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March 31

Space and matter shortly after the Big Bang

Hi

1. In the early Universe, just after the Big Bang, was there "as much space" as there is now but compressed into a smaller volume, or was there actually "less space"? If there was "as much space" then in what sense was the Universe "smaller"?

2. In the time shortly after the Big Bang, were particles and atoms in some sense actually "smaller" than they are now? Or did the formation of matter have to wait until enough space had been created to contain it?

86.177.108.189 (talk) 00:19, 31 March 2011 (UTC)

1. What's the difference?
2. There were no atoms. Only a subatomic particle soup. Dauto (talk) 00:33, 31 March 2011 (UTC)

If there was "as much space" then "as much stuff" could fit into it (e.g. all the atoms that now exist), yet that stuff would be "smaller" in some sense that I do not understand. If there was "less space" then "less stuff" could fit into it. In the latter case, as we get smaller and smaller, eventually there would be no room for the particles in your soup. Then what? Just energy in some other form? 86.177.108.189 (talk) 00:53, 31 March 2011 (UTC)

(edit conflict) I think I see what you are getting at. There was actually less space; in the sense that the stuff that was not space (matter and energy) was all closer together. The big bang and inflation created the space in which matter and energy organized itself into its current state. See Metric expansion of space and Timeline of the Big Bang and Inflationary epoch and Inflation (cosmology). Your sense is correct; all the "stuff" in the universe was compressed so there was a lot less room, even down to a singularity at the moment of genesis. --Jayron32 03:49, 31 March 2011 (UTC)

In simple terms, yes. The universe was much, much smaller, and all of the mass-energy was compressed into that very small space. I say mass-energy because at that density it's practically impossible for particles as we know them to exist, and it was all pretty much just high-energy photons. After a while, as the universe expanded, the energy density dropped, and particles started to condense out - starting with the really small ones like quarks and leptons. Check out Timeline of the Big Bang for more info. Confusing Manifestation(Say hi!) 03:45, 31 March 2011 (UTC)

Atoms were never smaller. But atoms only exist at low temperatures, because it doesn't take much energy to knock the electrons off, and it doesn't take much more than that to knock the nuclei apart. So physics is effectively different at higher temperatures, though the laws are the same. At even higher temperatures, the Higgs field gets knocked out of its nonzero vacuum state, and concepts like "electron" and "photon" break down, though the laws of physics are still the same. At even higher temperatures, nobody has any idea what happens (but I suppose the laws of physics are the same even then, by definition...)

Generally, things can be smaller at higher temperatures because there are more accessible fermion states. Ordinary matter is hard to compress because all of the low-energy electron states are occupied, and you aren't strong enough to push a substantial fraction of the electrons into higher energy states. But far more compact configurations of matter are physically possible when the energy is available.

I don't agree with ConMan's response. At high enough temperatures you can pair-produce arbitrary Standard Model particles, so all of the particle types are equally represented in the soup. (And, as I said, at even higher energies the low-energy particle types are meaningless.) I'm also unhappy with the idea that small things condense out first. Things condense out when there's insufficient energy to knock them apart.

I think the "Timeline of the Big Bang" article is of rather poor quality right now. The "inflationary epoch" is certainly misplaced; it should have no start time, since (1) A.B.B. times only make sense post-inflation, and (2) nobody has the slightest idea how long inflation lasted, nor what the pre-inflationary state might have been. I don't want to rewrite the article, though, because I don't really know very much about high energy physics. -- BenRG (talk) 05:56, 31 March 2011 (UTC)

• Thanks for the replies. I'm still a little confused about how we actually measure the size of things when space is not constant. In principle, could we take a 30cm ruler back to the time when the Universe was 30cm across and find that the ruler only just fitted (ignoring practical complications such as the conditions being too extreme for the ruler to survive)? Let's assume the answer is "yes". Then, over billions of years, space has expanded, but the ruler has stayed the same size? How does that work? Space must be expanding in all places, right, so why isn't it expanding "inside" the ruler, thereby stretching it? (Imagine the ruler is a drawing on the surface of a balloon. As the balloon inflates -- as space expands -- the ruler gets bigger.) This is what I don't understand. Thank you! 86.179.115.14 (talk) 12:58, 31 March 2011 (UTC)

I will say "yes" to your first question, although most solids vary in size with temperature and no solid can exist at those temperatures. A better answer is that the laws of the Standard Model haven't changed (it's thought) and various length scales can be derived from that. For example, the confinement scale of the strong force is about a femtometer, and that was the same back then. This is how the size of space is defined, essentially—it's the amount of space you'd need now to reproduce similar conditions in the lab. If the physical laws were different, there would be some fuzziness in how much the universe had expanded.

The reason rulers don't lengthen as the universe expands is the same as the reason they don't lengthen in other circumstances. Rulers are bound together by forces that, for complicated reasons, prefer a certain separation between particles and resist attempts to increase or decrease the separation. The laws of physics don't change, so the preferred separation doesn't change. There's nothing special about the recessional motion associated with the expansion of the universe; it is the same as any other recessional motion as far as the laws of physics are concerned.

Self-gravitation does act on rulers; it's constantly squeezing them. They don't collapse into black holes because the forces binding the ruler resist compression with a force that roughly follows Hooke's law (everything is like a spring under small enough deformations). Self-gravitation compresses the ruler until the opposing force matches the compression force, and the ruler remains permanently in that equilibrium state. It's slightly smaller than it would be without gravity, but it doesn't get smaller over time. If the cosmological constant is real then it also acts on rulers, trying to pull them apart, but because rulers resist pulling also, the effect is again just a slight change in the equilibrium size (much smaller than the effect of self-gravitation, which is already very small). If there were a pushing/pulling force directly associated with the expansion of the universe (which, I want to stress, there is not—Aristotle was wrong about that), it also would simply change the equilibrium size. -- BenRG (talk) 18:38, 31 March 2011 (UTC)

Ben, thank you for your very helpful answer. If I could prevail upon you again: At the time when the 30cm ruler only just fitted into the Universe, did it only just fit because it hit a boundary, or "edge", of available space? I'm guessing the answer to this is "no", but if there is no boundary or edge stopping the ruler extending further, then what would prevent us placing a longer ruler in the same Universe, thereby contradicting the proposition that the 30cm ruler only just fitted? 86.179.117.213 (talk) 01:04, 1 April 2011 (UTC)

When you hear figures like 30cm being quoted, those are the size of the visible universe at that time. In other words, the matter making up the present-day visible universe fit in a 30cm sphere (I'll take that to be the diameter, but a factor of 2 hardly matters). The universe presumably continues past that point, although we can't see it because the light hasn't reached us yet. We have no idea how large the entire universe is, nor what the nature of the boundary would be, if there is one.

But that doesn't mean your long-ruler question is uninteresting. It's actually quite subtle, and made me realize something I hadn't thought about before, which is that a quasi-rigid ruler that spanned the visible universe back then would actually be larger than 30cm now. The reason is that if all points on the ruler are at relative rest, then back then both ends of the ruler were moving rapidly inwards with respect to the Hubble flow, and therefore were Lorentz contracted with respect to cosmological coordinates (which take the Hubble flow as the local standard of rest). So if the coordinate length of the ruler then was 30cm, its proper length (which we would measure now) would have to be larger. Also, you run into difficulties with what it even means for a large solid object to exist at that time, because of synchronization issues. The time since the big bang is the same for all particles moving with the Hubble flow, but it would be different for different parts of the ruler.

So it's really necessary to measure the diameter with smaller rulers. 30 rulers of a centimeter each, maybe, which are moving with the Hubble flow. At the moment in question they all line up end-to-end and span the visible universe; a moment earlier they overlap and a moment later there are gaps between them. If you could gather them up today and arrange them end to end, they would total 30cm. -- BenRG (talk) 04:44, 1 April 2011 (UTC)

Thank you very much, that's very helpful. 86.179.115.50 (talk) 13:18, 1 April 2011 (UTC)

Shrinking Sun

According to the article Formation and evolution of the Solar System and Future of the Earth, the Sun is getting warmer and brighter by around 10% every 1 billion years because of the helium build-up at its core (nearly half the hydrogen has been consumed). This will wipe out Earth's life even before the time of the Red Giant. Now what the young-earth creationist use as evidence for their young Earth is the proof that the Sun is shrinking at 5 feet/hour. Try googling shrinking Sun. Is it really true? The two statements above seem contradictory. Please tell me which one is right. Aquitania (talk) 00:35, 31 March 2011 (UTC)

The evidence that the sun is shrinking is not very good, but I think the idea is that the sun is contacting, and therefore getting warmer in its core (since the extra density causes fusion to happen faster). Although like you I would have expected a warmer sun means a bigger sun, I think that's impossible: A bigger core (of the same mass) means lower energy production, so the core can't be any bigger than it is now. (In a red giant the core is small, but the outer layers are large.) Ariel. (talk) 01:11, 31 March 2011 (UTC)

Each Helium nuclei has half the electric charge and a quarter of the particles of the four protons it replaces. Therefore Sol has less volume (and higher density) and very slightly less mass. Hcobb (talk) 01:34, 31 March 2011 (UTC)

"...half the electric charge..." yes, but only because you have ignored the 2 positrons released when each of two proton pairs fuses into a deuterium nucleus - there is no overall loss of charge (obviously). "... a quarter of the particles ..." - I don't follow this at all - there are 4 nucleons both before and after fusion. Gandalf61 (talk) 09:24, 31 March 2011 (UTC)

Gandalf, Hcobb is talking about reducing the number of nuclei which is the number that appears at the ideal gas law PV=nRT, that governs pressure in non-degenerate matter. Dauto (talk) 12:28, 31 March 2011 (UTC)

And does the core of a star behave like an ideal gas ? As it is a plasma, I would have thought its equation of state would be much more complex. Gandalf61 (talk) 13:02, 31 March 2011 (UTC)

Yes, the core of a main sequence star does behave like an ideal gas. $P=\rho R^{*}T\,$ where $R^{*}\,$ is proportional to the number of particles per molecular weight $R^{*}\sim (2X+0.75Y+0.5Z)\,$. The quantities $X\,$, $Y\,$, and $Z\,$ are the hydrogen, helium, and metalicity mass fraction respectively. So hydrogen contributes two particles (a proton and an electron) per nuclei (which has a molecular mass equal to one): $2/1=2\,$, helium contributes three particles (a nucleus and two electrons) per nuclei (which has a molecular mass equal to 4): $3/4=0.75\,$, and metals contribute (n+1) particles (a nucleus and n electrons) per nuclei (which has a molecular mass equal to 2n): $(n+1)/2n\approx 0.5\,$. Dauto (talk) 15:17, 31 March 2011 (UTC)

When was the last time young earth creationist were right about anything? Dauto (talk) 03:27, 31 March 2011 (UTC)

The problem with that arguement, is that young earth creationists assume that that trend can be extended indefinitely backwards in time. This kind of error is sadly not uncommon. Plasmic Physics (talk) 07:32, 31 March 2011 (UTC)

It is physics 101 or an entry level astronomy class where you learn about the physics of a star, how stars exist by a balance between their mass and the laws of gasses. Gas particles repel eachother. The gravity of a body holds them back. If the mass of the star decreases, the gas particles are allowed to expand away from eachother. If too much of the gas turns into heavier elements thus no longer being a gas, the star ends up having less gas to fight the star's gravity and the star collapses under it's own weight. —Preceding unsigned comment added by 108.67.181.74 (talk) 04:11, 2 April 2011 (UTC)

Size of the universe

How big is the universe? — Preceding unsigned comment added by JoshuaDonald (talk • contribs) 04:36, 31 March 2011 (UTC)

We don't know. It could be infinitely large, or perhaps has finite limits but which the laws of physics do not allow us to probe. See Universe#Size.2C_age.2C_contents.2C_structure.2C_and_laws and Shape of the universe and Observable universe for some extended content on this matter. --Jayron32 04:39, 31 March 2011 (UTC)

There is an interesting concept explaining the big bang and the form of the universe: http://www.teach-nology.com/forum/showthread.php?p=46964 108.67.181.74 (talk) 04:21, 2 April 2011 (UTC)

Would I be able to donate extra skin and fat cells for $?

As I was in Germany as a toddler, I can't donate blood. _{(After over 20 years of not being in Europe, I clearly don't have CJD, but it'll take a lot to get that through the FDA's thick heads.)}

As I'm 11-13 lbs. overweight, and aware of how organs are sold for money, what about donating my extra skin and fat cells to anyone who may need it? Where do I go to get this to happen, and how much $ would I earn per lb.?

Other than that, what CAN I donate (that will replenish/regenerate, so no kidneys, for example) that will still net me some funds? --70.179.169.115 (talk) 11:26, 31 March 2011 (UTC)

I think you're out of luck. Dauto (talk) 12:24, 31 March 2011 (UTC)

Doesn't somebody need skin grafts at any point in time? Also, if fat tissue has been burned, that would need replacement too, right? --70.179.169.115 (talk) 13:18, 31 March 2011 (UTC)

For your second question you might be able to sell blood plasma and gametes (the second is easier for males then females). Googlemeister (talk) 13:15, 31 March 2011 (UTC)

Gametes? Okay then, where is the closest gamete donation center to 66502, please? --70.179.169.115 (talk) 13:18, 31 March 2011 (UTC)

As an aside, I will note that the latent period of CJD infection can run into multiple decades, with some speculation that it may take up to 50 years for symptoms to appear. TenOfAllTrades(talk) 15:13, 31 March 2011 (UTC)

The restrictions on donors with vCJD are borderline paranoia, given that the number of total cases is vanishingly small and the impending epidemic never happened. The restrictions on blood donation are restrictive because people are still paranoid about disease risks, and it leads them to refuse life-saving treatments. Better to deal with their fears ahead of time. I'm not aware of adipose tissue donation. Skin donation is almost entirely either autografts (i.e. from one spot on the patient to another) or from cadavers, and has the same restriction on European residence anyway. Semen/oocyte donation, as of 2005, now has the same restriction unlesss you're giving for someone that knows you and they're notified of the potential risk up front. You can't donate a kidney for money in the US anyway. There's a blood test for vCJD which has been proven on paper, but it'll probably be at least several years before it's commercially available, since getting it to work is one thing, nailing down specificity and sensitivity to a decent level is another entirely. For the record, routine blood donors are not paid (again, volunteers are felt to be safer). Plasma donation is paid in the US, even though the World Health Organization frowns on that practice. SDY (talk) 16:52, 31 March 2011 (UTC)

Out of interest here are the precautions taken in the UK against transmission of CJD in donated blood. A far worse disaster in the UK was the use of blood imported from US prisons in the 1980s. Alansplodge (talk) 18:32, 31 March 2011 (UTC)

We have an article on that topic, though it looks like the UK-specific article is yet to be written. People got scared for a reason. What's sad is that some of this same issue was repeated in China, but there it was shared needles resulting in something like a quarter of a million HIV infections (again, shortcuts for economic reasons). There it was the donors, haven't heard anything about the recipients. Modern processing techniques are fairly thorough, but I wouldn't be surprised if some slipped through. SDY (talk) 19:18, 31 March 2011 (UTC)

Obsolete or speculative physical theories

Are speculative physical theories that don't make any predictions that can easily be tested still considered to be "scientific"? Are obsolete physical theories considered to be unscientific? I ask because in this thread an editor is convinced that Einstein-Cartan theory is some combination of "wildly speculative", "not science", and "pseudoscience". In the end, he says it's mathematics, not physics. To me, that doesn't seem fair to established speculative physical theories (e.g., Brans-Dicke theory, string theory, quantum gravity). But I'm a mathematician, not an empirical scientist. I'd like a broader view on this question. Sławomir Biały (talk) 12:25, 31 March 2011 (UTC)

It is relevant to point out that our definition of hypothesis says "For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it." Even our article on theory says "Such theories are preferably described in such a way that any scientist in the field is in a position to understand, verify, and challenge (or "falsify") it." Keep in mind these are fairly narrow definitions, and alternate formulations end up being more about philosophy of science than about science per se.

The work of applied mathematicians, theoretical physicists and their ilk often falls through the cracks of easy-to-formulate definitions of science. Certainly marking string theory as 'pseudoscience' would be perverse. Though I am not that familiar with this notion of Torsion field physics, some of the views at the talk page constitute extremely hard-line bias towards empiricism as the only valid form of science. Consider this: lack of obvious testable predictions does not mean a proposition or theory is not falsifiable. If a case can be made for falsifiability, then you have a good claim that the theory is scientific under the Popperian scheme of science. SemanticMantis (talk) 15:22, 31 March 2011 (UTC)

Slightly off-topic, but: In general relativity you can think of continuous mass distributions (the stuff that appears in the stress-energy tensor) as a continuum limit of a bunch of tiny nonrotating black holes in vacuum. If they're rotating, the continuum limit has torsion. So it's easy to argue that Einstein–Cartan theory is more natural than general relativity, since it doesn't impose an arbitrary constraint on black holes in the continuum limit. The difference between Einstein–Cartan theory and GR is too small to be tested, but neither theory is to blame for that. If you wanted to discard one theory, it would have to be on the basis of Occam's razor. GR has simpler math, but E–C appears to me to have fewer arbitrary assumptions. Newtonian gravity has simpler math than GR, but GR has fewer arbitrary assumptions. So this argument would seem to favor E–C gravity. I suppose the broader point is that the testability of a theory depends somewhat on what alternatives are available. Every theory makes many predictions that aren't testable (because we don't have any labs on distant planets, for example). That doesn't matter until a rival theory comes along that predicts the same result in a lab on Earth but a different result on another planet. Suddenly the untestability of the distant-planet prediction becomes a problem. It's not fair to blame the new theory for that just because it was invented later. -- BenRG (talk) 23:20, 31 March 2011 (UTC)

Very interesting posts. Thanks! Sławomir Biały (talk) 12:55, 2 April 2011 (UTC)

Many theories have been replaced during modern science, for example the continental drift theory by plate tectonics, the cosmological constant by dark energy and the luminiferous aether/corpuscular theory both by variously concurrent theories of light (Wave–particle duality, neutrino theory of light, photon, Maxwell's equations, quantum optics, quantum electrodynamics, light transport theory, solid light, emission theory, etc). Nowadays, some scientists are looking to complete the Standard Model of physics by creating a Grand Unified Theory and using results from experiments such as at the Large Hadron Collider. ~AH1^(TCU) 23:30, 3 April 2011 (UTC)

Temperature induced nuclear fission

How do I calculate the theoretical ratio of free nucleons to nuclei in a nuclear plasma, as a function of temperature, pressure, and muclear binding energy? Plasmic Physics (talk) 12:56, 31 March 2011 (UTC)

I don't understand your question. could you elaborate? Dauto (talk) 00:49, 1 April 2011 (UTC)

At the temperature increases for a electromagnetic plasma gas, a new type of plasma develops. I say plasma gas, because a plasma is not a distinct phase like a solid or liquid, as a table salt is considered a solid example of a plasma. This plasma is a nuclear plasma gas - in a nuclear plasma gas, nuclear fission of normally stable nuclei is induced. In this process, the binding energy is overcome by the thermal energy. Since temperature is equivalent to the average thermal energy of a bulk sample, not all nuclei would have energies over the threshold required for nulear fission to be induced. In addition to this, there is a continueum of discrete fission products ranging from no fission, to individual nucleons. So, it is fair to say that across a change in temperature, a gradient of proportion should exist for a specific fission product. Plasmic Physics (talk) 01:37, 1 April 2011 (UTC)

Anyone? Plasmic Physics (talk) 23:29, 1 April 2011 (UTC)

If I understand you correctly you want to know how to calculate the concentration of free nucleons given temperature, pressure and assuming thermodynamic equilibrium. That is done the same way that the concentration of chemical species is calculated for a given reaction. You must calculate the Gibbs energy for the system and minimize it. Read Chemical equilibrium You will also find useful the article thermodynamic potential. specially the section Thermodynamic potential#The equations of state. Dauto (talk) 04:35, 2 April 2011 (UTC)

Helpful, how sure are you that it exists in a state of equilibrium? Plasmic Physics (talk) 07:20, 2 April 2011 (UTC)

It's your question. You must have some physical situation in mind. Good judgment must be used to decide whether thermodynamic equilibrium is present or whether a quasi equilibrium is a good approximation. Just note that if there is no equilibrium then your question is ill posed because you would have to know the initial condition (concentration of each relevant species) and then use each reaction rate (based on their cross sections and on the availability of the reactants) to integrate the evolution of the concentration of those species to find their final concentrations. Dauto (talk) 14:37, 3 April 2011 (UTC)

Thank you, I can use this information. Plasmic Physics (talk) 09:13, 4 April 2011 (UTC)

Isn't there an anti-hunger pill anywhere?

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the talk page discussion (if a link has been provided). --TenOfAllTrades(talk) 01:03, 1 April 2011 (UTC)

I had an anti-hunger pill just the other day. It's called the Big Mac. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:36, 2 April 2011 (UTC)

Green Laser

I have one 20mW green laser pointer. It does not burn matches (as I daydreamed) yet gives a slight sensation of heat on skin. It works on 3 AAA batteries (alkaline). My question is that if I add more voltage will it increase in power, say burn paper etc.  Jon Ascton  (talk) 14:10, 31 March 2011 (UTC)

No. Excessive voltage will simply destroy the laser diode. Roger (talk) 17:00, 31 March 2011 (UTC)

You are probably right. But I have heard that using a typical 3.7 volt Li-ion (rechargeable) battery will make it more powerful. What do you say to that...

What is the voltage of the current battery? A higher voltage will increase power output up to the rated maximum a further increase in voltage will destroy it. However it is most probably already operating at, or very close to, its maximum anyway. Roger (talk) 08:25, 1 April 2011 (UTC)

The current voltage, as I have stated above, is 4.5 volts (3 AAA batteries), yet a 3.7 volt is said to make it more powerful.

That is completely illogical - reducing the voltage while leaving everything else unchanged will reduce the power. Power = Voltage x Current. Roger (talk) 12:37, 2 April 2011 (UTC)

It's not so obvious. You regulate laser diode output by controlling the current provided, not the voltage. Some very cheap laser pointers may rely on the internal resistance of the alkaline battery as part of the circuit that regulates the current through the diode. A lithium-ion battery has lower internal resistance than an alkaline one, and might provide higher current depending on the design of the circuit.--69.248.117.99 (talk) 05:43, 8 April 2011 (UTC)

Not something that personally interests me but since it's something I've seen in sites I visit I believe red lasers tend to be far more cost effective if you just want something that will light matches. I believe you can get random Chinese laser of indeterminate power that will nevertheless light matches for around US$30 presuming it can get thru customs. While you can get green and other colour lasers that will do the job, their primary advantage to the hobbyist would be for looks. I presume you're already aware such a laser as yours is very dangerous (probably (3B) and could easily blind anyone who views the light directly and already have appropriate safety goggles. Nil Einne (talk) 17:24, 31 March 2011 (UTC)

Avoid using Class III and Class IV lasers in your home! Your basic assumptions about safety are Just Not Good Enough! Powerful lasers can scintillate, reflect obliquely, and behave in nonintuitive ways. A proper optical laboratory will take much more precaution far beyond just "don't look into the laser beam." You need the laser to be firmly mounted on an optical bench where it can not shine anywhere unexpected. You need the work area (and the rest of the room) to be totally nonreflective; avoid specular reflective surfaces, avoid certain materials in the furniture and walls, and so forth. Even diffuse reflection of powerful laser light can cause permanent eye damage. By definition, Class III and Class IV lasers can cause you physical harm - and most can cause permanent damage faster than it takes you to blink or avert your eyes. Playing with lasers is like juggling knives - fun for a while, but your first "minor accident" will cause permanent and irreparable injury/damage. If you like powerful lasers, get involved with an optical research laboratory and learn the safety procedures, just like the experts do. Nimur (talk) 20:56, 31 March 2011 (UTC)

You can also use a laser from a DVD burner. Instructions here. — DanielLC 20:27, 31 March 2011 (UTC)

Identifying an old timey flying machine

I'm trying to find the identity or history of what I believe is a (failed) pre-Wright flying machine. It's well known to pop culture because it appears as stock footage in many, many movies and television shows, but I know nothing about it so I can only describe it visually.

It appears as though someone has taken an old car and attached a giant parasol to a vertical shaft through the center of the car. There's some sort of engine 'pumping' the parasol up and down. Apparently the principle is that air will be pushed to the sides during the up-stroke but downwards during the down-stroke.

Of course, in the familiar stock footage, the car does not fly. It just sort of bounces up and down on its shocks. I don't think its wheels even leave the ground.

Thanks APL (talk) 16:53, 31 March 2011 (UTC)

Was it the Flugan? --Jayron32 17:21, 31 March 2011 (UTC)

Or is it the first machine in this clip? Alansplodge (talk) 17:44, 31 March 2011 (UTC)

Here is some video of the machine in question. It is called the "John Pitts Skycar". This is the patent for its unique form of "flight". --Sean 17:43, 31 March 2011 (UTC)

Well done sir! A different movie clip of the same beast (with sound) here. On the upstroke the 60 vanes making up the "parasol" opened and on the downstroke they closed, hopefully creating downforce. Not enough apparently. It appears on our List of aircraft (P-Q) but there is no article yet. Alansplodge (talk) 17:45, 31 March 2011 (UTC)

Wow. Thank you. That's exactly what I was looking for.

I didn't even realize that the parasol "propeller" actually rotated as well as oscillated up and down. APL (talk) 18:16, 31 March 2011 (UTC)

That's a big engine under the thing. If they'd just hit on the standard helicopter rotor, I wonder if it could have taken off. (no comment on what would come afterward...) Wnt (talk) 20:01, 31 March 2011 (UTC)

That device probably had a poor power to weight ratio. I wonder if a modern engine could get that contraption to work? Googlemeister (talk) 21:11, 31 March 2011 (UTC)

It looks a bit like an early attempt at the eventually-successful craft called the Autogyro. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:34, 2 April 2011 (UTC)

What is fertilising the blossoming shrubs in England?

I have not seen any bees around, or any other insects for that matter, at this time of year. So what is fertilizing all the blossoms please? Thanks 92.29.127.125 (talk) 19:21, 31 March 2011 (UTC)

Just because you haven't noticed any bees or other insects doesn't mean they aren't around. Also, just because there are blossoms doesn't mean anything has been fertilised. The blossoms attract the insects to fertilise them so the plant can produce seeds. It's seeds that are proof of fertilisation, not blossoms (and even then some plants can produce seeds without being fertilised by insects). --Tango (talk) 19:28, 31 March 2011 (UTC)

Surely bees pollinate, not fertilize? APL (talk) 20:21, 31 March 2011 (UTC)

The terminology is fine: fertilisation "is the fusion of gametes to produce a new organism." Bees are the vector of fertilization for many plants. "Fertilizing" in the sense of supplying nutrients to a plant is the spurious usage. SemanticMantis (talk) 20:26, 31 March 2011 (UTC)

Plenty of bumblebees up here in Edinburgh. I assume if it's warm enough for them in Scotland, it's warm enough in England. 86.135.222.99 (talk) 21:59, 31 March 2011 (UTC)

We have an article on Pollination which explains quite a bit. There are some plants which don't even require other organisms to pollinate them, but also many other creatures other then bees can pollinate, including butterflies, moths, wasps, flies and beetles, even ants. Vespine (talk) 22:17, 31 March 2011 (UTC)

Although plants which wind-pollinate don't go to the bother of producing blossom with petals, nectar et al - they're purely for the benefit of insect-pollinators. Oak trees for instance have a rather dreary green catkin effort with which to spread their DNA about. Alansplodge (talk) 14:18, 1 April 2011 (UTC)

Though I suspect there are at least a few pollinators around, I'll point out that a match-up between the timing of flowers blooming and pollinators emerging is not guaranteed. The phenology of plants and insects has co-evolved for a long time, and both have something to profit by matching up for this mutualism. However, different species may be attuned to different cues (e.g. photoperiod vs. temperature), and these can get mis-matched, especially when we consider climate change. There is much ongoing research into the consequences of these matchings getting fouled up, see e.g. [1]. SemanticMantis (talk) 13:59, 1 April 2011 (UTC)

I saw my first bumble bee in Hertfordshire at the end of February and since then I've seen several species including the big white-tailed ones and little black ones that I don't know the name of. I've also seen lots of hoverflies and one Large White butterfly. Alansplodge (talk) 14:25, 1 April 2011 (UTC)

I have now seen a few bees. 92.29.115.116 (talk) 10:33, 4 April 2011 (UTC)

April 1

milk

will putting milk thru a coffee filter remove radioactive iodine — Preceding unsigned comment added by Wdk789 (talk • contribs) 00:59, 1 April 2011 (UTC)

No. --Tagishsimon (talk) 01:04, 1 April 2011 (UTC)

why not — Preceding unsigned comment added by Wdk789 (talk • contribs) 01:29, 1 April 2011 (UTC)

Because iodine in milk doesn't form into large particles the size of coffee grounds. StuRat (talk) 01:36, 1 April 2011 (UTC)

The idea is that you can't separate radioactive iodine from normal iodine whithout the use of some very expensive equipment. Secondly, iodine is removed by chemical means which essentialy ruins the milk, rendering it undrinkable in any case. Plasmic Physics (talk) 01:41, 1 April 2011 (UTC)

what about a laboratory filter? — Preceding unsigned comment added by Wdk789 (talk • contribs) 01:45, 1 April 2011 (UTC)

I asked this here, and apparently it's hard to filter iodine. You could freeze the milk for about 2 months and 99.5% of the radioactive iodine will be gone by then. 70% will be gone after 2 weeks. Ariel. (talk) 01:54, 1 April 2011 (UTC)

To give an idea, as I've just added to the article, coffee filters pass particles under about 10 to 15 micrometers. Now by comparison iodine has a Van der Waals radius of 198 picometers (1.98 Angstroms). 1 micrometer = 1000 nanometers = 1 000 000 picometers, so the holes in a coffee filter are about 76,000 times larger than an iodine atom. Wnt (talk) 02:04, 1 April 2011 (UTC)

As stewed rat says, the iodine in milk is not present as crystals that can be filtered, it is dissolved. Similiarly, you can't filter table salt out of solution. Be carefull with your understanding of what filtration is. Plasmic Physics (talk) 02:13, 1 April 2011 (UTC)

Perhaps I should offer a bit more background for clarity. It's very common in research to encounter a .22 micron (220 nanometer) filter, which is still 1000 times larger than the iodine atom. By that point it gets quite hard to pass large amounts of fluid (depending of course on the amount of sediment). At smaller sizes molecular sieves are used, but generally in a different way - because it's no longer practical to wait for everything to pass through, instead they delay the molecules that can pass through them as they're dripped through in chromatography. When you get down to that scale, you generally rate them by the size of the molecule that can go through, such as 1000 daltons. Iodine is smaller than even that! Animals are equipped with gap junctions that work more like traditional filters though, because the cells with them are only 4 nm apart, the time delay isn't a big deal. (There are also tight junctions between cells that work like filters with a size that sometimes can be regulated).

But when you get down the the size of atoms, materials made out of atoms are weird to filter with. You can see ion channels set to pass specific sizes, but which won't pass anything larger or smaller than what they're set for. There's even a specific iodide channel in the thyroid,^[2] but alas we don't have an article for it. And if you go smaller than that - well, a filter that passes half of one of the smaller atoms won't pass anything; besides, any two surfaces half an atom apart are either going to spread out and accept solvent between them, or stick together and be held by Van der Waals forces.

The talk of biological channels suggests a possible practical solution, though I don't know if it works: live kelp and other seaweeds absorb iodide into themselves with great avidity, and one could hope that they might suck up radioactive iodide if left in milk for some time (before, presumably, dying) ... unfortunately you have to have a source of clean, live seaweed to start with! Wnt (talk) 02:50, 1 April 2011 (UTC)

Would you still be inclined to drink the milk following this method? Plasmic Physics (talk) 03:55, 1 April 2011 (UTC)

Well, it depends how desperately I want "cold" milk. And it's a proposal for an experiment, not a guarantee of success. ;) Wnt (talk) 05:24, 1 April 2011 (UTC)

In honor of the day, could the iodine in milk be reacted with ammonia to form nitrogen tri-iodide crystals, which might be more readily filtered out of the milk? Edison (talk) 04:00, 1 April 2011 (UTC)

I like the taste of ammonia even less than kelp. Plasmic Physics (talk) 04:10, 1 April 2011 (UTC)

a old civil defense movie said radioactive fallout was the size of table salt, why couldn't i filter it? would a activated charcoal filter work? what about this filter http://www.parowanprophet.com/Nuclear_War_Comes/water_filter_instructions.htm — Preceding unsigned comment added by Wdk789 (talk • contribs) 06:07, 1 April 2011 (UTC)

That movie is obviously... wrong. Fallout can be any size, fallout includes material of any size material, light enough to be carried by the wind. Is the iodine present in the milk as a result of fallout or a contaminated food cycle? Plasmic Physics (talk) 07:39, 1 April 2011 (UTC)

Think! If it was the size of table salt, how would it get into your milk at all, staying that size? 95.112.203.81 (talk) 10:53, 1 April 2011 (UTC)

Even if it's the size of table salt, it will dissolve in the milk. Filtering only works for particles which stay together, and don't dissolve. --87.169.34.172 (talk) 20:56, 3 April 2011 (UTC)

fallout, i think — Preceding unsigned comment added by Wdk789 (talk • contribs) 08:00, 1 April 2011 (UTC)

It's not fallout. A normal reactor makes iodine as it runs. If containment is breached (and the fuel melts) the iodine basically just evaporates into the air, so the particles are the size of atoms. In a bomb with fallout, sand and debris get irradiated and then the dust goes everywhere, it's different. Ariel. (talk) 10:43, 1 April 2011 (UTC)

With milk, I should be worried more about Strontium-90 because biologically it behaves like Calcium and has a much longer half life time. But I don't see how it should be distributed in larger amounts through the air. It is more likely to be washed away into the sea. 95.112.203.81 (talk) 11:09, 1 April 2011 (UTC)

Also, it should be noted, both iodine and coffee are brown. Coffee filters are designed specifically to pass brown liquids. As a test, take cream directly from the fridge; you will see that most of it won't pass through the coffee filter. Good <ahem> day. 71.95.147.208 (talk) 21:15, 1 April 2011 (UTC)

so would this work http://www.parowanprophet.com/Nuclear_War_Comes/water_filter_instructions.htm — Preceding unsigned comment added by Wdk789 (talk • contribs) 03:08, 2 April 2011 (UTC)

No, but that's not the whole of the truth. It surely won't work with milk. The instructions make up a very crude kind of ion exchange device. If there was heavy fallout from a nuclear bomb and you have no other water than freshly contaminated surface water then this might be a last resort. If you have access to water from a well then this has already been done naturally as the water seeps through the ground until it appears in the well. 77.3.139.229 (talk) 08:43, 2 April 2011 (UTC)

Our nearest neighbouring solar system

What is the nearest solar system to our own, and based on present technologies, how long would it take for us to send astronauts there? Flaming Ferrari (talk) 01:13, 1 April 2011 (UTC)

About 40,000 years with our currently fastest spaceships, if I recall correctly. --Belchman (talk) 01:32, 1 April 2011 (UTC)

According to this 2006 article, Epsilon Eridani is the next stop for the most intrepid real estate agent, a mere 10.5 light years away. However, our article states that the planet is "unconfirmed". Clarityfiend (talk) 01:31, 1 April 2011 (UTC)

The Proxima Centauri system is closest, but we have no way, with our current technology, to send astronauts there (alive). Also, we don't know if planets are present there. StuRat (talk) 01:34, 1 April 2011 (UTC)

I'm not an expert, but doesn't a solar system require a system of orbiting bodies, not just a star(s). Ergo, does a triple star with no suspected planets (Proxima Centauri) qualify? Plasmic Physics (talk) 01:45, 1 April 2011 (UTC)

I don't think we would be able to detect small planets. And how about asteroids, comets, etc ? What precisely is required to be a solar system ? StuRat (talk) 03:26, 1 April 2011 (UTC)

We can now detect planets that are pretty small, but only if they pass directly between the star and us (thereby dimming its light slightly). That's a low-probability occurrence. Looie496 (talk) 04:12, 1 April 2011 (UTC)

And saying 40,000 years with our fastest spaceships is misleading. We could design spacecraft that could get there faster (at a significant cost), but since we would still be talking about much longer then a human lifespan, we never bothered making something like that. Think about it like this. Our furthest mission we sent out was aimed at Pluto (5 light hours away). The nearest star is more then 7000x further. If the furthest you had to travel in your life was 1 mile, you wouldn't need to bother with a car or plane, you could make do with a bicycle and a wheelbarrow (which are far cheaper assuming you don't get one of those $5,000+ racing bikes). If you wanted to go 7000 miles away, then you might want to look into building some faster transportation. I would imagine 1% c would be possible with current technology if cost was not an issue. Googlemeister (talk) 13:09, 1 April 2011 (UTC)

You also need to taked development time into account. Even with unlimited funds, I don't think 0.01c would be possible in less than a few years. --Tango (talk) 18:23, 1 April 2011 (UTC)

Of course. We have the proven technology to build a building with a height over 2500 feet, but if we were starting to build one today, it wouldn't be done for at least a year. A 1% c spacecraft would be an engineering challenge greater then a tall building, but of course, in a different way. Googlemeister (talk) 14:17, 4 April 2011 (UTC)

And another problem is, if you designed, built and launched such a ship on it's multi-century journey, it would surely be passed by later, faster ships. This rather takes away any incentive to build the initial slow ship. StuRat (talk) 18:27, 1 April 2011 (UTC)

There have been good short stories about explorers heading out to a nearby star system in "cold sleep" only to wake up and find a prosperous centuries old colony. APL (talk) 01:05, 2 April 2011 (UTC)

That would seem preferable to the sleepers since most of the hard work of setting up the colony would already be done. Googlemeister (talk) 14:13, 4 April 2011 (UTC)

Googlemeister, I think you seriously underestimate the difficulty of the engineering involved. Even if cost were no issue, with current technology an attempt to build a craft capable of carrying humans to another star system would certainly fail. We don't know enough yet to design systems that can be kept operational and keep a human crew alive for such a long journey. We can barely manage 50% success at putting unmanned probes on or into orbit around Mars, and that is much easier. We need to learn a lot more about engineering spacecraft before such a long journey will be possible.--Srleffler (talk) 06:06, 8 April 2011 (UTC)

Jacob Barnett: amount of carbon created in the early universe

There's a 12-year-old prodigy who's got doubts about an aspect of big bang theory (check Google news today). Can anybody suggest what he means by this? (particularly the last two paragraphs -- the first grafs are fairly common):

"There are two different types of when stars end. When the little stars die, it's just like a small poof. They just turn into a planetary nebula. But the big ones, above 1.4 solar masses, blow up in one giant explosion, a supernova," Jake said. "What it does, is, in larger stars there is a larger mass, and it can fuse higher elements because it's more dense."

"So you get all the elements, all the different materials, from those bigger stars. The little stars, they just make hydrogen and helium, and when they blow up, all the carbon that remains in them is just in the white dwarf; it never really comes off.

"So, um, in the big-bang theory, what they do is, there is this big explosion and there is all this temperature going off and the temperature decreases really rapidly because it's really big. The other day I calculated, they have this period where they suppose the hydrogen and helium were created, and, um, I don't care about the hydrogen and helium, but I thought, wouldn't there have to be some sort of carbon?"

"Otherwise, the carbon would have to be coming out of the stars and hence the Earth, made mostly of carbon, we wouldn't be here. So I calculated, the time it would take to create 2 percent of the carbon in the universe, it would actually have to be several micro-seconds. Or a couple of nano-seconds, or something like that. An extremely small period of time. Like faster than a snap. That isn't gonna happen."

"Because of that," he continued, "that means that the world would have never been created because none of the carbon would have been given 7 billion years to fuse together. We'd have to be 21 billion years old . . . and that would just screw everything up."63.17.54.2 (talk) 03:33, 1 April 2011 (UTC)

I'll add to my own question. He seems to be saying that the earliest epoch of supernovae isn't early enough to have produced enough carbon to create planets by the time the earth was created, OR that the earliest epochS (plural) of supernovae wouldn't have cumulatively produced enough carbon.63.17.54.2 (talk) 03:41, 1 April 2011 (UTC)

Well, "earth made mostly of carbon" is his first mistake, it's only the 15th most abundant element. Looks like boy genius still has a thing or two to learn ;) lol.. (j/k) Vespine (talk) 03:58, 1 April 2011 (UTC)

I'm embarrassed that I didn't notice this big red flag -- obviously, the earth is "iron-centric" (so to speak) not carbon. But maybe the reporter transcribed him wrong or something -- maybe he's saying there aren't enough heavy elements in the big bang chronology? Otherwise, this is just embarrassing for him that he got quoted with such a huge error. This kid is phenomenally good at math ... he's very impressive. It's weird he could get wrong a basic fact like "amount of carbon in early planet formation." (Note: This is NOT an April Fool's Day joke -- you can look this up on Google.)63.17.54.2 (talk) 04:11, 1 April 2011 (UTC)

No i know, i did read about this kid, he did calculus by the time he was 8, sounds like a very clever kid, but i think the story is way over hyped. Carbon IS the 4th most abundant element in the universe, after H, He and O, but i'm not aware that this is a "problem". We have articles on Formation and evolution of the Solar System, Big Bang nucleosynthesis and Abundance of the chemical elements, I don't see anyone saying there's a discrepancy between what's observed and what's expected. Maybe there is, but I'll need more then a tabloid news story to convince me, whether the claim is made by a 12 year old or not. Vespine (talk) 04:17, 1 April 2011 (UTC)

Here is a Youtube video of the child in question: "Jacob Barnett talk about Einstein... And eats lunch". Now, with due respect (I mean, he is twelve) - the guy's not exactly out-doing Einstein. Really, he's just mumbling regurgitated jibberish that sounds like he just finished reading Chapter 3 of a Generic Pop-sci Cosmology book. Yes, it's fantastic that a guy this young is thinking about physics - but he's not exactly "innovating" cosmology as much as "misunderstanding" it. We get this sort of thing on the reference desk a lot. Loads of people are thinking about relativity and the formal mathematics that describe it; and loads of people find it to be a conundrum. And a few think they've resolved the conundrums by disproving modern theoretical physics. (See our RefDesk archives for innumerable examples). But this doesn't mean that all these enthusiasts are actually "smarter than Einstein." It's disappointing to see major media outlets like Time Magazine reporting that this is the new discovery that's going to shatter physics. Such reporting over-inflates a novice physicist's accomplishments. The kid's got a lot to learn - he may well develop a formal theory - but what we have right now is jibberish. Mr. Barnett has neither the necessary experience nor the access to the astrophysical data that would qualify him to make such sweeping assertions about the composition of stellar supernovae. If we were to subject his assertions to the proper scientific channels - that is, peer review in journals, and rigorous experimental and observational testing of his claims - the entire story would collapse. But, the media loves to take "boring" science topics and turn them into juicy human interest stories... Nimur (talk) 05:38, 1 April 2011 (UTC)

The kid is clearly confused. What's not clear is what is he confused about? He seems to be aware that larger stars release heavier elements when they explode but for some mysterious reason he is concerned about carbon's abundance. Dauto (talk) 06:32, 1 April 2011 (UTC)

I'm not sure exactly what he is trying to say is the problem, but he is clearly referring to the carbon creation bottleneck in big bang nucleosynthesis. Because there are no stable nuclei of mass 8, carbon-12 was not significantly created during the big bang. As a result, we assume that essentially all carbon in the universe had to come from supernova. He is correct that if the big bang were somehow slower, such that nucleosynthesis could last longer, then you could create appreciable carbon during the big bang. As far as I know though, there is no evidence of that (and at least some evidence against it). Dragons flight (talk) 07:06, 1 April 2011 (UTC)

Commenters elsewhere have suggested he's been coached by Creationists -- Creationists who (according to the commenters) include in their quiver of ignorance a "not enough carbon" arrow. His wikipedia page (!?) makes reference to a connection to a Christian school ... AND he's been celebrated on TV by one Glenn Beck. So maybe he's being exploited by "young-earth" morons.63.17.37.103 (talk) 02:16, 2 April 2011 (UTC)

Also, his family lives in Indianapolis -- a hotbed of ignorant fundamentalist Christians, as anyone can verify by going to lots of public places there and reading the inscriptions on the white trash's t-shirts.63.17.39.192 (talk) 07:55, 2 April 2011 (UTC)

See Jacob Barnett.63.17.37.103 (talk) 03:31, 2 April 2011 (UTC)

I did the prodigy thing long ago (sort of) - don't be fooled. The thing about mathematics is that it is quite easy to learn it quickly up to about the calculus level, provided you get good instruction to help you over the hiccups in understanding - to provide the step-by-step help of how actually to use the notation and work it to get a result. The way that kids usually learn it is simply inefficient - you just barely get into the swing of it in an hour, then you have half a week to forget what you learned, then you muddle through it the wrong way the next session and so on. I wish that schools would consider teaching groups of children the entire year's math class in a few weeks devoted entirely to that one subject, to improve efficiency. But standard instruction practices aren't so inefficient for learning about the real physical world, so those topics are more difficult for a prodigy to excel with. (the difference is that mathematical facts are connected, so if you learn 1, 2, 3, 4, and 5 in a day and practice working problems 1->2->3->4->5, you drill them all into your head at once; but physical facts are almost unrelated to one another) Moreover, to the degree that prodigies are good at devouring a book and regurgitating its contents, they are vulnerable to believe just pure balderdash when they read it - there's a lack of reasoned adult discrimination and skepticism about what sources to trust and which to recognize as obvious scams. Wnt (talk) 06:45, 2 April 2011 (UTC)

The question is "Can anybody suggest what he means by this?", NOT "Is he a genius?" or "What is your personal experience of having been (sort of) a math prodigy?" 63.17.37.103 (talk) 06:59, 2 April 2011 (UTC)

I think what he's saying^[3] is that he still hasn't read about Population III stars. So he thinks it would have taken an extra 7 billion years for the carbon to form to produce planets like ours (some hedging there; as quoted he is wrong about the Earth being made out of carbon, etc.; more likely something was left out).

From WP re Population III stars: "Their existence is proposed to account for the fact that heavy elements, which could not have been created in the Big Bang, are observed in quasar emission spectra, as well as the existence of faint blue galaxies." WHAT does this have to do with whether there was enough carbon 7 billion years ago to form the earth? Face it: The kid is being coached by "young-earth" Christian fundamentalists to spout a supposed contradiction in big bang theory. 63.17.39.192 (talk) 08:04, 2 April 2011 (UTC)

He was saying that the Big Bang was 21 billion years ago rather than 15 billion years ago (hmmm, that's not exactly 7...). Is that "young earth creationism"?? Wnt (talk) 11:35, 2 April 2011 (UTC)

No, he isn't. He's saying there's a big contradiction in the math, whereby the standard model shows 13+ billion years, but the supposed carbon content suggests earth would have to be 21 billion years old, and thus the Big Bang 28 billion. He's saying the math is phony -- as do the "not enough carbon" advocates of young-earth, in arguing AGAINST the Big Bang as an event. The point isn't the time that's passed, but the inaccuracy of the math that supports the standard model.63.17.33.200 (talk) 10:13, 4 April 2011 (UTC)

P.S. Jacob Barnett is up for deletion, if anyone has an opinion. Wnt (talk) 07:25, 2 April 2011 (UTC)

3D for one-eyed Jacks

Is there any 3D TV technology which would work for somebody with vision in only one eye ? StuRat (talk) 04:56, 1 April 2011 (UTC)

No. Is this an April Fool's joke? No current technology can synthesize depth perception in humans who only have one eye. We do not speculate about hypothetical technology on the Reference Desk. Nimur (talk) 05:29, 1 April 2011 (UTC)

As there are numerous monocular cues to depth perception, the question is quite reasonable, and your dismissal of it seems rather abrupt. -- ToE^T 11:04, 1 April 2011 (UTC)

Wiggle stereoscopy is one possibility, but it would probably yield headaches quicker than 3D glasses. -- ToE^T 11:13, 1 April 2011 (UTC)

Good answer. As an aside, many of the concerns about spending too much time watching 3D video based on binocularity is that current methods only use binocular cues, which trains the brain to ignore the monocular cues, since they don't work properly. SemanticMantis (talk) 13:47, 1 April 2011 (UTC)

You may also be interested in reading our Autostereoscopy article. While it does not specifically mention applicability to monocular 3D, several of the technologies would seem to apply. Has anyone here ever seen a Philips WOWvx screen which uses lenticular lenses? (Unfortunately, our Lenticular printing article gives a "morphing" example and not a "3D" one, but imagine such a thing with an LCD display behind it so that a different perspective is shown when you move your head.). -- ToE^T 14:29, 1 April 2011 (UTC)

Other possible technologies are Holography and Volumetric display (e.g. true-3D displays which use a 3D grid of light-emitting points). These produce an image that can be viewed from multiple viewpoints to "see around the corners". There are really 2 definitions of 3D displays: the limited stereoscopic sort where you can only see from 2 positions (one for each eye), or true 3D where you can actually move around an object (or equivalently, rotate it) to see multiple sides of it like examining an actual 3D object/sculpture. --Colapeninsula (talk) 13:22, 4 April 2011 (UTC)

Thanks for all the answers, so far. StuRat (talk) 23:31, 6 April 2011 (UTC)

Prevost theory of heat exchange

Prevost theory of heat exchange Statement & explanation pls.. —Preceding unsigned comment added by 114.79.154.72 (talk) 07:12, 1 April 2011 (UTC)

Early versions of the caloric theory of heat involved two "fluids" - a caloric fluid that was produced by hot objects, such as a fire, and a frigoric fluid that was produced by cold objects, such as ice. In 1790 Swiss physicist Pierre Prévost argued that there was only a single fluid involved - caloric fluid - and that cold objects cooled their surroundings because they absorbed more caloric fluid than they produced. See here and here for more details. Gandalf61 (talk) 08:30, 1 April 2011 (UTC)

parasite chain

I recently read the news that they discovered virophages, small viruses that can only replicate when they co-infect a cell with another virus. They basically function as parasites to that virus. When reading this I was wondering how long the longest 'parasite chain' we know is. Example: when a human is infected with a tapeworm, which in its turn has bacteria in its bowel, this would be a three-level chain. I know you have plenty of external parasites like lice, but in this case I am specifically referring to endoparasites, life within life.

I've been doing some quick google searches but that didn't turn up with anything, and wikipedia was no help either. Of course, since I am interested in the longest chain of parasites, liberty with the term parasite is warranted. Bacteria and viruses are also allowed. —Preceding unsigned comment added by 131.211.27.97 (talk) 09:07, 1 April 2011 (UTC)

I don't know, but a large parasite like Cymothoa exigua or Emerald cockroach wasp might help add a level to your chain. Ariel. (talk) 10:46, 1 April 2011 (UTC)

The longest chain likely involves Ichneumonid wasps. See a nice story about their lifestyle here: [4]. Note that you will find longer chains with parasitoids, which kill their host, compared to parasites, which do not. A parasitoid that targets parasitoids is known as a hyperparasitoid, so this class by definition has a length 3 chain. Googling /hyper-hyperparasitoid/ returns some hits, but many are from amateur blogs, and don't contain detailed species info. SemanticMantis (talk) 13:43, 1 April 2011 (UTC)

Pressure at the seabed

If you dropped a weighted 1 litre bottle or balloon of air into the sea above the Challenger Deep, by how much would it be compressed by when it eventually reached the seabed? After leaving it down there for a while to cool down, how close would this be to becoming liquid air? Thanks 92.15.8.176 (talk) 11:01, 1 April 2011 (UTC)

What temperature was the air before you dropped it? I have assumed 300K. By my calculations, the density of air at Challenger Deep temp and pressure would be 1208x greater then that on the surface. Assuming your balloon can tolerate this change (a bottle would not), it should be .827 mL at the bottom. I don't know if this would make liquid air since I don't have the appropriate graph handy showing the state of air at the various temps and pressures. Googlemeister (talk) 13:01, 1 April 2011 (UTC)

According to this, nitrogen cannot be liquified at temperatures above 147 degrees C, which is the critical temperature for that gas - as air is a mixture, things will be a little different but it suggests that the contents of the balloon (or squashable plastic bottle) will remain in a gaseous state. Mikenorton (talk) 14:02, 1 April 2011 (UTC)

Typo alert: the critical point for N₂ is minus 147 °C. The critical pressure is about 34 atmospheres, so at 1208 bar it would be a supercritical fluid rather than an ordinary gas (this is a gradual matter, but I doubt it would behave much like an ideal gas). –Henning Makholm (talk) 14:17, 1 April 2011 (UTC)

Thanks for spotting the typo, now fixed. Mikenorton (talk) 15:07, 1 April 2011 (UTC)

1208 bar was used with ideal gas properties. If the air starts to behave as a non-ideal gas at some higher pressure, then my volume is not going to be accurate. Googlemeister (talk) 14:52, 1 April 2011 (UTC)

(EC) The density of liquid air is about 870 kg/m³, which is about 710 times greater than the density of air, which is about 1.225 kg/m³ at sea level. But the article section Challenger Deep#History of depth mapping from the surface mentions a pressure of up to 1099 times the pressure at the surface (which is the same as air pressure at the surface). Boyle's law becomes increasingly inaccurate as the pressure of air approaches that of liquid air, but 1099 is a fair bit greater than 710, so it's fairly safe to say that a balloon full of air that's been pulled down to that depth would indeed turn into liquid air. 1 l of air at the surface would turn into 1/710 l = 1.41 ml of liquid air. Red Act (talk) 15:03, 1 April 2011 (UTC)

As indicated above, the contents under those conditions (the critical pressure for air being just over 37 atmospheres) would be a supercritical fluid, which is not a liquid in any normal meaning of that word. Mikenorton (talk) 15:40, 1 April 2011 (UTC)

I stand corrected. Red Act (talk) 04:26, 2 April 2011 (UTC)

The 1208 or 1099 bar down there makes the roughly 0 bar of space seem mild and harmless. If Red Act is correct, could there be pools of liquid air down there, with water floating above it like oil over water? 92.15.8.176 (talk) 15:15, 1 April 2011 (UTC)

I would expect it to mix into the water and actually be indistinguishable from what is usually described as "gasses disolved in water" at more familiar lower pressures. Roger (talk) 15:37, 1 April 2011 (UTC)

And even if it didn't, it would rise above the water, 870 kg/m³ being less dense than water (1000 kg/m³ at surface pressure, increasing very slightly with pressure). –Henning Makholm (talk) 15:59, 1 April 2011 (UTC)

As pointed out by others above, the ideal gas law will not be a good approximation at such high pressures. Van der Waals equation should work much better. Dauto (talk) 04:43, 2 April 2011 (UTC)

Butterfly effect

Consider going outside, flapping your hands violently and then wait for some months until CNN reports that some tornado has hit some particular town in the US. Then, if one assumes that flapping your hands caused the tornado, you could formulate this assumption as saying: "had you not gone outside and flapped your hands, that particular town would not have been hit by the tornado".

Let's look at this precisely. Consider the exact physical state of the Earth that corresponds to you going outside, flapping your hands, which evolves under time evolution to a final state corresponding to that town being hit by the tornado. Then we can consider an alternative initial state corresponding to you not going outside and flapping your hands, but everything else is left the same. Such a state would then not evolve to the final state where the town is hit by a tornado.

One can then object to this analysis by invoking quantum fluctuations. Both intitial states will actually evolve to some complicated superposition of "classical states". So, in both cases, you end up with a probability distribution over the possible states of the weather, and in both cases there is some probability that the particualr town will be hit by a tornado. Only if the probabilities are significantly different, can we say that flapping your hands outside caused the town to be hit by the tornado.

So, what does a fully fledged analysis from first principles show? Can the effect of flapping your hands be more dominant than the effect of quantum fluctuations as far as long range weather patterns is concerned on some time scale? Obviously, if you take the time scale too long, quantum fluctuations will dominate, take it too small and the effect of the hand flapping won't have led weather patterns to diverge much relative to the counterfactual initial state, so there may be some intermediary time scale on which there is a significant effect...

Count Iblis (talk) 16:03, 1 April 2011 (UTC)

No!190.148.136.60 (talk) 16:58, 1 April 2011 (UTC)

Yea, tornadoes don't form from slight air movements that grow over time. They start from temperature and humidity differences which cause supercells to form. So, while your analysis method seems reasonable, in general, it doesn't apply to this particular example. Perhaps a better example would be if you divert a small stream and wonder if this diversion will cause a new Grand Canyon to develop, or fail to develop. If you diverted the Colorado River too late, the Grand Canyon would have already formed, and, there being a big hole in the ground, water would have found a way into it to continue the erosion, in any case. Had you diverted it too soon, then, over time, as the course of rivers change, it would have likely find it's way back to a location where conditions were suitable for the formation of a Grand Canyon (not necessarily in the exact same spot, though). StuRat (talk) 17:37, 1 April 2011 (UTC)

The formalization of your question is something like the following: "Is the occurrence of a tornado Lyapunov stable with respect to a small perturbation of air caused by waving your hand?" I think most aeronautical engineers, global climate modelers, and complex systems theorists would say a resounding "yes", based on gut intuition (meaning that your hand-waving does not alter the course of the tornado's formation or non-formation); but to derive that gut intuition from first principles is downright impossible. In other words, most scientists will tell you the following: waving your hand had some effect on the weather. However, the effect was so small, that it is unlikely that it affected bulk air mass motion in a significant way; as a single event, your hand-waving activity did not alter the course of the weather. Read our Lyapunov stability article, read about techniques to mathematically model complex systems, and read about bifurcation theory, which formalizes the parameters that cause the outcome of a complex system to split into one of two states (e.g., "tornado happens" vs. "tornado does not happen"). As you can see, "affecting the system" by waving your hand is not synonymous with "causing a tornado." Nimur (talk) 21:28, 1 April 2011 (UTC)

Or read our article on the Butterfly effect, noting that the first paper on the effect was titled Does the flap of a butterfly’s wings in Brazil set off a tornado in Texas?. Our article explains why the answer could easily be yes. In short, I don't think the intuition of scientists who are familiar with chaos theory accords with yours. The basic reason is that atmospheric flow is very turbulent, and turbulence is generally believed to imply dynamical chaos, and therefore sensitive dependence on initial conditions (i.e., lack of Lyapunov stability). Looie496 (talk) 22:00, 1 April 2011 (UTC)

Admittedly, I am not an expert in the dynamic modeling of atmospheric weather phenomena. As Looie496 correctly points out, my intuition should not be interpreted as scientific fact. Nimur (talk) 22:37, 1 April 2011 (UTC)

In the OP's thought experiment, two different degrees of hand flapping are considered as alternative initial states. One can think of "degree of hand flapping as an input variable with a continuous range from "no flapping" which won't cause a tornado, to "super-gigantic hand flapping" which would manage to start a tornado. However the possible degrees of hand flapping are not continuous because they are quantised. Somewhere in the range there is a quantum step that makes the difference between tornado or no tornado. (This argument has to assume that thermal vibrations are deterministic.) Cuddlyable3 (talk) 12:30, 2 April 2011 (UTC)

The whole point of chaos theory is that perturbations, no matter how small, result in drastically different end states if you wait long enough than if those perturbations weren't there. As a weather system was where chaos was accidentally discovered, the Butterfly Effect is a nice catch-phrase illustration. Regardless of little consistencies and stabilities in your own town on a particular day, at some scale weather is chaotic, so you flapping your arms today would mean that, in a year or so, a tornado that was going to hit Kansas on Tuesday now hits it on Wednesday.

However, by the very same principle, there is no way to know, nor reason to care about, what would have happened had you not flapped your arms, for the reason that regardless of this, there was a tornado, and tornadoes happen regularly in Kansas. The very chaotic nature of weather systems gives it paradoxical stability - if you try to mess with the weather in a deliberate fashion, you will pretty much fail completely. (can someone help me remember what this is called, this chaotic/nonlinear resilience, which supposedly is featured into the London bus system?) SamuelRiv (talk) 07:35, 5 April 2011 (UTC)

Ok., but one should be able to say that the tornado wouldn't have been within some bandwith in time and space, had I not flapped my arms some time earlier. This assumes that the weather is exactly described by a deterministic model (which is chaotic). If we now take into account quantum fluctuations, then if you wait long enough after the arm flapping, you can no longer say that there is either a tornado or no tornado inside that bandwith, you have a probability for this, which is fundamental. The arm flapping may influence this, but this can be completely insignificant. So, for the statement to be true, one has to be sure that quantum fluctuations won't have washed out the effect of the arm flapping.

A dumbed down estimate can perhaps be give as follows. Since we consider thermal fluctuations to be deterministic, these are not relevant, so this suggests that it is easier to describe the system in terms of the molecules it consists of, instead of using some effective hydrodynamical description. In the classical description, you can say that the perturbation due to the hand flapping amounts to a shift in phase space of the system due to the displacement and change in velocity of a large number (n) of molecules.

The quantum fluctuations can be described in a dumbed down way as follows. You can think of phase space as being fuzzy, it is effectively divided in cells of volume h^3N, where N is the number of molecules. The effective uncertainty in a component of the position vector of a molecule is approximately the thermal de-Broglie wavelength of ${\frac {h}{/sqrt{mkT}}}$, while the uncertainty in the momentum components is ${\sqrt {mkT}}$.

Then, I think, we should compare the displacement in phase space due to the momentum change of the n molecules of 3 n m v to the displacement due to assigning each of the N molecules in the atmosphere a random uncertainty in momentum of magnitude ${\sqrt {mkT}}$, which amounts to a displacement of ${\sqrt {3mkTN}}$. Putting in tsome estimated numbers, I find that the latter distance is about 14 times larger, so this suggests that quantum fluctuations always dominate... Count Iblis (talk) 00:43, 6 April 2011 (UTC)

I see that I made a few mistakes here :( . I'll correct them tomorrow. Count Iblis (talk) 00:51, 7 April 2011 (UTC)

'Carbonating' a drink with N2O

Could a drink feasibly produced with nitrous oxide dissolved in it rather than carbon dioxide? I figure it wouldn't taste the same, but would the gas even go into solution?

Thanks, Daniel (‽) 17:00, 1 April 2011 (UTC)

Nitrogen is used to serve draught Guinness among other beers. --TammyMoet (talk) 17:24, 1 April 2011 (UTC)

Nitrous oxide is usually regulated. Medical-grade stuff is hard to get a hold of; almost everywhere else you can buy the gas, it will have a small amount of added sulfur to prevent huffing (a stupid, but common, problem). N2O has other hazards, including spontaneous decomposition and ignition. Finally, worth noting that CO2 works to form carbonic acid in solution (adding a sharp "tangy" taste); I don't think N2O will have that effect, but it can and does dissolve in water in small quantities. It is also common to see N2O in food as a whipped-cream propellant - the gas bubbles in and "aerates" the whipped cream. I'm not sure where those food processors and manufacturers get a hold of unadulterated gas - it's probably not easy. Nimur (talk) 17:49, 1 April 2011 (UTC)

Of course, other acids can be added. In the case of citric acid, it's probably better for you than carbonic acid, too. Also, does the N₂O form nitric acid ? StuRat (talk) 18:12, 1 April 2011 (UTC)

Whipped cream is made with Nitrous oxide if it comes from an can (Would not work with sour carbon dioxide). So drink a can of Whipped cream or by a small propellant bottle for a Whipped cream maker which looks ver similar to the ones used for making sparkling water.

.--Stone (talk) 21:17, 1 April 2011 (UTC)

The Henry's Law data for carbon dioxide and nitrous oxide are pretty similar: about 0.034 vs 0.024 for the solubility constant (respectively), and 2400 vs. 2700 for the temperature dependence constant. [5][6] I'm not so sure about the biological effects of having N2O coming out of solution in your stomach, however - it can't be buffered to a bicarbonate salt, and I haven't looked up relative anaesthetic potency. Wnt (talk) 11:47, 2 April 2011 (UTC)

I'm not sure where those food processors and manufacturers get a hold of unadulterated gas. Are you talking about the US? In Australia it's not hard for a catering or related business to buy food grade nitrous from a wholesaler. Vespine (talk) 23:19, 3 April 2011 (UTC)

List of nuclear reactors using MOX fuel

Hello, what is the list of nuclear reactors using MOX fuel in Japan? and in the world?--88.160.13.244 (talk) 18:54, 1 April 2011 (UTC)

Japan, as of January 2011: 1. Genkai 3, 2. Ikata 3, 3. Fukushima I 3, 4. Takahama 3 .[7][8] As of January 2011 there were 21 MOX fuel plants in France. I don't have other numbers handy. There are other MOX reactors in Belgium, France, Germany and Switzerland [9], as of 2009, at least. --Mr.98 (talk) 16:25, 2 April 2011 (UTC)

Info needed on Broyer Canyon, Brown County, Nebraska

Other than it's location [10], I can't find any info, such as it's history, and, specifically, who it was named for. Any help would be appreciated. StuRat (talk) 19:08, 1 April 2011 (UTC)

Also, going to the satellite or hybrid view, and zooming in as far as you can without losing the satellite image, there appears a white linear feature to the ENE of the canyon. This feature runs from the SW to the NE and looks to be man-made. It looks to be about 10 meters long. What is it ? StuRat (talk) 19:14, 1 April 2011 (UTC)

How about telephoning the Ainsworth Public Library and asking if their reference librarian can direct you to a book on local history? I've found that many small town libraries have local historians and/or local history book repositories that aren't published/available in the "outside world." As far as your mysterious white linear feature - well, the aerial photo is blurry, so it could be anything: a photographic glitch; a man-made structure; an exposed pipe or power line; a light-colored sand/gravel pit; it's not possible to tell from the aerial photo. Nimur (talk) 20:56, 1 April 2011 (UTC)

I'll second Nimur on checking the local library. As for the white object, it has some height to it, so I'd rule out glitch or depression - I'd say a building, or it's about the right size and shape to be a trailer, though I have no idea how it would've gotten there. Kmusser (talk) 17:28, 5 April 2011 (UTC)

Stanless Steel Grades

I've scaned several articals and charts pertaning to the various grades of Stainless Steel and could not find which grades of stainless steel a magnet will not stick to. If you could please E mail a chart that shows this or direct me to where I can view and down load a chart.

Thanks,

Peter Corcoran —Preceding unsigned comment added by 72.164.33.18 (talk) 20:22, 1 April 2011 (UTC)

Most austenitic steels will be non-magnetic, while most ferritic and martensitic steels will be magnetic. --Carnildo (talk) 01:39, 2 April 2011 (UTC)

300 series stainless has a higher iron content and is semi-magnetic. 400 series stainless is very slightly magnetic. To have an unnoticable magnetic characteristics, you would have to get nickel-chrome alloys like inconnel, hastalloy or waspalloy. The high nickel and chrome stainless steels are very expensive, though. They are aerospace materials that are used mostly for aircraft and spacecraft parts —Preceding unsigned comment added by 108.67.181.74 (talk) 04:04, 2 April 2011 (UTC)

April 2

911

is 911 a federal or local number — Preceding unsigned comment added by Wdk789 (talk • contribs) 02:54, 2 April 2011 (UTC)

Neither and both. See 9-1-1 for the history - it's the standard in Canada too. 9-1-1 call centers are locally administered, but the FCC and its Canadian equivalent set the standard. Acroterion (talk) 03:07, 2 April 2011 (UTC)

if u call from a cell phone without e 911 how does it route it to your city call center — Preceding unsigned comment added by Wdk789 (talk • contribs) 03:11, 2 April 2011 (UTC)

The very same article you were directed to above answers that question, if you read doen to the section titled "wireless telephones". --Jayron32 03:36, 2 April 2011 (UTC)

no it dont — Preceding unsigned comment added by Wdk789 (talk • contribs) 04:40, 2 April 2011 (UTC)

It did, but if you need more details, the article Enhanced 9-1-1 has more as well. --Jayron32 05:32, 2 April 2011 (UTC)

just answer me — Preceding unsigned comment added by Wdk789 (talk • contribs) 06:50, 2 April 2011 (UTC)

We did. We're not going to copy and paste the words from the articles here just because you don't wish to click the name... --Jayron32 06:52, 2 April 2011 (UTC)

it dont help i read it — Preceding unsigned comment added by Wdk789 (talk • contribs) 10:46, 2 April 2011 (UTC)

Wikipedia articles are written in the same English that we are speaking here. Some readers find that articles like these [11] [12] are easy to read. Cuddlyable3 (talk) 11:04, 2 April 2011 (UTC)

In summary, cell phones either transmit their geographical coordinates to the 911 station by a GPS system or location identified from the cell tower, or the caller has to tell the emergency reponders his/her location. ~AH1^(TCU) 23:20, 3 April 2011 (UTC)

Energy

A 10 W Fluorescent lamp and a 10 W LED Tube light blows for one hour. Will they use same amount / quantity / level of energy? —Preceding unsigned comment added by 122.172.158.243 (talk) 07:09, 2 April 2011 (UTC)

Yes, but the LED is more efficient - more energy is converted into light. Plasmic Physics (talk) 08:33, 2 April 2011 (UTC)

To clarify. "10 W" is the electric power taken by the lamp. After one hour each lamp has dissipated 10 watt-hours, which is the quantity of energy one pays for. The LED tube gives more light from its energy consumption and has a longer life, but it costs more to buy in the first place. Cuddlyable3 (talk) 10:51, 2 April 2011 (UTC)

You meant "glows" instead of "blows", I assume ? There's also the issue that they don't seem to always count the electricity used in the electrical ballast in the base. So, is that 10W the amount used in the bulb only, or including the ballast ? StuRat (talk) 15:38, 2 April 2011 (UTC)

If the flourescent is a compact fluorescent bulb, then the energy lost in the ballast or electronic circuit should be included. If it is, say a 4 foot 32 watt straight fluorescent tube snapped into a light fixture, I would expect additional energy to be used in the ballast. Edison (talk) 19:41, 2 April 2011 (UTC)

What plant is that?

I noticed this in Budapest, Hungary.

Amongst the branches of a tree there was a very distinct bulb of leaves that seemed to be separate from the tree, an individual plant, different in colour (vividly green, unfortunately not seen on the photos). I don't think it's a birds nest. What could it be?

http://i53.tinypic.com/3586yp1.jpg

http://i52.tinypic.com/25ti6wz.jpg —Preceding unsigned comment added by 109.74.50.52 (talk) 08:27, 2 April 2011 (UTC)

Might be mistletoe. 77.3.139.229 (talk) 08:51, 2 April 2011 (UTC)

I think you've nailed it. Thank you!

109.74.50.52 (talk) —Preceding undated comment added 09:51, 2 April 2011 (UTC).

Eggs and earthquakes

Does an earthquake destroy eggs? Clearly they are in danger being hit by some crashing building or to fall out of the nest and hit the ground, but aside of that, is an earthquake strong enough to shake them so violently that they break? 77.3.139.229 (talk) 11:26, 2 April 2011 (UTC)

If you were asked to predict whether the egg falling from the nest will break, you would need quantitative information on the peak acceleration (deceleration) of the egg, the resilence of the surface that it contacts, and the geometry and material stiffness of the particular species of egg. The same difficult-to-supply information is needed to answer your question. Cuddlyable3 (talk) 12:41, 2 April 2011 (UTC)

I see you are right and it would be better to ask for information about acceleration magnitudes from earthquakes, preferably related to the common scales for earthquakes.Where can I find such information? 77.3.139.229 (talk) 15:32, 2 April 2011 (UTC)

Assuming the egg didn't fall or have something fall on it, it would depend on what surface the egg is in on. If it's on a soft surface, like the container they come in from the grocery store (or, presumably the nest), it should be fine. On a hard table, with a strong enough up-down ground motion, it might crack. A side-to-side motion could knock it off the table, but we already excluded that case. It might also run into something on the table. Again, if it's soft, like a cereal box, it should survive, but hitting a hard object like a cereal bowl might crack it. StuRat (talk) 15:33, 2 April 2011 (UTC)

Ah, I see this splits the question into three different aspects: 1) could the first acceleration damage the egg? 2) (I didn't think of it previously) could a vertical acceleration that lifts the egg without damaging it be strong enough that it cracks on falling back (hitting the same material that sent it off flying)? and 3) is it possible that eggs laying next to each other are accelerated horizontally in a way that they hit each other so that they get damaged? Note that I am not especially interested in eggs, it is just some kind of place-holder for something fragile that everyone has a common experience about. 77.3.139.229 (talk) 16:09, 2 April 2011 (UTC)

I see. Stability also comes into play here, as items in stable positions won't tend to fall. So, things on shelves are more likely to be damaged than things on floors. Of course, the stability of other things which could fall on top also matters. A long item (say a lamp) balanced on it's end will also be less stable than one on it's side. One interesting result of this is that it may make sense to leave everything where it lands after the initial quake (as those positions will tend to be more stable) until the aftershocks subside. You might also move things into more stable positions that survived the first quake (like putting lamps on their sides on the floor). StuRat (talk) 16:29, 2 April 2011 (UTC)

It is the momentary distortion of the"egg shell"shape during impact which causes the structural failure of the shells cohesive integrity. To protect the shell from damage from violent motion it's important to make certain that what ever energy absorbing packing material you use (eg.styrofoam) must make perfect contact with the whole of the shell surface so that kinetic energy induced by motion will be transfered to the packing material evenly at all points of the shell thereby eliminating shell ditortion and breakage. I'm not a mathematition but I'll bet one of our wikipedien freinds here can come up with an equation for that concept.190.56.107.186 (talk) 17:24, 2 April 2011 (UTC)

Simply divide the force exerted on the egg shell by the area of the shell where the force is applied, to get the average pressure. If that's high enough, the shell will break. If the force is unevenly applied, then you'd need to know the maximum pressure. Don't forget the force on the opposite side of the egg, too, where it pushes against the container. StuRat (talk) 04:39, 3 April 2011 (UTC)

See peak ground acceleration and dome. ~AH1^(TCU) 23:17, 3 April 2011 (UTC)

Double-heading

Having just watched a double-header pass through my home town, I'm curious about the physics of double-heading steam locomotives. Presumably it is important that both engines exert roughly the same force, but how critical is this and how do the two crews arrange it, especially since communication between them is very limited?--Shantavira|^{feed me} 12:52, 2 April 2011 (UTC)

Why would communication be very limited? Wired telephony has existed since the 1800s, and presumably the crews today would have a wireless system, with in-ear receivers and noise cancellation systems in place to allow for ease of communication... --Jayron32 14:45, 2 April 2011 (UTC)

Or even more directly, it's hard to imagine that the operators in one locomotive don't have some more direct way to know what the speed/pressure/whatever is in the other locomotive. That kind of "communication" technology would not have to be very sophisticated, I wouldn't imagine. Though honestly I have no clue about trains. --Mr.98 (talk) 16:29, 2 April 2011 (UTC)

The simple fact is most steam locomotives didnt have wired telephones to other parts of of the train, and that since steam engines in the modern day are run for mostly the sake of nostalgia, they still dont. —Preceding unsigned comment added by 92.20.201.71 (talk) 00:26, 3 April 2011 (UTC)

I've wondered about the physics here, too. Here's how I've come to think about it:

One question is, what does the throttle setting on an engine actually do? Does it control how fast the engine tries to turn (i.e., in revolutions per minute), or how hard the engine is trying to work?

It's pretty clear that, for most engines, the answer is the latter. Think about a car: if you kept the accelerator pedal depressed with your foot to exactly the same position, you'd notice yourself going more slowly up hills, and more quickly down. If you jacked the car off the ground and kept the pedal depressed to the same position (or, more simply, put the transmission in neutral), the engine would rev to a very high speed indeed.

And in fact, typically what an engine's throttle does is control the rate that fuel is used. So by one of the most basic principles of physics there is, conservation of energy, the engine is going to try to do precisely enough work to transfer the amount of energy per unit time as is contained in the amount of fuel it's provided in that unit of time.

(Side note: some engines do have to move at a constant speed, but that's typically achieved by use of a governor, a basic mechanical feedback device which adjusts the engine's throttle so that the engine is always doing just the right amount of work to offset its -- possibly varying -- load, such that the speed stays constant.)

So, anyway, what happens if the two engines don't have their throttles set to precisely the same position, or if the two engines have significantly different power capacities, or for whatever reason aren't providing exactly the same force?

I used to think that the "stronger" engine would do all the work, and that the "weaker" would get a free ride. But no. If at any instant the stronger engine manages to do more work and pull ahead of the weaker one, the weaker one will see less resistance, and will speed up, until it is pushing, too.

The same physics end up applying in other situations. Suppose you've got a car that's stuck, and two of you are trying to push it, but you're not strong enough, and you hail a passerby, who agrees to help, and with the combined strength of three of you, you manage. Was it necessary that all three of you provided equal force? No. The force on the car is the simple algebraic sum of the forces provided by the three pushers. Every little bit helps.

I also wonder about those tag-along trailer bikes for kids. The adult on the bike in the front is clearly doing the lion's share (often all) of the work, but if the kid is actually pushing, would the adult feel the difference, that's he's having to do marginally less work to keep the train going? I think so. (It would also be instructive to interview people who ride ordinary tandem bicycles about their experiences when one rider is significantly stronger or is for whatever reason working harder than the other.)

Finally, I'm reminded of the story of two people who are trying to move a large, heavy piece of furniture through a doorway. They push and strain, but they just can't make it. A third person comes along and tries to help, but even with three people pushing and pulling, this way and that, they still can't get it to budge. Finally the newcomer says, "You know, I don't think we're ever going to get this thing into the room." "Into the room?", the other two exclaim. "We were trying to get it out!" —Steve Summit (talk) 17:24, 2 April 2011 (UTC)

Now, when I said, "the engine is going to try to do precisely enough work to transfer the amount of energy per unit time as is contained in the amount of fuel it's provided", that's a bit of a simplification. It can take a fair amount of engineering to realize a practical engine that can in fact transfer large amounts of power effectively and efficiently, even as the speed varies. It was probably simpler back in the days of steam, although even then, there were abstruse complexities having to do with, say, the cutoff. And the diesel-electric control section in our article on diesel locomotives goes into quite a bit of detail about how complicated the power control can be for a modern locomotive. —Steve Summit (talk) 17:37, 2 April 2011 (UTC)

In the days of the Midland Railway Company (who regularly used double header steam locomotives on the Settle-Carlisle Line where the practice was implicated in two accidents near where I live), the drivers were sufficiently experienced to know what sort of head of steam was required for different sections of the track, but I suspect that they just signaled to each other to approximately match power on setting off. If there was a big difference in power output, then the wheels would slip on the rails because they are linked to the pistons in the locomotive so they are much more likely to slip than those on the carriages. Dbfirs 18:01, 2 April 2011 (UTC)

It occurs to me that a considerably more interesting problem occurs when you have a helper engine at the rear, assisting one or more engines which are pulling conventionally from the front as a long train attempts to ascend a grade.

When two engines are both pushing (or pulling) from the same end, they're more or less rigidly coupled, so their speed stays the same, and the only thing that varies (that can vary) is the amount of force each applies.

But if some are pulling from the front, and some are pushing from the rear, the "slack" of the train comes into play. (The full train is far from rigid.) Some portion of the train will be being wholly pulled from the front, and some portion wholly pushed from the rear. If the rear engine(s) work a little harder than necessary, the demarcation point will move forward through the train (i.e. with more cars being pushed); if it/they slack off; the point will move back. Moreover, the feedback from this -- the point at which there's clanking as some car or another shifts from being pushed or pulled -- is invisible/inaudible to the engineers at both the front and the rear. So that must have taken some skill! —Steve Summit (talk) 20:29, 2 April 2011 (UTC)

Assuming the rear engine is not powerful enough alone to push the train, if he just goes at full throttle, the front engine controls simply adjusts their throttle until the required speed. The same principle occurs to both cases, one engine can just provide a constant force which adds to the force provided by the one which is regulating the speed. —Preceding unsigned comment added by 92.20.201.71 (talk) 00:23, 3 April 2011 (UTC)

Yes, there is some information about this problem at bank engine, but I suspect the physics of double-heading are different.--Shantavira|^{feed me} 08:26, 3 April 2011 (UTC)

In the days of steam it was not uncommon to see double headed trains being banked up the Lickey Incline, so two at the front and one at the back, or single headed trains being double banked, one at the front two at the back, and I'm almost sure (accepting that it was quite a long time ago) that some double headed trains also needed to be double banked, so two at the front and two at the back. All of which they seemed to manage without any problem. Mikenorton (talk) 09:04, 3 April 2011 (UTC)

Engine braking

When shifting down a gear to aid braking, where does all the cars kinetic energy go bearing in mind that the engine revs cannot increase instantaneously?--92.28.66.20 (talk) 16:11, 2 April 2011 (UTC)

We have an article on engine braking, though it could use some work.

I've always understood that you're essentially running the engine as an air compressor, and compressing air heats it up; therefore the kinetic energy is converted into heated gases that are released, either down the tailpipe or (I now learn from the engine braking article) in the case of a diesel engine, back out the intake manifold. —Steve Summit (talk) 16:23, 2 April 2011 (UTC)

Also if you have a petrol (US=gasoline) car, then the air intake valve will be closed, and the engine is trying to create a high vacuum in the air intake manifold. With a diesel car, there is no air intake valve, so the amount of engine breaking is somewhat less.  Ronhjones  ^(Talk) 20:24, 2 April 2011 (UTC)

Worth noting is that large diesel engines (the sort you would find in a tractor-trailer/articulated truck, not the sort you would have in your Volkswagen Jetta) are often equipped with compression release engine brakes, which pop open to vent the compressed air – and release the energy stored by its compression – as the piston reaches the top of the cylinder. This makes the engine braking much more effective in diesel engines that are so equipped, but can also make a terrific racket as the valves pop open and closed. TenOfAllTrades(talk) 16:31, 3 April 2011 (UTC)

We have an article on Regenerative brake (to make good use of the energy). Dbfirs 18:03, 2 April 2011 (UTC)

why electrical arcs don't flow straight

When observing an electrical arc flow from one electrode to another or lightning between cloud and ground, I can't help noticing that (the stream of electrons)the spark does not flow in a streight line. the charge, presumably trying to reach the other node by the most direct route, should,it seems,take a direct streight line. Instead it obviously wiggles around taking many momentary directions, none of which aim directly at the target and constantly overcorrecting untill,like a shark seeking it's prey,it eventually homes in on it's target. I've tried to find an article that explains this but no luck.Can anybody explain why it doesn't travel in a direct streight line.Phalcor (talk) 18:10, 2 April 2011 (UTC)

It doesn't take the staightest line, it takes the path of least resistance. The electric field is a messy, complicated thing and does not exist as a clean, continuous gradient. It is constantly changing and in flux, not the least of which is changes created by the electric arc itself as it propagates. The two ends of the path are, of course, the extremes of the potential difference, but in between the electric field isn't a clean, regular gradient between those extremes. The result is that the electric field itself displays chaotic behavior; the electric spark will take the path of least resistance always, but that path is somewhat random and always changing. Sparks are actually highly fractal in nature, so their shape and behavior is explainable if not predictable. --Jayron32 19:20, 2 April 2011 (UTC)

(EC)With respect to an electrical arc flashing between two electrodes (assuming they are at the same height): the arc is at a temperature of many thousands of degrees, and the air and ionized gasses in and near the arc expand and become lighter than the surrounding air, so they rise in an arch shape (that is where the 'arc" got its name in the early 1800's). As for lightning bolts, much is still not known per the Lightning article. Speculating here: A bolt between cloud and cloud or cloud and ground might move in other than a straight line because it is following higher conductivity paths where there is more moisture in the air, or where ice crystals have caused a separation of charge in the atmosphere, creating an ionized path. There is no reason that the ionized path of lower resistance should be a straight line. Edison (talk) 19:36, 2 April 2011 (UTC)

A Jacob's ladder is an easily made demonstration of an electric arc being carried upwards by air convection. Cuddlyable3 (talk) 21:58, 2 April 2011 (UTC)

The path a river takes might be a simple analogy. You'd expect it to go straight, but it actually follows the terrain of the ground, which may seem flat at first look but isn't when you look at it finely enough. StuRat (talk) 04:34, 3 April 2011 (UTC)

Its actually an excellent analogy, StuRat, and we can carry it further: as the river carves the ground, it encounters differing types of soil and rock, so its course will be altered as it affects all of those soil and rock types differently. It both affects its own course through its own erosion, AND it is highly dependant on small and numerous differences in its environment on its course to the ocean. This is exactly like a lightning bolt, which has to navigate through air whose properties are different all along its course, and the lightning bolt affects its own environment by changing the electric field along its path. --Jayron32 04:56, 3 April 2011 (UTC)

Some atmospheric conditions, such as wind, can modify the lightning into ribbons. ~AH1^(TCU) 22:57, 3 April 2011 (UTC)

Name this garden flower?

In south east England: http://img16.imageshack.us/i/unknownflower.jpg/ The plant is branching, so to look at there is a mass of flowers. The flower is wilting rather. Done on a scanner. What could it be please? Thanks 92.29.121.249 (talk) 18:21, 2 April 2011 (UTC)

Looks like a night-scented stock to me. --TammyMoet (talk) 18:51, 2 April 2011 (UTC)

Thanks very much. They could be night-scented stock but when searching for images of that, they look more like the illustration I found here http://www.suttons.co.uk/Shop/Flower+Seeds/Virginian+Stock+Confetti+Mix+Seeds+137036.htm so I think they are more likely to be Virginian stock.

Slightly off-topic but I think I scattered the seeds in the autumn, and they began flowering in late March. Another scatter-and forget seed I would recommend is Love-in-a-mist (latin name Nigella). The all-blue type looks better than the multi-coloured. They both self-seed so one seeding should give many years of trouble-free flowers.

Are there any other easy scatter-and-forget seeds anyone would recommend? Thanks 92.15.9.102 (talk) 08:34, 3 April 2011 (UTC)

If the flowers are on the smaller side, then Virginia stock is probably the one. There are a number of plants that, to quote my late father, "you only have to plant once", if you can get one of these plants then you won't need to replace it (or plant anything else!): Feverfew, mint, Leycesteria, any of the geranium family, aubrieta, herbaceous potentilla, Welsh poppy. My garden contains quite a few of these! --TammyMoet (talk) 09:14, 3 April 2011 (UTC)

Aluminum foil

Why is one side shiny and the other side dull? --70.244.234.128 (talk) 19:43, 2 April 2011 (UTC)

Aluminum_foil#Properties: "Aluminium foil has a shiny side and a matte side. The shiny side is produced when the aluminium is rolled during the final pass. It is difficult to produce rollers with a gap fine enough to cope with the foil gauge, therefore, for the final pass, two sheets are rolled at the same time, doubling the thickness of the gauge at entry to the rollers. When the sheets are later separated, the inside surface is dull, and the outside surface is shiny." --Mr.98 (talk) 19:46, 2 April 2011 (UTC)

Of course, it's not that difficult. (And I notice that our article doesn't supply a source for the claim that it is.) If manufacturing tolerances were the only concern, then the much-thicker sheets of heavy-duty foil could be manufactured in single thickness, and they would have two shiny sides. Of far more interest to the manufacturer, I suspect, is the fact that running two layers of foil through the rolling press simultaneously doubles their output. TenOfAllTrades(talk) 16:45, 3 April 2011 (UTC)

What has more hydrogen?

I read somewhere that a liter of petroleum (or gasoline can't remember) has more hydrogen in it than a liter of liquid hydrogen. What about water? Does a liter of water have more hydrogen in it than a liter of liquid hydrogen? ScienceApe (talk) 19:48, 2 April 2011 (UTC)

Liquid hydrogen has a density of 67.8 kg·m-3, which means that 1 cubic meter will have 67,800 grams of hydrogen molecules, or 135,600 hydrogen atoms. Petroleum is about 10-14% hydrogen by weight (according to our article). Petroleum is a mixture of a whole bunch of stuff, but according to List of crude oil products they seem to range in API gravity from 25-60, so lets take a nice middle of API gravity of 40, which translates to 141.5/171.5 = 0.82 g/cm3 or 820 kg/m3. 10-14% of 820 = 82.0 - 114.8 kg, which is 82,000 - 114,800 grams of hydrogen atoms per cubic meter. Divide those numbers by 1000 to get the per liter amounts. So no, on average petroleum does not seem to contain more hydrogen than pure liquid hydrogen, but those are large ranges we are working with; the densest (lowest API gravity) petroleum with the highest hydrogen mass (14%) may come close or even exceed the figure; this doesn't seem all that unusual as the types of intermolecular bonding that goes on in each substance is likely to be substantially different, accounting for differing numbers of atoms per unit volume. --Jayron32 20:13, 2 April 2011 (UTC)

Editing my response. The relevent comparisons are 67,800 grams of hydrogen per cubic meter for liquid hydrogen and 82,000 - 114,800 grams of hydrogen per cubic meter for petroleum. My math got confused for a second. So yes, clearly petroleum has mor hydrogen per cubic meter than liquid hydrogen. However, as I noted before this is unsurprising, as most of the hydrogen in petroleum is bonded via covalent bonds in large molecules, while the diatomic hydrogen in liquid hydrogen is in relatively small molecules. The intermolecular distances in a substance are somewhat larger than the intramolecular distances within a molecule; since petroleum has larger molecules, it can pack more hydrogen atoms in a smaller space. While by mass most of petroleum is carbon, by number of atoms it averages a little more than two hydrogens per carbon, so it is mostly hydrogen (by number of atoms), and the larger molecule size means that those hydrogens are, on average, packed closer together than in an equivalent volume of liquid hydrogen. --Jayron32 21:46, 2 April 2011 (UTC)

What about water? ScienceApe (talk) 02:21, 3 April 2011 (UTC)

Water has a density of 1000 kg/m3. 1/9 the weight of water is hydrogen. So 1000/9 = 111 kg or 111,000 grams per cubic meter. So, it too has more hydrogen per unit volume than liquid hydrogen. --Jayron32 02:27, 3 April 2011 (UTC)

This is truly a remarkable thing to point out. If you could "teleport" the oxygen out of a liter of water, and the two hydrogens bonded directly to one another instead, you'd be left with about 111 grams of liquid hydrogen. Which would want to expand about 65% under whatever conditions are given for the density figure above! In order to get it to fit, you'd have to increase its density to the brink of the transition to metallic hydrogen (1.08 to 1.33 g/cm³).^[13] I think that this emphasizes the difference between water and a typical nonpolar liquid loosely bound by Van der Waals forces. We recall things like methane, ammonia, hydrogen sulfide don't interact strongly enough with themselves to be liquid near room temperature. I think water is so dense because the network of hydrogen bonds holds it together almost like a solid, though with less stability. In a sense, if you think of the hydrogen bonds as a very weak covalent bond, you could almost think of a mass of water as a single molecule, like diamond. Wnt (talk) 04:01, 3 April 2011 (UTC)

I dunno. I don't find it all that remarkable, but then again my primary training and experience is as a chemist and chemistry teacher, so what I am likely to find commonplace and self-evident may be remarkable to others. Modern physics works roughly like magic for me, so I guess I understand your perspective here... --Jayron32 04:40, 3 April 2011 (UTC)

You're quite correct that water's propensity to form hydrogen bonds is what allows such an otherwise lightweight molecule to remain a liquid at room temperature, but hydrogen bonding is pretty much irrelevant to the fact that liquid water has a high number density of hydrogen atoms. Any solid- or liquid-phase hydrogen-rich molecule can be expected to exceed the hydrogen concentration of liquid hydrogen. If we consider completely nonpolar liquid methane (CH₄) at its boiling point (112 K), it has a density of 423 g/L (423 kg/m³). To a reasonable approximation one quarter of that mass is hydrogen, giving a hydrogen content of 106 kg/m³—within very close hailing distance to that of liquid water (and higher than the hydrogen content of water ice). If you want to compare with nonpolar molecules that exist at room temperature, hexane and cyclohexane contain 107 and 112 kg hydrogen per cubic meter. TenOfAllTrades(talk) 17:17, 3 April 2011 (UTC)

You make a good point; but those molecules link together more than two hydrogens into a single small unit. I can understand packing together hydrogen molecules by gluing them together with carbons. What amazed me about water is that it has the same number of molecules as liquid hydrogen, and so far as I know the molecules are bigger than diatomic hydrogen, yet they end up taking up less space. Wnt (talk) 17:32, 3 April 2011 (UTC)

That's because in chemistry, bond length and bond strength are inversely proportional; the intermolecular bonding in liquid hydrogen is the very weak london dispersion forces, so the distances between those individual H2 molecules will be quite long, comparatively speaking. For liquid water, the intermolecular bonding is via hydrogen bonding, a particularly strong type of dipole-dipole force, which being a stronger bond must also be a shorter bond; indeed much shorter to the point where the distance more than makes up for the increased H-H distance through that oxygen atom... --Jayron32 21:01, 3 April 2011 (UTC)

That's similar to what I said above ... but a lot clearer. ;) Wnt (talk) 22:04, 3 April 2011 (UTC)

Hissssss touch bringsssssss... decay!

In the fictional Judge Dredd comics, the touch of the evil Judge Mortis causes a person's body to instantly decay as if the person were already dead, causing said person to immediately die. If we assume such a thing is possible, is there a specific effect of the body decaying that causes immediate death? JIP | Talk 20:21, 2 April 2011 (UTC)

The scenario you mention as context is unscientific, and is therefore not within the scope of this desk. Regarding the specific question of what effects of decay could cause immediate death, this is interesting because it highlights key structures that are actively maintained in vivo. A few examples: (i) loss of integrity of major blood vessels, leading to massive internal bleeding; (ii) widespread loss of endothelial tight junctions, leading to multi-organ failure; (iii) loss of integrity of myelin sheaths on neurons; (iv) depolarization of membranes in crucial tissues like heart and brain. I am sure there are many others. -- Scray (talk) 20:40, 2 April 2011 (UTC)

You can rot while alive, see Gangrene and necrosis. Both can cause eventual death. --Jayron32 03:45, 3 April 2011 (UTC)

Of course, but those are piecemeal processes, generally. When systemic, they are rapidly fatal. -- Scray (talk) 04:49, 3 April 2011 (UTC)

Absoltely. Which is why I brought them up. Good to see we agree. --Jayron32 04:53, 3 April 2011 (UTC)

I don't really agree, because they don't answer the original question. Probably not worth further discussion, though. -- Scray (talk) 06:11, 3 April 2011 (UTC)

Human decomposition is a complicated process. Lots of individual parts of that process would be fatal were they to rapidly and systemically occur in a living human. Red Act (talk) 07:56, 3 April 2011 (UTC)

Spontaneous human combustion? ~AH1^(TCU) 22:53, 3 April 2011 (UTC)

Don;'t some hemorrhagic fevers cause necrosis on internal organs? At least they seem to in popular media, but not having studied medicine, I expect that the truth is much less sensational then depicted. Googlemeister (talk) 14:00, 4 April 2011 (UTC)

Necrotic flesh is dead, so it's not performing its function as a collection of cells anymore. If, for instance, part of your heart necrotized (for whatever reason), the muscles would no longer be able to properly pump blood. — The Hand That Feeds You:^Bite 16:30, 4 April 2011 (UTC)

snowflakes

Why do snowflakes have hexagonal symmetry? I know that it has something to do with the hexagonal arrangement of the water molecules, but could someone be more specific? Thanks. 74.15.137.130 (talk) 20:54, 2 April 2011 (UTC)

The Wikipedia article Snowflake says the flake's six-fold radial symmetry is because the crystalline structure of ice is six-fold, and mentions several possible growth mechanisms whose details remain controversial. Cuddlyable3 (talk) 21:35, 2 April 2011 (UTC)

Thanks. 74.15.137.130 (talk) 03:21, 3 April 2011 (UTC)

Remember that not all flakes are hexagonal. Some come in the form of "columns" or "needles" and other dendrites. ~AH1^(TCU) 22:51, 3 April 2011 (UTC)

Relativity paradox

Get a sample of a fissionable material that's just under the critical mass and accelerate it to near the speed of light. While it's moving, try to start a chain reaction. From a stationary view, it should have the critical mass and thus start a chain reaction, but an observer moving with the material would see that it doesn't have enough mass. What happens? --70.244.234.128 (talk) 21:46, 2 April 2011 (UTC)

Even the comoving observer will be able to detect the added energy from the acceleration, this added energy will, from his point of view, be the source of the criticality This isn't a paradox... The two will see the excursion happen at different times, but this is due to the relativity of simultaneity. Now, I am a physics retard, so someone next will come along and explain why my explanation is wrong, but that is how I read this situation. --Jayron32 21:50, 2 April 2011 (UTC)

To the observer who's moving with the sample, its mass will still seem to be less than critical because the relative velocity is zero. --70.244.234.128 (talk) 21:55, 2 April 2011 (UTC)

Yes, but the additional forces due to acceleration will be clearly evident. In accelerating the sample, the forces on the sample will create additional pressures which, to the comoving observer, will be the source of the criticality. If the comoving observer calculates the critical mass in conjunction with the forces introduced due to the acceleration, criticality will become mathamatically explainable. Criticallity is not solely mass-dependant. You can decrease the critical mass of a substance by, for example, placing it under pressure. Accelerating it rapidly can introduce that pressure. In other words, the comoving observer will see the mass remain constant, but will be able to detect a change in density due to forces introduced by acceleration; that change in density will be his reasoning for the criticality. Again, I am a physics retard, so please wait for corrections to my explanation... --Jayron32 22:00, 2 April 2011 (UTC)

If we don't take the acceleration literally, and just consider a lump of fissionable material, rest mass just under critical, moving relative to us with near speed of light, then the answer is: No, it won't go off. It doesn't go off in its rest frame, hence it doesn't go off in our frame. 70.244... is presumably thinking of the increase of "relative mass", a popular but ultimately useless concept, and the scenario proposed here is a fine example why it is useless. Bulk motion has no effect on processes that depend only on mass, i.e. it does not increase the mass. The effective mass of the lump can be increased if internal degrees of freedom are excited (e.g. heating it up), and this may indeed happen when forces due to a real acceleration act on it. --Wrongfilter (talk) 22:29, 2 April 2011 (UTC)

The critical mass is not a Lorentz invariant. Why would you expect it to be the same in any frame? —Preceding unsigned comment added by 92.20.201.71 (talk) 00:14, 3 April 2011 (UTC)

Sorry, my answer was incredibly ambiguous in a way which did not occur to me late at night , but that Dauto has well highlighted. To rephrase: The relativistic mass is not a Lorentz invariant (even when as the rest mass approaches critical mass). Why would you expect it to be the same in any frame? —Preceding unsigned comment added by 92.20.201.71 (talk) 11:48, 3 April 2011 (UTC)

It seems to me that the standing observer and the traveling observer are both totally irrelevant to action of the material. If the mass is increased to criticality it will just do it's thing and get really hot. not neccessarily go bang.Phalcor (talk) 01:40, 3 April 2011 (UTC)

Wrongfilter's answer above is the only correct one so far. Yes 92.20.201.71, your answer is also incorrect. Critical Mass, like any rest mass, is a Lorentz invariant and that's exactly the point here. 70.244.234.128's mistake is to confuse relativistic mass (That's the one that increase with speed) AKA energy with rest mass (That one doesn't change with speed and is a Lorentz invariant) AKA mass. Dauto (talk) 03:17, 3 April 2011 (UTC)

I agree with WrongFilter and Dauto.

I'm assuming in the following that the acceleration involved is small, and it's the object's speed that's what's actually of interest.

Unfortunately, the word "mass" by itself is actually ambiguous, since the word by itself is sometimes used to mean rest mass, and is sometimes used to mean relativistic mass. You can actually start a heated semantic argument about which of the two one should reserve the word "mass" by itself to mean, and a heated debate about the value or lack thereof of the concept of relativistic mass. But unlike the word "mass", the phrases "rest mass" and "relativistic mass" are at least unambiguous.

What's actually important in determining whether an object made of fissionable material will be critical is how many nuclei of the fissionable material there are. Mass is just used as a convenient easy-to-measure stand-in for the number of nuclei, which works because the two values are proportional (the element's atomic mass being the proportionality constant). The number of nuclei there are in an object clearly doesn't change depending on how fast the object is moving. So to remove the ambiguity of the word "mass" in the phrase "critical mass", you could think of the critical mass as being the "critical rest mass", although almost nobody uses that phrase. There is no paradox involved with critical mass, because the word "mass" in that phrase means rest mass, which doesn't change with the object's speed.

As explained in Critical mass, criticality depends on other things besides number of nuclei. And some of those things are indeed measured to change when an object is moving at great speed, due to length contraction. However, the Lorentz factors wind up balancing each other out, so the critical mass is again unaffected by an object's speed. But I won't get into that in detail, since you just brought up the potential paradox due to relativistic mass, and didn't bring up any length contraction issues at all. Red Act (talk) 03:49, 3 April 2011 (UTC)

April 3

Newton's Second Law

Newton's second law says that F = ma. If there a[re] several forces f_i acting on a particle, then Σf_i = ma. Does this last rule -- that the resultant force is the vector sum of the individual forces -- follow from Newton's second law, or is it an independent law? 74.15.137.130 (talk) 03:26, 3 April 2011 (UTC)

I don't know that that is a law so much as a basic mathematical concept. It predates Newton by some several centuries, and I doubt he considered it more important dwell upon than any other basic mathematical concept. See Euclidean_vector#Addition_and_subtraction for the basics, but I am pretty sure the details of simple vector mathematics were commonly understood and part of mathematical canon by the time Newton came around. --Jayron32 03:44, 3 April 2011 (UTC)

I think F refers to net force. In other words, F = Σf_i. — DanielLC 03:52, 3 April 2011 (UTC)

It has to be shown, of course, that vectors (which add and subtract like that by definition) are actually a good model for forces, so that the mathematical concept of vector addition corresponds to the physical concept of superposition of forces. One might think of some sort of interference between two forces of different origin acting on the same body. I do not know how Newton dealt with that or whether he had given this point any thought at all. The section Euclidean_vector#History is hardly existent, but it appears that the concept of a vector essentially was developed after Newton. The German article mentions Hermann Grassmann, 1844. --Wrongfilter (talk) 07:16, 3 April 2011 (UTC)

This is a consequence of the fact that Newton's second law is a linear differential equation, and so, roughly speaking, you can break down the force F on the left hand side into components, solve for each component, then add the individual solutions together again to get a solution for F - see superposition principle. Many (or perhaps most) physical laws are non-linear (there is a long list in the non-linear differential equation article) and general explicit solutions are not so easily obtained. Gandalf61 (talk) 08:30, 3 April 2011 (UTC)

But it's usually done the other way around. If a point mass is in a gravitational field, it will feel a force F_g, producing an acceleration F_g/m. If you push on it with a force F, then the acceleration becomes (F_g + F)/m. The fact that, no matter how many forces are acting on it, the net force can always be decomposed to include the gravitational force that would be present were there no other forces seems to be independent of Newton's Law. 74.15.137.130 (talk) 19:13, 3 April 2011 (UTC)

To be cleaner, we'll have to scrub ourselves from the inside-out too. How will we?

Sadly, the shower only cleans our outer shells. Yet in the meantime, metabolic filth keeps accumulating on our insides, causing us to visually age, get the old people smell, and eventually die from having too much of this inner filth.

In the future, what will be some ways to clean out the insides of our bodies? (And this would extend our life expectancies now would it?)

Until then, besides washlets, what are some ways to scrub ourselves from the inside-out in the present day? How well do they work, and will there be any side-effects? --70.179.169.115 (talk) 06:51, 3 April 2011 (UTC)

Enemas (Shakespeare's "clyster pipes") have been in use for centuries. We cannot give medical advice about effectiveness. I don't know whether there is any validity in the concept of death by "metabolic toxin". Dbfirs 07:57, 3 April 2011 (UTC)

Colonic irrigation. --TammyMoet (talk) 09:09, 3 April 2011 (UTC)

Eat enough vegetables, fruit, and wholemeal/wholegrain. See http://www.nhs.uk/livewell/5aday/pages/5adayhome.aspx/ 92.15.9.102 (talk) 09:28, 3 April 2011 (UTC)

In the future, we may use nanomedicine. Mitch Ames (talk) 09:57, 3 April 2011 (UTC)

You don't want your insides too clean. A healthy community of gut flora provide many essential services to the body. "The metabolic activities performed by these bacteria resemble those of an organ, leading some to liken gut bacteria to a "forgotten" organ." You could probably live without gut flora, but I'm happy to keep mine intact. SemanticMantis (talk) 14:31, 3 April 2011 (UTC)

Sounds like it's time for the great goldenseal debate... ;) no, I'm not saying it works for that... Wnt (talk) 17:24, 3 April 2011 (UTC)

Have we still not evacuated the washlet subject adequately for the OP yet? Cuddlyable3 (talk) 21:00, 3 April 2011 (UTC)

I'm not sure the idea of "inner filth accumulation" is really something supported by science. Maybe you should look into that a bit before you decide to "clean out your insides".. Our bodies are quite good at self regulating and self cleaning, unless you have something wrong with you, generally you only need to worry about the cleanliness of your outsides. Aging and "old people smell" isn't anything to do with inner filth that you could clean out, as far as I know it's ultimately related to telomerase shortening. Vespine (talk) 22:53, 3 April 2011 (UTC)

On the other hand, the notion that unspecified harmful substances routinely accumulate in the body and must/can be removed by means of some deliberate cleansing procedure is an ever-popular staple of medical pseudoscience. It must somehow resonate deeply with what people are prepared to believe. –Henning Makholm (talk) 23:16, 3 April 2011 (UTC)

There is such a thing as Bioaccumulation and I have never seen any evidence that humans are immune to it. Of course, you can't just scrub the mercury out of your system, but the I would expect that "unspecified harmful substances" do routinely accumulate in the human body just as readily as they do anything else. Falconus^{p t c} 12:57, 4 April 2011 (UTC)

Isn't this supposed to be the science desk? 'eventually die from having too much of this inner filth' is at best 'a little simplistic' Nil Einne (talk) 22:47, 3 April 2011 (UTC)

An abundance of dietary fiber may help. ~AH1^(TCU) 22:49, 3 April 2011 (UTC)

Actually there was an odd news story along this line that I just remember - C. elegans live longer if given just the right dose of thioflavin T, because it helps them clear out old misfolded proteins.^[14] Wnt (talk) 06:29, 4 April 2011 (UTC)

The good Dr. Kellogg was concerned for the cleanliness of his patients' intestines, every one of whom was plied with water, from above and below. His favorite device was an enema machine that could rapidly instill several gallons of water in a series of enemas. Every water enema was followed by a pint of yogurt — half was eaten, the other half was administered by enema, “thus planting the protective germs where they are most needed and may render most effective service." It is more practical to injest at one end yogurt with the doctor's famous cereal and let your washlet take care of the other. Cuddlyable3 (talk) 08:43, 4 April 2011 (UTC)

about black holes

i had a doubt if the universe is formed by big bang and all the mass and energy containing in the universe at present must co me from that singularity. if it happens like that according to law of conservation of mass and energy they cannot be created nor destroyed but how they came in action? — Preceding unsigned comment added by Tin roy (talk • contribs) 08:28, 3 April 2011 (UTC)

According to our Big Bang article, this event started from a state that was extremely dense not that was "nothing". The whole idea of a singularity is a bit weird--it's definitely not a nothing. A valid question would be "Where did all that matter come from before the singularity exploded?" It is an active area of study and an unsettled aspect of theory related to the Big Bang. It's...somewhat complicated. DMacks (talk) 09:28, 3 April 2011 (UTC)

Conservation of mass-energy is a consequence of homogeneity in time as per Noether's theorem. But there wasn't a homogeneity in time at the big bang singularity, because that singularity is a boundary, so conservation of mass-energy is not required to hold at the singularity. Besides, who is to say that the total mass-energy of the universe isn't exactly zero? After all, even in Newtonian gravity, gravitational energy is negative, and in general relativity the concept of gravitational energy is a complicated mess that doesn't even have a universally agreed upon definition. Red Act (talk) 09:45, 3 April 2011 (UTC)

Good question unsigned."how they came in action" sentence construction needs a little adjustment, but you get right to the 'heart' of the whole 'big bang' question. To say that it all started with an infinitely small, infinitely hot "point, spot, area, anomally, entity" is about as explanatary/nonexplanatary as the old idea 'god done it'. Even though perseived motions of some galaxies seem, by logical exrapolation, to indicate a single point origin, there's no reason to suppose that that extrapolation is the only possibility. could be the logic was taken to far, just as it has been with numerous other accepted ideas.big bang is a popular idea which I think will eventually be debunked.Phalcor (talk) 15:20, 3 April 2011 (UTC)

The Big Bang doesn't have to be "debunked". The singularity never happened and nobody claims that it did. It is, as you say, the (formal) result of an extrapolation from the observed conditions in the universe backwards in time. However, before the extrapolation reaches the singularity, the conditions in the universe (e.g. temperature and pressure) become such that none of our current physical theories can be applied any more. The missing time from that point to the singularity is at least the Planck time, i.e. some 10⁻⁴⁴ seconds. While there are some speculative ideas, it is fair to say that nobody really knows what went on before that time. --Wrongfilter (talk) 17:39, 3 April 2011 (UTC)

There are many theories on what triggered this big bang, for example brane theory and a big crunch of some previous universe. ~AH1^(TCU) 22:47, 3 April 2011 (UTC)

Moving a Space Shuttle

This URL is for an opinion piece about the future locations of the space shuttles. http://www.washingtonpost.com/opinions/shuttle_descent/2011/03/30/AFFsvHQC_story.html The piece says: "Moving, cleaning and preparing the shuttles for display will cost slightly more than $28 million apiece and require extensive precautions — the vessels are too fragile to travel in the rain and require two 747 jets to carry them". Is this true? How can a vehicle too fragile to be moved in rain survive the high vibration of takeoffs and the stresses of re-entry? When being moved by two 747's, are both the 747s lifting the shuttle or is the shuttle taken apart to be moved? Both these options seem unlikely. Thanks, Wanderer57 (talk) 16:08, 3 April 2011 (UTC)

Don't know about the storage plans, But Ive seen shuttle transportation on TV about a hundred years ago "it seems", and the shuttle rides piggyback on one 747. I read the article. Looks like journalistic error.Phalcor (talk) 16:30, 3 April 2011 (UTC)

One thought. the spokesman may have said something like, "We have two 747's available to move the shuttles". you could see how an uninformed journalist might miss-interpret that.Phalcor (talk) 16:51, 3 April 2011 (UTC)

Like this. I saw one fly over London once - maybe a hundred years ago ;-) Alansplodge (talk) 18:45, 3 April 2011 (UTC)

Let me guess: you woke up later with a hangover, yes? Struck by poster with apologies to Alansplodge who is only 74 years off. Cuddlyable3 (talk) 08:56, 4 April 2011 (UTC)Yes thank you. Just like that. — Preceding unsigned comment added by Phalcor (talk • contribs) 20:22, 3 April 2011 (UTC)

Cuddlyable3 you interjected between. tricky but funnier. however I can't imagine what it was doing over London since according to my memory those shuttle transport flights took place only INTRAcontinental not 'inter'. However that is/was how they were moved.Phalcor (talk) 21:36, 3 April 2011 (UTC)

Here's an article about the Shuttle/747 visit to London. Nanonic (talk) 22:23, 3 April 2011 (UTC)

Oh, ye of little faith Phalcot ;-) Alansplodge (talk) 00:01, 5 April 2011 (UTC)

As for the reference to the rain, maybe they mean it can't travel ON the 747 in the rain? As in the combination of being on the plane AND in the rain is what it's too delicate for. Vespine (talk) 22:45, 3 April 2011 (UTC)

Space Shuttle Enterprise 747 separation APL (talk)

And just because no one has mentioned it yet, of course there's the climactic scene in Moonraker where the shuttle is hijacked and takes off FROM the top of the flying 747. As many websites point out however this would have been impossible, not least because the the fuel for the shuttle's main engines is not carried "on board" but comes from the big tank it is attached to during take off. Vespine (talk) 06:23, 4 April 2011 (UTC)

A forgivable error since the shuttle didn't actually launch until 1981. Googlemeister (talk) 13:56, 4 April 2011 (UTC)

Of course, they have actually launched it that way, but not to orbit. Just for landing tests. Enterprise made five flights that way. APL (talk) 19:26, 4 April 2011 (UTC)

I can't resist posting this Shuttle Carrier space comedy. --Sean 16:26, 4 April 2011 (UTC)

Steam train in a tunnel

I am old enough to remember that passengers on a steam train would have to close any windows if they went into a tunnel, to prevent their compartment filling with smoke. But how did the driver and fireman fare on the open footplate? I can't believe that smoke deflectors would have been effective in a tunnel, or that the smoke would somehow remain within the tight space above the engine until the cab had passed under it. Surely they couldn't simply close their eyes (and noses). Was the cab somehow designed to trap a pocket of air?--Shantavira|^{feed me} 17:28, 3 April 2011 (UTC)

Cab forward design of engines is one solution.--78.150.224.119 (talk) 21:23, 3 April 2011 (UTC)

Well, conceivably the health and comfort of mere employees were not taken as seriously in those days as that of paying passengers. At the least, drivers and firemen would expect their work clothes to become filthy with smoke and coal dust; there are also references to locomotive drivers wearing protective goggles to be found aound the web. –Henning Makholm (talk) 21:31, 3 April 2011 (UTC)

I remember actually traveling on steam locomotives and I recall virtually all the smoke being left behind the engine. The smoke,having very little mass, would immediately lose it's forward momentum to air resistance. So by the time the smoke swirled down to the level of the windows the engine would be already passed the smoke zone, The smoke being available only to the passengers.Phalcor (talk) 22:10, 3 April 2011 (UTC)

This page from the Brunel Museum about the Thames Tunnel says; "...trains running through the tunnel were hauled by steam engines. Entering the tunnel the trains would go downhill towards the low point in mid-river before starting the climb back up to the surface. The steam engines would have to work hard pulling the heavy freight trains back up to the surface. The harder a steam engine works the more smoke it produces. In railway tunnels on land there are frequent shafts to allow the smoke to escape to the surface. No ventilation shafts could be built in the river so The Thames Tunnel was full of smoke making life very unpleasant for the steam engine drivers and firemen." Alansplodge (talk) 00:07, 4 April 2011 (UTC)

Me again. This page says "The Combe Down Tunnel was built in 1874... The tunnel has no ventilation along its 1 mile length, at the time of construction it as the longest un-ventilated tunnel in the UK. The lack of ventilation, on occasions caused problems to slow moving trains. In one instance a train's driver was overcome by smoke, on exiting the tunnel the train crashed in to a goods yard, killing the driver and two railway employees in the yard". Alansplodge (talk) 00:16, 4 April 2011 (UTC)

I have read about steam locomotives carrying hooded contraptions for use by the crew when travelling through tunnels. These contraptions were made of canvas and worn over the head and shoulders. They had glass lenses to allow the wearer to see out. There was also mention about drawing air from below the footplate, so perhaps these contraptions had pipes that could be connected to some area where there would be little or no smoke. I have also read about the crew lying on the footplate to avoid the worst of the smoke when in a tunnel, so it was definitely a problem. Dolphin (t) 00:58, 4 April 2011 (UTC)

This heritage rail newsletter includes a piece about a journey in the cab of a Fell Engine on the Rimutaka Incline in the 50s, where four engines were hitched to the train: ...there was a short whistle blast from the lead locomotive. Norm produced a damp towel from somewhere and shouted "Here wrap this around your face and get down as low as you can". [...] Very shortly we entered the first tunnel. The fiery exhaust which had previously shot so spectacularly metres into the air was now hitting the tunnel roof just above the funnel and raining down onto the locomotive. In no time the cab was full of choking sulphurous smoke and the temperature was rocketing up. Soon any exposed skin began to sting - it was becoming distinctly unpleasant. Suddenly there was a rush of beautiful cold air. We were out of the tunnel and the engine's doors had been flung open, oh bliss! "The next bugger's worse" shouted Norm. [...] Too soon the dreaded whistled signal from the lead loco. I wrapped the towel around my head again and crouched back down on the coal pile - at least it was getting lower, I thought, I could get down lower this time.

Soon the familiar rush of air pressure as we entered the tunnel. Once again the sulphur and quick build up of temperature. This time however it continued - hotter and hotter it became. Now even covered skin began to sting. Hotter and hotter still, breathing became like swallowing fire. "Hold your breath" I thought, but soon another was necessary. But each new breath seared the lungs - scared to breathe, scared not too. Panic must have been very close. "Control yourself, this will soon end!" But hotter and hotter it became. I felt dizzy and reached out for support - even the loco's walls were hot. Now I know what hell is like. [...] Forty years later I can still clearly recall that searing heat and the sulphurous taste. Gwinva (talk) 02:24, 4 April 2011 (UTC)

Thanks everyone. Very interesting reading, but nostalgia is no longer what is used to be. And to think we all wanted to be engine drivers when we were kids...--Shantavira|^{feed me} 10:54, 4 April 2011 (UTC)

I wonder what happened if a train was ever obliged to stop with the engine in the middle of a tunnel, so long that the water cooled down. I would expect that running the engine (long enough there to get up enough steam to move the train) would kill the engine crew. Perhaps having a locomotive engine on each end would solve this, unless the tunnel was long enough for both ends to be inside. Plus, with an engine on each end, perhaps they could cut fuel to whichever end was in the tunnel (again assuming it's not longer than the train), and thus reduce the problem. Or maybe they could just get up enough speed to coast through the tunnel ? StuRat (talk) 19:24, 4 April 2011 (UTC)

This forum suggests that oxygen to get it burning would be a problem: even refers to some engines dying down, so mid and end engines were added (as per your speculation). The page also has some good pictures of drivers' hoods, smoke deflectors, and the tale of one man steaming the skin off his face during one difficult tunnel trip... Interesting suggestion that the smoke deflectors were to prevent damage to the tunnel roof by deflecting the blast, rather than any concern for the crew. Gwinva (talk) 00:10, 5 April 2011 (UTC)

types of motion

There are a few different types of motion but couldn't it just be one type of motion that creates all other. Couldn't all motion be one type of motion but in different forms —Preceding unsigned comment added by 82.38.96.241 (talk) 19:41, 3 April 2011 (UTC)

Here are two articles that may interest you. This one is about motion. It mentions a scientist named Albert Einstein but before you read more about him, this article about Newton's laws of motionwill help you. Cuddlyable3 (talk) 20:46, 3 April 2011 (UTC)

Yes I have read that article in English but my question was about types of motion and whether there was just one type of motion in different forms —Preceding unsigned comment added by 82.38.96.241 (talk) 21:33, 3 April 2011 (UTC)

Well, there's linear motion and rotation, if that's what you meant. One can be changed into the other, but then it's a matter of terminology whether you call them two different types of motion or two manifestations of one form of motion. Similar problems exist with mass versus energy and electricity versus magnetism. StuRat (talk) 22:06, 3 April 2011 (UTC)

There are different types of motion defined by vector properties. For example, see uniform motion, uniform acceleration, circular motion, gravitational acceleration, free fall, terminal velocity and jerk. ~AH1^(TCU) 22:44, 3 April 2011 (UTC)

But all of these are just special cases of, well, motion. It's not an exhaustive classification of all possible motions. StuRat's example of linear motion and rotation is a bit better -- every smooth 3D motion is exactly one of these (or "nonmoving") at any point in time, but since one is a limiting case of the other, it's more a matter of how we analyse it than any deep difference.

I'm still struggling to find a sense of the question where the answer could be anything else than: Yes, of course all these kinds of motion are instances of a common underlying phenomenon, namely "motion". How could it conceivably be otherwise? Why do you even ask? –Henning Makholm (talk) 23:04, 3 April 2011 (UTC)

Er.uh.we didn't ask. you did.190.56.125.192 (talk) 23:18, 3 April 2011 (UTC)

I, too, am not sure I understand what's really being asked here, but perhaps Motion (physics) would be of use to you?

Motion should make more sense to you if you study a little bit of Newtonian mechanics, even at the elementary level that they would teach in a sixth form physics class.

There are different types of causes of motion, i.e., different types of force, and there is a decades-long effort underway to unify those forces, with some but not complete success. Is that perhaps what you're really asking about? Red Act (talk) 00:47, 4 April 2011 (UTC)

Motions are defined by the six degrees of freedom that a ship, boat or any untethered object can experience. It was long assumed that there is no difference between these motions until the Lorentz-Fitzgerald contraction hypothesis about speeds approaching the speed of light, which was later resolved by Einstein's theory of Special relativity. Cuddlyable3 (talk) 09:11, 4 April 2011 (UTC)

i was on about types of motion like linear and rotation and whether they are just one type of movement —Preceding unsigned comment added by 82.38.96.241 (talk) 15:59, 4 April 2011 (UTC)

pH of water containing dissolved substances and release rate of carbon dioxide

Hi. Where can I find publications about the correlation between the pH of either ocean water or water under experimental conditions and its effects on how quickly carbon dioxide and its dissolved carbonic acid counterpart can either be released into the surrounding air and how much dissolved gas the water can hold at a specific temperature? This is not a homework assignment. However I am considering researching and doing experiments using this idea on a non-curricular basis. Thanks. ~AH1^(TCU) 23:35, 3 April 2011 (UTC)

[15] may not qualify as a reliable source, but I can confirm that the information in it regarding CO2 and pH seems, at a first approximation, accurate and informative, so I recommend reading what it has to say on the subject. There is a very helpful graph which shows the relationship between pH and the various components of the carbonic acid-hydrogen carbonate-carbonate equilibrium. Strictly speaking, so long as the pH is kept at a level where there isn't an appreciable amount of the H2CO3 form present, there will not be substantial outgassing of CO2. Once the pH reaches a level that the equilibrium shifts to the carbonic acid form, you should see that the relevent equilibrium is the CO2-H2CO3 equilibrium, as covered the first part of the document I gave. These calculations seem very much like ones a student may encounter in a second-semester chemistry course (usually "Quantitative Chemistry") where intensive equilibrium calculations occur. You should have the background to work out the figures on the solubility of H2CO3 at various pHs given the information in that document. Heck, I am pretty sure I have done the problem directly, either when teaching this material myself or when tutoring students taking said class. --Jayron32 04:14, 4 April 2011 (UTC)

April 4

defrosting meat with sugar v. defrosting it with kosher salt

I notice that despite the fact that sucrose doesn't split up into Na+ and Cl- ions (the main component of salt's enthalpy of solvation), covering half-frozen meat with sugar will speed up the defrosting process significantly. It's only slightly slower than kosher salt, and it extracts about half the water from the meat that kosher salt would. Like kosher salt, the sugar appears to diffuse into the meat, and also appears to have a protein-denaturing effect, speeding up cooking time. How do I quantitatively calculate the energetics of the two processes? John Riemann Soong (talk) 03:43, 4 April 2011 (UTC)

The differences between adding sugar and salt to water vis-a-vis freezing point depression and the van 't Hoff factor are used as a first-year-chemistry exercise in examining colligative properties in a very broad and pedagogical sense, in that it teaches the basic math and concepts involved, but like so much that high school chemistry studenst are taught, reality is far more complex (this is done for a good reason; the same reason that 5 year olds are taught to ride bikes and 16 year olds are taught to drive cars). In truth, the way sugar dissolves is quite different than the way that salt dissolves. First of all, sugar is a molecule with lots of hydroxy groups on it that lends itself well to hydrogen bonding. This is why sugar does not dissolve appreciably in cold water, but if dissolved in hot water and then cooled, it forms a stable supersaturated solution known as syrup. Salt, on the other hand, has a much simpler response to temperature dependence in terms of its solubility; hot water dissolves more, and it precipitates as you cool the water. This is somewhat tangental to your question, but it does point out the complexity when trying to calculate these things. If you really want to calculate the enthalpies of solution for both sucrose and sodium chloride, for NaCl the number quoted at Enthalpy change of solution is -3.88 kJ/mol and for sucrose, is quoted here as +5.76 kJ/mol. In other words, dissolving sucrose is endothermic, so you can't count on that value to explain why it would melt the steak as fast as it does. As far as cooking differences, adding sugar to a protein like steak will tend to produce more maillard reactions than would adding salt; the steak may not cook faster but it will brown quicker. --Jayron32 04:01, 4 April 2011 (UTC)

Are either of these plausible -- won't the meat taste saltier or sweet? DRosenbach ^{(Talk | Contribs)} 05:25, 4 April 2011 (UTC)

Salting meat before cooking it is one way to increase browning, since salting tends to draw out intracellular juices, which contain some carbohydrates and produces maillard reactions when cooked, and which produces more tasty brown bits. Salt also tends to intensify meat flavors when used appropriately. Adding sugar will also have a similar effect, but I agree that sweatend meat doesn't sound terribly palatable; I think the best solution is to plan ahead and start defrosting the meat in sufficient time so as to not try to use your seasoning to do the job for you... --Jayron32 12:09, 4 April 2011 (UTC)

... and if you do need to defrost in a hurry, hot water is much more effective than either salt or sugar. Dbfirs 12:57, 4 April 2011 (UTC)

No need for heat (which can throw off cooking times and food texture), just immerse in slightly moving cold water (i.e. filled kitchen sink with the tap set to drip). When I try warm water, I also find it more difficult to tell if the item is completely thawed or just the outer layer. Matt Deres (talk) 14:52, 4 April 2011 (UTC)

Hot water isn't that effective. With a kosher salt preparation, the meat is fully defrosted by the time I'm done rubbing the chopped garlic, ginger, among other Asian-y spice preparations into the meat. (It's two birds with one stone.) And then when I wash off everything (including the kosher salt), a lot of flavour has been absorbed. I'm also really curious about the hysteresis of syrup. Is there a resource that covers this? John Riemann Soong (talk) 18:49, 4 April 2011 (UTC)

This is a cook's answer rather than a chemist's one. You can rub a steak with a mix of salt and sugar, and it will not come out too sweet. Will contrast well to a sauce including wine or balsamic vinegar. Similarly, for cured meats like bacon, use a mix of sugar and salt for best results. Or, for the wet cure of Wiltshire ham, salt, sweet cider and apple juice. "Sweet-cured" bacon is available in the shops. Itsmejudith (talk) 20:47, 4 April 2011 (UTC)

Tool to calculate what temperature I need to change the air to, to achieve a desired Relative Humidity (RH)?

Apparently, if the temperature is
Temperature  : 18ºC,
and the relative humidity is:
Relative Humidity: 65%,
if I heat the air to:
Temperature  : 35ºC,
the would give a relative humidity of:
Relative Humidity: 24%
Looking at the chart on the right, you'll see that this is correct, but, I need a better way to calculate this on the fly.
For example if the temperature is 25ºC and the RH is 60%, to what temperature to we need to heat the air to achieve a RH of 50%?
220.244.35.181 (talk) 10:21, 4 April 2011 (UTC)

You need 2 pieces of information, the vapor pressure of water at a given temperature and the desired relative humidity. Since RH = dew point/vapor pressure x 100, first use the current RH to find the current dew point, then find the temperature at which that dew point is exactly 50% of the vapor pressure, and viola... For your figures, if the temperature is 25 degrees C, the vapor pressure of water at that temperature is 3.2 kPa. If the RH right now is 60%, that means that the dew point is 0.6*3.2 = 1.92 kPa. If we want the temperature at which the current conditions will produce a 50% RH, we just do that backwards, 1.92 = 0.5*X, X=3.84 kPa, which occurs at a tad more than 28 degrees C. So the answer to your question is about 28 degrees C. You can do the same calculation for any set of conditions, so long as you know the current temperature and current RH. --Jayron32 12:06, 4 April 2011 (UTC)

One minor correction to my answer. Its not the dew point per se, it is the actual partial pressure of water vapor in the air right now, which is the same as the vapor pressure of the dew point temperature. My calculations still hold, but my terminology was a little sketchy. --Jayron32 12:15, 4 April 2011 (UTC)

Excellent answer, and helpful, in particular the formula ^{(RH = dew point / vapor pressure x 100)}, but perhaps there is an existing tool for this out there or a simple formula I could put into Excel? Actually, I'm a computer programmer - I can write a tool, but it will be based on a table of values instead of a perfect mathematical formula - but I'm satisfied with this compromise. Thanks :) 220.244.35.181 (talk) 12:34, 4 April 2011 (UTC)

Sure. You can combine the two equations into one based with some simple algebra, and get RH₁ * VP₁ = RH₂ * VP₂, where RH = Relative humidity expressed as a decimal fraction and VP = the vapor pressure of water at the given temperatures. If you wanted to do this in Excel, just copy the Temperature vs. Vapor Pressure data into the spreadsheet for easy referencing, and use a modified form of the equation VP₂ = (RH₁ * VP₁)/RH₂ and just look up the temperature associated with the target vapor pressure. It should be trivial to set up formulas in excel to do the calculation for you, but the calculation is simple enough with the table of vapor pressure data and a calculator you shouldn't need to go through that trouble. --Jayron32 14:03, 4 April 2011 (UTC)

OH, I see what you are asking. You could use the standard form of the Clausius-Clapeyron equation, using the latent heat of vaporization of water, via:

$\ln \left({\frac {P_{1}}{P_{2}}}\right)=-{\frac {\Delta H_{\mathrm {vap} }}{R}}\left({\frac {1}{T_{1}}}-{\frac {1}{T_{2}}}\right),$

If you use P1 = 1 atmosphere (760 torr or 101 kPa) and T1 = 373 kelvin (100 degrees C)(BP of water) you can find the vapor pressure of water at any other temperature. I am pretty sure that is how the table is set up. That will work better than the Antoine equation. --Jayron32 14:14, 4 April 2011 (UTC)

R, by the way, is the Gas constant, in this case the units for R should be the same as those for ΔH_vap... --Jayron32 14:18, 4 April 2011 (UTC)

Optical "Jacks" on the Back of my TV and Blu-Ray Player

Good Morning-- A month or two ago, we purchased a Vizio HDTV. On the rear panel, it has a space marked "Optical," with an almost-square, translucent plastic sensor. I have something plugged into almost every one of the other jacks (Coaxial, AV, PC, USB, RGB, HDMI), but have yet to figure out how this one works or what I could use it for. I found an owner's manual online that says

"When a digital audio signal is associated with an input which is selected for viewing, the digital audio associated with digital programming will be available on this SPDIF Optical connector for connection to your home theatre system. The white color band on the rear of the TV indicates this connection."

Over the weekend, we treated ourselves to a Vizio Blu-Ray player that was on sale. It has a similar Optical "jack" on its rear panel as well. Should I understand, then, that the audio signal will be transmitted from the Blu-Ray player to the TV without a need for a cable? Please forgive my newbie-ness, and thank you for your help! Kingsfold (Quack quack!) 12:01, 4 April 2011 (UTC)

You will need a S/PDIF connector cable. --Mr.98 (talk) 12:09, 4 April 2011 (UTC)

Mmm hmm. I did some further reading after posting this and also figured that out. In the words of Chris Farley, "I feel like a horse's patoot." Ha ha. Thanks much. Kingsfold (Quack quack!) 12:16, 4 April 2011 (UTC)

Additional pictures of the connector format (for the curious) at TOSLINK. TenOfAllTrades(talk) 12:30, 4 April 2011 (UTC)

Selenium oxidation

Would oxidation of L-selenomethionine produce red or black selenium? In my case, electrolytic oxidation produced a black residue. Thanks, --Chemicalinterest (talk) 12:25, 4 April 2011 (UTC)

Removing Hydrophobic Silicon Product from car windscreen

I have been using Rain-x on my windscreen with brilliant raindrop repellant effect but I have been told that another product has much longer lasting and non-misting qualities. But before I try the other product will I need to remove the Rain-x and if so, how? Thanks in anticipation. 92.4.40.87 (talk) 14:33, 4 April 2011 (UTC)

If it's oil-based, then dish-washing detergent should do the job. StuRat (talk) 19:05, 4 April 2011 (UTC)

Thanks Stu. I must confess to doing a bit of research since posing my question (which I should have done first off eh)? It is apparently a silicone based product that really sticks to the glass and which other users have had great problems removing. Oddly enough, the manufacturesr's own website suggests using a VERY mild abrasive such as Cif. But thanks again. 92.4.42.68 (talk) 20:03, 4 April 2011 (UTC)

Silicone greases are hard to remove. Go ahead an try detergent by all means, but I think you may find it insufficient. When using silicone oil in a chemistry lab, it's standard practice to use a base bath, often a sodium hydroxide in alcohol [16]. Silicone grease is used in the laboratory because it is pretty resistant to typical organic solvents (as well as fairly non-reactive). Buddy431 (talk) 20:22, 4 April 2011 (UTC)

Can I repair a laptop charger with graphite?

To preface: (A) My laptop and its components are under warranty, and I can certainly send the charger back for replacement; and (B) even buying a new charger outright is not prohibitively expensive-- they're like $20 or so. However, just for a challenge of it, and to feel like I could fix something, I'd like to try to repair it on my own.
I have a HP DV6646US laptop. The charger (or an extremely similar one) is pictured here. Thanks to having two sons in the house (almost 9 and almost 4) that use the computer, the small cylindrical piece that plugs into the laptop has been jerked back and forth too many times, and the connection between that and the contacts beneath it (within the black plastic end of the cord) has been severed. We can still usually achieve a power connection by holding onto the cord, pinching the metal end of the charger, and simultaneously twisting and pushing in an attempt to seat the piece so it touches the contacts. However, if the laptop gets bumped, the power connection is usually lost, and we then repeat the process.
Recently, to investigate, I completely removed the metal end. On it, there seems to be a small bump off to the side, as well as a smaller (than the cylinder) metal piece coming off the bottom-- the part that actually touches the power contact. Shining a light down into the plastic casing reveals where the end must contact, and a small cavity corresponding to the bump off to the side of the metal part.
Now the question. I was reading on a different section of the Reference Desk this morning and learned that Graphite conducts electricity. (Didn't know that. Learn something every day.) Might it be possible for me to either pack the plastic casing with graphite flakes enough to ensure a contact, or hand-shape a "bridge" out of a large pencil lead? What's the consensus? Might this work? Sorry this is so long. Just wanted to be as clear as possible. Thanks! Kingsfold (Quack quack!) 15:26, 4 April 2011 (UTC)

You may be able to work out a fix yourself, but be aware that doing this yourself may likely invalidate the warrenty for the whole computer, in other words if you try your homebrew fix on the charger, and then later something unrelated goes wrong with the computer, and you CAN'T fix it, if you try to get HP to fix it under the terms of the warrenty, they can refuse to do so, since you invalidated it by trying to fix the charger... --Jayron32 15:30, 4 April 2011 (UTC)

Also, graphite conducts, but it also crumbles and might go anywhere, possibly producing a short. If you want to fix it yourself (which, really, is not recommended - get a second one while HP fixes the first under warranty), get a suitable plug, cut off the cable and use some solder to re-attach everything where it belongs. --Stephan Schulz (talk) 15:55, 4 April 2011 (UTC)

Good advice all. It's one of those extended-warranty deals, not from HP directly, but yes-- I hadn't considered what they on the other end would think if the defective charger came back packed with graphite. Ha. My most likely plan was always to buy a second one and have the first one replaced, and almost certainly what I'll do. But... is the science of it valid? If I could somehow shape a disc of solid graphite and seat it down in there, and then put the metal part back in, it would most likely carry the charge, correct? Kingsfold (Quack quack!) 16:02, 4 April 2011 (UTC)

Possibly, but this is a "devil is in the details" situation. The exact composition and grade of the graphite will have a lot to do with performance, and its not as simple as cramming a pencil lead in there. So, while the replacement piece will be graphite, it needs to be the right graphite and your chances of jury rigging the thing yourself the right way is pretty slim compared to you just screwing it up. --Jayron32 16:26, 4 April 2011 (UTC)

Yes. Also, you can make resistors by drawing lines of various thickness and length with a (graphite) pencil on paper. Again, that's something recommended if you are alone on an island and need to fix your radio, not for production use. When I was much younger and much much stupider, I "fixed" the fuse on my cassette player by winding the contacts with soldering wire. I like to believe this was in the low-voltage part now ;-). --Stephan Schulz (talk) 16:31, 4 April 2011 (UTC)

Don't do it unless you want to buy a new computor. the socket where the plug fits is not one contact, it is two,and they must be kept seperate. the equipment is polarity sensitive, which means that if you accidentally put power to the wrong contact you may fry your computer.Just ramming some graphite in the hole won't do it. If you just want to fix something for the experience, you would do much better with something less technical. something less prone to expensive destruction. Maybe your kid's toy car,A window, The squeaky garage door. Electronics is not the way to start.190.56.16.64 (talk) 17:27, 4 April 2011 (UTC)

Are monkeys able to throw darts?

Or is this just an allegory for something extreme imprecise? Quest09 (talk) 16:33, 4 April 2011 (UTC)

I don't see why a monkey couldn't move his harm and hand in such a way as to cause a dart to fly through the air. The idea of "monkeys throwing darts" just refers to randomness; it is unlikely that said dart thrown by said monkey will be precise enough to hit the bullseye... --Jayron32 16:44, 4 April 2011 (UTC)

Maybe, they need fine motor abilities to throw a dart like a dart (instead of throwing it like a stone). Quest09 (talk) 17:19, 4 April 2011 (UTC)

True, but that they are able to throw a dart at all makes them substantially different than, say, a three-toed sloth or a bald eagle which wouldn't be able to throw a stone or a dart or really anything... --Jayron32 19:35, 4 April 2011 (UTC)

As Jayron points out, the usage is largely metaphorical. However, I see no reason why any number of monkey species couldn't be trained to throw darts. They do throw things as a natural behavior, and their limbs are mechanically close enough to ours. On a related note, here is an amazing image of an ape that has learned how to spear fish by watching people [17]. SemanticMantis (talk) 17:40, 4 April 2011 (UTC)

To be clear, he's just sticking a fish already caught by humans, not launching a spear at a moving target and hitting it: "Although the method required too much skill for him to master, he was later able to improvise by using the pole to catch fish already trapped in the locals’ fishing lines". So, I'm skeptical that any existing primate other than humans could throw a dart with any reasonable chance of hitting a small target, point first. StuRat (talk) 18:15, 4 April 2011 (UTC)

Yes, I didn't mean to indicate the orang was throwing a spear to hit a moving target, thanks for clarifying. However, I don't share your skepticism. Given suitable training, I think many primates could successfully stick a dart into a standard target from standard distance. SemanticMantis (talk) 18:54, 4 April 2011 (UTC)

In case anyone is interested, here's a nice scholarly article comparing throwing behaviours in humans and capuchins [18]. Capuchins are pretty good throwers, they would be good candidates for dart training. SemanticMantis (talk) 19:04, 4 April 2011 (UTC)

yes, I do thought it was metaphorical, just wanted to confirm it. Quest09 (talk) 17:58, 4 April 2011 (UTC)

Bold for first instance of abbreviations in journals?

I've sometimes seen articles written so that the first instance of an abbreviation (abbr.) was inserted in bold, which made it easier to find when reading further down in the text and having forgotten the expanded form of the abbr. Does anyone know any journals which do this? --129.215.47.59 (talk) 17:24, 4 April 2011 (UTC)

Himilayan glacial meltwater

I saw a "documentary" on PBS on US TV that seemed to suggest the following:

1) Due to global warming, the Himilayan glaciers will melt.

2) Once they do, they will no longer provide glacial meltwater to the major Indian rivers (Ganges, Yangtze, and Yellow River).

3) Those rivers will then dry up and millions who depend on them to irrigate their crops in China and India will starve.

This seems like questionable logic to me. If we assume that the precipitation falling in the Himilayas remains the same, then that same amount of water should still find it's way into those rivers. Is the issue that they think less precip will fall ? Or is it that the water will all flood down in the spring, and the rivers will then dry up in summer ? Or is it that glaciers even out precip cycles from year to year by acting as a buffer ? Do we have an article on this ? StuRat (talk) 18:07, 4 April 2011 (UTC)

That part of India has a monsoon climate. One of the characteristics of such a climate is that most of the rainfall for the year happens during a short span of months. For example, parts of India may get ~80% of their rain during only three months of the year. Snowfall / glaciers in the Himalayas provide a buffer. Some of the precipitation accumulates there and melts slowly over the year providing feed waters for the major rivers even in the dry seasons. If it gets hot and the glaciers completely melt away, the fear is that precipitation in the Himalayas will fall as rain that simply washes away rather than being stored. If that happens the rivers could run much higher during the wet season, resulting in frequent floods, and then run very low during the dry season, leading to droughts. Dragons flight (talk) 18:41, 4 April 2011 (UTC)

This talks about possible links between global warming and changes to the monsoon. This discusses links between Himalayan snowfall and the monsoon (and thus the growing season). -- Finlay McWalter ☻ Talk 18:45, 4 April 2011 (UTC)

(EC) The glaciers store water precipitated in the wet season, and deliver it during the dry season. Your last idea on buffering is the closest to correct. SemanticMantis (talk) 18:47, 4 April 2011 (UTC)

Human height and calcium

Our article Human height discusses how "good nutrition" is of great influence on height, giving several examples; but I haven't found an explanation of what nutrients are responsible. I immediately thought "Calcium!", and that article quotes an osteoporosis organization as saying that calcium is of great importance to bone density; but it does not mention bone length. The human height article claims that in the 1700s and 1800s, "Europeans in North America" were "far taller" than their European counterparts, and Netherlanders were shorter than other Europeans; but Britain and the Netherlands of the time were not impoverished, so I'm confused what nutrients were missing in Europe that seemed to stunt growth. It seems unlikely that only tall Europeans migrated to North America and interbred to produce "far taller" children.

I wondered as a layman whether human dairy consumption, which started around 6000 BC to 5000 BC according to our Milk article, had started an upward height trend among us humanoids; but the Calcium in biology article makes it look like there are several foods which I think were probably widespread that have more calcium per pound than fluid milk; and some large majority of humanity seems to have been lactose intolerant for the first few thousand years that some people did consume fluid milk ... so that theory seems pretty shaky.

So, what nutrients exactly are thought to be primarily responsible for the "good nutrition" influence on height? Comet Tuttle (talk) 18:42, 4 April 2011 (UTC)

Protein seems to be one factor. The body reacts to a lack of protein by stunting growth, so you get reasonably healthy, but smaller, people. StuRat (talk) 19:33, 4 April 2011 (UTC)

I have to disagree that English people, at least, were not improverished in the 17 and 18 hundreds. Starving to death was quite commonplace, I forget the medical euphanism used at the time, and food was very expensive. Due to poverty many people had very bad diets that did not provide the full range of nutrients. See for example http://www.bmj.com/content/337/bmj.a2722.full 2.97.220.102 (talk) 21:12, 4 April 2011 (UTC)

See Corn Laws for one of many relevant factors in the malnutrition of the time. And, not to get too Humanities on the Science desk, "Oh God! that bread should be so dear,/And flesh and blood so cheap." 86.164.73.72 (talk) 22:32, 4 April 2011 (UTC)

Infra red absorption

Does dark colored skin absorb infra red more thn light colored skin and therfore make the person with darker skin feel warmer under the same illumination--78.150.224.119 (talk) 19:07, 4 April 2011 (UTC)

Not answering for skin color specifically, but something dark in the visible spectrum isn't necessarily "dark" in the IR spectrum. Also note that dark objects also radiate more, so that might tend to balance out. StuRat (talk) 19:43, 4 April 2011 (UTC)

We had exactly this question not long ago, but I can't find it... can anyone else? --Tango (talk) 20:02, 4 April 2011 (UTC)

about two days ago, it got swiped out just after I answered that it was hard to find a way that could compare subjective feelings of warmth. Is that active or passive feeling? Richard Avery (talk) 21:57, 4 April 2011 (UTC)

Keeping PIR-controlled light on

The lights at work are PIR controlled and I keep having to get up and wave my arm about. Is there some device that will produce IR light every 10 minutes, say, to keep the light on? --129.215.47.59 (talk) 20:07, 4 April 2011 (UTC)

Place one of these objects (pictured to the right) somewhere in front of the sensor. Comet Tuttle (talk) 21:48, 4 April 2011 (UTC)

Do they also have a manual switch? I've seen some PIR lights where the timer can be defeated by switching them on and off then back on quickly. Don't know how common that feature is but worth a try. Vespine (talk) 22:29, 4 April 2011 (UTC)

Ribbons, or strips of aluminised-mylar balloon, hanging from the air-conditioning vent. Stick a Post-It over the sensor when you go home, so the lights don't stay on all night. Similarly, try a child's pinwheel in a location where the AC moves it and the sensor sees it. -- Finlay McWalter ☻ Talk 22:44, 4 April 2011 (UTC)