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I read somewhere many years ago that someone had done a study on meditation and sleep, and found that if you meditate for half an hour every day, you can get by on four hours of sleep with no ill effects. (My numbers may be wrong. It has been years since I read this, after all.) It seems like everyone has heard something like this, but I've never been able to find the study.
I've taken several Vipassana courses, and Goenka says that anapana meditation can completely replace sleep--but he also says that he can feel his sub-atomic particles vibrating, so I don't consider him a very reliable source. It's the same on Google--many of the people talking about meditation also talk about developing psychic powers and the like, and almost never cite any experiments.
I can see meditation, like any form of rest, slightly reducing the amount of sleep needed at night, but not eliminating it. StuRat (talk) 00:40, 2 May 2012 (UTC)[reply]
It would take an excedingly well designed and carefully conducted experiment to prove anything anyway, because anyone can train themself to reduce the amount of sleep required. During Word War 2 in the Pacific, soldiers got used to months on end with very little sleep. I enrolled at university when I was working full time - the boss let me take time off during the day to attend lectures providing I came back later in the same day to get my work done. In order to get all the assignments done, I reduced my sleep from 8 hours per night to 6 hours per night without any problems other than feeling sleepy for the first month or so only. I kept this up for 7 years until I had the enginering degrees I wanted. It took about another 3 years until I drifted back to 7 hours per night. I have also found that when changing careers, which I have done 4 times, the amount of time I sleep increases temporarily. So I would think that if you avoid mental stimulation (perhaps by doing too much meditation), you will need less sleep. I know some old retired folks who complain they onnly can sleep 4 hours or so each night. Given that they mostly spend their days sitting around watching television, I'm not surprised. Ratbone120.145.52.89 (talk) 02:23, 2 May 2012 (UTC)[reply]
I'm not sure about any specific studies about getting by on 4 hours sleep, but there have been a fair few studies about Vipassana and sleep e.g. [1][2][3]. They show that meditation does affect sleep in some ways, so it's certainly possible that it could reduce the need for sleep, but it seems unlikely you could go without any. From my POV as someone who has also tried Vipassana, I can understand that it might well be feasible to sleep less - if you can't sleep less, then it is hard to see how anyone could maintain meditating 2 hours a day every day. The real problem with meditation though is that we have no real idea what it's doing to our brains (mainly because we don't understand our brains to begin with) so it is very hard to get to the bottom of what effects it has. SmartSE (talk) 10:38, 2 May 2012 (UTC)[reply]
Maybe you could sleep better, if you meditate. Meditation is also a form of relaxation, which will help you fall asleep faster. 88.9.211.140 (talk) 13:18, 2 May 2012 (UTC)[reply]
Four hours per day, or 4 hours per night? In countries were meditation is practiced a lot, it is also usual to take a siesta. Count Iblis (talk) 16:46, 2 May 2012 (UTC)[reply]
I recently read an article — I'm sure in New Scientist magazine (paper edition) but annoyingly I can't now spot it — describing research suggesting that the natural human sleep pattern is better described as two 4-hour sessions than the traditional one 8-hour session, so that waking after 4 hours (or 8) is actually better than after, say, 6 hours. This (if true) would chime with the study the OP recalls. At the time of reading the article I was also struck by its correspondence with the Royal Navy's (and others') traditional Watch system of 4-hour watches. {The poster formerly known as 87.81.230.195} 90.197.66.211 (talk) 19:44, 2 May 2012 (UTC)[reply]
Do WBC numbers gradually go down as infections subside? I.e. as the number of infection causing microbes decrease or are there a steady number of WBCs at the infection site until the infection has completely gone, particularly in sterile environments such as urine? — Preceding unsigned comment added by 138.253.210.19 (talk) 12:07, 2 May 2012 (UTC)[reply]
Basically, keep the area clean, washed and properly dressed, apply herbal or chemical remedies, apply cold packs or hot packs, massage or light exercise to stimulate circulation, and hope for the best. This worked best with mild, recently diagnosed cases, of course. Otherwise, if possible, amputation was performed, especially if there was danger of deep tissue involvement or sepsis, which was essentially a kiss of death. The treatment is still basically the same for cellulitis caused by antibiotic resistant bacteria. Dominus Vobisdu (talk) 15:12, 2 May 2012 (UTC)[reply]
Cellulitis is apparently very closely related to erysipela (also frequently caused by Group A streptococcal infection).[5] For this Dioscorides recommended applying the leaves of "POLUGONON ARREN" (identified as "Polygonum-mas [Fuchs], Polygonum latifolium [Bauhin], Polygonum aviculare [Linnaeus] — Knotgrass, Centinode, Knotweed, Armstrong"[6]) Like most of Dioscorides' recommendations, there appears to be at least a grain of truth to this - see PMID16914113, PMID19616082, [7] - and like most of his recommendations, no real research seems to have been done in modern times to determine whether it works or not. (On the other hand, apparently Polygonum persicaria can cause erysipelas when used as toilet paper, according to one doctor in 1804. ;) [8]) Wnt (talk) 22:28, 2 May 2012 (UTC) hmmm - didn't search well enough. Also found [9][10] (which points at panicudine, 6-hydroxy-11-deoxy-13 dehydrohetisane) ; herb a.k.a. Sanguinaria ? (but the link target looks like something else?) [11]Wnt (talk) 22:50, 2 May 2012 (UTC)[reply]
The link to Dioscorides above suggests the leaves were simply applied to the wound. He wasn't always that detailed in his descriptions, though - I wouldn't be surprised if there were something more to it, like boiling the leaves (the active ingredient is heat-stable, after all, and while the ancients didn't understand sterile procedure it was not uncommon for them to hit on it accidentally). In general I think modern medicine focuses much more on internal medicine than the ancients - who even applied opium as a topical medicine, a usage which has only very recently been validated by discovery of peripheral opioid receptors. Wnt (talk) 16:39, 7 May 2012 (UTC)[reply]
if air were free space and a marble was the nucleus of a hydrogen atom and a grain of sand was the electron, would the air inside the atom be the same air indefinitely or would it mix with the air outside the electron cloud in some fashion? — Preceding unsigned comment added by 165.212.189.187 (talk) 12:50, 2 May 2012 (UTC)[reply]
It's fine to scale up an atom to a talkable illustration, but you can't invent a new component and expect to be able to say anything meaningful about it. There is no subatomic equivalent for the air in your illustration (which is 'stuff'); the free space at the subatomic level is 'not stuff', and mixing this 'not stuff' with that 'not stuff' is nonsensical. There's no 'stuff' to mix. — Lomn13:04, 2 May 2012 (UTC)[reply]
If you're thinking of the electron "shells" as being shiny sealed spheres, that is, as Lomn notes, a very false analogy. Those physics textbooks that depict particles as little billiard-ball thingies are, in general, doing you something of a disservice. You're quite right to note that an atom is almost entirely free space - but what can get in there depends on what's trying. Electrons are charged, so when another charged particle encounters the atom, the cross section (the likelihood of interaction) is very high - to a roaming electron, an atom it encounters seems like an unavoidably interacting thing. But to an uncharged particle like a neutron the electrons might as well not exist, and the neutron can sail through without hindrance - only in the fairly unlikely event that the neutron encounters the nucleus will an interaction occur (see Neutron cross section). And to the light, uncharged, weakly interacting neutrino an interaction is even less likely - the average neutrino can whiz through a whole planet (passing untold trillions of electrons on the way) without being deflected from its path at all. -- Finlay McWalterჷTalk13:20, 2 May 2012 (UTC)[reply]
No I'm not thinking of shells. if i were I wouldnt have asked the question I would have assumed that it was the same "non-stuff" indefinitely.165.212.189.187 (talk) 13:27, 2 May 2012 (UTC)[reply]
(edit conflict)More than that, there is no inside or outside of an atom, it just thins out like a rain cloud. If you want to be pedantic about it, each atom is the size of the universe. The key is quantum statistics, if you've heard about it - I'm sure someone here would be kind enough to explain it to you. Plasmic Physics (talk) 13:28, 2 May 2012 (UTC)[reply]
Otherwise, I don't understand where you are coming from with the idea of two kinds of free space, and that free space can mix with another free space. Last time I checkedm, free space was an abstract concept. Plasmic Physics (talk) 13:37, 2 May 2012 (UTC)[reply]
I think it is impossible to have meaningful DISTANCE in the universe without free space. Doesn't distance have some correlation with free space? — Preceding unsigned comment added by 165.212.189.187 (talk) 14:42, 2 May 2012 (UTC)[reply]
The oposite is true, for if there was only empty space how could you gauge distance? What would distance mean in an infinite abyss. It is the interaction between different things via forces that creates a sense of scale. The radiation from a star that you detect with your eyes appears to travel at the speed of light. This gives a sense of scale to the space. As does walking across the room using muscle power and friction of the floor, give a scale to the room. SkyMachine(++)14:51, 2 May 2012 (UTC)[reply]
If things at a distance interact via forces then the interveening space is filled with these force carriers + virtual particles. SkyMachine(++)15:18, 2 May 2012 (UTC)[reply]
Doesn't free space enable us to measure the volume of objects? isnt there free space sequestered in objects? wheter it be the same stale space or constantly replacing as a flame?165.212.189.187 (talk) 14:59, 3 May 2012 (UTC)[reply]
Free space is like emptiness - if you have a chest, which is initially completely empty, and you start adding items to it, the emptiness doesn't go anywhere; the chest is just less empty. Plasmic Physics (talk) 20:18, 3 May 2012 (UTC)[reply]
Look up Vacuum energy for an explanation of expanding space. Space itself is possibly a computational geometric illusion if the universe is contained in a singularity with no dimensionality. SkyMachine(++)07:27, 4 May 2012 (UTC)[reply]
I am not disagreeing with you. The point is empty space does not expand because emptyness is being added, something is added to the vacuum to create this expansion. SkyMachine(++)09:03, 4 May 2012 (UTC)[reply]
I don't want to write up a complete explanation on wikipedia I apologise but I would give basic guidance. The marble itself is contains only energy in what you would understand as a pulsating wave, the best visual picture would be the distance that you can stand from a stereo and still hear it, with a reasonably defined boundary. Outside and inside the boundary, of the nucleus is the same substance, space, or air in the example, but inside the boundary there is an energy field, when the core of the energy field is moved about the apparent (but non-existent) surface of the nucleus appears to move. But there is no solid surface of any kind, nor is there any solid interior within the energy field. (the stereo does not exist, only the sound energy field)
A different example would be the solar system, it appears to have form, you conceptualise a disc, even a sphere with a flat central disc within, and at all times people don't mentally draw to scale in their mind, the sun is tiny compared to the whoppers people draw. Imagine our solar system has only the sun and nothing else and you fire an indestructible bullet at it. Hitting anything in particular in the solar system if you fired that bullet would first be incredibly unlikely, further if it did hit the boundary of the sun, it would go into the energy field and zip out the other side like that ship on stargate universe because the energy field called the sun is not solid in any meaningful way. If the solar system were the nucleus, or even if the sun were the nucleus, there is still nothing but space and energy within what is incorrectly perceived as solid matter. Things can either be capable of reacting to particular types of energy fields or not. The comet evaporates, the ship sails through pushing things out of the way, the neutrino sails on through without hitting anything at all, and that is only the energy that is capable of interacting, let alone the energy lacking an order which is capable of reacting. Anyhow, I don't want to get into it in depth, but the marble is just energy like sound on the air, it has a perceived boundary, but no solid form. Penyulap ☏10:49, 6 May 2012 (UTC)[reply]
Maybe I can try. Anyway, yes, free space is being slowly added everywhere. The reason you don't notice your head slowly expanding is a combination of two things: A) the expansion is very slow, at a couple thousandths the diameter of a proton every second per meter; and B) "Space is expanding" means that things are getting farther apart, but the laws of physics are not changing. The nuclei of atoms and the atoms of molecules are still held together by the same forces as always, and they aren't going to go flying apart because a teeny force has been applied. Someguy1221 (talk) 03:23, 8 May 2012 (UTC)[reply]
That is what i've known for several years! I even suggested it here before! Can you direct me to other pages that address this idea?68.83.98.40 (talk) 05:05, 9 May 2012 (UTC)[reply]
I would love to, but you hardly ever see physicists write about it, except to discard the local effects as negligible. That is, unless the rate of expansion becomes extreme (see Big Rip and the paper that proposed it). But even those don't go into much technical detail for stuff at the local level. Then again, even though the current rate of expansion seems tiny (the width of a proton per second per kilometer), a device similar to LIGO should be able to detect it. Sure, it would probably have to be huge, and in space, and incredible precautions would need to be taken to prevent interference from...everything. But still, it seems to me that testing for local expansion is just an engineering problem. Someguy1221 (talk) 05:47, 9 May 2012 (UTC)[reply]
It also implies that when we look at things extremely far from us they are actually smaller than their present state because we are seeing them so far in the past (when they were smaller). Does that make sense?165.212.189.187 (talk) 14:09, 9 May 2012 (UTC)[reply]
Do children of people with speech impediments learn the speech impediment?
I imagine it depends on the impediment. Stuttering, for example, is not constant, so they also hear the non-stuttered word and can figure out what's it's supposed to be. A lisp, though, might be constant, and so kids might speak that way, too. I suppose once they start spending time with other people they learn the proper way to speak (possibly by being teased when they say things the wrong way). StuRat (talk) 22:56, 2 May 2012 (UTC)[reply]
I certainly think it's possible, but probably rare in this day and age. Most children will be exposed to television and other people, but if the main source of contact with language was with their parents then yes, I don't see why not. Children have an incredible capacity to learn by mimicking, but they don't have any innate sense of WHAT they're supposed to mimic. One thing I found really interesting when I went to Japan a long time ago is how many Japanese people have very heavy American accents when speaking english, even when their english wasn't very good, because the people they learn from and the television shows and movies they watch are predominantly American. Does that count as a speech impediment ;) Vespine (talk) 23:10, 2 May 2012 (UTC)[reply]
Children won't be in contact with just one adult, or to several adults with the same speech impediment, so I don't see the possibility that they develop a speech impediment by learning. I know for sure that children of deaf people are perfectly able to learn to speak a spoken language parallel to a signed language. XPPaul (talk) 23:10, 2 May 2012 (UTC)[reply]
Nell (film) included the premise that a girl was raised in isolation by a single parent with speech problems and she developed her own speech problems and idiosyncratic uses of language that made her difficult to understand. As far as I know the material for this film was pure fiction, but I don't see why it couldn't happen in principle. The necessary isolation would seem to be very rare, though. Most children are exposed to language from many sources. Dragons flight (talk) 00:32, 3 May 2012 (UTC)[reply]
Even if the child had little contact with people other than the parents, which might occur on a remote farm, I doubt the child would end up with a speech problem. It is unlikely both parents would have the same speech impediment. It would be very unusual that an adult with a speech impediment would be unaware of it, and surely, if the child reproduced the impediment, the parent would point out that it is wrong. If both parents have the same attrocious foriegn accent, that could be a problem, but most likely they would speak their own language at home anyway. I had school friends whose immigrant parents refused to speak any language but their own. But my friends grew up without any problem with English - they spoke just like the rest of us. Wickwack120.145.186.64 (talk) 01:17, 3 May 2012 (UTC)[reply]
I had a classmate growing up, both of whose parents who were themselves deaf since birth, and he spoke fine. As noted, people have exposure to language from many sources other than their parents. People's speech patterns are more determined by their peers than their parents, that most people will tend to speak with the accent and dialect of the people they grew up with, and not necessarily that of their parents. That being said, speech impediments can be genetic and hereditary, so it is possible to inherit a stutter or other speech impediment from your parents, but you don't learn such behavior from them, at least not in a lasting way. --Jayron3201:50, 3 May 2012 (UTC)[reply]
Personal anecdote. I have a bit of a stutter and two kids. I see no evidence of the kids "picking it up" just from hearing me. They imitate me in many ways, including, maybe especially, negative things I sometimes do despite trying not to. But speaking with a stutter is not one of them. And anyway, even if a kid did imitate a parent's stuttering they would quickly find other kids laughing at them and asking why they are doing that. I get laughed at and asked about it by other little kids these days--a strange feeling, I haven't been laughed at by kids for stuttering since I was a kid! Anyway, the reactions of other kids (both malicious teasing and 'good faith' confusion) would make any kid stop it if they are able to. Of course, there are degrees of difficulty--on the milder end it's no big deal and can even be somewhat endearing (as with Bob Newhart). I can imagine a kid, or even an adult, purposefully "cluttering" and mildly stuttering in that kind of way, although I haven't actually heard of anyone doing it on purpose. A couple other points--sometimes stuttering or a tendency toward it can be passed down like other traits. I don't think anyone understands the biological causes of it, but for some people like me there is a physical, neurological aspect (it isn't just psychological), and some evidence that there may be a genetic aspect. Also, lots of kids stutter and then grow out of it--which seems more of a developmental thing. All these things mean it would be quite hard to tell if a kid who stutters, and whose parent does too, is due to developmental, genetic, or imitative reasons. Usually with kids it is a developmental thing. As for other types of speech impediments, I don't know. Pfly (talk) 16:56, 3 May 2012 (UTC)[reply]
yes, but kids usually have many teachers from which to learn, which dilutes the effect. If they live on a desert island and the impediment is difficult for them to master because it requires unique geometry of the airway or vocal cords, and their sloppy imitation of it is accepted by their parents then they will speak with a less pronounced impediment. Penyulap ☏10:54, 6 May 2012 (UTC)[reply]
Virtual particles are not real, they arise in mathematical computations in an intermediary step and don't refer to physical observables. This means that you now don't have the usual restrictions that apply to physical particles, e.g. they can transfer momentum in a way that would violate causality for real particles. Count Iblis (talk) 17:02, 2 May 2012 (UTC)[reply]
...provided that the final physical observable satisfies the relevant physical constraints (e.g., causality, conservation rules, or whatever, after you sum up the superposition of the virtual particles). Virtual particles don't have to abide by all the same rules as physical particles, but they're not a freebie excuse to violate arbitrary laws of physics in the general case. Nimur (talk) 19:50, 2 May 2012 (UTC)[reply]
This sounds an awful lot like a homework problem. In any case, we have an article on molar absorptivity and the bromocresol green even has a graph of coefficients for visible wavelengths. Per our policy on reliable sources, you should be aware that the graph was made by a volunteer contributor "from experimental data obtained on 1999," (by an otherwise anonymous contributor "User:Nevermore78"), so if that's good enough for your purposes, by all means, have at it! You might consider seeking a more reputable source, though, such as your own lab experiment or a paper published in a source that is generally-regarded as reliable. Nimur (talk) 20:35, 2 May 2012 (UTC)[reply]
Why is it called bromocresol green? After all it is blue when basic and yellow when acidic. Is it green when neutral or somethign --150.203.114.37 (talk) 20:59, 2 May 2012 (UTC)[reply]
The question was not what I'd name it, or what you'd name it, but why it is named "bromocresol green". The answer is because it's a shade of green in its basic form. Besides, "bromocresol green" is ever so much snappier than "bromocresol blue-green".- Nunh-huh21:47, 2 May 2012 (UTC)[reply]
Bromocresol Green is pretty green near it's indicator point - check out this photo. I'm surprised there's no picture in commons of it - I think we have some in the lab, maybe I should take some photos. Buddy431 (talk) 00:40, 3 May 2012 (UTC)[reply]
Lifting buoyant things with just a few drops of water
Let's say I'd want to lift something really heavy (like a shipping container). After making a water tight "fence" around it, with just a few inches between the fence and the (almost empty) container, I fill the room between them with water. Would the container get buoyant because its density is smaller than the density of water? Or would it think: "Archimedes' principle is ok with me, but where's the water I supposedly displaced?" and stay on the ground? If the room between the fence and the container would be extremely small, I'd be able to lift the container by adding a drop of water, and energy preserving etc wouldn't allow that, so that's probably not going to happen. On the other hand, how big should the distance between container and fence be? At what time would the container know it's not a small experiment anymore but more a "container in a lake" situation where it is supposed to be buoyant? I guess it is exactly when there's enough water that can be lifted heigh enough to compensate for the weight of the container, but I'm not sure about it. And what would happen at the border of the inches-situation and the lake-situation? Joepnl (talk) 23:56, 2 May 2012 (UTC)[reply]
No, the drop of hypothetical perfectly fluid water is enough to lift the container, if you manage to make the fence close enough. The energy needed to lift the container comes from the water that runs down underneath the container. Of course, the drop of water has very litte energy, but it also lifts the container only a very very very small distance. More realistically, at very small scales with real water, adhesion and capillary effects will complicate things. But having an inch around the container is plenty to lift it by filling the hypothetical fence with water. This happens e.g. in a lock. --Stephan Schulz (talk) 00:02, 3 May 2012 (UTC)[reply]
(EC)I can't work out why you think this would work but I think you've misunderstood something about boyancy. The container will only ever "float" when it displaces an amount of water greater to its weight, it has nothing to do with the height of the water. After reading the above answer, I don't think the drop will lift the containter at all, even a tiny amount, it won't lift the container until the amount of water put into the container exceeds the weight of the object. The amount of water displaced in a lock is equal to the weight of the object, regardless of how small the lock is. If the lock with the object in it is too small to contain an amount of water which weighs as much as the object, it won't lift the object off the bottom. Vespine (talk) 00:09, 3 May 2012 (UTC)[reply]
No, you are wrong in this. Think about it the other way - start with a bathtub full of water, and a very nearly bathtub-shaped boat slightly smaller than the bathtub, and with a density a little bit less than water. If you put it into the tub, it will sink nearly to the bottom, displacing the water (which runs over the rim and is lost). But the boat will float in the remaining bit of water. And it will do exactly the same if you put the boat into the empty tub and then add the same amount of water you were left with in the first case - i.e. very little water is needed to float the boat. The water that "lifts" the boat does not know if half an inch to the east is the rest of the Atlantic ocean or the rim of the bathtub. --Stephan Schulz (talk) 00:32, 3 May 2012 (UTC)[reply]
No, that is not correct, you need enough water to displace the weight and for the suggested large container, a drop of water certainly will not float it. For instance, you can wade and even sit and lay down in the water at the beach if its shallow enough. But only when the water is deep enough can you float. The displaced water in the fenced area or the lock must be of sufficient volume to force the initial drop underneath it, since this larger body of water acts as a counter-weight to the ship's weight. --Modocc (talk) 00:50, 3 May 2012 (UTC)[reply]
I think the confusion here may arise from how we are thinking about the seals in the system. For instance, Fig. 6 shows a common illustration of an arrangement where hydrostatic pressure can be used to create a sort of "leverage" effect. So you can use a mouse to lift an elephant, if the seals are all perfect. If there is a perfect seal, then I think a drop of ideal fluid could lift arbitrarily large masses by a small amount, provided that it is supplied from below with enough pressure. This may not be what the OP meant, but I think it might help reconcile the different answers above. SemanticMantis (talk) 01:17, 3 May 2012 (UTC)[reply]
In reply to the bathtub example above, maybe what you aren't considering is that the water will spill OUT of the bath tub as you drop the object in, by the time most of the object is in the bath, most of the water will be OUT of the bath and the weight of the object will now greatly exceed the weight of the water left and it will indeed sink all the way to the bottom. Now if you had a bath tub with walls extending upwards so the water wouldn't spill over the sides of the bath, the water will instead spill over the sides of the bject and it will still sink. Vespine (talk) 01:24, 3 May 2012 (UTC)[reply]
Stephan Schultz is correct. Vespine and Modocc didn't understand the mention of locks. The arbitarily small amount of water will work just fine in lifting the object. The mass of water used has nothing to do with it. Seals have nothing to do with it - seals are not required. Think of it this way: Consider a bathtub three-quarters full of water. Place in it a shoebox sized object with a density (say) 90% of water. It will obviously float, with approx 10% of its volume above the water surface. In floating, it displaces 90% of its volume, so the water level in the bath rises slightly - some fraction of a millimeter. Now, construct around the floating shoebox sized object a thin rigid wall just slightly larger than the floating object, being carefull not to touch the object, so that you end up with the shoebox sized object floating in water contained within a thin "boat" floating in more water which is in the bath. Now, place a support post, that just fits, under the thin "boat". Now you can drain the water out of the bath. You still have the shoebox sized object floating in water within the "boat" - it has not moved up or down. And the water within the boat has a volume much less than the displacement volume! It works because atmospheric pressure on the water allows the mass of the floating object to be transfered to the container. Ratbone58.164.234.216 (talk) 01:37, 3 May 2012 (UTC)[reply]
Oh snap! Good explanation Ratbone. Now to work out wtf I was thinking. The 90% as dense as water thing maybe did it for me because a 90% water density object will NEVER sink, even if you DRAG it underwater; I was thinking of sinking boats the whole time, for some reason. maybe the "heavy shipping container" thing threw me, but of course the container still must be less dense then water or else it won't float to begin with! I was obviously a bit denser then that in this case ;) Vespine (talk) 02:02, 3 May 2012 (UTC)[reply]
Ok, I was definitely wrong, I'm not denying it, but I think I worked out my confusion; because there MUST be a point where the object you are trying to float WILL squeeze the water out of the "bath" and NOT float, the unstated premise is that the container it self must be at least up to the waterline of the object! Right? Which ratbone's great example illustrated clearly. If the container isn't up to the waterline of the object, then the object WILL touch the bottom, which is a bit of a tautology really. 02:16, 3 May 2012 (UTC)
There is a limit, which is controlled by the cohesion of the water molecules to each other, and the number of molecules in a droplet. If you spread your floating layer of water molecules to single-molecule thickness, it will seperate to the point where it will no longer support your object. As long as you have enough water to maintain cohesion, an object will float on it. But there is a minimum. It is much smaller than intuition would indicate, but it is there. --Jayron3205:28, 3 May 2012 (UTC)[reply]
Physically, capillary force will limit it. If the water layer is thin enough, the object will be pulled very strongly to the bottom, squeezing out water. The force gets stronger as the gap closes; if the surfaces are accurately the same shape essentially all the water can be forced out, and intermolecular forces between the two surfaces take over, producing a strong bond between the two.--Srleffler (talk) 17:02, 3 May 2012 (UTC)[reply]
Is that true? I would have expected it to pull water into the crack between the object and the bottom... Wnt (talk) 20:37, 3 May 2012 (UTC)[reply]
In a capillary, liquid is drawn into the tube. There is an inward force on the walls of the tube, just as there is on the liquid, but only the liquid moves because the walls of the tube are solid. If the walls of the "capillary" can move, as in the case above, the force can pull water into the gap, or can pull solid material into the gap. Which occurs depends on which is more energetically favourable. For objects that are not submerged, fluid can definitely be forced out of the gap. This is used in optical contact bonding. For a submerged, buoyant object I suppose it might not work out the same, since the capillary forces would be working against the fluid's pressure.--Srleffler (talk) 18:00, 7 May 2012 (UTC)[reply]
(ec)A drop of water is not sufficient to float a large ship, nor will a dozen water molecules float a thimble, but I was wrong too, for the largest ships' displacements in these locks are larger than the remaining volume. The ships do need clearance, thus in addition to adequate depth, there has to be an adequate water volume to separate the objects. --Modocc (talk) 06:17, 3 May 2012 (UTC)[reply]
Ratbone, something is wrong. Consider your system, before you add the "boat". You write "In floating, [the object] displaces 90% of its volume, so the water level in the bath rises slightly - some fraction of a millimeter." This glosses over an important question: how much does the level in the bath rise? Since the object displaces a fixed volume of water (by the law of buoyancy), the change in the level of the bath depends on the size of the part of the tub that is not occupied by the object. If the tub is smaller, the displaced volume of water must rise higher.
When you add the thin "boat", if nothing moves the height of the water inside of the boat depends on the size of the original tub. This is clearly a contradiction, so something has to move—either the object changes height within the boat or the boat changes height within the tub.--Srleffler (talk) 17:02, 3 May 2012 (UTC)[reply]
The fact that you don't need the displaced water can be verified by doing this experiment: Float a wide base plastic cup in a slightly larger bowl and compare the weight of the cup with that of the water you used. --Modocc (talk) 18:08, 3 May 2012 (UTC)[reply]
Cool,the problem is "official" :). Still not completely convinced though. See the picture. Archimedes. The grey thing is a very heavy container (but its density is lower than that of water). At the bottom, the container balances on a very small (1 cm thick, perfectly square) stick (the scale of this work of art isn't correct, imagine a very small line). Now I add a liter of water. As we already found out, the container doesn't mind if it floats on an inch of water or an ocean, and makes room for the water by going up. The room at the sides is only a micrometer wide so the only place for most of the water to be stored is at the very bottom. A liter contains 1000 cm3 water, so the container would be lifted 10 meters (33 ft). So by lifting 1 liter of water let's say 20 meters and pooring it into the structure, I'd be lifting a huge weight 10 meters up. I guess I just made an error, but if not: after this I attach a rope to the structure, connect it to a generator, release the water and the container will go down again. The generator would generate much more electricity than I needed to lift a liter of water. Joepnl (talk) 23:05, 3 May 2012 (UTC)[reply]
The energy in and out should be about the same (minus loss in your output), for you are lifting a small amount of mass, water, a long distance and dropping a larger amount of mass, the container, a short distance. The energies are the product of their weights and the distances. --Modocc (talk) 23:24, 3 May 2012 (UTC)[reply]
That's the reason for this Reductio ad absurdum. I only lift the water, say, 20 meters. But in turn, the water lifts the container 10 meters. That's 1 kg x 20 m and say 50,000 kg x 10 m. It should be equal, which is what I don't understand. Joepnl (talk) 23:39, 3 May 2012 (UTC)[reply]
Side note: if I used a pump to put in the water at the very bottom, I probably would have to a use a very strong pump, supposedly having the same end result as just pooring some water on top of the structure. Joepnl (talk) 23:56, 3 May 2012 (UTC)[reply]
Either your 50,000 kg container is too dense so it is not buoyant or you are not using enough water to fill the separation underneath. Moreover, the separation is the entire area underneath the container and not just the middle extension as you might be thinking. --Modocc (talk) 00:18, 4 May 2012 (UTC)[reply]
Modocc now has it right. The error made by Joepnl is that while he/she contrived a long thin stick in a bottom cylinder so as to produce a large rise while not needing any much volume of water in the cylinder, he forgot to estimate the volume created, as the large heavy floating object rises, directly underneath that floating object - the volume of water thus accumulated co-axial with the long thin extension. Also, Joepnl is one of a number of posters who are focused on whether a small volume of water can lift a large volume object, floating in a just large enough rigid container, though a large distance. Well, it can't, but that is NOT part of the original posters's question. The OP only asked if you could get it to float. Floating is floating regardless of whether it rose off the bottom 1 meter, 100 m, or 1 mm. NOTE: Even though the water required to lift the object a significant distance is not insignificant, it can still be a heck of a lot less than the volume of the object. Ratbone58.169.234.93 (talk) 01:29, 4 May 2012 (UTC)[reply]
At this stage, unless you are comfortable with the Archimedes Paradox article, don't post unless you have tried an experiment with real objects. A plastic cup - say the typical sort with sloping sides - within another cup will do fine. Put some water in the inner cup with water as well to increase its density. Ratbone58.169.234.93 (talk) 01:29, 4 May 2012 (UTC)[reply]
Joepnl was the original poster, so he was asking a followup question, and I have agreed with you whole heartily as to his mistakes, but we shouldn't be discouraging postings unless they are disruptive. --Modocc (talk) 01:50, 4 May 2012 (UTC)[reply]
I guess I should be silent for quite some time now.. Please consider the last question as never have been asked. Thanks everyone for the explanations! Joepnl (talk) 01:50, 5 May 2012 (UTC)[reply]
There is a simple and general solution to the apparent "paradox", which only assumes constant density. If the heavy object rises then there is a space A near the top of the container that was originally occupied by water and is now occupied by the object. And there is a space B near the bottom of the container that was originally occupied by the object and is now occuiped by water. Spaces A and B have the same volume - call this V. And suppose the centres of gravity of spaces A and B are separated by a vertical height h. Then the gain in potential energy of the object is Vρogh where ρo is the density of the object. And the loss in potential energy of the water is Vρwgh where ρw is the density of water. So the net energy gain is V(ρo-ρw)gh. But because the object floats we know that ρo < ρw, and so this net energy gain is negative i.e. energy is lost when water is added to the container and the object rises up to a new floating position. Another way to see this is to realise that pushing the object back down again to its original position will require doing work against the buoyancy of the object, so (potential energy of new floating position) - (potential energy of old "pushed down" position) = -(work done pushing object down) < 0. Gandalf61 (talk) 08:21, 4 May 2012 (UTC)[reply]
Nice, Gandalf61. My inattentive thoughts were initially too impetuous, but the Archimedes Paradox has been much easier to think about that way when the objects are fully submerged like that, such as explaining the separation of various volumes of oil and vinegar. --Modocc (talk) 11:52, 4 May 2012 (UTC)[reply]
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