Wikipedia:Reference desk/Archives/Science/2007 December 19

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December 19

atmosphere and technical atmosphere

hey Just wondering if when they are talking about atmospheres of pressure in papers on air flow [vortices etc] are they talking about a regular atmosphere [14.7 pounds per square inch] or a technical atmosphere [14.02 pounds per square inch] ?

Also a stupid one, if a shockwave of 10 psi can destroy a building, how come a steel container can withstand something like 100 kpsi?

Thanks —Preceding unsigned comment added by 80.6.37.199 (talk) 01:01, 19 December 2007 (UTC)

On your second question:

• design: the building was not designed for this, but the steel tank was.
• square-cube law: The building is much bigger. bigger means different: an ant, scale dup to the size of a man, would collapse under its own weight.
• Static versus dynamic: The tank handles a static load, A shockwave has a very high rate of change. This is the difference between being punched and being shoved. Shoot an armor-piercing round at the tank: the tank will fail at far less than 100Kpsi.
• Tension versus compression: the tank is carefully designed to withstand pressure from within. Evacuate the tank and place it in an a 100Kpsi environmant, and it will be crushed.

-Arch dude (talk) 01:39, 19 December 2007 (UTC)

Arch's other points are clearly correct, but the one about dynamic pressure needs going into. You feel a difference between a punch and a shove because (A) with a shove you have more time to set up your muscles, and (B) a fast-moving fist is rapidly decelerated by contact with your body, which requires considerable force, and you feel the equal and opposite reaction; a shove does not involve a similar deceleration. Reason A is clearly irrelevant to the case of a shock wave. As to reason B, I don't know. Does the interaction of a shock wave with a fixed obstacle cause a greater pressure to build up against the obstacle? If not, I would not expect the armor-piercing round to penetrate the 100Kpsi-capable tank "at far less than 100Kpsi" if fired from inside it. --Anonymous, 03:33 UTC, December 19, 2007.

I have a different take on this - we're not told that the steel container is sealed in any way - or what size it is relative to the building - I don't know where ANYONE got the idea that it's a tank - the OP didn't say anything about that. So I don't buy any of Arch's points - nor any of Anonymous's points either. Let's consider something like a steel shipping container - and a small building made of brick or concrete of similar dimensions. My belief is that buildings are primarily built to survive compressive loads - their own weight, the weight of the things inside them - with little concern over pressure (which tries to stretches the surfaces by pushing them inwards - requiring tensile strength). Things like bricks, glass and concrete are great at handling compressive loads - but apply a tensile (stretching) load and they come apart really easily. Steel, however, is excellent at handling tensile loads - we make steel cables for example. So for two identically-sized and shaped structures - one made out of steel and the other out of brick, I'd put my money on the steel one in this kind of situation. Notice that a brick wall can comfortably support the weight of a 5 storey building - but you can easily knock it down by whacking it face-on with a sledge-hammer. You can whack away at a shipping container all day with a sledge hammer - and all you're going to do is make some dents - you won't be able to destroy it. SteveBaker (talk) 17:12, 19 December 2007 (UTC)

I assumed a scuba tank because the original question said "something like 100kpsi." That's a lot of pressure -- more than 5,000 atmospheres. -Arch dude (talk) 19:40, 19 December 2007 (UTC)

art therapy murals with hiv/aids patients

Who are the leading practioners and theorists in the use of art therapy? Who are the same in regards to HIV/AIDS patients?Voyage17 (talk) 04:38, 19 December 2007 (UTC)voyage17

The art therapy article may be of use. MrRedact (talk) 05:54, 19 December 2007 (UTC)

Anomalous expansion

Why does water expand anomalously when teperature isbrought down from 4 deg celsius to 0 deg celsius. —Preceding unsigned comment added by 218.248.2.51 (talk) 07:00, 19 December 2007 (UTC)

It's to do with the molecular structure and the nature of the hydrogen bonding. See Density of water and ice. --jjron (talk) 07:07, 19 December 2007 (UTC)

Right. The reason ice is less dense than liquid water is due to the hollows in its crystal structure, which is held together by hydrogen bonds. As the temperature gets close to the freezing point, the molecules start bonding together into little groups that are "trying" to grow into crystals, but it's not quite cold enough for that to happen. As it is, they still start to take up more space. Also see Dipolar nature of water in the same article. --Anonymous, 07:11 UTC, December 19, 2007.

liquid and air

in a water container which contains one litre of water, what is the concentration of air that is mixed with water. ther will be some air at the top of the water. but does the water contains air inside it? 59.92.22.117 (talk) 08:18, 19 December 2007 (UTC)

taking of sparcling water it would be several liters of CO₂. For natural water it depends if it was heated before botteling, but the solubility of N₂ and O₂ at given temperature should be in the literature. I have a look.--Stone (talk) 08:24, 19 December 2007 (UTC)

N₂ 2.33 cm³ cold water 1.42 cm³ hotwater

O₂ 4.89 cm³ cold water 2.46 cm³ hotwater

Stone (talk) 08:29, 19 December 2007 (UTC)

Yes, some air dissolves into water. That's how fish manage to breathe underwater. As fish use up the oxygen - splashing and wave action cause more air to be dissolved from the surface replenishing the supply. In a home aquarium, a single goldfish can live in a bowl and get enough oxygen from air dissolving into the water from the surface - but if you want to keep dozens of fish, you need a pump that blows bubbles up from the bottom of the tank to ensure that more air gets dissolved into the water as the fish use it up. You can show this in a little experiment: If you put an open pan of water onto the stove with a thermometer in it - and increase the temperature really slowly - but never letting it reach 100 degrees centigrade, you can see bubbles start to form just before the water gets hot enough to boil - these bubbles are the dissolved air coming out of solution. As you can see from Stone's numbers, hot water can't hold as much air in solution as cold water - so as you heat it up the air comes out as bubbles. SteveBaker (talk) 13:20, 19 December 2007 (UTC)

Think sodas. That air at the top of the bottle is filled with CO2. The soda itself is also filled with CO2. The amount of CO2 increased by increasing the pressure of the gas. Shake the bottle, you will cause CO2 to air out of soda but since CO2 will be trapped inside the bottle, the pressure will increase. If you leave the bottle along for a while, the soda will reasorbe the CO2 again. This applies for any liquid and gas. NYCDA (talk) 19:56, 19 December 2007 (UTC)

It may help you to learn about the common water quality parameter, Dissolved Oxygen (DO). There's a lot of information on the internet about it. Typical water quality standards in North America require watershed managers to try and keep DO above 7 mg/L, or 7 ppm, in streams and rivers, any less and many fish species can't survive. Generally natural water bodies range from 7-10 mg/L. Oshkosk 11:08, 26 December 2007 (EST)

Species

note: this is not a homework question, but a question of my own I though up when doing my homework

If two different animals (for the sake of argument lets say a mouse-like creature) evolved from two different ancestors are were isolated from each other in that the two species never met, but the conditions of their two different environments were exactly identical, and they therefor over thousands / millions of years evolved to have identical physical appearance, would they be able to mate if they did come into contact with each other and would they produce fertile offspring? Weasly (talk) 11:56, 19 December 2007 (UTC)

I'm not a biologist, but I'll give it a shot. First of all, the phenomenon of unrelated species evolving similar features due to their similar environment is called convergent evolution, just in case you're not familiar with that term. To answer your question, in order to mate, two animals will have to have a very similar layout of chromosomes. But there's no reason to expect that two different species with similar features will have a chromosome layout that is at all similar. They might both develop a dorsal fin, but the dorsal fin gene for Species A might be on Chromosome 5, and for Species B it might be on Chromosome 11. There's nothing about the environment that's going to "drive" the physical properties to have their genes in the same place on the same chromosomes. The two species may even have a completely different number of chromosomes. If the chromosomes don't match up, they're not going to mate successfully. -- Coneslayer (talk) 12:19, 19 December 2007 (UTC)

Or, put more succinctly: looking and acting in an "identical" fashion just means they have a similar phenotype. It does not mean they have a compatible genotype. It would be an incredible, unbelievable, impossible coincidence for two organisms which had very different genetic ancestors to somehow evolve a compatible genetic code, even if they superficially look similar. --24.147.86.187 (talk) 12:32, 19 December 2007 (UTC)

Yes - I agree. One point for the questioner though - if you went back far enough up the evolutionary tree, you'd eventually come to a point where both animals have descended from a single ancestor. However, we're presuming that point was long enough ago that there are some really significant differences between your two starting-point species. Given that...no, it's not likely that the creatures would be able to inter-breed. However, even with convergent evolution, the converged species rarely look that identical - as our article convergent evolution shows - the hummingbird and the hummingbird-moth are considered to be an example of convergent evolution between a bird and an insect...but that doesn't mean that hummingbird-moths have only two legs or that hummingbirds go through the catapillar/pupae phase of development! They've converged into exploiting the same niche - and the adaptations necessary to do that have converged - but the parts of their life-cycles that don't relate directly to feeding from nectar-laden flowers have not converged at all - nor are they likely to in the future. SteveBaker (talk) 13:10, 19 December 2007 (UTC)

I believe the problem with this question is, it assumes that two animals separated from each other over millions of years will some how not diverge from each other. I find this to be unlikely, unless there was significant gene flow, but of course, then they wouldn't be segregated. If you separate two animals for a significant period of time, even in similar enviroments, and they survive over millions of years, they will inevitably diverge. 64.236.121.129 (talk) 14:56, 19 December 2007 (UTC)

To expand on this, there are other factors that determine evolution besides enviroment. You have to take into account the food supplies too. Competition for food, and predators. Even if the other enviroment is identical, the food supplies and the predators, certainly will not be. Natural selection is influenced from the outside remember. Take the oceans for example. The enviroment is... well water. But living beings can evolve differently because of those other factors. 64.236.121.129 (talk) 15:05, 19 December 2007 (UTC)

64, you're talking about divergent evolution, while the rest of us are talking about convergent evolution. Also, most people use the term "environment" to include the other organisms living in it. —Steve Summit (talk) 15:10, 19 December 2007 (UTC)

I'm answering the original question, not expanding on the other user's answers. And yes, some do, but there aren't too many places on earth that have both similar enviroment, in terms of geology, climate, etc, and similar flora and fauna. Inevitably, two animals separated which are able to survive for millions of years, will diverge due to numerous circumstances, specific to their enviroments. 64.236.121.129 (talk) 15:19, 19 December 2007 (UTC)

Evolution are caused by mutations. Helpful ones survive and are carried to future generations. Harmful ones dies out. Environment plays a factor in determining which ones would be helpful ones but it cannot cause any particular mutation to take place. Environment nudges evolution in a general direction but it can't force it. If you evolved a dog and a cat for millions of generations, they may be able to mate if they ended up compitable which is extremely unlikly. Today hourse and donkey can mate, (they give birth to mules which can't mate with either horse nor donkey nor other mules) but after millions of generations, it's unlikly they will still be able to. NYCDA (talk) 20:11, 19 December 2007 (UTC)

Bibliographic database

Hello, I am looking for a free online bibliographic database of scientific peer-reviewed articles, preferably full-text. I am using Google scholar at the moment but I would really like an alternative. My specific interest is in water-related environmental problems. Thank you in advance. Espole (talk) 11:57, 19 December 2007 (UTC)

I would suggest starting with this similar question from earlier this month. It got a pretty thorough answer, although I'm not sure how much applies to your specific field of interest. -- Coneslayer (talk) 12:24, 19 December 2007 (UTC)

Thank you so much for your very fast response. I probably should have found that question + answer myself, somehow. But you're right, the specific databases mentioned do not really apply to environmental/water related subjects. So it's back to google scholar for now. Espole (talk) 13:02, 19 December 2007 (UTC)

Once questions fall off this page and go into the archives, they're not really easy to find—I just remembered reading it recently, so I was able to track it down. Someone may still come along with a suggestion that's more specific to your subjects. -- Coneslayer (talk) 13:05, 19 December 2007 (UTC)

Well, it's not quite what you're looking for, but the EPA has some information about water quality in each of the individual states in the United States here. You could also try downloading some of the relevant Planet Earth articles from here as a starting point, and use the references and author names to track down the actual journal articles they're based on. Hope that helps! -- HiEv 14:38, 19 December 2007 (UTC)

Hi, I'm the one who wrote the response to that question that Coneslayer referenced. From what you're describing as your subject (water-related environmental problems), I would say that you have a couple of possibilities:

1) Use Agricola - the freely available online journal index of the holdings of the United States National Agricultural Library in Washington, D.C. They ought to have some stuff on your subject. Keep in mind that "agriculture" is not just about farming - it includes stuff on the environment and water resources, too.

2) There's a "family" of databases that includes some that will probably be very useful to your search called Cambridge Scientific Abstracts or, "CSA" for short. This is NOT a free online database, but it is quite common for research libraries to carry CSA - especially if the library is connected to a university that offers degrees in agriculture or engineering. If you're in the U.S., a Land-grant university would almost be guaranteed to subscribe to CSA. To see whether a library carries CSA go to its web page and look for some link that will provide you with their electronic resources or databases (different libraries call it different things), or just give the reference librarian a call. If you are affiliated with a library that offers these databases you might be able to contact the reference staff and see if it is possible for you to access these databases remotely via your home or office computer. Otherwise, if you find a library that subscribes to CSA (and if the library allows the public to use its facilities - some libraries restrict access to their own patrons), then you may have to physically go to the library and access CSA through its computer terminals in person. Some of the databases that CSA carries that could help you in your search are:
- Biological Sciences, covering Biomedicine, biotechnology, zoology and ecology from 1982-Current
- Biology Digest, covering Life sciences, evolution, genetics, behavioral science from 1989-Current
- BioOne Abstracts and Indexes, covering Biological, ecological and environmental sciences, and offering full-text articles, from 1998-Current
- EIS: Digests of Environmental Impact Statements, covering exactly what it says it does, from 1985-Current
- Environmental Sciences and Pollution Mgmt, covering Environmental biotechnology, engineering, pollution from 1967-Current

There are other databases that could be helpful, too, but these are a good start. Hope this helps. -- Saukkomies 10:38, 19 December, 2007 (UTC)

Genetics Question - Naturally multicoloured hair (Eg brown and blond)

I was just wondering how this work genetically. While the majority of my hair is brown, near the front of my head (Above my eyes) my hair is somewhat blondish. With what little understanding i have of genetics i thought this was quiet impossible or at least rare. My hair was also somewhat lighter when i was a child. Cheers, Kingpomba (talk) 16:18, 19 December 2007 (UTC)

Uneven production of Melanin. 64.236.121.129 (talk) 16:24, 19 December 2007 (UTC)

Could it be sun bleaching ? In that case, I believe UV in sunlight destroys the pigment in some of the hair. I had that when I was young. StuRat (talk) 17:15, 19 December 2007 (UTC)

There are different possibilities that could explain naturally multi-coloured hair, but the bottom line is that the exact mechanism is not known. Firstly, there is the the non-genetic mechanisms such as sun-bleaching. As StuRat suggests, UV can cause photo-bleaching of melanin. Genetically speaking, we can look at other animals that have spatially variable hair colour (think German Shepherd dogs, for example). In most animals the major genes responsible are MSH, MC1R and ASP.

Here is how it works: MSH is a hormone that binds a receptor on the surface of melanocytes (the cells that produce pigment) called MC1R, causing it to to produce dark pigments (called eumelanin). This eumelanin is then "injected" into hair as it grows, giving darker hair. However there is another gene called ASP (Agouti signalling peptide, named after the agouti which shows a characteristic colour pattern) that makes a protein which can also bind to MC1R. When ASP binds MC1R it causes it to "switch" the cell from making dark eumelanin to yellow/red phaeomelanin. So which version of these three genes an animal has largely determines what colour its hair is (there are other genes that have effects, and new ones are discovered all the time. For example, last month it was found that a defensin gene is important in modifying MC1R signaling in dogs.)

However, this doesn't explain how hair colour varies within an animal. To explain this, we have to consider how an animal can vary the expression of the genes. It turns out that the ASP gene is very complex. The gene contains a number of exons that under go alternative splicing, giving the animal the ability to create a number of different ASP proteins from the same gene. These different ASP proteins have varying potency in switching the melanocyte from making dark to light pigment, so depending on which ASP version is expressed, their hair colour could vary. The final part of the story, as I'm sure you have already worked out, is that the animal has the ability to express different ASP versions in a spatial manner. For example, it may express a really potent ASP on its belly (resulting in light hair) and a really weak ASP on its back (resulting on darker hair). This is how these mice generate their unusual variation in hair colour. Incidentally some animals also are able to vary ASP expression over time, so when they are young they may express a potent ASP and as they grow older they change to a weaker one. Others vary ASP expression seasonally, giving winter and summer coats.

So, you could see how your hair could be explained by differences in expression of alternative ASP transcripts. There is a problem, however. And that is that there is no strong genetic evidence that the human ASP gene plays a significant role in human hair colour. The gene exists in humans and it doesn something, but we can't pin it down to hair colour. For some reason MSH and MC1R seems to account more for variation in human pigmentation. So, we don't know for sure what the mechanism is in humans, but the principle is likely to be the same: spatial regulation of genes that effect human pigmentation, (most likely MSH and/or MC1R).

On a final note, I should say this is a simplified version. Animals actually have a third level of regulation: they can control ASP expression to vary pigmentation within a single hair, giving banded hairs or frosted tips. This permits some of the spectacular hair patterns seen in some mammals. Humans can't do this, which is why any variation in our hair colour is pretty subtle and generalised. Rockpocket 19:41, 19 December 2007 (UTC)

Oak tree type identification

Acorns are small, almost round. What kind of Oak tree is this leaf cluster (front and rear view) from?

Area is South Florida, 20 miles inland from Gulf coast, 200 yards uphill from river. Twig from branch blown off on windy day.

Multimillionaire (talk) 18:10, 19 December 2007 (UTC)

I do not know the "official" term. Here in South Carolina, we call them "Winter Oaks" because they have leaves all year round. In the Fall, all the large leaves fall off in chunks and small leaves come in. Then, in the Spring, the small leaves fall off and large leaves come in. While it is nice to have green trees (other than pines), it is a pain to have leaves falling off the tree practically all year long. -- kainaw™ 18:14, 19 December 2007 (UTC)

That ain't much to go on, but I see nothing to rule out what my redneck friends used to call the live oak (Quercus virginiana) when I lived in Tampa, probably the same tree Kainaw is talking about. The tree itself is bulky, with its first branches practically on the ground. It gets huge. There should be orchids and moss all over it. --Milkbreath (talk) 18:59, 19 December 2007 (UTC)

I was going on the small acorns and the large leaf clusters that are dark green on one side and light green on the other (as well as being a southeastern variety). I know, it isn't much. An example of a very bulky one is the Angel Oak. It has some pictures that show how bulky and low-lying the branches get. -- kainaw™ 20:00, 19 December 2007 (UTC)

red robin

Robins are brown, with an orange breast, at least in the US. I see that in the UK and Australasia, different birds are called robins, but they all seem to have the orange color (from a quick browse at the wikipedia pages, linked from robin). So, my question is why is there a song about a red robin, and a restaurant chain Red Robin and a character in the kids' TV show Peep and the Big Wide World who is red and a robin (she's definitely red, and I'm pretty sure she's a robin)? Ingrid (talk) 18:57, 19 December 2007 (UTC)

I think what you call orange, others might call red (especially a long time ago, as exact meanings of words can shift over time). I haven't looked it up, but I suspect that "orange" is of French origin, and may not have existed in English prior to the Norman invasion. Perhaps "red" was used to describe what we now call orange, prior to that time. -- Coneslayer (talk) 19:00, 19 December 2007 (UTC)

The song is called "When the Red, Red, Robin Comes Bob, Bob, Bobbin' Along". It was written by Harry Woods, the prolific tin-pan-alley songwriter who also wrote "Try a Little Tenderness". I suspect that slight zoological inaccuracies didn't bother him a bit and that he didn't even consider "rufous, rufous robin" or "reddish-orange, reddish-orange robin". They don't "bob", either, if you want to be picky, they strut a few steps and freeze, strut and freeze, head held rigid, like a wind-up toy.

The bird is known in some parts as "robin redbreast" in reference to its color. "Red" is close enough; it's not bright enough a color to be a very good orange, I think. I'd have to guess that the chain is named after the song. As for "Chirp", there are only so many primary colors. It doesn't bother you that the duck is blue? --Milkbreath (talk) 19:34, 19 December 2007 (UTC)

Ever tried rhyming with "orange"? If I was writing a song about a robin, I would use all the artistic license I could muster rather than tackle that. Rockpocket 19:50, 19 December 2007 (UTC)

The US robin and the UK robin are pretty much unrelated. The UK variety is a tiny little bird - and it's chest feathers are much more red than the US robin (which is a relatively large bird with a more orangey chest) - although the photos we have here seem to make them look much more similar in colour than I think they really are. Since (almost certainly) the UK version of the robin was named first - and when British people came to the Americas, saw this new bird with a orangey/red chest and none of the UK kind, just got into the habit of calling these new birds "robins" too. That doesn't change the christmas-card image of a red-chested robin. SteveBaker (talk) 19:53, 19 December 2007 (UTC)

To expand on the topic: While the American Robin is not closely related to the European Robin, it is closely related to the European Blackbird. When my wife and I were in Paris, we were fascinated by the "soot-covered robins" we saw there—the Blackbirds scratched and hopped around just like American Robins, and had essentially the same shape and size, and even the distinctive eye-ring. North American blackbirds, on the other hand, are unrelated to the European Blackbird and the American Robin—they are Icterids. So the American Robin is closer to the European Blackbird than either of them is to the European Robin or the Red-winged Blackbird! —Preceding unsigned comment added by Coneslayer (talk • contribs) 23:31, 19 December 2007 (UTC)

As I recall, the colour we now call "orange" used to be called "red", and was regarde as simply a shade of red. This changed after the introduction of the fruit "orange" - which gave its name to the colour. 23:38, 19 December 2007 (UTC) —Preceding unsigned comment added by DuncanHill (talk • contribs)

The article Orange (word) may help here. DuncanHill (talk) 23:40, 19 December 2007 (UTC)

Famously, in the film Mary Poppins the bird that appears during the song 'A spoonful of sugar' is an American rather than a European robin. AndrewWTaylor (talk) 00:30, 20 December 2007 (UTC)

It's also two male robins making the nest together, a fact I noted on the WP page long ago, but which has been removed to make room for a book-length "synopsis" of the film. Sigh. Matt Deres (talk) 01:57, 21 December 2007 (UTC)

Also, red-haired people are said to have ... well, red hair. But it's not actually red, as in postbox blood red. It's closer to orange, sandy, coppery etc depending on the shade. It's never actually "red". Context usually determines what words mean. -- JackofOz (talk) 01:01, 20 December 2007 (UTC)

The Robin is a member of the Thrush family (scientific name is Turdidae). This family has quite a number of species that are called Robins, mostly within the Genus Turdus. There is, for instance, the Mountain Robin (Turdus plebejus), the American Robin (Turdus migratorius), and the Rufous-backed Robin, (Turdus rufopalliatus), to name a few. Not all of the birds that have the name Robin look like the classic red-breasted Robin in Disney movies. And then to complicate things, there are some Thrushes that look like red-breasted Robins that are not called Robins. In North America it is quite common for people to confuse Thrushes with Robins. The basic rule of thumb is that Robins have redder breasts than Thrushes, whose breasts are sometimes almost orange or yellow. -- Saukkomies 21:07, 19 December 2007 (UTC)

Thanks, everyone. I'm not sure how to reply to someone up above. About Quack, the blue duck, I never gave it a thought. My 5yo asked what kind of bird Chirp was, and they don't say it often, so we were trying to guess. It got us wondering about the whole red robin thing, so I thought I'd ask. I've always wondered about the red hair thing too, but didn't put the two together. Thanks for the education! Ingrid (talk) 02:30, 20 December 2007 (UTC)

In todays "Times" there is a photo of a white breasted robin!--88.110.51.242 (talk) 09:47, 20 December 2007 (UTC)

Evolution in action! Will the improved camoflage of the white robin enable it to better hide (in snowy conditions) from predators and therefore out-perform it's rivals? Will the lack of the red feathers (which are only present in male robins - and therefore part of the whole mating thing) mean that female robins will spurn him - and therefore this genetic change will vanish in a single generation? Only time can tell! (I'm betting on it dying off). SteveBaker (talk) 13:07, 20 December 2007 (UTC)

What is Fd with respect to antibodies?

The Fd fragments are the most central part of the Fab fragments in this figure, the outside peptides are usually known simply as the "Fab light chain". The other papain cleavage product is the Fc fragment.

What is Fd with respect to antibodies? Thanks. --Seans Potato Business 21:07, 19 December 2007 (UTC)

The Fd fragment is the heavy chain portion of the Fab fragments produced by papain digestion of an IgG molecule. Rockpocket 22:21, 19 December 2007 (UTC)

Biggest featureless snowman made by a single person without using machinery?

Hi. Does anyone know the record, if there is one, for the biggest (tallest, heaviest, largest in volume, longest, widest, thickest, etc) featureless snowman made by a single person without using machinery (eg. bulldozers, automatic lifting machines, levers, etc count as machinery; snow shovels, snow ramps, winter gloves and boots, etc, don't count) and without help from other people? I recently created a snowball so big I couldn't push anymore, if you can imagine, then patted thick layers of snow over it to attempt to roundenify, then put some snow on that, and shaped the snow on there into a snowball, then put more snow on that, and shaped it into yet another snowball. I then patted snow around the whole figure, to fill in the gaps in-between the snowballs. Soon after, someone pushed and beheaded my snowman at a 50-degree angle, and the head fell to the ground, which was covered with snow. I tried, without getting help, and without success, to lift the head back on the snowman, but I did get it halfway. So, after another snowstorm, I patted layers of snow on it so that it looks osmewhat like an elongated ovaloid. It now weighs about five times as much as I do. So, I plan to put more snow on that, shape it into a snowball, and put yet more snow on that. The whole thing, which is still just a baseball (bottom snowball of a snowman), is already about 1.5 m by 1.5 m by 1 m. If I succeed in doing so, which by then the snowman would weigh about half a tonne (OMG!), how close would it get to the record, if there is one? Thanks. ~AH1^(TCU) 22:33, 19 December 2007 (UTC)

Guiness World Records, who would probably be the one to have such a record, doesn't appear to list any records for snowmen, or surprisingly, even snow sculptures.[1] You could apply to them to have your creation listed, but at this point it'd be difficult to prove to them that you didn't use any machinery. MrRedact (talk) 02:41, 20 December 2007 (UTC)

I suspect they do have records for scupltures. Bear in mind that the number of records on their website is only a small proportion of the records they have, as they mention when you search and fail [2] Nil Einne (talk) 08:15, 21 December 2007 (UTC)

Time and relativity

I was thinking about the answer that you gave to my previous question sometime last month about speeding/slowing time using movement relative to a television. I'm a little confused about the answers I got, that the effect of motion is sqrt((1+v)/(1-v)). Might I ask again with a different scenario? 40,000 years ago, an alien 20,000 light-years away sat in its spaceship, viewing earth through its super-advanced telescope, and and began to move constatly at .5c. The first image it sees through its telescope is that of earth 60,000 years ago, ie 40,000 YA + 20,000 light-years. 40,000 years later, it has arrived at earth, and is obviously seeing earth in the present (since the time is now and the distance for light to travel is 0). The alien thinks it has watched 60,000 years of earth's history in just 40,000 years, so time appears to have been sped up 1.5x, which is not consistant with the sqrt((1+v)/(1-v)), ie sqrt(3), answer that I got last time. Some clarification, please? 68.18.198.218 (talk) 23:07, 19 December 2007 (UTC)

This is where the slowing time comes in 40000 years have passed on the earth, but not on the spaceship, which has less time elapsed. Graeme Bartlett (talk) 00:56, 20 December 2007 (UTC)

Wait... so the alien thinks its going faster than .5c, since it just traveled 20,000 light years in less than 40,000 years, but earth people only think it's going at .5c? Why? —Preceding unsigned comment added by 68.18.198.218 (talk) 01:31, 20 December 2007 (UTC)

Anyone, human or alien, can describe the situation with respect to any coordinates they like, as long as they respect the (coordinate-independent) physics. With respect to the earth's rest frame, the alien's speed is .5c. With respect to the alien's rest frame, it's 0. If you divide the distance from the earth's rest frame by the time from the alien's rest frame (or by the alien's proper time) then you'll get a ratio larger than .5c. The alien sees 60000 years of history in 40000/γ years, which is a ratio (Doppler shift) of (60000/40000)γ = (3/2)(2/√3)) = √3. -- BenRG (talk) 02:45, 20 December 2007 (UTC)

Possible to convert impact force in joules to force in kilograms?

Hi. Is this possible to do? If so, how do you convert it? Also, how do you convert the mass of an object and its speed into impact force in joules? Or would this not work because it is really kinetic/potential energy? Is it because some of the energy would be absorbed by the air/target? Does the density of the target matter? What if the object is swinging from a fulcrum point, do you include the whole objects mass at the speed or adjust to the rest is moving at lower speeds? I could use the asteroid impact calculator, but if the object is too small, it burns it up in the atmosphere, so it can't calculate on-Earth impacts. Does whether the projectile/target explodes/ruptures affect the final number? If the projectile is connected to a still-to-ground object, does it affect the final number? Does impact area affect the final outcome? Does it work the same way for projectiles such as air and water as it does for denser ones such as rocks or bullets? Or, is this measured in atmospheres? Can you ocnvert atmospheres to impact force in kilograms? Would results be similar if, say, a still object weighing 20 kg sat atop the target, and if a projectile hit the target at the equivalent of 20 kg of impact force? Or would it be different because the still object's force would be negligable in microgravity, while the moving projectile would still take effect because its mass doesn't change? Do any gravity variations (noticeable ones) affect the final outcome? Can you calculate impact force in joules by knowing the amount of gravitation (say, Earth), air resistance, if any, and distance between object and ground, for an object dropping vertically to Earth? What speed would an object have to move downward at, say at a height of one metre, to match the average speed of an object dropped from that height? No complicated university-level formulas, please. Thanks. ~AH1^(TCU) 23:07, 19 December 2007 (UTC)

Without reading your whole question... See joule. It is a kg m²/s². You cannot arbitrarily drop the meters and seconds. -- kainaw™ 23:16, 19 December 2007 (UTC)

Hi. So, a joule equals a kilogram travelling at one metre per second? Or, do you calculate the number of joules by multipiling its weight in kilograms by the speed in metres per second squared? Sorry, I think I used to be able to remember, but then I forgot, and is this kinetic or potential energy? Thanks. ~AH1^(TCU) 23:24, 19 December 2007 (UTC)

In terms of kinetic energy, E = 1/2 m v^2, so a 1 kg mass moving at 1 m/s has only half a joule of energy. However, 1 J = 1 Nm, so the work you do in exerting a force of 1 Newton over 1 metre, and hence the work done in pushing that 1 kg mass 1 m at an acceleration of 1 m/s^2. Confusing Manifestation(Say hi!) 00:25, 20 December 2007 (UTC)

A joule is a measurement of energy (not a measurement of kinetic energy or a measurement of potential energy). It could be the kinetic energy used to move something or the potential energy available to move something. After reading your question, you are asking what is basically a very common test question on any introductory physics exam. Ie: A person lifts a 102g apple one meter high against Earth's gravity (9.86 m/s²). As with most introductory physics, it is just a matter of getting the units correct. We need kg m²/s². The apple is 0.102kg - so that gives us the kg. If we multiply that by the distance, we get 0.102kg × 1m = 0.102kg m. Now, if we multiply that by gravity, we get 0.102kg m × 9.86 m/s² = 1 kg m²/s² = 1 J. As you can see, all you need is mass, distance, and acceleration. That could be mass actually moved over a distance with some acceleration (kinetic) or mass that could be moved over some distance against some acceleration (potential). -- kainaw™ 01:52, 20 December 2007 (UTC)

Creationism vs. science/evolution

Hi. I was just thinking, what if we could divide the Earth's scientific 4.5 billion-year age into seven equal parts, to represent the seven days of creationism? If the seventh day and the rest takes up too much space of our time-scale, would it work if we divided it into six parts to represent the first six days? If that doesn't work, what if we made the scale exponential, rather than linear, so that the time representing the first day is much longer than the time representing the seventh? Also, how did we figure out the Earth's scientific ~4.5 billion-year age, did we see that uranium-238 samples were half uranium, half something-else, and used the half-life of uranium to determine this? Or did we use the Earth's estimated age to calculate the half-life of uranium-238? Or are the two unrelated and this is just a big coincidence? If they used the half-life of uranium, wouldn't that tell you when the uranium itself was created, not when the Earth was created, since the uranium could have existed long before the Earth (ie. when the supernova erupted that created the nebula that our sun was created from), and the temperatures of the Early Earth, as far as I know, were not high enough to create uranium out of heavy metals? So, wouldn't it have been generated before the Earth was created? Thanks. ~AH1^(TCU) 23:18, 19 December 2007 (UTC)

The order of creation would not fit the observed sequence from the geological record. Even if you split it to six equal parts. David D. (Talk) 23:21, 19 December 2007 (UTC)

I believe this may be covered in Day-age creationism. bibliomaniac15 23:24, 19 December 2007 (UTC)

To address a specific point, determining the half-life of a radioisotope does not require reference to the age of the earth. It can easily be measured from the decay rate (think Geiger counter) of a sample of known mass. Also, radioisotope dating does not depend on when the atoms were created through nucleosynthesis—the atoms don't "know" that themselves. Radioactive decay is just a statistical process whereby in a given interval of time, each atom has a certain probability of decaying. The dating is accomplished by comparing the amount of the original isotope to its decay product(s), so what matters is how long the uranium and its decay products would be confined together (as, say, a rock in the earth). -- Coneslayer (talk) 23:39, 19 December 2007 (UTC)

The thing is, the age of the earth has been determined by a few different unrelated methods. Sure each method in isolation can be argued against, if you argue that part of the method is flawed, such as you argue about decay uncertainty. But when several completely unrelated methods arrive at roughly the same figure, it is harder to argue that all the different methods are flawed and it is just a great coincidence they all give the same false result since they relied on unrelated methods to arrive at their conclusion. We even have an article called Age of the Earth. Vespine (talk) 00:05, 20 December 2007 (UTC)

This idea doesn't really work - no matter how you dice up the time between the big bang and now (paraphrasing our Creation according to Genesis article for brevity):

• First day: God creates light. - OK - I can buy that, the big bang produced a bunch of electromagnetic radiation - which we'll take as "light". The light is divided from the darkness - um well, maybe.
• Second day: God creates a firmament and divides the waters above it from the waters below. Well, I guess water and all other matter gets formed a short while later. It's a bit odd to single out water from all other chemical compounds...and we've quietly avoided mentioning that early galaxies and stars were mainly hydrogen and helium. The Oxygen needed to make water can't come about until we get onto the second generation of stars. But OK - so we're into the second generation of stars here.
• Third day: God gathers the waters together, and dry land appears. Then God brings forth grass, herbs and fruit-bearing trees on the Earth. - This works - planets form after stars - water first on earth, then dry land...OK. Grass was a fairly late addition to the earth. It didn't come about until about 65 million years ago...but that's OK.
• Fourth day: God creates...the stars. - No, no, no! This is bad - this is where it all falls apart! We don't get stars until AFTER grass and trees? But the sun is a star! No, stars means no water - we needed stars on day one or two! We're WAY out of whack here!
• Fifth day: God creates birds and sea creatures; - No, again, not gonna work. Fish were around 500 million years ago - they easily pre-date grasses, and indeed ALL land plants. Birds aren't around until the later years of the dinosaurs.
• Sixth day: God creates wild beasts, livestock and reptiles upon the Earth. He then creates Man and Woman - No, again, we really can't have reptiles coming along after birds. Birds are descended from reptiles and reptiles pre-date grasses and fruiting trees...this is WAY out of whack.
• Seventh day: God, having completed his work of creation, rests from His work. - Well, good for him. The stress of the whole work week seems to have confused him a bit.

So, you see, while you can kinda-sorta bend the language to make the first three days of creation work out OK, from day four onwards, it's just WRONG. You really can't have stars coming after grass and fruit-bearing trees. —Preceding unsigned comment added by SteveBaker (talk • contribs) 14:47, 20 December 2007 (UTC)

Nice post Steve, I was a bit lazy above, you did it justice. David D. (Talk) 18:13, 20 December 2007 (UTC)

For what it's worth, the ...and God divided the light from the darkness on the first day is sometimes interpreted as the creation of time—a rather useful thing to have in a Universe. TenOfAllTrades(talk) 18:44, 20 December 2007 (UTC)

Hmmm so it took a day to create time? Ow! My head hurts! This could have been made better if the events had been re-ordered to Day 1, Day 4, Day 2, Day 5, Day 3...but no, day 6 is still a problem. He has to make reptiles, then birds, then people. But reptiles and people came on the same day - and that's a different day to birds. There is no way to fix that. I conclude that it's all nonsense and God either doesn't exist or he has a really bad memory for dates. Either way, he blew the entire omniscient thing - so he's outta here. QED. SteveBaker (talk) 20:59, 20 December 2007 (UTC)

Another interpretation is that, even if some God exists, his activities are not necessarily accurately recorded in human mythology. Our current media can't get technical details right- why would we expect the ancient Jews, with their largely oral passing down of knowledge, to do better? Friday (talk) 20:19, 21 December 2007 (UTC)

Which is fine, so long as you are consistent about it. If you choose to ignore what this account of creation says because "someone wrote it down wrong" - then you must also be prepared to ignore many of the other things that are said. The ten commandments are in just as much trouble - it's pretty clear that they had to have been written down wrong too because there are at least two completely different versions of them. If the two single most important things the old testament says are wrong (How it all started and what the rules are) - there is not one single thing that's said in the entire book that can then be trusted. Ordinarily, this wouldn't matter - I'm sure most books contain errors here and there - but this is a book that people are supposed to base their entire lives upon. If you can just start picking and choosing which bits you like and which you don't - then it's hardly a bible anymore - it's a kiddies story book. However, there are a great number of people (most of whom seem to live here in the USA) who take that particular section of the book extremely literally and are trying to get it taught in schools on an equal basis with evolution. That's hardly tenable if you think it's been mistranslated to the point where that very creation event is so completely screwed up. SteveBaker (talk) 21:40, 21 December 2007 (UTC)

Do people get dirtier or cleaner as they grow up?

Do people get dirtier or cleaner as they grow up? Let me explain....

When I was in 6-9th grade, in my physical education class, we used to run and do other activities, and then we used to go back in the locker room and put on our clothes and goto our next class (without taking a shower). Now I'm 22, and there is no way in the world that I would ever in my life run or play a sport and not take a shower immediately and put on new clothes. If I dont, I will get itchy and maybe get athletes foot or jock itch, etc...

Do we sweat more when we get older compared to when we were in our teens? Can someone help clear this up? Thanks —Preceding unsigned comment added by 76.167.138.192 (talk) 23:34, 19 December 2007 (UTC)

Its due to different sweat glands. Children sweat exclusively through eccrine sweat glands. During puberty we develop apocrine sweat glands, which produces both more and a different "type" of sweat. It is this type that generates sweat odor, due to the bacteria that breaks down organic compounds in the sweat. Rockpocket 23:49, 19 December 2007 (UTC)