The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Why did humans evolve to feel pain from abnormally high CO2 levels, rather than abnormally low O2? Unlike the former, the latter would allow people to avoid going into areas with high N2 and little or no O2 (nitrogen asphyxiation) --75.15.161.185 (talk) 02:55, 17 January 2011 (UTC)[reply]
You might find the articles on Carotid body and hypoxia interesting. I think the answer is that we didn't really evolve a mechanism to detect low Oxygen levels, but CO2 is actually toxic, so it was much easier to evolve a mechanism to detect high levels of it. Keep in mind that it is incorrect to assume that EVERY single trait or mechanism is evolved for fitness. There are a lot of traits or mechanisms which are evolved sympathetically or inversely due to another trait which is evolved for fitness. For a very basic example, why aren't antelope legs thicker and stronger and less prone to breakage? Because longer and leaner legs are better at running. In the same way, why did we evolve that CO2 will kill us in the first place? Obviously, we didn't, it's just the result of us evolving to breathe oxygen. Vespine (talk) 03:54, 17 January 2011 (UTC)[reply]
And where on earth do you naturally get an extra high nitrogen level? The only likely place with low oxygen is high altitudes, which are usually very cold too, so no extra protective measures are needed. Graeme Bartlett (talk) 04:03, 17 January 2011 (UTC)[reply]
In electronics compartments near anything highly flammable. Many people have died when they go into a compartment to repair electronics without first venting the N2 and adding O2. --75.15.161.185 (talk) 04:08, 17 January 2011 (UTC)[reply]
I suspect that Graeme meant naturally occurring places. Sure, modern humans can create unusual atmospheres, but in order for low oxygen levels to have been an important evolutionary pressure for our species, our ancestors would have had to encounter low oxygen levels with some reasonable frequency. However, the presence of low oxygen levels (without also having high CO2 levels) would seem to be a very rare condition in the natural environment, and hence not something that humans would be expected to have evolved a response to. Dragons flight (talk) 04:13, 17 January 2011 (UTC)[reply]
It should be noted that large amounts of carbon dioxide actually form carbonic acid when dissolved in water; thus the carbon dioxide literally tends to create acidosis of the blood. This is a very large perturbation of body chemistry, and the body's response to it really is not all that impressive. To consider how much further evolution could go with such things, consider that mosquitoes are able to smell carbon dioxide and follow it for about 100 feet to their victims - despite, of course, producing it themselves! Wnt (talk) 08:47, 17 January 2011 (UTC)[reply]
As a rule – or at least as a rule of thumb – we mammals are utter crap at evolving new signalling and sensing pathways because we just don't run through generations fast enough. We can tinker with existing pathways and mechanisms, but developing 'new' sensors is improbable virtually to the point of impossibility. So is there anything in our biological heritage that includes a tropic response to nitrogen gas? Even more broadly, are there any organisms known which respond actively to concentrations of nitrogen? (I don't count dying/not dying a a 'response' here.) Motile microbes which will move up or down a nitrogen concentration gradient, for instance? TenOfAllTrades(talk) 15:31, 17 January 2011 (UTC)[reply]
It seems unlikely, given that nitrogen makes up the bulk of the atmosphere. It's hard to do a definitive search, though, because sensors for fixed nitrogen are very common, and I can't think of a way to set up a search that filters them out reliably. (The bacterial systems that fix nitrogen could be thought of as nitrogen gas sensors, but I expect that they always operate at saturation under normal conditions.) Looie496 (talk) 18:32, 17 January 2011 (UTC)[reply]
Evolution often finds solutions that are merely "good enough". Detecting lack of oxygen rather than excess CO2 would be better, but it would be very rare that it would actually make a difference to reproductive success. Also, you wouldn't want to lose the ability to detect excess CO2 because there are situations where you get a CO2 build up without a significant drop of oxygen levels (too many people in an enclosed place, dissolved CO2 in a lake suddenly coming out of solution (see Limnic eruption), etc.). That means you would need both abilities, which is a drain on resources. Being able to detect a lack of oxygen may not be worth the cost. --Tango (talk) 19:26, 17 January 2011 (UTC)[reply]
I think that bats, bloodhounds, and star-nosed moles would each disagree with you in their own special way. While it seems like some mammals are "terminally differentiated", reproducing too slowly to evolve quickly or even to prevent losses of useful little things like vitamin C from the genome, we yet see that some of the longest-lived mammals somehow evolved rapidly in form and function to become humans, which was one of evolution's more curious accomplishments. And of course there remains a vast pool of various little shrewlike things that outnumber all the rest of us, just waiting to start down some new evolutionary path and claim a new place in the limelight. (Oh, and note the comment about O2 and the carotid body above) Wnt (talk) 22:03, 17 January 2011 (UTC)[reply]
Detecting N2 directly would be very difficult/impossible because it is non-polar which means it is difficult for any other molecules to grab hold of, after all, this is why there is so much of it in the atmosphere, because it doesn't react with anything. For species that fix nitrogen using nitrogenase, there is no need to have a tropism to it because N2 is everywhere. SmartSE (talk) 00:49, 18 January 2011 (UTC)[reply]
Well, as I wrote above, your own answer explains how it could be done: to build a biological N2 detector, all you would have to do is couple nitrogenase to a detector for fixed nitrogen, of which there are many examples. But as you also say, such a thing would be useless, because N2 is everywhere. Looie496 (talk) 22:07, 18 January 2011 (UTC)[reply]
Future space journeys
in future the man will find better ways for solve weightloss problem in space jurnays . i forcast that this mystry is hidden in comets
and sattlite and space craft groups will have diffrent missions . we will find severel mystrys of planets and moons with particle sending method that i want to publish . i have good ideas for this. a. mohammadzade — Preceding unsigned comment added by A.mohammadzade (talk • contribs) 05:02, 17 January 2011 (UTC)[reply]
Hello, I'm guessing English isn't your first language so apologies if there is a question there which I'm not seeing. The reference desk is for people who seek referenced answers to specific questions relating to science. Do you have a question? Vespine (talk) 05:43, 17 January 2011 (UTC)[reply]
that is so ,my mother toungh is turkish ,so i have some difficultys in english . I have write my special questions about solar system
last jan 11 under the subject "any one with new ideas for creation theories of solar system "wich shows my new theory upgrading from new explanation of objects and planets belts and astroids in solar system .
I wrote them not to find replays but for showing nessesity for development and changing in thus theories A.mohammadzade jan 18 iran—Preceding unsigned comment added by 78.38.28.3 (talk) 04:03, 18 January 2011
Why should there be health problems? Even if there was mold on it it would probably be harmless (most, but not all, molds are harmless when eaten (as opposed to inhaled)). What do you mean by "seed bread" - all bread is made from seeds. Ariel. (talk) 11:00, 17 January 2011 (UTC)[reply]
The term probably refers to Whole grain bread. It may also refer to Seed cake. Not sure which the OP means. Regarding health effects, presuming that there isn't any alergic concerns (i.e. you wouldn't have negative health effects from eating it fresh) and it isn't rotten or spoiled (as the OP says, no mold) then stale bread is just "dried out", i.e. slightly less water than fresh bread. I would say that such bread is perfectly safe, again with the caveats that there is no spoilage and there is no allergy concerns. --Jayron3213:59, 17 January 2011 (UTC)[reply]
I regularly eat soda-bread which contains sunflower seeds, linseeds and sesame seeds. Maybe something like this is what the OP is referring to. I agree that there are few health risks in eating stale bread, with or without seeds. Our stale bread (not the soda bread) is made into breadcrumbs for use in other dishes. I'm still here! Oops, sorry that's WP:OR. Richard Avery (talk) 14:16, 17 January 2011 (UTC)[reply]
Yes, it does seem so (although I can't say with 100% certainty). Chlorine is very common in the environment - from ordinary salt, so it gets used as the acid plus when it's time to neutralize the acid it makes ordinary salt, and salt is used for other things as well (sodium is the main driver in nerves). However not all animals have stomach acid, acid breakdown is not the only form of digestion. Ariel. (talk) 11:52, 17 January 2011 (UTC)[reply]
No: In most insects, midgut pH is either mildly acidic or neutral. Lepidopteran and trichopteran larvae, scarabaeid beetles, and nematoceran flies have alkaline midguts, .... --Sean15:27, 17 January 2011 (UTC)[reply]
Your reference to the midgut confuses the issue -- humans also have basic midguts. HCl is secreted in the stomach, but bicarbonate is secreted from the pancreas, and a look at our midgut and foregut articles seems to establish the change of foregut to midgut at the point of fusion with the bile duct -- looking at the bile duct article reveals that this duct meets with the pancreatic duct and enters the duodenum at the ampulla of Vater. Thus, insects are hardly unique in having basic midguts -- I'd say humans and most mammals do to. DRosenbach(Talk | Contribs)19:17, 17 January 2011 (UTC)[reply]
e/c Any context? Can't find anything about it on Wikipedia, but it appears to be a product name by the Sterling (Kohler) plumbing company for a range of bathroom and kitchen products: see [1]. --jjron (talk) 17:48, 17 January 2011 (UTC)[reply]
" Vikrell is a solid composite material made of resins, fiberglass and filler that is exclusive to Kohler Company." [2] (See "shower stalls FAQs" box at bottom right of page). It apparently has integral pigment rather than a paint-like top layer, hence chips don't show. 81.131.68.227 (talk) 17:52, 17 January 2011 (UTC)[reply]
My family has been kicking around a recipe for corn cob jelly, and our most recent attempt at making it was somewhat of a flop. According to the package, pectin requires acid to work, and the typical way of doing this is to add lemon juice. The problem is that corn cobs don't make for a very strong flavor and the end product was rather more lemon-tasting than I'd like. Other than laboratory supply of citric acid (or hydrochloric for that matter!) is there a source of food-grade acid that isn't quite as strong a flavor as lemon juice? I was thinking vinegar, but that's unlikely to work well with a sweet product like a jelly. SDY (talk) 20:16, 17 January 2011 (UTC)[reply]
I don't know where you live but in NZ you can buy citric acid and tartaric acid in most supermarkets. However from my experience in making paneer, citric acid still imparts a fairly strong taste. Haven't though of trying tartaric acid for some reason. You could try various acidic fruits I guess. Pineapple or green kiwifruit perhaps? Perhaps even lime will be a taste you find okay. While looking in to tartaric acid for making paneer I found this [3] where they also tried lactic acid and ascorbic acid (you'll want to be careful you don't overdose on vitamin C I guess). Finally you may want to do a few tests, perhaps you're using way more lemon juice then you need? Nil Einne (talk)
C is water soluble and it's very hard to get an overdose. A and D and the other fat-solubles are the problems for overdose. I'll have to look at a different grocery store. Safeway (US, Washington state) doesn't carry citric and tartaric from what I've seen, though I guess I've never asked. SDY (talk) 20:46, 17 January 2011 (UTC)[reply]
The vitamin C article says it exhibits remarkably low toxicity, the LD50 for an average person would be over 800 grams, and "The mechanism of death ... may be more mechanical than chemical". :) 81.131.16.71 (talk) 20:58, 17 January 2011 (UTC)[reply]
Okay no concerns for ascorbic acid then so that's one possibility. I should clarify the citric acid and tartaric acid I'm thinking of is normally available in crystalline form, see [4].
This result from a search for 'where to buy citric acid' may be helpful [5] (the purpose there may not be food related but most of the suggestions sound like they will be fine). In particular a brewing shop may be something to look in to. I know someone who makes their own energy gels and citric acid is used, so perhaps a health food or sports/exercise supplement shop will also have something (although they may just want to sell you premade stuff). [6] (UK apparently) suggests a home brewing shop as well hence my recommendation.
P.S. Reading the forum suggestions a little more closely, it also sounds like you may not want to (try to) purchase too large quantities...
I don't see why it couldn't carry one away. Flash floods can remove houses from their foundations, and in terms of absolute weight, a house is heavier than a tank. "Destroy" may be a harsh word, but I could see a tank being lifted off its treads and moved by such a flood. --Jayron3221:34, 17 January 2011 (UTC)[reply]
From M4 Sherman: 66,800 pounds / (5.84 m * 2.62 m * 2.74 m) = .723 g/cm3 leading to the surprising result that tanks float. Of course that assumes that it's a cube, which it isn't. It's probably denser than that, but it's still reasonably close to the density of water, so water will have no trouble carrying it. Houses float too BTW, that's the main reason flash floods can move them. Ariel. (talk) 21:57, 17 January 2011 (UTC)[reply]
I don't believe so, or at least not to a catastrophic degree. Many modern main battle tanks are capable of deep wading, which means they can drive through water that's as deep as they are tall (with the help of a snorkel) - see File:Zwei_Leopard_2A5_beim_durchqueren_eines_Gewässer.ogg where two modern Leopard 2 MBTs ford a river, with only their snorkels and the ends of their gun barrels above water. They can only achieve this if they're heavier than the water they displace (that is, that they don't float). It seems other MBTs, including the T90 and the Abrams M1 can deep wade too. So that demonstrates that, fully immersed in water, they have enough net downforce to allow the treads to engage enough to drive the vehicle through the river at some speed (which shows they're not just on the ground, they're still quite firmly on the ground). There have been fully amphibious ("swimming", which means floating) tanks, like WW2's Swimming Sherman, but those either needed an inflatable float (see DD tank#Sherman DD) or to be specifically designed to float (like the lighter Expeditionary Fighting Vehicle). Now whether the driver of a wading tank fancies the idea of driving it around in what has become essentially a murky, obstacle-filled, fast-flowing river is another matter. The wading capability is designed either for hot landings on beaches from landing craft, or for fording rivers, so they're not designed to be terribly effective at doing anything but going in a straight line in water, and not for very long. -- Finlay McWalter ☻ Talk22:23, 17 January 2011 (UTC)[reply]
Maybe it's the difference between loaded weight and unloaded. Probably the number given in the article is for unloaded. Also a tank is not a cube, so the simplistic volume calculation is certainly too large. I was just going for an order of magnitude calculation. Ariel. (talk) 22:54, 17 January 2011 (UTC)[reply]
There's not much difference, that I can figure, between the loaded and unloaded weight. Looking at the Leopard 2, I reckon its ammo (43 rounds at 25 kg/round) weighs 1075kg, the fuel (1160 litres of diesel at around 0.84 kg/litre) weighs 975kg, and if three of the four crew swim for it (say 3 x 100kg) that's 2.3 tonnes. That sounds like a lot (it's more than two cars) but when you consider the full Leopard 2 weighs in at a jaw-dropping 62 tonnes, the laden/unladen differential is only 4% or so. -- Finlay McWalter ☻ Talk23:17, 17 January 2011 (UTC)[reply]
It seems that a "flash flood" can mean anything from an accumulation of rainwater at low points of streets where the water is essentially standing still, to a vertical wall of water roaring through a canyon downstream of a failed dam. A tank should have decent chances of operating in the former, but has essentially no possibility of surviving the latter.
What causes a (metal) cooking pot (no handle) to rock from side-to-side when on a stove burner (electric in my case) just as the water is about to boil? This motion can be halted temporarily by grasping the pot briefly. When released, the rocking resumes.--Koosharem (talk) 01:20, 18 January 2011 (UTC)[reply]
Even before proper boiling, bubbles form in the water. These bubbles can exert forces on the walls of the pot. It could also be from Cavitation, which is the net effect of lots of tiny shock waves created by tiny bubbles collapsing. --Jayron3203:03, 18 January 2011 (UTC)[reply]
how risky is it for those that have unprotected sex with someone that is hiv+ but has an undetectable viral load? I know that most people get HIV from other people that have just gotten it because those people have the highest amounts of replicas of the virus in their bloodstream. I know it is less likely that you would get hiv from someone on antiretrovirals or that is undetectable but is it nearly safe sex or not? Are there any statistics on this? Where would I find the answer to this question?Thisbites (talk) 01:29, 18 January 2011 (UTC)[reply]
Arthur C Clarke and others have postulated "Gossamer thin sails" for interstellar travel using light presure.Since light by definition is massless how can it exert pressure to 'fill' the sails?
John Cowell118.208.117.68 (talk) 02:15, 18 January 2011 (UTC)[reply]
Photons (light) have momentum even though they have no mass. In modern physics, relativistic momentum is more complicated than just the simple "mass × velocity" relationship; in fact, momentum is related to the mass, velocity, and energy of the particle, according to a Lorentz transform. (So, even zero-mass photons can have non-zero momentum). This was formalized by Einstein as part of the theory of Special Relativity. Nimur (talk) 02:25, 18 January 2011 (UTC)[reply]
Photons are not massless. They have no rest mass (or to put it another way, at rest they don't exist), but while in transit they do have mass. Ariel. (talk) 03:01, 18 January 2011 (UTC)[reply]
There's no disagreement about the physics here - this is strictly a matter of semantics and terminology. I use the term "mass" to specifically refer to rest mass - as do many physicists. An equally-valid but different definition of the unqualified term "mass" refers to the sum of the rest mass plus the normalized kinetic energy, per mass-energy equivalence. Photons have an exactly-zero rest mass. Many physicists (myself included) thus say "it has no mass." Many other physicists dislike this terminology, and always use "mass" to refer to relativistic mass. I don't think we need to devolve in to word-mungling pedantry over this, because we're all in agreement about the actual phenomena. See the mass article, the terminology section, and the list of reference texts and papers for a bunch of different opinions about which definition is "better." Nimur (talk) 04:08, 18 January 2011 (UTC)[reply]
I wasn't arguing with you (not sure if you thought I was), it was a reply to the OP. I prefer to assign the word mass to relativistic mass because that's the one you need to use for calculations - momentum, gravity, inertia, etc. The trouble with doing so is that relativistic mass is not a constant (because it depends on who you are comparing it with), so I understand the arguments for assigning it to rest mass. Ariel. (talk) 04:22, 18 January 2011 (UTC)[reply]
Energy in a magnet.
For more than 20 years I used a 3 inch magnet on a daily basis.It was so strong it would fly out of my hand if I got too close steel and the only way to release it from the deck of my truck was to slide it to the edge and carefuly remove.As a tool of trade for a scrap metal buyer it even exerted a 'pull' on 304 and 316 stainless steel.It was used for holding steel for welding,holding spring doors open etc.It would have lifted the equivalent of hundreds of tons over the years without diminishing in strength.
How can so much potential energy be incorporated in something so small,how is it stored and calculated,and surely there must be a multitude more practical uses for such a mini powerpack other than computers and maybe speakers?
John Cowell118.208.117.68 (talk) 03:07, 18 January 2011 (UTC)[reply]
The nutshell answer is that a magnet exerts force, which is neither energy nor work. Work, rather, is force acting over a distance. When the magnet leaps from your hand to the steel, it's done some work, because it's moved. However, it's then stuck to the steel and does no further work. For it to move again, you've got to do work of your own (counteracting the work the magnet did) to get it back away from the steel. As for other practical uses (I'll leave aside whether they're more practical, as computers are way up there), magnets are essential to electric motors, generators, transformers, and medical devices. — Lomn05:14, 18 January 2011 (UTC)[reply]
I was thinking about this the other day again because magnet questions are quite common on the ref desk. Maybe someone has used this analogy before but I thought a spring analogy might be good at illustrating the difference between force and energy. A loaded spring exerts a strong force, try holding a strong spring closed just with your arms for a long time! It can take a lot of energy on YOUR part. But a spring can only do an amount of work relative to its length and force it was loaded with to begin with. Once a spring is "unloaded" that's it, no more force. Same as a magnet. Vespine (talk) 05:48, 18 January 2011 (UTC)[reply]
OP, This is by no means the first time a human has had this thought! :) Magnets are quite baffling until you understand how they work. It's the mystery of magnets that has led men on life-long fruitless and often fraudulent attempts at gaining "free" energy/money (Steorn, for example). Until a material is discovered that can block magnetic fields, no "work" can be done by them, just simple attraction. They are still fun to play with thoughZzubnik (talk) —Preceding undated comment added 12:39, 18 January 2011 (UTC).[reply]
For those of you wondering, the song in the link Jayron gave is the source of the "Fucking magnets, how do they work?" Internet meme (which may not really be a meme, the talk page argues...). Also, I never realized people got hung up about the use of the word "miracles" in that song :rolleyes: TomorrowTime (talk) 15:16, 18 January 2011 (UTC)[reply]
I'd like to point out the enormous work I do every day by exerting a force of mumble Newton with by behind to the seat of my chair - not to mention the nightly work quota I exert on my bed. ;-) --Stephan Schulz (talk) 17:32, 18 January 2011 (UTC)[reply]
The Tesla is not actually a unit of energy, so you can't say how much energy it takes to make a magnet of a certain strength. And yet, it would be interesting to know how much actual energy it takes to turn a non-magnetic chunk of metal or rare earth into a powerful magnet like the one described; and conversely whether there is any theoretical way by which the entropy of the magnet as it degrades from perfect order could be used to drive a thermodynamic process that produces work. Hmmm - is this the same as a measurement of any excess thermal energy released if the magnet is pulverized under a powerful ram? I would think that the amount of energy needed to create two magnets of opposite polarity must exceed the amount of energy they release by coming forcefully together - I suspect that this is by some large factor - I wonder what physical factor describes this necessary limitation on the ease with which permanent magnetism can be induced in a material. Wnt (talk) 06:10, 19 January 2011 (UTC)[reply]
I suspect that the 'crushing' process would actually be endothermic, not exothermic. Ordered, aligned spins in a ferromagnetic material have a lower energy than randomly oriented spins; you have to put in energy to break the alignment. At the Curie temperature, a phase transition occurs when you move from aligned to random spins; this shows up as a measurable endothermic bump by differential thermal analysis. Similarly, if you just pull aligned-spin particles or domains apart without jumbling their orientations, that costs you energy as well — the energy of aligned spins is lower than the energy of the free or separated particles. TenOfAllTrades(talk) 14:30, 19 January 2011 (UTC)[reply]
Well, I have to admit, you're right about that. My intuitive feeling was that a pile of powdered magnet shouldn't spontaneously assemble into a powerful magnet ball - I wonder if that was also false. Wnt (talk) 18:07, 19 January 2011 (UTC)[reply]
Will an object past the event horizon of a black hole inevitably reach the singularity?
An object around a gravitational body like the Earth can orbit indefinitely if its velocity is sufficiently high, but is it possible for an object to remain stationary within a black hole? Likewise, can an observer past the event horizon perceive other objects? By definition, light can not escape the horizon, so would it be impossible for photons to reach the observer from further within the black hole? —Preceding unsigned comment added by 68.40.57.1 (talk) 03:27, 18 January 2011 (UTC)[reply]
Yes, in case of Schwarzschild black hole, object that crosses event horizon reaches the singularity sooner or later. All the paths inside of event horizon lead to singularity. So harder it tries to avoid, sooner it reaches singularity. For other types of black holes (charged or rotating black holes), there is possibility of avoiding singularity. I am doubtful whether an object can remain stationary within a black hole. About your last question, are you asking whether photons from within black hole can reach observer who is outside event horizon? No, photons cannot escape from black hole. Or, are you asking whether observer within the black hole can observe photons? Yes, observer falling inside black hole continues to observer things according to his clock, he cannot determine whether he has reached event horizon or has crossed it. - manya (talk) 04:21, 18 January 2011 (UTC)[reply]
To clarify, I was asking whether the observer within the event horizon can detect photons from further inside the black hole. Also, your statement regarding the observer not being able to determine whether he has reached the event horizon is in contradiction of the article on it. --68.40.57.1 (talk) 04:34, 18 January 2011 (UTC)[reply]
No, it is exactlyt confirmed by the event horizon article. Let me quote it for you. "An observer crossing a black hole event horizon can calculate the moment they've crossed it, but will not actually see or feel anything special happen at that moment." --Jayron3204:40, 18 January 2011 (UTC)[reply]
I presume you meant to say "within the event horizon", not "within the singularity". Yes, for a while an observer inside the event horizon will be able to see an object that's further inside the black hole, that fell in shortly before the observer. However, the object will rapidly move further away from the observer, due to the extreme tidal forces, and the object's image will become red shifted, to the point where the observer soon won't be able to see it at all. In other words, the appearance of the object will qualitatively appear very similar to the appearance of an infalling object as seen from an observer that's outside the event horizon. Red Act (talk) 06:16, 18 January 2011 (UTC)[reply]
You have to be specific about what you mean by "further inside", because black hole spacetimes are nothing like the ordinary flat space where concepts like "inside" are normally defined and make sense. The most obvious thing you might mean by "further inside" is that the Schwarzschild r coordinate is smaller. Outside the event horizon, that coordinate measures distance from the center of the hole, more or less. Inside the event horizon, though, it measures time. The singularity is in the future, not in a particular place, and "further inside", in this sense, would really be "later in time". You can't see the future, even inside a black hole. You can, however, see objects that crossed the event horizon before you did. The easiest way to understand how this works is to look at a diagram like the one to the right. Ignore everything but the upper right quadrant. The straight diagonal line is the event horizon; below and to the right of that is the outside world; above and to the left is the black hole interior. The singularity is the boundary of the grey region. The grey region itself is nothing (it's not part of the solution). The past is down, the future is up. Light travels along 45° diagonal lines. You can only cross the event horizon from right to left, since you're limited by the speed of light. If you draw two sub-light worldlines crossing the horizon, it's easy to see that light from the first one will reach the second, so you can see someone who crossed the horizon before you did. You will hit the singularity before you see them hit the singularity, though. The animated blue lines are lines of constant Schwarzschild r. -- BenRG (talk) 07:25, 18 January 2011 (UTC)[reply]
Ticklish sensation near forehead
If an object is brought close to my forehead, but does not touch it, my forehead becomes sensitive and starts tingling and becoming very "ticklish", for lack of a better term. For several years, I've asked certain people if they've had the same sensation, and I've only met one girl who did. I have unsuccessfully tried testing the sensation with my eyes closed. As the object (any object) is brought closer to the forehead, the sensation deepens. It used to be really bad when I was a child, but now as an adult, I hardly even think about it anymore. It just popped into my head a minute ago and I decided to ask about it :)Reflectionsinglass (talk) 03:56, 18 January 2011 (UTC)[reply]
You are not alone.[7] -- I'm particularly interested in this comment from DocCathode:
"Nothing supernatural about it. It's a mixture of a sense of danger/discomfort, the urge to move away, and the repression of that urge.
"To prove this, you need a friend who trusts you and follows instructions. Tell them to stay still, and to open and close their eyes when you tell them. Begin approaching with finger about two feet away. Tell them to close their eyes. Move the finger foot closer and tell them to open their eyes. Tell them to close their eyes. Move the finger to six inches away. Tell them to open their eyes. Tell them to close their eyes. Move the finger to three inches. Tell them to open their eyes. Tell them to close their eyes. Move the finger to two inches. Tell them to open their eyes. Tell them to close their eyes. Move the finger to an inch. Tell them to open their eyes. Tell them to close their eyes. Move the the finger to half an inch from their forhead. Tell them to open their eyes. Tell them to close their eyes. Slowly and quietly move your arm away from them. Tell them to open their eyes.
"The tingling sensation is most intense the last time, despite the fact the no object is near their forehead."
I read an article that had say something about the death of mamots in 35000years ago that may be general for last happening for dinosoros 0 the radiation of any supper nova can kill dinosoros
in some million years ago. A.mohammadzade jan 18 iran —Preceding unsigned comment added by 78.38.28.3 (talk) 04:23, 18 January 2011 (UTC)[reply]
3500 years ago? Are you thinking about Noah's flood (Nuh in Islam)? According to the (Christian) Ussher chronology this occurred 2348 BCE. Modern science places the dinosaurs extinction to the Cretaceous–Tertiary event 65.5 million years ago (as Calliopejen1 noted), and woolly mammoths to about 10 thousand years ago. BTW, several web-browsers have spell-checkers for their text-entry boxes; you should consider installing one for all the languages you speak. CS Miller (talk) 05:36, 18 January 2011 (UTC)[reply]
Actually, the OP said 35,000 years ago, not 3,500 - no need to drag young earth creationism into this. As you note, mammoths were still alive and well at that point, so it's a curious date to bring up. Our article on 35,000 BC No, we don't really have an article on that date, but it is a nice redirect... doesn't mention anything particularly germane. 15:08, 18 January 2011 (UTC)
There is really no question that the asteroid killed the dinos. Headline writers and popular science in general will never tire of stirring up controversies, but a panel of 41 international experts have met and agreed that there is consensus on the cause. This is mentioned in the articles. Imagine Reason (talk) 00:00, 19 January 2011 (UTC)[reply]
Actually, I killed the dinosaurs. It was a time travel mistake, sorry, but when you gotta sneeze, you gotta sneeze. I take no responsibility for the mammoths, though. I think Baseball Bugs did them in. --Ludwigs200:04, 19 January 2011 (UTC)[reply]
Lespedeza are commonly used in the Southeastern U.S. and meet all of your requirements except edibility. Not sure if it will grow in the Bay area, however. --Jayron3205:53, 18 January 2011 (UTC)[reply]
never say death star for pulsars
the crab nebula is sending several rays and is alive there in space . the heart of the star is sending palses so we ought never say the super nova has died . a. mohammad zade iran --78.38.28.3 (talk) 06:06, 18 January 2011 (UTC)[reply]
i think that the earth was shining for some million years . if you want to know why then that will explain with my new theory a. mohammad zade
Why don't you ask whether your theory is consistent with the evidence so we can critique it for you? To do so, you would have to explain it. It is true that the elements heavier than iron came from supernovae in the Earth's distant past. 71.198.176.22 (talk) 06:06, 18 January 2011 (UTC)[reply]
thanks for giving commnets .i will soon write my theory hear i have some problems in safe evaluation andpublishing . so i save it such as patent . it will wrote here as soon as i published .--78.38.28.3 (talk) 06:13, 18 January 2011 (UTC)[reply]
I really don't understand why people who have a pre-existing conditions are making SUCH a big deal out of having to pay more for insurance. I understand they get mad if they are denied, but they should have to pay more. It's the same way I have to pay more for auto insurance because I am younger and have had several speeding tickets in the past few years, I am a greater risk. Many (not all, but many) CHOOSE to have these pre-existing conditions. Many people who are obese, choose to have several other related problems, many people who high cholesterol choose to have it, same with so many other conditions. Is there a flaw in my thinking? I'm already paying over $200 a month for insurance when I don't ever use it because of all these abusers, when I am perfectly healthy, take care of myself, follow a healthy diet, and go to the gym 5 days a week. If everyone was covered, it would just make the problem worse and more expensive for everyone. —Preceding unsigned comment added by 76.169.33.234 (talk) 07:44, 18 January 2011 (UTC)[reply]
What country are you from? People there might be grateful they don't live here in Australia. Here, if you have a pre-existing condition, you can be denied any benefits for treatment of that condition for 12 months after taking out the insurance; but after that, you're fully covered like everybody else. There's no alteration to premiums, though; that's strictly outlawed. -- Jack of Oz[your turn]08:00, 18 January 2011 (UTC)[reply]
USA. I don't know how people think in Australia or in other countries, but I work in a pharmacy and my customers think just because they are taking a cholesterol medication, they can eat whatever they want. My customer was joking about it the other day. —Preceding unsigned comment added by 76.169.33.234 (talk) 08:04, 18 January 2011 (UTC)[reply]
Yes, insurance companies have to discriminate, but it's sometimes hard to be tough on those with self-inflicted conditions while being fair to those whose ailments are innocently gained. HiLo48 (talk) 08:09, 18 January 2011 (UTC)[reply]
No, insurance companies don't have to discriminate, but only if you run a system of compulsary insurance. This is what happens, in one form or another, across most of the developed world: compulsary insurance with a ban on discrimination. Physchim62(talk)12:39, 18 January 2011 (UTC)[reply]
I'm actually kind of struck by your first sentence. My fiancee, in trying to get private coverage, has been rejected by every insurer in California due to a pre-existing condition, which we're told will continue to be the case for another couple years. This is not a matter of paying more - she's not even allowed in the existing high-risk pools. I hate to think where she'd be if neither she nor I had a job. HIPAA and COBRA (expensive) do ignore pre-existing conditions, but they are not available to everyone. As for whether people choose to have a pre-existing condition, I have no comment. Someguy1221 (talk) 08:15, 18 January 2011 (UTC)[reply]
HIPAA is a health information privacy act, not an insurance company. COBRA is Federally mandated insurance coverage for those who recently left employment. I do not see how those apply in the context you are using. -- kainaw™17:28, 18 January 2011 (UTC)[reply]
Further, California has a state managed program specifically for high-risk patients who have been denied insurance. It is explained here. -- kainaw™17:31, 18 January 2011 (UTC)[reply]
I wasn't even aware of that plan, thanks (but thankfully she has a job, and I don't even want to know how much that costs). I was referring to HIPAA health plans, by the way. I was using both that and COBRA as examples of coverage potentially available to individuals with pre-existing conditions who do not get such coverage through their current employer, or who are unemployed. Someguy1221 (talk) 00:04, 19 January 2011 (UTC)[reply]
Really it is a question of what costs we think are fair to spread across society, and which we don't. If you happen to be develop a terribly expensive health condition, through no fault of your own, should society bear this cost, or should you? Thinking from a position behind the veil of ignorance, one might prefer to spread such costs across society. Also, you note that some health conditions are in part caused by deliberate choices. This may be true, but most health conditions are not, and what sort of surveillance regime would be necessary to monitor which people this applies to? Such surveillance would likely be prohibitively expensive, as well as intrusive on privacy. Thinking forward into the future, as genetic health data becomes more readily available, it is plausible that insurance companies could very easily calculate your health risks to a much greater precision. (Assuming this were legal.) Is this something you would want? It is essentially just an extension of your principle of paying a premium that reflects your health risks. It would assign costs much more precisely to the individual, but it would change the nature of health insurance as we know it. Now, health insurance effectively insures against the risk that you will get Alzheimer's, for example. In the future, perhaps it would already be known that you will get Alzheimer's (even now, there are some genetic markers identified that are highly correlated with it). Then, since your premiums would already reflect your future disease, you would bear the cost for your Alzheimer's treatment, and your insurance would only be effective against risks such as being hit by a car and needing emergency surgery. Would this be preferable? To me, probably not. YMMV. Calliopejen1 (talk) 11:11, 18 January 2011 (UTC)[reply]
Generally this is misplaced, although the degree to which disease is a "choice" could be more scientific. After all, obesity and even high cholesterol are controlled by genetic and other propensities (I suspect that there should be a dramatic role for epigenetics here...) I feel that nothing but prejudice controls what people like the OP pick out as a "choice" - after all, the commuter who suffers injuries in a traffic accident also made a choice, right? The skier who leaves his testes with a buried pole on the slopes, likewise. The HIV victim, few would disagree, but what about the victim of flu or rotavirus or meningitis or malaria, who could have avoided it all just by staying inside his front door?
It may be more for the humanities desk to answer what the point is of having insurance if suffering a diagnosis means being denied insurance. Why not just keep your money and pay as you go, with no private bureaucrats pretending to serve you by driving up costs? The problem is, no one wants to be diagnosed with anything, and as they are servants only of corporations and government the doctors are trusted far less than Mafia bookies, so preventative care becomes a pretty myth. Wnt (talk) 15:30, 18 January 2011 (UTC)[reply]
"Why should society pay for the consequences of someone's bad choices?" begs the question of bad things happening to people who have in no way brought it on themselves. It is a reasonable question whether a society should spread the medical costs across all members, or have a "Every man for himself and the devil take the hindmost" lifeboat ethic. A person can be bopping along, healthy as a horse at 20 and at 30, and at 40, never took a sick day, eating right, not smoking, exercising regularly, then suddenly they have some crippling injury or ailment, like a debilitating and persistent and ineradicable infection, or a crippling injury, or cancer, or heart disease, or insulin dependent diabetes, with little hope of getting individual health insurance from a for-profit insurer. Many Americans live in a fantasy world where they will always have a policy from work. If the hospitalization means you can't work, and you don't have or lose your employer-provided insurance, you are just out of luck when you need surgery or hospitalization which might cost $100,000. Figure on losing the home and spending every dollar of retirement savings. "Move in with the folks" is not an option when they are dead and gone. Even if someone with severely impaired health found a private insurer, it would cost more per month than they could pay, especially if they are not healthy and can only work part time or a lesser pay level than their previous fine career allowed. "Paying more for insurance because of a preexisting condition" may mean paying an extra $12,000 a year more than the basic insurance, or even more than that, which the unwell person simply cannot afford. According to a report, "80 percent of people with diabetes were uninsured after they lost health insurance coverage due to loss of a job or job change, divorce, change in income or health status, or a move. " It is not presently affordable for them. Over 50 million Americans have no health insurance, so that if they do go to see a doctor or have tests, they must pay "list price," typically several times what the cost is for those with insurance, since Blue Cross et al reduce the price to a fraction of what the doctor, hospital or lab says it should cost. For instance, Xrays that the insurer writes down to $100, and which cost me $15 out of pocket, would have cost the uninsured $350. An EKG that would have cost the uninsured $1100 got written down by the insurer to under $300 (and only cost me under $30). Edison (talk) 16:59, 18 January 2011 (UTC)[reply]
Fom a european persepective the "devil take the hindermost" American health care system, or lack of it, is scandalous. Add that to guns being used freely, with gun-murders being 100 times more common per capita. They are not good adverts for the US. 92.24.183.183 (talk) 14:42, 19 January 2011 (UTC)[reply]
While I agree with all that you said (in particular, many medical conditions are not or not fully the result of irresponsible choices), there is also another aspect: It might be cheaper to pay for the effect of someones bad choices. Sick people typically can contribute less to society - imagine Stephen Hawking without universal health care. Similarly, desperate people will do desperate deeds. Would you rather pay for someones cancer treatment via a social insurance system, or pay for more police to keep desperate husbands, wives, or parents from robbing banks to pay for treatment? --Stephan Schulz (talk) 17:24, 18 January 2011 (UTC)[reply]
This is a valid point, but it really doesn't go far enough. Society has prevented disaster by various back-door ways of paying for health care for the poor, such as hospitals providing care and then just not getting paid for it, then working the costs into care for other patients. But hospitals have become more and more commercialized, with less profitable sites even shutting down, and if political efforts to correct the situation are rebuffed, then you're left with a situation where a segment of the population denied access to health care would begin to turn on it as an enemy. The effect of even a single ambulance bomb would be devastating (and how do you apply security precautions?). The effect of three or four simultaneous attacks against all remaining hospitals of a metropolitan area would essentially put major health care out of commission for a hundred miles in any direction - even if such a homegrown al Qaida didn't manage to get their hands on the radiation sources inside the hospital ... Wnt (talk) 05:12, 19 January 2011 (UTC)[reply]
I have a concise answer: The argument (that people with pre-existing conditions should just suck it up and pay a lot more for their medical insurance) makes complete sense from an actuarial point of view, but it collides with many people's belief that a society should take care of its sick, even though this makes insurance more costly for the more-healthy. Comet Tuttle (talk) 18:37, 18 January 2011 (UTC)[reply]
Yes. Once we have decided we will not let people simply die on the street, then we must assess the cost of emergency treatment and conclude that an ounce (or penny) of prevention is worth a pound (dollar) of cure, therefore the next step is to try to fund preventative care. Because whether through taxes or insurance premiums, you still have to pay for the sick, so might as well pay less for better results. SamuelRiv (talk) 22:10, 18 January 2011 (UTC)[reply]
This isn't really a science issue and is OT on the RD anyway but that probably applies to most of this discussion. The above is one of the arguments for measures to tackle obesity, smoking and other problems as well as encouraging healthy eating, exercise etc in countries with some sort of socialised medical care. Of course depending on the measures this can lead to claims of nanny state, food police, sin tax and whatever else and measuring the efficacy of such measures is generally difficult at best. And I've seen it argued smokers at least actually cost the system less in the long run, particularly where there are other costs (e.g. in NZ where a government funded pension is something most citizens past a certain age are entitled) due to the shorter lifespan even with their added medical bills. (Of course you then get in to complicated issues like whether they contribute less.) Unrelated to this but related to the earlier point you also get the complex issue of how much should be spent on treating people with a given expected outcome. For example, is it worth spending $100k on treatment that may increase the chance of living past 5 years from 5% to 10%? (Very simplistic of course, the outcome of many treatments come in things like improved quality of life which are generally subjective.) Ironically this was seen to some extent in the US with the recent debates when the death camps nonsense came up. Nil Einne (talk) 22:46, 18 January 2011 (UTC)[reply]
Most of the others have hit the main points here, but I just want to point out that insurance that covers you when you are healthy, but not when you are sick, is not really insurance. That's just a series of subsidized physical exams. The entire point of insurance is that you pool the resources of many so that when others are in hard times, they have resources as well. It is a sign of how screwed up the American medical system has become that the basic notion of insurance has been completely forgotten by most Americans, who just understand it as "the way I pay for routine checkups and prescriptions." It's about spreading the risk, plain and simple. --Mr.98 (talk) 03:30, 19 January 2011 (UTC)[reply]
The deal with paying for routine checkups is that's how the insurance companies manage their own risk. The costs of dealing with tragic diseases goes up considerably the later they are treated; insurance companies actually save themselves money by making sure you go to the doctor regularly to for physicals, and to get even "nuisance" issues checked (like the non-specific and usually benign but occasionally deadly "Flu-like symptoms"). The ideal "deal" between insurance companies and their customers is something like "You agree to get checked by doctors more often, and we'll cover it when shit goes really bad". Same deal with prescription coverage; people would forgo necessary medicine if it's too expensive, and on the bulk these people will end up costing the insurance companies much more if you end up in the hospital getting treated for something your medicine could have prevented. This is not a defense of the American insurance industry at all; they've basically dropped the ball with regards to their fiduciary responsibility towards their clients. But in theory, the system is supposed to work as I describe. --Jayron3205:26, 19 January 2011 (UTC)[reply]
Isn't it the insurance company's fiduciary duty to do the bare minimum to brand the sick person with a permanent record of poor health, and help their client (the employer) to get rid of the problem before it amounts to a major expense? Wnt (talk) 18:11, 19 January 2011 (UTC)[reply]
I am the OP, sorry it took me so long to get back to this post....
Edison, you are really sucked into the idea that obesity and high cholesterol is almost all about genetics, when it has little to do with it. The issue here is that for a genetic defect (not sure if this would be the right word) to be present, it would require the proper environment. Almost every single obese person eats horribly and that is a choice. Same with many people with high cholesterol. You can be thin and have high cholesterol, but if you really take a look at it, almost every single person with high cholesterol is overweight, many of them even obese. If you look at both groups, neither one in almost every consumes a "healthy" or a low calorie diet (low cholesterol diet in the high cholesterol patient) and they almost never exercise if they do at all. Most these people "think" they know how to diet, but they have no clue, they think 3000 calories a day or more is a diet. They think exercising is walking around the block or taking the stairs instead of taking the elevator. Try going into the gym and pounding the weights for an hour and then doing 45 minutes of hardcore cardio 5 days a week and then lets see if you still have high cholesterol or are obese after a year doing that and consuming a low calorie diet. I can guarantee you over 90% of the people will be cured as long as they keep it up.
Now lets discuss choices in life. Everything you do is a "choice." Many or all of them involve some degree of risk. Everyone knows that driving a car involves risk, you can get into an accident. Some people choose to take that risk and some paranoid people or people that have been in very bad accidents that have not recovered emotionally choose to not take that risk. So is it a choice? Yes, it is. At my age, I choose to take the risk of maxing my car out to see how fast it goes on the freeway. I know there is more risk involved going very fast, but if I had children, I would not take that risk. Same with skiing, there is a risk involved. An example that may be more clear would be weight lifting, there is a great deal of risk involved. Personally, I choose not to do some exercises at the gym because of the risk involved. And yes, even with sex and contracting HIV there is a risk. Have you not heard of getting tested yourself and having your partner tested before you have unprotected sex? Do you think its a good idea to have sex with a woman or a male that has had 50 partners in the past? Would you take that risk? Some people would, some people wouldn't. That is called a choice. There is a distinction between acceptable risk and unacceptable risk.
The real issue here is that many diseases are preventable. Look at most people with type 2 diabetes. If they lose the damn weight and exercise, most of them would be cured. I work with one of them, he has either Jack in the Box, Kentucky fried chicken, or McDonalds every single day. Then he has 2 snickers and peanut M&Ms on top of it. He has high cholesterol and is overweight because of all that junk too. He never goes to the gym and has no interest at all in dieting. His blood sugar was dangerously high before he found out (at work by the way). As previously mentioned, going to the doctor for preventative care can reduce the chances of contracting several diseases or at least you can cut down costs to treat the disease if you catch it early. Most people don't even do that and it costs us healthy people tons of money. Some older women don't get mammograms as often as they should, others don't get them at all. Some older people don't get colonoscopies. Other people don't get their yearly physicals and dont people don't want to pay for their medication and think they know better than their doctor. In the end, it costs us money. It just hurts my wallet and others when I take good care of myself, eat healthy, exercise, and get regular checkups and do everything necessary to stay healthy and other people don't and I have to pay for it. There is no reason why I should have to. ALSO, let me add something to what I originally said. I don't have an issue with supporting people who are disabled and cannot work, I don't have a problem paying for their healthcare. I'm also kind of OK supporting some people who's income is around the poverty level, but then again, I do believe if they really wanted to, they could somehow, someway, come up with the money. I mean just imagine, the last time you really wanted something you could not really afford, didn't you figure out a way to come up with the money? I always do and so do many other people. —Preceding unsigned comment added by 76.169.33.234 (talk) 09:34, 20 January 2011 (UTC)[reply]
I'm gonna skip all the non-sense rant about having to burden the expenses of other people's choices (Welcome to life in society. Go be an hermit if you don't like it) and go directly to the only point of your post worth commenting on. YOU SHOULDN'T SPEED IN THE FREEWAY JUST FOR THE FUN OF IT. I sincerely hope that you get caught next time you do it, making the freeways safer for the rest of us. Dauto (talk) 16:27, 20 January 2011 (UTC)[reply]
To all the "Blame the victim" ranters: Heart disease, strokes, type 1 diabetes, (and even type 2 diabetes) and cancer, not to mention infections and injuries, happen all the time to those who take good care of their bodies. Some diseases are more prevalent among those who eat greasy food 10 times a day , smoke and never exercise, but you could still fill any number of hospital beds with those victims who are "blameless." Edison (talk) 22:35, 21 January 2011 (UTC)[reply]
You have two formulas under the section "Timescale"
Two different science textbooks are quoted for the source of these formula:
B. Gladman et al. (1996). "Synchronous Locking of Tidally Evolving Satellites". Icarus 122: 166. doi:10.1006/icar.1996.0117. (See pages 169-170 of this article.
Formula (9) is quoted here, which comes from S.J. Peale, Rotation histories of the natural satellites, in J.A. Burns, ed (1977). Planetary Satellites. Tucson: University of Arizona Press. pp. 87–112.)
I fixed the link for you, and placed a link on the doi from the reference. Hopefully someone has access to read the article and can check for you. Ariel. (talk) 10:49, 18 January 2011 (UTC)[reply]
The article is available online here (PDF). It gives the first formula and cites to Peale. I didn't look thoroughly for the second formula - maybe someone else can do that? (Note that the Wikipedia article does not cite the second formula to this journal article specifically, though perhaps it also comes from here.) Peale does not seem to be available online anywhere. (I searched in google books using a variety of ISBNs that seem to be associated with the book, and I didn't get any results.) If you are interested in verifying the formula in the original source, the Burns book seems to be available in many university libraries and large cities' public libraries,[9] or you can buy it through Barnes & Noble for $1.99.[10]Calliopejen1 (talk) 10:54, 18 January 2011 (UTC)[reply]
An object hanging on a string
On this page: http://www.croomphysics.com/notes/app_hewitt/chapter2.pdf (page 11) I found an answer to a question that confuses me: "Consider what would happen if you suspended a 10-N object midway along a very tight, horizontally stretched guitar string. Is it possible for the string to remain horizontal without a slight sag at the point of suspension?"
Answer: "No way! If the 10-N load is to hang in equilibrium, there must be a supporting 10-N upward resultant. The tension in each half of the guitar string must form a parallelogram with a vertically upward 10-N resultant."
I understand this for a guitar string and a 10-N load, but what if the string is replaced by a strong rope, and the load is only 1 N. Surely it must be possible to pull at both ends of the rope with enough force to make it remain horizontal without a sag??? Actually, I tried this myself with a piece of rope that I pulled apart and a pair of scissors, and there was no perceptible sag. My reasoning is that a stretched rope must be able to exert an upward directed normal force in the same way as a table exerts an upward directed normal force. Am I correct?? Lova Falktalk13:05, 18 January 2011 (UTC)[reply]
No. Your rope cannot exert a force at right-angles to itself. The only way it can hold something up is if it is pulling up at the point of the suspended object (to cancel the object's gravitational downward pull). If it's pulling up, it must have a vertical component to its direction, which means it's distorted down from perfectly horizontal. Once you recognize "one mass, one string", there's no basis for making a cutoff "only if the mass is less than a certain amount" or "only if the string has certain elasticity". For a very light mass on a very stiff string, the deflection is just very small (because the mass is light, doesn't require much upward pull, and that can be accomplished without much deflection because the string is so non-stretchy). DMacks (talk) 13:13, 18 January 2011 (UTC)[reply]
(edit conflict) No, there should always be a sag, but the sag may not be perceptible under certain parameters. A non-ridged string should always sag in the middle if supported only at the ends, regardless of how hard you pull it. What your eye defines for you as "horizontal" may have a higher tolerance than a true horizontal. In fact, horizontal is one of the least stable positions for such an arrangement, if you look at something like bridges; all rope bridges sag in the middle; if you try to make them not sag, then you end up putting so much force on the ropes as to make them too close to the breaking point for safety. In Suspension bridges, you often engineer the roadway to sort-of "reverse sag", that is many such bridges actually have a hill in the middle, in effect redirecting the stress into the ground anchors on either side of the bridge. --Jayron3213:16, 18 January 2011 (UTC)[reply]
Indeed, the rope will sag under its own weight, even if you don't have any additional suspended mass. If the rope's mass is uniformly distributed along its length, it will form what is known as a catenary curve. TenOfAllTrades(talk) 15:12, 18 January 2011 (UTC)[reply]
Another perspective: in physics problems, 'rope' is often modeled as a mass-less object that has tensile strength but no compressive strength. Real ropes DO have compressive strength, especially large diameter ropes of short length. A short length of thick rope (~6" diam X 3' long), anchored at both ends can support an upright load-bearing catenary like the gateway arch. This would not usually be considered 'sagging'. SemanticMantis (talk) 17:37, 18 January 2011 (UTC)[reply]
I seem to recall an unintentional verse in a book by a distinguished scientist:
as you can see here. Of course, he's talking about the weight of the cord itself, but the sentences just before that are about the case of a weight hanging from a cord whose own weight is negligible. According to Martin Gardner in a Mathematical Games column reprinted in Martin Gardner's Sixth Book of Mathematical Games from Scientific American, Whewell was annoyed to learn about the "poem" and had the wording changed in the next edition. Gardner misquotes the "poem" slightly, though. --Anonymous, 05:10 UTC, January 20/11.
Even the ground will sag if enough weight is put on it. Compressive strength means only that the material resists sagging, not that it avoids it entirely. Wnt (talk) 18:42, 19 January 2011 (UTC)[reply]
Sure, I just wanted to point out the limitations of the way string is often modeled for simple problems. In particular, a string modeled with no compressive strength cannot take the shape of an upright catenary, but a real rope can. This may help explain some of the confusion between real-world problems and physics 101 type stuff. SemanticMantis (talk) 20:59, 19 January 2011 (UTC)[reply]
Not really. It's a really, really small distance, so there are some theories that it's the fundamental granularity of the universe, but none of the well-accepted, well-proven physics theories hold that there is anything special about that length. It's just the length unit you get if you attempt to scale units such that major physical constants come out to unity ("natural units"). Keep in mind that the mass unit you get when you do that (the Planck mass, is 2.2 x 10-9 kg, about the size of a human egg cell (see Orders of magnitude (mass). -- 140.142.20.229 (talk) 18:46, 18 January 2011 (UTC)[reply]
As it says in Planck length: "In some theories or forms of quantum gravity, it is the length scale at which the structure of spacetime becomes dominated by quantum effects, giving it a discrete or foamy structure, but other theories of quantum gravity predict no such effects." Basically, we don't know what happens at such small scales. --Tango (talk) 21:56, 18 January 2011 (UTC)[reply]
I think you might fairly say that it's the absolute smallest a black hole that can exist. Any smaller, and the Compton wavelength gets bigger; but the Schwartzschild radius gets smaller. Which means that the hole is too fuzzy to fit in the hole, so to speak. So if you have a black hole that is evaporating by Hawking radiation, something ought to give out at least mathematically around this time; the Heisenberg principle says you're not supposed to know where the black hole is that precisely, but how is it going to get away? You can play a merry chase through Planck mass, Planck length, Planck momentum, Matter wave to figure this out, but one word of caution - I initially looked up de Broglie wavelength to see how the math worked out and had a curious disagreement by a factor of 2 pi (on the Planck momentum; with the de Broglie wavelength you can't say a mass has a given wavelength without giving it some arbitrary velocity). It turns out that there's a distinction between the "reduced" and "non-reduced" Compton wavelength as explained in that article. A distinction which I don't understand... you'll need a real physicist for that... :( Wnt (talk) 05:02, 19 January 2011 (UTC)[reply]
Coal mining efficiency
I saw on a TV show this gigantic drilling machine many hundreds of feet below the surface around Pittsburgh, PA and started thinking about the massive amount of energy that must be needed to turn the thing's huge and undoubtedly heavy drill bits against the resistance of the earth it was drilling through, and the energy needed to move the thing forward, along with all the energy used for the other trolley cars, lights, ventilation systems, and of course the energy expenditures to raise the mined material back to the surface, and I wonder roughly how much energy quantified as an amount of coal (I know the machines don't take coal for fuel, but I want to know the figure in terms of coal) the average coal mining plant expends in all the actions it takes to extract 100 tons of coal? Just a very ballpark estimate is all I'm after here. For instance, do they use about a ton of coal's worth of energy to get 100 tons? Do they use over 50 tons' worth? Thanks. 20.137.18.50 (talk) 18:38, 18 January 2011 (UTC)[reply]
This is a very important and valuable analytic tool: it is formally known as EROEI (energy returned on energy invested). It is heavily studied by economists, business analysts, and geoscientists and engineers in the mining and production industries. I know quite a bit about the ballpark numbers for the oil industry, but unfortunately not for coal; I imagine coal mining experts know similar metrics for coal mining. I have heard reputable petrophysicists claim that the EROI for tar sands is dramatically and dangerously approaching 1.0 in the long run; this means that it is economically unsustainable (in other words, you must use one full barrel of oil to power the extraction of one barrel of oil). Coal mining is different from petroleum, because the energy to extract coal comes from many sources: electricity (... from coal); chemical energy (from explosives... and you could trace the energy budget farther back to the factory, to electricity, and again, ...to coal); and petroleum (...imported from the oil industry). The oil industry, on the other hand, powers almost all of its field operational energy budget using energy derived from oil - so the budget is easier to balance. (Machines, drills, motors, trucks, and so on, are all diesel or even fuel-oil powered). As discussed in the article I just linked, the EROI is very difficult to measure exactly. Nonetheless, the EROIE definitely does impact the business model of large-scale energy extraction. Here is an OilDrum node on the EROI of coal. Let me know if you need help deciphering the energy-budget numbers in there. ("Lower-" and "Higher-" heating values, and so on, are all "engineering adjustments" that cloud the nice, pure theoretical thermodynamic analysis of "how many pounds of coal did we burn?") And, as one post anecdotally claims, if you still live in an area where coal can be mined with a pick and shovel, (like Indonesia), you burn zero pounds of coal to extract 1 pound of coal - a net EROI of "infinity." I would posit, based on comparative prices between coal and oil in BBOE, that coal extraction is significantly more energy-efficient than oil - let's say, 1 ton of coal burned to extract 10 tons of coal (in a developed, mechanized, American Wyoming strip mine). In the spirit of providing solid, numerical references, there's no substitute for the cold, hard economic and production statistics collected by the United States Department of Energy, and made available at no charge to the public through the Energy Information Administration website. Nimur (talk) 20:57, 18 January 2011 (UTC)[reply]
Some of your questions are obliquely answered in the article Ship of the line. In the earliest era of European warship building when trial-and-error and guesstimation ruled, stability was indeed a problem, as witnessed by the fates of HMS Mary Rose (1509) and Sweden's Vasa, but by Victory's era Naval architects worked by well-established scientific laws. Some of the more basic means of achieving stability are ballast below the waterline and the 'tumblehome' or inward angling of the upper decks, which significantly improved weight distribution. 87.81.230.195 (talk) 19:25, 18 January 2011 (UTC)[reply]
Well seeing as the Victory has been "out of the water"/in dry-dock for almost a century, I'd expect that most photographs that exist of the hull are "out of the water". Roger (talk) 20:12, 18 January 2011 (UTC)[reply]
My mistake, I thought it was in the water. Still, that doesn't answer my question: does anyone know where I could find a picture of the whole thing, or an accurate model? I mostly want to see the bottom. --T H F S W (T·C·E)20:53, 18 January 2011 (UTC)[reply]
A centreboard is a useful addition for stability. Trouble is, that article doesn't give much history. I'm personally aware of them being used on some sailing ships of the nineteenth century. HiLo48 (talk) 22:07, 18 January 2011 (UTC)[reply]
A centreboard or keel, as I learned earlier here, is mostly to keep the ship in a straight line. Anyways, thank you, the site Karenjc pointed out is exactly what I was looking for. --T H F S W (T·C·E)00:37, 19 January 2011 (UTC)[reply]
Actually, a centerboard is mostly to keep a ship from drifting sideways with the wind. As a side effect, it does reduce rolling, but it adds little if anything to improve real stability, as it does not significantly change metacentric height. A keel can serve either or both purposes, drift reduction and increasing stability. --Stephan Schulz (talk) 19:35, 19 January 2011 (UTC)[reply]
According to the OED, the first use of the word "volume" to mean loudness of sound occurs in Byron's Werner, 1822: "I heard‥, Distinct and keener far upon my ear Than the late cannon's volume, this word—‘Werner!’". And it was defined in a musical dictionary as early as 1786 to refer to "the compass of a voice from grave to acute: also to its tone, or power". WikiDao☯00:40, 19 January 2011 (UTC)[reply]
Recently, a friend had me watch a video of someone putting a candle in a microwave oven and turning it on. This produced some neat effects, supposedly creating "plasma". (The video was not made by professionals.) My question(s) are: Is this actually plasma? And regardless whether it is or not, what exactly is happening?
Avicennasis @ 07:19, 14 Shevat 5771 / 19 January 2011 (UTC)
I have seen such experiments in reality. a flame is already very slightly ionized. Apparently, the microwaves transfer energy to the plasma, ionizing it further and enlarging it, though I don't know the exact mechanism by which this happens. 157.193.175.207 (talk) 07:47, 19 January 2011 (UTC)[reply]
There are many such videos on YouTube. If you can name it, someone has microwaved it, with comic effect. "Coconut in a microwave" isn't as impressive as you'd think, but I remember when I looked for it, I found it.
There is a wide subset of videos about "ball lightning" in a microwave. I think that this is overly promoted - it is simply that fire is conductive and absorbs more energy, and sometimes the gasses continue to glow a moment after they escape from a hole, etc. that has been built for this purpose. I don't think that the sort of energy or structure present in real ball lightning is actually duplicated --- but if someone disagrees, by all means let us know! Wnt (talk) 17:55, 19 January 2011 (UTC)[reply]
Where does the bigger flame come from? My guess is that the heat from the microwave heats up the candle and/or wick, so that more fuel is available to be consumed by the flame. I do not believe that the energy for the bigger flame comes from the microwaving directly, as microwaves do not burn all by themselves. 92.29.123.151 (talk) 23:40, 20 January 2011 (UTC)[reply]
I understand the process of freezing damages the cell-structure (water/liquid expanding as it freezes), and then means that when cooked they lose some of their flavour (I know, I've worded that terribly, but have a quick read of the Frozen vegetables article, and I'll have a look for some bette source)... this extract points to the difference in texture between frozen and fresh veg.this source argues that frozen veg are higher in nutritional value than fresh (or, as the case may be, not entirely fresh vegetables). this source also argues that frozen veg are less at risk from contamination, as long as they are not frozen, defrosted and then refrozen - Although, having said that, I am sure that I have seen other sources before that argue that frozen veg in bags that have not been properly sealed are at risk from contamination. Darigan (talk) 13:16, 19 January 2011 (UTC)[reply]
It could also be related to the way they are cooked after being frozen -- are you boiling them in water? I've always found that makes veggies taste a lot more bland. -- JSBillings13:48, 19 January 2011 (UTC)[reply]
OR answer here: I have found that frozen vegetables taste better when steamed than when boiled; the "steam in the bag they came in" varieties are particularly close to their fresh cousins. Some vegetables take to freezing better than others. I find frozen carrots and frozen corn-on-the-cob to be pale comparisons to their fresh versions, while green beans (haricots) and garden peas are usually fairly comparable. I'm not much of a fan of many cruciferous vegetables in any form, so I can't comment on frozen vs. fresh broccoli or cauliflower or brussel sprouts. --Jayron3215:48, 19 January 2011 (UTC)[reply]
With peas, it's vastly superior to freeze (or can, though I find canned peas unappetizing) them rather than shipping them "fresh" to a supermarket: the sugar in peas breaks down incredibly rapidly, making it nearly impossible to get good fresh peas, other than by growing them yourself. This is mentioned in Pea#Use, though I'm surprised we don't have anything more on this. I think typically, peas need to be blanched and preserved within a couple of hours of being picked. Buddy431 (talk) 17:15, 19 January 2011 (UTC)[reply]
I think your example of corn is illustrative of a few things. Really fresh corn (as in, you put the pot on to boil while you run out to pick the ears) is unbelievably good; it barely even needs a blanching, you just want to warm it up for the butter. Within a day, it's good, but not nearly the same kind of thing. If you IQF freeze it at that point, you'll get a pretty decent product - good enough that it's better than the so-called fresh corn you find in grocery stores that's already 2-3 days old, if not more. Canned corn is pretty abysmal. So you've got a weird sort of graph where really fresh is best, but frozen is better than just about anything else. The trouble with many vegetables, particularly carrots and peas, is that freezing them wrecks the crispness; the flavour might not change much, but the mouth feel is completely different. Matt Deres (talk) 19:00, 19 January 2011 (UTC)[reply]
That's the problem I have with frozen corn: it loses the snappy mouthfeel that makes fresh corn-on-the-cob so tasty. I usually buy my corn at the local farmer's market the day I plan to use it; when it is in season it's usually picked within 24 hours before I buy it. I find all canned vegetables taste more like can than vegetable, so I avoid them pretty much at all cost. --Jayron3219:23, 19 January 2011 (UTC)[reply]
Wouldn't the vegetables that are used by the frozen vegetables processors be those most manageable for that process? There are lots of varieties of a vegetable. Those destined for freezing are likely to be those that have the handling characteristics that best lend them to mechanical manipulation—from the field to the packaged and frozen product. If any tradeoffs have to be made, taste might get sacrificed in favor of the ease of large scale mechanized agriculture. Even the nonorganic but fresh vegetables on the supermarket shelf might tend to be those varieties of a given vegetable that don't require those qualities that lend themselves so well to the highly mechanized freezing (and harvesting) process but may instead retain some of those qualities that made them desirable in times gone by. Bus stop (talk) 22:23, 19 January 2011 (UTC)[reply]
The one exception, I think, is tomatoes, where the canned ones can have better flavor than either fresh or frozen. Freezing destroys them, and even farmer's markets can't usually handle them at the peak of flavor -- canners, however, can process them directly out of the field. Looie496 (talk) 00:12, 20 January 2011 (UTC)[reply]
I'll second that; canning tomatoes also has the practical effect of concentrating the flavor components. I find good canned tomatoes to be more intensely "tomatoey" than even fresh-off-the-vine-minutes-before tomatoes. Which is not to say that fresh tomatoes don't have their place; canned tomatoes make a better sauce than fresh, but I wouldn't ever use them in a salad. --Jayron3201:27, 20 January 2011 (UTC)[reply]
Electrical
Hi I have some basic doubts in electrical I am an electrical student please help me
1)Why we maintain voltage as constant not current?
2)In producing AC there comes both +ve AND -ve voltage in both the ends (slip rings) but in power line only phase has while neutral remain null.
3)Is human body a conductor?
4)If a coil connected to power supply produces magnetic flux will that flux link on that same coil and induce a emf?
5)Fan is an inductive load thus on using it there should be 90° phase out b/w Amps and Volt if so won't it affect Transformer?
Regarding #3, everything is a conductor under sufficient voltage. The human body, being basically a giant bag of salt water (an electrolyte) is actually a pretty decent conductor, even under moderate voltages. Regarding #4, in order to produce an emf through the coil, you must move the coil in relation to the magnet (or visa-versa). Regarding #6, my understanding is that light bulbs (and resistance heaters, and other similar devices) behave roughly the same under AC and DC conditions, as the effects of resistive heating are the same regardless of the direction of the current; in other words the AC or DC nature of the current does not play into Joule's first law. I will let someone who actually knows about this answer the rest (and correct my mistakes). --Jayron3215:42, 19 January 2011 (UTC)[reply]
It is not possible to maintain a constant current except under carefully controlled conditions. "Voltage" is another name for "electro-motive force" (EMF) which you can compare with "pressure" in water pipes. The supply of both electrical and water services aims to maintain a constant "pressure" so that the amount of electricity or water that flows when something is turned on can be reliably predicted. In the case of water, it is usually the tap that controls how much water flows, but, for electricity, it is usually the resistance or reactance of the appliance that determines how much current flows (though dimmer switches work like taps).
AC supply does not have positive and negative. Usually one side of the supply is connected to earth and for this reason is called "neutral", but it doesn't really matter whether this is done or not except for safety reasons. Both "live" and "neutral" wires behave in exactly the same way (except when one is shorted to earth), so there is really no difference between them if they are isolated from "earth". Three phase supply is generated and transmitted with three "lives", each one being 120 degrees out of phase with each of the others. Sometimes there is no "neutral" (delta configuration), and power can be transmitted without any other conductor. More often, each of the phases is generated at a fixed voltage to a common wire "3-phase neutral" which is usually connected to earth. The three main wires for the three phases still carry the main current because the three currents in the three phases will cancel each other out if they are equal, but the common neutral serves to carry any residual current if the phases are not balanced.
Just one minor addition to Jayron's answer to #4: If AC is connected to a coil, then the flux does indeed produce an induced EMF in the same coil becuase the current is constantly changing. See autotransformer. Dbfirs18:24, 19 January 2011 (UTC)[reply]
As far as I know, single-wire earth return is never used in the UK. (I've tried it, unofficially, but probably illegally.) Dbfirs22:17, 19 January 2011 (UTC)[reply]
A/C can have potential on both sides of circuit (although obviously not positive/negative, since it's A/C). Voltage can only be measured as a difference - there is no such thing as an absolute voltage. A/C in households is designed so that the earth is one side of the circuit, and since we stand on the earth, to us the feels like neutral. But it doesn't have to be that way. If you isolate your A/C generator completely from the Earth, then both sides "have" potential (although of course that's meaningless since you need two sides to measure anything). An interesting side effect of this kind of isolation is that you can't get shocked by touching just one wire - you need two to get shocked. Unless of course two different people happen to each touch one wire at the same time and you complete the circuit through both of them via the Earth. You can also make D/C with one side hot and the other neutral - you just need to attach one side to the earth. Ariel. (talk) 22:35, 19 January 2011 (UTC)[reply]
Well if you want to be pedantic, AC does have positive and negative on both sides, it just changes 100 or 120 times each second, so I meant that you can't label either conductor positive or negative. Good point that DC can have "live" and "neutral". Is it often supplied this way (other than in motor vehicles)? Dbfirs23:09, 19 January 2011 (UTC)[reply]
Most circuit diagrams have a source and ground, rather that a positive and negative. Computer power supplies are also wired this way - a common ground for everything, and different wires for various voltages/rails/polarities. Ariel. (talk) 00:17, 20 January 2011 (UTC)[reply]
Yes, good point, though voltages are quoted positive or negative with respect to the "ground". Is this just because the mains supply is grounded? My laptop just has 19v DC with no ground, but the circuitry probably has an artificial "ground", possibly connected to mains "earth" (I haven't checked). Did early wet and dry battery circuits also have a "ground"? (I was really meaning long-range supply of DC, but this is relatively rare.)Dbfirs13:05, 21 January 2011 (UTC)[reply]
Mains supplies provide a constant voltage so that any number of appliances can be connected and disconnected without affecting one another. Each receives the standard voltage and only the total current varies. A constant current mains supply is impractical because the current to an appliance would change every time another appliance was connected, and dangerously high voltage will be delivered if no appliance is connected.
A basic two-wire or "single-phase" AC supply usually has one wire called neutral connected to earth which we may call 0V. The voltage on the other wire alternates between +ve and -ve voltages.
The human body is a conductor. See the article Electric shock.
An emf is induced in a wire in a changing magnetic field. A coil is an example of an inductive load. When a coil is connected to a DC power supply, the current in the coil grows slowly because it produces an increasing magnetic field that induces an emf that opposes the supply voltage. For the same reason, when a coil is connected to an AC supply the current is slow to follow the voltage changes. The time delay can be expressed in degrees where a full alternating cycle is 360. If the coil has no resistance, the current lags the AC voltage by 90.
A fan motor is an inductive load. When the fan shaft rotates the motor is also a generator of emf that opposes the supply voltage.
The filament of a lamp bulb glows because of the heating effect of current flowing through its resistance. The heating power is proportional to the voltage squared (so both positive and negative voltages give heating). An AC supply with rms (root mean square) voltage equal to the voltage of a DC supply has the same heating power as the DC supply. So there will be no change in the lamp brightness if one switches between the two supplies. Actually the brightness flickers at double the frequency of the AC cycles but you cannot see this because mains supply frequency is too high. Cuddlyable3 (talk) 22:59, 19 January 2011 (UTC)[reply]
Rephrased: relaxing voices
Sorry to the board, it wasn't supposed to be a medical question. I will attempt to rephrase the question. Why do some voices, e.g., Bob Ross's, cause people to relax? I've read on other forums that people will watch his show to help them fall asleep. Thank you very much! Reflectionsinglass (talk) 18:54, 19 January 2011 (UTC)[reply]
To answer a question with a question, why is some music relaxing and other music exciting? Why do some people find traffic noises soothing, and others find it irritating? Ariel. (talk) 22:37, 19 January 2011 (UTC)[reply]
Ice expanding, minimum density
It is my understanding that when water is cooled (at standard pressure), it reaches a maximum density at 4°C (due to hydrogen bonds, and then starts to expand as it is cooled further. As it transitions to Ice Ih it expands by about 9%, and then continues to expand as it cools further. At what temperature does ice reach its minimum density? I did a quick websearch and found [12] which indicates that it is at 70K. Is the minimum density really this cold? — Preceding unsigned comment added by Csmiller (talk • contribs) 20:10, 19 January 2011 (UTC)[reply]
Under Ice#Characteristics it says: "The density of ice is 0.9167 g/cm³ at 0°C [...] Density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm³ at −180 °C (93 K).", quite the opposite of your statement. But it doesn't say what ice does on further cooling or where minima/maxima of density are. Another image on commons ([13]) also implies that density rises when ice is cooled. Oh, just read through your link again, and as I understand it, ice increases its density when heated up starting from 0K to 70K, then it apparently decreases again--178.26.171.11 (talk) 21:03, 19 January 2011 (UTC)EDIT: The minimum density should be at 0°C then (unless there's a way of "superheating" ice above that without melting it at standard pressure.--178.26.171.11 (talk) 21:05, 19 January 2011 (UTC)[reply]
I'm trying to pin down whether an item would be a high risk to cause an allergic reaction. The ingredients listed on the website for it are: Water, denatured alcohol (<5%), sodium iminodisuccinate (<1%), zinc diricinoleate (<1%), cocamidopropyl betaine (<1%), menthol (<1%), microorganisms (<1%), citric acid (<1%), polydimethylsiloxane emulsion (<1%). The microorganisms in this product are non-genetically modified, naturally sourced, non-pathogenic (i.e. do not cause disease) dormant bacteria, and are the primary “active ingredients” in this formulation. They work by eating up all of the accumulated dander, dead dust mites, and dust mite fecal matter that has accumulated in your mattress/ pillows/ furniture/ car upholstery over time, eventually converting those allergens into carbon dioxide and water.
Obviously, people can be allergic to just about anything, but do any of these items seem like likely candidates? Their use of "naturally sourced" bacteria kind of raised my eyebrow, for one thing. I've heard of cleansers touting their "enzymatic action!" before, but not bacterial. Anything else on there look weird? Matt Deres (talk) 20:37, 19 January 2011 (UTC)[reply]
Wow. That's like an ingredient list that includes "...chemicals. All our chemicals are safe, trust us..." To give a parallel example with a more defined set of natural microorganisms, consider the regulation of raw-milk cheeses by the U.S. and Australia. Wnt (talk) 20:52, 19 January 2011 (UTC)[reply]
You also may take interest in the zinc diricinoleate (the basic component there is ricinoleic acid, with two conjugated to zinc. See [15][16][17] for some leads. (It is widely used, but I'd like to know who puts castor oil in chocolate? Remind me to avoid that brand...) Wnt (talk) 21:03, 19 January 2011 (UTC)[reply]
Apparently this is being done by Hershey's, Nestle, and Mars, Incorporated, as part of a campaign to sell cocoa butter to the cosmetics industry and replace it with cheap substitutes in chocolate.[18] Which is just one small reason why American chocolate doesn't taste like chocolate. And people wonder why this country keeps running record trade deficits... Wnt (talk) 04:18, 20 January 2011 (UTC)[reply]
This site: http://www.cosmeticsdatabase.com/ is pretty good for that kind of thing. You can either look up individual ingredients, or register an account and enter all the ingredients of a product and it will give you a grade. (Not just allergies, any kind of potential risk.) Ariel. (talk) 22:52, 19 January 2011 (UTC)[reply]
That site looks helpful - thanks; I'll give it a look when I get some time to play around. I don't know if it matters, but the substance in question isn't a cosmetic, it's for spraying on beds and other furniture to reduce dust mite allergens and odour. Matt Deres (talk) 23:12, 19 January 2011 (UTC)[reply]
Water and brick question
My daughter has a science project in 5th grade this week. I was watching the discovery channel last night and the segament was about taking a 5gal. water jug,filling it a 1/4 with wate, connecting a hose to it,then connecting the end to a hot water bottle.Then take 5 blocks and put them on top of the water bottle.Once that is complete,turn the 5gal. jug upside down about 4ft. high ,then the water should fill the bottle and knock off the bricks. What is the topic of this project? — Preceding unsigned comment added by Jeffryan777 (talk • contribs) 22:01, 19 January 2011 (UTC)[reply]
You could also discuss conservation of energy. Lifting the 5 gallon jug takes work (in the literal and technical sense of the word). That work is transferred, via the hydraulic pressure, to lift the blocks. One useful property of hydraulic machines is that they can multiply force - so it can be possible to lift some pretty heavy cinder-blocks (which requires a large force), by exerting a smaller force over a large distance to lift the water (hence, to pressurize the fluid). (The force is increased, but the energy is conserved). Nimur (talk) 23:33, 19 January 2011 (UTC)[reply]
"Radiation therapy may lower testosterone to the low-normal range in some men" source - so yes. (That could be worked out a lot quicker by googling "radiation lower testosterone") SmartSE (talk) 22:35, 19 January 2011 (UTC)[reply]
Plant hardiness - temperature versus sunlight volume
It's about -20C outside these days, though my apartment (apart from near windows) is around 20 degrees at all times. I have a Creeping Charlie that was placed too close to a window and began to die. However, the ambient temperature was never at or below freezing.
This made me wonder about plant hardiness and why some plants cannot tolerate super-freezing temperatures. If a tropical plant like a banana tree was given ample, full-spectrum artificial light but kept at an ambient temperature of 5~10C, would it still die? If yes, why? There wouldn't be any cell damage from freezing... The Masked Booby (talk) 01:14, 20 January 2011 (UTC)[reply]
I don't know, but a conjecture is that different enzymes work best at different temperatures. Perhaps the plants that like warmth have enzymes that only function at those temperatures. Ariel. (talk) 06:16, 20 January 2011 (UTC)[reply]
Yes, it's basically the same reason why humans die if their body temperature is to far away from 37°C (without freezing). The physiology of most life forms is tuned (by evolution) to certain ranges of environmental and internal variables, and if you cross the thresholds, the processes in the cells don't work anymore as they should. That's the same principle for plants, animals and even single celled organisms (some bacteria that thrive in warm shallow sea water won't grow at all or even die in cold shallow sea water, for example). --TheMaster17 (talk) 10:33, 20 January 2011 (UTC)[reply]
This previous question covers some of the relevant points (I was posting as 131.111). Chilling can damage plants because it disrupts the cell membranes by making them solid, instead of fluid which then makes them leaky, allowing all the parts of cells to mix, whcih is not good news at all. A banana plant will certainly die at 5-10C because they have never evolved to cope with those temperatures. Ariel's point about enzymes is probably partially true, but the disrupting of cell membranes is more of an issue - unlike us, plants have to cope with a wide range of temperatures and so they have enzymes which function over wider ranges, or will have isozymes for different temperatures. As to how some plants survive super-freezing, it's pretty complicted! There are some details at Ecophysiology#Temperature (unfortunately unreferenced, but I can vouch for its accuracy as I wrote it from lecture notes - I will try to reference it some day!) and combined these allow trees like larch in Siberia to survive liquid nitrogen, because the cells are placed in suspended animation. If you want a paper discussing this, this one might be a good start. SmartSE (talk) 15:43, 20 January 2011 (UTC)[reply]
Pregnancy and radiation-blocking smocks...
Here in China pregnant women wear smocks with a thin lead liner in the workplace. I can understand the need for such clothing if someone worked in an area with serious radiation potential, like an x-ray equipment factory or something. However, 99% of these women only ever sit in front of a computer doing routine tasks. I suspect this practice, like many medical habits in China, is based on no real proven science. Is there anything to gain from such clothing? I didn't see any indications in the Electromagnetic radiation and health article... The Masked Booby (talk) 01:17, 20 January 2011 (UTC)[reply]
Well, considering that lead doesn't even block EMF I don't know what they're trying to achieve. I would be much more worried about exposure to lead! Even if it is sealed, what if a section becomes exposed due to wear or tear? Lead rubs of extremely easily onto hands or clothes, even just touching it and then handling food or inadvertently touching your mouth sounds like a much higher risk then sitting in front of a computer or monitor. Vespine (talk) 03:35, 20 January 2011 (UTC)[reply]
I'd hesitate to concur -- while lead doesn't attenuate all forms of electromagnetic radiation well, it does do a great job for x-rays, for example. This may not relate to the circumstances posed in a positive fashion (it may reveal the ignorance of Chinese women and/or their husbands), but your blanket statement is certainly incorrect on the whole. DRosenbach(Talk | Contribs)05:02, 20 January 2011 (UTC)[reply]
EMF |= electromagnetic radiation. I didn't think computers and lcd monitors are significant sources of EMR, unless you have a wifi or bluetooth transmitter or something. It's hard to find reliable sources to look this up because of all the fear mongering but my guess is there would be small amounts of things like radio waves and stuff coming out of a normal computer, but there's certainly no ionizing EMR coming out of your computer. Vespine (talk) 05:24, 20 January 2011 (UTC)[reply]
It could have started with ladies worried about the X-Rays emitted from older model CRTs (Which, for all I know might still be in wide use in China.). Once these sorts of things start they usually become divorced from their rational underpinnings pretty quickly, so it's not hard to imagine that some ladies would still wear them even if they never use anything that emits anything dangerous. APL (talk) 15:30, 20 January 2011 (UTC)[reply]
Biology vs. the Cosmetics Industry
(My last question of the day...) My wife, like many women, spends a fair bit of money on facial cleansers and moisturizers, always used in conjunction. She also makes a big stink about my need to have empty pores on my face in order to be "clean". I am skeptical of this entire process. I've read Cleanser, Sweat gland, Acid mantle, and Sebaceous gland and have not been able to definitively confirm or refute my contention that: stripping oil from your face with cleansers and then applying moisturizer is equivalent to doing nothing at all and letting your skin regulate itself, it just costs loads more. But again, none of those articles directly say whether this is truly necessary or not. Can anyone shed some scientific light on this? The Masked Booby (talk) 01:28, 20 January 2011 (UTC)[reply]
This is not a medical diagnosis request. This is a question about the biological/chemical function of the face and the utility of cosmetics. I am inherently distrustful of the cosmetics industry given their proven non-sense like conditioner making your hair "healthier" and would like to know if facial cleanser/moisturizers fall into the same sphere. I included the bit about my wife for color, not because I'm going to print out your replies and wave them in her face and say SEE! WIKIPEDIA SAID SO! The Masked Booby (talk) 01:38, 20 January 2011 (UTC)[reply]
You aren't just stripping the oil off of your face, you are stripping all of the stuff that tends to get stuck to the oil, like dead skin cells, dirt, (for many women) makeup, etc. It may be quite difficult to remove, for example, dead skin cells from pores with just soap, while an astringent cleanser which dissolves the oil the skin cells are stuck to will make it much easier to get them out. Bacteria like to feed on these dead skin cells; this can be a primary cause of acne. The deal is, since you just removed all that oil, you need to replace it to prevent your skin from drying out, hence the moisturizer. In summation, it isn't the skin oils per se that need removing, its all of the stuff that is in the oil. --Jayron3201:37, 20 January 2011 (UTC)[reply]
I guess the question is, Does that stuff really need removing? Where is the science behind it? (PS: Agree with comment about marital harmony.) HiLo48 (talk) 02:52, 20 January 2011 (UTC)[reply]
Which is a fair question. I'm more familiar with the argument against shampoo-conditioning, which is a somewhat similar arrangement: the hair is cleaned of oil (and the attached dirt) and then has a moisturizer (hair conditioner) added back on. Our article on that argument can be found at the humorously titled "no poo", though it's a pretty poor article. Western habits (and obviously Chinese ones as well) on cleanliness are hugely influenced by social expectations, to the point where the "necessity" of having to shower multiple times a day, for example, borders more on ritual purification than anything to do with an increase in health or other objective goal. As with anything else, moderation is probably the sensible option. Matt Deres (talk) 03:02, 20 January 2011 (UTC) Quick aside - I got a chuckle by reading that our article on cleanliness has been flagged for "cleanup" for seven months... [reply]
@HiLo48 for some people, probably not, but for others definately. I am a life-long sufferer of acne (I basically have the exact same skin problems at 34 that I had at 14); through years of trial and error I have found that some products work for me, and some do not, and I use those that do. Clearly, for people who have acne, skincare can be tricky business. It's one of those "if you don't have the problem, you just don't understand" sort of deals. For people without acne problems, washing daily with the bar soap they use for the rest of their body works fine. For others, however, it just doesn't cut it. --Jayron3203:35, 20 January 2011 (UTC)[reply]
I seem to remember discussing something similar about washing hair too, but can't find an archive link. If you're correct, it almost certainly has something to do with differences in skin flora. I found this which says "soap may reduce the normal skin flora, leading to an increased colonization of the skin with coagulase-negative staphylococci; this effect has been linked to the shift in skin pH caused by soaps. Lastly, it has been found that applying agents that specifically inhibit gram-positive cocci, such as antibacterial soap, generally increases gram-negative rods." and this paper tells a similar story. I think it's probably difficult to give you a definitive answer and as everyone else is ORing so will I - I think that cleansers + moisturisers change the balance of skin flora and that if you then stop using them, your skin condition detiorates because the equilibrium was being maintained by the products. For those of us who don't use such products (myself included) our skin flora is in equilibrium, and generally speaking we don't suffer from unhealthy skin. Carrying on, we obviously evolved in a world without soap, and our skin produces oils for a reason, I see no reason why you would need to replace this with something else. (Maybe you can experiment with your wife's face, only letting her clean + moisturise one side and come back with photos in a few months) Interestingly, I don't think anyone has done any metagenomic studies of skin flora, which would be a very interesting thing to do, when comparing you and your wife. SmartSE (talk) 16:12, 20 January 2011 (UTC)[reply]
What about situations where skin flora is "off" in the absense of products, but correctly balanced with them, before such products were used by the person? I had acne before I started using products... Your explanation isn't consistant in that skin problems exist in absense of even the existance of skin care products. It would only make sense if skin problems didn't exist prior to people using skin care products. However, that is demonstratably false. --Jayron3216:29, 20 January 2011 (UTC)[reply]
I don't think anyone is suggesting that corrective action is never a good thing - at least, that's not what I'm saying. If you've got a busted leg, wearing a cast is probably a good idea, but when it seems that virtually everyone is wearing one, I think it's justifiable to say "Look, there are negatives to wearing these things." Such comments aren't really directed at the people with broken legs, they're just reminders of the "If it ain't broke, don't fix it" adage. Matt Deres (talk) 19:50, 20 January 2011 (UTC)[reply]
Fair enough. I actually agree with you on that; many people use uneccessary or even harmful products under the misbegotten notion of retaining a "youthful appearence" whatever that means. Much of the skincare industry hinges on the fact that people believe they can avoid looking their age by smearing some gunk or another on their face. Sometimes, however, that gunk does actually help people with a real problem. It's not the gunk, per se, that's the problem...--Jayron3220:13, 20 January 2011 (UTC)[reply]
WP:OR Face wash products work well. They just include sticky substance which once applied to your face you must wash your face thoroughly with lot of water to remove it, and any other dirt/oil on your face, if any, also washes out along with the water :) - manya (talk) 04:10, 20 January 2011 (UTC)[reply]
Welcome to Wikipedia. You can easily look up this topic yourself. Please see calcium oxide. For future questions, try using the search box at the top left of the screen. It's much quicker, and you will probably find a clearer answer. If you still don't understand, add a further question below by clicking the "edit" button to the right of your question title. . DMacks (talk) 11:04, 20 January 2011 (UTC)[reply]
Is there anybody to reply me positively
1.Is a photon massless?
If yes,then why does it has particle nature as a particle has a must property of mass and it also has momentum?
If no,then why it cannot be proved?
2. Is a vacuum really vacuum or not?
If yes,then why does there exist a dark energy as energy cannot be held without any medium?
If no,then what does there exist?
3. Does a string really exist?
If yes,then what is the matter the string made of?
If no,then what is the cause of producing charge in an electron?
4. Do the photons carry the energy from one place to another?
If yes,then why does the intensity of radiation decrease gradually and if an electro magnetic radiation is one kind of transverse wave,then the main property of this kind of radiation should be transfer of energy not the particle and it definitely needs a medium to traverse?
5.What is the situation before the Big Bang? Is it a cyclic process?
6. What is the way to transfer energy from one place to another?
If it is vibration of different mode which produce different kind of energy,then is it possible to construct the T.O.E. equation?
You asked a lot of very hard questions, so it is impossible to answer them all here. You should look at the articles on Wikipedia and ask if you have specific questions.
1. A photon has no rest mass, though it does have momentum. Who says that particles must have mass? It's perfectly possible to conceive a massless particle.
2. Vacuum#In_quantum_mechanics and Vacuum energy explain this better than I could. The exact nature of a vacuum is complex - however it is quite well defined in quantum theory. The idea that energy cannot be held without a medium is just a hypothesis and may not be true.
3. String theory is still a matter of debate, and it's not clear if any version of it is true. Therefore nobody is certain what the strings are made of, or even if it makes sense to ask if they are made of anything (just as Einsteinian space-time is not made of anything, and electrons are, in standard models, made of electron without any internal structure).
4. Photons do indeed carry energy. Intensity of radiation decreases with distance from the source because photons spread out as they travel and the further from the source you are, the fewer photons hit you (see inverse-square law).
(edit conflict)Almost identical to previous response, but I've written it now and don't want to discard it.
1. If you mean "does a photon have zero rest mass ?" then the answer is yes, although the question is somewhat meaningless as a photon is never observed at rest. This does not prevent a photon being a particle.
2. If you mean "is the vacuum empty" then the answer is no - any vacuum in our universe will contain the electromagnetic field, its quanta (photons), a large number of passing neutrinos and a "sea" of virtual particles.
3. If you mean the strings in string theory then we don't know whether they really exist.
4. Yes, photons carry energy. The intensity of radiation decreases with distance because the flux of photons per unit area decreases as the area over which the photons are spread increases. For large photon fluxes the intensity appears to follow a continuous curve; for small photon fluxes the continuous model breaks down and individual photons are observed. You can recover the continuous model by averaging the photon flux over a long enough period of time.
5. We don't know what was before the Big Bang. We don't even know if this question makes any sense.
6. In quantum field theory, you can think of energy as being carried by waves in quantum fields or by the momenta of particles associated with those fields. These are dual models - "reality" is both, not one or the other. A field does not need a medium. Gandalf61 (talk) 15:40, 20 January 2011 (UTC)[reply]
@OP: Regarding 3: What does "really exist" mean? String theory is a model just like many other models. It is useful insofar as it matches observations, and has a useful predictive power. Is an electron a little ball, a standing wave, a probability distribution? It is all of these, depending on which model you use. None of this is wrong, though some models better match observation, and some are more useful in certain applications. Is light a wave or a particle? Neither, it is just light, but we have wave-based models of light which are useful in some explanations (see diffraction, refraction, etc) and we have particle-based models of light useful in others (see photoelectric effect). If you commit yourself to "The Truth" rather than "Consistent with observations" you miss the point of science. It is perfectly fine and consistant to have multiple, accepted models of the same phenomenon, and each of these models is "real" insofar as any can be. So, stop worrying about if strings "exist" or what they are "made of" and instead focus on what the model teaches us about how the universe works. --Jayron3216:00, 20 January 2011 (UTC)[reply]
It remains to be seen whether or not string theory is a useful model of reality capable of offering testable predictions. In this context, showing that string theory is capable of making new verifiable predictions is basically the same as showing that strings "really exist". Dragons flight (talk) 16:28, 20 January 2011 (UTC)[reply]
That's kinda the point; though it would be better to say that "really exist" misses the boat in that it implies only a single "right" answer; after all if strings really exist, than other models which do not contain strings, really don't exist. Having a paradigm that searches for the One Right Answer completely misses the point of science. Lets go back to the light example. Does light really and truly exist as a particle or does it really and truly exist as a wave? If you commit yourself to that mindset, you are left with three very unsatisfying results:
Light is only one or only the other (observationally inconsistent; light clearly behaves like a particle in some situations, and like a wave in others)
Light is both at the same time (logically inconsistent; a little ball and a mode of movement don't occupy the same class of nouns even. It's akin to claiming that something smells like the color red. It has a poetic appeal, but it doesn't make any logical sense)
Light switches between the two modes, depending on the type of observation (seems better at first, but it begs the question about what light is doing when it isn't being watched.)
People have grappled with this concept for a very long time, the only satisfying result comes when you come to realize that there is a difference between reality and perception, and most importantly reality is not observable at all at the most fundemental level. All you can say is that your mind perceives an object or phenomena to be real, but you have no way to confirm that. Look at your keyboard. How can you confirm your keyboard exists, as an entity seperate from your internal, mind-created construct of what it is. At some point, you need to accept that as true. But that's still an unproven (and unprovable) proposition. When we deal with scientific concepts which are only observable in the second or third order, where we are further removed from the observable properties of it, these sort of problems become manifest in the situation. Back to light, rather than trying to decide what light "really" looks like, and "really is", change your paradigm to just accept that light is what it is, and is fundementally unconcievable apart from the models we make to describe it. Accept that, while light exists and is consistent, our models being by definition imperfect representations, can never fully capture what it means to be light, and let yourself be OK with that. Understand that the two competing and mutually exclusive models of light work in their own domains, are uncontradicted by other models, and so are as close to "real" as we can get, insofar as anything is "real". On that level, string theory may be "real", but also be willing to accept other, competing, and apparently mutually exclusive models as equally "real" insofar as they contradict neither logic nor observations. --Jayron3216:48, 20 January 2011 (UTC)[reply]
What happens in general when an electron collides with a proton? My understanding is a neutron and a neutrino are produced, but where is a good reference for the dynamics prior to the moment of collision? Also, in particular, how does the electron's de Broglie wave shape change as it transitions from free to collided? 71.198.176.22 (talk) 21:10, 20 January 2011 (UTC)[reply]
In general, nothing happens when an electron collides with a proton. They pass clear through each other. Electrons in s orbitals have a (locally) maximal probability to be found right at the nucleus, and don't appear to suffer any wear and tear from that.
In order to something interesting to happen between an electron and a proton, either the electron must spontaneously break into a neutrino and a W- boson, and the W- must then hit the proton and convert it to a neutron, or the proton must turn into a neutron and a W+ which combines with the electron to form a neutrino. Both of these possibilities are energetically disfavored and so happen extremely seldomly, except if the proton really wants to be a neutron, in which case see electron capture.
De Broglie waves are not really a good model for describing particles that turn into other kinds of particles. You'll need a quantum field theory for that. –Henning Makholm (talk) 01:59, 21 January 2011 (UTC)[reply]
Actually, electron-proton collisions (and resulting inverse beta decay into a neutron) happen when a neutron star is formed. At densities such as those of a white dwarf, it is the electron degeneracy pressure (the statistically-favorable Pauli exclusion principle) that holds the dead star up from further gravitational collapse. But when the mass is great enough that this pressure is overcome, the electrons will literally collide with protons to form neutrons (and neutrinos), which is seen as neutron-degenerate matter (that last article has a more-complete explanation). SamuelRiv (talk) 03:18, 21 January 2011 (UTC)[reply]
Hm, yes. I didn't consider that case. However, I don't that it should actually be understood kinematically as the electrons being pushed into the protons by the pressure of the collapsing star. In the (slightly facetious) language I'm using above, it would not be a case of "the proton really wanting to be a neutron" (because the proton is in a high-energy shell within the nucleus), but "the electron really wanting to become a neutrino" (because the electron is in a high-energy state within the degenerate electron gas).
But I am now puzzled why the expression for Chandrasekhar's limit appears to be completely independent of the mass of a neutron (and in particular to the difference in mass between a neutron and a proton, which ought to be important for when electron capture becomes favorable) –Henning Makholm (talk) 08:57, 21 January 2011 (UTC)[reply]
Research of Light-Dependent reactions as an energy source
If that's the case, the answer is "cut down the tree and burn it". Plants are already a very efficient way of storing energy from the sun; I'm not sure we can do it better in a laboratory outside of the plant than plants are already doing it on their own. There are actually some pretty advanced ideas on how to use photosyntheis to generate energy for us, but they all involve letting plants do the actual hard bits. Biofuel in general is all produced via photosynthesis, albeit indirectly. There is also the use of Algae fuel produced in Photobioreactors. There's some really interesting stuff being done in the field of Biological hydrogen production which uses photosynthesis by plants to produce hydrogen for use in fuel cells. --Jayron3221:53, 20 January 2011 (UTC)[reply]
Why is S2O32- impossible as a molecule? So far I've found its 3D structure is a very unstable zig-zag shape, but is there a better reason? THanks. EDIT: I am actually going from a Lewis drawing which I have written the formula for, unaware that there is actually a differently shaped molecule thiosulphate for the formula. I will try to describe it: the Oxygen and Sulfur form a chain, with oxygen on both ends. They are all covalently bonded on both side (obviously excluding the end atoms). The two electrons are added to both end oxygen to fill the outer level. 24.92.70.160 (talk) 03:32, 21 January 2011 (UTC)[reply]
To answer why your molecule doesn't work: the short answer is that the thiosulfate arrangement is most stable; your arrangement may end up with a very unbalanced formal charge distribution (and indicator of an unlikely structure) or it may have an unstable molecular orbital arangement. Incidentally, Molecular orbital theory has a much better predictive power for molecular structures than Lewis Theory does. The deal is, it is much more complex than Lewis theory, but it gets the "right" answer more times than Lewis theory; for example MOT correctly predicts that the oxygen molecule is a diradical, something impossible to draw in a Lewis structure and still maintain symmetry and a double bond. MOT is capable of describing a symetrical, doubly bonded, diradical oxygen which more closely matches the actual structure. --Jayron3204:06, 21 January 2011 (UTC)[reply]
In general, sulfur is rather amenable to long chains S-S-S-S etc. (S8 for example: see allotropes of sulfur). But any attempt to do this with oxygen fails. Tetraoxygen almost but not quite has the potential to exist, and other forms of solid oxygen go a different path. I remember asking about this before and hearing something about the extra orbitals in the outer shells of sulfur coming into play, but I'm afraid I didn't quite understand how it worked then, so... Wnt (talk) 05:11, 21 January 2011 (UTC)[reply]
Another thing to consider is that 5-atom molecules tend to (almost) universally assume a Tetrahedral molecular geometry. If you've got 5 atoms to try to fit into a structure, start there. Early chemistry students have a hard time thinking "three dimensionally" so don't often see the symmetry and stability of that shape; and often what results is all sorts of strange arangements, either linear or cyclical in nature. Always start with one of the basic molecular geometries (180 degrees, 120 degrees, or 109.5 degrees) and only go on to more complex structures if those don't work. --Jayron3205:31, 21 January 2011 (UTC)[reply]
The Ethiopian mountain Erta Ale is in the historical land of Punt at the fringes of ancient Egyptian influence. (see File:Egypt_NK_edit.svg) It superficially resembles a traditional notion of Mount Horeb. To me it would seem to make sense that Moses might have scouted the location before settling on the equally remote region to the east of the river Jordan as a place to which to withdraw. In modern times it is a continually active volcano, with a pool of lava that has been stable and accessible for the past hundred years. Which raises some questions in my mind...
Was Erta Ale similarly active near the end of the Eighteenth dynasty of Egypt a bit more than three millennia ago? Or could other volcanoes along the Rift Valley have been similar then?
Does the outgassing from a volcano like this create a usable reservoir of water to which a nomadic tribe might expect to come to drink? Is it reasonable that hammering into the rock could do something useful to release it if the level is low?
Suppose you have a thick rope and a large ceramic bucket. Is it possible to fill the bucket from a lava pool like that pictured, and pour it into a mold or work on while molten, in such a way to create tablets which could be presented as "inscribed by the finger of God" (and recognizably not by any method known to skilled craftsman of ancient Egypt)? Wnt (talk) 04:12, 21 January 2011 (UTC)[reply]
Except that it doesn't match other parts of the Exodus narrative. If other scholarly consensus is to be believed, the Crossing the Red Sea occurred at either the Gulf of Suez or "Lake Timsah", a freshwater body just to the north of the northern tip of the Gulf of Suez. The Stations of the Exodus lays out a pretty consistent route, and none of it ends up anywhere NEAR Ethiopia. Furthermore, the Biblical Mount Sinai (usually identified as identical to Horeb), while its location is unknown, is generally placed either in or near the Sinai proper. While many of the stations lack modern locales with certainty, Ezion-Geber is well attested to and it is also nowhere near Ethiopia. Exodus 19 makes it clear that it took 3 months to get to Mount Sinai. How they got from the Gulf of Suez to Ethiopia in 3 months is beyond me, especially as the only route takes them back through Egypt; probably not the best way to go. --Jayron3204:36, 21 January 2011 (UTC)[reply]
(ec)I don't want to start a huge humanities detour - I doubt I would hold my own in a proper archaeological and biblical debate about this. Generally I'm going by the idea that Moses is described as going to Horeb in Exodus 3, then returning to Egypt [19] so (at least at the first mention it need not necessarily be en route. I don't know for sure that Mount Horeb is truly a place, or has some more general status (like "Air Force One", which is not a literal single aircraft). I was mostly giving the idea behind this as an explanation for the rather peculiar questions about Erta Ale. Wnt (talk) 04:51, 21 January 2011 (UTC)[reply]
No, never heard of him. I see he placed Mount Sinai in Saudi Arabia... in general, it's hard to prove any unconventional idea based on historical evidence, since the evidence necessarily points at the conventional interpretation. But it is all too easy to propose one. That's why I want to take this from the other end and say, if I were at Erta Ale, could I strike the rock and make water come out of cracks in the rock? Could I scoop up some lava and make some impressive looking non-carved words in stone tablets? And if so, then is Erta Ale the only such place, or are there others? Wnt (talk) 04:56, 21 January 2011 (UTC)[reply]
No I don't think you can make/find water that way (without God's help of course :) Water usually flows from springs that are below the water table, but a volcano rises above it. Plus water from a volcano is mixed with sulfur and other chemicals and is not drinkable (water is frequently mixed with lava and a steam explosion is a common cause of an eruption). Lava would make a very poor casting material. It has a very coarse texture, and would show shapes very poorly. Plus it doesn't match the description of the tablets which were extremely heavy (and lava rock is very light), and were sapphire blue. Ariel. (talk) 07:58, 21 January 2011 (UTC)[reply]
Already edited myself and changed it back to tourism. Only problem is that the links are still pointing to wrong articles.. This I cannot change. —Preceding unsigned comment added by 132.72.226.107 (talk) 07:19, 21 January 2011 (UTC)[reply]
This is the wrong place for this, but I checked history of the article and reverted it back to before the vandalism. But I don't understand what you mean by "links are still pointing to wrong articles" - can you explain? Ariel. (talk) 07:35, 21 January 2011 (UTC)[reply]
Ok, I'm not touching it again.. just tried to change it and you reverted my changes :-).
so just try to follow the links and see for yourself. If they point to the articles they claim to be pointing to, than everything is all right. check it.
Here: Wikipedia:Administrator intervention against vandalism to request a ban, but before going there the user needs to be warned (but he has been). Normally go here: Wikipedia:Abuse response. The links were not changed by the vandal - it looks like Haaretz changed their site. This is not uncommon. It would be great if you could search their site and find the new location of those articles. Don't just remove the references like you did, find the new url for them. Ariel. (talk) 07:51, 21 January 2011 (UTC)[reply]
10x for the help. About finding pro-Israeli articles at Haaretz site - yeah right.. why don't you have a go :-). Well, have a nice weekend. gotta go. —Preceding unsigned comment added by 132.72.226.107 (talk) 07:58, 21 January 2011 (UTC)[reply]
I'm not sure what you're referring to since no one else discussed pro-Israeli articles at Haaretz. I can't find any sign of the article on Haaretz but as Ariel has said, speaking generally it's hardly uncommon the articles disappear in site reorganisations or whatever. Some websites don't even bother to keep articles for that long trying to encourage subscriptions to archives etc. In any case, I doubt Haaretz removed the article because it was "pro-Israeli". It was on Haaretz at one stage as proven by this archive.org[20] archive which I added to the article. Nil Einne (talk) 09:47, 21 January 2011 (UTC)[reply]
trusting science?
I'm not sure if it's a scientific question or not; but I have a religious friend who says:"Science can't be trusted because it's always changing and scientists always make mistakes.".I do trust science, but is this some kind of faith? Is it a good reason not to trust science at all? do we have enough reasons to do so?--Sina-chemo (talk) 11:40, 21 January 2011 (UTC)[reply]
Without modern science, life expectancy would be far lower. Travel, communication, technology would not exist as they do. Without science, we would be living in the middle-ages. Science definitely makes mistakes, but the beauty of it is that science is free-form, and constantly updating itself, constantly challenging ideas in the search for truth. Your friend has been (struggling not to say brainwashed) given somebody else's opinion. Besides, I bet this "science hater", uses products developed by "science" all day every day, and is, as such, a hypocrite.Zzubnik (talk) 11:58, 21 January 2011 (UTC)[reply]
Heh, Scientists will say that's exactly why you should trust them, because they are willing to correct mistakes. But really science isn't meant to be taken on trust, the entire point of it is that anyone can duplicate the results for themself. You need to distinguish the different sciences though, some are far more definitive than others. In some fields (physics, chemistry) you can do a direct experiment to answer a question - you should trust those. But in others you only get your info by doing a statistical analysis (some aspects of biology), and those are less reliable. Scientists know this, and do the best they can. Also, there are some fields where the info comes from modeling (climate, cosmology), or basically educated guesses (archeology). Those are the least reliable IMO, because you can't actually do an experiment. That doesn't make them automatically wrong of course, but nothing beats an actual experiment. I hope I don't get in trouble for listing specific fields. But I will note that when physics depends on statistics, it requires a much much higher confidence for experiments than biology does. Ariel. (talk) 12:07, 21 January 2011 (UTC)[reply]
Organisations that refuse to consider that they make mistakes go whacko. Every organisation makes mistakes: quality organisations openly put them right when they become apparant, but bad organisations cover them up to avoid losing face. Correcting mistakes is part of the process of adapting to a changing environment. If they will not adapt, they die. 92.15.25.92 (talk) 12:11, 21 January 2011 (UTC)[reply]
@Sina-chemo: Here's the deal with science and why you can trust it: Humanity arrives at knowledge multiple ways, but we can reduce it down to a few basic methods, broadly speaking:
We can use our senses to observe the world around us, and we can use logic and reason to connect our observations together and draw conclusions about what we observe
the diameter of the nucleus in the atom is 1fm.Does it mean that the protons and neutrons have a certain diameter(or volume Or even shape, spherical, for example)too? what about other subatomic particles? are particle just some small dots with extended properties such as elecric fields? or they have some sort of a size or volume?--Sina-chemo (talk) 11:57, 21 January 2011 (UTC)[reply]
You can define the the radius of an object as the length scale associated with the energy required to probe its structure. So far we know that baryons and mesons do also have internal structure, and thus a finite radius, but other particles, like leptons, quarks, gauge bosons and neutrinos, have, in the energies accessible to modern science, no discernible structure. Thus, to our knowledge, they are point particles. —Preceding unsigned comment added by 129.67.37.227 (talk) 13:36, 21 January 2011 (UTC)[reply]
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