Wikipedia:Reference desk/Archives/Science/2013 June 6
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June 6
editWhat is a Quasi-satellite
editWhen i just first learn quasi-satellite, I don't get it really. On Earth article it said earth has 8000 artificial satellites. Venus only have one temporarily quasi satellite. I don't know if that one body around Venus will crash into Venus. Is their quasi-satelltes or flying asteroids around Mercury. Because few centuries in the future it won't matter if Earth will get swallowed up by sun because technologies are constantly shaping. I hear one proposal is to use flying asteroid to manually move Earth outward which actually can let earth's life last 5-6 billion years longer. I don't know is there flying asteroids around Mercury and Venus, if technologies can alter its orbits. With the nudging effects can it be used with any random asteroids or only quasi-satellites around the parent planets.--69.233.254.115 (talk) 02:42, 6 June 2013 (UTC)
- I have never heard it before. I just heard quasi-satellite have number code names, because Venus have one temporarily satellites, i don't know is quasi-satellites all temporairly or some of them are permanent. Is there flying asteroids by the sun?--69.233.254.115 (talk) 03:49, 6 June 2013 (UTC)
- The solar system is unpredictable on a billion-year timescale; see Stability of the Solar System. For information about near-sun asteroids, see Vulcanoid asteroid and Aten asteroid. Bobmath (talk) 04:41, 6 June 2013 (UTC)
- Maybe File:InnerSolarSystem-en.png this will help. The map shows green dot is for flying asteroids, all i got to do is to count the green dots in the picture. I now remember between Mercury and Venus there is 13 green dots and between sun and Mercury there is one dot. You linked me to the article of Vulcanoid asteroid and Aten asteroid, I don't think there is any celestial objects between sun and mercury, then how come the spacecraft never track it? If there is asteroid between sun and Mercury I thought any spacecraft which gone past it suppose to have tracked it. Yea, many space satellites actually been to sun. Then how come is so hard to study anything between sun and mercury? Do spacecraft get sensitive when it gets too close to the sun?--69.233.254.115 (talk) 01:16, 7 June 2013 (UTC)
Does time dilate in stationary light clock?
editA stationary light clock is shown in the following link in which a light pulse traces out a path of length 2L in between the two mirrors separated by a distance L in the physical space of three linear dimensions.
http://en.wiki.x.io/wiki/File:Time-dilation-001.svg
Although it seems a pulse back and forth in between the mirrors separated by a distance L but in reality the same pulse covered a greater distance than L in its progression of time and therewithal traces out a path equal to the apothem of light cone.
Explanation:
Please click on the animation “A race: There and Back two runners and a time-keeper, a meterstick”in the following link.
http://physics.syr.edu/courses/modules/LIGHTCONE/events.html
If this doesn’t work then click on the following link
http://physics.syr.edu/courses/modules/LIGHTCONE/
Scroll down and then click on EVENTS and SPACETIME of PRIMEVAL RELATIVITY. Scroll down and then start playing animation of “A race: There and Back two runners and a time-keeper, a meterstick”
Let’s the two runners run in between two points A and B separated by distance L. Although they covered a distance of 2L in the physical space of three linear dimensions but in reality [4-dimenional space] it’s not 2L in their world lines as you can see clearly in the animation.
When they start running from point A to B
1- Each runner reaches B diagonally at later (in time) and
Similarly when they starts running from point B to A
2- Each runner reaches A diagonally at later (in time)
This means none of the runners returns to their original position (in past and this impossible) A or B but reach there at later (in time).
Now an example of this animation can give you a quick idea of a pulse moving from A to B and then from B to A in the aforementioned stationary light clock in the physical space of three linear dimensions as well as through space-time if you imagine one of the runners is a pulse.
"Since a pulse never comes back to its original position (past) in its space-time continuum therefore is the distance of 2L appeared in stationary clock authentic and time dilates in aforesaid [stationary] clock?" (Is time dilation / length contraction Real?)162.157.235.1 (talk) 05:05, 6 June 2013 (UTC)Eclectic Eccentric Kamikaze
- All of the links you gave above appear to be broken. Dragons flight (talk) 05:30, 6 June 2013 (UTC)
- The question seems to have been copy-pasted from here. I fixed the links. However, I don't think I understand the question. The distances like 2L in light-clock-related arguments are distances in 3D space, not 4D spacetime. Diagonal distances in spacetime diagrams (measured with the Pythagorean formula) are meaningless. There is a spacetime "distance", called the spacetime interval, but it's calculated differently and I don't think it's useful here. -- BenRG 07:29, 6 June 2013 (UTC)
- Hmmm, this is pushing the limits of Fair Use, without actually being that much use. I'd recommend the OP, or if not then anyone else, do some work to rephrase it. Last thing we need is somebody accusing us of copyvios to go along with all the other crap. Wnt (talk) 17:56, 6 June 2013 (UTC)
Let’s try this way
We all know that the speed of light in vacuum is exactly 299,792,458 metres per second. Apparently, a pulse covers a distance of L = 299 792 458 m in one second but in reality (4-dimensions) the same pulse covers a greater distance than L in its space-time continuum.
Let A and B are the two points in a vacuum separated by distance L = 299 792 458 m. Although it seems both A and B are moving on the surface of cone as time progresses in forward direction (upward in the light-cone diagram) but in reality both original points A and B are left behind in the past as soon as a pulse starts moving from point A to B in time t.
A’ ----------------------------- B’
A ----------------------------- B
This means after one second, a pulse reaches point B’ (original point B was left behind in the past due to progression of time ) diagonally from point A which was left behind in the past (not from point A’ which can be seen progressing with time) unless i am missing something. So we get a distance AB’ after joining A and B’ with a straight line thus a pulse a cover a distance of AB’ > L = 299,792,458 m.162.157.235.1 (talk) 05:29, 7 June 2013 (UTC)Eclectic Eccentric Kamikaze
- The spacetime distance AB' is actually zero. Look at Spacetime#Light-like interval. That happens because the metric of spacetime is hyperbolic. Dauto (talk) 15:54, 7 June 2013 (UTC)
For this, do we not need another nearby event in the space-time. Anyway it's not applicable here.
Effects of marijuana as a drink
editHi everyone, I was thinking this would be, technically speaking, a medical question, so I've decided to ask here. I was watching an old Indonesian film, Darah Perjaka (1985), which deals with a gang of marijuana dealers who are shipping their product as "tea" (I have no idea if the producers were aware of the English-language slang, but that's not relevant here). The main characters discover that the tea is actually marijuana after someone uses it to brew tea then gets high ("smashed" would probably be a better term, as he was completely out there) after drinking some. Physiologically speaking, would that even have an effect (assuming only one or two glasses of "tea" for a 100 kilograms (220 lb) man)? The marijuana "tea" was mixed with hot water, if that has anything to do with it. — Crisco 1492 (talk) 07:47, 6 June 2013 (UTC)
- Check out the article on cannabis tea. 88.112.41.6 (talk) 08:01, 6 June 2013 (UTC)
- WHAOE, alright. Thanks, the answer is right there: "Without proper decarboxylation and preparation of the glandular material, this method of ingesting cannabis yields low psychoactive effects, as tetrahydrocannabinol, the primary psychoactive agent in cannabis, is not a water-soluble compound." Assuming this uncited sentence is correct, the tea in this instance should not have had that kind of effect as it was not prepared specifically as a way of imbibing marijuana. Thanks again. — Crisco 1492 (talk) 08:12, 6 June 2013 (UTC)
- Yep, you got it, that sentence is correct. The only caveat I can think of is some people I know brew their (normal) tea looseleaf, and then slurp down the dregs at the end of the cup. So in that case maybe cannabis tea could yield psychoactive effects. SemanticMantis (talk) 14:08, 6 June 2013 (UTC)
- Hmm... didn't pay attention to whether it was bagged or looseleaf (and they certainly didn't show the character drinking the dregs). Thanks for the information. — Crisco 1492 (talk) 14:33, 6 June 2013 (UTC)
- I have made marijuana tea (many years ago). It tastes very nasty. You have to mix it with massive amounts of sugar to make it drinkable at all, and even then it's a battle against nausea. (It did get me stoned, though, as I recall.) Looie496 (talk) 14:59, 6 June 2013 (UTC)
- Thus making it even more unlikely that someone could have unknowingly confused it with regular tea. ;) — Crisco 1492 (talk) 15:39, 6 June 2013 (UTC)
- I don't know for sure, but I bet that smugglers could purify honey oil from the marijuana and spray it on bulk tea (honest Camilla sinensis) and package it as teabags. I don't know if they would fool a dog, though... Wnt (talk) 17:53, 6 June 2013 (UTC)
- This is... a little detailed. Considering the level of realism (or lack of it, rather) in popular Indonesian cinema in the 80s (this same film had an obviously Javanese [note the "v"] person playing a ninja who commits seppuku after getting a scratch, a woman seemingly killing others with what appears to be air freshener to the eyes, and a whole bunch of wire-fighting), I doubt the producers got that involved. Although I now have a bit greater respect for the border patrol people. — Crisco 1492 (talk) 23:23, 6 June 2013 (UTC)
- I don't know for sure, but I bet that smugglers could purify honey oil from the marijuana and spray it on bulk tea (honest Camilla sinensis) and package it as teabags. I don't know if they would fool a dog, though... Wnt (talk) 17:53, 6 June 2013 (UTC)
- If you want marijuana in your tea, buy a respectable brand of Earl Grey, such as Tetley's or Red Rose, boil your water, and decant it over two bags in a large mug. After pressing and removiving the bags, add sugar and milk to taste. Having steeped half an ounce of cleaned and ground marijuana in a stick of melted butter, and used the butter to cook a box of Betty Crocker or Duncan Hnes brand instant brownies according to the box instructions an hour earlier, dunk the brownie slices in the tea, and enjoy. μηδείς (talk) 00:00, 7 June 2013 (UTC)
Combined cycle plants
editWhat's the difference in general between combined cycle power plants and coal-fired power plants in terms of carbon emmissions? Thanks, 163.202.48.125 (talk) 08:46, 6 June 2013 (UTC)
- A new combined cycle natural gas plant generally has around 60% thermal efficiency, while new coal plants are around 40% thermal efficiency. Further, methane has a higher energy content per carbon atom, meaning for the same energy content you expect about 1.6 times as much CO2 from coal as from natural gas. Combining these two effects, and a modern coal plant produces about 2.4 times as much CO2 in order to generate the same amount of electricity as a modern combined cycle gas plant. For the plants actually in use today, rather than new one's with all the best innovations, coal tends to produces about twice as much CO2 per unit of energy as natural gas. Dragons flight (talk) 09:13, 6 June 2013 (UTC)
- For some useful followup, try combined cycle power plant, life-cycle greenhouse-gas emissions of energy sources, and fossil-fuel power station. Dragons flight (talk) 09:16, 6 June 2013 (UTC)
Mystery
editWhat is the biggest mystery in science? (Or biggest mysteries) Pass a Method talk 11:07, 6 June 2013 (UTC)
- Lists of unsolved problems should give you a start. AndrewWTaylor (talk) 11:22, 6 June 2013 (UTC)
- I already knew about that page, but it does not list it in order of importance/significance. Pass a Method talk 11:37, 6 June 2013 (UTC)
- Importance/significance is going to be a matter of opinion. We don't do that here. But you are free to make up your own mind. HiLo48 (talk) 12:06, 6 June 2013 (UTC)
- And indeed that might be it :-) . {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:26, 6 June 2013 (UTC)
- Its not if you ask "whats the most funded scientific research?" which suggests high demand, or "which scientific mystery is the most quoted in the media and journals?" etc. Pass a Method talk 13:57, 6 June 2013 (UTC)
- You can get a feel for the funding levels for broad topics in the USA by browsing the website of the National Science Foundation ( nsf.gov ). You can search past awards by keyword, and if you dig around you can find totals for each section and year. SemanticMantis (talk) 14:05, 6 June 2013 (UTC)
- Importance/significance is going to be a matter of opinion. We don't do that here. But you are free to make up your own mind. HiLo48 (talk) 12:06, 6 June 2013 (UTC)
- I already knew about that page, but it does not list it in order of importance/significance. Pass a Method talk 11:37, 6 June 2013 (UTC)
- Martin Gardner claimed that the biggest mystery is: Why is there something instead of nothing?
- I recall in mathematics there is the Clay Millennium Prizes list. Wnt (talk) 17:59, 6 June 2013 (UTC)
- The answer to tat question is simple: There is something, because there is a utter lack of nothing. Plasmic Physics (talk) 23:16, 6 June 2013 (UTC)
- That is, if you take a secular approach to the question. Martin, being religious, probably attempted to prompt to the audience into contemplating religion as the source of an answer. I admit, I use this thought provoking question occasionally, for just that reason. Although, I synthesized it independently. Plasmic Physics (talk) 23:40, 6 June 2013 (UTC)
- Religion has almost nothing to do with science, largely tends to ignore it (when it's not denying it), and should really never be brought to this ref desk. HiLo48 (talk) 21:46, 7 June 2013 (UTC) HiLo48 (talk) 21:46, 7 June 2013 (UTC)
What exactly do service dogs for diabetics detect?
editI once saw a boy who had a service pet, a dog, whose job was to let the boy and his parents know if his blood sugar was getting too low by barking or otherwise getting the masters' attention (it was trained to only do so when it should). I wonder, what changes about a human whose blood sugar is getting too low that comes off their body that the dog can detect? Olfactory obviously, but what, is my question. Is there a different chemical in higher or lower than normal concentration in the exhales or perspiration of hypoglycemics? 20.137.2.50 (talk) 15:48, 6 June 2013 (UTC)
- Diabetic ketoacidosis#Signs and symptoms Rmhermen (talk) 16:21, 6 June 2013 (UTC)
- Right. More generally, low blood sugar leads to ketosis, which results in acetone, a highly volatile compound, being exhaled. Looie496 (talk) 16:26, 6 June 2013 (UTC)
- Interesting. The intro paragraph at Diabetic ketoacidosis says "DKA is diagnosed with blood and urine tests; it is distinguished from other, rarer forms of ketoacidosis by the presence of high blood sugar levels." not low. 20.137.2.50 (talk) 16:33, 6 June 2013 (UTC)
- Just a stupid thinko on my part -- I meant low insulin, not low blood sugar. Note though that ketoacidosis is an extreme form of ketosis. By the time ketoacidosis has set in, the dog has already failed to do its job. Looie496 (talk) 16:43, 6 June 2013 (UTC)
- Ah, OK. Then I remembered wrong too. So the dog does not bark necessarily when the blood sugar gets too low; it barks when insulin levels get low, which probably more often coincides with higher blood sugar. 20.137.2.50 (talk) 16:51, 6 June 2013 (UTC)
- Just a stupid thinko on my part -- I meant low insulin, not low blood sugar. Note though that ketoacidosis is an extreme form of ketosis. By the time ketoacidosis has set in, the dog has already failed to do its job. Looie496 (talk) 16:43, 6 June 2013 (UTC)
- Interesting. The intro paragraph at Diabetic ketoacidosis says "DKA is diagnosed with blood and urine tests; it is distinguished from other, rarer forms of ketoacidosis by the presence of high blood sugar levels." not low. 20.137.2.50 (talk) 16:33, 6 June 2013 (UTC)
- Right. More generally, low blood sugar leads to ketosis, which results in acetone, a highly volatile compound, being exhaled. Looie496 (talk) 16:26, 6 June 2013 (UTC)
- Guys, you're floundering here - this is one of those cases where our many critics would say we outta be bringing references to the question, and this one is not hard to look up! Don't come to the party without bringing something!
- According to [1] , " Our dogs are trained using scent detection techniques to identify changes that occur in human body odor when blood sugar levels move above or below normal ranges. " Which is certainly believable - either condition is a major alteration in biochemistry. Wall Street Journal agrees, and says that research is ongoing to find the odorants, which means I assume at least then they weren't known. [2] Wnt (talk) 17:49, 6 June 2013 (UTC)
- Interesting. Here at the volunteers section of that site you linked to, it asks people with insulin dependent diabetes to offer scent samples by wiping their forehead with some gauze and measuring their blood sugar, which indicates that what the dog's taking can come out of the person's skin. 20.137.2.50 (talk) 18:08, 6 June 2013 (UTC)
Hail and windscreens
editIs it useful to put a finger in your windscreen during hail to prevent it for breaking?--90.165.116.251 (talk) 15:51, 6 June 2013 (UTC)
- No. --Jayron32 18:15, 6 June 2013 (UTC)
- Especially if you are driving! SemanticMantis (talk) 18:33, 6 June 2013 (UTC)
- I suppose the thinking here is that your finger might dampen out vibrations and thus remove energy from the system. I could maybe imagine that helping in some manner - but I doubt by very much. SteveBaker (talk) 19:20, 6 June 2013 (UTC)
- I didn't touch this one because I can't imagine how you'd begin to figure out the answer. Any ideas? I suppose somebody tests windshields against hail - plenty of stuff comes up in a search. It looks like many of the impacts in images (but not all) have quite localized damage though, which makes me wonder how much a finger matters if it isn't right in the path of the hail ... not sure if having it in the path of the hail is something to recommend, either. But someone has to know some theory about it. Wnt (talk) 19:45, 6 June 2013 (UTC)
- Yes!! Absolutely. holding the glass may help prevent it from shattering. Dauto (talk) 21:46, 6 June 2013 (UTC)
- Are there even any cars still on the road without shatterproof windshields? DTLHS (talk) 22:15, 6 June 2013 (UTC)
- Are you sure of that? It has long been the received wisdom in Australia, particularly on dirt roads in country areas, that when approaching a vehicle travelling in the other direction, or getting close to a vehicle going in the same direction (e.g. about to overtake it) the driver and front seat passenger should touch the windscreen to help prevent breakage from stones flying up. I'm sure many people still do this. But this has been shown to be not only useless, but dangerous. It won't prevent a windscreen from shattering if that's what it's going to do, and if it does, you're much more likely to sustain damage to your hand than you would if it were somewhere else. Mythbusters busted this one some time ago. -- Jack of Oz [Talk] 22:23, 6 June 2013 (UTC)
- Dauto, surely as a physicist, you must know that introducing a quasi-node into a system reduces its flexibility? If anything, you're more likely to induce shattering, rather than prevent it. Plasmic Physics (talk) 01:03, 7 June 2013 (UTC)
- I doubt it's that easy to say - after all, your finger isn't a node - if the hail hits the windshield it will move. (But I can't say for sure it won't have some negative effect!) Wnt (talk) 03:59, 7 June 2013 (UTC)
- Unless people can provide a reference, they should really refrain from writing "No" or "yes absolutely". That's as good as saying 'someone at the pub told me once'... Not appropriate replies for the ref desk. Vespine (talk) 04:31, 7 June 2013 (UTC)
- Blah blah blah... Dauto (talk) 15:45, 7 June 2013 (UTC)
- Unless people can provide a reference, they should really refrain from writing "No" or "yes absolutely". That's as good as saying 'someone at the pub told me once'... Not appropriate replies for the ref desk. Vespine (talk) 04:31, 7 June 2013 (UTC)
- I doubt it's that easy to say - after all, your finger isn't a node - if the hail hits the windshield it will move. (But I can't say for sure it won't have some negative effect!) Wnt (talk) 03:59, 7 June 2013 (UTC)
- Dauto, surely as a physicist, you must know that introducing a quasi-node into a system reduces its flexibility? If anything, you're more likely to induce shattering, rather than prevent it. Plasmic Physics (talk) 01:03, 7 June 2013 (UTC)
- From a scientific view, this doesn't require a reference anymore than does "A balloon is will pop when you poke it with a needle." On the other hand, an assertion of how much force is required as a function of a particular set of variables, does require one. Plasmic Physics (talk) 04:50, 7 June 2013 (UTC)
- Someone seems to have provided a reference. -- Jack of Oz [Talk] 05:25, 7 June 2013 (UTC)
- That is why is said quasi-node. It really depends on how hard you're pressing against the window. The harder you're pressing, the more you increase the probability that it will shatter under impact. That correlation is scientifically, logically justifiable. However, putting numbers to it is a more difficult endeavor. I can't say how hard you'd have to press to make a significant difference in flexibility. Plasmic Physics (talk) 04:50, 7 June 2013 (UTC)
- Reducing the flexibility by introduction of a quasi-node is exactly the reason why that may help. The flexing of glass induces the shatter. That's also why it is harder to shatter a smaller piece of glass. Dauto (talk) 15:45, 7 June 2013 (UTC)
Geometric Optics (Refraction)
editHello! I am a grade 10 student who received a physics quiz (on geometric optics) back recently, and I am having a bit of dispute with two true-or-false questions.
The first, which is likely very open to interpretation, is, "A light ray is either reflected or transmitted when it strikes a surface such as a piece of glass." This particular chapter is on refraction of light, and I said false, arguing that (1) in this particular situation it should be "reflected or refracted" instead of "transmitted" and (2) in some (if not most) situations, can't glass do both?
The second, "Blue light bends more than red light, so blue light travels slower than red light." I said true, because in a note (incidentally straight from the textbook) it said, "Dispersion occurs because each colour of visible light travels at a slightly different speed when it goes through the glass prism. Violet light slows down more than red light when it enters the prism. That is why you see violet light being refracted more than any other colour (that is, bending more toward the normal than any other colour). Red light is refracted the least" (bold for emphasis). Since blue is closer to violet than red, I said it was true.
It was just a quiz, but it means the difference from an 89% to a 95% :P. Was I right? Was I wrong? Thanks for your input! 174.93.65.84 (talk) 20:27, 6 June 2013 (UTC)
- You're right on both accounts. The only thing I would change in your comment, is the reference to the light being refracted instead of transmitted. That doesn't make sense since in order to be refracted, it must be transmitted. The two terms can be taken as synonyms here. But your other point stands. refraction and reflection will often happen simultaneously. Dauto (talk) 21:41, 6 June 2013 (UTC)
- (ec) What a terrible thing for a teacher to pose a true-false question on such a subject! Reflection, transmission, and refraction, are not either-or choices! Tell your teacher that he or she has presented a false dichotomy and asked for a true-false answer. In any reasonable treatment of optics, light is reflected, refracted and transmitted at the same time. We use a coefficient of reflection (and its related parameter, the coefficient of transmittivity). What's worse: this is not advanced physics! It's perfectly reasonable for a grade-10 physics student to learn proper equations to model simple reflection and refraction of light at an interface. Your teacher should be teaching, using, and understanding those equations!
- And the second question - the speed of blue light and red light depend on the material! Complicated materials - like the glass you find in any ordinary camera lens - have very complicated index of refraction. The index is not constant - it varies with frequency - which is called dispersion. Unless your teacher has specified the type of glass - and specified the index of refraction - and specified how the index of refraction varies with wavelength (color of light) - there's no way to answer the question! Furthermore, "violet light" is poorly defined. It can be interpreted as either monochromatic, short-wavelength light; or as a mixture of two monochromatic colors (red and blue) - or in practice, a mixture of many different colors (wavelengths) of light. When your computer screen shows the color violet, it's a mixture of red and blue light, and small amounts of lots of other colors too.
- The reality is, your teacher has a very specific set of answers that he or she wants to see. You have to conform, to some extent, to those expectations. But if your teacher is reasonable, he or she will allow you to receive credit by showing that you understand the topic in great depth. If you study up on these details, and present a clear explanation for why the test-questions were invalid, your teacher should give you credit. But, your teacher might not necessarily acquiesce to proper reasoning; it is a reality of life that not everybody is interested in correct and complete understanding of optics. Nimur (talk) 21:48, 6 June 2013 (UTC)
- I am now wondering why it is possible to see clearly through a window. Card Zero (talk) 21:58, 6 June 2013 (UTC)
- Because behind the scenes, an engineer cared about details you never even thought to care about. Your window-glass has almost the same index-of-refraction as ordinary atmospheric air; and the pane of glass has tolerances that are very well-controlled so that it is an optically-smooth surface. Humans have been building and perfecting optical glass recipes for thousands of years, and today's materials are much better than those from thousands of years ago. The glass has a very high transmittivity at all optical wavelengths; it is almost perfectly colorless to your human eye. All you have to do to see how important these details are is to build yourself a container with a glass window, and submerge the container under-water! Suddenly you won't be able to see in straight lines and all the colors outside will be wrong... Nimur (talk) 22:05, 6 June 2013 (UTC)
- Now I'm wondering why it's possible to see clearly through the air, but according to sunset, it isn't! So that's OK, story checks out. Card Zero (talk) 22:28, 6 June 2013 (UTC)
- Note that according to soda-lime glass its index of refraction is 1.5, which is scarcely a match for air. Window glass is transparent because the bending of light that occurs at one boundary is undone at the other. (Consider a camera lens - it is transparent so long as it is in focus. A flat pane being at focus with infinity) Wnt (talk) 19:33, 9 June 2013 (UTC)
- But the dispersion ... if you look at the diagram at the top of Dispersion (optics), it shows light spreading out to a width of about a third of the thickness of the glass it has travelled through. This would make a view through a window into a blurry smear, even though the direction of the light was corrected by passing the second boundary. Possibly the diagram is unrealistic, or only applies to the kind of glass that prisms are made from. In the latter case, the difference between the refraction of that kind of glass and the refraction (dispersion) of air must be absolutely enormous, since light from distant objects travels through miles of air without noticeable dispersion. Card Zero (talk) 21:25, 9 June 2013 (UTC)
- Well, if you look through a pane of glass as thick as an effective prism, the view will be bad. Still, it's not as bad as you'd think from the division of the light, because all those rays get bent back to parallel again at the far side of the pane. Just because you're looking at a ray from a few millimeters over from where it would be without a pane of glass, doesn't mean that it is off by that much in terms of angle, because the view from a few millimeters over is almost (but not quite) the same. I think. Yes, I should bring sources here and not doing so I'm risking being wrong myself, but I know glass doesn't have a refractive index of 1! If something were pretty much transparent, with a refractive index same as air, it would be invisible. [3] It is those edge effects that give away glass when we look at it as being there. Wnt (talk) 23:32, 9 June 2013 (UTC)
- But the dispersion ... if you look at the diagram at the top of Dispersion (optics), it shows light spreading out to a width of about a third of the thickness of the glass it has travelled through. This would make a view through a window into a blurry smear, even though the direction of the light was corrected by passing the second boundary. Possibly the diagram is unrealistic, or only applies to the kind of glass that prisms are made from. In the latter case, the difference between the refraction of that kind of glass and the refraction (dispersion) of air must be absolutely enormous, since light from distant objects travels through miles of air without noticeable dispersion. Card Zero (talk) 21:25, 9 June 2013 (UTC)
- Note that according to soda-lime glass its index of refraction is 1.5, which is scarcely a match for air. Window glass is transparent because the bending of light that occurs at one boundary is undone at the other. (Consider a camera lens - it is transparent so long as it is in focus. A flat pane being at focus with infinity) Wnt (talk) 19:33, 9 June 2013 (UTC)
- Now I'm wondering why it's possible to see clearly through the air, but according to sunset, it isn't! So that's OK, story checks out. Card Zero (talk) 22:28, 6 June 2013 (UTC)
- Because behind the scenes, an engineer cared about details you never even thought to care about. Your window-glass has almost the same index-of-refraction as ordinary atmospheric air; and the pane of glass has tolerances that are very well-controlled so that it is an optically-smooth surface. Humans have been building and perfecting optical glass recipes for thousands of years, and today's materials are much better than those from thousands of years ago. The glass has a very high transmittivity at all optical wavelengths; it is almost perfectly colorless to your human eye. All you have to do to see how important these details are is to build yourself a container with a glass window, and submerge the container under-water! Suddenly you won't be able to see in straight lines and all the colors outside will be wrong... Nimur (talk) 22:05, 6 June 2013 (UTC)
- I am now wondering why it is possible to see clearly through a window. Card Zero (talk) 21:58, 6 June 2013 (UTC)
Hi! I am also a grade 10 student from India. I know scattering of light is inversely proportional to the fourth power of wavelength; that is why blue light scatters more than any other visible light color. Is this the same reason (=inversely proportional to the fourth power of wavelength) why blue light refract more than any other visible light color? 106.209.202.129 (talk) 05:47, 10 June 2013 (UTC)
A problem of too much Lactic Acid exists?
editIs there any Medical Diagnosis whatsoever referencing to a state in which one's body produces more lactic acid than normal, so that a person feel pain while doing aerobic exercise? Ben-Natan (talk) 23:36, 6 June 2013 (UTC)
- Yes: lactic acidosis. Looie496 (talk) 23:46, 6 June 2013 (UTC)
- How come the article doesn't have a "Treatment" chapter? Ben-Natan (talk) 04:04, 7 June 2013 (UTC)
- Try somewhere like WebMD instead. --Jayron32 04:10, 7 June 2013 (UTC)
- Note that as per the article, the condition has a number of different causes and by it's nature is not something likely easy to treat. So I'm not sure that there is likely to be a treatment (and sources seem to back me up on this although one does suggest a few not particularly promising options but seems to be concentrated on critical cases with severe underlying causes where the condition appears to be most prevalent) beyond treating the underlying conditions if at all possible and managing the condition itself if necessary for example by limiting exercise and when it does cause problems managing and treating the symptoms particularly the serious ones and. Nil Einne (talk) 15:15, 7 June 2013 (UTC)
- Try somewhere like WebMD instead. --Jayron32 04:10, 7 June 2013 (UTC)
- How come the article doesn't have a "Treatment" chapter? Ben-Natan (talk) 04:04, 7 June 2013 (UTC)