Wikipedia:Reference desk/Archives/Science/2013 April 9

= April 9 =

Colour of water
Hi, there was a question once at Colour of water about why the water in the pool in the image at the right looks equally blue regardless of whether one is looking through a few centimetres (at the edge of the pool) or several feet (in the centre of the pool). "Common sense" would suggest that the more water you looked through, the bluer it would be. AFAIK, no satisfactory answer was ever provided. Does anyone have an explanation? 86.171.43.156 (talk)


 * Water is very faintly blue (or blue-green, in the case of sea water). So, a small amount of it will appear clear, unless blue dye has been added or something blue is behind it, like the bottom of the pool painted blue.  In your example, the water in the bucket certainly doesn't look as blue.  StuRat (talk) 03:00, 9 April 2013 (UTC)


 * When water is deep enough, it appears black. Plasmic Physics (talk) 03:19, 9 April 2013 (UTC)


 * I don't see how any of that answers the question. Why does the water in the bucket look much less blue than the same thickness of water at the side of the pool? (We take it on trust that the pool is tiled throughout with the same white tiles as are visible around the edge.) Why does the deepness of the blue not reduce dramatically at the sides of the pool where you are looking through an increasingly small distance of water? 86.171.43.156 (talk) 03:35, 9 April 2013 (UTC)


 * What do you mean? Stu just answered that in a direct manner, what part of his answer do you not understand? Plasmic Physics (talk) 03:48, 9 April 2013 (UTC)


 * I think they're saying that there is a point near the wall where you are only looking through as much water as is in the bucket, yet it looks far more blue. I suspect the answer is simple scattering. The water in the pool is all scattering the blue reflected off the bottom of the pool. Since the bucket is opaque and white, it will look far more clear. Vespine (talk) 04:05, 9 April 2013 (UTC)


 * (ec) I think I understand. He was assuming that the light 6 inches below the waterline shines straight in 6 inches, hits the edge of the pool, then reflects right back out of the pool, just as it does in the bucket.  However, most of the light that hits 6 inches below the waterline is reflected downwards to the bottom of the pool, while other light reflects back up from the bottom of the pool, hits that spot 6 inches below the waterline, and back out again.  Thus, this light has traveled through a lot more than 1 foot of water total, and had the redder waves absorbed, leaving a distinctly bluish tint.


 * A horizontal, opaque, white surface, 6 inches below the waterline, should appear white, not blue. StuRat (talk) 04:09, 9 April 2013 (UTC)


 * According to the caption the bucket is floating. Thus, the depth of water in the bucket is not the same as that in the pool.  Spinning  Spark  11:27, 9 April 2013 (UTC)


 * That is not the point... 86.128.0.95 (talk) 11:37, 9 April 2013 (UTC)

The meltwater pool on top of a glacier does look very blue. --Stone (talk) 08:09, 9 April 2013 (UTC)


 * I think it's because your pool has a blue liner and your bucket is white. Also, if you ever look at a large swimming pool with a diving-depth deep-end it is noticeably bluer. There are also effects from disinfectants in the water, especially pools, depending on what you use. Some municipal water supplies have a greenish tint for this reason. Shadowjams (talk) 14:05, 9 April 2013 (UTC)


 * As I mentioned above, "we take it on trust that the pool is tiled throughout with the same white tiles as are visible around the edge". If that is not the case then all bets are off. 86.128.0.95 (talk) 17:23, 9 April 2013 (UTC) Also, the effects of tints in the water do not seem relevant to the question of why the water looks very blue right to the edge of the pool, or why the bucket (assuming it is the same water as is in the pool) is much less blue than when looking through equivalent distance of water at the edge of the pool.


 * It looks to me like the white tiles only go 4 rows below the edge (5 if you include the edge tiles). StuRat (talk) 17:28, 9 April 2013 (UTC)


 * I agree it seems a bit odd that you can't see any trace of the tile divisions below the waterline, but I still believe that the tiling (or, probably, imitation tiling) stretches down into the pool. What do other people think? 86.128.0.95 (talk) 17:55, 9 April 2013 (UTC)


 * Well, we're questioning the very premise of your question, and now you're trying to fiat a basic premise of the facts. I do think water in fact will scatter more light the more of it light has to go through, and I don't think that your picture is comparing apples to apples. We're surprisingly good at answering the question "why does this thing that doesn't happen happen" here at the reference desk, but you may have stumped even us this time. Shadowjams (talk) 21:43, 9 April 2013 (UTC)
 * If the pool has a blue liner then the whole purpose of the photo is destroyed, and the caption "Water in an indoor swimming pool appears blue against a white background, right up to the waterline. The same water inside a floating white bucket appears only slightly blue." is a deception. There seems no reason for someone to do that, which is why I take it on trust, though I cannot prove it, that the pool does not have such a liner. 86.128.0.95 (talk) 22:35, 9 April 2013 (UTC)


 * I think the question has been answered- more blue photons are trapped in the water medium and scattered in the pool. May I suggest the OP do some real life experiments :) Ap-uk (talk) 22:37, 9 April 2013 (UTC)


 * Here's an experiment you can do that I think is related (I discovered this accidentally). Take a basic white porcelain sink, with nothing in it, and fill it with a few inches of water.  Then put your hand into the water.  When you do, you will see (probably) that the water appears to take on a reddish tinge -- the entire pool of water, even far away from your hand. Looie496 (talk) 22:54, 9 April 2013 (UTC)


 * It seemed to me that Looie was pulling our legs. But, as I was about to wash the dishes, I tried this (in a regular stainless steel kitchen sink).  No such red tinge occurred, of course.  But what happens if a dispersant is added?  It happens that I have an expired box of dispersible piroxicam  (a painkiller you mix with water and drink).  I stirred in several tablets until the plug was a bit hard to see.  Then put a red object in.  Still no red tinge!.  Just a red blur around the object.  I reckon StuRat has the key to it - the pool in the picture has the tiles below the water blue in colour (except for the upper three rows), just like many pools I've seen.  Wickwack 124.182.36.200 (talk) 23:51, 9 April 2013 (UTC)
 * Of course the danger of any experiment is that it may fail if the conditions are varied. I just tried it again with my bathroom sink, and it works as described.  The water in the sink appears to have a slight bluish tinge when there is nothing in it; when I put my hand in the tinge becomes reddish. Looie496 (talk) 01:49, 10 April 2013 (UTC)


 * I've seen this happen, but it does need to be a situation (like a shiny white sink) where your hand is very much the dominant colour, which reflects back. And it usually works best in sunny conditions. 86.161.209.128 (talk) 08:28, 10 April 2013 (UTC)


 * Couple things to note:
 * The picture has been edited/processed after capture; no information is given about what color the ambient lighting had and what processing was done to the picture.
 * The pool probably had a blue liner, which is quite common. (I've seen big fish tanks that measure a few feet across. I don't remember seeing any noticeable blueness when looking through the tanks sideway.)
 * The bucket may not be that opaque. The little blueness in the water inside the bucket may be the blue reflected light in the pool showing through.
 * --98.114.98.123 (talk) 12:33, 10 April 2013 (UTC)


 * The water in the bucket does not look blue to me! Pool_and_bucket.jpg--Aspro (talk) 21:22, 11 April 2013 (UTC)

Mus musculus anatomy and behavior, plus trap physics
Some few minutes ago, I heard the snap of the mousetrap in the kitchen, and I went out soon enough that the mouse was still twitching and its tail still moving around. This prompted a few questions in my mind that I've not been able to answer with a Google search: Nyttend (talk) 04:42, 9 April 2013 (UTC)
 * Why does a trapped mouse twitch? Is it something neurological that's comparable to what causes a chicken to move uncontrollably after being beheaded?
 * What does a healthy Mus musculus do with its tail in daily life? Balance?  I've only ever seen the species (1) in traps, or (2) running around on my floors, seemingly not using its tail.
 * Why do traps often flip upside down when set off by a mouse? Is the spring so powerful that its momentum forces the trap to go upside down, or is there some other explanation?


 * 1) All animals may twitch shortly after death, including humans. The muscle cells remain alive, and have energy, for some time, but only receive random nerve impulses, so move randomly.  If you apply an electric current, you can cause the twitching yourself.  This is the basis for the fictional idea that you can bring the dead back to life with a lot of electricity, as in Frankenstein.


 * 2) Yes, balance. You'd need some high speed film to see it using it as a counterbalance during quick turns, etc.


 * 3) Yes, the momentum of the spring does it. StuRat (talk) 04:46, 9 April 2013 (UTC)


 * Agreed with Stu. But if you suspect the mouse is still alive, put it in a plastic bag and step on it to put it out of its misery. μηδείς (talk) 11:31, 9 April 2013 (UTC)


 * I can't recommend you do that, you might get prosecuted for cruelty to animals! Wnt (talk) 22:23, 13 April 2013 (UTC)

Orbital Debris
After reading the "orbital debris" article, and a lot of the references, I just can't quite understand why so much stuff stays there. (1)Surely whenever there's a collision between objects, or even a close pass, they must both end up with a change in velocity that would eventually de-orbit them? (2)Is a "Graveyard orbit" one that is slowly decaying away from Earth? or is it just a stable orbit that's out of the way above the valuable stuff? (3)How big would an orbiting object have to be to actually attract other objects to itself by gravity? I hope someone can help me with this, thanks in advance. 122.108.189.192 (talk) 07:34, 9 April 2013 (UTC)
 * If they collide they just get orbits which aren't so circular in general. Reducing the speed of an object that is in a circular orbit puts it into a more elliptical orbit but whatever happens unless it encounters drag from the atmosphere it eventually gets back to where it started (ignoring other gravity effects, pressure from sunlight solar wind, magnetism etc.). For low earth ones that means they will probably decay faster but for higher ones it simply means you have an expanding cloud of debris. The graveyard orbit is just one that's out of the way, I don't think of it as a complete solution myself. The stuff up there is too small and far away from each other for gravitation to have an effect that matters. Dmcq (talk) 08:19, 9 April 2013 (UTC)


 * There is no minimum size an object has to be to attract other objects. However, the gravitational attraction of small objects is very easily overcome by other forces.  In particular tidal forces prevent the formation of bodies by gravity inside the Roche limit.  Spinning  Spark  11:19, 9 April 2013 (UTC)


 * Over time, collisions will cause objects to either go into low enough orbits that atmospheric drag causes them to re-enter and burn up, or go into high enough orbits that they stop colliding with things. However, collisions in orbit are actually very rare - it would take centuries (at least) for what is up there to clean itself up through collisions.
 * Graveyard orbits are just high enough orbits to be out of the way. They are potentially still a problem if you want to go through that orbit (to get to geostationary orbit, for example) or if two things in graveyard orbits collide and some of the parts get knocked into orbits that cross low earth orbit (although, the further out you go the more room there is, so such collisions are unlikely).
 * See Hill sphere for details of stable orbits around satellites. For objects in low earth orbit, the object would have to be denser that any naturally occuring materials for anything to orbit them (it isn't enough for an object to be very massive, it needs to be small too or orbits around it have to be too large to avoid colliding with it). There will still be an effect from gravity even if there isn't a stable orbit possible, but for any realistic satellite it won't be a measurable effect. --Tango (talk) 11:26, 9 April 2013 (UTC)


 * By the way, graveyard orbits for (former) geostationary satellites are only a little bit above the geostationary altitude. Because the Moon is slowing down Earth's rotation, we will have a problem again in 30 or 40 million years or so, when the geostationary height will be higher up due to the slower rotation of the Earth. But I don't know how stable the satellite's orbit is over such a timescale. Icek (talk) 14:37, 9 April 2013 (UTC)
 * Thank you all, that gives me a much better grasp of the situation. 122.108.189.192 (talk) 06:35, 10 April 2013 (UTC)

How do u explain this
— Preceding unsigned comment added by Yoglti (talk • contribs) 13:45, 9 April 2013 (UTC)


 * Simple, it's fake, the video is edited. - Lindert (talk) 14:04, 9 April 2013 (UTC)


 * There's so many much better fakes I can't see why this one was posted here. Dmcq (talk) 14:15, 9 April 2013 (UTC)


 * I agree that it's fake. However, I think it's time-lapse photography (as opposed to being edited with the glass of water replacing the glass of ice).  The utility room or garage where the demo takes place must be cold enough to freeze the water over several hours.  Note that it is possible to freeze water instantly, if you can make it into a supercooled liquid first (why does that link lead to an article on glass blowing ?) .  Or, of course, you can also just cool it very quickly, say by dumping dry ice into it (stand back !). StuRat (talk) 14:26, 9 April 2013 (UTC)


 * Supercooling gets there, I agree the other should probably go there too. Anyway here's a proper demonstaratio of water turning of ice quickly Dmcq (talk) 14:38, 9 April 2013 (UTC)


 * I added "supercooling" to the dab at the top of "supercooled liquid". StuRat (talk) 15:39, 9 April 2013 (UTC)


 * "Demonstaratio" = a method of evaluating the effectiveness of any demonstration = (time audience spends staring at demonstration) / (time audience spends staring out the window). :-) StuRat (talk) 15:44, 9 April 2013 (UTC)


 * Sure, supercooled water will freeze suddenly like that - but adding the salt would have been enough to add the necessary "nucleation sites" and to cause it to freeze even faster than the demo purported to show. So we know that it wasn't super-cooled.  Even if this was super-cooled water, all of the nonsense with the lighter and the straw would be superfluous - and because salt actually lowers the freezing point of water, it would make matters harder.  So the odds are good that this was done in a very cold garage over many hours.  The clue that this is such a simple fake is that the lighting in the background of the room and on the table changes rapidly as the ice forms - clearly indicating that this is a speeded-up video and light through some window is changing due to the sun moving across the sky.  So, yeah - it's another boring YouTube fake...yawn.  It's becoming *so* common for people to make these science-looking demos - and easily more than half of them are obvious fakes like this one - it's really childish and it's annoying because it un-educates gullible people - making them even more stupid than they were at the outset! SteveBaker (talk) 16:14, 9 April 2013 (UTC)
 * when i grew up in canada, it would get so cold the words would freeze as they came out of your mouth, and you had to collect them and carry them inside and thaw them out by the fire to find out what the other guy said. Gzuckier (talk) 19:12, 9 April 2013 (UTC)
 * Is that why everything Canadians say sound like "Eh"? --Wirbelwind( ヴィルヴェルヴィント ) 20:22, 9 April 2013 (UTC)

It isn't supercooled ice or supercooled water, it's supersaturated solution of potassium acetate or sodium acetate. That is, there are no camera tricks, its just that someone gave a bogus explanation to a real video. I've done this demonstration a hundred times in chemistry class, though I didn't pretend what was happening was ice. See this video which largely mimics exactly what is showed above, except that it gives the actual, correct chemical explanation. -- Jayron  32  21:52, 9 April 2013 (UTC)
 * I'd have thought if that were so the crystals that were dropped into it would have acted as nucleation centres but nothing happened. I think the more obvious explanation above as indicated by the lights changing is the more probable. Dmcq (talk) 22:50, 9 April 2013 (UTC)

biology
Is there is a realation between diabetes and alzheimer's disease? — Preceding unsigned comment added by Titunsam (talk • contribs) 18:28, 9 April 2013 (UTC)
 * Google is excellent at this sort of question.
 * Well, it's ok to get a rough idea. If the OP is interested in actual details, PubMed is far better. The is a lot of circumstantial evidence for a link. Current thinking seems to revolve around various different aspects of diabetes, or more accurately metabolic syndrome. 1) Vascular damage 2)Metabolic damage due to hyperglycaemia, 3)Low level systemic inflammation and 4) The effects of high insulin levels on Amyloid β deposition. Now, the first three of these are definitely risk factors for developing neurodegenerative diseases, but whether they specifically promote Alzheimer's is still an open question. The last is a very interesting, possible direct causal link. Interestingly, Alzheimer's may cause central insulin resistance as well, so there may be an interaction both ways. Fgf10 (talk) 20:36, 9 April 2013 (UTC)


 * There's an idea floating around that Alzheimers should be considered "Type 3 Diabetes".   The last is a scientific article. Pull quote: "We conclude that the term “type 3 diabetes” accurately reflects the fact that AD represents a form of diabetes that selectively involves the brain and has molecular and biochemical features that overlap with both type 1 diabetes mellitus and T2DM." -- 205.175.124.30 (talk) 21:43, 9 April 2013 (UTC)

Is it true that Homo sapiens idaltu is younger than Homo sapiens sapiens?
^Topic ScienceApe (talk) 21:53, 9 April 2013 (UTC)
 * According to several Wikipedia articles, including both Anatomically modern humans and Homo sapiens idaltu, yes. The earliest Homo sapiens sapiens fossils are believed to be dated to ~ 195,000 years ago, while the earliest Homo sapiens idaltu are dated to ~ 160,000 years ago.  Of course, that's just what we know, it's possible that either or both of those dates could be pushed back if new fossils are found, but it appears, based on the (admitedly very limited) data we have right now, the oldest known Homo sapiens sapiens is older than the oldest known Homo sapiens idaltu.  -- Jayron  32  21:57, 9 April 2013 (UTC)
 * Our article says sapiens idaltu has archaic features and is presumed ancestral to sapiens sapiens. μηδείς (talk) 22:05, 9 April 2013 (UTC)
 * Well, the article makes it more muddy than that. There are oldest HSS fossil is still older than the oldest HSI fossil (which would then require a time machine for the latter to be an ancestor of the former); analysis of features seems to point to HSI being older than HSS, but until we have that "smoking gun" of an HSI fossil which is older than 195,000 years, then that is just conjecture.  On the basic chronology of the fossils we have, the oldest HSS is older than the oldest HSI.  Other questions in this vein remain open.  -- Jayron  32  22:26, 9 April 2013 (UTC)
 * Archaic features doesn't imply ancestral. It could just have changed less since the most recent common ancestor. --Tango (talk) 11:38, 10 April 2013 (UTC)


 * A scan of the recent literature indicates that the classification of idaltu as a separate subspecies is not well established. Pretty much every recent discussion uses qualifiers like "proposed" or "suggested" or "purported". Looie496 (talk) 22:42, 9 April 2013 (UTC)
 * Does it make sense to speak of subspecies being older or younger than each other? The split from one species into two subspecies happened at a particular (impossible to really define) time, so both are the same age. The only way they could be different ages is if there is a third subspecies involved (either they both split off from that third subspecies at different times, or the first split was into, say, HSS and HSX and then HSI split off from HSX and HSX died out. Is there a proposed third subspecies "inbetween" HSS and HSI? --Tango (talk) 11:38, 10 April 2013 (UTC)


 * Worry about ranges based on one specimen relies on the rather nave (in the academic sense) assumption that fossil attestation is a perfect reflection of time range. You are looking at what is a statistical sample with fossils, not a complete record. No palaeontologist believes that the first or last found fossil of a species is the first or last actual individual of a species. There are a slew of dinosaur species the last specimen of which was found a million or half a million years before the KT event and none after.  That doesn't mean that dinosaurs started going extinct in anticipation of Chixulub.  When only half-a-dozen specimens of a species that existed for 5 million years are known, it's highly improbable any of them will date to that species first or last decade of existence. μηδείς (talk) 17:24, 10 April 2013 (UTC)

Is this a conspiracy theory?
Is there any truth to the story that someone once invented a method of fully recharging standard alkaline batteries - but that Big Battery bought up the rights to the technology and have been sitting on it for years?

Someone mentioned this to me recently, but it sounded to me like a variation on the old 'the oil companies are intentionally keeping the water-powered car down' or 'the major pharmaceutical companies already know the cure for cancer but there's more profit for them in keeping people on chemotherapy for years, so they don't tell anyone' BS, so I was sceptical.

Any ideas about this? Thanks. --146.90.55.190 (talk) 22:46, 9 April 2013 (UTC)
 * Sounds like bullshit to me. -- Jayron  32  22:50, 9 April 2013 (UTC)


 * There's nothing new about recharging dry cells - alkaline or regular carbon-zinc. Hobby electronics magazines now and then publish the details on how to do it - generally using a pulsed and/or periodically reversed current.  The trouble is, it just isn't cost effective.  Just about every type of cell (primary or secondary) has a finite life:  The lifetime is determined by the fact that a given cell type has a certain approximate number of charge/discharge cycles that it can tolerate.  Cells in general deteriorate while held at full charge by trickle changing as well.  With dry cells the change/dicharge lietime is very short.  You may only get 2 or 3 cycles before the capacity drops to a very low value.  Another factor is that dry cells are designed to be leakproof, but under normal use only.  If you recharge, you will likely get leakage, damaging your battery powered eqipment.
 * As a general principle, you can assume that the idea that big companies conceal usefull things is complete nonsense. If it works and is cost effective, somebody somewhere will let the cat out of the bag.  In countries that have a strong patent regime, you generally can only patent a manufacturing process or implementation - you cannot patent a function.  For example, if I invent a novel and very simple circuit to pulse-charge a battery, I could patent it.  That will (in theory anyway) stop you from copying my circuit.  But if you invent a completely different circuit that does exactly the same thing, and market it, my patent is not infringed, and there's absoulutely nothing I can do about you.  You've rendered my patent useless.  What the circuit does, ie pulse charging, cannot be patented. Patents and other forms of rights are just simply not observed in many countries anyway - especially Asian (except Japan & Korea) and communist countries.  Communism fundamentally has a problem with any sort of intelectual property.
 * Wickwack 124.182.36.200 (talk) 00:16, 10 April 2013 (UTC)


 * You may want to see Recharging alkaline batteries, which isn't all that great of an article, and Rechargeable alkaline battery, which is better. Red Act (talk) 01:34, 10 April 2013 (UTC)


 * the theory I have heard is that there is the technology for a battery that lasts 30 or40 years, without recharging ever68.36.148.100 (talk) 04:16, 10 April 2013 (UTC)


 * Sure, but they're radioactive. See nuclear battery.  Still, having one in your pocket has to make you feel warm all over.  StuRat (talk) 04:26, 10 April 2013 (UTC)


 * Stanford's Grid Storage project is reportedly working on batteries that should last 30 or 40 years, but that's not without recharging (they are thinking of these as rechargeables that can go through >40,000 cycles without deteriorating). I can see that being easily misinterpreted as a battery that lasts 40 years period. Someguy1221 (talk) 04:33, 10 April 2013 (UTC)


 * Nickel-iron batteries, a very old rechargeable technology, last a very long time, typically 4 to 10 times the life of a lead-acid under similar conditions, but they are very expensive - that's why you don't see much of them. Wickwack 124.182.36.200 (talk) 04:46, 10 April 2013 (UTC)


 * What do you mean by 'bought the rights'? 1 There was a patent on the technology and they bought it? 2 Or they paid the inventor to shut up forever? If it was 1, the patent will be published someday and it will also expire. So the company would lose its opportunity cost of exploiting the idea. If it was 2 we won't ever know. OsmanRF34 (talk) 12:25, 10 April 2013 (UTC)
 * Technically if the patent exists it is already published; patents aren't secret (except in the cases of national security). Adding just to Wickwack's answer, this sort of statement also misunderstands the nature of invention, which is rarely a "one guy figures out the only way to do it and nobody else would have been able to copy him." In truth, big companies have huge industrial R&D labs, all in competition with each other, and they are all working in the same fields and reading the same literature and checking out all the new patents (and even patent applications) that come out. So the idea that one guy would do this and could be silenced... it's not likely. There have been a few cases of people discovering things really out of left field that were not really in line with what others in their line of work were doing, but they are the exception, not the rule. Invention has not really been about lone geniuses for over a century now. --Mr.98 (talk) 12:44, 10 April 2013 (UTC)


 * It's not a cover-up. Alkaline battery rechargers are commonplace! Just do a Google search on "buy alkaline battery charger" and you'll see dozens of them for sale for around $25 - even on Amazon.com!   The reason they aren't popular is that they don't really work very well - and for most people, they aren't cost-effective.  Sure, you can get *SOME* charge into a dead disposable battery - but not much.  It'll go dead again much more quickly than it originally took to drain it.  Also, the alkaline batteries will tend to leak - and the more times you try to recharge it, the worse these effects get.


 * Whether these things are cost-effective is difficult to say. Let's suppose you use 80 disposable AA's per year.
 * Right now, Duracel AA's cost $5 for 8 batteries - so if you just toss out your batteries, it'll cost you $50 per year.
 * If recharge your AA's once and then throw them away to avoid the leakage problems - and let's suppose each one gets back only half of it's original charge when you recharge it. This contraption cuts your battery purchases by 1/3rd.  Now you only need 52 batteries - so you spent $25 for the charger and $33 for batteries ($58) instead of $50 on batteries alone...so you don't quite break even in the first year of use.  So that battery usage rate, you'll break even after around 13 or 14 months...it's not a terrible investment.
 * Duracel rechargeable batteries cost $8 for four...$2 each. If you buy 8 of them, plus a charger (they are less complicated than alkaline battery rechargers - I see them for $8) - you can fully recharge each battery ten times - then you spent $16 for a year's worth of batteries and $8 for the charger instead of $50 (alkalines) or $58 (alkalines plus recharger) - and you break even after only 6 months!  Much, MUCH better than with alkaline battery rechargers.
 * HOWEVER: The actual math depends critically on the number of batteries you need SIMULTANEOUSLY. If you only need 1 battery - but you replace it 80 times in a year - then using a rechargable battery is MASSIVELY the best choice.  The initial outlay on battery and charger is $10 and you save $40 in the first year alone!  But if you have enough gizmos that you need 80 batteries at once - and each one is only replaced once a year - then you can't possibly use rechargables - you spend $160 on batteries and $8 for the recharger!  It would take over three years to break even!!  Recharging your alkalines in that scenario would definitely be worthwhile.
 * So it all depends on your usage - but for most people, recharging your alkalines is just not worth the hassle. SteveBaker (talk) 15:07, 10 April 2013 (UTC)


 * ... and it's not a new idea. I was recharging carbon-zinc batteries fifty years ago, but with very limited success.  They worked for a short time in low-current applications, but I never succeeded in restoring anywhere near half the original charge.    D b f i r s   18:20, 10 April 2013 (UTC)


 * How long until they start referring to "Big Battery" as "Big Batta"? μηδείς (talk) 17:14, 10 April 2013 (UTC)
 * a related question; how many times can you recharge a lemon battery? might need to make lemonade later in the day after running a light the previous evening. Gzuckier (talk) 19:02, 10 April 2013 (UTC)

Color Question.
Say I have a Orange. I know that the orange color is due to the orange photons not been absorbed into the fruit as energy.

However I had thought that the mechanism of interaction of the non orange photons was one in which the molecules at the surface of the fruit vibrate in various modes and are turned into a kind of kinetic energy. Now I read in the "color of water" article that electrons can also be involved. Is this correct and can more detail be given on this mechanism which I am assuming does not rely on electrons being promoted to higher shells? Ap-uk (talk) 22:58, 9 April 2013 (UTC)
 * Have you seen color, maybe specifically Color. There isn't "one" way that color is created. Vespine (talk) 00:14, 10 April 2013 (UTC)


 * Visible light pretty much all falls in the range of electron transitions - that is, saying "the molecules at the surface of the fruit vibrate in various modes" to absorb certain colors is not typically correct, as the the rotation and translational movement of the molecule as a whole fall in the microwave and infrared regions of the spectrum, respectively (see microwave spectroscopy and infrared spectroscopy for details). Thus the "non-orange" photons are mostly being absorbed by the electron transitions. The article electromagnetic absorption by water indicates that in the case of water, there are no electronic transitions in the visible region, but it does have absorption in the visible region due to overtones from the infrared vibrational bands. These absorb most strongly at, for example, 2662 nm, but there is weak absorbance at frequency multiples, e.g. 1331 nm and 665.5 nm, some of which fall in the red-orange-yellow end of the spectrum, resulting in a very pale (because of weak absorbance) blue color. - 71.35.98.207 (talk) 17:08, 10 April 2013 (UTC)


 * I guess what confuses me is that if the electrons are promoted due to the photons moving them them to a higher shell then why do they not re-emit the light? Ap-uk (talk) 17:43, 10 April 2013 (UTC)
 * well, they sometimes do, but due to conservation or energy or whatever the re-emitted photons have lower energy, i.e. longer wavelength. as in fluorescence Gzuckier (talk) 19:58, 10 April 2013 (UTC)


 * I thought quanta was a specific packet of energy, why should energy be "lost"? I don't think my oranges glow in the dark though ;) Ap-uk (talk) 20:27, 10 April 2013 (UTC)
 * Light can interact quite transiently - i.e. reflection or light scattering. Note that reflection can cause an effective change in color - see Tyndall effect, Rayleigh scattering.  It can be absorbed and then reemitted, typically at a lower frequency- fluorescence.


 * A key thing to remember about light interacting with matter is that there are rules: momentum and energy both need to be conserved at the same time. So for example a fast-moving electron, all by itself, can't emit a photon - heck, in its frame of reference it is at rest.  The same applies in reverse, so you can't just absorb a photon into an isolated electron and move it.  The interaction has to be more complicated - photons can push two things apart, for example, which allows its large amount of energy to be taken up by a target while transmitting just its very small amount of momentum.  For example, pushing an electron in an atom into a higher energy level.  But if the electron can find other ways to slip back down in energy - by knocking into other atoms, for example - then it doesn't have to give the photon back intact.  You can argue that eventually it "makes change" in photons - assuming the system stays at the same temperature, eventually all the energy taken up in big visible photons will be given back in low energy blackbody radiation, which at room temperature is infrared.  Wnt (talk) 23:32, 10 April 2013 (UTC)