Wikipedia:Reference desk/Archives/Science/2011 September 13

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.

September 13

Reason why muscles require excercise to stimulate growth

Is it true that muscles are the only organ in the body that require exercise in order to stimulate their growth? Like for example, if you are bed ridden, your muscles will begin to suffer from atrophy right? My question is, why is this? My guess is because of our evolution and how our species has been through many periods where famine ran rampant, so our bodies had to evolve a way to preserve as much energy as possible without wasting on muscle development unless it was absolutely necessary. Would this be a fair statement to make? Are there any other animals that do not suffer from this? Meaning their muscles will continue to grow whether exercise is stimulating them or not. ScienceApe (talk) 02:03, 13 September 2011 (UTC)

That's not entirely true. Neurons develop more dense connections with each other the more you work your brain. Your immune system develops antibodies the more infections you get, so it gets stronger with use. There are lots of systems within your body which atrophy with less use. --Jayron32 02:27, 13 September 2011 (UTC)

But neurons aren't organs, and neither is the immune system. I'm also not sure if "growth" is really appropriate to describe them either. I can accept that your brain or your immune system is better if they are "worked out" but are they growing? ScienceApe (talk) 03:04, 13 September 2011 (UTC)

The brain isn't an organ? That's news to me! --Jayron32 03:23, 13 September 2011 (UTC)

And we know from astronauts that if bones don't bear weight regularly, they lose density. Probably every organ must be used to remain at full efficiency. It just that with many, like the heart and lungs, you never get the chance to see what happens to them if not used for a while. StuRat (talk) 02:37, 13 September 2011 (UTC)

Right, heart and lungs are constantly being used. What about skin? I just recall hearing a doctor say that the muscles are the only organ that must be maintained in order to function properly. But would my hypothesis on why atrophy occurs be valid? ScienceApe (talk) 03:09, 13 September 2011 (UTC)

Well, skin seems to atrophy if contained in a cast. I think your logic is sound. The body tries to conserve energy any way it can, and therefore neglects to maintain anything not currently in use. StuRat (talk) 03:15, 13 September 2011 (UTC)

Gorillas eat and sleep all day long, yet they don't seem to suffer from this problem. Count Iblis (talk) 15:27, 13 September 2011 (UTC)

Not all day, they don't. A sloth might be a better example. I would guess they are rather weak. StuRat (talk) 18:12, 13 September 2011 (UTC)

I would just point out that your heart and lungs do lose strength over time if you don't exercise them. This is especially notable if you have some sort of injury to them — I know someone who had some severe lung issues several decades ago, and requires a lot of exercise to keep her lungs at "normal" strength. People who do not exercise much have all sorts of issues regarding blood pressure that are cardiac in origin. --Mr.98 (talk) 22:46, 13 September 2011 (UTC)

Forensic pathologists can detect from the robust bone structure and ligament attachments if the deceased was, say a blacksmith, and can tell if he was left or right handed, so besides microgravity causing bone density loss, hard work, high impact exercise, or weight lifting can cause bones to become more robust. See also [1]. Edison (talk) 18:03, 13 September 2011 (UTC)

"the muscles are the only organ that must be maintained in order to function properly." that's clearly wrong. If you deprive a person of sensory information or social contacts (therefore, not stimulating his brain), his brain would stop function properly. Apparently, his neuronal mass would suffer from this deprivation. Quest09 (talk) 21:48, 13 September 2011 (UTC)

Strange Rodent Found in Yorktown Heights, NY USA. Please help identify.

File:MVI 0226 — Preceding unsigned comment added by Barbaricslav (talk • contribs) 02:26, 13 September 2011 (UTC)

You didn't upload any file under that name. Please try again. --Jayron32 02:28, 13 September 2011 (UTC)

How do I load a miniclip? Barbaricslav (talk) 02:29, 13 September 2011 (UTC)

See Special:Upload. StuRat (talk) 02:31, 13 September 2011 (UTC)

(edit conflict) See Help:Files. The only video format accepted at Wikipedia is .ogg; if you are unable to use that format you may want to upload your video to a site like Youtube and then post a link here. --Jayron32 02:33, 13 September 2011 (UTC)

Or grab some stills in JPG format. StuRat (talk) 02:33, 13 September 2011 (UTC)

OK Here http://www.youtube.com/watch?v=J4ZS78cck1s Barbaricslav (talk) 02:48, 13 September 2011 (UTC)

Looks like a dark brown hamster to me. Not sure of the exact species. They aren't that exotic. --Jayron32 02:58, 13 September 2011 (UTC)

We found it wild in the woods. We thought the eyes looked strange...Barbaricslav (talk) 02:59, 13 September 2011 (UTC)

In that case, it may be a vole, which resemble mice except that they have shorter, hairier tails (mice have longer, bald tails). I still think it looks like a hamster; hamsters are widely kept as pets, and there may very well be feral populations in many places. Hamsters have impressively large cheek pouches in which they store food; though they often look like other small rodents when their pouches are empty. Maybe someone with more expertise can chime in, but my first choice would be a hamster, my second would be a vole. --Jayron32 03:05, 13 September 2011 (UTC)

And since you mentioned the eyes, I checked closer; the eyes on your video look very much like those of the Golden hamster, which despite the name is often bred in many color varients. --Jayron32 03:10, 13 September 2011 (UTC)

If it was as tame as that when you found it, it is not a wild animal -- probably somebody's pet hamster that either escaped or was "liberated" because the owner got bored with it -- which unfortunately happens pretty frequently. Looie496 (talk) 06:01, 13 September 2011 (UTC)

I think it's tragic that people just release hamsters into the wild like that ... when there are hungry pet snakes which would surely enjoy their company. StuRat (talk) 02:37, 14 September 2011 (UTC)

What do you have against hungry wild foxes or coyotes? Googlemeister (talk) 13:09, 14 September 2011 (UTC)

Screw torque and strength of grip

My question relates to dental implants, but the sort of data I am interested in is currently completely ignored in the literature and I am supposing that it would be equivalent to screws in wood, so I ask thus:

If I screw 2 identical 3-inch screws into two planks of equivalent wood -- one 3.5-inches thick and the other 0.5 inches thick -- and the wood type is sufficiently dense to cause the screws to torque-out (and they do so at the same toque value), is it true to say that the screw placed into the plank that completely envelops the 3-inch screw (and is thus exerting equal-and-opposite torque on the entire length of the screw) is stuck in the plank in a sturdier fashion?

I ask this because dental implants are placed into jawbones and there is consensus that implants that lock at particular torque values are sufficiently sturdy, but I wonder if we can easily be fooled because it is quite possible for only a very limited length of bone along the length of the implant to be causing all the locking and we can't really determine this with current technology. (For those knowledgeable about dental implants, I am speaking of primary stability and not about osseointegration -- thanks!) DRosenbach ^{(Talk | Contribs)} 03:08, 13 September 2011 (UTC)

I would think both would be equally stuck in place, provided the wood, or bone, didn't split. However, since splitting is more of a risk with thinner bone or wood, this must be considered. Then, in the case of the bone, it seems there would also be concern that the screw might damage or irritate whatever was beyond the bone (a carpenter would also be concerned about this). StuRat (talk) 03:34, 13 September 2011 (UTC)

Thanks! DRosenbach ^{(Talk | Contribs)} 05:43, 13 September 2011 (UTC)

There is little, if any, relationship between the torque applied to a screw thread, and how well it is 'stuck in' (whatever that means) unless (a) one is dealing with a particular set of materials, (b) one is dealing with a particular length of engaged thread, and (c) one is dealing with engaging threads made to similar - and close - tolerances. Given all the variables involved with dental implants, I'd think (WP:OR) that 'torquing out' would be a fairly unreliable indication of the soundness of a dental implant screw - but on the other hand, I'm not sure that there would be better methods either, without extensive statistical analysis of clinical trials etc. AndyTheGrump (talk) 03:50, 13 September 2011 (UTC)

I thought it would be fairly obvious that by 'stuck in,' I meant to refer to the manner in which a screwed screw cannot be unscrewed unless a degree of torque exceedingly that which was used to place the screw were used to reverse it -- in other words, it is wedged in the wood by the wood's force upon it and cannot be removed unless a greater force is applied in the opposite direction.

And saying that there is little to no relationship unless we are dealing with a particular set of materials or a particular length of engaged thread appears to me to be meaningless because, unless you specify your 'particulars,' any given material or length happens to be a particular material or length -- so, again, I don't really understand what you're trying to say. The fact is that dental implants, is ultimately successful, integrate into the bone in about 3-4 months, until which time the primary stability is relied upon to maintain its rigid positioning. But why is torquing out a "fairly unreliable indication" of the implant-bone-rigidity soundness? Perhaps you're just speaking from a very advanced physics/carpentry perspective, but I don't think I really understood any of the points you were trying to make. Sorry :( DRosenbach ^{(Talk | Contribs)} 05:43, 13 September 2011 (UTC)

Lack of bright colors in mammals

Mammals seem less colorful than insects, fish, amphibians, and reptiles. That is, there aren't too many blue, green, violet, or purple mammals (except for maybe eye color). When mammals are colorful, it seems to just be a portion of them, such as (in primates) a mandrill's snout and butt (an orangutan is all orange, but usually more brownish-orange than bright orange). So, why is it that mammals are mostly "earth tones" while other animals are not ? Or, put another way, why do we have the coloration of moths rather than butterflies ? StuRat (talk) 04:55, 13 September 2011 (UTC)

"no other member in the whole class of mammals is coloured in so extraordinary a manner as the adult male mandrills" - Charles Darwin

The exception that proves the rule, I suppose Jebus989^✰ 08:44, 13 September 2011 (UTC)

Because it doesn't improve the ability of individually brightly colored mammals to have brightly colored babies. --Jayron32 04:57, 13 September 2011 (UTC)

Being less conspicuous makes one less susceptible to predators. Giraffes are pretty brightly coloured, but can fight off most potential predators with a decent kick. HiLo48 (talk) 05:04, 13 September 2011 (UTC)

1. Because mammals have a purely melanin-based form of pigmentation. No one probably knows exactly why, but we lost all the other pigments other animals have and instead are left only with melanin, pigments that cause blacks, browns, reds, and yellows. But no blues and greens. Blue pigments have also actually been lost far earlier by all vertebrates. Not just mammals, but all vertebrates. The only vertebrate which has blue pigments are members of the fish family Callionymidae (dragonets), which independently reevolved a unique vivid blue color-containing organelle known as cyanophores.
2. Why then do birds and reptiles and frogs and fish and mandrills have blue and green colors? This is because coloration in animals are produced by two different methods - pigmentation and structural coloration. Structural coloration does not rely on pigments but on tiny microscopic structures (in the vicinity of nanometers) that scatter light in a certain way. The blue we see on a turkey's head or the iridescent greens and blues in a peacock's feathers are all structural coloration and are not caused by actual pigments. You won't be able to get a blue dye by squashing Dendrobates azureus, never mind that they're highly poisonous. ;) And yes, even the blue on mandrills are structural coloration.
3. Mammals have fur. Structural coloration can be produced by structures on bare skin, scales, exoskeleton, and the fine mesh on feathers, but not by fur. This is why mandrills are only blue in exposed skin. The closest we can get is by varying melanin deposition in different stages in hair growth resulting in striped hair which gives a certain... subtlety to what really is just brown and black and white fur. Bleurgh.
4. Mammals, on average, also have very poor color vision in contrast to other animal groups. Reptiles, amphibians, fish, cephalopods, crustaceans, and birds see at least as many colors as humans, usually far more (including the ability to see polarized light). Even insects have some form of color vision usually extending into the ultraviolet spectrum. In contrast, most mammals are dichromats, able to distinguish only three colors - blue, green, and yellow. They are also usually red-green color blind. This is probably because our common ancestors spent around 200 million years as scurrying nocturnal creatures perpetually underfoot dinosaurs and other giant reptilians. And nocturnal creatures have little use for color vision. This is also why most invertebrates which don't even have a sense of sight are brightly colored, forms of aposematism and crypsis against their normally visually acute non-mammalian predators. Mammals, on the other hand, usually eat other mammals or grass, it's a case of the color blind eating the color blind. The reason why a tiger is perfectly confident with his jarring orange and black stripes among green grass is because most of his prey can't tell the difference. Humans having color vision was a fortunate stroke of fate, as once upon a time in a steamy jungle somewhere, a group of herbivorous monkeys fancied fruit. And in order to tell ripe fruit from nasty unripe ones (as well as tender young red leaves from nasty rubbery old ones), they had to see red (angreh monkeh! cf. birds and red berries). That evolutionary pressure resulted in us today being trichromats and being able to enjoy M&M's even when the green ones taste exactly like the red ones.^{[citation needed]}
5. The previous reasons excludes old ladies with blue hair, which are a paraphyletic clade of mammals which have evolved independently to fit in.-- Obsidi♠n Soul 08:18, 13 September 2011 (UTC)

Acceleration

If a car produces 200BHP and 500lb-ft of torque, would it accelerate faster than a car with 400 BHP and 300 torque at a higher rpm? Both cars are of equal weight and shape. Just the engine is different.--213.107.74.132 (talk) 17:12, 12 September 2011 (UTC)

The RPM affects the BHP and torque, but doesn't figure in to it, here, since the BHP and torque are already known. Also, are we considering the possibility that the wheels will just spin, or do we assuming we maintain traction at all times ? StuRat (talk) 17:21, 12 September 2011 (UTC)

I know the rpm affects it, i'm not worried about it. If Car A has 200BHP and 500lb-ft torque at X rpm, and car B has 400BHP and 300 torqu at X rpm, which goes 0-60 fastest and which has highet top speed (MPH)? Both has traction. — Preceding unsigned comment added by 213.107.74.132 (talk) 17:24, 12 September 2011 (UTC)

Because these figures only provide the peak output, it is impossible to answer this question. Torque and HP are dependent on each other. Torque = (HP x RPM)/a coefficient. If you know the torque and the RPM then you know the HP. These figures are just intended to give a rough idea regarding vehicle performance. The reason torque figures are provided in vehicle specifications is to give a sense of the engine's low RPM output. If two vehicles are identical, aside from the engine, you would need a graph of engine out put over the RPM range (in torque or HP) in order determine which would be faster. --Daniel 18:42, 12 September 2011 (UTC)

Look at these:

3000rpm 360BHP 630 TQ
4000rpm 497BHP 693 TQ
5000rpm 542BHP 569 TQ REDLINE

Versus this higher-reving engine:

4000rpm 436BHP 572 TQ
5000rpm 509BHP 535 TQ
6000rpm 719BHP 629 TQ

These show 2 Engines, one with higher redline than the other. This shows the curve from 3000rpms before the redline. One has higher TQ, and one has higher HP. — Preceding unsigned comment added by 213.107.74.132 (talk) 18:56, 12 September 2011 (UTC)

That is true, but it doesn't change what I said. Torque and Horsepower are directly related and these figures confirm it. (630 TQ X 3000 RPM)/5252 (coefficient in this case) = 360. Your question can be boiled down to the very simple; which is better for acceleration, peak horsepower or peak torque? The problem is there isn't an answer. In order to determine which vehicle will accelerate faster, you need to look at the entire torque or hp curve, not just the peak. --Daniel 19:53, 12 September 2011 (UTC)

How about these: (TQ=Torque in lb-ft)

1000rpm  91BHP 477 TQ
2000rpm 229BHP 601 TQ
3000rpm 360BHP 630 TQ
4000rpm 497BHP 693 TQ
5000rpm 542BHP 569 TQ REDLINE
5000rpm is the redline

versus this one:

1000rpm  41BHP 214 TQ
2000rpm 196BHP 514 TQ
3000rpm 319BHP 559 TQ
4000rpm 436BHP 572 TQ
5000rpm 509BHP 535 TQ
6000rpm 719BHP 629 TQ REDLINE
6000rpm is the redline.

With max traction and equal weight and drag, which will do 0-60mph(0-97km/h) fastest and top speed in MPH (162km/h = 100 MPH).

Is it possible for a car to go more MPH than HP? The TQ always seems to peak before the HP for some reason...

Is it possible for a car to go more MPH than HP? Do you mean a car with higher top speed in MPH than the maximum engine power in HP? A lot of small cars do this, e.g. the current Fiat 500 has 69BHP and a top speed of 99MPH, and one variant of the Smart ForTwo does 92mph from 71BHP. --Colapeninsula (talk) 09:42, 13 September 2011 (UTC)

What about cars with 200-600 BHP

• • • • • Which of the 2 Power curves will be the fastest?--213.107.74.132 (talk) 12:32, 13 September 2011 (UTC)

It is still not possible to answer definitively without the gear ratios. Since the vehicles have different power curves they would need different gearboxes and final drive ratios to achieve an optimized acceleration. If you want to ignore the gearbox and get a rough idea, graph the HP or torque across the rev range for both vehicles, then calculate the area under each graph. The one with the large area is probably faster. --Daniel 19:11, 13 September 2011 (UTC)

Horsepower

How many HP,BHP,PS and/or lb-ft do you need to make a car that weighs 2,500 lbs, has a frontal area the same size as the McLaren F1 and has a drag coefficient of 0.32, to go 300 MPH? — Preceding unsigned comment added by 213.107.74.132 (talk) 09:28, 13 September 2011 (UTC)

If it is air resistance limited, then a 25% increase in top speed would require a 95% increase in horsepower. So, using the McLaren benchmark, it would need about 1200 hp. Of course that neglects the role of rolling resistance and and the fact that adding that many horses is probably impossible without also increasing the weight considerably. Dragons flight (talk) 14:39, 13 September 2011 (UTC)

So how come the Bugatti Veyron Super Sport can go only 268 MPH? Surely fifteen-hundred pounds of weight cannot make that much difference (32 mph) to the top speed, can it? BTW, how much more BHP is needed for 350MPH? Don't forget drag is even higher(Maybe a doubling in BHP will only increase speed by ~15% - i'm not sure, just a guess -) than before, so the 95% increase horsepower for 25% more speed rule may now be incorrect. — Preceding unsigned comment added by 213.107.74.132 (talk) 15:01, 13 September 2011 (UTC)

Once you get into high speeds above about 220mph, you can also no longer ignore the fact that air is compressible, so the simplified fluid dynamics models no longer apply. Googlemeister (talk) 16:12, 13 September 2011 (UTC)

It also isn't entirely about frontal area, at that speed the actual aerodynamics are equally if not more important. --Daniel 19:14, 13 September 2011 (UTC)

Is it true that Charles Darwin was not a scientist?

Topic says it all. ScienceApe (talk) 14:04, 13 September 2011 (UTC)

What defines a scientist? I'm sure that one can construe various definitions that do not consider Charles Darwin a scientist. Our "broad sense" definition, though, of "one engaging in a systematic activity to acquire knowledge" seems to fit the bill nicely. Darwin was a scientist. — Lomn 14:14, 13 September 2011 (UTC)

What a strange question ! In modern terminology, Darwin was certainly a scientist. But in the vocabulary of his period, he would more likley have described himself as a "naturalist". Gandalf61 (talk) 14:27, 13 September 2011 (UTC)

Right. Also maybe a natural philosopher or a natural historian. For a modern usage, we have the journal The American Naturalist, which covers evolution and ecology (among other topics). SemanticMantis (talk) 14:36, 13 September 2011 (UTC)

See the last two paragraphs (or one paragraph, depending on how one reads it) of the lead of Scientist; the word was not widely used in the UK until after Darwin's time, having been coined only in 1833. Deor (talk) 16:01, 13 September 2011 (UTC)

Darwin was notoriously systematic and detailed. That was one of the primary reasons it took him so long to publicize his revolutionary idea. If his super-careful study of many vastly different species of organisms did not make him a scientist, few people should be considered one. Imagine Reason (talk) 16:33, 13 September 2011 (UTC)

In my mind, the OP's statement that the "Topic says it all" says an awful lot about the OP. One would hardly ask such a question WITHOUT a "hidden" motive, so the topic probably doesn't say it all. Taking the title literally, maybe it should be moved to he Language ref desk. HiLo48 (talk) 17:29, 13 September 2011 (UTC)

One should assume good faith rather than speculating on the OP's "hidden motive" and this is clearly the correct ref desk. Edison (talk) 17:54, 13 September 2011 (UTC)

Questions are frequently not perfectly written. To fully answer someone's question it is often necessary to work out what they really wanted to find out. To not go beyond the literal meaning is often selling a questioner short. HiLo48 (talk) 17:59, 13 September 2011 (UTC)

"Chares Darwin was not a scientist" is Creationist trolling, although not very common as far as I know. I expect ScienceApe saw the claim on a Creationist site and wanted to know how scientists would respond to it. Looie496 (talk) 18:42, 13 September 2011 (UTC)

Neither of the Wright brothers held a pilots licence. Therefore they couldn't have invented the aeroplane. It must have been created by an Intelligent Designer instead... ;) AndyTheGrump (talk) 19:12, 13 September 2011 (UTC)

Are you saying that the Wright Brothers were not intelligent, or that they did not design their aircraft? Googlemeister (talk) 19:58, 13 September 2011 (UTC)

No. AndyTheGrump (talk) 23:54, 13 September 2011 (UTC)

[As the original poster, you would have done better by making the heading "Charles Darwin" instead of "Is it true that Charles Darwin was not a scientist?" and by making the original message "Is it true that Charles Darwin was not a scientist?" instead of "Topic says it all."

—Wavelength (talk) 20:34, 13 September 2011 (UTC)]

[I am revising my message by using the grammatical second person.

—Wavelength (talk) 21:33, 13 September 2011 (UTC)]

Charles Darwin was definitely a scientist in the early-to-mid 19th century British understanding of the profession. He was, though, a very late embodiment of the Romantic conception of science — his greatest scientific hero was Alexander von Humboldt. In his youth he went exploring (like Humboldt) and gained a lot of acclaim for that. As he grew older he spent more of his time collating other people's work, and some time conducting small-scale biological experiments at his home. And of course he eventually published his theories on evolution. There is really no way you cannot consider him a scientist. The idea of what it meant to do biological science changed quite a lot, though, over the course of the 19th century. A lot of work Darwin did looks decidedly antiquarian to people just a generation later. One might say, in a poetic vein, that if Newton was the last of the magicians (pace Keynes), then Darwin was the last of the Romantics. --Mr.98 (talk) 22:10, 13 September 2011 (UTC)

Charles Darwin was as much a Scientist as anyone has ever been. Even to this day he is a role model for many scientists and even many non-scientists, like me. Vespine (talk) 22:43, 13 September 2011 (UTC)

What I was indicating is that what it means to be a scientist is different at different points in history. If Charles Darwin magically showed up here tomorrow, many of his methods and approaches and ways of thinking would make him seem like a lovable old crank, not a modern biologist. But that's just because biology has changed a lot, and the professionalization of scientists has changed a lot since his time. Whereas if you picked someone from 1900, or 1920, they'd seem much more "modern" even if they were transported to the present. The late 19th century was a period of major transformation of the profession. --Mr.98 (talk) 01:47, 14 September 2011 (UTC)

Wow, I had no idea people would think I'm a creationist. That's a first. I'm an atheist and I accept evolution... I would think my screenname would have given that away though. I was just asking this question because I was under the impression that Charles Darwin was a layman who just happened to put forth a revolutionary scientific theory. ScienceApe (talk) 04:00, 14 September 2011 (UTC)

No. See Charles Darwin#Childhood and education and Charles Darwin#Works. PrimeHunter (talk) 04:09, 14 September 2011 (UTC)

He had a partial medical education and had read a lot of books. When he was on the Beagle he was more or less a "gentleman scientist". The fact that he did a good job on that voyage (systematically writing everything up, creating some compelling and ultimately correct theories about geology, etc.) lead to his being appointed a Fellow of the Royal Society. So again, by the standards of his day, he was certainly a "scientist" by the time he started publishing on evolution, decades later. He did not have a specialized degree for biology, but again, this was not standard in the early 19th century, before science completely professionalized. --Mr.98 (talk) 12:58, 14 September 2011 (UTC)

Could you cite some method from Darwin that would make him look like a 'lovable old crank'? His voyage, even if performed with simple means, seems pretty solid to me (scientifically speaking). Quest09 (talk) 22:47, 14 September 2011 (UTC)

approximate width of an actual circle

Empirically, given a circle with radius width, what is it's usual approximate width? (i.e. the width of the 'circumference'). Mathematically, this would be 0, but obviously in the real world that would make it invisible, and in that case what's to say that it's a circle there at all (and not a square or an unfilled outline of a unicorn with width 0)? So obviously real-world circles do have a width, and, empirically, what is this? 82.234.207.120 (talk) 15:01, 13 September 2011 (UTC)

The width is double of the radius, and the circumference is about 3.14285 times the width. — Preceding unsigned comment added by 213.107.74.132 (talk) 15:05, 13 September 2011 (UTC)

To be precise, the circumference is about 3.14159 times the width. You appear to have very precisely noted the approximation for pi (22/7); unfortunately this approximation deviates from the real pi after the 3rd decimal place. Weasley one (talk) 16:05, 13 September 2011 (UTC)

It sounds to me like you're talking about the width of a line used to draw a circle, but that's not a property of the circle itself, nor can anything be generalized: width of border can vary from 0 (consider a black circle on a white background, or consider a circular road sign) to an arbitrarily high value. Real objects do not require borders of meaningful width; their dimensions simply are. — Lomn 15:19, 13 September 2011 (UTC)

A fine pen nib is typically 0.2-0.3mm in width, if that's what you mean.--Shantavira|^{feed me} 15:32, 13 September 2011 (UTC)

I seem to recall an ANSI or ASME standard for line thicknesses. For a standards-compliant technical draft drawing, the width of the line for a circle depends on why you are drawing the circle. (For example: a circle drawn to indicate an extension of a fillet or round, for purpose of demarcating radius, is thinner than the actual part line; a circle used to indicate radial arrangement of objects is thinner than a circle indicating a machining instruction). Have a read at the line thickness in CAD Standards article. That article links to ISO 128, but I seem to recall an American standard (ANSI or ASME) that had different standard lines. I'll look this up in my drafting textbook when I get home. Nimur (talk) 15:45, 13 September 2011 (UTC)

From textbooks on visual science, the threshold value for a thin dark line is such that a thinner line can be seen than a dot of the same width. An extended dark line on a light background can be amazingly thin and still seen. For a bright line in darkness, it is the brightness rather than the visual angle that is the limiting value for a thin line. Edison (talk) 14:13, 14 September 2011 (UTC)

All this talk about a circle should be about the annulus whose border thickness is (R - r). Cuddlyable3 (talk) 13:04, 15 September 2011 (UTC)

Cosmetic Surgery

I was wondering, what are the most common significant cosmetic procedures? By significant, I mean something that is not an outpatient procedure (i.e. requires an overnight stay in the hospital.) Rabuve (talk) 16:34, 13 September 2011 (UTC)

Note that Wikipedia cannot provide any medical advice.Your doctor should be the adviser on such questions for a given patient. As general information, a review of the literature on plastic surgery shows that some pretty drastic procedures, involving surgical drains, for instance, send people home the same day, so "significant" is strangely defined here. Googling outpatient plastic surgery produces facelift, nose job, lip enhancement, boob job, tummy tuck. Medical Faculty Associates of George Washington University say "Virtually all cosmetic surgery can be done as an outpatient. Some patients choose to spend one or two nights in the hospital." They mention the option of home nursing care. You did not mention what country you are in. For the US, "Basics of the U.S. Health Care System"(2010) By Nancy J. Niles, page 120 describes the 4000 "Ambulatory surgery centers" which do 8 million operations or procedures a year, with plastic surgery being a commonly done procedure, on an outpatient basis. Even back in 1988, an article in "Working Mother" magazine said that most plastic surgeries were done on an outpatient basis. I could not find the requested list of plastic surgeries "which require an overnight stay in the hospital" but complications or special patient conditions (such as accident or burn victims) might be a factor in requiring hospitalization after what is typically outpatient surgery. "The Encyclopedia of Cosmetic and Plastic Surgery" (2009) page 25 says that breast reduction may be done in a hospital or an outpatient surgery center, for instance. Edison (talk) 17:33, 13 September 2011 (UTC)

Thanks for the answer. It was just as I expected; mostly it's the surgeris we think about right away. Rabuve (talk) 18:29, 13 September 2011 (UTC)

Surface tension

Another stupid question from my side, regarding Surface tension. I have read that the cause of surface tension is due to unbalanced forces on the top layer of particles in a liquid; an unbalanced downward force, perpendicular to the surface of the liquid. But, when we speak about surface tension, we represent it as a force (per unit length) along the surface of the liquid. Can anyone explain? Thanks! Lynch7 17:04, 13 September 2011 (UTC)

Sure, the "Unbalanced" perpendicular component of the force generates a potential energy which is proportional to the surface area. That's equivalent from the energetics point of view to having a surface tension. An other way to look at it is that the forces responsible for the surface tension are present everywhere but in the bulk they always cancel out. Dauto (talk) 21:24, 13 September 2011 (UTC)

Thank you Dauto. Well, I understand that dimensionally, Energy per unit area translates to Force per unit length, which is equal to the dimensions of Surface tension. Can I know how exactly the "per unit area" part comes in here? There is an unbalanced force, so there is free energy on the top layer, but how does it translate to energy per unit area? Thanks :) Lynch7 02:53, 14 September 2011 (UTC)

The larger the surface area is, the larger the number of molecules with missing neighbors will be. So the total potential energy is proportional to the surface area. Dauto (talk) 03:05, 14 September 2011 (UTC)

stability of solar systems?and star cluster and great walls....

Do we know about a multi-star system that is not hierarchical, which is stable? Is it theoretically possible? does a star cluster have a hierarchic? another thing, is it possible that a star after supernova, will be drag by a gravity of planet that rejected by an other solar system? I mean that ex-star will begin to rotate over him. is it possible that a planet will have more mass than some stars? and finally, last thing, what is the status about the "great walls"? I mean is it a new discovery? Exx8 (talk) —Preceding undated comment added 21:49, 13 September 2011 (UTC).

It looks like English isn't your first language, so let me try to break your questions down and answer them:

1) Can a star cluster be stable without being hierarchical ? I assume by that you mean it doesn't have a massive star which has mid-sized stars orbiting it and mini-stars orbiting them. Actually, that "hierarchical" system never exists, as far as I know. The far more common system has many stars of similar masses all orbiting one another. And, yes, I think it can be stable, but perhaps others can say how stable (thousands of years ? millions ? billions ?).

2) Is it possible for a small star to orbit a massive planet. I would say no. They could orbit one another, but the center of rotation (barycenter) would be outside the planet.

3) Are "great walls" a new discovery ? I don't know what you mean here. I'm guessing, since your first 2 questions were about astronomy, that this isn't about the Great Wall of China. StuRat (talk) 02:02, 14 September 2011 (UTC)

He's talking about Sloan Great Wall. Dauto (talk) 02:45, 14 September 2011 (UTC)

Or possibly CfA2 Great Wall. Dauto (talk) 02:47, 14 September 2011 (UTC)

The latter is the original great wall discovered some 20 years ago Dauto (talk) 02:50, 14 September 2011 (UTC)

In the long run all gravitationally bound systems are unstable. The question is in what time scale does the instability take over. For instance, Star clusters do evaporate. Dauto (talk) 02:56, 14 September 2011 (UTC)

"blue light" and time of day

In a textbook on plants, I'm stumbling on the "blue light-dependent system" of photosynthesis in certain plants, particularly shade plants. The textbook states that, in this model, blue light activates stomatal opening, and later on says that rapid opening of stomata is triggered at dawn ("when light is composed largely of blue wavelengths") and "during brief exposures to sunflecks". I'm sure I'm being confused by my simple human assumption that blue light would be blue light that I can see. Dawn and sunflecks do not strike me as being particularly 'blue' at all. I can't find a good link on the web or WP to times of day when there is more 'blue light' though, nor exactly what this means from a visual/time of day cycle. How should I be interpreting this blue light association? What about a sunfleck is more blue than shade? 82.71.20.194 (talk) 22:01, 13 September 2011 (UTC)

This is complicated. First of all, atmosphere scatters blue light more effectively than it scatters red light. When it is midday at your location, the sunlight has the least distance to travel through the atmosphere to reach you; therefore both the blue and the red light reach the surface effectively. When the sun is barely above the horizon, however, (in the morning or in the evening, or in winter near the Arctic circle), the path the light has to travel through the atmosphere is much longer and blue does not reach you as efficiently as red. At that time the relative balance of colors is shifted towards the red or orange. Now when the Sun is below the horizon, the opposite may be true: Earth curvature blocks the red (remember, it is scattered less, so more of it travels the direct path from the Sun), but the more-scattered blue can bypass the Earth curvature; therefore before sunrise or after sunset there are times when everything looks bluish. This, of course, depends a lot on the cloud cover, terrain, etc., so it's not always the case. Sharp shadow, too, may look bluish under some conditions, for the same reason: more red arrives directly form the sun and is blocked by the object that casts the shadow, but relatively more blue arrives from elsewhere in the sky and bypasses the object that casts the shadow. This is a fairly weak effect, however; usually too weak to even notice. Finally, there is a so-called Purkinje shift, which makes us see blue as more bright (compared to yellow) under dim light. This is a property of the human retina, however (rod receptors are more blue-sensitive than L and M cone receptors), and obviously has no effect on plants. Regarding the plants: chlorophyll can absorb both red and blue light; but chlorophyll-based photosynthesis is not the only light-dependent process in most plants. I know that orchids do not grow well under purely red or purely blue light; people who grow orchids indoors usually mix the "cool" and "warm" daylight fluorescent lights at 1:1 or 1:2 proportion. I do not know if the stomata opening is triggered by blue light only, but it should not make much of a difference because the amount of both blue and red light increases sharply at dawn and decreases sharply at dusk. The relative changes in red vs blue balance are more subtle. Hope this helps. --Dr Dima (talk) 23:22, 13 September 2011 (UTC)

N.B. You may also want to look up phototropin and cryptochrome, either here on Wiki or in the published articles. --Dr Dima (talk) 23:33, 13 September 2011 (UTC)

Note that on cloudy days, the direct red light may be blocked by clouds, with only the blue light getting through. StuRat (talk) 02:07, 14 September 2011 (UTC)

Interesting... Would plants adapted for polar night conditions (in the tundra, northern edge of taiga, etc.) also have more blue-light-dependent photosynthesis? 67.169.177.176 (talk) 00:39, 14 September 2011 (UTC)

Lightsaber

Don't the Jedi knights in Star Wars need to wear fireproof suits to protect them from the radiant heat emitted by their own lightsabers? I know those things use plasma, and that stuff is EXTREMELY hot! 67.169.177.176 (talk) 23:35, 13 September 2011 (UTC)

Lightsabers have variously contradictory physical properties. They are fictional. The nerds over at Wookipedia say that apparently the plasma is contained in some kind of force containment field, which also contains the heat. This has nothing to do with real physics. --Mr.98 (talk) 23:53, 13 September 2011 (UTC)

Solid light, possibly? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:17, 14 September 2011 (UTC)

I always pictured it as an extremely powerful laser that magically stops after a meter or so. If so, then it wouldn't generate much heat when just cutting through clear air, but would when it encountered and object. StuRat (talk) 02:10, 14 September 2011 (UTC)

The problem with the laser thing is that (like you said) a laser doesn't stop, it keeps on going. Also, it won't clash with physical objects or other laser lightsabers, it will pass right through them as if you were holding a flashlight. Plasma has the same kind of problem, even if you can contain it in a magnetic field (good luck with that) it won't clash with objects either. My idea that I pulled out of my ass is to use something like what the T-1000 is made out of. I guess millions of nanomachines that can morph into various objects. They should have good thermal conductivity but robust enough to tolerate being heated up. Just contain them in a lightsaber style handle thing, then when you turn it on, they morph into a blade which is then heated to intense temperatures by a power source. ScienceApe (talk) 03:53, 14 September 2011 (UTC)

Are you sure about the part where you said that plasma won't clash with objects? I've seen the History Channel show Star Wars Technology, and they said that plasma can behave as a solid when magnetically confined (and frankly, I can see how this can happen). 67.169.177.176 (talk) 00:59, 15 September 2011 (UTC)

Umm, and lasers "won't clash with physical objects"? So how do you account for their widespread industrial use for cutting? Indeed, how do you account for their use in pointing at PowerPoint images? If photons aren't bouncing off of the screen and being absorbed by the cones in your own retina, how do you manage to see them?—PaulTanenbaum (talk) 01:35, 15 September 2011 (UTC)

I think he/she meant that lasers won't clash with other lasers, as lightsabers do. Magnetically confined plasma, though, can clash with other plasma, see Diamagnetism for a more detailed explanation. 67.169.177.176 (talk) 01:47, 15 September 2011 (UTC)

Light doesn't bounce off of light. I was thinking of having a collapsible retroreflecting pole as the blade, with a mirror at the top, in order to cap the light to keep it from hitting the ceiling. The pole would give the weapon the ability to clash with another. →Σ _{^talkcontribs} 02:43, 15 September 2011 (UTC)

Lol that's not what I meant. Clash in the combat sense. When you swing a sword against an object, you encounter resistance. If you were to swing a "plasma sword" against something, you may burn it, but you won't encounter any resistance. It would be like swinging a flashlight or laser pointer at something. Diamagnetism is way too weak, you won't encounter resistance. That doesn't make for a very good sword. As for swinging two plasma swords together and having them clash magnetic fields? Michio Kaku seems to believe that they won't clash either. See the following, http://www.youtube.com/watch?v=wp_Hq1f8-0E&feature=related ScienceApe (talk) 19:28, 15 September 2011 (UTC)

Yeah, and he's also found a way to solve this problem: use a telescopic rod of high-temperature ceramic to enable parrying. I wonder if that will work. 67.169.177.176 (talk) 04:14, 16 September 2011 (UTC)

I don't think so. While the ceramic is heat resistant, it's also brittle. Not really something you want to smack things with. ScienceApe (talk) 05:27, 16 September 2011 (UTC)

Reinforce it with tungsten filaments, maybe? :-) 67.169.177.176 (talk) 06:01, 16 September 2011 (UTC)