Wikipedia:Reference desk/Archives/Science/2010 October 16

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October 16

Wedge Constant:- newton laws of motion

please tell what is wedge constant and where and how to use it? —Preceding unsigned comment added by Alche stalwart (talk • contribs) 04:57, 16 October 2010 (UTC)

In what context did you find the wedge constant? I have not heard of it and a search on google mostly returns this question and your questions at answers.com and /www.physicsforums.com. I also found something called so in telescopes but no references to newton laws of motion. --Gr8xoz (talk) 09:48, 16 October 2010 (UTC)

Do you by any chance mean the wedge product (also known as an exterior product)? The wedge product does have applications in Newtonian mechanics. For example, see Geometric algebra#Torque for a presentation of torque in terms of a wedge product. However, in Newtonian mechanics, things are more commonly instead expressed in terms of the cross product, which is closely related to the wedge product. A cross product is the Hodge dual of the bivector formed by a wedge product; see Cross product#Cross product as an exterior product. Red Act (talk) 14:05, 16 October 2010 (UTC)

EDTA reaction

I did the following reaction in a lab with magnesium sulfate.

Is MgSO₄ + EDTA^4- → MgEDTA^2- a redox reaction?

Why does EDTA lose 4 electrons before the start of the reaction?--72.145.140.75 (talk) 16:15, 16 October 2010 (UTC)

I used 10 mL of a solution that my teacher called "EDTA buffer." What exactly is EDTA buffer? I used Calmagite for endpoint detection.--72.145.140.75 (talk) 16:17, 16 October 2010 (UTC)

The "EDTA solution" link in your web-link says that "EDTA has four protons", which is in agreement with our EDTA article's discsussion of it having four acidic groups. Your page gives a recipe for a buffer with pH 10, and our page talks about how "EDTA^4-" is the four-way-deprotonated form--that's all consistent with an alkaline solution containing EDTA in which the acids have been deprotonated. See the "Nomenclature" section of our article for the variations in these naming patterns. Note that if EDTA had lost 4 electrons it would be +4 not -4. DMacks (talk) 17:24, 16 October 2010 (UTC)

The page that I have linked to prescribes Eriochrome Black T to be used as pH indicator. I actually used Calmagite in the lab. Nobody told me what "EDTA buffer" was made up of. Is it possible that I used something other than ammonia buffer?--72.145.140.75 (talk) 17:30, 16 October 2010 (UTC)

It doesn't actually matter what else is in the "EDTA buffer", as long as there is EDTA and probably that it's got an alkaline pH in order to make sure the ETDA is in the highly deprotonated form. As you noted in the reaction, only the EDTA^4- actually participates in the titration (not the ammonia, or whatever else buffering agent was added)--one of the neat things about chemistry is that only a few details matter, and other variables might just be facts that do not alter the results you need (analogy: it doesn't matter what color coat you're wearing, they will all keep you warm the same way, and the presence of shoelaces vs velcro straps doesn't affect your coat at all). Likewise, it doesn't matter exactly what indicator you use, as long as it indicates the situation you need indicated in a noticeable way. Comparing our Eriochrome Black T and Calmagite pages, you can see they are both indicators of the same type of thing--changing color when complexed to certain types of ions. DMacks (talk) 17:57, 16 October 2010 (UTC)

aging and sensory capacity

It is commonly known that aging reduces one's visual and auditory capabilities. Is the same also true for other senses? For example, balance (part of the vestibular system)? That is, is there a general decline in sensory capacity with aging? --Halcatalyst (talk) 16:34, 16 October 2010 (UTC)

Hearing definitely declines with age, particularly with respect to higher pitches becoming harder and harder to hear. As for visual senses, I don't think acuity is affected more than it is earlier on when you get glasses etc. but I can be proved wrong on that! You are more prone to getting things like cataracts, though. I'm not aware of any growing defecit in other senses like taste, smell or touch but again I welcome suggestions. Regards, --—Cyclonenim | Chat  20:28, 16 October 2010 (UTC)

(OR warning) From my observations, I would conclude that other senses do deteriorate, but the effect often is less obvious. There is also an enormous variability in the deterioration. In some people it begins in "middle-age", whereas some 90-year-olds have sight and hearing that is still good. Perhaps someone can find some research on other senses? Dbfirs 21:57, 16 October 2010 (UTC)

Elliptical Orbit vs Circular Orbit problem

A satellite has an elliptical orbit at altitudes ranging from 230 km to 890 km. At the high point it's moving at 7.23 km/s.

I'm supposed to find the radius of a circular orbit in which the total orbital energy of the satellite is the same as for the elliptical orbit above.

I know that the total energy of a circular orbit is given as E=-GMm/2r and that the total energy of an elliptical orbit is given by E=GMm((1/r1)-(1/r2))

When I set those two equal, the GMm should cancel and leave me with r1-r2/-2=r r=330 km. That answer doesn't match the answer that I'm given, what am I doing wrong?199.94.68.201 (talk) 17:46, 16 October 2010 (UTC)

Are you sure that equation for an elliptical orbit is right? If you treat a circular orbit as a special case of an elliptical one, you get E=GMm((1/r)-(1/r)), which can't be right, surely. Our Specific orbital energy article gives the energy for an elliptical orbit to be -G(M+m)/2a where a is the semi-major axis. (Please note I know nothing about orbital mechanics) Rojomoke (talk) 18:48, 16 October 2010 (UTC)

I am also skeptical to the formula E=GMm((1/r1)-(1/r2)) for the same reason. I also note that you have done a alegebraic misstake,

GMm((1/r1)-(1/r2))=-GMm/(2*r) => 1/r1-1/r2=-1/2*1/r => r= -(1/2)/(1/r1-1/r2) => r=-(1/2)*r1*r2/(r2-r1) = 155 km.

This value satisfy the first equation.--Gr8xoz (talk) 19:43, 16 October 2010 (UTC)

-G(M+m)/(2a) gives the specific orbital energy, the orbital energy will be E=-G(M+m)*m/(2a) if the satelite has much less mass than the planet then you can use E=-GMm/(2a) and for a circular orbit a=r you get E=-GMm/(2r) --Gr8xoz (talk) 20:37, 16 October 2010 (UTC)

Train tracks and leaves

I saw a poster on the train today about when it's Autumn and the leaves fall, there's an effect where the high pressure between the rail and wheel creates a very slippery substance that means the trains have to travel slower and brake earlier in badly affected areas. Is there a name for this effect, and do we have an article on it? Regards, --—Cyclonenim | Chat  17:53, 16 October 2010 (UTC)

Slippery rail. -- Finlay McWalter ☻ Talk 17:54, 16 October 2010 (UTC)

Thanks, very quick! Regards, --—Cyclonenim | Chat  17:55, 16 October 2010 (UTC)

Shouldn't that be British Rail?92.30.154.94 (talk) 18:10, 16 October 2010 (UTC)

You're showing your age! Alansplodge (talk) 20:29, 16 October 2010 (UTC)

tunnel diode

what is tunnel diode —Preceding unsigned comment added by Omveer Singh Gurjar (talk • contribs) 19:51, 16 October 2010 (UTC)

Tunnel diode--Gr8xoz (talk) 20:21, 16 October 2010 (UTC)

Sapience

Is sapience something that all humans are innately born with, or is it something which must be achieved with the help of others? Can sapience be achieved by other species with enough effort and teaching? I'm thinking here of Alex the parrot. --95.148.105.245 (talk) 22:27, 16 October 2010 (UTC)

I don't believe the word even has a definite meaning. Looie496 (talk) 23:41, 16 October 2010 (UTC)

I think what Looie means is that sapience is, like the related notion of Consciousness itself, difficult to define for purposes such as answering a question like yours: "Although humans realize what everyday experiences are, consciousness refuses to be defined, philosophers note." Which is kind of weasily and awkwardly phrased, but you get the idea. It is very difficult to meaningfully compare the quality of "subjective experience" between one species and another (and even really between one person and another, in some ways -- the school of psychologists known as the Behaviorists tried to simplify things by pretending "subjective experience" just did not exist at all!) Clearly "sapience" or "consciousness" does exist, and clearly whatever it is is different in humans than in, say, parrots (even those raised from birth in a learning-rich captive environment). The difference clearly exists, too, but since the phenomenon itself is so difficult to define, it is for the same reason difficult to say what precisely that difference is. "Language" has something to do with it, but is not necessarily the most important aspect of it. The human Neocortex is recognized as being one key neuroanatomical feature underlying human "sapience", and other species simply do not have (as much of) this biological feature. WikiDao ☯ (talk) 01:51, 17 October 2010 (UTC)

One possible answer regarding sapience is to instead deal with concepts such as Metacognition, which is a developed form of self-awareness. Sapience is highly tied up with these concepts. --Jayron32 02:01, 17 October 2010 (UTC)

Nuclear Physics

"The advent of high energy ion colliders in Europe and North America caused a remarkable advance in Nuclear theory. New and surprising experimental results and exciting new theoretical insights and predictions are continuously being published while large number of puzzles still remain to be investigated. This is an exciting time to be a theoretical physicist."

Any truth to this? 74.15.136.172 (talk) 22:43, 16 October 2010 (UTC)

Do you have any reason to believe that McGill University's Department of Physics [1] would be lying to you? TenOfAllTrades(talk) 23:26, 16 October 2010 (UTC)

McGill's Department of Nuclear Physics, lie to ME about the thrills of nuclear physics in order to recruit students?! How preposterous! 74.15.136.172 (talk) 23:40, 16 October 2010 (UTC)

Sure. If you're a mathematical genius and you plow through ten years of graduate and postgraduate eduction, it's an exciting time to be a theoretical physicist. Looie496 (talk) 23:44, 16 October 2010 (UTC)

What would count as "proof" for your purposes, OP? WikiDao ☯ (talk) 01:53, 17 October 2010 (UTC)

Have most of the important problems in nuclear theory been tackled, or is there a genuine endeavour to answer basic but interesting questions about the nucleus? 74.15.136.172 (talk) 02:04, 17 October 2010 (UTC)

We have several resident physics enthusiasts here; I will leave your now somewhat clearer question to them. Cheers! :) WikiDao ☯ (talk) 02:32, 17 October 2010 (UTC)

Note that the original text on the McGill web site said "this is an exciting time to be a nuclear physicist," not "this is an exciting time to be a theoretical physicist," which is an important distinction. I'm not a professional physicist, but I think it indeed is an exciting time to even just read about what's currently going on in theoretical physics as an outsider. However, the stuff that I find really exciting that's going on would count as high-energy physics, not nuclear physics. But that's just me.

One important consideration when contemplating pursuing a degree in any kind of physics is what the job market is likely to be like when you finish. And I know a bit about that from my sister, who was the chair of a small university physics department until a couple years ago. She says that it's very difficult to get a job as a physicist nowadays (even counting before the recent recession), and it's a lot harder now than back when she got her PhD a couple decades ago. A lot of universities have been trimming down or eliminating their physics departments (and again, that's even counting before the recent recession). A PhD in physics is certainly a valuable degree to get, but in reality it's more likely to lead to a career as a computer programmer in the financial industry, or something like that, rather than a career as a physicist. Red Act (talk) 02:58, 17 October 2010 (UTC)

The phrases "nuclear physics", "theoretical physics", and so on, are used vaguely and interchangeably in the "mass media", so caution is warranted when evaluating any assertion about some particular sub-field in physics. But it is safe to say that high energy physics, including most research that could be called "nuclear physics", has seriously suffered from a lack of public interest (and funding) over the last two decades. The "advent of high energy ion colliders" mentioned by the OP happened in the early 1960s - it's really a matter of historical interest, not a current state of affairs. By the 1980s, we had numerous particle accelerators: a SLAC, a Synchro/Cyclotron at Berkeley, a Tevatron at Fermilab, Brookhaven - plus numerous other large military and DoE projects - and we were building a Superconducting Supercollider that would put all the rest to shame. But then something unpredictable happened - maybe attributable to the end of the Cold War, or maybe attributable to failures to create practical nuclear fusion power plants, or failure to make practical neutron bomb weapons, or so on. And the funding began to evaporate. (Let's be frank: the Government pays nuclear physicists to make power plants or to make bombs - the "important questions" that the Federal Government is interested in have little to do with nailing down subtle relativistic trajectory compensations for 9.2 TeV hadrons). Remaining "interesting questions" did not seem to warrant funding. SCS was cancelled; our national nuclear laboratories switched gear from "design" to "maintenance" ("stockpile stewardship"); and theoretical high-energy physics just got silly. As reported in this New York Times article, the status of funding at major physics research centers has been severe - around these parts, the Stanford Linear Accelerator Center was hit really badly - its budget was sliced; the facility was dissociated from the University; and I recall numbers on the order of 1,250 Ph.D jobs being affected (a combination of pure layoffs of researchers at the facility, a re-shuffling of engineering and physics faculty at the University proper to work other projects, the cancellation of major projects, the "lights-out" on many graduate students' Ph.D. funding, and so on). That's an unheard of number of research positions to slash. SLAC, now a National Laboratory "unaffiliated" with Stanford, is presently floating by on the LCLS, an X-ray / LASER project that is essentially a repurposing of the particle-accelerator facility (and the only experiment now running in "the tube"). And, with a decades-long strategic change in Department of Energy policy on the design of nuclear weapons, there are far fewer applied and theoretical positions working for the government. So, it's a really rough time to be a nuclear physicist in Northern California (or elsewhere in the United States). Meanwhile, the European dedication and commitment to continued funding of CERN (while we in the U.S.A. are canceling and repurposing our major national high-energy physics laboratories) means that a lot of very smart and very talented researchers are heading (and staying) in Europe.

At the same time, nuclear engineers are doing alright (and bear in mind that this is a very different discipline from nuclear physics, despite its focus on the same fundamental concepts). With so much effort devoted to re-thinking our entire energy economy, nuclear engineers and power plant experts have no trouble finding work on active projects, consulting for energy companies, or working for the military (Nuke School is always looking to recruit, and if you have any kind of nuclear physics or nuclear engineering training, theoretical or otherwise, they will contact you trying to recruit you when you graduate). But don't expect a lot of "theoretical" physics - it's a little bit on the "practical" side.

From the purely academic standpoint: have we answered all the interesting questions in nuclear physics? Well, that's subjective. We have described the atom to incredible levels of detail. We know how to fission and fusion atomic nuclei, and have the technology to do both. We have a pretty solid understanding of the basic structure of the nuclear particles - protons, neutrons - and we have a pretty well-tested explanation of the internals of a subatomic particle. We can keep trying to collide heavier and heavier particles, but for what purpose? There's the elusive quest for some disruptive shakedown of established physical law that shatters "everything we know" about nuclear physics - enabling a feasible cold-fusion reaction, for example - but from a scientific standpoint, I see no reason to believe such a revolutionary discovery is "just around the corner." What important questions do you have about nuclear physics?

This is a very exciting time to be a theoretical physicist. The problem is, though, "exciting" gets pretty exhausting after a while. Nimur (talk) 03:51, 18 October 2010 (UTC)

Thanks for the thorough response! 74.15.136.172 (talk) 15:16, 18 October 2010 (UTC)