Wikipedia:Reference desk/Science

May 26

The gulls have started laying their eggs...

As usual, I can see a black-back nest from my window and I was watching the mother gull today. When not sat on the eggs and keeping lookout, she was stood up so as to allow her eggs to cool slightly, or turning the eggs with her beak and feet to ensure even temperature distribution. I had a moment of realization that the poor hen will be up and down, doing this day and night for the next month or so, with little opportunity for sleep (the male bird brings her food but I don't know where he goes at night). I do feel kinda sorry for her.

Now I'm wondering, which requires the most energy expenditure - constantly tending and protecting an egg until hatching, or nurturing an embryo inside the body for the same period of time? --Kurt Shaped Box 09:30, 26 May 2007 (UTC)

You also have to consider not only energy use, but convineance. It's a lot easier to feed yourself when you aren't carrying around a large weight. Actually, come to think of it,this might be why birds lay eggs, it would make sense, since they would struggle to fly with the weight of a foetus, wouldn't they? -- Phoeba Wright^OBJECTION! 11:24, 26 May 2007 (UTC)

I'm pretty sure that's the accepted thinking - someone correct me if I'm wrong... --Kurt Shaped Box 15:07, 26 May 2007 (UTC)

Do pregnant bats fly? I think the egg thing is just the way they are. After all, those eggs still have to be formed inside the hen, and she has to fly around carrying the preformed eggs inside her, or at least the materials required. --0rrAvenger 17:40, 26 May 2007 (UTC)

Perhaps marsupials have the easiest job for the mothers. They don't even seem to notice when they give birth, as the offspring are so small at the time. They don't have to tend any eggs, either, as the offspring find their own way to the pouch and attach to a nipple. StuRat 18:02, 26 May 2007 (UTC)

I wonder if laying eggs is as painful as childbirth in humans? It's very hard to tell if a bird is in pain. When my budgies lay, the hen gets a sort of 'intense' look in her eyes - but that could just be the result of her concentrating and putting all her energy into pushing... --Kurt Shaped Box 09:48, 27 May 2007 (UTC)

Nuclear forces

I'm trying to come up with some simple diagrams explaining why nuclear fusion is difficult. The main reason, as I understand it, is that at most levels of interaction the hydrogen ions are positive and thus will repel themselves due to electrostatic repulsion. However if you can get them close enough, the nuclear force should kick in and make them fuse. My questions are: 1. what approximately are the radii that the electrostatic repulsion and nuclear force are active for hydrogen ions? How close do they have to be, in other words, before they fuse? Is this the Coulomb barrier? and 2. why does it release energy? I know that you can calculate the binding energy etc. by looking at the missing mass etc. but in a physical sense what is the mechanism of the energy release? The example given in nuclear fusion seems to say that most of the energy released in a D-T reaction comes from the ejection of a neutron and the subsequent recoil — is this a good way to think about it? (I find fission easier to conceptualize if instead of thinking of it as "converting matter into energy" I think of it as two positively charged nuclei repelling one another suddenly; is this an analog to that?)

Thanks for the help. This is not homework, this is just a non-scientist trying to make sense of this so I can convey the information to other non-scientists. I think I get most of it though I'm having trouble making use of some of the pages (i.e. Coulomb barrier) which seems to require a lot more knowledge of quantum mechanics than I have to even use it (i.e. knowing what "permittivity of free space" means, which even when I click on it is written in 100% technical language). --24.147.86.187 00:35, 26 May 2007 (UTC)

The coulomb barrier is how hard you have to throw the 2 atoms to get them to stick together - that's why fusion requires so much heat to work. That is, you give it lots of energy to get over the barrier; then it gives that energy back plus a bit more.

The non quantum introduction to nuclear is the semi-empirical mass formula or liquid drop model, which largely balances strong force and coulomb repulsion.

These balance out to something like this curve: binding energy per nucleon graph. Between H and O the binding energy rises sharply because the number of nucleons on the surface (which are less tightly bound) compared to the total number of nucleons goes down. Above Fe, the coulomb force dominates.

The D-T reaction (H2+H3) produces He4 (+n). He4 is quite special because 2 protons and 2 neutrons both match the magic number 2 - this allows for a larger than normal binding energy (this is a quantum effect from the idea that both neutrons and protons exist in shells like electrons in atomic orbitals).

--h2g2bob (talk) 06:39, 26 May 2007 (UTC)

Energy needs to be kept by the atom to overcome coulomb forces, which are repulsive. Energy is given away by the binding force which is attractive. It sounds dumb, but it's the best I can come up with. --h2g2bob (talk) 06:57, 26 May 2007 (UTC)

I have searched for a picture of the potential, this is the best one I found. The source of the energy liberated in a fusion is the acceleration caused by the potential difference between the outside region and the center of the well. You can see that the question whether energy is liberated or captured depends on the height difference. http://upload.wikimedia.org/wikibooks/en/7/7a/Fhsst_atomnucl6.png

How close do they have to be, in other words, before they fuse? It is roughly 1fm, the size of the resulting nucleus. However if you really use the Standard Model on this, you will only get the probability of a fusion and this probability will depend at least on the relative speed and the distance at the point of nearest approach. I have no idea how the probability will vary exactly with these parameters, it depends a lot on the details and is way over my head.

I was told by a chemistry teacher I once had that if the Hydrogen before it is fused is wieghed then it would wiegh more than the fused Helium, the lost mass is turned into energy.67.125.159.224 23:26, 26 May 2007 (UTC)

The sum of the mass of a core of deuterum and a core tritium is more than the sum of the mass of a core of helium and a neutron. The rest of the sentence is problematic. Mass cannot be turned into energy because mass is already energy. The energy of an object can be measured from different inertial frames. If the frame moves fast relative to the object the energy measured will be higher than when it moves slow. If the frame of reference does not move at all relative to the object, the measured energy is called the rest energy, rest mass or simply "mass".

Equivalent Resistance

Hello. The formula for equivalent resistance for a parallel circuit is R_equivalent = 1/R₁ + 1/R₂ + 1/R₃. How was this proved? Thanks. --Mayfare 00:54, 26 May 2007 (UTC)

It's 1/R_equivalent = 1/R₁ + 1/R₂ + 1/R₃. Proving it is quite simple. If you take a very simple circuit consisting of a perfect voltage source of voltage V, and three resistors in parallel, firstly, you know that the each resistor has no effect on the current running through the others. The current through each resistor is V/R_i. The sum of the currents through the resistors is V/R₁+V/R₂+V/R₃, or V*(1/R₁+1/R₂+1/R₃). Ohmic resistance is defined as R=V/I, or 1/R=I/V, so 1/R_equiv=V*(1/R₁+1/R₂+1/R₃)/V, and therefore 1/R_equiv=1/R₁ + 1/R₂ + 1/R₃. Someguy1221 01:03, 26 May 2007 (UTC)

If R = V/I, then does that mean R_equivalent = V/I_sum? Since V_s = V₁ = V₂ = V₃, can R_equivalent = V/V(1/R₁ + 1/R₂ + 1/R₃) be correct yielding to R_equivalent = R₁ + R₂ + R₃, the formula for equivalent resistance for a series circuit? I am confused. --Mayfare 01:38, 26 May 2007 (UTC)

Everything in there is correct except the last step. 1/(1/R₁ + 1/R₂ + 1/R₃) is not the same as R₁ + R₂ + R₃. For ease's sake, let's change the resistances to a, b, and c. If 1/(1/a+1/b+1/c) equaled a+b+c, this would imply that 1/(a+b+c) equals 1/a+1/b+1/c. This is logically impossible for positive values, as the former gets smaller as terms are added to the denominator, and the latter gets larger. Someguy1221 02:44, 26 May 2007 (UTC)

One way to think about (and remember) this is that for resistors in parallel, the conductances add, just as the resistances add for resistors in series. The conductance, (measured in Siemens (unit), ℧, sometimes referred to as "mho") is defined as 1/resistance. —Steve Summit (talk) 13:09, 26 May 2007 (UTC)

For completeness's sake let us also mention that the starting point for all this is Kirchhoff's circuit laws. They tell us that in the case of the resistors in parallel, each one gets the same voltage, and in the case of serial connection, we all have the same current flowing through them. Simon A. 17:45, 26 May 2007 (UTC)

Elephants mammary glands

Why do elephants have their mammary glands at the front of their bodies unlike other mammals which have them towards the end of their bodies? 144.138.100.49 03:31, 26 May 2007 (UTC)

Thats not actually so. Most mammals have a number of mammary glands distributed along the milk lines, parallel with the anterior/posterior axis of the ventrum. For example, mice have 5 pairs of mammary glands, the most anterior being between their forelegs, which is the same relative position as human and elephant mammary glands. The unusual things about elephants is that that have a single pair, not the position of that pair. Of course, the most likely reason the have a single pair is because of their small average litter size of just over 1, and pretty much all mammals that have a single pair have them anteriorly positioned. If you are interested in how the glands form in the position they do, "this paper" (PDF). offers some insight into the transcription factors involved in regulating their development. Rockpocket 07:15, 26 May 2007 (UTC) (amended due to Steve Summit's excellent examples, of a few that don't, leading to further research, below Rockpocket 18:20, 26 May 2007 (UTC))

I think the Original Poster can be forgiven, though, given that our Elephant article states that "Unlike most mammals, female elephants have a single pair of mammary glands located just behind the front legs." And while you maybe right about "pretty much all mammals that have a single pair have them anteriorly positioned", many of the examples we're all most familiar with (goats, horses, deer) have them in a posterior position. —Steve Summit (talk) 13:00, 26 May 2007 (UTC)

It occurs to me that we're overlooking the most familiar exception to that quoted rule of thumb: us. On the human female, a single pair of mammary glands are located just behind the front legs. (It's just that we call our front legs 'arms', and 'just behind' becomes 'just below' now that we're walking erect.) TenOfAllTrades(talk) 13:35, 26 May 2007 (UTC)

It's interesting to note that people who have a third nipple do indeed have it along the milk lines. --TotoBaggins 18:07, 26 May 2007 (UTC)

Good points, Rockpocket and Steve. So, our domesticated milk-giving mammals are the exception: they have several glands, and they are all quite posterior. So, why is that? If these milk lines that Rockpocket mentioned spread all the way along the belly, why are they so concentrated to the rear? Don't the arrangement of a mouse looks much more useful than such a bulky udder? Actually: are there udders in non domesticated mammels? Simon A. 17:32, 26 May 2007 (UTC)

So I have a done a little more reading on this and it turns out that my original comments are a little misleading (so I've struck them). There are actually a range of positions of mammary glands across mammalia, for example:

Easy access?

Easy access?

Species	Anterior (thoracic)	Intermediate (abdominal)	Posterior (Inguinal)	Total
Cattle	0	0	4	4
Goat, sheep, horse	0	0	2	2
Pig	6	6	4	16
Cat	4	2	2	8
Dog	4	2	2-4	8-10
Rat	6	2	4	12
mouse	6	0	4	10
Guinea pig	0	0	2	2
Human, elephant, primates	2	0	0	2

However, there is much variation within species, both in number and absolute position, and the reason the positions are so defined and pronounced in domestic animals is due to inbreeding and human interference. For example 50% of the dairy calves are born with more than 4, but the extra teats are "removed" when the calf is only a few days old, so they can better fit into the milking machine (think of that next time you enjoy a glass of milk!). I'm afraid that's not true. Very rarely are calves born with extra teats. Healthy, well formed udders are genetically selected for, and cows are not inbred. Genetics in the dairy industry is quite advanced. A healthy, happy cow is also good for the farmer. Sometimes a cow will have an extra teat, but it's usually not functional and not really an issue at all. The other thing to consider is spatial distribution, there are no more than six in any given region, so if you wish to have more than six, you have to spread them out along the AP axis. However, I can't find any information as to why some species have only two at the anterior and others only two at the posterior, beyond mechanistic explanations. This is mere speculation, but it could be for reasons of access. The image of the goat shows how the position to the posterior allows the kid to suckle with ease. Obviously it makes sense for human and primates to have anterior glands, since we are bipedal and hold our young. Perhaps the posture of elephants make it easy for the young to suckle under their forelegs. Of course it could also simply be one of those accidents of evolution. I got most of this from Animal Science and Industry, Merle Cunningham, ISBN 9780130462565. Rockpocket 19:33, 26 May 2007 (UTC)

Well, at any rate, I think that Rockpocket deserves the Wikipedia Reference Desk Above-And-Beyond-The-Call-Of-Duty award for conspicuously thoroughly researched and presented data! —Steve Summit (talk) 20:18, 26 May 2007 (UTC)

The cat/dog/rat totals don't add up correctly. As for being an accident in evolution.... I'm not so convinced myself. Two things come to mind when talking about elephants. One is their size, obviously, and the second is the amount they travel in any given day. Maybe the location of the glands has to do with not staying still? --Wirbelwindヴィルヴェルヴィント (talk) 20:59, 26 May 2007 (UTC)

Oops. Thats embarrassing - I have fixed them now, thanks. My guess would be you are probably right. The image seems to demonstrate that the position of the elephant gland allows the calf to suckle from a position at the side of its mother. This would be most helpful to suckle on the move, avoiding the risk of being trampled on. The human and primate anterior positioning permits a similar thing. In contrast, grazing animals will stand still most of the time the young suckle. The size of the animal is also an issue, and whether the mother lies down to suckle her young. There are also issues about directing the young to the nipple. Some animals use pheromone type cues, meaning the young have to use their own olfactory function to feed. In other species, the mother plays a much more active role, physically guiding the pup to the nipple. All of these factors would impact on the evolutionary pressures driving mammary gland positioning. BTW, Steve, I have recently acquired a professional interest in another aspect of suckling, so this research was not entirely altrustic. Rockpocket 21:18, 26 May 2007 (UTC)

Bird identification

I'm in the Pacific Northwest, and I saw a bird that I thought was a juvenile crow, but although it looked black from a distance, its feathers (on its body anyway) were really dark variegated metallic tones. It looked pretty much like a pigeon-sized crow, but its head (or maybe its crown feathers) seemed smaller. Anchoress 03:33, 26 May 2007 (UTC)

maybe some kind of starling. -- Diletante 14:59, 26 May 2007 (UTC)

Thanks for the reply, but I kinda doubt it. This bird looked amost exactly like a crow, except it had a slightly sleeker head and up close its feathers were a really dark - almost black - metallic pattern. And it was much smaller, of course. But still pretty big for a bird. The pic provided was a completely different shape. Anchoress 18:44, 26 May 2007 (UTC)

Could be a Jackdaw? They're sometimes found in North America, although it's on the wrong coast if it is (!). More likely, it could be a Common Grackle, Rusty Blackbird, Brewer's Blackbird or Brown-headed Cowbird, all of which are native to or visitors of your area. Any good? --YFB ¿ 19:25, 26 May 2007 (UTC)

Wow, thanks for those links! The Grackle was the closest, although the distinguishing feature of the bird I saw was the almost invisible metallic markings over its whole body, but the shape of the Grackle is definitely very close (the bird I saw had less of a ruff tho). Thanks again! Anchoress 00:53, 27 May 2007 (UTC)

No problem :-) I think, based on your location, that it's likely to be the Bronzed subspecies (Quiscalus quiscula versicolor) which looks like the one at the top of this page. The amount of colouration you see will depend heavily on the lighting conditions and the state of the bird's feathers, but it's hard to say with certainty without a photo. There don't seem to be any other species in my National Geographic Field Guide to the Birds of North America which match your description, so I'm reasonably sure it's one of the species I linked. Try to get a snap if you see it again! --YFB ¿ 02:07, 27 May 2007 (UTC)

Exor gate

Any idea what is the table for 3 bit EXor gate?

It's not well-defined. I tend to imagine a parity generator.

It's very well defined and it is a parity generator. It's also the same as 2 two input xor gates. An even number of 1's generates a 0 and an odd number of 1's generate a 1. This is true for any xor gate of any size input. --Tbeatty 06:19, 26 May 2007 (UTC)

That's well-defined as a relation which (a) is useful and (b) the two-input XOR is a natural limiting case of, but it's not clear that the 3- or more input forms are meaningfully "A or B but not both", which is what I think of as the definition of "exclusive OR". —Steve Summit (talk) 12:15, 26 May 2007 (UTC)

I didn't get that with the "2 two input xor gates", but I suspect this is what you meant as the answer to the question:

In 1	In 2	In 3	Out
0	0	0	0
0	0	1	1
0	1	0	1
0	1	1	0
1	0	0	1
1	0	1	0
1	1	0	0
1	1	1	1

Is that correct? —Bromskloss 09:55, 26 May 2007 (UTC)

Two XOR gates where A and B feed the first gate - then C and the output of the first gate feed the second gate - would form a function which is of some use. But XOR is defined as a two-valued function and the term simply isn't used by circuit designers or programmers for devices or functions with more than two inputs. The definition can be expanded in more than one way - you could have a function like a 'Parity generator' which produces a '1' if there are an odd number of '1' bits on the input - or you could make a function 'true if exactly one input is true' - or a function 'true if all but one input is true' - any of those things would behave like XOR for two inputs - which one should be the definition of XOR for more than two inputs? I'm a programmer - and I used to be a circuit designer - and I've never heard of anyone using the term XOR for more than three two inputs. Hence any truth table you might come up with for such a device would be entirely arbitary and ought to have a different name that more clearly explains what the function is - there is no one clear generalisation of XOR that everyone would agree on. SteveBaker 14:54, 26 May 2007 (UTC)

Steve: An engineer might agree with you but I'd imagin that a mathematician might find the parity the only consequent choice. For AND and OR gates, we generalization is obvious, and this is mathematically because they are associative and commutative operators. This allows you to arrange all the operands (ingoing signals) in an arbitrary order and always pair off neighboring ones by ANDing them and then replacing the pair by its result. In other words: If we have only binary AND gates with fan-out 1, and we arrange them in an arbitrary way (barring feed-back, of course) to get a single output, we always end up with the same man-inputs AND. The same holds for OR, and if you try it for XOR, you are bound to end up with parity. Simon A. 17:38, 26 May 2007 (UTC)

I do circuit design today and multiple input XOR gates are used all the time. It's provable that (A XOR B XOR C) => (A XOR B) XOR C => A XOR (B XOR C) => (A XOR C) XOR B. There is no ambiguity at all in logic. You can use the truth table above (which is correct). Since the two input XOR seems intuitive, start there. A XOR B = (A AND B*) OR (A* AND B). A XOR C = (A AND C*) OR (A* AND C)). B XOR C = (B AND C*) OR (B* AND C). Once you drop those identities into all the equations, you will find there is no alternative definition. A XOR B XOR C is very well defined and suffers no logical ambiguity. --Tbeatty 05:34, 27 May 2007 (UTC)

Or in short, "XOR is also associative and commutative, and therefore the gneralization to three operands is just as obvious as with AND and OR." I'm surprised that Steve Baker didn't see it that way. Oh, but now I notice Steve Summit's point: if you think of the English language meaning of "or", you get a different generalization. I think my comment as to that is, "who cares about English?" --Anonymous, May 27, 2007, 05:38, edited 06:02 (UTC) after counting Steves in the thread.

It's clear that the generalized, three-or-more-input operator is useful. My only quibble (and it is indeed a minor one) is that I think the useful name for the generalized operator is something like "parity generator". But if you want to call it "XOR", or "Wakalixes", I can't stop you. :-) —Steve Summit (talk) 06:08, 27 May 2007 (UTC)

I agree with Steve's first sentence above, but I think that WP should set an example of the correct use of "XOR". We have to differentiate between what is verifiable and what we assume to be common sense. Here are two references:

"exclusive OR n. a logical operation working on two variables..." (The Concise Oxford English Dictionary and The New Oxford American Dictionary)

and:

"exclusive disjunction. If p and q are statements, then..." (The Concise Oxford Dictionary of Mathematics)

In other words, XOR is defined only for two inputs. There is no formal justification for the term "3-input XOR gate", even though everyone thinks they know what it is. --Heron 12:01, 27 May 2007 (UTC)

How about the logic that Xor gives 0 for same value( 0 or 1) of n input( ex:-0000 or 1111) and 1 for different value( 0 & 1) of n input(ex:-0101 or 1010)??59.92.240.228

That's not an interpretation I've ever heard. Do you have a reference for that? It does, however, raise the issue of the XNOR gate, which is straightforward if you define it (correctly) as NOT (A XOR B), but confusing if you define it as an 'equivalence gate', which implies a different truth table from the correct definition for > 2 inputs. --Heron 22:18, 27 May 2007 (UTC)

Catalysis and equilibrium

An interesting point has come up in relation to chemical equilibrium. How does a catalyst reduce the time needed for a reaction mixture to attain equilibrium, reactants $\rightleftharpoons$ products? I think that it speeds up either the forward reaction or the backward reaction, but not both as seems to be suggested in some places. Do anyone know of a good primary source that can be cited to support this idea?

My understanding is that a catalyst reduces the activation energy for a specific reaction by providing an alternative mechanism by which that reaction can proceed. The activation energies for the forward and backward reactions are not related to each other because the mechanisms are different, so I see no reason why the catalyst should affect both reaction rates. Is this right in general? Petergans 17:57, 26 May 2007 (UTC)

Nope. A catalyst does indeed speed both the forward and the reverse reaction—remember, the alternative reaction mechanism that the catalyst provides will work in both the forward and reverse directions.

See also Catalysis#Catalysts and reaction energetics. TenOfAllTrades(talk) 18:24, 26 May 2007 (UTC)

Looking at it mathematically, consider the Arrhenius equation. For the forward reaction, we have $k_{f}=A_{f}e^{{-E_{af}}/{RT}}$, and for the reverse, $k_{b}=A_{b}e^{{-E_{ab}}/{RT}}$. At equilibrium, the forward rate of reaction equals the reverse rate. So, we'd have $k_{f}\cdot [A][B]=k_{b}\cdot [C][D]$, where A, B, C, and D are reactants and products. The position of equilibrium, that is, ${\frac {[C][D]}{[A][B]}}={\frac {k_{f}}{k_{b}}}$, equals ${\frac {k_{f}}{k_{b}}}={\frac {A_{f}e^{{-E_{af}}/{RT}}}{A_{b}e^{{-E_{ab}}/{RT}}}}={\frac {A_{f}}{A_{b}}}e^{{-(E_{af}-E_{ab})}/{RT}}$. Everything in the last expression is a constant (at constant temperature) even when a catalyst is added, since it reduces activation energy of both the forward and reverse processes equally, so $(E_{af}-E_{ab})=const$. Borbrav 20:28, 26 May 2007 (UTC)

There is nothing wrong with this argument for reactions for which it can be assumed that $k_{f}\cdot [A][B]=k_{b}\cdot [C][D]$ or that similar expressions will apply. However, the law of mass action is not universally valid because rate expressions do not universally follow stoichiometry. Secondly, for a multi-step reaction there may be more than one maximum in the energy vs. reaction coordinate plot. Will the catalyst affect both of them? Thirdly, in a multi-step reaction the rate-determining step may be different in forward and backward reactions. Will the catalyst affect both of them? Fourthly, an enzyme may initiate a chain of reactions of which it can possibly reverse only the first one but not the rest.

The key word in my question is general. Petergans 22:52, 26 May 2007 (UTC)

About Contacts

1) Why is it that after wearing my contacts for about the whole day, around the pupil of my eye (supposed to be gray due to the contact) gets brown (my natural color)?

2) What's protein buildup?

3) Can someone link me to a site showing all the decoration contacts available?

I would look myself, but I need to leave somewhere (I'm in a hurry). I didn't want to forget to ask. PitchBlack 20:43, 26 May 2007 (UTC)

How about you look things up yourself when you have time, then come back and ask about what you can't figure out yourself? --Tugbug 23:18, 26 May 2007 (UTC)

Yeah, youre partially right. Can someone still help me on 1 and 2? 74.161.71.66 00:48, 27 May 2007 (UTC)

More nipples

Why don't birds have nipples? --84.67.135.166 22:48, 26 May 2007 (UTC)

Because they never evolved them. They're not mammals. — Kieff | Talk 22:57, 26 May 2007 (UTC)

What's with the evolution? Birds are fed by the yolk in their eggs. When they are born, they still have some of that stuff in their tummies, so there's no need. .

Plus, while mammal babies need milk because they don't have good teeth yet, chickees already have a gizzard with teeth to take care of seeds and stuff. If they don't have teeth, they swallow stones to act as teeth. Besides many birds can care for themselves right after they're born, according to our article, bird. --JDitto 01:32, 27 May 2007 (UTC)

Birds developed neither nipples nor breastfeeding. Indeed, as said above, they evolved different strategies of caring for their young. However, some birds did evolve something remotely resembling breast milk. Please see our Crop milk article. Cheers, Dr_Dima.

H3

I was reading about the Lunar Regolith and read about the massive amount of H3 that is in it. I also was reading the Fusion article and it talked about H3 + H3 reactions which would produce no radiation. If there is plenty of H3 on the Moon and we get there safe and sound how much energy does it take to fuse together H3?67.125.159.224 23:39, 26 May 2007 (UTC)

I think the idea of "plenty" that you have right now is a lot different from what the article means. Like there are "plenty" of diamonds in namibia, but that does not really mean namibians can burn diamonds to heat their houses. Tritium is also highly radioactive all by itself, fusion or not.

May 27

Momentum of the world trade center collapse

The official theory for why the world trade center and WTC7 collapsed at nearly free fall speed is that the heat of the fires in those buildings, plus structural damage, weakened at least one floor; and then the floors above the damage crashed through the floors below the damage, all the way to the ground, under only the force of gravity. This theory proposes that the mass of the collapsing part increased with the addition of more dislocated floors, and that the velocity of the collapse increased against the resistance of the lower structure, and that the momentum of the collapse increased more rapidly with its vertical descent[1][2]. All of this is necessary to account for the nearly free fall speed of the collapse, i.e. nearly the same speed as an object falling in a vacuum, an observation which is agreed upon by the official account, and multiple video and seismic measurements. Additionally this theory proposes to account for material ejected sideways during the collapse by the pressure of condensed air pushed laterally by the collapse. But the official theory leaves many questions unanswered. First of all, how does the velocity of the collapse increase against resistance from the lower structure, considering that free fall speed is the maximum falling speed in a vacuum of any object no matter what the mass of the object? Secondly how does the momentum of the collapse increase more rapidly if the mass of the collapse is increasing, considering that more massive objects gain momentum more slowly than less massive objects? Thirdly wouldn't an increase in the rate of the momentum change mean that an outside force must be acting on the collapse, since the rate of change of momentum is the force of gravity, and the net force of gravity of a closed system is constant according to the conservation of energy? Fourthly how does the collapse compress air despite the open core which should allow the air to escape without resistance? Fifthly how does compressed air eject heavy perimeter columns as far as 450 feet horizontally, into the World Financial Center 3[3]? Sixthly if the fire is so widespread that all of the columns, interior and exterior of at least one floor failed then why is the fire not visible around the entire perimeter of the building? Seventhly if the steel was heated to the point that it weakened then why was the steel not glowing red? Lastly, how does this collapse hypothesis account for the pulverization of the buildings? Thanks for your assistance. Oneismany 00:05, 27 May 2007 (UTC)

That is a lot of questions. I will make a start:

First of all, how does the velocity of the collapse increase against resistance from the lower structure, considering that free fall speed is the maximum falling speed in a vacuum of any object no matter what the mass of the object? The collapse does not archive the free fall speed, it *is* slowed down by the resistance. However the resistance is not very large compared to the gravitational pull, so the slowing is a small effect, and the collapse *almost* archives the free fall speed.

If the resistance of the lower structure is such a small effect that it barely decreases the velocity of the collapse, then how did the structure hold the weight of the upper part to begin with? Presumably the building could stand up against gravity for 30 years since it didn't previously collapse. Oneismany 15:58, 29 May 2007 (UTC)

Secondly how does the momentum of the collapse increase more rapidly if the mass of the collapse is increasing, considering that more massive objects gain momentum more slowly than less massive objects? The gravitational force is proportional to the mass of the collapse. The momentum gain of the collapsing mass is proportional to the force pulling it. So the momentum gain increases with the collapsing mass. Whoever said that massive objects gain momentum more slowly than less massive objects is telling garbage.

Newton's law of universal gravitation $F=G{\frac {m_{1}m_{2}}{r^{2}}}$ is not garbage. Acceleration is proportional to altitude. Force is also defined as mass times acceleration. F = m₁ a₁, so a₁ = F / m₁, so $a_{1}=G{\frac {m_{2}}{r^{2}}}$. This means that, if force is constant, instantaneous acceleration of an object is inversely proportional to the mass of that object, i.e. the rate of change of velocity decreases the greater the mass of a body. As momentum is instantaneous velocity times mass, this means that more massive objects gain and lose momentum more slowly than less massive objects. This not a new result. It is well known that speeding up and slowing down in a heavy vehicle is more difficult than in a light vehicle. Yet the progressive collapse hypothesis contends that as the collapse gained mass the momentum increased faster which is impossible. Mass is intertia, more mass means more resistance to force and more self-gravitation. Oneismany 15:58, 29 May 2007 (UTC)

Thirdly wouldn't an increase in the rate of the momentum change mean that an outside force must be acting on the collapse, since the rate of change of momentum is the force of gravity, and the net force of gravity of a closed system is constant according to the conservation of energy? The momentum change is the momentum change. It is caused by the force of gravity, but it is not the force of gravity. The force of gravity on the collapsing top part is proportional to the mass of that collapsing part. As the mass of the collapsing part increases while it picks up more rubble, the force of the gravity on that part increases too. I cannot see how the conservation of energy would be related to any of this.

The rate of change i.e. the derivitave of momentum, is force, it is not caused by force. As discussed above, force is mass times acceleration, and is also proportional to altitude. If the collapse is a closed system and gravity is the only force acting on the collapse, the conservation of energy says that the net force cannot increase, i.e. the momentum cannot speed up. If the momentum is speeding up, then there must be an outside force acting on the collapse. Oneismany 15:58, 29 May 2007 (UTC)

• You may be interested in our articles on the various conspiracy theories surrounding the collapse of the World Trade Center. See Controlled demolition hypothesis for the collapse of the World Trade Center and 9/11 conspiracy theories. Our article (which you've linked already) on the collapse of the World Trade Center contains a great deal of information, as well as links to a wealth of scholarly reports. This Desk probably isn't a good place to rehash in detail all of the conspiracy theories around 9/11, nor to debunk them. TenOfAllTrades(talk) 01:25, 27 May 2007 (UTC)

Ugh, do we really need to bring up the conspiracy theories here? It's obvious none of them are correct. We're all hiding from the obvious truth. The martians want us to be afraid, so they filled the buildings with nano machines that eat at it like termites. 9/11 is just a cover up! -- Phoeba Wright^OBJECTION! 01:40, 27 May 2007 (UTC)

I don't think that calling conspiracy theory is appropriate here. A conspiracy theory usually makes arbitrary claims that cannot be falsified so there is no point in discussing these claims. All questions stated here are in a form where they allow for an answer or at least some sensible reply. Why should we not try to give the replies?

-- Phoeba Wright^OBJECTION! 02:16, 27 May 2007 (UTC)

First of all, how does the velocity of the collapse increase against resistance from the lower structure, considering that free fall speed is the maximum falling speed in a vacuum of any object no matter what the mass of the object?

The speed of collapse clearly cannot be the free fall speed in vacuum. There has got to be some slowing due to drag and the energy that has to be given over to collapsing the lower floors. However, that slowing is likely to be pretty negligable once there are enough floors of rubble pancaked together. So claiming free fall is likely to be an exaggeration - but a very slight one.

If the resistance of the lower structure is such a small effect that it barely decreases the velocity of the collapse, then how did the structure hold the weight of the upper part to begin with? Presumably the building could stand up against gravity for 30 years since it didn't previously collapse. Oneismany 15:58, 29 May 2007 (UTC)

Secondly how does the momentum of the collapse increase more rapidly if the mass of the collapse is increasing, considering that more massive objects gain momentum more slowly than less massive objects?

Momentum is mass times velocity. The mass increases as more and more floors join the falling rubble pile - the velocity increases because it's accellerating under gravity. Accelleration under gravity is independent of mass - remember Gallileo dropping the two balls off the leaning tower of Piza (actually, that never happened - but it's a good story!).

Momentum is mass times instantaneous velocity. Instantaneous velocity is independent of mass, that is the lesson of Galileo. But instantaneous acceleration is proportional to altitude, see above. If mass is increasing then it should slow the increase in momentum because mass (inertia) is resistance to momentum (motion). Oneismany 15:58, 29 May 2007 (UTC)

Thirdly wouldn't an increase in the rate of the momentum change mean that an outside force must be acting on the collapse,

Yeah - it's called "Gravity".

Gravty is not a net outside force on this system because the force of gravity has always been pulling the towers down and they were balanced against the force of gravity, as evidenced by the fact that they stood for 30 years without collapsing. If there is a new force acting on the system it is not gravity. Oneismany 15:58, 29 May 2007 (UTC)

since the rate of change of momentum is the force of gravity, and the net force of gravity of a closed system is constant according to the conservation of energy?

The rate of change of velocity is due to gravity...yes. The force due to gravity is indeed constant (for constant masses) - but force equals mass times ACCELLERATION - so under constant force with constant masses, the accelleration is constant - which means that the velocity is increasing - and since momentum is mass time VELOCITY, so is the momentum. Conservation of energy is not involved here - the kinetic energy gained by the falling rubble is equal to the gravitational potential energy it loses. If this were not true, nothing would ever fall at all!

But force is not constant, it depends on altitude, see above. The instantaneous acceleration depends on altitude and if mass is increasing then the acceleration (force per unit of mass) is decreasing. A greater mass is pulled by a greater force, only if acceleration is constant, which it is on the Earth's surface or at a certain altitude, but not if the altitude is not fixed. Conservation of energy stipulates that the total force of an isolated system cannot increase or decrease. The force of gravity is not an outside force because it is not new to this system. If the momentum is speeding up then the force is increasing, which means there must be an outside force. Or, the theory is wrong. Oneismany 15:58, 29 May 2007 (UTC)

Fourthly how does the collapse compress air despite the open core which should allow the air to escape without resistance?

Air has viscocity - it can't escape freely through all of the openings - as each floor collapses on the floor below, the air between the two has to go somewhere - some (no doubt) is pushed down the central core - some escapes through holes in the falling rubble pile - but the rest is compressed - it builds up pressure - and that pressure can blow out windows and even more substantial parts of the structure.

That is a plausible explanation except that there is no reason to suppose the air pressure would break through the glass or concrete before it escapes by another path. It would need to be proved. The observation that glass and concrete are blowing laterally does not prove it is done by air pressure, it is possible that the air pressure was not high enough to do that and it would have to ba accounted by some other hypothesis. Oneismany 15:58, 29 May 2007 (UTC)

Fifthly how does compressed air eject heavy perimeter columns as far as 450 feet horizontally, into the World Financial Center 3[4]?

If the pressure is high enough - that's perfectly possible. Suppose it built up a pressure similar to what's inside a car tire...that's not that much...right? Well, that's 35psi over atmosphere. 35 pounds of force pushing against every square inch of a concrete column. Imagine a foot-thick concrete column. Every foot of length weighs about 150lbs - and has a surface area exposed to the blast of 144 square inches. A 35 psi air blast pushes against the column with a force of 35x144=5000lbs! That's plenty enough to blow it a long distance. But more than that - if the column was on one of the floors close to where the planes hit - it would have to fall 1000 feet or so - that took many seconds - so even if it was moving laterally quite slowly - it had many seconds to move outwards - and would therefore land a long way from the foot of the building - but with all that high pressure air jetting out sideways from the building - I don't have any problem imagining it travelling 450 feet outwards. From 1000 feet - that's only about a 20 degree angle from the vertical,

Again it is possible that enough air pressure might be able to push material laterally, but it would have to be proved that this theory fits the data, which hasn't been done. How massive were those perimeter columns? I read that they were 30,000-60,000 tons. Also if they came from a high point on the towers presumabley the air pressure was less because the "collapse" was, er, slower at that point, according to the theory. Oneismany 15:58, 29 May 2007 (UTC)

Sixthly if the fire is so widespread that all of the columns, interior and exterior of at least one floor failed then why is the fire not visible around the entire perimeter of the building?

I would imagine that it was all funneled upwards through the hollow center of the building - the aircraft tore their way fairly deeply into the center of the structure - and those were BIG buildings. But in any case, the glass, concrete and steel around the sides of the building furthest from the impact were still relatively intact. All of those columns only failed at the last moment when the whole thing pancaked down - there just wasn't time for the flames to move outwards at that time.

Okay, that sounds reasonable, but the calculations by Bazant et al propose a total collaps of at least one floor which presumably includes the perimiter and the core columns. Additionally steel conducts heat so presumably the whole floor or group of floors would have to be heated until all the steel reached the same temperature. And what about those people that were standing, alive and waving at cameras in the holes made by the planes (in the North Tower anyway), precisely where you would expect the temperature to be greatest if the jet fuel was concentrated there? Oneismany 15:58, 29 May 2007 (UTC)

Seventhly if the steel was heated to the point that it weakened then why was the steel not glowing red?

It must have been - deep inside the building. But one of the reasons for the collapse was that the steel they used was of a grade that softens significantly long before it's at red heat. Remember - those beams were under a lot of force before any of this happened - they were designed with some large safety factor - but as the heat increased - and because it was there for so long - the crystalline structure of the metal would have started to degrade long before it got red hot. I don't know for sure whether there was enough of a safety factor to allow them to get red hot - but I kinda doubt it. But in any case - it would have been the beams deep inside the structure that were undergoing the most heating - and you couldn't see them from the outside.

Again that sounds reasonable except when you take into account that steel conducts heat and a whole floor or group of floors failing would mean that presumably the perimeter columns would have to be heating up too. Now there was what looks like molten metal pouring down the side of the building during the collapse but that doesn't even fit the 'fire-weakened-steel' hypothesis, though it doesn't necessarily refute it either because it could be something else that only looks like molten metal .... Oneismany 15:58, 29 May 2007 (UTC)

Lastly, how does this collapse hypothesis account for the pulverization of the buildings?

I dislike your use of the term 'hypothesis' here - I think we're beyond that stage. But anyway - a bazillion tons of steel and concrete hitting the lower floors at a hundred miles an hour (or whatever it was) has an insane amount of crushing power. When it all finally hit the ground everything in the lower part of the rubble would obviously have been crushed to powder. No surprises there! The amount of kinetic energy in that falling structure was incredible - the energy had to go somewhere - and most of it would have gone into the upper levels pulverising the lower levels.

A hypothesis is an attempt to explain data, the term doesn't reflect the degree of success or failure, but OTOH it does imply that the attempt is somewhat provisional. The progressive collapse hypothesis is a provisional hypothesis, since it does not yet account for all the data. In particular it is at odds with Newtonian mechanics vis-a-vis the conservation of momentum and the conservation of energy, discussed earlier. It proposes that the structure beneath the crashing upper floors gave way easily despite being more massive than the upper floors. It proposes that the momentum increased because the mass of the collapse increased, yet instantaneous acceleration of an object decreases with increased mass. It proposes that the momentum speeded up yet it does not account for the increased force. The method by which the kinetic energy (momentum) increased so rapidly has not be adequately explained; the potential energy of the building is irrelevant if the kinetic energy cannot substantially increase. How does a building crush itself into powder? Oneismany 15:58, 29 May 2007 (UTC)

So - I don't think there is anything whatever surprising here. What happened to those buildings was precisely what good science predicts would happen. There is no mystery.

On the contrary, this is an astounding result unprecendented in scientific history! Jet fuel is a phenomenal form of propulsion if it can cause a steel framed building to pulverize itself! Or, the Twin Towers were phenomenally weak. Or, this theory is insufficient to account for the phenomena. Oneismany 15:58, 29 May 2007 (UTC)

SteveBaker 06:04, 27 May 2007 (UTC)

Thanks, Steve.

Speaking of "good science", it's also worth noting that those buildings actually survived the impacts of large jet aircraft traveling at speed. That's some pretty insane crushing power, too, and yet both structures had enough redundancy to withstand it -- as they were designed to. With the memory of the B-25 that had hit the Empire State Building in mind, it was a design goal that the Twin Towers be able to withstand aircraft impact -- and it's a testament to the engineers who designed them that they did. However, it was not a design goal that they be able to withstand intense, widespread fire fueled by a plane's full load of jet fuel -- and of course that's what did the buildings in. —Steve Summit (talk) 06:23, 27 May 2007 (UTC)

That is assuming that the conclusion is true, that the fire is what did the buildings in. But a theory cannot assume its conclusion, or it is circular reasoning and explains nothing. Oneismany 15:58, 29 May 2007 (UTC)

Yep - I agree. It was amazing they stayed up as long as they did - it was a testament to clever engineering. The fact that they did survive for almost an hour with that kind of damage gave something like 80,000 people the time they needed to escape the two buildings. The cost of designing and constructing buildings to withstand every single eventuality would be prohibitive - so you've got to go with the most probable events - and being hit by an airliner while it's completely full of fuel when you are such a long way from the routes these planes are supposed to fly was a long shot indeed. One could certainly argue that they were actually over-engineered. As terrible as the loss of 2700 lives was - that (and the fourteen who died when that bomber hit the Empire State Building) are the only people in all of history to have died as a result of large planes smacking into tall buildings. That's less than the number of people who die in US road accidents every single month. Risks that small are statistically hardly worth protecting against. SteveBaker 06:48, 27 May 2007 (UTC)

(edit conflict)

And yet, we had already learned in the years since 1972 (and before the WTC collapse) that steel-frame buildings are vulnerable to being weakened by prolonged fire. The beams in the World Trade Center had minimal (by modern standards) fire protection; modern building codes require quite a bit more. I know those codes were reexamined after 9/11, but I'm not sure whether changes were made.

You can't engineer against every foreseeable catastrophe, it's true, but you can learn from the ones that happen. One silver lining to be plucked from even the worst disaster is the empirical evidence it can yield that you could never afford to reproduce experimentally. We may not choose to require newly-built skyscrapers to withstand intense, widespread fire fueled by a plane's full load of jet fuel, but the knowledge gained from the collapse of the Twin Towers may yet make other buildings safer in the face of more realistic threats that they can be expected to encounter. —Steve Summit (talk) 07:22, 27 May 2007 (UTC)

One of the more interesting anecdotes is about asbestos. As we know, flaking asbestos causes asbestosis. Since it can only be causes by asbestos, lawyers had a field day with it and it became a huge liability so it had to be removed everywhere. As I understand it, replacement fireproofing is not nearly as effective or adhesive as asbestos. The planes would have damaged whatever fireproofing existed so I doubt the change would have saved the buildings but it would be interesting to see if asbestos would have given more time for evacuations. Incidentally, I am not minimizing the health consequences of asbestos, but if it didn't have a very specific disease it probably wouldn't have been removed. For example, if it just caused generic cancer that couldn't be attributable directly to asbestos, lawyers wouldn't have been so succesful. It wouldn't surprise me if the asbestos replacement was just as lethal but in a general non-attritubale way. --Tbeatty 07:00, 27 May 2007 (UTC)

If the buildings were so well designed then how did the upper floors crash through the lower structure so quickly (in the progressive collapse theory)? Oneismany 15:58, 29 May 2007 (UTC)

One other thing: recently, a span of the steel reinforced Bay Bridge in San Francisco collapsed after a fuel truck caught fire underneath it. I believe it has just been repaired. <gasp> a gasoline fire sufficiently weakened the steel so that it collapsed under it's own weight even though it was designed to withsand many times it's weight in traffic when the temperature was much lower. This is not a new phenomena and explosives and conspriacy theories are not required to explain that gasoline or jet fuel fires could cause structural collapse. --Tbeatty 07:36, 27 May 2007 (UTC)

Not the Bay Bridge itself but part of the "Maze" of elevated ramps on the Oakland side. I don't know exactly where it happened, but if the truck was at ground level it could have hit a support, which would have contributed some effect. —Tamfang 08:45, 28 May 2007 (UTC)

• The bridge that melted was at latitude 37.827463 N, longitude 122.29274 W. (In Google Maps, the map view has apparently been updated to remove the upper road, but the satellite view still shows it.) --Anonymous, May 29, 2007, 22:54, edited 22:56 (UTC).

Not all "steel" melts at the same temperature, it all depends om the composition of the alloy. Some steel alloys are tuned to handle heat, shear, impact, etc., and there is a vast range of possible trade-offs. Gasoline is not the same thing as jet fuel, and 'low test' gasoline burns hotter than jet fuel. You must examine all of the specifications of the relevant substances. Without more information, the Bay Bridge incident cannot be compared to the Twin Towers. Besides, just because part of the WTC steel may have melted does not mean that is what happened to cause the buildings to implode in about 10 seconds (which is the time according to the official theory). Additionally the official theory denies that the heat was great enough to melt steel. Who said anything about a conspiracy, anyway? Oneismany 15:58, 29 May 2007 (UTC)

I noticed the "requirement" that the steel glow red before it is structurally weakened. This is so outrageously false I can't even imagine how it's been propagating through the conspiracy theorist community. Anyone who has ever soldered will know that some metals can melt (turn entirely liquid) and never even remotely glow. Incandescence explains the process of glowing; steel mentions the melting point of several common alloys; all the facts are easily obtainable. Nimur 18:34, 27 May 2007 (UTC)

It is not a requirement, it is just a question. Steel is known to glow before it gets hot enough to melt; if you say that steel that is heated to weakening need not glow, then you must know more about it than me. Oneismany 15:58, 29 May 2007 (UTC)

Finally, I would like to comment on the scientific method. Whatever quantitative, theoretical explanation we have, experiment must always trump preconceived predictions. This is the tenet of modern science. Empirically, it has been observed that when an airplane hit the World Trade Center, the building collapsed. At the risk of sounding crass, this experiment has even been repeated. Two out of two trials have demonstrated the result of a large commercial airliner hitting the tower. If, hypothetically, somebody's structural model or simulation of the tower predicted that it should withstand that impact, then that simulation or model is wrong. Nimur 18:34, 27 May 2007 (UTC)

The building did not "collapse" when the airplane crashed into it. It did not "collapse." It exploded, and much later than the collision, despite evincing virtually no structural weakness in the intervening time. The experiment was not repeated because one building burned (smoldered) longer but collapsed faster than the other. OTOH WTC7 did actually collapse, six hours after it was damaged, but no airliner had crashed into it. The simulation or model in question proposes that fire caused each of these collapses, but this theory does not fit the data. Ergo the theory is insufficient. If our theory is wrong then we need to propose a new theory. Oneismany 15:58, 29 May 2007 (UTC)

SteveBaker wrote: "I would imagine that it was all funneled upwards through the hollow center of the building - the aircraft tore their way fairly deeply into the center of the structure - and those were BIG buildings." Just to note: the original poster was talking about World Trade Center 7, which was NOT touched by the airplanes. It's a different building than the two towers. Our article says that the NIST (as of 2006) can't account for the fall of building 7, with the lead investigator saying "truthfully, I don’t really know. We’ve had trouble getting a handle on Building No. 7."

I'm generally not one for conspiracy theories, but to my knowledge the government still does not know exactly how WTC7 fell, so it's still an open question. The questions of the original poster, in other words, are necessarily not the deluded ramblings of a conspiracy theorist. zafiroblue05 | Talk 18:41, 27 May 2007 (UTC)

"We don't have enough data" so (because we don't like Bush) lets assume it was the largest conspiracy the world has ever seen involving dozens of goverments (not only US citizens died in the attacks) and tens or hundreds of thousands of people "who know the truth". That would explain everything wouldn't it? Mieciu K 19:59, 28 May 2007 (UTC)

Well it is possible that the buildings exploded because of Muslim mind rays, on the other hand. Oneismany 15:58, 29 May 2007 (UTC)

Is the universe getting lighter, heavier or neither?

My son thinks the universe is getting lighter because stars are constantly converting mass to energy (fusion), where energy (photons) has no mass. I am under the opinion that in a closed system (albeit a very big one), these is no net change in mass. Could someone help us amateurs settle this arguement? 66.66.169.162 02:41, 27 May 2007 (UTC)

I don't know too much, but I don't think it's possible to lose mass, just move it around. -- Phoeba Wright^OBJECTION! 02:58, 27 May 2007 (UTC)

Errr... so I guess this equation means nothing to you: E=m*c^2. --Taraborn 19:24, 30 May 2007 (UTC)

We currently have an unexpected edit war on this topic. It seems nobody can ever settle this issue but my personal opinion is: No, there is no net change in the mass of the universe. Actually I believe that it is not only constant, but precisely zero, but that second part is just speculation.

The total mass and energy of the universe are not well-defined quantities. Actually, there's no global conservation of energy in General relativity. The density of mass in the universe is decreasing as it expands, and the density of energy is also decreasing. If you want to restrict the problem a bit, forget about general relativity, and just ask about whether or not mass is destroyed in nuclear fusion, then it's a different question. Unfortunately, it's also a question without a simple answer. The mass of a system is in general not the same as the sum of the masses of its constituent parts, so it depends on what you want to look at to find a net change. A photon has no mass, but a system of several photons (say, a bunch of photons in a box) can have mass. --Reuben 04:15, 27 May 2007 (UTC)

tell your son he asked a great question, though - a very entertaining thought Adambrowne666 04:54, 27 May 2007 (UTC)

Yes, it's definitely a great question. The problem is that cosmologists are still working on understanding the question, let alone knowing the answer! --Reuben 06:48, 27 May 2007 (UTC)

When you are talking about things on a cosmological scale - with relativity and all of these other weird effects getting involved, it's better to talk about conservation of mass+energy - not just mass alone. The two things are interchangeable. Imean, sure, your star is emitting massless photons - but elsewhere in the universe, photons are being absorbed and producing new mass. As far as we know, mass+energy is conserved perfectly. In that sense, the amount of 'stuff' in the universe isn't changing at all - although it does change form. SteveBaker 06:53, 27 May 2007 (UTC)

oooh, but brings up another question. The universe is expanding. That seems to imply that the general theory of relativity warpage of space is decreasing as the mass-energy is spread out more. That would seem to imply that the gravitational influence of the universe on any specific atom is decreasing over time. Does that mean it's getting lighter? --Tbeatty 07:43, 27 May 2007 (UTC)

But there's not any global law of conservation of energy in GR. And mass+energy doesn't quite work either, as mass is already included as a pat of energy. There are local conservation laws, but the total energy and mass are in general undefined. --Reuben 14:43, 27 May 2007 (UTC)

Lead acid batteries

When charging lead acid batteries does it mean that when the charge cycle gets shorter and shorter that instead of having used the battery less and less that the battery is actually loosing capacity until it finally appears to charge almost immediately but actually have no capacity left? Is this a charactteristic of lead acid batteries? 71.100.5.249 03:36, 27 May 2007 (UTC)

Yes, this commonly occurs in old batteries. See lead-acid battery for some background. Nimur 04:36, 27 May 2007 (UTC)

It's exacerbated by the fact that you should avoid totally discharging lead-acid batteries - they are designed to be kept fully charged pretty much all of the time (as in a car for example). When the capacity of the battery gets worse, it's more and more likely that you'll somehow run it completely down - so the battery gets damaged more and more because it's capacity gets less and less and you run it down more and more frequently. It's interesting that this is the complete opposite of Nickel-Cadmium (NiCd) batteries which should always be run completely down before recharging them - and failure to do so will cause them to have shorter and shorter discharge times. SteveBaker 05:21, 27 May 2007 (UTC)

How about Nickle-Metal Halide batteries? Should they be completely discharge or kept fully charged by trickle charge? 71.100.5.249 07:55, 27 May 2007 (UTC)

Trickle is fine according to our memory effect article, q.v.--Shantavira|^{feed me} 09:30, 27 May 2007 (UTC)

more:em waves

hi thanks for previous answers... it looks my project idea was strong enough that someone has edited it. kindly lemme kno about the proceedings. anyway one more query whether electromagnetic waves are deflected by magnetic fields ..as strong as in an atom.(yes/no)?.why Sameerdubey.sbp

I think you are looking for your previous question? Here. As for whether electromagneic waves are deflected by magnetic fields, your best bet for an answer is Electromagnetic radiation (which does answer that very question). Best of luck with the project. --TeaDrinker 08:28, 27 May 2007 (UTC)

Year 12 Chemistry

While studying for exams i came across several things which I was unsure of:

1. CH3CHCOOHCH3 - is this Propan-2-oic acid or 2-methylpropanoic acid (I think it is the former, though not sure.)
2. Chloroethane can react with NaOH to produce Ethanol. Can it react with H2O in the same way? Can H2O be thought of as HOH (similar to NaOH)?
3. Concerning Gas Chromatography, as the components move through the column they separate due to their differing degrees of absorption to the mobile and stationary phases. When a component is attracted to the stationary phase, can it be said that it has condensed, and then the attraction to the mobile phase has made it evaporate again? Is this a correct way of looking at the process?
4. Also in Gas Chromatography, why is the coil heated? Is it to vaporise the sample, or to ensure that it stays vaporised as it moves along?
5. When titrating ammonium hydroxide (volumetric analysis), why is a back titration used rather than a direct titration with HCl. The answers so because ammonium hydroxide is volatile and may evaporate. It also says because it handling should be limited in its undiluted form due to safety reasons. Could another answer be: because ammonium hydroxide is a weak base and wouldn't provide a clear end-point when titrated directly with HCl?
6. During the production of sulfuric acid (Contact process) if the number of passes over the catalyst beds is decreased, what effect would this have on the reaction rate? Why?
7. In the equilibrium reaction 4NH3 + 3O2 <--> 6H2O + 2N2 , if water vapour is added to the system, what is the effect on the forward reaction rate? (The answers say unchanged, but i thought decreased, b/c according to Le Chatelier's principle, the back reaction will increase to get rid of some H2O.
8. During the contact process, what type of chemical reaction is 2SO2 + O2 <---> 2SO3? (Is catalytic oxidation correct?)

Thank-you very much D3av 09:17, 27 May 2007 (UTC)

I'm in year 12 doing chemistry aswell, I will try to answer your questions.

1. CH₃CHCOOCH₃ is an ester, you cannot have a carboxylic acid group in the center of a carbon chain, as it uses 3 of the carbons bonds
2. NaOH is ionic H₂O is stable covalent bonding, and thus cannot be thought of as a hydrogen hydroxide.
3. .
4. .
5. .
6. .
7. The forward reaction should be unchanged, but the back reaction will accelerate giving a net shift towards products
8. .

Mnay of your questions are clearly from a different course to mine, or I cant remember from GCSE. So sorry I cant answer them all.

Ok let me give these a shot

1. It looks like 2-methylpropanoic acid. Also known as isobutyric acid. Although your notation seems a little off as the CH₃ is hanging off in the middle of nowhere.
2. H₂O can sometimes be thought of that way in the liquid/aqueous form. It looks like you are probably working in aqueous conditions, so yes, the reaction would occur (at least according to my organic chemistry book). See Haloalkane#Reactions_of_haloalkanes. In other forms, I agree with the previous post.
3. Kind of? The analyte is attracted to the stationary phase, but it's not quite condensation. See adsorption. Note the "D". Not aBsorbtion.
4. By the time the sample gets to the coil, it should already be vaporized (by the injector).
5. I pretty much agree with all of those. Ammonium hydroxide appears to be weak base, but I believe the main reason is that by the time you titrate to the endpoint, a considerable amount may have evaporated. (Ammonium hydroxide being aqueous ammonia). As an analogy, imagine doing a titration of carbon dioxide in pop (soda).
6. I'm actually not sure. Maybe someone more familiar with catalysis can answer.
7. I think this one might be tricky. Adding water vapor will shift the equilibrium, meaning the rates are equal to each other. So I imagine that adding water vapor will increase the rate of the backward reaction, also increasing the rate of the forward reaction. I'll have to get back to you on this.
8. Correct. See Contact process.

Let me know if you have any follow-ups. --Bennybp 15:06, 27 May 2007 (UTC)

Thanks very much for your help. After asking some other people similar questions, I agree with all your answers. The answer to Q3 was especially helpful.

If anybody can help further with questions 6 and 7 , that would be fantastic.

[Further to Q7, some things to think about: say you have 2SO2 + O2 <---> 2SO3 at equilibrium. If you increased pressure, you would expect both forward and back reactions to speed up (more pressure always means faster rate). Yet increased pressure would make the equilibrium shift to the right (less particles). Does "shifting to the right" mean that the forward reaction speeds up? Does this mean the back reaction slows down? Seems like there are some contradictory points here. Can someone please clear up which parts are true?] D3av 08:35, 28 May 2007 (UTC)

Ok I've seem to have found a page with a better explanation for question #7 here. Basically, I think you (and me a little bit) are trying to convert Le Chatelier's principle from "equilibrium position" to "reaction rate". At equilibrium, the rates are always equal (that's the definition I think). When that is disturbed, the rate for one direction increases, which kind of disturbs the other side, etc, until it returns to equilibrium. At the new equilibrium, the reaction rates may be different from their initial rates, but still equal to each other. Also, the equilibrium is constant for any change except for temperature, I believe. Here is another good page. It looks like maybe wherever you got your answers from may have over-simplified, or was maybe not clear enough (i.e. at the moment you add the water vapor, the forward rate is unchanged, while the backward reaction rate increases.) Hope this helps :) --Bennybp 16:12, 28 May 2007 (UTC)

Thanks for those websites D3av 09:58, 30 May 2007 (UTC)

The Pill

I've been often reminded that the pill is not a 100% reliable form of contraception, so what are the chances of getting pregnant on it. I know someone whos on it, and theire period is several days overdue, is the most likely explanation really that she is preganant, or can these things vary? Although she said its not prone just to be late like this.

See Combined oral contraceptive pill#Effectiveness. --Allen 12:12, 27 May 2007 (UTC)

Also, morning-after pill. --TotoBaggins 13:36, 27 May 2007 (UTC)

Which is illegal in many places...Mr.K. (talk) 20:01, 27 May 2007 (UTC)

Keep in mind we can't give medical advice- but many of the newer birth control pills can also shorten or even eliminate periods. -- Phoeba Wright^OBJECTION! 15:03, 27 May 2007 (UTC)

Get her to check the label/advice sheet which comes with the pill. If you're in the UK, you can phone up NHS Direct or ask a pharmacist. --h2g2bob (talk) 19:25, 27 May 2007 (UTC)

Handycam

I have a handycam with a swivel LCD screen.Any idea how the display information on this gadget and other cell phones are sent to the small LCD screen? Also it senses whether the screen is tilted and automatically inverts the picture.Any idea how that works??~~

The data is sent over a ribbon cable or some similar connector. There is probably a video processing integrated circuit or microprocessor, and the text/data is probably composited into the image before it is displayed on the screen. As far as the tilt-sensor, there are many possibilities. A small encoder or even an analog potentiometer is the most likely sensor, or perhaps something as simple as a rotary switch similar to a motor switcher. Because the screen is rigidly attached, it would not make sense to use some other direction-sensor such as an accelerometer or mercury switch, though a conceivable Rube Goldberg camera might want to use those sensors for something fun and trivial. Nimur 18:39, 27 May 2007 (UTC)

The data is usually converted to serial form so that it can be sent through the hinge on a thin, flexible serial cable, rather than a wide, fragile ribbon cable. They use electronics like the Smart Mobile Hinge Link (rubbish name, but they probably stopped trying to make up catchy names after they came up with "TOSLINK") from Toshiba, which is based on LVDS. --Heron 22:07, 27 May 2007 (UTC)

Any idea what can cause the tilt mechanism to fail overtime?~~

Most likely, mechanical stress on the hinge connector. Nimur 17:19, 28 May 2007 (UTC)

I would have thought it would be the repeated flexing and unflexing of the cable rather than the mechanical components in the hinge. SteveBaker 13:47, 29 May 2007 (UTC)

By "hinge connector," of course, I mean the electrical connector in the mechanical hinge. Steve Baker's clarification is more valid than my wording... Nimur 02:38, 30 May 2007 (UTC)

Question about a disease

I am not asking for medical advice. Recently, my friend said that he had a "disease" that made him immune to bacterial infections and caused him to have a high white blood cell count. My question is, does this "immuno-proficiency" (I just made that up) disease exist? or is my friend just making up a bunch of crap? Coolotter88 15:00, 27 May 2007 (UTC)

Uh, wouldn't that be leukemia? -- Phoeba Wright^OBJECTION! 15:04, 27 May 2007 (UTC)

I doubt the bacterial immunity though, since leukemia causes high white blood cell production that is basically useless to immunity. Splintercellguy 16:14, 27 May 2007 (UTC)

Your friend is pulling your leg. alteripse 17:56, 27 May 2007 (UTC)

Uh, I've read that in a short story in a sci-fi magazine. Let me see if I can find it. – b_jonas 09:53, 28 May 2007 (UTC)

Are you sure he just doesn't have mold? --Tbeatty 04:44, 29 May 2007 (UTC)

What body parts are seen as interesting or valuable to keep?

Being an anatomist, or perhaps even a taxonimist, it would make sense that they have an admiration for the body (anything alive having a body, not just humans).

Let's say with this admiration, they have a desire to collect fragments or wholes of bodily tissues and/or bones.

For the bones, the skull is definately something that would be kept. For tissues, perhaps the brain and the heart, but what other things (anything that can be retrieved from the body) can be collected as "interesting 'data'"? PitchBlack 16:29, 27 May 2007 (UTC)

Penis? Having a collection of stuffed/mounted (NO PUN INTENDED AT ALL) animal penises on the wall would certainly be a talking point at parties... --Kurt Shaped Box 16:37, 27 May 2007 (UTC)

And likely the last party you'll ever be at... --Wirbelwindヴィルヴェルヴィント (talk) 19:26, 27 May 2007 (UTC)

It's my party and I'll get my penises out if I wanna. --Kurt Shaped Box 20:18, 27 May 2007 (UTC)

I did read once about a luxury ship or house that the owner had decorated with many lavish and strange things... the leather on the seats of the bar were made out of the foreskin of a whale's penis. Anyone know what that was? I'd like to remember -- Phoeba Wright^OBJECTION! 20:56, 27 May 2007 (UTC)

see Icelandic Phallological Museum Bendž|Ť 09:47, 28 May 2007 (UTC)

Human horn? Assuming we are talking about artistic value rather than trafficking in human organs, any highly unusual case would be interesting for at least a specialist. A brain tumor the size of baseball-sized hail, a twinned spleen, that sort of thing. As far as animal parts, the most bizarre thing which was once commonplace that comes to mind would have to be the elephant-foot ashtrays. Personally, I would rather display an old trepan and leave the squishy stuff alone. Eldereft 19:58, 27 May 2007 (UTC)

Sounds like the whole Bodyworlds exhibit. Root⁴(one) 23:08, 27 May 2007 (UTC)

I was thinking more of just average body parts, not bizzare or unusual things. And now, lets talk about humans. There's skulls, blood samples, maybe semen (but that would be hard to get right?), heart, brain, maybe all the bones crushed and powdered... what interesting (but average) things can be collected from the human body? PitchBlack 00:35, 28 May 2007 (UTC)

Hard to get? Get a 5 cent plastic cup from wal-mart, go up to a guy on the street, give him the cup and a 20$ bill, show him to a public restroom, and wait. -- Phoeba Wright^OBJECTION! 03:21, 28 May 2007 (UTC)

And maybe a magazine or two... It's much easier for a girl to find a guy to reproduce with than reverse. --antilived^{T | C | G} 05:21, 28 May 2007 (UTC)

A German fellow of my acquaintance, who is a caretaker for a property up in Desolation Sound, has quite the collection of mounted bear penis bones. He is apt to introduce them as effective conversation starters when given the chance, though I have observed that with certain company the subject has rather a chilling effect on the immediate discourse. As to Pitch's particular question, human skin comes readily to mind. I've heard of some libraries Special Collections containing Books bound in human skin, and I vaguely recall recently reading something about tattooed individuals making provisions for their "artwork" to be saved/displayed subsequent to their deaths. -- Azi Like a Fox 11:50, 28 May 2007 (UTC)

Penis *bones*? --Kurt Shaped Box 14:35, 29 May 2007 (UTC)

Yes. See baculum. --Carnildo 23:13, 29 May 2007 (UTC)

I wish I had one of those. --Kurt Shaped Box 22:29, 30 May 2007 (UTC)

Do we have an article on electrical burns?

I've created and populated Category:Burns, but can't find an existing article on electrical burns. Am I missing a different names or something, or does it just not exist? Carcharoth 16:33, 27 May 2007 (UTC)

I'm not sure if there's significant additional information on electrical burns; as far as I know, the burning is caused by resistive heating from the current. However, death by electrocution is often caused by ion imbalance in the heart. Though an electrical burn may accompany death by electrocution, I don't believe they are the same. You can create an article anyway, so long as you document your sources! Nimur 18:43, 27 May 2007 (UTC)

Interesting. Thanks. Unfortunately, my only source so far is Wikipedia:Reference Desk... :-) Carcharoth 18:49, 27 May 2007 (UTC)

Sorry, don't have an exact citation, but I have seen electrical safety films which showed electrical burn due to high voltage contact (7200 volts AC) which said that the burning was deeper in the tissue than typical from burns due to fire. They showed the worker's arm opened up like a beef roast to remove internally burned muscle tissue. (He survuved and was an object lessson to use all protective gear). In other words, electrical burns are different from thermal burns. Edison 14:47, 29 May 2007 (UTC)

Contraception

You know how they say condoms are only like.. 98% effective and the pill is about 97% effective.. so what would the percentage effectiveness be for using both? It obviously wouldnt be 195% as there is still a risk, and I doubt it would be an average of the 2 as using the condom with the pill would increase effectiveness more than 97 percent, not decrease the effectiveness of the condom from 98% etc. Christopher

It is more a question of mathematics. The answer is most easily written as that the condom removes 98% - the pill then removes 97% of the remaining 2%. This means there is a 0.06% chance because 2-(2*0.97)=0.06 81.93.102.185 17:06, 27 May 2007 (UTC)

1 - (1 - 0.98) * (1 - 0.97) = 1 - 0.02 * 0.03 = 1 - 0.0006 = 0.9994 = 99.94%

Ohanian 18:40, 27 May 2007 (UTC)

Ohanian's math is correct assuming that there is no interaction between the two random processes; I don't know if that claim can be made for something as complex as an epidemiological study of contraception effectiveness. There are other problems with this statistic - is the device "ineffective" if it fails due to improper use? As such, you should consider all these statistics rough estimators. Nimur 18:46, 27 May 2007 (UTC)

It's easier to think of it like this: the failure rate of the pill is 3% of the 2% it is needed. ${\frac {2}{100}}\times {\frac {3}{100}}={\frac {6}{10000}}=0.06\%$ As Ohanian said, this is 99.94%. --h2g2bob (talk) 19:14, 27 May 2007 (UTC)

Extra caution is required for the effectivity figures, as they may be averaged over users with different compliance (medicine) or carefulness. Especially the effectiveness figures for condoms varies widely: If you count only people who know how to propely use it, you get something well above 99%. If you take into account those poeple, who mix is with latex-dissolving lubricant, don't squeeze the reservois, put it on too late, loose it, or do any of the many other little mistakes possible, the figure is much lower. Simon A. 06:10, 28 May 2007 (UTC)

To simplify the above a bit, the same people who are likely to misuse a condom (say put it on wrong) are also likely to misuse the pill (miss taking it frequently), so the two are not independent events. Thus, the chances that both will fail is much higher than the 0.06% calculated for independent events. StuRat 05:21, 29 May 2007 (UTC)

I have seen much lower effectiveness rates stated for condoms than the 98% rate stated. For one thing, they break sometimes. The Columbia University Health Center site, GoAskAlice [4] says that out of 100 women whose partner uses a condom "typically,". 14% get pregnant in a year. For those who use condoms "perfectly, 3% become pregnant.The "failure rate" is misleading in that it implies 100% of couples having frequent sex without contraception would achieve pregnenacy each year. That only happens in soap operas. That highly relevant number does not often appear. Many couples trying to have children fail to achieve pregnancy without medical intervention. Edison 14:49, 29 May 2007 (UTC)

Washing hands and static electricity

I just washed my hands, and upon walking past my TV found that only the hairs on the parts of my arms that were washed, were standing on end. The rest of the hair wasn't. How come? 81.93.102.185 17:01, 27 May 2007 (UTC)

That seems opposite to the normal behavior, where static charge builds up in dry environments. Maybe all your hairs would have stood up, but some form of crusty buildup on the unwashed parts overcame the coulomb force? Nimur 18:53, 27 May 2007 (UTC)

Or drying your hands and arms rubbed the hairs so they were already standing a little, and thus loose and closer to the telly. Eldereft 20:07, 27 May 2007 (UTC)

If you want your hair to stand up on a Van de Graaff generator it has to be very washed and unconditioned. Same with a CRT. --Zeizmic 20:13, 27 May 2007 (UTC)

I suspect you washed the oil off the hairs that stood up. Oily hair doesn't stand up. This is why "moisturizer" (oil) is used on hair to prevent "fly-away hair". StuRat 05:00, 29 May 2007 (UTC)

Shock

From Shock:

Opinion varies on the type of fluid used in shock. The most common are:

• Crystalloids - Such as sodium chloride (0.9%), dextrose (5%) or Hartmann's solution.
• Colloids - For example, synthetic albumin (Dextran™), polygeline (Haemaccel™), succunylated gelatin (Gelofusine™) and hetastarch (Hepsan™).
• Combination - Some clinicians argue that individually, colloids and crystalloids can further exacerbate the problem and suggest the combination of crystalloid and colloid solutions.
• Blood - Essential in severe haemorrhagic shock, often pre-warmed and rapidly infused.

Now hold on a second, wouldn't clinicians and EMTs and whoever know if crystalloids or colloids further exacerbate the problem, or not? [Mac Δαvιs] ❖ 17:24, 27 May 2007 (UTC)

This is a debate that dates back at least 50 years. There are advantages and disadvantages of both fluids. No two patients in shock are exactly alike, and it is rather difficult to recruit people arriving at the ER in shock into a truly randomized trial. Animal research can be found to support either position. Everyone does agree that rapid restoration of circulating volume is essential for survival. Search medline for "shock resuscitation fluid" and you find lots of more detailed discussions of the issue. alteripse 17:54, 27 May 2007 (UTC)

Lactated Ringer's solution

Why is Lactated Ringer's solution call "lactated?" [Mac Δαvιs] ❖ 18:45, 27 May 2007 (UTC)

Our article, which you linked, states that there is NaC3H5O3 (Sodium lactate) added. Nimur 18:50, 27 May 2007 (UTC)

Precisely. Though I was going to quote the "28 mEq of lactate = 28 mmol/L." bit. Still, I'd be curious to know if you (Mac Davis) got to that article via my burns question above, with stops at Category:Burns and burn (injury) along the way? :-) Carcharoth 18:52, 27 May 2007 (UTC)

I did :) [Mac Δαvιs] ❖ 21:03, 27 May 2007 (UTC)

And which also actually led to my shock question above, in which I went from burn (injury) to Hypovolaemic shock to Shock (medical). [Mac Δαvιs] ❖ 21:07, 27 May 2007 (UTC)

Experiments which can be performed with a TV

I have a 6-year old TV which is performing rather well, but which soon will have to be phased out. Are there any scientific experiments I can conduct with a TV (emittance of photons, electromagnetic fields, etc), and/or parts of it, even experiments which may be fatal to the TV? I am hoping to get a good list of experiments worth doing, so as to conduct a bit of original research. Thanks a lot for your help. I chose this category instead of Miscellanous because of the answers I am hoping for... :) 81.93.102.185 20:45, 27 May 2007 (UTC)

This will depend on the type of TV. A CRT experiment may be fatal to YOU. -- Phoeba Wright^OBJECTION! 20:59, 27 May 2007 (UTC)

I think he meant it was a CRT-TV, and that he wasn't going to take it apart (as in, "not fatal to the TV")

Definitely. The Frankin Bells is a nice little project that you can do pretty fast, and is complicated enough to be a science project.[5]. Can't find the article on it, though. [Mac Δαvιs] ❖ 21:03, 27 May 2007 (UTC)

You can see the magnetic field of a strong magnet if you put it close to the screen. It distorts the colors of the picture. Try it with some magnets. See if you can predict the distortion patterns caused by sets of magnets in different arrangements. This experiment may cause permanent damage to the TV, but it is safe for you. Please don't play with the electrics inside, ok?

You could connect and face a video camera to the TV and put the system into a feedback loop. It might be interesting to see what kind of visual a digital camera could make when the camera is rotated, zoomed, up real close, off to the side (but with the TV still in view. Then add the magnet and make things even more fun. ;-) (but not to the camera!) Root⁴(one) 23:23, 27 May 2007 (UTC)

Be sure to play with the lighting if you do that as well. Make things Pitch black and occassionally turn on a flashlight or light a match. Root⁴(one) 23:26, 27 May 2007 (UTC)

Thanks, these are all good ones that I will look into. Keep them coming if you want to, the whackier the better (and I wouldnt mind suggestions that means the end of my TV :))81.93.102.185 23:46, 27 May 2007 (UTC)

You could take the entire electronics out, put a new glass in front and make it an aquarium. Maybe not very scientific, but certainly cool and it destroys the TV. ^^

I wouldn't. The flyback transformer remains charged (~30,000 volts or 30 kV) even when the TV is unplugged. While the amperage is low (sub-20 mA, if memory serves), if you don't know exactly what you're doing, your curiosity can be fatal. Even those who are qualified sometimes make mistakes - a good friend of mine was thrown ~2 meters and got a concussion and a dozen stitches for being in a hurry while fixing one. -- MarcoTolo 01:27, 28 May 2007 (UTC)

Contrary to popular belief, not everybody who opens a TV set is instantly electrocuted. However if you think that pulling the plug is sufficient precaution, you should probably not try this one: http://www.aquahobby.com/tanks/e_tank0307d.php

The magnet (which may indeed destroy the TV) and the feed-back camera thing are without doubt the best experiments to play with - do the magnet thing last in case you do damage the TV. If the TV does get some permenant-seeming problems, turning it off an on again several times over - with at least a 30 second wait between each time - will sometimes restore it to normal operations. Failing that, if you can get a hold of a 'degaussing coil' you will almost certainly be able to fix it. If you are doing the feedback camera experiment - you might want to bring in a large mirror too - that produces some interesting effects). While you have the camera and TV handy - you might ask students why they look different when they see themselves on a TV compared to seeing themselves in a mirror. There are two interesting differences - one is that when you look at yourself in a mirror you can't avoid staring right at your own eyes - no matter how you turn your head. The camera can avoid that. Also, the mirror appears to swap your left and right - but the camera does not. When you see yourself on TV, you truly see yourself as others do - in the mirror, you always see a mirror image of yourself. This is why nobody ever thinks that their driver's license photo looks like them. In fact, it's probably a very good likeness - but you're only used to seeing yourself in the mirror so the "you" that you recognise isn't the real you - it's a mirror image! Anyway - it's fun to have kids try to use a mirror to comb their hair or something - then switch them over to using the TV+camera setup to do the same task! It's quite disorienting when you switch back and forth between them. SteveBaker 03:48, 28 May 2007 (UTC)

Don't believe the all hyp that suggests you will need a new tv when analogue signals are phased out. All you need is a set-top box and the right leads. Your tv doesn't even need a scart socket. Oh, and a decent aerial. That's always assuming you can receive the digital signal. I can't and I live in a big city.--Shantavira|^{feed me} 08:13, 28 May 2007 (UTC)

Bjork opened up her tv to see how it operates. You can be like Bjork. (yes, see warnings above) (subtitled version for deaf/HoH) —Pengo 03:24, 30 May 2007 (UTC)

Faeces in urine

My cousin has been talking about how he has been having bowel problems etc, and has had blood present in his urine, and now tells me that he has found fecal matter in his urine, as confirmed by doctors. He has been getting tests for it, but I am just wondering if anyone has any ideas as to what it could be. Christopher

What's the medical term for coughing up faeces, anyway? I used to drink with this old drunk who told me that he had that happen to him when he had cancer. --Kurt Shaped Box 21:20, 27 May 2007 (UTC)

The article on fistula might be helpful to you. Actually, looking at it, it's a shitty article (so to speak), but several of the external links at the bottom are more accessible and informative. And specifically, it could be this form of fistula. Anchoress 21:49, 27 May 2007 (UTC)

The Effects of Music on Plants

Yes, this is for school. But, my science partner and I have found nothing. We are testing how much music is good for a plant. We were just wondering if anyone else has done anything on that and can tell us the result. Or found any articles, thanx --Ninjawolf 23:10, 27 May 2007 (UTC)

Try some of the articles in these google searches: GOOGLE SCHOLAR and plants "music therapy" study. Anchoress 23:29, 27 May 2007 (UTC)

Mythbusters have done it, and it proves that death metal is the way to go. :p --124.197.9.207 antilived^{T | C | G}(forgot to log in) 00:23, 28 May 2007 (UTC)

Although at that volume, good luck with your neighbors -- Phoeba Wright^OBJECTION! 04:43, 28 May 2007 (UTC)

You might want to include a discussion about causality, correlation, and the scientific method when you discuss this experiment or any results for your final project. Sometimes, experiments can show a correlation (a "link") between things (such as music volume and plant growth). Sometimes, repeating the experiment many times can confirm this "link" (strong correlation). If this link was strong, you should investigate a causative link ("music causes plant growth") - but first you have to demonstrate the correlation by a repeatable controlled experiment. Once this is established, you can try to find a good reason why this link exists. The best way to start is examining various physical laws and how they apply. I have not performed this experiment, but I doubt you will find a correlation between ambient music level and plant growth; my understanding of plant tropism leads me to believe that there is no effect. Nimur 14:58, 28 May 2007 (UTC)

Actually - I don't think it's impossible that loud rock music has a beneficial effect on plant growth. This is just a hypothesis - but it's not entirely unreasonable: Think about this - the plants are being kept in an enclosed greenhouse without the natural airflow caused by the wind. As they absorb sunlight and CO2 and emit oxygen and water vapor through their leaves, the lack of natural airflow might result in a localized depletion of CO2 and an excess of O2 and H2O in a layer close to the leaves - resulting in the plant being unable to photosynthesize as efficiently as it would in the wild. OK - so add some really loud rock music - full of low frequencies and abrupt changes in frequency - might this not shake the leaves and enable a natural mixing of gasses from near the surface of the leaf? A gentle Brahms lullaby with very little bass content - and probably played much more quietly than the rock music might not be enough to cause that agitation of the leaves. Similar arguments might apply to talking to your plants (oh jeez - I just realised that I might have to apologize to my mother for what I said when I caught her talking to her plants...ack...the sacrifices we make for science!). Sure, it's a long shot - but it definitely sounds kinda plausible given the megre experimental results we have to go on and I don't think it's a good idea to dismiss this idea without more experiments. However, I most certainly don't expect that the result would be "Plants have auditory organs and can 'think' and as a result can hear and appreciate music and they prefer Motörhead to Brahms"...that's just crazy talk. But if my wild (and utterly untested) hypothesis turned out to be correct - then merely providing a slow speed fan close to the plants might prove even more effective than Spinal Tap (even if turned up to 11). SteveBaker 05:24, 29 May 2007 (UTC)

Heck, even if you were just scaring off whiteflies it would give you a healthier plant. Gzuckier 18:59, 29 May 2007 (UTC)

Agreed; hence the need for a carefully controlled experiment. If the airflow is causing the growth-rate change, and the music is causing the airflow, then this result is repeatable. It will boil down to a matter of word-mincing: does music make the plant grow, or does air-flow make the plant grow? The answer to that question depends on whether the music and the airflow are separable effects. Nimur 02:44, 30 May 2007 (UTC)

Eggs and matches

There is a question on the Miscellaneous desk that has to do with chemistry: Wikipedia:Reference_desk/Miscellaneous#Eggs. Also, can you answer me how hard it is to reverse the combustion of a safety match? A.Z. 23:40, 27 May 2007 (UTC)

It depends on what you mean by "hard". In theory it would be possible to reverse combustion. In reality...not so much. Combustion is a chemical reaction - in order to reverse the process one would have to be able to add ridiculous quantities of energy and figure out how to re-align all the atomic/molecular structures of the match pre-combustion. In all practical terms, reversal is not possible. -- MarcoTolo 01:18, 28 May 2007 (UTC)

It's not so much to do with chemistry as it is information theory and nanotechnology. The word "reverse" in the question is just too vague in this context. Forget about whether the chemistry can be driven in reverse. Think instead of these kinds of questions:

• Since almost all of the combustion products went up in smoke - drifted off into the atmosphere and dissipated widely, how would we retrieve all of them in order to use them as inputs to the 'reversing' process?
• What about reconstructing the insanely complex DNA molecules in the wood of the matchstick that was burned away?
• We don't have a way to record the precise structure of the wood fibres in enough detail that we could reconstruct them even if we knew how!

...(insert a million other similarly cogent arguments here!)...

which taken together means that it's utterly impossible in all but the most theoretical sense. So you have to start relaxing some of the requirements...well, maybe we don't have to restore every single molecule to it's original position - maybe we're allowed to use new materials - but if that's allowed then can we just toss out the original burned match and bring in a nice new one and claim that we "reversed" the effects? Either end of that spectrum of possibilities is laughable. But where in the middle of that range of possibilities the questioner stands determines the answer to the question. But if forced to come up with a one word answer - it would have to be 'no'. It is truly a dumb question.SteveBaker 03:30, 28 May 2007 (UTC)

As I said on the other reference desk, isn't the real answer to the question to do with entropy? Once you light a match or cook an egg, you are disassembling a well-structured object and producing a disordered system. The entropy of the system has increased. Reversing entropy is very, very difficult to do. We only have localised increases in entropy on this planet because the Sun is providing the energy needed, but with a large decrease in entropy for the Sun (ball of hydrogen converts to photons scattered throughout the universe). See also Arrow of time, Irreversibility, and Entropy (arrow of time). Carcharoth 06:23, 28 May 2007 (UTC)

I don't think it's a dumb question. And in an extremely loose sense, photosynthesis in trees is a reverse reaction of burning wood. Burning a match turns wood and oxygen into carbon dioxide, water, and energy; a growing tree does the opposite. --Allen 15:51, 28 May 2007 (UTC)

As I said - it depends on how loosely you are prepared to interpret the question. Tossing out the old match and taking a new one out of the box could be said to have reversed the reaction if you are prepared to interpret the question sufficiently loosely - and if you interpret it as a requirement for a perfect reversal in every possible sense then it's clearly impossible because of Heisenbuerg's uncertainty principle. So - pick wherever along that range you feel happy - but you still aren't answering the question. SteveBaker 19:44, 28 May 2007 (UTC)

You're right; photosynthesis is no better an answer than the others. But I think even questions that don't have a clear answer can be useful. Not everyone has thought about these issues enough to see the spectrum of interpretations you laid out, and having some sense of the endpoints and some points along the path can increase their knowledge and understanding. --Allen 20:39, 28 May 2007 (UTC)

May 28

What is the largest encyclopedia ever existed?

I have read from a webpage (from wikipedia) that Wikipedia is larger than Britannica. I would like to know if other (online, offline, like books) encyclopedias exists (or existed) who are larger than wikipedia. Thank you.

See Wikipedia:Size comparisons, Wikipedia is one of the biggest encyclopaedia known to human kind, depending on how you see it, maybe the biggest. --antilived^{T | C | G} 11:17, 28 May 2007 (UTC)

Though it will never be, nor aspire to be, as big as The Library of Babel. ;-) --140.247.240.18 14:10, 28 May 2007 (UTC)

Ironically, even with the larger article and word count, Wikipedia is readily available in electronic form and can thus be miniaturized to small volume (such as a few hard-hard-drives - I don't know how many terabytes it would take to save the whole encyclopedia, but this collection of Public Domain classical music just set my own system back a couple of gigabytes....) Nimur 15:03, 28 May 2007 (UTC)

The pages themselves are usually fairly small, it's the images that take a bunch of space. Still, even with all the images on commons and all the text on en., I imagine it would be very possible to store almost the entire encyclopedia on a single computer... actually, it sounds like a fun project :) go through the dumps and clean up articles and release them in a permenent "checked" version. Kinda like the Wikipedia CD, but online -- Phoeba Wright^OBJECTION! 16:07, 28 May 2007 (UTC)

Such projects have existed (in both commercial and non-commercial forms) but I think they have not had a lot of success. Nimur 00:34, 29 May 2007 (UTC)

Why is Ostrich meat Red?

If it is part of the bird family, why is Ostrich Meat Red and not the same as a Turkey or chicken, perhaps this is a trivial question but, I would like all the facts on this matter for peac of mind. — Preceding unsigned comment added by 41.241.11.179 (talk • contribs)

See White meat article. Dr_Dima.

That doesn't really answer the question. Ostrich meat is not dark like chicken drumsticks; it looks like beef. I'd like to know why, also. I would guess it has something to do with the fact that ostriches do not fly. --Tugbug 20:17, 28 May 2007 (UTC)

Lagrange points with other bodies nearby

Lagrange points

Why don't the Lagrange points of, say, Sun–Earth get ruined by the other bodies in the solar system? Is it that the gravitational pull from the other bodies average out since they don't move along with the Sun–Earth system and therefore pull in different directions at different times? —Bromskloss 13:41, 28 May 2007 (UTC)

As explained at Lagrangian point#Stability, the effect of the rest of the solar system on Lagrange points is enough to complicate the orbits quite a bit, but (the rest of the solar system being quite light and a long way away) is not enough to de-stabilize the L₄ and L₅ points. It does destablize the orbits about the other three points, but this is small enough to just require slight correcting maneouvres every so often. Algebraist 17:05, 28 May 2007 (UTC)

OK, but the other objects aren't necessarily lighter and farther away than Earth, right? —Bromskloss 19:45, 28 May 2007 (UTC)

Well, they are all much further away - they may not be lighter though - the outer planets are all pretty huge. Since the gravitational forces due to those more distant bodies is inversely proportional to the SQUARE of the distance - their effect diminishes rapidly as they get further away. The distinctive factor about L4 and L5 (as opposed to the other Lagrange points) is that they form peculiar (unless you are a mathematician!) 'virtual' gravity sources - if you are close to one of those empty points in space, you'll get pulled towards them - you can even orbit them! This makes an object at one of those two points fairly insensitive to small disturbances - since this virtual gravity well will pull them back in again. But at the L1/2/3/6 points, the balance between the various forces is unstable - if you are exactly at the Lagrange point, you're theoretically in perfect balance between gravity of Earth and Moon and the "centrifugal" forces involved - but any small displacement from that point will result in you being pulled further and further away. So at (for example) L1, a teeny tiny occasional tug from (say) Jupiter - however small - will be enough to gradually move you away - and eventually you'll smack into the Moon or the Earth or get flung out of the Earth/Moon system altogether. SteveBaker 20:00, 28 May 2007 (UTC)

You say others are further away, but what exactly do you mean? There are surely instants when other planets are closer to one of the points than both Sun and Earth. —Bromskloss 20:26, 28 May 2007 (UTC)

Actually - I didn't read the question properly. I was thinking about the earth/moon lagrange points - not the Earth/sun. But still, the L1/2/3/6 points are unstable and the L4/5 points are stable - so in all likelyhood the same thing applies. SteveBaker 22:16, 28 May 2007 (UTC)

Radioactivity

Knowing the half-life of a substance like Polonium-210 or Plutonium-239, how do I calculate how many alpha particles would be ejected, theoretically on average, per hour or so from a given sample size (say, 1 microgram of each)? --140.247.240.18 14:17, 28 May 2007 (UTC)

You start by computing the number of atoms in a microgram using the mass of a single polonium atom. Then you convert the half life to a decay rate by using the formula you can find in Radioactive_decay under the section decay timing. Now compute the number of atoms that are left after one hour using the exponential decay formula slightly above in the same article. The difference between both numbers is the number of atoms that decayed. The number of aplha particles is the same, provided that the decay sequence does not produce multiple alphas per atom.

That sounds reasonable. Thanks! --140.247.240.137 19:26, 28 May 2007 (UTC)

Distillation of ethanol, temperature

When a mixture of ethanol and water is heated and reaches the boiling point of ethanol, will the temperature stay the same (approx. 78.5°C) until all the ethanol has evaporated, or is it possible to heat such a mixture to, say 85°C, at ambient pressure? --62.16.173.45 14:34, 28 May 2007 (UTC)

The mixture will approximately stay at the same temperature until the ethanol has evaporated. It is not totally accurate, there are some effects when you go into detail. Destillation talks about the variation of the boiling point of ethanol in a solution. There is also the possibility of Superheating.

Thank you! --62.16.173.45 18:15, 28 May 2007 (UTC)

ARUN ARUN QUES ABOUT PENIS

to what extent I should retract my foreskin to wash smegma?

You should never retract your foreskin in a way that feels in painful to you. If you are still growing up, your foreskin may not be fully retractable. That is completely normal.

Right. The condition of the foreskin not being fully rectractable is called phimosis, and our article on the subject states that it is common for boys and vanishes when growing up. For older teenagers and adults, it can, however, cause inconvenience or pain. So if you are still young and it is not painful, don't worry, otherwise, better go and ask a doctor for advice. And don't get worried by the phimosis article -- to my taste it is a bit technical and medical, so if you really want to get clear information, don't feel embarrassed to simply ask a doctor. Simon A. 17:09, 28 May 2007 (UTC)

Our article on phimosis is really a bit strange. I would suggest to read this instead: http://www.nocirc.org/publish/pamphlet4.html.

Red Rice - Health benefits

What are the health benefits of the Red Rice available in India? Is the nutrition value the same as Brown Rice? - Priya

The red rice article claims that it is a "pest" or weed, because less edible grains grow per plant. I don't know if it is actually unhealthy. Nimur 00:38, 29 May 2007 (UTC)

Regression analysis for tidal water levels

I'm doing some studying on the behavior of tides. I've made a big table of water levels at different times over two days, and I made a big graph of it. Of course, the tides go according to a sinusoidal function, but both the gravitational effects of the Moon and the Sun affect tidal water levels, so therefore, the function of water levels would be in this form:

(where L is water Level and t is Time)

L = A + B sin(C(t)) + D (sin E(t + F))

Where A would be the mean water level, B would be the amplitude of the lunar component of water levels, C would represent the period of the moon, D would be the amplitude of the solar component to water levels, E would represent the period of the sun (it would be equal to 2π*24), and F would be an offset between the start of the lunar cycle and start of the solar cycle.

I'm trying to figure out the numerical values of all those lettered coefficients. Now, I could figure all of those out with astronomical/oceanographic data (the period of the sun, the moon, the mean water level) besides B and D. For those two, I'd need to do a regression analysis from the data I tabulated earlier.

I don't know how to do regression analysis by hand (though I guess I could figure it out or try to learn it), so I looked all over the internet for a regression analysis program. I found a bunch that do regression analysis, but none of them do sinusoidal regression analysis. A polynomial regression analysis would work fairly well except that to find out the corresponding sinusoidal function, I'd have to do some super-complicated reverse Taylor series...

So my question is: Does anyone know a freeware/shareware/demo program that can do a sinusoidal regression analysis for something like this? If not, is there an easy way (without spending hours messing with taylor series) to figure out how to find the corresponding sinusoidal-sum equation from a polynomial equation? Jolb 16:53, 28 May 2007 (UTC)

First, you won't see the dependency on the Sun with only two days of data. Second, local conditions such as the shape of the coastline may strongly affect the data. Now to your question: Whenever you have function which you thin is composed of a sum of sines with different amplitudes and phases, you want to do a Fourier analysis. I am sure that there is free software to do this, but you can also do it easily with even only a little programming skills, or even with a spreadsheet program. Unfortunatly, our articles on Fourier transform and Fourier analysis do not breally strike me as very accessible for beginners, so a good textbook on engineering math might be a better choice to learn about it. But for a starting point, try the following (and then learn from your textbook, why this does what it does): Assuming that you have measured the tide at N times t_i and got the values h_i, calculate

$W_{c}(T)={\frac {1}{N}}\sum _{i=1}^{N}h_{i}\cos(2\pi t_{i}/T)$

and

$W_{s}(T)={\frac {1}{N}}\sum _{i=1}^{N}h_{i}\sin(2\pi t_{i}/T),$

where T is time length that you expect to be a period. Change T a bit, from a bit less than half a day to a bit more than it. When is $W_{c}^{2}+W_{s}^{2}$ maximal? If you have more data, try also with values for T around one month. Have fun. Simon A. 17:22, 28 May 2007 (UTC)

Blind sugar-eating dogs

A friend of mine once told me that sugar makes dogs go blind. Is that true? --Taraborn 18:23, 28 May 2007 (UTC)

It seems really unlikely - dogs are going to get sugars in their diet no matter how healthily you feed them. I guess the most likely issue is if the dog is diabetic. Blindness is a commom symptom of untreated diabetes - and it's likely to be exacerbated by increased dietary sugar. But a healthy (or at least non-diabetic) dog shouldn't have any problems. None of the dog books I have mention sugar in their long lists of 'normal foods' that can be lethal to dogs (chocolate and grapes for example). SteveBaker 19:49, 28 May 2007 (UTC)

Is chocolate toxic to gulls, as a matter of interest? I've always erred on the side of caution and never given them any food that's remotely chocolatey. I know that it's toxic to parrots. Anyone know? --Kurt Shaped Box 21:04, 28 May 2007 (UTC)

Yes, theobromine, the stimulant component of chocolate (often mistaken for caffeine, which is only present in chocolate in trace ammounts), causes theobromine poisoning in many animals (dogs, horses, parrots) because they are unable to metabolise it quick enough. Laïka 22:05, 28 May 2007 (UTC)

I wonder what the toxic dose for a human would be? --Kurt Shaped Box 22:21, 28 May 2007 (UTC)

See Death by Chocolate? ;) --Krsont 22:40, 28 May 2007 (UTC)

Is it possible to get to proxima centauri in a practicle timescale?

I did some research about faster than light travel. It made me think that interstellar travel was possible, though it is overwelmingly expinsive. Is most of the second sentence variable? Fquantum ^talk 20:48, 28 May 2007 (UTC)

You don't need to travel faster than light to travel to nearby stars - it just takes a while. But yes, it'd still be prohibitively expensive, since you'd need a large ship for a voyage that takes a generation (at least). WilyD 20:51, 28 May 2007 (UTC)

Even at the speed of light it would take 4 years (though it would seem less to those actually travelling, per relativity). It's way beyond our current technology to get there. With our fastest spaceship it will take 17,000 years. See interstellar travel. --h2g2bob (talk) 21:18, 28 May 2007 (UTC)

Interstellar Travel is not a good place to look for sources, see one of the categories for details. Spacecraft propulsion would be a better place to look for sources. Thanks anyway.

Our fastest ship would arrive there a useless hunk of junk since the reliability of our engineering isn't good enough to last 17,000 years without maintenance. The solar sail approach (with massive lasers doing the work from orbit somewhere) is probably the way to go - but we don't have the technology or the funding or the will or enough knowledge of the destination to do that. Right now, we're better off building HUGE orbital telescopes - or perhaps a telescope array on the back side of the moon - we'll get more information about more stars more quickly and more cheaply than with robotic probes. SteveBaker 22:12, 28 May 2007 (UTC)

Glasses effect

Is there any corrective effect of glasses directly on eyes? For instance if one wore glasses for 1 hour, would there be a slight sight improvement without them? --Brand спойт 21:52, 28 May 2007 (UTC)

I believe that some lenses can train the eye to focus more clearly, although it will depend on why you need glasses and how they are prescribed. I personally wore glasses until around when I was 9, and my vision is actually better than 20/20 now. -- Phoeba Wright^OBJECTION! 22:32, 28 May 2007 (UTC)

i'm not sure about the training aspect but i doubt it. the basic principal behind glasses does NOT affect how ur eye works--rather it changes the incoming image so that it can be suitable for your eyes. take them away and you're back to the image your eyes can't properly focus.

What would happen if I were to eat lugduname?

What would happen if I were to eat Lugduname? would it burn a hole through my tongue? --Krsont 22:29, 28 May 2007 (UTC)

Net Ionic equation

Is there any website where you do a net ionic equation?

Ionic equation has information. If you learn how, you can do a net ionic equation anywhere! On the bus, in a treehouse... Nimur 00:47, 29 May 2007 (UTC)

Simple Static Mechanics Problem

I have 3 coins lying motionless on a frictionless surface. The 3 coins are all the same mass and size. The coins are arranged such that each coin is touching the other 2 coins. (the lines connecting their centers form an equilateral triangle) I apply a force F to a coin (#1) directly towards another coin (#2). In that instant, what are the forces on coins 1, 2 and 3 (the remaining coin)? Aepryus 00:00, 29 May 2007 (UTC)

The point of contact will be a theoretical "single point" on each circular edge. The force will act along the normal to the mutual tangent. This will be the same as the line connecting the centers of each coin (if they are all the same size). Since these lines form an equilateral triangle, you will have 60-degree angles. Now you just need to assume that the force you apply is totally delivered to the opposite edge of the coin (no compression); a bit of trigonometry will tell you the numerical relations of the force. It will also depend on where you push the first coin (i.e. which point you are touching); in the ideal case, your force will always act normal to the tangent line of the circle. Nimur 00:51, 29 May 2007 (UTC)

Assuming static equilibrium, the total force must sum to zero in each orthogonal direction.