 1960's. The source impedance of the high voltage AC determined the current rather than the skin of the condemned. The resistance of the human skin for a given electrode placement may suddenly decrease when a sufficient current passes through it, due to disruption of the skin. Dry skin has higher resistance than wet skin, perspiring skin, or bleeding skin. The route of the current has a big factor in determining the danger. The heart or brain are not good places to have current passing. Edison (talk) 14:38, 24 July 2009 (UTC)

BTW, do you know the highest voltage (I mean like from live wires, not lightning and stuff) that a human ever survived? I've heard of one guy who was reported to have survived being zapped with 750V DC (he was bare-handing a live generator in an express diesel, see Pioneer Zephyr), and a few who survived 600-650V DC from touching the electric rail in the subway, but I don't know if any of this is true. 98.234.126.251 (talk) 23:55, 24 July 2009 (UTC)

Did this chap touch the wire?[10] Warning shows man being killed by electricity. —Preceding unsigned comment added by 79.75.60.53 (talk) 23:07, 25 July 2009 (UTC)

That was 1500V DC, and I could see it was almost instantly fatal. What I was asking was, what's the highest voltage electric shock that anyone ever survived? Thanks for the video, though, it was interesting in a scary kind of way. I'll take care not to touch any live wires :-) 98.234.126.251 (talk) 00:52, 26 July 2009 (UTC)

You can survive any voltage as long as you are not in contact with earth and are wearing and equipotential suit. does Live OH line working count?

I've seen the Helicopter Linemen episode on the History Channel, so I know what you're talking about. I'm asking about electric shocks from live wires, though (not from lightning strikes or Tasers or anything like that, but from live wires only). BTW, an equipotential suit is called a Faraday suit cause it acts like a Faraday cage. I've changed the link to point to that article; hope you don't mind. 98.234.126.251 (talk) 02:42, 26 July 2009 (UTC)

The current capability or Coulombs of current stored are more important than the open circuit voltage. School kids routinely touch Van de Graaf generators charged to hundreds of thousands of volts, but without a capacitor or Leyden jar attached up to store a dangerous amount of electricity. A "live wire" likely has tens of thousands of amps of sustained current available until the circuit breaker at the substation opens or a fuse blows. I would expect to die if I touched a live wire at 12kv, 4kv, 2400 volts, 480 volts, or 240 volts. 120 volts could well be lethal, and has been many times, depending on conditions, such as how well grounded the victim is and what path the current follows through the body, and for how long. For lower voltages, there are probably situations where it could be lethal. If a patient is on a grounded metal operating table, for instance, quite a low leakage voltage could be lethal, depending on the route of the current. Cows may refuse to give milk if they feel 1 or 2 volts of stray voltage, and the dairy operator are forced out of business. Prudence dictates observing applicable electrical safety codes. Edison (talk) 03:47, 26 July 2009 (UTC)

"I would expect to die if I touched a live wire at... 240 volts"? I personally survived getting zapped with 240 volts AC, as I said before. I wanted to know if anyone survived touching a live wire at 480 volts or higher. Thanks for that bit about the cows, though. 98.234.126.251 (talk) 23:03, 26 July 2009 (UTC)

The internal resistance of the human body between any two randomly chosen points ( a few inches apart of course) is approximately 700 ohms.

So, what would be the total resistance of the human body (including resistance of the skin, but not of the clothes/shoes) for a same-hand/same-foot pathway (which is, I believe, the pathway of the electric current in the majority of accidental electrocutions, including my own little incident with those Christmas lights)? 98.234.126.251 (talk) 05:50, 30 July 2009 (UTC)

Oh, I see now why somebody can survive getting zapped by 600V DC from an electric rail -- it's the victim's foot that usually touches the rail, and the current flows through the foot to the ground -- so the victim ends up with third-degree burns on the foot, but the heart and the brain remain unaffected. I still don't see how that railroad mechanic could get zapped from a 750V DC generator and still survive, though. 98.234.126.251 (talk) 07:30, 30 July 2009 (UTC)

How dehydrated was I?

Last night I felt really dehydrated and I whipped up a two quart (8 cups) pitcher of (sugar free) iced tea. In the hour before bed I drank it all. This morning I felt really good and barely needed to pee. I did pee, but not a huge pee, just a regular morning pee. Assuming I am not "retaining water", how dehydrated was I? Possibly dangerously so?--70.107.76.121 (talk) 11:34, 24 July 2009 (UTC)

From the dehydration article, the symptoms progress as follows:

Symptoms of mild dehydration include thirst, decreased urine volume, abnormally dark urine, unexplained tiredness, irritability, lack of tears when crying, headache, dry mouth, dizziness when standing due to orthostatic hypotension, and in some cases can cause insomnia.

In moderate to severe dehydration, there may be no urine output at all. Other symptoms in these states include lethargy or extreme sleepiness, seizures, sunken fontanel (soft spot) in infants, fainting, and sunken eyes.

The symptoms become increasingly severe with greater water loss. One's heart and respiration rates begin to increase to compensate for decreased plasma volume and blood pressure, while body temperature may rise because of decreased sweating. Around 5% to 6% water loss, one may become groggy or sleepy, experience headaches or nausea, and may feel tingling in one's limbs (paresthesia). With 10% to 15% fluid loss, muscles may become spastic, skin may shrivel and wrinkle (decreased skin turgor), vision may dim, urination will be greatly reduced and may become painful, and delirium may begin. Losses greater than 15% are usually fatal.

You can judge best, and we cannot offer a diagnosis, but you haven't mentioned any symptoms which would suggest it was anything more than mild. AlmostReadytoFly (talk) 12:36, 24 July 2009 (UTC)

Also note that drinking very large volumes of water can have adverse medical effects (including death). But we cannot offer medical advice. A woman who died in 2007 from participation in a radio station's "water drinking contest" consumed about 4 times the water you did. I would expect that if someone were suffering from severe dehydration, the water would not have to be flavored, like your "sugar free (artificially sweetened?) tea". Maybe you just liked the taste of the tea. Edison (talk) 14:21, 24 July 2009 (UTC)

There's also water loss through sweating & breathing to take into account. Still, it's an interesting question: where did all that water go? --Tagishsimon (talk) 14:33, 24 July 2009 (UTC)

Absorbed by cells perhaps. Googlemeister (talk) 15:06, 24 July 2009 (UTC)

This page linked from one of the wikipedia articles may be interesting in this regard. [11]. There's a lot of water outside of cells. Sweat is taken from the plasma, but that gets replenished to a certain extent from other souces. Our article only has consumption for the resting state which would be about 2.5 qt/day. In actual cases of dehydration it is important to not just replace water, but also electrolytes in the right combination [12]. -- 71.236.26.74 (talk) 20:48, 24 July 2009 (UTC)

Some (myself included) enjoy unsweetened iced tea over the sweetened kind. Doesn't have to be artificially sweetened. —Akrabbim^talk 15:16, 24 July 2009 (UTC)

When I lived in Tucson, I used to come back from summer bike rides and drink more than that, regularly. An ordinary-sized male in good shape needs to be down about two gallons before getting to the point of really serious dehydration. The risk of heatstroke is much higher. Looie496 (talk) 15:43, 24 July 2009 (UTC)

Just because you get away with it doesn't mean it's a good idea, though. Risk of kidney stones goes up if you let the urine in your kidneys get too concentrated. The whole "drink eight glasses a day" fad was probably overblown, but it's good to stay hydrated. --Trovatore (talk) 18:20, 24 July 2009 (UTC)

RE: death by water, see: Water intoxication, hyponatraemia, Leah Betts and Anna Wood (schoolgirl). --Mark PEA (talk) 18:54, 24 July 2009 (UTC)

So, it seems the answer is, I probably wasn't dangerously dehydrated just mildly so (since I had no symptoms other than great thirst) and I probably shouldn't drink much more than that at a single sitting (not that I was planning to). The tea was artificially sweetened but only mildly so. I hate sugary (as in actual sugar) drinks when I'm thirsty. I find them cloying and that they don't really satisfy my thirst deeply. By the way, hydrate is a terrible word in my opinion that is used way too much. Thanks all.--70.107.76.121 (talk) 22:22, 24 July 2009 (UTC)

angular momentum to momentum

What is the equation which converts momentum to angular momentum? -- Taxa (talk) 14:25, 24 July 2009 (UTC)

Have you seen the articles linear momentum and angular momentum? The latter gives:

$L=mvr\sin \theta \;$

where m is the mass, v is the speed (magnitude of the velocity vector), r is the distance from the origin and $\theta$ is the angle between the velocity and the radius vector. So

$L=pr\sin \theta \;$

where p is momentum. Of course, this doesn't apply to all situations (e.g. it wouldn't apply to spinning bodies). AlmostReadytoFly (talk) 15:13, 24 July 2009 (UTC)

Or in other words, L = r X P, where the bold represents vectors and X represents the vector cross product. It should be noted that Angular momentum depends on the origin of coordinates, in addition to the velocity of the reference frame. Rkr1991 (talk) 16:08, 24 July 2009 (UTC)

medicine

what is mesecentric adenitis ? how is caused ? —Preceding unsigned comment added by 117.201.12.2 (talk) 15:47, 24 July 2009 (UTC)

See adenitis. There is not a single cause. There are thousands of possible causes. -- kainaw™ 15:51, 24 July 2009 (UTC)

Perhaps you mean "mesenteric adenitis". If so, you could try this link. Tonywalton ^Talk 15:53, 24 July 2009 (UTC)

Wavelength versus radius

Have any electromagnetic wavelengths been detected which are shorter than the electron radius? -- Taxa (talk) 16:54, 24 July 2009 (UTC)

I'm not sure about shorter, but wavelengths about the same as an electron radius (maybe slightly shorter?) are in some gamma rays.
electron radius: 2.81794 x 10-15 m
gamma rays: around 10-15 m Dogposter (talk) 17:11, 24 July 2009 (UTC)

Gamma rays are often denoted with their energy instead of their wavelength. In the case of photons: E = h * c/wavelength

where:

h = 4.135 × 10−15 eV s

c = 3 * 10^8 m/s

A quick googling find cosmic gamma rays with energies of more than 100 giga eV. So doing the math:

wavelength = 1.24 * 10^-17, far shorter than the classical electron radius. :-) EverGreg (talk) 22:01, 24 July 2009 (UTC)

Electrons are point particles and have no radius, so no. — DanielLC 05:40, 26 July 2009 (UTC)

So what are these point particles made of?

DC vs AC

continuing from the discussion on electrocution etc...which is more dangerous DC current or AC current???If so why??? —Preceding unsigned comment added by 117.193.130.131 (talk) 17:16, 24 July 2009 (UTC)

As our article on electric shock notes, AC and DC have differing effects and thresholds. Additionally, AC's effects are highly dependent on the frequency (at low frequencies, it approaches the behavior of DC). As such, there is no good one-or-the-other answer to which is most dangerous. — Lomn 17:51, 24 July 2009 (UTC)

Sure there is. You're right that there are lots of details you can go into, but the short answer is that for the frequencies and voltages one is likely to encounter, AC is more dangerous. --Trovatore (talk) 17:58, 24 July 2009 (UTC)

Fair point. As an engineer I've perhaps got an unfair standard of "likely to encounter"; I've seen people lock up on HVDC sources several times. — Lomn 18:07, 24 July 2009 (UTC)

Well…sorta. It is more precise and correct to say that in our civilisations, dangerous voltages are oftener present as AC than as DC, and that one doesn't generally encounter DC at dangerously high voltage. However, that doesn't address the question of whether DC or AC is inherently more dangerous. —Scheinwerfermann ^T·_C18:09, 24 July 2009 (UTC)

The same voltage is ordinarily more dangerous as 60-cycle AC than as DC. That's because of the effect on the heart. --Trovatore (talk) 18:15, 24 July 2009 (UTC)

Mr Trovatore U claim that AC is more dangerous.I would like to know the exact detail why it is so.Also your statement on effect on heat is unclear.Please clarify —Preceding unsigned comment added by 117.193.139.242 (talk) 04:46, 25 July 2009 (UTC)

That might be because the peak voltage is higher. e.g. 230V AC has a peak of around 326V (No. of cycles doesn't matter - so long as it is a sine wave). Also ISTR that someone told me that the voltage does not matter that much, it's more where the current flows through - route 15mA across the chest and it's goodbye...  Ronhjones  ^(Talk) 18:52, 24 July 2009 (UTC)

This might be an urban legend, but I've always heard that an AC shock will cause you to grab on to whatever you're holding, but a DC shock will throw you across the room (or maybe the other way around...I'm kinda fuzzy on the details). Is there any truth to this? -RunningOnBrains^(talk) 18:30, 24 July 2009 (UTC)

Electricians or others who work around electricity know not to use their person as a voltage detector, but they still avoid touching a wire with the palm of the hand, for fear the hand would clutch it and be unable to let go, whereas if it contacted the back of the hand the contact would more likely get broken. Of course if a lethal current passes through the back of your hand, you are still dead. (Original research:)In my personal experience, AC or DC can each cause painful shocks and muscle contractions. I've felt 120 VDC and 120VAC from high current sources and cannot recommend either. Radios and TVs used to have high voltage DC B+ supplies for the vacuum tube plate circuit, and shocks from that were painful and dangerous, since they could be a couple of hundred volts. AC or DC voltage sufficiently high can literally burn a hole in the skin, thereby reducing the contact resistance, so only the impedance of the source and the relatively low internal resistance of the body limit the current. In the "War of the Currents," the Champion of Direct Current, Mr. Brown, challenged George Westinghouse to an electrical duel, where each would take a jolt of his favored current, then the voltage increased and the process repeated until one cried "Uncle!" Westinghouse declined to participate. In animal tests done by the DC proponents in the 1880's AC appeared to be lethal at lower voltages than DC. The notion of AC electrocution as capital punishment followed several gruesome and highly public electrocutions of electrical workers atop utility poles, when they encountered the high voltage AC used for arc lighting. The 2400 volt AC then common was clearly more dangerous to pass through the body from inadvertent contact than the 110 volt DC then in use, although I am confident that 110 DC could also cause a fatality, given sufficient contact area or sufficiently low resistance, and current continued for a sufficient time. Edison (talk) 19:28, 24 July 2009 (UTC)

(WP:OR) I don't think 110V (DC or AC) would cause a fatality -- I've personally been zapped with 240V AC, and I'm still alive, as you can see. I can personally testify, though, that it hurts like hell. 98.234.126.251 (talk) 00:08, 25 July 2009 (UTC)

I have actually read in my textbook that an AC shock is always attractive and a DC shock is repulsive. A quick googling gives this, so as Lomm says, there are a whole lot of factors to be taken into account. But, for household frequencies and voltages, an AC shock is definitely more dangerous. Rkr1991 (talk) 03:35, 25 July 2009 (UTC)

So in other words, an AC shock makes you hold on tight to the wire, and a DC shock makes you fly halfway across the room... :-) 98.234.126.251 (talk) 05:12, 25 July 2009 (UTC)

Maybe not halfway across the room, but certainly enough to take your hand off quickly. Rkr1991 (talk) 07:20, 25 July 2009 (UTC)

It's only my personal experience, don't try this at home. AC voltage is definitely repulsive under certain conditions. 120 VAC is good for about 2-3 feet, 240 VAC is good for five feet at least. Whether that's involuntary muscle contraction or instinctive/aversive escape from pain, I dunno - but you definitely fly through the air. I've never deliberately placed my open palm onto a live voltage, so I can't speak to the grasping phenomenon. Actually I have done that, but with an electric fence, which deliberately uses short pulses - and both of a DC and AC fence controller deliver terrific shocks, the difference was that AC could still give you the shock with weeds growing up and touching the fence. Don't know if that helps. Franamax (talk) 08:53, 25 July 2009 (UTC)

And if it illuminates further: electric fencers deliver 400-1200V in the short pulse, but not a lot of current. You get the blinding pain, but you're still standing in the same place after. Contacting household wiring (the discussion about "likely to encounter" above) puts you into contact with a large supply of electrons, so the total power transfer is likely much larger. I think maybe that is what moves you across the room so effectively. I suppose I'm just lucky. Franamax (talk) 09:01, 25 July 2009 (UTC)

Do electromagnetic waves have any width?

The classic diagram of an EM wave shows its oscillating electric and magnetic fields, e.g. this.

Are these E and B vectors actually occupying real 3D space? Is the wave actually wider in places and taller in others?

Or is an EM wave more like an infinitely thin piece of fishing line, with varying E and B intensity along it?

Ben (talk) 17:29, 24 July 2009 (UTC)

Yes, they do. Try reading this. Dogposter (talk) 17:45, 24 July 2009 (UTC)

An electromagnetic wave is not as one-dimensional as that picture suggests. In the simplest case of a plane wave, the entire space is filled with compies of that picture, so to speak. But the E and B vectors themselves do not occupy 3D space, the dimension of their components is not distance or length. —Preceding unsigned comment added by 81.11.170.162 (talk) 17:53, 24 July 2009 (UTC)

We depict the magnitudes of the E and B vectors by their lengths, but that is just to make it easy to draw. They don't really have a length that varies, it is the field strength that is varying. --Tango (talk) 19:30, 24 July 2009 (UTC)

If light has to pass through an aperture or slit, its passage from source to detector is affected in interesting ways. A discussion of how passing through an aperture or slot in a conductive wall affects radio frequency waves would be interesting. FM broadcast, say 100 megaHertz, might be an interesting frequency, or perhaps 900 mHz used for phones. If the receiver is in a Faraday cage,how well will the radio waves pass through a slit of varying proportions, or a small variable aperture? Do any interesting nonintuitive things happen, like diffraction or polarization? Edison (talk) 20:04, 24 July 2009 (UTC)

This sounds rather like a homework type question, but I can help you by pointing out that radio waves are like light waves with a bigger wavelength. Your 100 megahertz wave is about 5000000 times bigger than a light wave, so it will have similar properties but at a different scale. You can read Diffraction, Waveguide, polarization, Slot antenna. A waveguide for a FM radio frequency is a large construction and would not be used in practice. Graeme Bartlett (talk) 22:27, 24 July 2009 (UTC)

I'll take this over as a definitely non-homework question. My FM radio antenna, CB antennas (never had one) and Wi-Fi antennas all have different optimum lengths. This implies a three-dimensional aspect to photons/EM waves, dependent on wavelength/energy. And by imperfect analogy, neutrons and electrons get "smaller" in "cross-section" as they get more energetic (which is why high-energy particles travel farther through matter). So there certainly does seem to be a size aspect, and slits and cages only seem to confirm it. So can we think of actual "wiggles"?

And further, if we shoot polarized photons at a Faraday cage that has a rectangular mesh, can we separate the electric and magnetic fields inside the cage? These questions torment me! :) Franamax (talk) 08:11, 25 July 2009 (UTC)

If you put a radio inside a good Faraday cage you shouldn't get any signal. You can try it: put a radio inside your microwave (which is a Faraday cage). Try putting your cell phone inside and calling it.Computeridiot34 (talk) 18:11, 25 July 2009 (UTC)

I'm thinking more about a "bad" Faraday cage. A microwave oven has apertures much smaller than the radio wavelength. We need a leaky cage to pursue my thoughts. Can we separate the electric and magnetic components of the field leaking through by varying the rectilinear dimensions of the cage? My microwave has round holes in the shielding, so I wasn't able to get just the magnetic bits of the ringtone. ;) Franamax (talk) 01:30, 26 July 2009 (UTC)

A Faraday cage with either round or rectangular holes by definition CANNOT polarize EM waves. To get polarized photons, you need a Faraday cage with long narrow slits in it. 98.234.126.251 (talk) 23:47, 26 July 2009 (UTC)

This is most definitely not a homework question :), just something I have occasionally wondered about. I thought I'd ask any pro physicists out there for the answer, rather than trying to revise Maxwell's equations and work it out from scratch.

I was thinking of a laser pulse - it's clearly a narrow beam, as you can see by flashing a laser pointer at a wall. What's a good way to imagine the photons in such a pulse? Are they like lots of little darts flying along through my living room in a straight line?

Ben (talk) 21:17, 25 July 2009 (UTC)

I saw a Faraday cage used for EEG recording, made of chickenwire, with perhaps a 1 inch mesh. People joked that it would keep out em waves larger than pingpong balls. It seemed to shield against 60 hz electrical interference, and pretty well blocked AM and FM (U.S.). Signals. As the mesh varies down to aluminum screenwire (perhaps 1 mm mesh) or up to fence wire (perhaps 4 inch mesh) what is the effect on the shielding ability of various wavelengths? Edison (talk) 03:34, 26 July 2009 (UTC)

Aluminum screenwire would keep out all radio waves and also all microwaves with a wavelength of more than (I think) 2 mm, which is why it's used for microwave oven windows (to keep the oven from microwaving everyone in the kitchen) and also on the air intakes of the Stealth fighter (to keep radar waves from reflecting off of the turbine blades inside). 98.234.126.251 (talk) 23:43, 26 July 2009 (UTC)

Engines in Space

Does every engine that could move a spaceship have to expel matter or heat or something in the opposite direction to travel? SGGH ^ping! 22:08, 24 July 2009 (UTC)

One engine which could move a spaceship, in space, without having to expel heat or something in the opposite direction would be a winch. As the cable is reeled in the spaceship moves toward the takeup reel. The winch could be mounted on an asteroid. The center of mass of the spaceship and asteroid would remain in the same place, but the the asteroid outweighed the spaceship by a factor of several million, the motion would be mostly on the part of the spaceship. Technically, the asteroid would be moving in the opposite direction to the asteroid, as surely as if you lifted the ship with a long hydraulic jack from an object behind it. The resulting acceleration could be far greater than that due to the gravitational attraction of the small asteroid and the spaceship. A Dean drive or other scifi "reactionless thruster" would seem to violate Newton's laws. Maybe cutting edge physics offers some out via wormholes, string theory, other dimensions, or whatever. Telekinesis seems about as (un)likely a solution to the problem of reactionless thrust. Edison (talk) 22:29, 24 July 2009 (UTC)

Yes. See Newton's third law. APL (talk) 22:30, 24 July 2009 (UTC)

Yep. It's a necessary consequence of the law of conservation of momentum. (The 'something' you expel doesn't have to be material, mind you. Photons will do the job, so you can get a miniscule thrust just from pointing a flashlight behind you.) TenOfAllTrades(talk) 22:35, 24 July 2009 (UTC)

We have a detailed article on Spacecraft propulsion. There is an entire section there discussing the (im)possibility of active propulsion without a reaction mass. There are also hypothetical models of reaction-mass-less drives like the Alcubierre drive, but it is unclear if that model is even consistent with the laws of physics, let alone how to build one. --Dr Dima (talk) 22:46, 24 July 2009 (UTC)

The relevant articles are working mass and Tsiolkovsky rocket equation. Luckily, as KE ∝ mv², if you can accelerate the mass to a very high velocity, you can get lots of reaction while using up only a small amount of working mass; see Hall effect thruster for an example. -- Finlay McWalter Talk 22:53, 24 July 2009 (UTC)

Interestingly, in a curved spacetime, it is possible for a spacecraft to move around without using a reaction mass for propulsion, by “swimming”, i.e., by cyclically adjusting how its weight is distributed in a particular way. However, this effect is vastly too small to be of any practical use in real situations. See the August Scientific American for an interesting article on this. Red Act (talk) 23:04, 24 July 2009 (UTC)

We should of course mention the possibility of using Solar sails - those work without reaction mass - providing there is a nice big source of light nearby. But any kind of "engine" would need to expel reaction mass. The engines that require the least are things like ion thrusters - because the thrust an engine produces is proportional to the momentum of the exhaust jet - and momentum is a product of both the mass of the exhaust and its speed - you can use less reaction mass and get the same amount of thrust if you propel it faster. Ultimately, propelling the exhaust out at close to the speed of light would be good. Additionally, these machines use electrical power to accelerate the exhaust - so they can be powered by solar cells and avoid the need to consume chemical energy. That gives an ion thruster the ability to produce a sustained propulsive force for an extremely long time without running out of either chemical fuel or reaction mass. But ultimately, it'll wear out. Another idea is the Bussard ramjet which is supposed to collect interstellar hydrogen in a magnetic 'scoop' and use that both as fuel and reaction mass. Such a device would have to be moving at an ungodly speed to collect enough of the stuff to be useful though. SteveBaker (talk) 23:45, 24 July 2009 (UTC)

A space elevator would also work without reaction mass (I'm not sure if it would count as a winch, though). 98.234.126.251 (talk) 00:11, 25 July 2009 (UTC)

Now consider how a wench could move a spaceship. Edison (talk) 03:29, 26 July 2009 (UTC)

Yeah, I get the picture! ROFLMAO!!! 98.234.126.251 (talk) 23:06, 26 July 2009 (UTC)

Maybe a magnet attracted to an object might move a ship in zero gravity; super high powered magnet in the future could do the trick —Preceding unsigned comment added by 214.13.64.7 (talk) 08:46, 26 July 2009 (UTC)

Would a railgun (or coilgun) count under this definition? 98.234.126.251 (talk) 23:08, 26 July 2009 (UTC)

Eiffel Tower sticks to the Moon !!!!!!!!!!

I had an argument with my friend and I hope I will be proved correct quickly on this. Could I stick the Eiffel Tower to the Moon with one small piece of bluetac? —Preceding unsigned comment added by 92.18.90.155 (talk) 22:20, 24 July 2009 (UTC)

It depends what you mean by "stick". The moon has gravity (about 1/6 of the Earth's). The Eiffel tower if stood upright would sink right in and stay all on its own unless some force was acting on it to pull it away, and it would have to be a force of some power given the mass of the Eiffel Tower. The way you've asked this question leads me to believe that you thought an object on the moon would simply float away if not stuck or tied down in some way, which is not the case. If you were on the moon next to an Eifell tower, you wouldn't be able to move it with ten elephants. Even if the moon was gravity-less, if the Eiffel Tower was on its surface, and there was no force acting upon it, it would stay; it wouldn't need to be "stuck" at all. If there was a force acting on it, the bluetac would work to the extent of its sticking power combined with the amount you used, that is, whatever extremely small or large power of sticking it had would only "win out" against the force if the force was commensurately larger in degree pulling the Eiffel Tower away. All this is to say that I think your question doesn't really make sense because it assumes facts in error.--70.107.76.121 (talk) 22:31, 24 July 2009 (UTC)

(EC):The Bluetac would seem unnecessary. The Apollo lander stuck to the moon just by landing, since the moon has gravity. Just find a level solid rock for a site and lower the tower gently into position. No wind to blow it over, so no anchoring required. The view would be magnificent! Edison (talk) 22:33, 24 July 2009 (UTC)

But I think it would lack some of the parisienne 'atmosphere' :-) SteveBaker (talk) 23:36, 24 July 2009 (UTC)

groan... --Tango (talk) 23:54, 24 July 2009 (UTC)

Are we certain the Apollo lander did not have Bluetac on the bottom of its legs86.4.181.14 (talk) 14:50, 25 July 2009 (UTC)

Heh, I get it now. When I first read this, I was thinking much more about the "atmosphere" in the public washrooms just near the base of the Tower and how much nicer it would be to smell only yourself in the spacesuit. Ahh, the "atmosphere" of Paris! :) Franamax (talk) 07:13, 25 July 2009 (UTC)

To generalize this, yes and no. You are talking about two different forces, the gravitational and electromagnetic forces. Your little piece of Bluetac exerts both (the "stickiness" is an example of the EM force). Gravitational force acts over long distances and varies with mass. Electromagnetic force acts much more strongly over a much shorter distance and varies with charge. If you could set up a magical situation where both the Eiffel Tower and the Moon were falling through free space with just enough counterforce on them to prevent them "sticking together" gravitationally, then magically place that bit of sticky stuff in between them, the extra mass of the Bluetac would draw the two bodies together and once they all touched, the EM forces (the stickiness of the Bluetac) would possibly speed the bodies up at the last few microseconds, and would hold them together just a little tighter. It would then take just as much force to separate the Tower and the Moon in free space as it would to separate two ashtrays here on Earth. So, in our magic world, yes; in our real world, not even close. Franamax (talk) 07:37, 25 July 2009 (UTC)

I'd like to point out that the Eiffel Tower is made of wrought iron and is electrically conductive, therefore it would not retain static electricity and would not stick to Bluetac. FWiW 98.234.126.251 (talk) 08:47, 25 July 2009 (UTC)

So you're saying that it's not possible to glue metal objects together? It's not the overall static charge, it's the very local distribution of forces that give rise to the effect. Alternatively, it's the overall balance of charge that matters and even single electrons are important. I'd have to check my Feynman to review how few electrons are needed to split the Earth in two. The localization of force becomes very important. Franamax (talk) 09:17, 25 July 2009 (UTC)

Or here's something better: in my magic experiment, I already specified that we had counterforces for gravitational atttraction between the Tower and Moon. We indeed will also need to compensate for net charge. The Moon will have a net electrical charge, either positive or negative. The Eiffel Tower will presumably still have Earth's net negative charge when we tow it out for the experiment. So we will have to magically compensate for that too, using the inverse-square rule.

However, when we introduce the Bluetac, we introduce a new charge (magically). This will cause a redistribution of charge over the entire conducting body of the Eiffel Tower, so the net force will still be the same as our ashtrays. (Static electricity per se has nothing to do with it actually, we are talking about EM forces exchanged between individual molecular bonds) Franamax (talk) 09:29, 25 July 2009 (UTC)

Oh, so Bluetac uses glue. I was under the false impression that it uses static electricity. I stand corrected. 98.234.126.251 (talk) 01:02, 26 July 2009 (UTC)

explanation: in case anyone wonders about the problem, here is my impression of why the OP asked this: both he and the person he "bet" with thinks there is no gravity at all on the moon, that if you placed something there it would just float off. Unless of course you attached it to ANY extent. 82.234.207.120 (talk) 18:00, 25 July 2009 (UTC)

Of course, due to Newton's third law, gravity and the force the ground applies to the tower cancel. Conclusion: the tower isn't stuck to the ground by gravity.

To the OP: if there's no gravity on the moon, how do you explain the Apollo footage? --Bowlhover (talk) 22:08, 25 July 2009 (UTC)

Your post is just an invitation for moon hoax conspiracy idiots to drop a line, and you know what does and should happens to them.--70.107.76.121 (talk) 22:44, 25 July 2009 (UTC)

Good job, Buzz! Now if someone would do the same to the 9/11 conspiracists and the Holocaust deniers... 98.234.126.251 (talk) 00:59, 26 July 2009 (UTC)

I'm looking forward to the circa 2040 footage of old Barack Obama punching a persistent birther in the face. :) --Sean 13:33, 27 July 2009 (UTC)

What do you mean by the term "persistent birther"? 98.234.126.251 (talk) 22:59, 27 July 2009 (UTC)

These idiots. --Sean 13:28, 28 July 2009 (UTC)

Heavy Boots! APL (talk) 17:40, 26 July 2009 (UTC)

E=mc²

In terms of Einstein's equation is the energy "stored" as angular momentum and if not how is it "stored"? -- Taxa (talk) 23:08, 24 July 2009 (UTC)

In terms of E=mc², the energy is "stored" as mass. That equation is the energy something has when it’s not moving, and hence has no momentum or angular momentum. Red Act (talk) 23:13, 24 July 2009 (UTC)

_{I knew someone would answer while I was typing. Grr.}

It's "stored" as mass. For example, if a Uranium 235 nucleus is hit by a neutron and undergoes fission, the products have slightly less rest mass than the U-235 nucleus and the neutron, and the difference becomes energy, in the form of heat and gamma rays.

However, if you think of a moving particle, it also has energy due to linear momentum (energy due to movement i.e. kinetic energy). In this case the total energy E is given by:

$E^{2}=(mc^{2})^{2}+(pc)^{2}\,\!$

So far, I've talked about rest mass, which is the mass a particle has if it's not moving. You can use E=mc² to think of a relativistic mass, which increases if the particle has more linear momentum.

$m_{\mathrm {rel} }={\frac {1}{c^{2}}}{\sqrt {(mc^{2})^{2}+(pc)^{2}}}$

See also Mass in special relativity for a hopefully better explanation, if you haven't already. AlmostReadytoFly (talk) 23:39, 24 July 2009 (UTC)

Impacts into Jupiter

Jupiter had a large impact recently, and another a few years ago. Does this information allow any estimates of the probability of a major impact into Earth? The diameter of Jupiter is 142,984km, the diameter of Earth is 12,756.2km. The cross sectional area of Jupiter is therefore 126 times that of Earth. 78.147.128.100 (talk) 23:41, 24 July 2009 (UTC)

Not really, two impacts is not a statistically significant sample. In fact, you can draw any curve you want through two points. A larger number of known impacts with a distribution of impactor size would be needed to draw any conclusions. Franamax (talk) 23:53, 24 July 2009 (UTC)

Not really - Jupiter is very massive so its gravity tends to pull in asteroids and comets far more than Earth does. In fact, it has been theorised that Jupiter "vacuumed up" lots of debris in the early days of the solar system and without it the Earth would be bombarded far more often (perhaps so much so that life couldn't have evolved, at least not to the extent it has). There are also different amount of debris in different parts of the solar system. There are astronomers searching the sky for Near-Earth objects and they have a pretty good idea of how many there are (by extrapolating from the bits of sky they've searched - there is still plenty of sky to search). --Tango (talk) 23:59, 24 July 2009 (UTC)

Tango, not that I'm saying you're wrong or looking for an argument, but do you have sources on Jupiter actually "sucking in" other bodies? I'd think it more plausible that orbiting bodies would be accelerated far away than actually crashing into the planet. In other words, a near miss is more probable than a direct hit. It does seem that Shoemaker-Levy 9 was gravitationally bound, but was that an exception or a rule? Just asking for my own benefit. Think of this as "Impacts into Jupiter, part the second". :) Franamax (talk) 07:07, 25 July 2009 (UTC)

See Jupiter#Impacts for a mention of the vacuum cleaner metaphor (with a reference). --Tango (talk) 16:48, 25 July 2009 (UTC)

I dont't think Jupiter's gravity played that great a role in the Shoemaker comet hitting it. Perhaps Earth is Doomed. Edison (talk) 03:25, 26 July 2009 (UTC)

wave versus particle

If the alternation between the magnetic filed and the electrostatic field of a light wave were to not propagate by the "leap frog" propagation and remain stationary for only one cycle would that explain the idea of a particle of light some call the Photon? -- Taxa (talk) 23:54, 24 July 2009 (UTC)

I'm not quite sure what you're asking here, but I'm willing to bet the answer is no. A photon isn't a temporary stationary field, and quantum physics can't be explained using classical electrodynamics. AlmostReadytoFly (talk) 00:02, 25 July 2009 (UTC)

A photon is never stationary (it has to travel at the speed of light), so that's certainly not going to work. --Tango (talk) 00:05, 25 July 2009 (UTC)

Do stationary waves propagate? -- Taxa (talk) 00:44, 25 July 2009 (UTC)

Do you mean do standing waves propagate? They do. They propagate back and forth in a defined space. One common model of the electron is to treat it as a standing wave rather than a particle. Indeed, under wave/particle duality; any particle which is localized (not necessarily stationary, just contained in a finite space) is generally held to be a standing wave. The deal with photons is, they cannot be held still, or even confined to a define probability space the way that electrons can; so photons are clearly not "standing waves". --Jayron32 03:13, 25 July 2009 (UTC)

I read somewhere that all photons are at all possible places in the universe at the same time due to their velocity (c). Can this be correct?

That would be the case if photons traveled at an infinite velocity -- but they don't -- they travel at the speed of light -- so this is clearly wrong. If what you read was right, then how come the signals from the Mars Rovers take half an hour to get here? 98.234.126.251 (talk) 05:40, 30 July 2009 (UTC)