Science desk
< August 7	<< Jul \| August \| Sep >>	August 9 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

August 8

Color of Water

Resolved

– StuRat (talk) 15:27, 8 August 2008 (UTC)[reply]

What color is it? Some one said on TV tonight it was slightly blue. Is that correct? —Preceding unsigned comment added by 79.76.225.183 (talk) 00:45, 8 August 2008 (UTC)[reply]

Yes. See our cunningly-named article color of water for more information. Algebraist 00:47, 8 August 2008 (UTC)[reply]

Yes I ve just seen it. No more replies needed thank you! —Preceding unsigned comment added by 79.76.225.183 (talk) 00:49, 8 August 2008 (UTC)[reply]

Monitor colors keep changing

The colors on my CRT monitor keep changing very slightly (over a periods of a few seconds), giving pink, pale green or pale blue shades. What could be causing this please? Is it the monitor of the video card? —Preceding unsigned comment added by 79.76.225.183 (talk) 00:54, 8 August 2008 (UTC)[reply]

It kind of sounds like there is a strong but distant magnetic field near your monitor that is turning. When did this start happening? Also, colors changing on a CRT monitor usually means that it is going bad/about to die. --mboverload @ 00:57, 8 August 2008 (UTC)[reply]

I'm not sure how many replies you'll recieve here You may wish to post this at the Computing Reference Desk. —Cyclonenim^T@lk? 10:24, 8 August 2008 (UTC)[reply]

Also can happen if your cables are a bit loose. --Wirbelwindヴィルヴェルヴィント (talk) 16:44, 8 August 2008 (UTC)[reply]

Is your cell phone near it? They often change power output when checking in. The magnetic field will perturb the electron beams slightly and hitting the wrong parts of the shadow mask. Saintrain (talk) 22:57, 8 August 2008 (UTC)[reply]

I dont mind this thread being mved to computing if someone can do it —Preceding unsigned comment added by 79.76.208.36 (talk) 22:59, 8 August 2008 (UTC)[reply]

If the color change is localized (more on one side or corner), I'd suspect it's near a device on that side that's giving off a magnetic field. If the color change is uniform across the screen, I'd go with the loose connector explanation. Check to see if any of the pins are out of position. Also, you can check if it's the monitor by plugging the computer into another monitor. If you don't have an extra, borrow one from a friend or neighbor, just for a test. StuRat (talk) 16:32, 14 August 2008 (UTC)[reply]

Anywhere on earth?

Is there any where on earth where your urine can freeze before it hits the ground (assuming your are standing up when releasing it) —Preceding unsigned comment added by 79.76.225.183 (talk) 01:03, 8 August 2008 (UTC)[reply]

No. That's a silly myth / hyperbole. The density and thermal conductivity of air is so low that even if its temperature was absolute zero it wouldn't be able to freeze your urine in the ~1 second it takes to reach the ground. Dragons flight (talk) 01:07, 8 August 2008 (UTC)[reply]

How about if I wizz off a mountain ? :-) StuRat (talk) 01:11, 8 August 2008 (UTC)[reply]

Trust StuRat to be always thinking outside the box. I often thought he was out of his box anyway ;) —Preceding unsigned comment added by 79.76.225.183 (talk) 01:16, 8 August 2008 (UTC)[reply]

The thermal conductivity of urine should be considered. If a man is relieving himself off the edge of a very high cliff, as the urine descends a tube of frozen urine would form around a liquid core. After a certain amount of fall, the urine would become a solid rod. The rod would continue to fall, with a tube above it. The walls of the tube would become thicker in the downward direction until a sold rod is formed. This assumes that the fall is large enough and the temperature is low enough. This also assumes there is no turbulence within the urine stream. AndMe2. 66.52.8.251 (talk) 04:55, 8 August 2008 (UTC)[reply]

I could maybe start to believe what Andme2 is suggesting if he could explain how to whizz off a high point and keep the liquid in a stream. My experience (not extensive you understand) is that the stream breaks up into droplets not unlike rain, as any liquid poured in a thin stream from a height. Adding the rider 'this assumes no turbulence' is not practical in the proposed scenario. Richard Avery (talk) 07:07, 8 August 2008 (UTC)[reply]

Well let's assume it is a stream of water coming from a very large hose pointing downward. I wonder how large the hose would have to be, and what the flow rate would have to be, to prevent the water from breaking into drops. Or would it always break up into drops if it falls far enough? Maybe there is a principle here about falling water that I don't know about. As for turbulence, a basic principle could assume no turbulence. This would be modified to account for practical causes of turbulence in any particular case. (For instance, according to the "law" of gravity, a feather will fall as fast as a lead weight. This principle is modified to account for air resistance in relation to weight.) AndMe2 66.52.8.251 (talk) 08:03, 8 August 2008 (UTC)[reply]

May not qualify as somewhere "on Earth", but see these news stories: [1], [2]. Gandalf61 (talk) 09:18, 8 August 2008 (UTC)[reply]

What about the freezing point depression associated with the wastes dissolved in urine. How much solute is in urine?Coolotter88 (talk) 13:00, 8 August 2008 (UTC)[reply]

These videos suggest that it's totally possible. --Shaggorama (talk) 18:25, 8 August 2008 (UTC)[reply]

On back of an envelope I'd estimate a drop of water at 30 C would need to fall about 10,000 times it's diameter in order to freeze in air of -30 C. So yes, if you toss water in the air, then you will gets some frozen mist as very tiny particles of spray freeze (< 0.1 mm, typically), but most of the water will nonetheless reach the ground as liquid. To answer Stu's question, that suggests you'd need to urinate off a 20+ m cliff before a substantial volume would freeze during the fall. BTW, there is also a Mythbusters episode where they show liquids decidedly not freezing as it falls through several feet of deeply chilled air. Dragons flight (talk) 19:24, 8 August 2008 (UTC)[reply]

Hi. However, I've heard in some places spit freezes before it hits the ground, or your breath freezes into ice crystals, but there's less mass involved, and thus less heat. Thanks. ~A H 1^(TCU) 23:31, 9 August 2008 (UTC)[reply]

Did your back-of-envelope calculations include evaporation? That will vary greatly based on the size of the droplet. Evaporation effects can be significant if you're talking about freezing hot liquids. I'll bet that the square-cube law will make this work if you assume small enough droplets. APL (talk) 14:17, 11 August 2008 (UTC)[reply]

Paradox?

A train is traveling at 100mph in a westerly direction. A small fly is traveling at 20mph (wrt to the ground) in an easterly direction along the rail track. At the moment of impact, the fly's velocity is instantaneously changed from +20 to -100 mph. At the precise moment of change of velocity, the fly must be at rest wrt ground. But since fly is in contact with train, train must also be instantaneously at rest. So, does the fly stop the train? —Preceding unsigned comment added by 79.76.225.183 (talk) 01:46, 8 August 2008 (UTC)[reply]

One second before contact, at that precise moment, must the fly be at rest with regard to the ground? --Kjoonlee 01:56, 8 August 2008 (UTC)[reply]

The error is in assuming the change is instantaneous and that the fly and the train each have a single velocity. The change will be gradual due to deformation of the fly and the train. That deformation resolves the apparent paradox - parts of the fly and parts of the train will be travelling at varying velocities. Each part of the fly will, at some point, be stationary, which I guess means some tiny amount of the train will also be stationary for a time, but that's perfectly possible if you allow for deformation of the train. --Tango (talk) 02:05, 8 August 2008 (UTC)[reply]

The problem with this 'paradox' is that it can't decide how physically realistic it's being. If it's being realistic, then the train and fly are not particles, they undergo deformation, and the change is not instantaneous, as Tango points out. Thus there is no paradox in this case. If, on the other hand, we're being very unphysical, and model the train and fly as particles, unable to deform, then the change of velocity is instantaneous, and it makes no sense to ask what the velocity of the fly is at that moment; it simply isn't well-defined in this crude model. Again, there is no paradox. The paradox arises if we unphysically model the fly and train as particles and then impose the physical condition that the fly, in changing velocity, must go through the velocities in between. Algebraist 03:05, 8 August 2008 (UTC)[reply]

Each atom of the fly is at some point stationary because its velocity has to change sign. No part of the train ever needs to come to rest. Someguy1221 (talk) 04:17, 8 August 2008 (UTC)[reply]

Are you sure? At the moment when the part of the fly in contact with the train is at rest, can that bit of train be moving? I suppose so, if we accept that "in contact" actually still involves a small separation, held apart by electromagnetism. Again, it's a matter of exactly how physical we're being. --Tango (talk) 02:53, 10 August 2008 (UTC)[reply]

The statement of the problem speaks of "the moment of impact". A moment, as the word is used here, means a point in time of zero duration. So yes, both the train and the fly are stationary for that zero duration. AndMe2. 66.52.8.251 (talk) 04:29, 8 August 2008 (UTC)[reply]

Also in a real world situation the train is pushing air out of its way, and this air will greatly slow the fly to a stop and declerate it almost very close to the trains speed well before the fly hits the train. The deformation would amount to a microscope region of metal or glass being tensioned. No part of the train would necessairly need to come to rest, if it was inside a vacum this would happen and the impact would be more severe.--Dacium (talk) 04:43, 8 August 2008 (UTC)[reply]

At the moment of change in velocity, the velocity wrt the ground is not zero. Instead, it cannot be calculated because both the distance travelled and the time are zero and 0/0 is indeterminate. --Bowlhover (talk) 04:50, 8 August 2008 (UTC)[reply]

Which is why you would take the limit as delta t approaches zero - giving the instantaneous velocity, dx/dt. So the train does not need to come to a stop, even momentarily. PhySusie (talk) 12:22, 8 August 2008 (UTC)[reply]

Ummm, are these 1-D trains and flies? Up and down and right and left, the directions the fly-parts spread, are also WRT the ground. Saintrain (talk) 22:38, 8 August 2008 (UTC)[reply]

PhySusie: The limit does not exist when, as in the OP's scenario, the change in speed is instantaneous. It's meaningless to ask for the velocity at the moment of change because it's not defined. --Bowlhover (talk) 07:07, 9 August 2008 (UTC)[reply]

Thermocouples

The flame failure devices in gas fires are usually called thermocouples, but how can a thermocouple act to shut off a gas valve in the absence of an amplifier? Are they, in fact, some other sort of heat activated mechanical device by any chance? —Preceding unsigned comment added by 79.76.225.183 (talk) 01:58, 8 August 2008 (UTC)[reply]

I think it works like an ordinary thermocouple in that when a heat is applied to one end of the thermocouple a Seebeck voltage is generated. This generated voltage will be used to activate a solenoid valve. Seebeck voltages are typically small but should be enough to power a sensitive electromagnet. Jdrewitt (talk) 09:51, 8 August 2008 (UTC)[reply]

Thermocouple voltages are in the millivolt region, so how is that enough to activate a solenoid? —Preceding unsigned comment added by 79.76.149.61 (talk) 12:16, 8 August 2008 (UTC)[reply]

According to Thermocouple#Heating_appliance_safety, the sensor is a thermopile (effectively lots of thermocouples in series), also called a "pilot generator". It generates 750 mV [3], which is enough to operate a standard "millivolt gas valve". Other systems use a single thermocouple and an amplifier. --Heron (talk) 16:45, 8 August 2008 (UTC)[reply]

Aha! Do you have any links to millivolt gas valves? —Preceding unsigned comment added by 79.76.208.36 (talk) 20:50, 8 August 2008 (UTC)[reply]

You could look at the Honeywell VS820. There's a link to the PDF data sheet at the bottom of the page. --Heron (talk) 21:17, 8 August 2008 (UTC)[reply]

Why does quantum mechanics only work on a small scale?

And what is the cutoff point? One atom = Spoooky! Two atoms? Hello, Newton!Hey, I'm Just Curious (talk) 04:13, 8 August 2008 (UTC)[reply]

Quantum mechanics applies to all objects, but for most purposes, Newton's laws are sufficiently accurate. To build a rocket, for example, it would not be necessary to calculate the wave functions of every atom in every component. Not only is that level of accuracy not required, but parts cannot be engineered with such precision. --Bowlhover (talk) 05:02, 8 August 2008 (UTC)[reply]

See also: correspondence principle. Quantum mechanics would not have been accepted as a sound theory if it conflicted with the results of classical mechanics. It's a common misconception that quantum mechanics somehow invalidates classical mechanics. It does not; rather, it (among other things) changed our view of the scope of classical mechanics and electromagnetics. -- 98.26.182.245 (talk) 05:38, 8 August 2008 (UTC)[reply]

I mean like, supposedly there's a "wave function collapse" or something like it when you look at the results of the photon double slit thing. That's one photon. Is the cutoff point where this nonsense(?) stops 17 photons at a time?, 8,099 photons at a time, or what?

Someday I'll ask you about Schrodenger's cat.--Hey, I'm Just Curious (talk) 06:05, 8 August 2008 (UTC)[reply]

Well, there is microphysics (subatomic physics), macrophysics (Newtonian physics, and gigantophysics (stellar physics). They're all different. But there is some overlap. For instance, electrons, apples, and galaxies all obey the "law" of gravity - they have mass. AndMe2 66.52.8.251 (talk) 06:22, 8 August 2008 (UTC)[reply]

The cutoff is thermodynamic irreversibility, basically. The essence of quantum mechanics is that you get wavelike interference between different "histories", i.e. different ways that you might have arrived at the same final state. To put it another way, you get quantum effects when which-way (welcher Weg) information is lost. This can't happen to thermodynamic objects because they're constantly emitting blackbody radiation, and that radiation contains information about the object's path (not necessarily in a recoverable form, but that doesn't matter for the purposes of quantum mechanics). You sometimes hear that large objects exhibit double-slit interference in principle but with such a small wavelength that it can't be observed, but that's not true; thermodynamic objects don't self-interfere at all because they broadcast information about themselves on a timescale shorter than the time it takes to do the double-slit experiment.

However you don't need thermodynamic irreversibility for the double-slit pattern to disappear; leaving any which-way information behind is enough for that ("any" meaning at least one quantum, I think). If you have a device at one slit that records the passage of a photon in a thermodynamically reversible way, say by two stable states of a molecule, the interference pattern will still disappear. The difference is that you could in principle unmeasure that information, e.g. by routing the photon through the slit a second time and reversing the measurement process, in which case the interference pattern would reappear. It would be a very difficult experiment but it's not actually forbidden by the second law of thermodynamics. It's when thermodynamic irreversibility kicks in that you can safely stop worrying about quantum interference, because the second law guarantees that you won't see it. This is, incidentally, why it's so hard to build quantum computers: they have to operate in a state of perfect thermodynamic reversibility. (More accurately, it's only the "computational degrees of freedom" that have to, but that's hard enough.)

There might also be an unknown physical process that kicks in before thermodynamic irreversibility and has the same effect of "permanently recording the which-way information". If so, we should be able in principle to detect it and find out when it happens. On the other hand, if the process kicks in after thermodynamic irreversibility then there's no way to experimentally determine when it happens or indeed whether it happens at all. People argue about whether it's logically coherent to never resolve the real path a particle takes, but you can't extract any experimental predictions out of that disagreement. Well, some people think you can. But at any rate it's a philosophical debate at the moment, not a scientific one. -- BenRG (talk) 12:37, 8 August 2008 (UTC)[reply]

Regardless of everything above quantum effects using fullerenes and complex biological molecules have been shown by Zeilinger and his team: Anton Zeilinger#Atom and macromolecule interferometry. --Ayacop (talk) 14:14, 8 August 2008 (UTC)[reply]

cooling/heating vortex

Does anyone know the name of the vortex shaped device where you put in compressed air and cold air comes out one side and hot air out the other side and it has no moving parts or power. And can they work on water?--Dacium (talk) 04:38, 8 August 2008 (UTC)[reply]

AFAIK water cannot be compressed substantially, so if device works on expansion of compressed air, then it wouldnt work with water. —Preceding unsigned comment added by 79.76.221.121 (talk) 04:41, 8 August 2008 (UTC)[reply]

It's not vortex shaped, but is it a vortex tube? --Bowlhover (talk) 06:30, 8 August 2008 (UTC)[reply]

Do any types of dementia result in loss of tact

I have noticed that many people as they age loose the social limits most people put on their communications. This results in older people being much more likely to make insulting statements that 1) they don't seem to notice they have made and 2) would never have made in their earlier years. I wondered whether this is a form of dementia or loss of societal imposed constraints. —Preceding unsigned comment added by 202.92.75.130 (talk) 05:11, 8 August 2008 (UTC)[reply]

Some old folks become crabby - many things irritate them. They respond by involuntarily becoming unpleasant. Perhaps that response is instinctive - it is a way of saying "Don't tread on me". Some sociologists claim that human beings have only two instincts - fear of loud noises and fear of falling. I think we are loaded with instincts. They all played a part in survival in the stone age, and became wired in. Instead of being a conscious action, the response became a knee-jerk reaction. That played a part in survival. They didn't have to learn the hard way, by experience. But to return to the original subject, some old folks become easily irritated, hence the instinctive response. It is instinctive self-defense. AndMe2 66.52.8.251 (talk) 06:05, 8 August 2008 (UTC)[reply]

I guess it needs to fit with other indications to know if it is specifically part of dementia, but I've observed it as coming from people with onset of dementia (later to become dotty or mildly violent) and others who are just plain frustrated with getting old and dependent reacting in a crabby way. I wonder if that's also a part of dementia, the social forgetting. Crabby ones could be reverting to type under pressure. Sweet ones probably always were sweet. Googling is tricky because "insult" is used as an effect (affect?) in medical terminology for this condition. Julia Rossi (talk) 06:19, 8 August 2008 (UTC)[reply]

Many age-related dementias do present with personality changes, including labile affect and extreme irritability. (See our article on dementia, and the links therefrom to Alzheimer's disease, frontotemporal dementia, and others.) Of course, not all crankiness is due to dementia—some people may be suffering from undiagnosed depression or other mental illness, while still others may just have a mean streak. TenOfAllTrades(talk) 13:31, 8 August 2008 (UTC)[reply]

So which of the above is bothering you? —Preceding unsigned comment added by 79.76.208.36 (talk) 22:52, 8 August 2008 (UTC)[reply]

Them insulting people may not be intentional, they may have lost the ability to know which statements will be taken as insults. This may also be true of a small child, for example, who, when introduced to a 100 year old, may ask "why aren't you dead, yet ?". StuRat (talk) 15:21, 8 August 2008 (UTC)[reply]

Hey, you kids! Get off my reference desk! Deor (talk) 15:58, 8 August 2008 (UTC)[reply]

Well, yes, Julia. I agree that some people are naturally sweet and others are naturally nasty. Saints or devils. The great majority of people are somewhere in between. Perhaps there is a bell curve for this innate characteristic. National character - a learned set of responses - also plays a part. I think you live in Paris, but I will say this anyway. Some of the French have a learned tendency to be nasty, but others are very pleasant. Perhaps the bell curve for the French is even inverted - like a shallow bowl - because of these learned national habits. The bowl is shallow because behavior taught by example does not easily overcome natural characteristics. Speaking of all nations, there is a gender bias to it as well. Women obviously tend to cluster somewhat toward the right side of the sweet/sour bell curve. (Though a few women are far over on the left!) For both genders, I think repeated past personal experience with others plays a part in it as well. From time to time, people also temporarily shift their usual position on the curve in response to outside circumstances. This could be involuntary, like a fit of rage, or voluntary as a conscious decision. Also, talented people tend to be unpleasant. They are sensitive to very faint signs, like an expert tracker. But the gross experiences of life are very irritable to them. Many, many examples could be given, in all walks of life and in all professions, of talented people who are S.O.B.'s. As exceptions, talented artists (such a painters) do not seem to be unduly crabby. However as exceptions to these exceptions, talented opera singers are sometimes prima donnas. Quite a lot of talent goes unused because irritability causes opportunities to be denied - other people don't want unpleasant persons around. AndMe2 67.150.190.106 (talk) 15:44, 8 August 2008 (UTC)[reply]

I have been told (apropos a grandparent who tended to disrobe whenever unattended) that social constraints and inhibitions are among the first learned behaviours to disappear in some types of age-related dementia or other severe stress: physical and verbal agression are two such behaviours normally controlled by social rules. Comments made under such conditions tend neither to be nice nor nasty in tone; the affect is frequently missing and statements, however unpleasant the contents, are made flatly, as fact. ៛ Bielle (talk) 16:34, 8 August 2008 (UTC)[reply]

I seem to recall that social inhibitions vary in strength as you age anyway, being strongest when you're about 14 (if I recall correctly) and weakening after that as you age. So some of this is just a natural result of getting older. 79.66.38.215 (talk) 17:20, 9 August 2008 (UTC)[reply]

@ 67.150 -- appreciate your thoughtful reply. Can relate to much about creative types and their polarities. Confidence and insecurity comes into it too I guess. From age 14 you say 79.66.38 -- there must be a precipitous drop in the graph from 14 into the teens -- that's scary. Julia Rossi (talk) 10:16, 10 August 2008 (UTC)[reply]

Physics of boat towing

Hello,

This question concerns the physics involved in towing a boat.

The scenario is a tug boat towing an oil tanker.

One argument is that at the moment t when the tug boat is actually pulling the tanker, the towing cable will be perfectly straight.

The other argument is that even at the moment t when the tug boat is pulling the tanker, the towing cable will be sagged, given the forces of gravity and friction acting on it.

I am also wondering if the shape of the cable changes when the tanker and the tug boat are maintaining the same speed and when the tug boat accelerates (the acceleration then being transmitted to the tanker through the cable).

how does it work?

if anyone could illustrate this with graphics, it would be perfect.

thanks! —Preceding unsigned comment added by 194.167.55.204 (talk) 08:17, 8 August 2008 (UTC)[reply]

The shape of a uniform cable secured at both ends and hanging under its own weight with constant horizontal tension is called a catenary. The shape of the catenary is determined by the ratio of the horizontal tension to the weight per unit length of the cable - the larger this ratio, the shallower the catenary. If the tug accelerates, the horizontal tension increases, the ratio increases, and the catenary curve becomes shallower. If the horizontal tension is very large compared to the weight per unit length of the cable (i.e. you have a very large force or a very light cable) then the catenary may become so shallow that it is indistinguishable from a straight line. Gandalf61 (talk) 09:08, 8 August 2008 (UTC)[reply]

A comment on the "indistinguishable from a straight line" part. This may well be true when viewing the cable from the side. However, if you look down the length of the cable from one end to the other, even a very subtle deviation from a line becomes quite visible. StuRat (talk) 15:15, 8 August 2008 (UTC)[reply]

-- Thank you for this very precise answer. —Preceding unsigned comment added by 194.167.55.204 (talk) 11:01, 8 August 2008 (UTC)[reply]

Also note that the shape will somewhat distort if the cable droops down into the water. The additional buoyancy will push that section upwards slightly from where it would otherwise fall. Then, when lifted out of the water, the additional weight of the water will make it lower than it would otherwise be, until all the water drips off and dries up. StuRat (talk) 15:13, 8 August 2008 (UTC)[reply]

The water does not just drip and dry. Instead, the tension in the cable causes the strands of the cable to tighten relative to each other, which forcefully expells a lot of water (at least for hemp cables, and at least according to Patrick O'Brian.) Also tension will lengthen the cable, which changes the mass/length. -Arch dude (talk) 14:21, 10 August 2008 (UTC)[reply]

Apparently William Whewell's 'Elementary Treatise on Mechanics.' (1819) contains the accidentally-poetic lines: "...no force, however great/Can stretch a cord, however fine/Into an horizontal line/Which is accurately straight." Whewell was not amused when this was pointed out and changed the text in the next edition. Links to more detail here AndrewWTaylor (talk) 16:50, 9 August 2008 (UTC)[reply]

Mamma mia! It's the ABBA rhyme scheme! -- Coneslayer (talk) 11:53, 11 August 2008 (UTC)[reply]

Water to Ice

Why is it that water increases its volume when it turns to ice? Minor Contributer (talk) 08:40, 8 August 2008 (UTC)[reply]

Our article on ice says that water expands on freezing "due to hydrogen bonds forming between the water molecules, which line up molecules less efficiently (in terms of volume)". Gandalf61 (talk) 08:52, 8 August 2008 (UTC)[reply]

Also Bismuth expands slightly when cooling from a melt —Preceding unsigned comment added by 79.76.149.61 (talk) 12:19, 8 August 2008 (UTC)[reply]

Permeability of plastic

Anyone know where I can find data on high permeable plastic films? Particularly ones that will allow o2 and CO2 to pass? For instance, how permeable (perms?) is cellophane (plastic wrap)? —Preceding unsigned comment added by 128.113.56.182 (talk) 13:28, 8 August 2008 (UTC)[reply]

The relative permeability of most plastics is 1. :) -- Katavothron (talk) 13:35, 8 August 2008 (UTC)[reply]

Thats great, though some what outside the scope of my question. :P —Preceding unsigned comment added by 128.113.56.182 (talk) 13:51, 8 August 2008 (UTC)[reply]

Semipermeable membranes are often made of plastic. Rmhermen (talk) 14:26, 8 August 2008 (UTC)[reply]

Contact_lens#By_constructional_material, and links therein, may be of some use regarding oxygen permeability. -- Coneslayer (talk) 15:32, 8 August 2008 (UTC)[reply]

Dialysis tubing is pretty permeable stuff. According to this study it's certainly permeable to CO2 and probably O2 as well (the study reports negligible change in [O2], but my guess is that was due to the strength of hemoglobin). --Shaggorama (talk) 18:05, 8 August 2008 (UTC)[reply]

Yeah, we used the stuff for a biology GCSE practical. —Cyclonenim^T@lk? 19:11, 8 August 2008 (UTC)[reply]

I'll tell you where I look for such info. My workplace has a subscription to Knovel, which gives us online access to many technical reference books. There are books in this collection that have exactly the type of data you are seeking, I believe. Sorry I cannot point to an "open" source. ike9898 (talk) 13:20, 9 August 2008 (UTC)[reply]

Beta plus decay and conservation of mass

What am I missing? A proton decays to a more massive neutron, and in the process ejects a positron, losing mass, AND 0.96 MeV of energy? -- Aeluwas (talk) 14:52, 8 August 2008 (UTC)[reply]

See Talk:Positron emission#Error?. -- Coneslayer (talk) 15:03, 8 August 2008 (UTC)[reply]

Thanks, but, um... The two article mismatch. Positron emission (and Carrionluggage on the talk page) says energy comes out of the decay (on the right side); Beta decay says energy is used (on the left side). Which one is it? :)

I'm guessing the beta decay article needs editing? -- Aeluwas (talk) 17:20, 8 August 2008 (UTC)[reply]

According to this link, among others, the beta decay article is wrong. I'll get to it, then. :) -- Aeluwas (talk) 17:24, 8 August 2008 (UTC)[reply]

Actually, I'll leave it to someone else. I can't correct the sentence after the equation (which would have to be part wrong for the article to be wrong). -- Aeluwas (talk) 17:37, 8 August 2008 (UTC)[reply]

I think the positron emission reaction "takes" energy from the binding energy of the parent nucleus, and some of that energy ends up as kinetic energy in the outputs. So whether the energy term is on the left or the right depends on whether you count the parent nuclear binding energy as being an input or not. I never took nuclear physics, though, so hopefully someone else can comment. -- Coneslayer (talk) 17:45, 8 August 2008 (UTC)[reply]

Yes, Beta decay#β+ decay is describing the case of an isolated proton, which requires energy input, while Positron emission is describing the decay of a carbon-11 nucleus, which doesn't. I added a bit to the Positron emission article to clarify this. The proton and neutron masses that are usually quoted only make sense for nucleons in isolation. The mass of a nucleus is less than the sum of the masses of the constituent nucleons considered as free particles (except of course for hydrogen-1 and administratium-1, where it's equal). -- BenRG (talk) 20:17, 8 August 2008 (UTC)[reply]

Water for the West

Wondering why it wouldn't be possible to increase rain fall in the West by pumping sea water into the many large dry lake beds. They already contain salt, so that shouln't be a problem. 129.112.109.253 (talk) 15:33, 8 August 2008 (UTC)[reply]

The volume of pumping required, were the rest of the scheme reasonable, renders the whole thing moot. You're talking hundreds of trillions of gallons of water per year. — Lomn 16:02, 8 August 2008 (UTC)[reply]

However, as Death Valley is below sea level, one could theoretically connect a siphon from the Pacific Ocean and have the water flow by force of gravity alone. The actual effect on local climate would likely be negligible though; probably not enough to justify the cost of constructing (and maintaining - salt water is very corrosive to both concrete and metal) the 400+ km long pipe (about one third of the length of the Trans-Alaska Pipeline). -- 128.104.112.147 (talk) 17:36, 8 August 2008 (UTC)[reply]

What you're suggesting has actually sort of happened already (by accident). An engineering failure caused the Colorado river to be diverted into the Salton sink, resulting in the formation of the Salton Sea. It's the largest lake in California, but its existence doesn't make socal any less of a desert. It takes more than a lake to make rain. --Shaggorama (talk) 17:58, 8 August 2008 (UTC)[reply]

It's an interesting concept, and it could work, provided you can feed ocean water into a below sea-level area using gravity. However, the resources needed to do this might be better spent on a desalination plant to provide fresh water directly. StuRat (talk) 18:28, 8 August 2008 (UTC)[reply]

Totally possible if you wanted to dig a canal from the ocean to Death Valley in California. It would make quite a nice lake. There are easier ways to get filtered water, however. --mboverload @ 19:11, 8 August 2008 (UTC)[reply]

I commute across Death Valley a dozen times a year, and one of our topics of conversation (the drive gets a bit long...) is "What if the Sierra Nevada sprung a leak and this all suddenly filled up to sea level?" --jpgordon^∇∆∇∆ 16:57, 9 August 2008 (UTC)[reply]

I believe there were plans some time ago to do this sort of thing with a huge pipeline through the mountains in North Africa. More recently they've discovered water under the sand and have begun extracting it - I don't know what a huge saltwater lake would have done for that. Dmcq (talk) —Preceding undated comment was added at 16:08, 10 August 2008 (UTC)[reply]

Central Australia is below sea level, this scheme has been suggested. Experts say that the rainfall would not increase as a result. sorry I haven't any further details. Polypipe Wrangler (talk) 10:40, 13 August 2008 (UTC)[reply]

Too Many Magnetic Minerals in me Coffee

I like me coffee. Sometimes though, depending on where I get it. Maybe the Volcanic soil is higher in Iron or something else, I'm not sure what, but some Magnetic, or Electromagnetic reaction activation sequence in my coffee mug. Basically, if I'm drinking my coffee, and lots of it, and listening to my radio driving by an electro field called the highways and streets, in Los Angeles, there are power lines galore. And/or if I'm listening to my Ipod, especially ecstatic. I feel like my brain is out of wack. My concentration is taken away and focusing on anything for a long period of time is hard work. Like reading a simple book. I could give up all these things and live the secluded life, or I could find some sort of fix. I'm thinking of rigging something up in the kitchen. My question is this: Could I, when boiling my water, put a pretty good sized magnet on the side of the pan minimize ingestion of Magnetic particles? I mean, would this help or make it worse? I'm thinking the magnetic particles would stay in the pan. Or would it just activate them and make them even more magnetic? Regarding the ipod. I feel like I'm doing that old Electromagnetic Therapy shock stuff they do to people in the Psych wards. In a mass population, I see how this can help in a pessimistic attitude. Instead of healing the Mentally Ill, just make the average citizen mentally unstable, so in a sense, the mentally ill will not be alone. Balancing the averages I guess. Anyways, if any scientists here know of great fixes for this silent epidemic of policy/protocol/politic in control theory, I'd greatly appreciate any helpful advice. Cheers, --i am the kwisatz haderach (talk) 16:29, 8 August 2008 (UTC)[reply]

Wow. Are you sure you're not just feeling the effects from the caffeine? -- MacAddct  1984 ^{(talk  contribs)} 17:02, 8 August 2008 (UTC)[reply]

I agree with MacAddct; this is probably the most bizarre question I've ever read here, and I've read some doozies. I have something to tell you that might help, or it might make your freak out even more. If you're worried about "magnetic particles", you shouldn't be worried about your coffee, but your breakfast cereal. Many breakfast cereals contain an ingredient called "reduced iron" which is actually metallic iron particles, which you can extract with a magnet. See [4]. They're perfectly harmless though; your stomach acid oxidizes the iron and after that it's not ferromagnetic any more. 128.165.101.105 (talk) 18:41, 8 August 2008 (UTC)[reply]

"Sometimes though, depending on where I get it." Is that an actual pattern ("often happens with Store A coffee, never with Store B"), or is this really two unrelated variables (you get it from different places, and there's no relationship between where you get it and the occurrence of...this effect). DMacks (talk) 18:56, 8 August 2008 (UTC)[reply]

1. Electromagnetic fields are not trying to kill you. 2. Don't take this the wrong way but many things can cause the symntoms you describe. Heck, you could be right in some sense and have heavy metal poisoning. Who knows? We can not give medical advice so all I advise you to do is see a doctor and tell him your feelings. The only thing I drink is highly filtered water so I can assure you I am not under their control. --mboverload @ 19:09, 8 August 2008 (UTC)[reply]

I think something other than your coffee needs to be checked. :) Just kidding. In all seriousness, it is probably the effects of the caffeine rather than magnetic iron dissolved in your coffee. bibliomaniac 1 5 19:12, 8 August 2008 (UTC)[reply]

That too. Caffine IS a drug, after all. And drugs have side effects. --mboverload @ 19:16, 8 August 2008 (UTC)[reply]

Thanks. I see that my question isn't structured properly. A quasi-subconscious-metaphor-ishness. And it is because the information I'm getting is based on personal collection, like a stamp, coin, or baseball card collection. LSD. No, I'm not on it. Basically, I test certain markets. Using my body as a lab. A Consumer Report in Biology of Chemical Engineering and the FDA. I'll go to different demographic neighborhoods and drink or eat only these types of drinks or food. I was using coffee as an example. Lets say for a week I'll drink only Arrowhead water. Then I'll switch it up and drink a bunch of Coca-Colas, or Starbucks. Hence, Coffee the example in research questioning. This may deal with Soundwaves and Light. For instance, drinking a cup of jo, then going to see 'The Incredible Hulk'. Maybe the industrial sound, lights, and magic (what's in the cup) can give me a headache. Maybe it's just the caffeine. I'm just thinking of a GamesTheory on research done on human beings. Unfortunately much of the psychological drug treatment is done on mentally ill peoples, so when using this data to control a mass population, it could lead to an entire population of people being treated as you would that of an insane person. Possibilities people, I'm not saying that this is happening or that I'm a conspiracy theorist. My question is it possible to a) put some sort of additive into food supply, b) add some sort of electrowave/pulse into a targeted environment, like an Electro Magnetic Pulse, or like an Electric Grid you use to keep your dog in your yard, c) something to the effect of Transcranial_magnetic_stimulation on a Mass Population? Lets not bandy insane/sane questioning, and/or whether this is implemented in any cities in the world, but the question-thought should be looked at as--Could we do this, and if so, HOW? Cheers, --i am the kwisatz haderach (talk) 20:14, 8 August 2008 (UTC)[reply]

You need to separate your questions then. If you are talking about your practical experience, the best thing to do would be to start documenting your own experience in a notebook. Maybe a pattern will emerge if you keep records. If you want to ask a theoretical question, maybe you should start a new thread. But to answer your last question - yes, yes and yes. But not with any technology we possess today or are likely to have in the near future. Franamax (talk) 20:46, 8 August 2008 (UTC)[reply]

I'm going to try to respond to your questions in turn. First, A) there are lots of additives in your food already. For instance, see Water fluoridation. B) you answered your own question with the dog fence example, but it's worth noting that the mechanism of adog fence and an EMP are incredibly different. An EMP a wide range magnetic pulse that is a side effect of a high altitude nuclear blast that wipes out the activity of electronics in a large area. An electric dog fence is a perimeter that causes an electric dog collar the activate and shock the dog if it is crossed. EMPs can't be used for population control beyond interfering with electronics, and electric fences need their targets to wear a device to control them. C) TMS is focused on isolated areas of the brain, so there isn't really any reason to fear "TMS on a mass population" because there is no way to perform such a focused procedure on a wide area unless everyone was wearing some peice of equipment on/in their heads that would permit it.

In general, I think your fears are largely unwarranted and you should further research the effects of electromagnetic (more specificaly magnetic) energy on the body and brain. If you are interested in how large organizations manipulate the psychology of wide populations to their benefit, you should read up on advertising, propaganda, and subliminal messages. If you want to protect yourself from the influences of others on your mind, you would be more effective turning off your TV and closing your newspaper than putting a magnet against your coffee maker. --Shaggorama (talk) 14:24, 10 August 2008 (UTC)[reply]

==OH BOY==125.21.243.66 (talk) 14:05, 11 August 2008 (UTC)[reply]

Structure of liquid water

I was just watching 'The enemies of Reason', the documentary by Richard Dawkins and someone in it, a proponent of homeopathy, said that no one knows the structure of liquid water. Now since no-one picked him up on this, I would be lead t believe this is true but I thought I should best check here before I commit myself to it. Is it true? 92.4.189.176 (talk) 19:41, 8 August 2008 (UTC)[reply]

No, it's not true. The structure is one oxygen atom with two hydrogen atoms joined by single bonds at an angle of 104.45° to each other. Perhaps they are talking about the types of bonds between water molecules in the liquid state ? This is primarily hydrogen bonds. See water#Chemical and physical properties. StuRat (talk) 20:03, 8 August 2008 (UTC)[reply]

I assumed it was something more complex than that because the man who said it was a doctor of rheumatology and I learnt about bond angles and hydrogen bonding for my A level. Thanks anyway. 92.4.189.176 (talk) 20:06, 8 August 2008 (UTC)[reply]

Water molecules do form large-scale networks of hydrogen bonds that are quasi-stable and this is an area of ongoing research. No connection yet to homeopathy. Franamax (talk) 20:58, 8 August 2008 (UTC)[reply]

The homeopathy bit was irrelevant; I was just trying to set the scene in the hope that someone else may have watched it. 92.4.189.176 (talk) 22:18, 8 August 2008 (UTC)[reply]

You're probably referring to water memory. Useful if you need to store some data for 50 femtoseconds. --Heron (talk) 21:07, 8 August 2008 (UTC)[reply]

Actually, the claims are perfectly correct. The structure of liquid water is indeed an on going area of research. It is correct that the local structure is "one oxygen atom with two hydrogen atoms joined by single bonds at an angle of 104.45° to each other" (Having said that, the bond angles and interatomic distances are sometimes disputed). However since water is a liquid, it has a disordered structural arrangement and so the atomic configuration of water at long range or even intermediate length scales (anything beyond around 0.5 - 1 nm or so) is not easily known or predicted, since it is not simply a periodic arrangement of basic structural units as in a crystalline solid. The basic structural units (water molecules H2O) are instead arranged in a disordered (but not neccessarily random) manner. There are many studies of liquid water by the method of neutron diffraction. However, this is an extremely challenging technique to apply to liquids and amorphous materials since the atomic correlations become so diffuse at extended length scales. Methods such as isotopic substitution in neutron diffraction may help to yield these atomic correlations but this research is still on going and there is still much controversy over the intepretation of the results. The same applies to many liquids, amorphous solids and glasses since the experimental techniques available to obtain the atomic structure of materials (e.g. neutron and x-ray diffraction) are still extremely challenging when applied to non-crystalline materials. Ultimately any theoretical models on the structure of water must be based on definitive experimental data which is not yet available...I'm taking a wikibreak so might not check this page but if you are interested in getting some more information on the extent of current understanding on the atomic structure of water and the current experimental limitations then please leave a message on my talk page and I could point you to a few references. Jdrewitt (talk) 21:41, 8 August 2008 (UTC)[reply]

Wikipedia:Reference desk/Archives/Science/2008 August 8

Contents