Wikipedia:Reference desk/Archives/Science/2009 October 7

= October 7 =

Hubble space telescope
I am having a doubt that how the hubble space telescope takes the picture of the galaxies because galaxies size itself in lightyears and the light emitted from a star are any other object will travel in straight line. If this is true then the light that is received by the hubble from distant object will be a small proprotion of the light emitted from them with that light received how they are developing the image of the galaxies and many huge objects. —Preceding unsigned comment added by Dineshbkumar06 (talk • contribs) 01:53, 7 October 2009 (UTC)


 * A very good observation. A galaxy has 100,000,000,000 stars. Sometimes more. Each one produces an average 1,000,000,000 times the lighting of all the daylight falling on all the fields, mountains and oceans in the entire world. Even so, it still takes a light gathering area 100,000 times your eyes' to make those pictures. Sagittarian Milky Way (talk) 02:09, 7 October 2009 (UTC)
 * Also, most of Hubble's pictures are actually exposures taken over many hours and even days. The total exposure time for the Ultra Deep Field image was over 11 days. Unlike our eye which can only capture photons in "real time", digital cameras like the ones in hubble can "add" the photons up over a long time. Vespine (talk) 06:12, 7 October 2009 (UTC)
 * Sort of like having realy long persistence of vision ... plus being able to keep you eyes absolutely still for a very long time ... and never blinking ... Gandalf61 (talk) 10:49, 7 October 2009 (UTC)
 * We need that persistence of vision, because all the benefits of the larger lens are used just to make the image bigger: galaxies are very far away making them look very very small. Sagittarian Milky Way (talk) 11:47, 7 October 2009 (UTC)
 * And a long time ago. →Baseball Bugs What's up, Doc? carrots 11:55, 7 October 2009 (UTC)
 * That's not true. The main lens is large in order to capture more light, making the image brighter. The magnification in a telescope is done by the eyepiece and isn't that important. --Tango (talk) 18:06, 7 October 2009 (UTC)
 * What I was trying to say was that making the image brighter by enlargening the lens size from human eye to Hubble Space Telescope is about the same as the dimming caused by magnifying it so they cancel out and have no effect. Magnifying that much in the Ultra Deep Field is unavoidable if you want to show any detail at all. Sagittarian Milky Way (talk) 12:21, 8 October 2009 (UTC)
 * To more directly answer your question... yes, light does travel in a straight line (for the most part) but not all of it is perpendicular. Some of it is angled slightly down.  It's the same reason you can see a tree or skyscraper that is much much taller than you. ~ Amory ( u  •  t  •  c ) 12:53, 7 October 2009 (UTC)


 * Hmmm ? To see a tree or skyscraper that is much much taller than you, you look up. What does "not all of it is perpendicular" mean - perpendicular to what ?? Gandalf61 (talk) 14:10, 7 October 2009 (UTC)
 * By perpendicular I guess Amory means "at right angles to Amory's chest", or it could be "at right angles to Amory's face" if Amory looks up by rotating eyeballs but not head. Cuddlyable3 (talk) 19:32, 7 October 2009 (UTC)
 * I think maybe I get what the OP is trying to say, this has actually completely blown me away also... Just try to imagine this: A star is a big ball which radiates photons in all directions. Those photons travel away from the star in straight lines (mostly). The inverse square law states that the energy is inversly proportinal to the square of the distance, does that roughly equate to the "number of photons" is inversly proportinal to the square of the distance? In any case. Say you are looking at our closest neighbour star, 4 light years away, photons from that star are hitting your retina all the time, move to the side one centimeter and photons from that star are still hitting your retina!! So that means that if you make a sphere with a radius of 4 light years with the star in the middle, photons from that star are still passing through every single square inch of that "sphere". For that close star that's about 200 square light years of space!!! For Betelgeuse which is 640 light years away, that's an area of 5 MILLION SQUARE LIGHT YEARS! And every single square inch has Betelgeuse photons passing through it!! ZOMG. I know photons don't have mass, but still, I find it mind boggling. And that's not even mentioning photons from something like the Andromeda galaxy 2.5 million light years away which is still visible with the naked eye! Vespine (talk) 22:42, 7 October 2009 (UTC)
 * And considering that there are 139,000,000,000,000,000,000,000,000,000,000,000 square inches in every square light year.. now THAT is alot of photons. Sagittarian Milky Way (talk) 12:44, 8 October 2009 (UTC)

Simple Chem Question
Assuming complete combustion:

C2H6O + 2 O2 → 2 CO2 + 3 H2O

If I am given the number of grams of water produced, can I simply perform a stoichiometric conversion to find the number of moles of ethanol in the initial reactants? Acceptable (talk) 02:18, 7 October 2009 (UTC)
 * Yes. Assuming the reaction were to be balanced, of course. DMacks (talk) 02:21, 7 October 2009 (UTC)

Honey bee identification
I have some honey bees in my room. How can I identify what species they are? They are not bumblebees. Mac Davis (talk) 03:04, 7 October 2009 (UTC)
 * Only with some difficulty. There are many species of honey bee worldwide but it is a tricky business telling one from the other, see here - 86.4.186.107 (talk) 10:01, 7 October 2009 (UTC)
 * Do you keep them in a shoebox? 87.81.230.195 (talk) 15:04, 7 October 2009 (UTC)


 * Depending on how much light your room gets (and your budget and patience), you could start introducing a series of potted plants and seeing which ones the bees like. Eventually you could narrow it down, based on the existing literature about which species of bees prefer which plants.  --M @ r ē ino 15:55, 8 October 2009 (UTC)
 * Ooh, should have thought of this first: take a photograph of the bees. Find out who the appropriate contact is at your state's [Agricultural Board or Agricultural College, and email the photo to that person.  Usually both the boards and the colleges have it in their mission to welcome random questions from the citizenry. --M @ r ē ino 16:01, 8 October 2009 (UTC)

How are Retin-A and Renova different?
They both contain tretinoin, but are marketed differently by the same company. --68.103.141.28 (talk) 03:45, 7 October 2009 (UTC)

why isn't cholesterol soluble in acetone?
Acetone is usually miscible with most organic compounds. Is it the utter lack of aromaticity in cholesterol? John Riemann Soong (talk) 04:41, 7 October 2009 (UTC)
 * Well acetone is pretty polar, hence it's solubility with water. Cholesterol, despite the hydroxyl group, is essentially a large, bulky hydrocarbon, interacting with non-polar molecules.  That makes it great for membranes, but is the reason it is only slightly soluble is water, and presumably) acetone. ~ Amory ( u  •  t  •  c ) 12:48, 7 October 2009 (UTC)

I never tried it, but the data sheets for cholesterol say it is soluble in acetone,. Are you sure it is not soluble in acetone? --Dr Dima (talk) 22:01, 7 October 2009 (UTC)


 * Yeah, but in my experience acetone often dissolves whatever substances diethyl ether does, especially a wide range of not-very-polar organic acids. In my lab experience, cholesterol is not soluble in acetone -- it remains a large chunk in your test tube no matter how much acetone you pour into it. John Riemann Soong (talk) 03:14, 8 October 2009 (UTC)


 * How wet is your acetone? Acetone is notoriously hygroscopic; and a small amount of water in the acetone could mess up the solubility of the colesterol.  Anyone who has ever gotten a few drops of water in melting chocolate and seen it "seize" will understand what is happening with your cholesterol; they are both due to the same effect, which is the small amounts of water causes the non-polar molecules to aggregate and it becomes impossible to get them to dissolve properly.  If you have some scrupulously dry acetone, it will probably dissolve the cholesterol just fine.  However, even a moderately humid day will cause the acetone to absorb enough water from the air to mess this up.  -- Jayron  32  04:52, 8 October 2009 (UTC)


 * Well it's lab grade acetone. You squeeze it out to clean your glassware, so it isn't exposed to moisture generally. Even my lab TA told me that acetone wouldn't dissolve my cholesterol. John Riemann Soong (talk) 03:12, 9 October 2009 (UTC)

Red blood cell
what is a red blood cell —Preceding unsigned comment added by 82.111.23.189 (talk) 08:42, 7 October 2009 (UTC)
 * See red blood cell. Red Act (talk) 08:52, 7 October 2009 (UTC)

Data for floor area ratio (FAR)?
Where can I find maps, isopleth maps, FAR-to-distance from city center graphs, or at least lists, for floor area ratio of cities around the world? Maybe they'd use floor area per acre instead? It'd be cool to see and compare them to scale. For example, some city might have the largest area of 20.00 or greater some other city might be the largest area over 2.00, LA would probably vie for the largest square miles in it's class.. Cubic volume of built structure per land area would be better indicator for "how much structure/square mile", (for example, the Washington Monument or a stadium would count), but I bet nobody cares about m³/ha. Do they make FAR that adjusts for the percent of block covered by non-private parts of the block (i.e. streets, parks and sidewalks)? Sagittarian Milky Way (talk) 11:24, 7 October 2009 (UTC)
 * The US might be the only country that uses FAR. 78.147.129.9 (talk) 15:08, 7 October 2009 (UTC)

Are there any species with multiple hearts?
Organ redundancy seems like a good thing (I'm glad I have two lungs and two kidneys) and an extra heart (if it were in parallel with the first) would take a huge load off of a single heart over a lifetime.20.137.18.50 (talk) 12:53, 7 October 2009 (UTC)
 * Well, Time Lords have two hearts (one for casual, one for best), but they're fictional. Pais (talk) 13:01, 7 October 2009 (UTC)
 * I looked in Heart and it seems to be mostly about the human heart. I think there are other types of creatures (maybe insects or sea-going creatures) that have multiple hearts. I can think of plenty of organs it would seem useful to have two of. Although the second brain in the stegosaurus didn't help much when it came time for extinction. →Baseball Bugs What's up, Doc? carrots 13:03, 7 October 2009 (UTC)
 * I knew I had seen this somewhere recently. The octopus (which is a cephalopod - see below) has three hearts. I guess the two skinny ones balance out the fat one. →Baseball Bugs What's up, Doc? carrots 13:05, 7 October 2009 (UTC)
 * Note: Dinosaurs did not actually have two brains. That's since been debunked. Says so right in the article. APL (talk) 02:35, 8 October 2009 (UTC)
 * Earthworms vary somewhat by species, but typical examples have five hearts / aortic arches (depending on how specific you want to get with terminology). &mdash; Lomn 13:09, 7 October 2009 (UTC)


 * (several ec's) Earthworms and Cephalopods have more than one. Here's an interesting discussion from howstuffworks.com. Zain Ebrahim (talk) 13:11, 7 October 2009 (UTC)
 * I just found Abby and Brittany Hensel, two humans who share a single circulatory system with two hearts!20.137.18.50 (talk) 13:27, 7 October 2009 (UTC)
 * Two humans with two hearts in total. Ironically, they are the real Minnesota Twins. →Baseball Bugs What's up, Doc? carrots 13:30, 7 October

2009 (UTC)

Animals with multiple "hearts" usually have less ambitious hearts compared to the mammalian / bird 4-chambered heart. The squid heart has one type of heart for pumping hemolymph through the circulatory system and one type of heart for pumping hemolymph through the gills -- plus as a mollusk the squid's predecessors had an open circulatory system.
 * Crocodilians also have 4 chambered hearts. And the 4 chambered heart is actually two 2 chambered hearts -- they are just fused and result in more efficacy -- the squid's dual hearts are thus similar to our single one.  DRosenbach  ( Talk 23:54, 8 October 2009 (UTC)

There probably wasn't an evolutionary pressure to evolve more than one mammalian heart, because the "strain" usually kicks in around old age, and evolution is notoriously cruel towards the elderly. John Riemann Soong (talk) 13:49, 8 October 2009 (UTC)

Eating raw flour
When I was a kid, my mother tried to dissuade me from eating too much raw cookie dough or raw cake batter out of the mixing bowl by telling me that eating too much raw flour was "bad for you". Is this actually true in any sense, or is just a cautionary tale. (Obviously "too much" is open to interpretation, but the implication was that raw flour was "bad for you" in quantities that baked/cooked flour wouldn't be.) Pais (talk) 12:55, 7 October 2009 (UTC)
 * Did you suffer any ill effects from it? Other than weight gain? Keep in mind that the paste used by kiddies is (or used to be) largely flour and water, in case the little idiots tried to eat it. →Baseball Bugs What's up, Doc? carrots 13:00, 7 October 2009 (UTC)


 * Usually they tell you not to eat raw cookie dough because of the raw eggs.
 * Certainly it can't be too bad for you. Cookie dough ice-cream is a popular and delicious flavor. (Even if it does sometimes come with warnings about uncooked eggs. Salmonella is probably delicious too.) APL (talk) 13:02, 7 October 2009 (UTC)
 * Most commercial cookie dough ice creams are using a dough-like substitute. It generally lacks the leavening and omits the raw egg (substituting either pasteurized eggs or some less food-like substance). &mdash; Lomn 13:07, 7 October 2009 (UTC)
 * Sure, but there's about a zillion local ice cream shops that make their own ice-cream, and put warnings on their cookie dough ice-cream. APL (talk) 13:20, 7 October 2009 (UTC)
 * Very true. I just wanted to note that, if someone is really concerned about the possibility of salmonella, there are safe forms of cookie dough ice cream.  Myself, I like the hard stuff, risk be damned. &mdash; Lomn 13:54, 7 October 2009 (UTC)


 * The usual danger reported from raw cookie dough, cake batter, and the like is the possibility of salmonella from raw eggs. Raw flour is just floury and pasty, in my experience.  Our article notes that it has the potential to go rancid (depending on how it was processed), but that's going to be nasty whether you cook it or not. &mdash; Lomn 13:03, 7 October 2009 (UTC)
 * Well, as a follow-up, it appears the FDA has reported salmonella in flour in some cases. I don't think it's nearly as likely as it being in eggs, but it's a possibility. &mdash; Lomn 13:07, 7 October 2009 (UTC)
 * Well, I never suffered any noticeable ill effects from it, but then I never actually succeeded in eating much raw batter or dough because she was preventing me from doing so. Now as an adult I will sometimes mix up a batch of cookies and polish off about half of it before baking, also with no ill effects. (Salmonella doesn't scare me - what doesn't kill us makes us stronger.) But what does occur to me is that I can't think of any recipes where flour is intended to be eaten raw (apart perhaps from cookie dough ice cream) - every recipe I can think of that calls for flour, expects the flour to be either baked or otherwise cooked (e.g. in gravies and roux). Pais (talk) 13:09, 7 October 2009 (UTC)
 * "What doesn't kill us makes us stronger"—it doesn't really apply in terms of food poisoning, which is awful and worth avoiding if you can. It doesn't make you stronger, it just makes you feel utterly and totally miserable. --Mr.98 (talk) 13:42, 7 October 2009 (UTC)
 * Actually in general terms it's a cliche that is often wrong. For example getting a sunburn may not kill you. At least not initially. Smoking a few cigarettes ditto. Or since we're talking about food, drinking/eating 300ml of cream each day, particularly if you are young and lead an active life. None of these however are particularly healthy activities and most probably are not going to make you stronger. Exposing the immune system to potential pathogens may be of some benefit but it's not always going to make you stronger and there are other things to consider. A number of the toxins you are exposed to by poor food will have negative effects including potentially carcinogenic effects. (Of course many of the toxins won't be destroyed by cooking so if they are present it may not make much difference if you cook the dough first.) This doesn't mean you shouldn't be worried about every single little thing. In fact I often eat things which are a bit dubious. However I don't do it under the belief that it's definitely going to make me stronger. Rather I've decided to accept the risk of potential both short term and long term harm. In other words, I don't think the risks from uncooked flour are really something to worry about but I definitely wouldn't assume it's going to make you stronger. Nil Einne (talk) 14:00, 7 October 2009 (UTC)
 * I wasn't actually being serious about "What doesn't kill us makes us stronger" with respect to salmonella poisoning. Pais (talk) 14:25, 7 October 2009 (UTC)
 * I also recall reading on our chicken egg article that only 1 in 30,000 eggs are contaminated, and according to Salmonella article, 30 deaths resulted from the 142,000 people who got infected, I think I can handle the 1 in 71,000,000 chance of dying each time I eat raw cookie dough. It compares very favorably to the 1 in 2,560,000 chance of dying in a car accident on a typical day.  Googlemeister (talk) 14:13, 7 October 2009 (UTC)
 * I do actually agree that the salmonella threat is extremely exaggerated, with "appears in the health section of the New York Times" type odds (anything that shows up there, you have a better chance of winning the lottery than contracting). I'm just saying, it doesn't really make you stronger. It just sucks! --98.217.71.237 (talk) 15:03, 7 October 2009 (UTC)
 * The odds are probably better than that for a healthy adult, too, since obviously an affront to the system like food poisoning will disproportionately kill those who are already compromised in some way. I'd be interested to know how many of those 30 people were otherwise healthy adults, and unsurprised if the answer was "none". --Sean 17:04, 7 October 2009 (UTC)
 * I think the problem is the raising agent. Cookies are usually made with some sort of raising agent, such as baking powder, cream of tartar, bicarbonate of soda, and the chemical reaction which makes the cakes rise should be occurring in the oven - not in your gut! That could give you some real pain, especially if you're a kid. --TammyMoet (talk) 17:08, 7 October 2009 (UTC)

Your mother was dissuading you from getting too big for your britches, that's all. Vranak (talk) 18:36, 7 October 2009 (UTC)
 * Aren't there people who eat raw egss because they think it's healty? Ala rocky balboa? . Vespine (talk) 00:08, 8 October 2009 (UTC)
 * I have witnessed such a thing. Vranak (talk) 00:15, 8 October 2009 (UTC)

I love raw cookie dough while I'm eating it, but later my stomach gets upset if I've eaten too much. So, maybe it's not much more unhealthy than the baked cookies, but it can make you feel bad. ike9898 (talk) 13:42, 8 October 2009 (UTC)
 * If you try eating raw bread dough, don't eat much of it, because it rises a lot more then cookie dough and can be extremely uncomfortable. Googlemeister (talk) 14:26, 8 October 2009 (UTC)

the fluorescent light tube
Could someone explain ( I might be in the wrong section ) when say a fluorescent tube rated at 65w or one rated at 80w.... when lit, the consumption of electricity to it if checked with a monitor is always higher than the tube is rated at ? where as with an ordinary 100w standard incandescent bulb the consumption does show as 100w

Regards  George Atkinson  —Preceding unsigned comment added by 86.145.161.70 (talk) 14:13, 7 October 2009 (UTC)


 * Is the monitor or power meter recently lab calibrated? How accurate does the manufacturer specify it to be? IDoes it indicate watts or are you working from amps and volts, with an unknown power factor and irregular waveform? Is the voltage the nominal voltage, and is the input power free from harmonics? Edison (talk) 17:21, 7 October 2009 (UTC)
 * Most voltmeters and ammeters when measuring AC actually respond to the average rectified voltage or current but are calibrated to show an RMS value. The calibration is only correct for sine waves and a power measurement using these instruments to find V x I is only correct if V and I have the same phase. These conditions are met if the load has a Power factor of 1.0. Filament lamps have a power factor of 1.0 but flourescent lamp ballasts often have a power factor below 1.0. A Wattmeter that measures true power into a loads of various power factors is a specialised instrument. Cuddlyable3 (talk) 19:19, 7 October 2009 (UTC)


 * How much higher is it? --Tango (talk) 19:34, 7 October 2009 (UTC)
 * quotes a power factor 0.6 for presumably an ordinary fluorescent light. The low PF of an inductive ballast may be raised by an added capacitor. Cuddlyable3 (talk) 10:10, 8 October 2009 (UTC)
 * Many/most ballasts sold now are electronic. The current waveform is quite nonsinusoidal. Edison (talk) 18:42, 8 October 2009 (UTC)

moving in space
If you put the space shuttle at the L1 point, would the solar winds be sufficient to make it move back towards earth? How close to the sun would you need to be most likely to have an equilibrium where it would not move because the extra gravity from the sun would be balanced by the solar wind? Googlemeister (talk) 14:23, 7 October 2009 (UTC)
 * Since the non-trojan Lagrange points (that is, L1-L3) are unstable, something will disturb the shuttle. I'd bet that orbital irregularities or the Moon or Venus would do it before the solar wind would, but the solar wind is a good candidate.  As for how far you'd have to offset... estimate the force of the solar wind, throw in the surface area of the shuttle and the distances to the L1 point and you've got a fairly simple system of equations.  Estimating the force of the solar wind looks to be the trickiest part, as it's highly variable and has both slow and fast components. &mdash; Lomn 15:16, 7 October 2009 (UTC)
 * The solar wind isn't constant, so it's impossible to compensate for it that easily. You need active stationkeeping to stay at L1. You can stay in a bounded, but non-periodic "orbit" of L1 for quite a while (maybe months, I'm not quite sure), though - that is, you roughly circle the point but don't repeat the exact same path each time, but you always stay fairly close to the point. --Tango (talk) 15:55, 7 October 2009 (UTC)
 * Which is called a Lissajous orbit. Sagittarian Milky Way (talk) 22:43, 8 October 2009 (UTC)

electrolytes
The Wikipedia electrolyte article references a Webmd article that gives:


 * 1 quart (950 mL) water
 * ½ teaspoon (2.5 g) baking soda
 * ½ teaspoon (2.5 g) table salt
 * ¼ teaspoon (1.25 g) salt substitute (potassium-based), such as Lite Salt or Morton Salt Substitute
 * 2 tablespoons (30 g) sugar

The problem is that Morton produces another salt substitute with no sodium and twice the potassium. The question is which substitute is actually right. What is the proper proportion of sodium and potassium and what about phosphorus and magnesium? Through which ingredients can one add them and in what proportion? 71.100.5.245 (talk) 21:13, 7 October 2009 (UTC)

Your question is a little too broad, you ask which substitute is right, but right for what? In order to answer your question, I'll assume you are asking which is closest to human plasma. This is an important question to ask because the fluid in the veins, the fluid in cells, and the fluid in between the cells all have completely different amounts of electrolytes in them. Also, it doesn't really matter that you replace fluid exactly right as long as you get close. Why? Humans have these wonderful things called kidneys, which tend to figure out electrolyte imbalances with far more grace than we can, but I digress. The formula above contains sugar, which is actually not an electrolyte, and will not contribute to the tonicity of the solution after it enters the intravascular space, so we will concentrate on water, sodium, potassium, chloride, bicarbonate, calcium, and magnesium, the most important constituents. Sodium is generally around 140mmol/L, potassium is about 4.3mmol/L, calcium is 2.5mmol/L, chloride is 100mmol/L, bicarb is 25 mmol/L, and phosphate is 1mmol/L. I'm sorry to give you such units, but I'll let someone else calculate that out.

You might be interested to know that it is very rarely necessary to give electrolyte in such exacting fashion. As far as I know, there are no commercially available solutions in the US (for consumers or hospitals) of either oral or intravenous fluid, that have a perfect balance. If the kidneys can't sort it out, we can always add each individual constituent alone to correct abnormalities. In the medical profession, the fluids one gives to a patient depend more on a doctor's specialty training than anything else. The closest stock solution we have is lactated ringer's, but I hear they have some fancier stuff in Europe. Tuckerekcut (talk) 00:28, 8 October 2009 (UTC)
 * Right means avoiding either extreme...


 * from lliams, Stanish, and Micheli. New :York: Oxford University Press, pp. 97-113.
 * (see Electrolyte_imbalance)


 * Another Electrolyte Chart


 * From Maughan and Shirreffs, 1998. Fluid and electrolyte loss and replacement in exercise. In :Oxford textbook of sports medicine, 2nd Edition. 71.100.5.245 (talk) 02:33, 8 October 2009 (UTC)
 * So assuming we need only consider extracellular values (that sweat and intracellular values are automatic) what then are the sources and intake or extracellular values for phosphorus and magnesium in grams per liter? 71.100.5.245 (talk) 02:48, 8 October 2009 (UTC)

Well, the RDA of Mg is 6mg/kg/day for an adult. The plasma value should be about 2mmol/L, expressed in grams/liter this would be about 50mg/L. When we give Mg in TPN, usually we use 10mEq/day (which is 5mmol/day). Phosphorus is given in the form of phosphate, the RDA is 700mg, and the plasma level should be about 1mmolar. This corresponds to about 100mg/L. TPN calls for 15mmol/day of PO4. This is an order form for TPN I found on the internet, seems legit enough. It may answer some of your questions as to how much patient's get when they are completely nutritionally dependent. Tuckerekcut —Preceding unsigned comment added by 146.189.236.79 (talk) 19:36, 8 October 2009 (UTC)

"Living wall" vertical planting using felt?
Hi all,

I am thinking about how to construct a "living wall" or "Green wall." I've seen some sources say, without using too much detail, that one can use a layer of felt stapled against a layer of plastic.

Would felt be a good medium for plants to grow through? I'm guessing the plants are just pushing through the felt and their roots are pushed between the felt and the plastic? Has anyone heard of doing anything like this?

Thanks! &mdash; Sam 63.138.152.238 (talk) 21:16, 7 October 2009 (UTC)


 * I was under impression that green wall is made with plastic containers attached to the wall. With felt, I would be really concerned about it deteriorating and falling off under the weight of the growing plants. Also, mold will proliferate, and rotting felt will smell; which is probably not what you want. There may be green-wall DIY manuals on the web someplace; you should probably search for those. --Dr Dima (talk) 22:11, 7 October 2009 (UTC)


 * Fresh willow sticks can be woven together to make a fence and they will sprout leaves and grow. 78.146.183.133 (talk) 23:06, 7 October 2009 (UTC)


 * This looks like a good place to start reading. SteveBaker (talk) 02:25, 8 October 2009 (UTC)

Cooling pop
What would cool down faster? A two liter bottle of pop that came straight from the store and is then put into the fridge and is therefore still pressurized or a bottle that has had the top off, put back on, and then put into the fridge? Dismas |(talk) 22:35, 7 October 2009 (UTC)
 * I'm not smart, but my assumption is that the less stuff you have, the faster you can change its temperature. "Depressurizing" is another way of saying "letting stuff out", so I assume you can cool it faster when there's less stuff in there.  All else being equal, of course.  --Sean 22:41, 7 October 2009 (UTC)


 * All other things would have to be amazingly equal! The mass of that tiny volume of CO2 you'd release would be truly negligable compared to about 2kg of soda.  I'd want to know what effect the pressure and dissolved CO2 would have on thermal capacity and conductivity - those could potentially have a much bigger effect.  I don't know what the answer is though! SteveBaker (talk) 02:21, 8 October 2009 (UTC)


 * Isn't there like an associated temperature drop with the pressure release? What's that process called? You know in the same way a gas bottle gets cold after it releases some gas. Also probably quite a small effect but maybe more significant then the mass reduction. Vespine (talk) 03:56, 8 October 2009 (UTC)
 * I just realised that will happen regardless whether you open the bottle before or after you put it in the fridge so shouldn't have an effect on the outcome. Vespine (talk) 03:58, 8 October 2009 (UTC)


 * Well, when the top is opened and the CO2 comes out of the soda, the temperature does drop, due mostly to adiabatic cooling; that is since you cannot get something for nothing, the decrease in pressure does work, and the energy for that work comes from a drop in temperature. So the depressurized soda will cool down faster, but only because the depressurization process itself causes a drop in temperature, so that bottle gets a "head start".  The effect will only matter if you do it immediately before putting it in the fridge, and even then it will be a small effect; the depressurized soda will reach equilibrium with the fridge a few minutes ahead of the sealed bottle, so its not enough to make much of a difference at all. -- Jayron  32  04:44, 8 October 2009 (UTC)
 * But heat conduction is proportional to the difference in temperatures, so it would contribute toward slower cooling if a temperature drop due to pressure release occurred before putting it in the fridge instead of after. On the other hand, there'd also be a contribution in the opposite direction, due to the pressure release being smaller if it occurs when the soda is cooler.


 * It's a complicated question, with lots of tiny effects. I don't know which effect would dominate, or even which direction some of the effects go in.  And unfortunately I don't think the question can be resolved with a simple kitchen experiment, since I think the difference would be too small to measure reliably, without high precision lab equipment.  Red Act (talk) 04:57, 8 October 2009 (UTC)


 * It would cool more slowly, but I think that what Jayron is saying is that it would reach a specified cooler temperature sooner. Awickert (talk) 05:06, 8 October 2009 (UTC)


 * It also depends on when you start the clock. If bottle A and bottle B are both at 25 deg C, and you are cooling them both to 5 deg C, then you need to define when the clock is started to say which is faster.  If we start the clock before bottle A is opened, then bottle A cools faster since it gets from 25 deg C to 5 deg C before bottle B does.  However, if you are measuring the instantaneous rate of cooling (the differential cooling) at any point along the way after you put them in the fridge, then B will be cooling faster at most points along the way.  That's because A does more of its cooling in a big burst at the beginning, so differentially, it cools slower the rest of the way.  But saying it cools faster, when measuring the average rate of cooling from 25-5 deg C is perfectly accurate.  There is just a difference between avereage rate and instantaneous rate and most people will understand this problem to be looking at the former, and not the latter, given the wording of the OP's question.  -- Jayron  32  05:15, 8 October 2009 (UTC)
 * Yeah, you're right. I was partially responding to Vespine's comment about "whether you open the bottle before or after you put it in the fridge".  However, the OP doesn't say anything about opening the bottle after it's been in the fridge, so presumably the temperature is to be measured immediately upon removal from the fridge, without (re)opening the bottle in either case.
 * However, we still don't know what the answer to the question should be, since whatever effects the loss of a little CO2 has on the soda's specific heat capacity and thermal conductivity have not yet been addressed. There's more going on here than simply adiabatic cooling of an ideal gas.  That may well be the dominant effect, but I wouldn't take that for granted.  Red Act (talk) 06:12, 8 October 2009 (UTC)
 * I think the best way to answer this question is empirically. It's not hard after all. While not of direct relevance, the Mpemba effect illustrates that this is the sort of thing where you have to be careful answering purely theoretically. Ultimately there are enough variables that it may just vary from repetition to repetition. Nil Einne (talk) 12:15, 9 October 2009 (UTC)


 * If yo can precool several litres of a freezing solution or glycol in water say to -18 degrees, you can dip your softdrink bottle in and get a much quicker cool than a fridge.  Doing it below zero should make it quicker than using ice water. Graeme Bartlett (talk) 11:21, 8 October 2009 (UTC)


 * Yes, but if cooling curves display significant non-linear or chaotic behavior, than the difference between a slow cooling in a 4 deg C fridge in air and a rapid cooling in a -18 deg C liquid could result in wildly different cooling curves, which would not be directly applicable to the fridge situation. If you really want to do the experiment, buy a few dozen identical bottles of the same soda, and run the experiment yourself.  The tricky issue would be measuring the temperature of the sealed soda inside the bottle which is supposed to remain unopened.  However, a contact thermocouple which is insulated from the fridge air, and in contact with the bottles, should do reasonably well.  -- Jayron  32  23:02, 9 October 2009 (UTC)
 * Releasing 1 liter of gas from the soda against a pressure of 1 bar requires 100J of energy. If 100% of that energy goes toward cooling the soda, and if the specific heat capacity of soda is about the same as that of water (4.1813 J/(g·K)), then the 2kg of soda will be cooled by only 0.012°C. Doing an experiment involving temperature differences that small would require not only a high-precision temperature sensor, but also a fridge that maintains a constant temperature much more precisely than a normal kitchen fridge does.  Red Act (talk) 00:38, 10 October 2009 (UTC)