Wikipedia:Reference desk/Archives/Science/2011 April 20

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

April 20

Getting rid of double chin's fat

If you go on a diet + exercise program and start to loose weight, will the fat of a double chin go away? Or is it some more resilient fat deposit? —Preceding unsigned comment added by 212.169.181.129 (talk) 00:02, 20 April 2011 (UTC)

Each person's body characteristics are unique. No general statements can be made except if you go on a properly supervised diet and exercise program, and lose weight, you will have more positive health outcomes in many aspects of your life. However, as to what such a diet will do to specific body parts and their shapes and sizes; there is no way to make a general statement, everyone is different. In other words, you shouldn't stop exercising and start eating junk food all day merely because your double chin doesn't go away... --Jayron32 00:10, 20 April 2011 (UTC)

Probably, yes. Excess fat under the chin is normally associated with obesity. However, flabby skin may remain, which can be just as bad. StuRat (talk) 00:24, 20 April 2011 (UTC)

A science question concerning light years

I have wondered about the following question for a while, and I haven't been able to figure i out. Can you please help?

Television signals are radio waves which travel at the speed of light. The first commercial TV broadcasts began about 1950. How far have these radio waves travelled in light years?

Thanks —Preceding unsigned comment added by 66.222.179.213 (talk) 01:40, 20 April 2011 (UTC)

Well, it's been 61 years, so those signals would have traveled 61 light years.. Mind you, they weren't designed to be beamed into space, neither in direction or power. So even if theoretically there is any signal left 61 light years away, it would almost certainly be completely undetectable above the "noise". Especially considering the power of the signal follows the inverse square law. Vespine (talk) 01:46, 20 April 2011 (UTC)

You may enjoy this informative XKCD image that illustrates the answer to your question (~61 light years) with its placement of 'expanding shell of radio transmissions' [1](note the logarithmic scale). SemanticMantis (talk) 02:00, 20 April 2011 (UTC)

"if there is any signal left..." I would expect that the signal did not cease to exist as it travelled 61 light years. "..it would almost certainly be undetectable above the noise.." That depends on the antenna array used by hypothetical extraterrestrials. How many dishes of what size located how far apart would be required? Edison (talk) 14:03, 20 April 2011 (UTC)

Maybe 20 years ago I read a science fiction novel where a strange electromagnetic signal being received on earth was translated to be images of Hitler opening the 1936 Olympic Games. Those Games were transmitted by television to 20 or so locations around Germany. So it's not a new idea, and the distance would now be 75 light years. HiLo48 (talk) 02:54, 20 April 2011 (UTC)

You're thinking of Contact, a 1985 novel by Carl Sagan. TenOfAllTrades(talk) 03:00, 20 April 2011 (UTC)

Yes, of course. Thank you. HiLo48 (talk) 03:09, 20 April 2011 (UTC)

Spy camera-type hardware to use as ocular implants for the blind - Why do I never hear of them?

See, this spy camera is nearly the size of our eyes. (There are some smaller models like this one, which appears small enough to fit in a child's eye socket.) If components are small enough to all fit into something that can fit into one's eye sockets, why do I not hear of the blind receiving these implants to help them see again? --98.190.13.3 (talk) 03:49, 20 April 2011 (UTC)

Because we can't yet interface the camera with the visual cortex. Shoving a camera into someone's skull does nothing if the brain can't interpret the signals as "vision." A lot of research is focusing on this issue, and there are lots of very clever schemes being investigated, but we aren't quite there yet. --Mr.98 (talk) 03:58, 20 April 2011 (UTC)

But this and this would seem to be steps in the direction you're asking about. HiLo48 (talk) 04:01, 20 April 2011 (UTC)

Definitely. Very clever schemes. Unclear which will be the one(s) that will end up being most successful in the long run. I wouldn't be at all surprised if we had some very good bionic eyes in the next two decades. But my understanding is that most of them are still too expensive, and too crude, for much practical use at this point. Making a camera is of course trivial; making that camera interface with the brain is not. --Mr.98 (talk) 11:59, 20 April 2011 (UTC)

Would a rail gun give recoil?

I understand relatively how a rail gun works; it uses a magnetic field to accelerate a projectile, if I'm not mistaken.

I'm writing a short story, and I would like to ask those more educated than myself: Would a shoulder mounted rail gun give recoil?

I'm not entirely sure how Newtons law's would affect the situation involving magnets. I await your answers. —Preceding unsigned comment added by 66.91.44.187 (talk) 05:28, 20 April 2011 (UTC)

If an object is leaving the gun, the gun must recoil with the same momentum that the object leaving the gun has, but in the opposite direction. The source of the force accelerating the leaving object, whether it is exploding gunpowder or a magnetic field, is irrelevent. --Jayron32 05:31, 20 April 2011 (UTC)

Thank you so much, this definitely answers my question. —Preceding unsigned comment added by 66.91.44.187 (talk) 05:33, 20 April 2011 (UTC)

Jayron32 has answered your question using the principle of conservation of linear momentum. You might find an answer expressed using Newton's third law of motion to be simpler. Newton's third law can be explained as Forces always occur in pairs. If object A exerts a force F on object B, then object B exerts the same force F on object A but it is in the opposite direction. In the case of the rail gun, if the gun exerts a force F on the projectile then, simultaneously, the projectile exerts the same force F on the gun but in the opposite direction. So the same force F is applied simultaneously to both bodies but that doesn't mean they have the same acceleration. The small projectile is given a high acceleration and quickly achieves very high speed. The gun with its greater mass is given a smaller acceleration and achieves only a small speed before being stopped by the surrounding structure. Dolphin (t) 05:57, 20 April 2011 (UTC)

If a cannon fired a 1 kg projectile at 500 meters/second, the recoil should be somewhat greater than if a rail gun fired a projectile of the same mass and velocity, since the conventional cannon would also expel the gases and unburned particles of the gunpowder charge. Edison (talk) 13:58, 20 April 2011 (UTC)

I suppose you could design a recoilless railgun that propelled a counterweight in the opposite direction to the projectile. Make the counterweight more massive than the projectile so that it has a lower acceleration and lower top speed. Let the counterweight eject itself from the back of the railgun. Either retrieve the counterweight after each firing and reuse, or maybe load with two-part shells so each projectile has its own counterweight. Dibs on the patent. Gandalf61 (talk) 15:19, 20 April 2011 (UTC)

The impulse would be lower. —Preceding unsigned comment added by 84.92.32.38 (talk) 19:31, 20 April 2011 (UTC)

As it says in the article on Newton's Laws, the Third Law does not apply when electromagnetic fields are considered (the field can carry off momentum). So it is possible to build a recoil-less rail gun, there being no mechanical recoil, the reaction being carried off by an EM field Robinh (talk) 23:52, 21 April 2011 (UTC)

If you want to carry momentum away from the gun, you need a radiant EM field, i.e. an electromagnetic wave. If you're talking about accelerating a bullet, the EM wave coming out the back of the gun would be very intense. I daresay that the EM wave might be more destructive than the bullet. --Srleffler (talk) 17:47, 22 April 2011 (UTC)

Let's crunch some numbers. A photon's momentum is its energy divided by the speed of light (see photon). So, the energy released as EM would need to be equal to the momentum of the projectile times the speed of light. Our article, railgun, mentions a US Navy device that accelerates a 3.4kg projectile to 2.4 km/s. That means the energy release by EM would need to be 3.4*2,400*300,000,000 J = 2.4 terajoules. Orders of magnitude (energy) says that's just under the orbital energy of the Mir space station. The Mir space station got that energy from a rocket engine burning for a period of about a minute (ish - I don't really know the length of the rocket burn, and you need to remove a bit due to atmospheric and gravity drag, but that's not important). The rail gun would need to emit that energy almost instantly. So, in conclusion, I agree with Srleffler that the EM would do more damage than the projectile (unless it was able to dissipate prior to hitting anything and was at a frequency that isn't absorbed by air, I suppose). --Tango (talk) 18:07, 22 April 2011 (UTC)

If there was not salt in oceans

what was happened if there was not salt in ocean water?--78.38.28.3 (talk) 09:55, 20 April 2011 (UTC)a.mohammadzade

All living things would be radically different. Life evolved in the context of water containing a certain combination of electrolytes, which are now are an integral part of biology as we know it. See cells, cell membrane, cell potential, electrochemical gradient, membrane transport and action potential just as a start. --- Medical geneticist (talk) 10:19, 20 April 2011 (UTC)

Your skin would become all wrinkly when you swam in it. --Aspro (talk) 10:17, 20 April 2011 (UTC)

Absurd "if." Salt is in oceans because salt (NaCl) exists, and water dissolves it. To have no salt in oceans would require the amazing position of saying that water can not come in contact with salt. Fresh water exists because water in clouds has essentialy no salt in it - fresh water in aquifers is "old rain". And, yes, some aquifers are brine (having salt in them). Collect (talk) 11:15, 20 April 2011 (UTC)

It's a hypothetical situation. Dauto (talk) 13:58, 20 April 2011 (UTC)

Of course it is, but you can't give a sensible answer to this kind of hypothetical question without considering why the thing you've changed is different. You can't just change the salinity of the oceans in isolation. You need to make sure your new world is still consistent with the laws of physics. If you throw physics out the window, you have nothing to work with and can't get any answers at all. --Tango (talk) 18:32, 21 April 2011 (UTC)

Hmmm, I thought there wasn't much salt in the oceans when they formed on Earth. Count Iblis (talk) 17:12, 20 April 2011 (UTC)

A different way of approaching the question is could life have evolved on Earth without the elements Sodium and Chlorine being present? Exxolon (talk) 17:34, 20 April 2011 (UTC)

Many organisms (not explicitly adapted to be salt tolerant) actually prefer to keep their intracellular environment lower in sodium and higher in potassium than we observe in the modern oceans. Those preferences have been used to suggest that the last universal common ancestor may have developed under conditions with appreciably less sodium and perhaps more potassium than we observe in the modern oceans. (Though on the other hand, the common ancestor may simply have realized that exporting sodium and importing potassium was a good way to live.) Dragons flight (talk) 21:02, 20 April 2011 (UTC)

I think all life died and all of oceans became waste water in less than one month.--78.38.28.3 (talk) 03:19, 21 April 2011 (UTC)

THE best way of transferring water up to top of the hill

what is THE best way for transferring water up to top of the hill?--78.38.28.3 (talk) 09:55, 20 April 2011 (UTC)a.mohammadzade

I don't understand your use of the word "mentions". Maybe if you posted here in your native language, we can get someone to translate it to English for us and give you a meaningful answer? --TammyMoet (talk) 10:52, 20 April 2011 (UTC)

"بهترین روش برای انتقال آب به بالای کوه کدام است " —Preceding unsigned comment added by 78.38.28.3 (talk) 03:03, 21 April 2011 (UTC) چند وقت پیش یک سیستم در نظر داشتم ایجاد کنم که اب را در ارتفاع پایین به بخار تبدیل می کند و در بالادست (بالای کوه یا ارتفاعات )دوباره به اب تبدیل می کند این سیستم همان شیوه ای است که خداوند در طبیعت قرار داده سیتمی که اب اقیانوسها را به بالای قله 8800متری اورست می فرستد نه پمپی در کار است ونه لوله کشی .به نظر بنده بهترین روش و ارزان ترین روش انتقال آب این است"--78.38.28.3 (talk) 03:09, 21 April 2011 (UTC)

the best way may be which the nature does , vaporation in down , and devaporation on top ,without pomping and pipes .--78.38.28.3 (talk) 03:16, 21 April 2011 (UTC)

Google Translate, which isn't perfect, say's that's Persian for "The best way to transport water to the top of a mountain which is" (sic), so in proper English the question is presumably "What is the best way to transport water to the top of a mountain?". Red Act (talk) 03:15, 21 April 2011 (UTC)

THANK YOU VERY WELL >THOSE ARE MY MEANING. —Preceding unsigned comment added by 78.38.28.3 (talk) 03:21, 21 April 2011 (UTC) It was for my spelling "mountain" —Preceding unsigned comment added by 78.38.28.3 (talk) 03:25, 21 April 2011 (UTC)

We have these articles, that may help: fa:چرخه آب (Water cycle), and pump (fa:پمپ). Generally, we try to engineer a water distribution system that doesn't require sending water up hill. In the middle-east, elaborate systems called fa:کاریز or قناة in Arabic - (Qanat, for the English-speakers) is sort of like a man-made artesian well (fa:چاه آرتزین). When it is unavoidable, and we must send water up-hill, we usually use large electric pumps. We have diagrams of many types of water pumps at our article. The largest types of pump I am aware of are radial piston pump, though I am not a water utility specialist.

Near to where I live, we have a reservoir called Hetch Hetchy, which is unfortunately on the opposite side of a mountain from where most people live. You can see photos of the gigantic pipes that were built to carry water over the Sierras and eventually all the way to the greater San Francisco region. I've driven past this particular vista-point many times, and often wondered how they make the water flow up-hill; I still don't know if it's ultimately a gravity pump (i.e., the reservoir is higher than the final destination, so the water is simply siphoned over this hill), or if energy needs to be added via electric pump to make this particular climb. (It's on CA 120 near Old Priest Grade Road and Moccasin Reservoir, if anyone knows what I'm talking about). You can't miss it, if you're driving to Yosemite. I'd wager that it's one of the steepest up-hill aqueducts in the United States. Nimur (talk) 04:11, 21 April 2011 (UTC)

Since you're from Persia, you might also be interested in an ingenious way the Persians employed to cool their buildings, thereby moving water from a qanat: Windcatcher, in Farsi: بادگیر. — Sebastian 07:32, 21 April 2011 (UTC)

For an older (and in my humble opinion, more elegant) approach, see Archimedes' screw. --Rixxin (talk) 09:13, 21 April 2011 (UTC)

Using an aquaduct is an old solution to crossing a valley. 92.24.189.51 (talk) 10:17, 21 April 2011 (UTC)

you have good ideas and very informations about my nation , and our last irrigation systems , cooling buildings and our way of refrigerating food in underground .THANK YOU--78.38.28.3 (talk) 11:05, 21 April 2011 (UTC) last iranians was prefer to find upper code for water flow to their farm or garden , and had not pomp,to upgrade level of water code--78.38.28.3 (talk) 11:12, 21 April 2011 (UTC)

I don't understand the word "kode" here. If the problem is a lack of electricity at the site, then solar and/or windmill energy might be the best way to power the pumps. Placing those at the top of the hill would probably provide for the best results, especially in the case of a windmill. Note, however, that these will provide a rather intermittent flow of water. If this is just for irrigation, that may be acceptable. However, if you also need a supply of water available at the top at all times, then a tank or pond of some type is needed at the top. Also, if the hill is high, it might make sense to use a series of pumps which each pump to a tank a bit higher up, rather than one huge pump at the bottom. Sump pumps have floats and only turn on when there is water to pump, so those might be the best choice here. StuRat (talk) 17:26, 21 April 2011 (UTC)

Rat population dynamics

There was a public health expert on the radio yesterday discussing the public health consequences of an ongoing strike by sanitation workers. He said that if the trash piles up uncollected for more than about 3 weeks the city will have a dramatic increase in rat numbers. He went on to explain that three weeks of plentiful food is all it takes for the rat population growth rate to reach a "tipping point" where a previously stable population in equilibrium with its limited food supply suddenly adjusts to its new increased food supply. I'd like to understand the population dynamics at work. Is it a case of increased fertility or is a decreased mortality the main factor. What makes "about three weeks" be a critical period? The city under discussion is Johannesburg in South Africa - a large metropolitan city with a population of several million people (and who knows how many rats). Roger (talk) 08:50, 20 April 2011 (UTC)

Brown_rat#Reproduction_and_life_cycle--Aspro (talk) 10:22, 20 April 2011 (UTC)

That doesn't explain the mechanism of a population explosion. Do litter sizes directly increase in response to improved nutrition? If so, how long does it take to occur? Rats that are already pregnant on day 1 of the sanitation strike can't contribute to such an increase. Surely a sustained period of plentiful food would be required to increase fertility - I can't see how for example a single good meal could cause "superovulation".

Does decreased mortality play a role? My "gut" says that lower mortality would take considerably longer than three weeks to greatly influence total population size. I supose what I'm really after is a statistical demographic analysis of a rat popultation explosion in response to increased food supply.

I remember seeing a documentary - I think on Nat Geo TV - about the rat population explosions in parts of India that occur in response to bamboo forest coming into seed at the same time, iirc, every 40 or so years. That process took substantially longer than simply the gestation period of the rats - in fact it took several "generations" for the population to "explode". Roger (talk) 10:44, 20 April 2011 (UTC)

Yes, I saw that too. I recall that not only did a higher percentage of baby rats survive, there were also more born per litter and less time between litters at the peak. Then, when the food supply disappeared, the rats started starving and would eat anything they could find. One interesting effect is that it doesn't actually seem to be in the interest of the species to do this population explosion followed by starvation, but it is in the individual interest of each rat to have as high of a percentage of their genes in the surviving rats as possible. Seems like their are some lessons about human overpopulation in there. As far as a "tipping point" goes, there may be a certain amount of time and excess calories needed for the rats to switch to higher fertility mode. StuRat (talk) 23:47, 21 April 2011 (UTC)

Rates live in a rate race. Young rats have very high mortality ratios that favour older rats. With a plentiful food supply most young rats can survive and so the population starts to exploded. As the increase is counted on a generation bases – it takes a minimum of three weeks to make this assertion. That section seems to make this clear to me. Maybe your trying to read too much into it.--Aspro (talk) 13:15, 20 April 2011 (UTC)

Mice and rats are actually well known for eating their young. I don't know for sure, but I suspect the "tipping point" is that once the rats are old enough, reducing their food supply means that they come into your house looking for any scrap, rather than being peacefully eaten by their mothers. Wnt (talk) 17:26, 20 April 2011 (UTC)

Notoungulata

Hi!

In the Notoungulata article it is mentioned that these animals lived also in Asia (there is a map as well). What is the explanation of this, as South America was not connected with other continents in the time of Notoungulata (57 mya)?92.84.196.241 (talk) 10:24, 20 April 2011 (UTC)

Go back to the "Notoungulata" article and under "taxonomy" click on "convergent lines" It's all very well explained.Phalcor (talk) 14:07, 20 April 2011 (UTC)

Those from Asia, are not real notoungulates, but notoungulat like creatures? 92.86.240.138 (talk) 14:13, 20 April 2011 (UTC)

No, Phalcor, you misread the article. Notoungulates in South America evolved (via convergent evolution) to fill many of the niches other mammals filed on other continents. But it's not the case that Notoungulates evolved twice (or thrice, given the two disjoint areas in South America). One explanation for the disjointness of areas is that fossilization is a rare event. We may not have any fossils from some areas where Notoungulates lived. I have, however, no idea if there ever was a land connection from Asia to South America during the last 57My. --Stephan Schulz (talk) 15:42, 20 April 2011 (UTC)

Our article on notoungulata is actually out of date, I believe -- or rather, the map is out of date. The putative Asian members consist of Arctostylopida, which were once thought to be notoungulates but are now classified differently. It would clearly be impossible to have a monophyletic group of land mammals from Asia and South America starting 57 million years ago (as our article says), because South America had already been separated for around 40 million years by that time. Looie496 (talk) 16:57, 20 April 2011 (UTC)

(Edit Conflict) Googling on the subject, some authorities have evidently suggested that the Notoungulates originally evolved in East Asia (as mentioned here) but there seems to be some debate (as here) about whether the sub-orders or families in Asia (and those in North America) that have previously been classified within the Order Notoungulata are truly members or not. The ancestry of Notoungulata also seems less than certain. it would be interesting to know how those who endorsed the Order's monophyly explained their distribution. As in all science, everything is open to revision in the light of new evidence or improved analyses. In short, the OP may well be right. {The poster formerly known as 87.81,230.195) 90.197.66.111 (talk) 17:18, 20 April 2011 (UTC)

Yes, as my response above indicates, the OP is absolutely right. I have just taken a shot at fixing the Notoungulata article to give a more up-to-date picture. I can't fix the map, unfortunately. Looie496 (talk) 17:37, 20 April 2011 (UTC)

Thank you for the answers! 109.96.200.104 (talk) 06:59, 21 April 2011 (UTC)

I removed an absurd bit of math in the lede to that article, which said that, since they existed from 57 million years ago to 11,000 years ago, they were around for 56,989,000 years. This reminds me of this funny dialog:

KID: "Hey mister, how old is that dinosaur ?"

GUARD: "200,000,007 years old."

KID: "How do you know so exactly ?"

GUARD: "Simple, it was 200,000,000 old when I started working here, seven years ago." StuRat (talk) 18:06, 21 April 2011 (UTC)

Hollow plant stems

What are hollow plant stems like those from dandelion good for? 95.112.153.119 (talk) 12:54, 20 April 2011 (UTC)

Hollow structures can provide stability without additional mass; for example many birds have hollow bones, which provide strength, but are also light enough for the bird to fly (see Bird_anatomy#Skeletal_system. In the case of dandelions, the hollow stem may allow faster production (i.e. less resources needed to produce) while still providing the strength and function that a stem is supposed to provide. It should also noted that some cousins of dandelion (like Catsear) do not have hollow stems, so its likely one of those multitude of traits which is "optional". --Jayron32 14:36, 20 April 2011 (UTC)

The hollow stems are also good for amusing young children et. al.. If you take a 6 - 8 length of dandelion stem, the thicker the better, squeeze the bottom half inch and separate the two halves so that the two sides separate into two outward curving 'reeds' then place the 'reed' end inside the mouth and blow gently. Once you have acheived a 'note' then with hands cupped around the open end and some tongue trilling, you're away. The summer evenings will fly by! Richard Avery (talk) 15:41, 20 April 2011 (UTC)

Isn't the white sap poisonous? --TammyMoet (talk) 19:52, 20 April 2011 (UTC)

Not that I know of. Dandelions are quite edible, and parts of them, or their close relatives, find their way into all sorts of recipes. I've had dandelion greens in a salad often enough, and being a cousin of chicory, dandelion root makes a decent ersatz coffee substitute. The flowers (pre-puffball stage) are perfectly edible and are often used to make wine. I've never heard that the sap was particularly toxic; if it were it would make all of the other parts toxic as well, which they clearly are not. --Jayron32 20:06, 20 April 2011 (UTC)

As child I was told the sap was toxic (which it really isn't). I think this is a common myth at some places. Likewise, any unknown berries were called "birds berries" and declared poisonous. 95.112.153.119 (talk) 20:17, 20 April 2011 (UTC)

Yes, I remember being told that dandelion sap was poisonous. I wonder where the idea came from, and if there are any unpleasant chemicals in the sap. Dbfirs 22:42, 20 April 2011 (UTC)

I don't think I was told it was poisonous but I do remember that it is quite bitter and not very pleasant tasting. Vespine (talk) 23:03, 20 April 2011 (UTC)

Yeah, I was never told (or didn't bother to listen to those trying to tell me) it was poisonous, and discovered the same thing. It tastes crap. HiLo48 (talk) 23:48, 20 April 2011 (UTC)

I also prefer beefsteaks, French fries and chocolates. I put the dandelions in vinegar (in a jar that previously contained gherkins. Yes, yes, I reuse nearly everything) and eat it in quantities like mustard. (Oh, I see, I have different customs with mustard, too. So that is 3-5 tablespoons per dish.) I hope the vinegar also releases the minerals from phytic acid. 93.132.132.156 (talk) 00:12, 21 April 2011 (UTC)

The sap is interesting because it's latex. I sometimes wonder about its potential for craft activities (but it's probably easier to go out and buy a big bottle of latex than harvest several hundred dandelions).  Card Zero  (talk) 10:44, 21 April 2011 (UTC)

As a child, I was told it would make me wet the bed if I ate it, hence the alternative (and French-equivalent) name piss-a-bed. I now fail to see a mechanism by which this could be true, and I've never known anyone to experience it. I did discover, as a child, that the sap stains your skin, and so can be used to give yourself temporary tattoos. This is also how I know eating the sap doesn't make you piss. 82.24.248.137 (talk) 22:07, 21 April 2011 (UTC)

It is said to be (without mentioning any mechanism) to be a diuretic, which is simply another word for "it will make you piss". 93.132.132.156 (talk) 22:36, 21 April 2011 (UTC)

Well, yes (I deliberately stuck to the terms used in the folk-name), but being a diuretic isn't as specific as making you urinate while asleep, or even making you urinate at all: it just fills your bladder quicker. And, given children pretty commonly get the stuff on their hands and end up eating it, we can clearly see that any effect it has is much less dramatic than the folk tradition has it. And it certainly doesn't involve any sleep-triggered weeing (which was the ridiculous claim). 82.24.248.137 (talk) 22:11, 22 April 2011 (UTC)

Smell of salt

When I pour salt into boiling water, there is a characteristic smell of salt. I thought that this may be due to small droplets which are created as the ascending vapor bubbles reach the surface transporting the salt, or just by the flow of air and vapor which may transport very small salt grains, but the smell is also there when I heat water that has been salted when it was cold, long before it boils. This leads me to the question: What is the vapor pressure of sodium chloride at e.g. 80 degrees Celsius? The sodium chloride vapor pressure (or the vapor pressure of the Na⁺ or Cl^- ions for that matter) shouldn't be higher above the solution than above solid sodium chloride, it wouldn't be soluble (up to 356 g/l or more, depending on temperature, a concentration that I certainly didn't reach) otherwise. Icek (talk) 12:54, 20 April 2011 (UTC)

It's a common misconception that something has to strictly be a gas for you to smell it. It merely needs a mode to get into your nose. It's quite possible that very small salt crystals could become airborne, as you say transporting "very small salt grains", or in the case of a solution very tiny droplets of salty water could become airborne which can transport the salt to your nose. These sorts of macromolecular mixtures of particles are called Colloids, and a description of various types can be found at Colloid#Classification_of_colloids. There are lots of ways for salt to get to your nose, either in solid or solution form, which do not require detectable amounts of "NaCl" gas, which do not exist at all under normal household conditions. According to this MSDS, sodium chloride has a vapor pressure of 1 torr at 865C, which likely means it is immeasurably small at merely 80C. --Jayron32 16:57, 20 April 2011 (UTC)

Also, if this is iodized salt, is it possible you are smelling the iodine (which has a very strong odor) ? StuRat (talk) 17:35, 21 April 2011 (UTC)

Iodized salt contains no iodine anymore than regular salt contains chlorine. Iodized salt contains iodide or iodate which has many more differences from iodine than the mere change in spelling. Yes, elemental iodine contains a very distinct odor, but you don't find elemental iodine in iodized salt. --Jayron32 23:43, 21 April 2011 (UTC)

Iodized salt contains no iodine ? Since both iodide and iodate contain iodine, that means the iodized salt does too. And salt contains chlorine by the same logic. Now, if you mean it doesn't contain elemental iodine and chlorine, then OK, but you need to say it that way. StuRat (talk) 09:55, 22 April 2011 (UTC)

Also, iodized salt certainly tastes different, and I believe I can smell the difference, too. StuRat (talk) 00:13, 23 April 2011 (UTC)

Iodized salt contains either the I^1- ion or the IO₃^1- ion. Both of those ions will have a different taste than the chloride ion in normal salt; as well the counterion for introducing the iodide and iodate ions is often potassium, which will introduce its own taste. Additionally, the mechanism by which you "smell" pure sodium chloride is the same for smelling "iodized" salt. When you think of volatile iodine, that is elemental iodine, that is I₂, which is not I^1- or IO₃^1-. Iodide and iodate have no vapor, and so do not have a strong smell (unless they get into your nose as already described above). Iodine (I₂) is highly volatile and has a distinct smell. There is no I₂ in iodized table salt. What you are doing is confusing the properties of very different substances with similar names. --Jayron32 00:53, 23 April 2011 (UTC)

Edible plant parts

I can't find an article about that. Worse, there are many articles that try to cover it. When I look at the plant in my garden, I get hungry and start to wonder what can be eaten. I somewhere heard that all parts of rosaceae are edible. Is that true? What about hazel leaves and catkins? Sorry if this looks near to trolling. 95.112.153.119 (talk) 13:19, 20 April 2011 (UTC)

No, it doesn't look like trolling, it does look like an honest question, which I will endeavor to honestly answer. The term for an "edible plant part" is a Vegetable. However, there are no general rules for which plants, or which parts of which plants, are automatically edible. Take cashews for example: The seed itself is edible, but surounded by a shell and a fruit which is pretty toxic. Contrawise, the apple has a very edible fruit whose seeds contain cyanide, which is toxic (see Apple seed oil). Then you have stuff like pokeweed, which is toxic in raw form, and edible when cooked properly. Your best solution to deciding what to eat is to first research the specific plant in question. --Jayron32 14:19, 20 April 2011 (UTC)

It is certainly not true that all parts of rosaceae are edible. The family includes many fruit trees, whose wood is obviously not edible. Looie496 (talk) 16:31, 20 April 2011 (UTC)

This depends on what exactly is meant by "edible". Pearwood is surely not chewable, but neither is raw sweet corn. Salad, in contrast, is chewable, but contains nearly nothing to nourish you. So aside from the normal use of the word, I would not exclude that some woods are "edible", in some sense. 95.112.153.119 (talk) 17:44, 20 April 2011 (UTC)

"Salad....contains nearly nothing to nourish you". No, its packed with vitamins, minerals, antioxidants etc. There is much more to food than mere calories. Datrk leaf vegetables such as cabbage are better for you than lettuce, but lettuce is still good. 92.15.24.113 (talk) 21:21, 20 April 2011 (UTC)

I think that's a myth. It's mostly indigestible cellulose and water. (See Green Salad: "Due to their low caloric density, green salads are a common diet food.") The tiny amount of minerals is largely indigestible, too, as it is bound to phytic acid and for vitamins there are richer sources elsewhere. 95.112.153.119 (talk) 22:01, 20 April 2011 (UTC)

Compare the nutrition tables from dandelion with lettuce, OK dandelion leaves if prepared are also called "salad", but so is potato salad. 95.112.153.119 (talk) 22:37, 20 April 2011 (UTC)

Both lettuce and dandelions are packed with nutrition, and luckily have few calories. The dandelion table simply includes more nutrients than the lettuce table does. Neither of the tables include antioxidants etc. I agree that eating a lettuce is not quite as good as darker-leaved vegetables, but its still good. Something very important is that eating veg and fruit fills you up and thus avoids you eating high-calorie junk food. If you were starving then yes, a Big Mac would be more nutritious for you than a plate of salad, but few people reading this are going to be starving - most will be overweight and consuming too many calories than is good for them, particularly in North America. OP, I'm willing to bet that you are not underweight. 92.28.253.8 (talk) 10:05, 22 April 2011 (UTC)

Actually I was slightly underweight during childhood and adolescence. Now I am in my late forties and gaining some additional weight. I bet you are not underweight, despite your mainstream healthfood? If your stomach is trained to do work, it will start to work even if you don't need food. This is what most people in the western world think of as hunger. If you don't need food, the simplest thing to do then is to ignore the feeling and your colleagues' strange looks for the sound of a rumbling belly. 95.112.196.91 (talk) 12:24, 22 April 2011 (UTC)

Here's why you should eat lots of fruit and veg: http://www.nhs.uk/Livewell/5ADAY/Pages/Why5ADAY.aspx Persionally, I also think that since we evolved eating plenty of fruit and veg, it is wise to continue to do so for optimum health. 92.15.5.152 (talk) 20:34, 22 April 2011 (UTC)

Some salads are nutritious, others aren't. A garden salad is high in fiber, vitamin A and vitamin C, and has a bit of iron and calcium, too: [2]. Adding some meat (or nuts or beans) to the salad provides for protein, too: [3]. Croutons add starch. Egg adds cholesterol. Then salad dressings add fat and sugar. So, a salad can be a full meal: [4]. StuRat (talk) 18:21, 21 April 2011 (UTC)

Vegetable is the key word and I really don't know why it didn't come to my mind. Thus I fond List_of_vegetables and List_of_plants_with_edible_leaves. Nevertehless, it looks kind of futile trying to list *all* edible parts in one or two articles. Wouldn't it be better to have some box in each plant article stating the edible parts? (The way it is done with main properties of chemical elements). 95.112.153.119 (talk) 17:44, 20 April 2011 (UTC)

Again, you'd have to define "edible". Just about anything that doesn't kill you (at least, kill you mostly instantly) and which can end up in your digestive system somehow is considered "edible" by some culture. And even much of the stuff that kills you, people have found ways to render it less toxic (see the aforementioned pokeweed). --Jayron32 20:01, 20 April 2011 (UTC)

In the context of this question I think of "edible" as "non-toxic when eaten raw in quantities reasonable for other kind of food" 95.112.153.119 (talk) 20:23, 20 April 2011 (UTC)

Note that means you're counting things like cassava and probably cashew nuts as inedible Nil Einne (talk) 23:09, 20 April 2011 (UTC)

(Second try, somehow the first answer didn't get through) Yes, in the context of this question, cassava and a lot more things would not be considered edible (if not further processed). But I make this restriction only to not further complicate the original question. Any answers the like of " beans are poisonous if raw but edible if properly cooked" are highly welcome. 93.132.132.156 (talk) 00:58, 21 April 2011 (UTC)

For safety sake it's also important to bear in mind that many toxic plants are easily mistaken for non toxic plants. There can be a problem with accurate identification. So if you feel a desire to eat plants from your garden (the gatherer instinct) it might be a good idea to plant seeds or plants that are known to be safe to eat.190.56.14.28 (talk) 21:28, 20 April 2011 (UTC)

My garden behaves in a quite autonomous way. Everything I deliberately plant will almost surely not grow. Full grown trees, weeds and the roof tiles from the little house are among the few things the slugs don't eat. That is why I'm putting it the other way round and start from what I find there. 95.112.153.119 (talk) 22:17, 20 April 2011 (UTC)

All gardens behave in an autonomous way unless they are controlled. plants that are commonly eaten by humans have been selected and developed over countless generations for good reasons. If a plant is not eaten by local organisms, there is virtually always a good reason for that too. Those reasons would include considerations like unpalatability, indigestability, toxicity, thorns, tough husks etc. Sufficient botanical knowledge for safe eating would have to be a lot more extensive than "how to grow a vegetable garden" and there's a wealth of information about that.190.56.14.125 (talk) 23:13, 20 April 2011 (UTC)

And then you face the challenge of countries like mine, Australia. An Aboriginal culture thrived here for 40,000 years, on a plant collection almost entirely different from that known to the rest of the world. Unfortunately much of that culture and knowledge base about what was good to eat and how to prepare it was destroyed before we bothered to learn it. So there's still plenty of good food there. We just need to (re)discover it. HiLo48 (talk) 23:43, 20 April 2011 (UTC)

So you perfectly understand my purpose, only that the reason why the knowledge was lost (or never existed) is different. 93.132.132.156 (talk) 23:56, 20 April 2011 (UTC)

(ec) What I already harvested are dandelion leaves, blackberry leaves (intended for making tea) and ground elder (not really my taste but abundant). I could not find out if hazel leaves and catkins are edible. The shrubs have to be cut anyway and I am too big a niggard to grant anything to the slugs that could otherwise be used. Petals from wild roses are to show up soon, and I think the can be eaten or dried for tea, too. Young raspberry sprouts are really, really full of little thorns, especially near the ground and thus ward off the slugs. Ivy is clearly not for food. Common grasses are probably not toxic, but as I am not a ruminant I can't take profit from eating. There is some kind of juniper shrub but I am not certain if I can use the berries safely as spice. There are lots of unidentified "herbs" but ion total not enough to bother if they are edible or not. 93.132.132.156 (talk) 23:56, 20 April 2011 (UTC)

Elder berries are great for making a delicious rich red wine.190.56.18.243 (talk) 02:24, 21 April 2011 (UTC)

Richard Mabey wrote Food for Free, which gives details of edible wild plants in Britain. Since that book was written, it is now known that nettles have tiny calcium structures in them that damage kidneys and bladders, so only the young green tops should be eaten. 92.28.253.8 (talk) 10:10, 22 April 2011 (UTC)

Human kindness

So, in this article there's a reference to an OECD study which among other things tried to report "kindness" by country which includes things like volunteering, helping strangers, etc. However, this is self-reported, so people may be lying. I seem to recall reading about an actual study where people pretended to be injured on the street in different countries and tracked the response time and rate from general populace. Can someone help me find this or any other study that's not based on self-reporting? --216.239.45.4 (talk) 16:40, 20 April 2011 (UTC)

Desmond Morris did such studies as part of (I think) his TV series The Human Animal though he may simply have been replicating earlier studies. Our article links to videos of the episodes. I'm sure I've read that book, but I don't recall offhand whether this was in it. Matt Deres (talk) 19:56, 20 April 2011 (UTC)

I would be interested to see how efforts to get objective measures of this would be designed. It's obvious that in every society you get some very caring, sharing people, and some selfish bastards. (That's a simple Australian expression whose meaning should be pretty clear.) But the societies would also differ in so many other ways too. How to isolate the sought after variable is the challenge here. HiLo48 (talk) 23:38, 20 April 2011 (UTC)

The stuff that Morris presented was very basic stuff. Essentially they had someone lay down on the ground, apparently unconscious and they timed how long it was until someone stopped to help. IIRC, the two instances they showed on the video were one from a small Mediterranean village and one from a large city (New York or London or something). In the small village, help was offered almost instantly - the first person to see the "casualty" knelt down to check on him; in the big city, the casualty was simply stepped over. Morris wasn't attempting to examine whether different nationalities or ethnicities were more or less helpful, however, he was pointing out that people in large cities are forced to shield themselves from the crowd to the point where normal human compassion is over-ridden.In smaller communities, people can interact with virtually everyone in some kind of meaningful way (know their name, etc.) while in large cities being that open would be completely overwhelming, if not impossible. In response, people "fence off" the masses around them to the point where they almost don't identify them as being human (or at least worthy of human interaction). Matt Deres (talk) 01:23, 21 April 2011 (UTC)

What an interesting question for the science desk! It's not easy to come up with truly objective and culturally independent ways to measure this. Some ideas off the top of my head:

1. Act as a beggar, and divide the money collected by the average income. (To remain true to the spirit of the givers, the researchers should pass the collected money to a charitable cause.) Problems with that: (a) In countries with a good social net, people will feel less need to give to a beggar. (b) You would need several beggars per measured region to neutralize variations in gender or age preferences.
2. Inquire in lost-and-found offices how many items are collected per year.
3. One value for which good data exist is income equality; I'm wondering if that can be used for this purpose; I can imagine a correlation to kindness, at least in a free country. — Sebastian 07:54, 21 April 2011 (UTC)

Given that many people in a wide variety of cultures, perhaps all cultures to some extent, place what is essentially a karmic value of one form or another on actions that an observer may identify as kindness, I think distinguishing between unconditional kindness (altruism) and kindness as a cultural virtue, a form of reciprocal altruism (even if the benefit is expected to come much later such as in an afterlife etc), might be difficult even if you asked each person why they did what they did. I guess many people may not know exactly why they did what they did. "Kindness" seems like a difficult thing to measure. Sean.hoyland - talk 11:24, 21 April 2011 (UTC)

(OP here) I think I don't care if it's cultural or pure altruism. It certainly wouldn't matter much to a person who needs this sort of help. I also don't care if one can't measure "kindness" in general, but only a specific element of it, such as willingness to help strangers which is not nearly as vague. 216.239.45.4 (talk) 16:38, 21 April 2011 (UTC)

This American Scientist article from 2003 may interest you then. Sean.hoyland - talk 17:38, 21 April 2011 (UTC)

Thanks, that's exactly the sort of thing I wanted. --216.239.45.4 (talk) 19:31, 21 April 2011 (UTC)

pvc

does pvc yellow from light or only abs — Preceding unsigned comment added by Kci357 (talk • contribs) 21:37, 20 April 2011 (UTC)

I think that needs a bit of elaboration/clarification before it's likely to get an answer. You need to expand the seeming abbreviations of "pvc" and "abs", and clarify whether you mean "yellow" as a verb (meaning gain a yellowish colouring). It's not really clear at this stage. HiLo48 (talk) 02:24, 21 April 2011 (UTC)

The question is about polyvinyl chloride and acrylonitrile butadiene styrene.

My girlfriend has lots of PVC dog agility equipment that's been kept outdoors in the sunlight for in some cases over a decade, and so far at least it hasn't yellowed at all that I can tell. Red Act (talk) 02:55, 21 April 2011 (UTC)

There are different grades of PVC some will yellow, some won't. If you want to be sure get CPVC or check that they PVC you are buying is rated for UV exposure. I don't know about ABS, but I imagine it's similar. Ariel. (talk) 04:11, 21 April 2011 (UTC)