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Is it safe to mix isopropyl alcohol and ammonia?[edit]
Is it safe to mix isopropyl alcohol and ammonia? It will be used for cleaning (e.g. glass). William Ortiz (talk) 00:45, 15 July 2008 (UTC)[reply]
I don't know, but would caution against mixing your own chemicals, since some combos, like chlorine bleach and ammonia, can produce toxic gases. I'd just use diluted ammonia for window cleaner, since it works well without the alcohol. StuRat (talk) 02:30, 15 July 2008 (UTC)[reply]
Sigma-Aldrich is selling a 2.0 M solution of ammonia in isopropanol (see [1]), so the two chemicals are unreactive. --Bowlhover (talk) 08:05, 15 July 2008 (UTC)[reply]
first it should be bo problem to mix IPA with ammonia because we will say their tendency is base both. but be careful for the ammonia, its odor and vapor is quite irritated, with eye and nose especially.
second if to clean glass I would recommend any alcohol is enough, most glass cleaning agent formulated from butyl cellosolve. anyway try a litlle first with coated glass eg. computer monitor, TV which claimed coating something on screen to protect your eyesight. the coating may be peeled off.
for me, water with drop of dish washer is perfect to clean glass.........ninjaw
s it true that due to Earth's rotation, water and air masses turn in different directions in both hemispheres. For example, if I am draining water from a sink in Sydney, would the water really rotate clockwise but in Los Angeles, it would rotate counterclockwise? What is the source of this phenomena? Do we have an article on this? Can someone perhaps shed some light on this?--A Real Kaiser...NOT! (talk) 06:27, 15 July 2008 (UTC)[reply]
It's called the coriolis effect, which has a section on draining water. Essentially, the effect is too weak on such small scales to matter compared to random influence and the shape of the sink/bathtub/etc. Someguy1221 (talk) 06:38, 15 July 2008 (UTC)[reply]
This has always interested me, since childhood (and unlike the poster in a thread above, no we don't all time travel into the future one year per year, I've remained stuck in little kid mode!) when I would sit in the bathtub and twirl the draining water backwards - it would always go back into clockwise rotation, basically obeying the right-hand rule. Is it at least generally true that everything drain-wise we commonly see in every day life spins clockwise? Does anyone have a counter-example? Southern hemisphere 'pedians are welcome to post, but please type backwards.
I've always been curious about the no-Coriolis explanation - why do businesses design right-hand bathtubs? These are the questions that plague me :) Franamax (talk) 06:50, 15 July 2008 (UTC)[reply]
Well I just filled my sink and let it go...it made a nice counterclockwise cyclone even though I'm in the northern hemisphere :-p Someguy1221 (talk) 07:25, 15 July 2008 (UTC)[reply]
In the northern hemisphere, the Coriolis effect applies a small tendency to rotate draining water counterclockwise. This is the reason low-pressure weather systems rotate in that direction north of 0 degrees. --Bowlhover (talk) 07:39, 15 July 2008 (UTC)[reply]
Hmm. I get kitchen sink = clockwise, bathroom sink - didn't work 'cause of the plug thingy, bathtub = clockwise (after I found the plug, I only take showers). My family and friends are going to think I'm a bit weird when I visit them over the next few weeks and puddle around their houses :) I do recognize the paradox vs. the Coriolis effect and I'll stop when I find a ccw drain, honest. Otherwise, Someguy will have to mail me their sink. Ahh the unsolved mysteries of childhood - thanks all for the input! Franamax (talk) 21:50, 15 July 2008 (UTC)[reply]
I don't know about bathtubs, but I've certainly seen water in drains rotate in both directions, as well as water in toilets. The direction of water in any specific toilet, though, is constant because the water used to flush it is injected in the same way every time.
To answer the rest of the OP's question, the Coriolis effect does have a significant effect on Earth's weather. It generates cyclones and anticyclones, determines the direction of the prevailing winds, and is partially responsible for ocean currents. --Bowlhover (talk) 07:39, 15 July 2008 (UTC)[reply]
Is there any relation between Dental infections or dental procedures and loss of eye sight —Preceding unsigned comment added by 195.229.236.211 (talk) 08:10, 15 July 2008 (UTC)[reply]
In a system as complicated as the human body it is difficult to say without more details. (Standard Wikipedia Disclaimer: The reference desk does not offer medical advice.) The interdependencies and what ties into what within a living organism, particularly a set as complicated as mammals. If you're really concerned about it, my first guesses would be a drug interaction, possibly between any anesthesia you were given and any other medication you were taking, or depending on how invasive the procedure it is possible there was nerve damage. You also mention infections, and given the proximity of your mouth to your central nervous system I suppose it might be possible the infection traveled. Take the above with a grain of salt, as I'm not an expert, but my short answer to your question would be, "Yes, anything is possible. If you've had any kind of weird changes in your medical condition after a procedure, see a doctor." EagleFalconn (talk) 13:06, 15 July 2008 (UTC)[reply]
I'm confident that the answer is "No" directly, but "Yes, possibly" indirectly. Dental surgery could, like any other surgical procedure, allow infections to take place which may then cause loss of sight. As EagleFalconn also said, there is also the possibility of drug interaction or nerve damage. I'm going to take a guess that you are concerned about either your or someone else's loss of vision since this is the second post you have made regarding loss of vision. I really suggest you ask a physician if you are concerned because honestly, they won't bite. — CycloneNimrodTalk? 20:36, 15 July 2008 (UTC)[reply]
They probably don't need my two cents, but it looks a lot like a variety of stink bug that we see pretty often in Indiana. EagleFalconn (talk) 13:00, 15 July 2008 (UTC)[reply]
I can't see how it looks like a stink bug (or shield bug in UK) The mystery beetle had a separated head and it is about twice as long as it is wide. The stink bug has the head joined directly to the thorax and is about about as long as it is wide. I find it hard to disagree with your initial phrase EF. Richard Avery (talk) 13:52, 15 July 2008 (UTC)[reply]
To be honest I agree with you, I'd always wondered why they were called stink bugs. I'd never experienced any particularly putrid odors. My guess is that its a regional misnomer, but the snide remark wasn't really necessary. EagleFalconn (talk) 14:27, 15 July 2008 (UTC)[reply]
Yup, you're right, I'm sorry for that. Richard Avery (talk) 19:37, 15 July 2008 (UTC)[reply]
Remember that common names may get applied to multiple species. See Boisea trivittata for the "stink bug" that EF is refering to - which is similar looking to the unknown bug. Rmhermen (talk) 20:22, 15 July 2008 (UTC)[reply]
The BBC link mentions that it looks similar to arocatus roeselii. In my opinion they look so similar that I would bank on it being one of them. Wikimedia Commons has an image which is labelled as arocatus roeselii. See below. Very close likeness of the markings. Arocatus roeseliiRichard B (talk) 14:35, 15 July 2008 (UTC)[reply]
Just so we're clear where the confusion lies (come on, does anyone here really think they can out-classify the London museum of natural history? Especially given that we're just working off of a single image from an article, and they have live samples), from cnn.com:
“
The bug resembles the Arocatus roeselii, which is usually found in central Europe but is a brighter red and lives on alder trees.
Entomologists suspect that the new bug could be a version of the roeselii that has adapted to live on plane trees but acknowledged that it could be an entirely new species.
Why is putting sugar into a vehicle's gas tank bad for the engine? Dismas|(talk) 08:25, 15 July 2008 (UTC)[reply]
According to this Snopes article, sugar is insoluble in gasoline and cannot even reach the engine. Instead, it's blocked out by two filters specifically designed to keep contaminants out of the engine. --Bowlhover (talk) 08:42, 15 July 2008 (UTC)[reply]
The Straight Dope also discussed this as an SD Staff Report, and indicated that it would, in fact, be bad for the engine. When objections surfaced along the lines of the Snopes article, they tackled the question again and came to the same conclusion, this time after conducting an experiment. (It apparently didn't ruin the engine, but certainly put it out of commission for the time being.) -- Captain Disdain (talk) 11:54, 15 July 2008 (UTC)[reply]
A note of clarification. Both the Snopes article and the Straight Dope article suggest that while a large quantity of sugar in the gas tank could immobilize an automobile, it has nothing to do with any direct effect on, or harm to, the engine. Rather, the accumulation of gasoline-insoluble sugar is apt to clog up the 'sock' or the fuel filter, starving the engine for gasoline. TenOfAllTrades(talk) 14:02, 15 July 2008 (UTC)[reply]
For a more general answer - everything2 is not considered a reliable source by wikipedia's policies, and it is a site that anyone can sign up and add content to, so you probably could not use this as a source e.g. if you were to write a paper. It may be worth your time to check out the sources that it lists at the bottom though. --Random832 (contribs) 18:24, 18 July 2008 (UTC)[reply]
Can one person create the sound of a barber-shop quartet?[edit]
I watched a cartoon recently where one of the characters sings a song in the style of a barber-shop quartet i.e. 4 harmonised tunes all sung together.
This got me wondering. Is there any physical reason why a single person couldn't produce the sound of many notes (e.g. a chord or a harmonised tune) using only one voice? Presumably, if a single speaker connected to an amplifier can play music comprising many different notes and instruments at one time, a human's vocal chords can do the same? Could someone train their voice to do this?
Beyond the specific and limited capabilities of throat singing, though, I'd say the answer is No. A typical speaker can produce arbitrarily complex waveforms, because it's constantly driven by a magnet, which pushes air in whatever pattern is encoded in the signal. The voice, though, is closer to a musical instrument, with a single vibrating surface to generate the sound, driven by resonance when wind is passed over it. You're not singing by actively vibrating your vocal chords; you're pushing air over them, which makes them vibrate. You can vary your throat shape to accentuate harmonics, but I would think you can't make completely independent sounds. jeffjon (talk) 15:06, 15 July 2008 (UTC)[reply]
You might be interested in the electronic sound effect called chorus effect.Atlant (talk) 16:55, 15 July 2008 (UTC)[reply]
Let me guess, the cartoon is Family Guy and the character is Brian? --antilivedT | C | G 23:54, 15 July 2008 (UTC)[reply]
I'm going for a "No". Most barbershop music requires tenor, baritone, and bass singers, so you would need a pitch alterering device as well.--Shantavira|feed me 07:11, 16 July 2008 (UTC)[reply]
More precisely, tenor, lead, baritone, and bass. Lead is roughly a second tenor, but is not called a tenor. It's not impossible that one person with a large range could sing all of these -- actually a lot of barbershop tenors are natural basses, because barbershop tenor is normally sung falsetto.
Barbershop baritone is one of the most thankless roles you can imagine -- it's extremely difficult, because you're typically on the third or the seventh, but no one hears you because you're in the middle of the chord and don't have the melody. I'm a natural baritone, but sang lead because I don't have a good enough ear for barbershop baritone. --Trovatore (talk) 07:23, 16 July 2008 (UTC)[reply]
If you run and walk the same distance, will you burn the same amount of calories. —Preceding unsigned comment added by 199.166.15.246 (talk) 17:35, 15 July 2008 (UTC)[reply]
Here is some quantitative data on the amount of calories burnt for different body masses and different activities. --Bowlhover (talk) 18:05, 15 July 2008 (UTC)[reply]
i note that the graph on that page is oxygen/time (essentially calories per time) vs velocity. since the OP asked about calories per distance, that turns out to be the slope of the graph. now, the slope of the graph for walking up to the point where running starts and the slope of the running graph after that is about the same, indicating that in fact the calories used per distance is about the same whether running or walking, if you don't try to walk at an unusually rapid speed when you would more naturally be running. this agrees with what i've heard elsewhere, which is that calories per distance for a human is essentially constant with velocity except at very high velocities, and also at very low velocities, but that's just because the 2000 calories a day you need for your basic metabolism becomes significant. this also makes sense evolutionarily, where efficiency would be something that would be selected for, except at war emergency power life or death speeds. but of course, arguments from evolution can be used to support either side of an argument if you're clever. Gzuckier (talk) 19:47, 16 July 2008 (UTC)[reply]
about "some naive hypothesis at odds with basis of physik "[edit]
1--Can i have page history from july o9 08 till july 15 08 ?
2--It was my mistake that part of my writing above subject is not edited ? I am new user. I wrote three hypothesis: I- About a hypothetic particle that supposed to be the only basis component of common particles. II- About some " corrections" in the formula of Lorents-Ajnstain. III- About the gravity charge as +,- f^0.5 (That is +,- G^0.5 ). This charge together with electric charge supposed to be the only forces in equilibrium in ten kind simple common particles. They (Hypothesis)are naive because are not supported by sophisticated math. It used an simple math because the writer is illiterate on high math, so in physic.
But they are controversial with basis of contemporary physic, linked together to prove that no-thing can be created by nothing,that the supposed unique particle can not be created can not be destroyed, that the annihilation of matter is a wrong concept and the photons are common particles ( structured by the same unique particles.) which for outer frame are both electric and gravity null charged .
The user hoped that any bright lad or lads will find interesting the meaning of the hypothesis to search further and fill the lots of gaps. 70.248.135.115 (talk) 17:56, 15 July 2008 (UTC)[reply]
Just click "history" at the top of the page on any page in Wikipedia to get the history of edits to the page. Click on a version number and you'll see the page exactly as it was on that version.
Wikipedia is not a place to post your original work and ask others to critique it. It is a collection of references from published, respectable resources. You appear to be in need of a message board specializing in physics - and one specializing in basic English grammar. -- kainaw™ 18:02, 15 July 2008 (UTC)[reply]
Why don't leaves form a thin layer like a bag over a tree?[edit]
I was struck going under some trees by how many branches they had with leaves all higgley piggledy up the trunk with one lot of leaves covering another and gaps all over the place. I would have thought the most efficient form would have all the branches extending out about the same amount with the leaves at the end forming a sheet facing out. I'm sure it wouldn't be difficult to evolve that way if it were actually best, but if you look under tree you'll see they are nothing like that. Why aren't trees more like that? Dmcq (talk) 18:37, 15 July 2008 (UTC)[reply]
This is going to sound really snarky, but a short answer would be because intelligent design is probably wrong. That is to say, you're correct, that probably would be the most efficient arrangement. However, as you correctly identify, evolution has not yet favored that particular growth pattern. Its almost assuredly not impossible. In fact, its even possible that trees are approaching that kind of an arrangement. But they have to get there incrementally. Also, its entirely possible that the dome shape you imagine is not the most efficient, possibly for reasons of what the other trees in the area are shaped like (and therefore what spaces are available) etc. EagleFalconn (talk) 19:00, 15 July 2008 (UTC)[reply]
Thanks everybody for the replies, lots of ideas there. Nothing I could even begin to thinking of doing something like running a simulation with, especially by intelligent design I'd have to be God to be really sure my design was intelligent! I guess trees are quite different from each other so there can't be a unique best solution. On the point of whether tree have had enough time to evolve this, if you have a look at umbel you'll see something like what I was thinking about for flowers but even small plants don't seem to do this with their leaves. By the way the picture on the right of the carrot flower directly contradicts the text about the stalks being the same length. ;-) Dmcq (talk) 21:45, 15 July 2008 (UTC)[reply]
A dome would have gaps between the leaves, by having a three dimensional arrangement you fill in those gaps. There are certainly more efficient arrangements, but presumably they don't offer a large enough benefit, or have some downside, so trees haven't evolved that way. Trees have been around for 100s of millions of years, I think evolution would have achieved an optimal arrangement of leaves by now if such an obvious one existed. --Tango (talk) 19:28, 15 July 2008 (UTC)[reply]
Be interesting to know what the downsides might be. Perhaps it isn't best for leave to be in full sunlight and the top leaves are sacrificial to some extent, but then I guess they'd flop around or droop or something like that Dmcq (talk) 21:45, 15 July 2008 (UTC)[reply]
Trees probably don't grow according to centralized planning. Each little part of the tree is probably given a little autonomy in adapting best to its particular conditions. So you get something that looks a little irregular but is obviously efficient enough to work. That's all evolution gives you: just enough to work and not get totally out-competed. Anyway, your assumption about what is "optimal" is contingent on a number of assumed conditions about the particular light the tree could get, the spacing of trees between one another, wind conditions, the "cost" to the tree in terms of generating leaves, etc. I'm not sure your design would be ideally optimal in all conditions (and the question of how the tree would "know" how big to make each branch also probably introduces some sort of need for an energy-intensive feedback system as well). --140.247.241.142 (talk) 19:32, 15 July 2008 (UTC)[reply]
This answer and the next seem to directly contradict each other as to a cause to get the same result! And I can't make my mind up as to which one sounds more probable. Yes the individual leaves probably do compete with each other. And yes the whole tree might benefit and so be more successful if leaves cooperated in letting light through. I tend a little bit more to the former. As to a feedback system for knowing how much to grow and when to stop - tat would be fairly straightforward I'd have thought. Just keep growing whilst the light flickered a lot.~~
The sun moves.. Leaving gaps between the leaves means that leaves on the far side of the plant still receive light even when the light comes from the other side.. Also the wind moves the leaves around meaning that this sort of built in margin for error is useful.87.102.86.73 (talk) 19:51, 15 July 2008 (UTC)[reply]
See last question and answer, this assumes it is in the best interest of the tree to share the light around. I'm not ure that is right becaue it also allows light to fall below the tree and o allows compeitors to grow.Dmcq (talk) 23:21, 15 July 2008 (UTC)[reply]
Think of Cactus. Whenever evaporation is more of a problem than a chance (evaporation pulls the nutrients up the tree) plants do grow in balloon shape. 93.132.180.33 (talk) 20:27, 15 July 2008 (UTC)[reply]
Not sure the shape has anything to do with being efficient at using resources to gain energy from the sun. More like cutting down the problems caused by the sun.Dmcq (talk) 23:21, 15 July 2008 (UTC)[reply]
Some shrubs do (sort of) see Hedge (barrier) the foliage is so dense that more than a few inches inside the hedge all that there is is dry branches..87.102.86.73 (talk) 20:29, 15 July 2008 (UTC)[reply]
Yes, very interesting. They are much more like what I was thinking of. However they use up an awful number of branches to achieve the effect. Less branches with ends that opened out like the picture on the right in the article on umbels to hold the leaves would enable them to grow bigger with less expenditure on branches I'd have thought. Dmcq (talk) 23:21, 15 July 2008 (UTC)[reply]
The shape of a tree is a compromise between many different factors. A spherical tree such as a cactus is best for water retention, but this comes at a cost in photosynthesis efficiency (half the surface is shaded at all times). Big leaves are great for gathering sunlight, but are highly flammable, succeptible to wind damage, and leak water like a sieve. Pine needles are wind-resistant, burn without generating much heat, and are fast to regrow after a fire, but don't gather much sunlight.
It's funny that pine grow more in cold conditions if their leaves are bad at collecting sunlight. Trees seem to be just plain ornery. Dmcq (talk) 23:21, 15 July 2008 (UTC)[reply]
Like I said, it's a compromise. Pine needles aren't that great at gathering sunlight, but they are easy to replace, they burn without damaging the tree much, they aren't damaged by high winds, and they shed snow easily. A big-leaf tree might gather more sunlight, but that doesn't help much if the leaves get ripped off or burned on a regular basis. --Carnildo (talk) 22:53, 16 July 2008 (UTC)[reply]
There is no single "best" tree shape. Evolution ensures that any given tree species is near-optimal for its enviroment, but the wide range of environments and the number of different ways of responding to them means that there are many different shapes for trees. --Carnildo (talk) 22:28, 15 July 2008 (UTC)[reply]
Who knows? Perhaps there is a best tree shape or at lease a very much more restricted number of shapes that are optimal for their conditions than are anywhere near what happens in nature. I don't think I'm anywhere near perfect and yet evolution designed me (Go on, contradict me. No - oh well!). I guess the question I put does go somewhat towards asking what is an efficient tree shape, after all my thoughts about that were obviously wrong. Dmcq (talk) 23:21, 15 July 2008 (UTC)[reply]
Building on the answer above that they may just not have had time to evolve a shape like I was thinking: Fractal shapes can give something that looks like a tree, perhaps the answer that they are good enough for the job because they only compete with other trees is right, and they just haven't the need or maybe even the capacity to develop enough additional complexity to be other than a simple fractal. Dmcq (talk) 23:21, 15 July 2008 (UTC)[reply]
I think a big part of it is that a sphere may not be as effecient as you think. A sphere is effecient for containint volume and MINIMIZING surface area. It's in the benefit of the plant to maximize the surface area (and therefore the number) of leaves facing the sun. Also, by having a broken, tiered surface as most trees have, light gets to almost all sides and levels of the tree at any given time, so every area that needs food (for the most part) gets it. If it was just a big bag of leaf material draped over the tree, the further one gets from the equator the less light would be received by the tree: a large section of leaves would never see direct sunlight because of the earth's tilt. Of course, as 87.102 pointed out, with all the diversity in the world, there certainly are plants that sort of fit your idea. --Shaggorama (talk) 12:08, 16 July 2008 (UTC)[reply]
Well, more than one leaf facing the same direction when one leaf is occluding the other doesn't really give the tree the benefit of the full surface area of each; what needs to be maximized is the total amount of light being absorbed by the leaves. A single "bag of leaf material" would be easily torn by wind; with multiple layers the inner layers wouldn't be self-sustaining, so we have the present "design" as the most effective compromise. --Random832 (contribs) 17:01, 17 July 2008 (UTC)[reply]
I think we need to not imagine a lone tree on a hilltop, but a young tree trying to establish itself in the middle of a forest. A dome would be inefficient in that scenario. APL (talk) 13:02, 16 July 2008 (UTC)[reply]
there's also an ecological/evolutionary component. i.e. (as i was taught, can't verify it from my experience) trees which grow in dense forests tend to have a canopy of leaves which grab all the light, for purposes of competition. if they don't, another tree will, leaving them in the dark. on the other hand, trees which tend to grow less densely tend to have canopies which let much more light through, because any advantage to the individual tree is overshadowed by the advantage to the tree's progeny growing near the parent of getting some light through. this was supposed to explain why some leaves are so serrated, etc., and why some are huge elephant ear leaves and some are just little things. Gzuckier (talk) 19:33, 16 July 2008 (UTC)[reply]
Wind damage. A larger continuous surface will be more affected by strong winds. Also more likely to shake destructively. Polypipe Wrangler (talk) 04:56, 17 July 2008 (UTC)[reply]
Wind damage can take out whole limbs, as can a number of other factors. Leaves can be eaten away by anything from giraffes to bugs. It makes sense for a tree's branch structure and leaves to take on forms that can survive the whatever is likely to cause damage. The human body, likewise, seems to have all kinds of redundancy. Pfly (talk) 05:04, 17 July 2008 (UTC)[reply]
I had a look at forest and the trees there didn't seem to have a flat top unlike what I would expect. But having a look round at other trees under baobab and cypress there are lone trees with the sort of flat top I would expect in a forest. The dragon tree is more rounded at the top, the start of quite a good dome shape. It has quite thick branches though. The wind damage idea sounds interesting, I guess there might be less wind resistance with gaps for the wind to go through so branches an be thinner. Dmcq (talk) 10:54, 18 July 2008 (UTC)[reply]
Constructal theory might have shown that the branching needed to make the proposed tree would make for inefficient transport of water from the roots. This is just one of a myriad of fascinating factors which seem to influence trees, thanks for a great question! EverGreg (talk) 21:58, 21 July 2008 (UTC)[reply]
while wearing glasses may help a person suffering from myopia by focussing rays from objects on the retina, wont it alter the relative distance of the object from the eye? for instance an object at infinity will appear to be at the focal point of the lens. so do objects appear closer/further than they actually are?
59.180.19.237 (talk) 20:43, 15 July 2008 (UTC)[reply]
As someone who wears glasses for somewhat severe nearsightedness I can tell you that it takes about a day or two to get used to the change in depth perception caused by a stronger prescription. During those one or two days I find myself reaching for things about an inch closer than they really are.
I'm not sure if that answers your question or not, but I hope it helps. APL (talk) 20:59, 15 July 2008 (UTC)[reply]
Per APL, objects do indeed appear to be in the 'wrong' place in space—at least, at first. The brain very rapidly adapts to the 'distorted' view, and you can start to confidently reach for your pints once again. I don't have a link for you, but studies have been done involving the use of glasses which deliberately distort vision (including going so far as to invert vision: [2]). Depending on the degree of distortion, subjects were able to perform tasks relatively normally after a period of acclimatization (hours or days). The brain is quite adept at integrating the feedback from the body's musculoskeletal system with vision information to build a consistent internal model of reality. TenOfAllTrades(talk) 21:18, 15 July 2008 (UTC)[reply]
thanks. but what i dont understand is, in the case of a diverging lens, the image is always formed between lens and focal point(am i right?)-so even very far off objects will appear to be at the focus. so does that mean that people wearing glasses perceive everything to be within the focal length of the lens?
59.180.73.240 (talk) 04:44, 16 July 2008 (UTC)[reply]
effectively yes, I think you're right - this is true for people with short sight - and the image should be within the range in which they can see ie near things.87.102.86.73 (talk) 11:12, 16 July 2008 (UTC)[reply]
It sounds like you have been studying optics, particularly thin lenses - so that's good. Just a small misunderstanding I think. Keep in mind, the lenses in our eyes take incoming light and focus it onto the retina. The image distance is always the distance between the lens and the retina - so pretty constant. The way we do this is by changing the shape (and thefore the focal length) of our lens. For many people, our lenses do not quite focus the light correctly and the light is focused too soon or too late. That is why corrective lenses are used, they cause the light to be focused directly on the retina. If the eye tends to focus the light too early, we use diverging lenses to spread it slightly so it focuses later, etc. So objects don't 'appear' to be hovering at the focal point of the lens in front of us anymore than the original object does. The image is not in front of us - it is on our retina. Hope this helps. PhySusie (talk) 11:23, 16 July 2008 (UTC)[reply]
I'm sure they meant the 'constructed image' or 'apparent focus' or whatever it's called - what is it called?87.102.86.73 (talk) 13:12, 16 July 2008 (UTC)[reply]
I think what you're looking for is virtual image. On a slight tangent from the question, I can't find a source for this but an experiment was once described to me where a group of people were given glasses that inverted their visual field, and after a day or two they all adjusted so that when the glasses were removed, they saw everything upside. The brain's a neat thing/ --Shaggorama (talk) 15:53, 18 July 2008 (UTC)[reply]
