Wikipedia:Reference desk/Archives/Science/2011 February 26

= February 26 =

Entropy Quote
Entropy currently has the following unreferenced quote: "Any method involving the notion of entropy, the very existence of which depends on the second law of thermodynamics, will doubtless seem to many far-fetched, and may repel beginners as obscure and difficult of comprehension."

- Willard Gibbs, Graphical Methods in the Thermodynamics of Fluids (1873)

Unfortunately, it doesn't seem like their is a digitized version of the 1873 Graphical Methods in the Thermodynamics of Fluids. Can anyone confirm this quote with a reliable source?Smallman12q (talk) 02:30, 26 February 2011 (UTC)
 * The same quote appears in the collection of his scientific papers vol 1 (Relevant area of Graphical Methods.. is on page 11) available on archive.org here (record overview here). Nanonic (talk) 02:52, 26 February 2011 (UTC)
 * Thanks!Smallman12q (talk) 04:00, 26 February 2011 (UTC)


 * "Graphical Methods in the Thermodynamics of Fluids (1873)" looks like a reference to me. Just because there isn't a link to an online version doesn't make it unreferenced... --Tango (talk) 23:42, 26 February 2011 (UTC)

Sucking the wind
Once upon a time, the waters of the earth were thought to be infinite, and we poured all manner of crap into them because we did not know that the crap didn't just get diluted to oblivion, and eventually caused damage.

Are we on a similar path today with wind energy?

A few windmills here and there certainly don't have a noticeable impact on anything. But, if a few hundred of them become a few thousand or a few tens of thousands, will converting the energy of the wind to motion and thence to electrical power "slow down" the wind enough to have an impact on something else? What if the wind, like the water, is not an infinite resource, for us to use up as much as we can?

Seems inconceivable -- but we once thought that of the oceans, too. DaHorsesMouth (talk) 04:26, 26 February 2011 (UTC)


 * It's not inconceivable at all. Large objects, such as mountains, do have a profound impact on weather and climate, see Rain shadow and we are well aware how man-made structures affect weather and climate (see Urban heat island, which notes that one side benefit of these manmade hot spots is how they decrease the likelyhood of tornadoes; which is why it is rare that tornadoes will hit major cities).  It is not inconcievable at all that large-scale windfarms could alter weather and climate patterns in many ways; indeed I don't think anyone is claiming that they wouldn't.  The question over their usage isn't that they are zero-impact; literally NO power source is to be zero-impact; its that the negatives of windfarming, while very real, are also very much smaller than the negatives of burning fossil fuels.  I don't think anyone claims that the technology is harmless, just less harmful than what we are doing now.  Environmental effects of wind power would be a good place to look at some of the real concerns with windfarming.  -- Jayron  32  04:46, 26 February 2011 (UTC)


 * The impact of wind power on climate has been studied in . They found that over 100 years the magnitude of the impact is one fifth of that of current power production. Wind power gives a direct effect on the climate while CO2 will accumulate and the effect will increase with time. They also showed that the impact will partly be the opposite of that from C02. Wind power slows down the heat transport from the equator towards the poles while the polar regions (not sure about definition.) will be most effected by CO2 warming. They calculated simulated wind power usage at the same scale as the current total energy usage, 15 TW.(All fuels, renewable power, nuclear and so on, excluding the the solar energy used by plants in farming and so on.). This article suggests that the oceanic heat transport could also be sensitive to differences in wind patterns.
 * It is interesting to compare the scale of the different energy flows:
 * Total solar power: 3.8*10^26 W
 * Solar power hitting the earth: 174 000 TW (1 TW=1*10^12 W)
 * Total wind power :1000-4000 TW (conflicting estimates, better figures probably known)
 * Total photosynthesis 75-2250 TW (Depends on if you count energy used by the plant it self and other issues with the definitions.) (approx. 25% of the photosynthesis are used or directly affected by humans.)
 * Geothermal power from radioactive decay and cooling of the inner parts of the earth: 44 TW
 * Total human power consumption: 15 TW (In technological systems, not solar energy or non fuel biomass in e.g. agriculture, forest.)
 * Total tidal power: 3.75 TW
 * Total wave power: 1-10 TW
 * Total human electricity production: 2 TW (uses about 5 TW primary energy.)
 * Total human wind power production in year 2009: 0.04 TW


 * If human power consumption continues to increase with 3% a year or 20 times in a century (Approximately the increase year 1900 to 2000) it is obvious that wind power is not unlimited but it can make a significant contribution to power usage at today's level. With 3% yearly increase in power consumption not even the total solar power on earth is enough year 2350.
 * --Gr8xoz (talk) 12:44, 26 February 2011 (UTC)


 * Depending on the scale of wind production, large-scale wind farms could potentially slow local/global wind speeds by a measurable amount according to numerical modelling studies. See the following articles from LiveScience: Nov 2004 Nov 2008 Oct 2010. ~ A H  1 (TCU) 18:40, 26 February 2011 (UTC)

Availability of the generic Adderall XR
"In 2009, Barr and Shire reached a settlement agreement permitting Barr to offer a generic form of the drug beginning April 1, 2009."[8] I just read the above quote in Wikipedia. Last month I was told by three pharmacies in my home town that the company is no longer going to make the generic capsule. I have ADHD and the capsule was working well for me. The price was right too. Does anyone else make a generic capsule? The brand is too expensive for me even with the help of insurance. Thank you. —Preceding unsigned comment added by 24.197.183.193 (talk) 06:00, 26 February 2011 (UTC)
 * Barr is owned in a roundabout way by Teva who still have generic Adderall listed as a product on their website. Global Pharma still have generic Adderall XR listed on their website. The best people to contact for confirmation of continued availability would be those companies. Nanonic (talk) 06:27, 26 February 2011 (UTC)

Humbucking pickups and 60Hz hum
I have an electric guitar with humbucker pickups, which are designed to cancel out 60 Hz hum. I am thinking about getting a guitar with P-90 pickups, with are not humbucking. I have a lot of compact fluorescent in the house and I am worried about picking up hum (from them and any other sources). Will these cause hum on the guitar? Will any compact florescent bulb in the house cause hum, or only ones on the same circuit breaker? Bubba73 You talkin' to me? 06:39, 26 February 2011 (UTC)
 * Compact fluorescents put out electromagnetic interference, but mostly in radio frequencies interfering with radio reception. Your main problem with guitar pickups will be magnetic fields.  You should keep any power cords away from the pickup leads or guitar.  Electric motors will have a much bigger effect than lights. SO keep these away too.  If cords have to cross, do this at right angles. Keep the cords short. Do not create earth loops. Graeme Bartlett (talk) 22:28, 26 February 2011 (UTC)


 * Then I'll probably be OK. No motors except when the A/C or an appliance is running, and they aren't close. Not too many power cords running around.  Thank you.  Bubba73 You talkin' to me? 00:31, 27 February 2011 (UTC)


 * Modern florescent lights use electronic ballasts (both CFLs and tubes), but old ones used magnetic ballasts - those will probably interfere. One way to tell is simply to listen - the old ones hummed a little. A second way to test is wave your hand under the light. With modern fixtures your hands will simply "smear" out, with old one you will see a sort of strobe effect and you'll see images of your hand in various positions. (The old ones flashed at 60hz, modern ones at many thousands of hz.) Ariel. (talk) 01:29, 27 February 2011 (UTC)


 * Thanks. Some of the CFLs are up to 7 or 8 years old.  Sometimes they start making a sound when they are going bad.  There are a few long tube florescents in the kitchen that make noise - they may be the old type, but they are not on most of the time.  (BTW, I ordered a guitar with non-humbucking pickups tonight.)  Bubba73 You talkin' to me? 05:19, 27 February 2011 (UTC)

What's the problem with non-native species?
Why are conservationist groups so concerned about the introduction of non-native species to new environments? It's not like it's a new phenomenon (species have been migrating around the planet for hundreds of millions of years, e.g. the Great American Exchange) and it actually seems quite unnatural to try and prevent non-native species from taking hold on new territories. I know new species may be detrimental to the survival of native ones, but that's what natural selection is all about, no? Who are we to get in its way? --Leptictidium (mt) 10:50, 26 February 2011 (UTC)


 * The funny answer would be: Than have fun with the tigers in your suburb and the crocodiles in the public pool. Frogs do not migrate from Africa to Australia and rats were unable to cross over to New Zealand so why should humans help them. Humans are simply stupid to know what they are doing and at the end they do harm to their environment that it become less providable to live there.--Stone (talk) 11:11, 26 February 2011 (UTC)


 * "but that's what natural selection is all about, no? Who are we to get in its way?" -> http://en.wikipedia.org/wiki/Naturalistic_fallacy#Other_uses 213.49.110.245 (talk) 11:53, 26 February 2011 (UTC)
 * Rabbits in Australia. Vimescarrot (talk) 12:23, 26 February 2011 (UTC)


 * In the Sahal the sourthern part of the sahara desert  people use non native   herds of cattle and goat  which unlike  camels   strip the  grass  right down to there roots this leaves the ground bare   and the soil gets blown away   and eventually it causes  desertification which is land turning into desert this is a real damaging effect  on the enviroment.  Also  non native goats  and wildboar  have been extremely damaging to the enviroment  and wildlife populations.  —Preceding unsigned comment added by 109.77.244.8 (talk) 12:34, 26 February 2011 (UTC)


 * Humans can speed-up the introduction of new species many times the natural rate. The human activity in an area is adapted to the historical environment there, it can be costly to adapt to handle the consequences of new weeds, or other spices. Evolution is most efficient when there are many weakly connected habitats and high biological diversity. If all habitat with the same conditions get the same ecosystem then it is mush more sensitive to changes, say fore instance that a new pest develops. --Gr8xoz (talk) 13:16, 26 February 2011 (UTC)


 * See non-native species and invasive species for more examples of the damage they can cause.--Shantavira|feed me 13:37, 26 February 2011 (UTC)


 * However, non-native species do not always cause damage. They may simply take over from an equivalent native species. Concern about this (such as concern over the loss of the red squirrel to the grey squirrel and its associated pox) seems to me to be conservatism rather than conservation (unless, perhaps, conservation is its sub-category). See damage for a discussion of the different meanings that the word takes on when used within different value systems - oh wait, that doesn't work (it's just a disambig page). Well, imagine it did. 213.122.25.248 (talk) 14:39, 26 February 2011 (UTC)


 * The main problem is that invasive species tend to fill an occupied ecological niche and outcompete the original species in a way that alters the proportions of predators and prey. The introduced species often creates a rapid directional selection in the other species within that ecosystem and those species cannot evolve quickly enough to adjust to this new state. Notable examples of invasive species include the emerald ash borer, dandelion (especially New Zealand), large blooms of Nomura's jellyfish (not strictly invasive but oceanic changes are encouraging blooms), purple loosestrife, the common reed, and the historical Y. pestis. ~ A H  1 (TCU) 18:31, 26 February 2011 (UTC)


 * While the mechanism is true it is not necessarily clear that it is a problem. It can be a problem if it affects human activity in a negative way or if for some other reason the old ecosystem is valued higher than the new one.--Gr8xoz (talk) 23:29, 26 February 2011 (UTC)


 * Another problem with invasive species is that they may hybridize with native forms. This is important with things like killer bees, coy-dogs and mosquitoes transmitting West Nile virus.  Hybrids have a larger gene pool to draw upon, and can evolve rapidly, e.g. hybrid speciation.  Though measures of environmental damage usually focus on the loss of species, I would suggest that the evolution of new species could also be a major environmental challenge. Wnt (talk) 00:53, 28 February 2011 (UTC)


 * Did we just call speciesation and rapid evolution an environmental challenge? What else is the biosphere supposed to do? Mac Davis (talk) 14:19, 28 February 2011 (UTC)


 * It would be an environmental challenge for us. Clearly the biosphere is free to do as it "wishes" - even extinction represents a natural reaction to circumstances - but when such change is imposed on a rapid timescale by human action, it doesn't seem all that natural or benign. Wnt (talk) 16:35, 28 February 2011 (UTC)


 * Scientific American did a short interview in the Feb '11 issue with Mark A. Davis, who argues that invasive species aren't all that bad, in general. Certain examples, such as the brown tree snake in Guam, aside, the introduction of exotic species to new locations isn't necessarily a negative thing, he says. The interviewer summarizes by saying "the field needs less emotion and more science." The interview leaves me with about 100 questions, though, because it's very short and superficial. Davis does have a new book out called Invasion Biology, which might be more informative. -IceCreamAntisocial (talk) 18:10, 28 February 2011 (UTC)


 * Change isn't necessarily bad, and even changing an area into a desert is only bad by human standards, since most humans don't get much out of a desert. Environmentalists tend to hold values that say we should keep all environments as they were, before human intervention.  Also, they value biodiversity, while, given free movement around the world, you tend to get a smaller number of "most successful" species, which wipe out the less competitive ones that accumulated on isolated islands.  Thus, less competitive species, like many marsupials, might be doomed to extinction.  One exception is that some environmentalists think the cure for an out-of-control non-native species is to introduce the predator which controlled it in it's native environment. StuRat (talk) 17:04, 2 March 2011 (UTC)

Converting % and ppm to g/kw-hr
I am working on a project, to determine the level emissions from generators. The values from the Gen. sets using an exhaust gas analyzer are in % and ppm, which has to be compared to international standards,which are in g/kw-hr. what is therefore the conversion rate. For example,CO and CO2 are in percentage (%), while HC and NOx are in parts per million (PPM).I will be most gratefull to be assisted in converting to g/kw-hr. Sample: CO=6.62%;4.71%;3.67% etc CO2=5.63%;7.27%;7.84% etc HC=136ppm;145ppm;152ppm NOx=40ppm;60ppm;68ppm

Thank you in anticipation —Preceding unsigned comment added by 41.78.80.94 (talk) 12:40, 26 February 2011 (UTC)
 * You need to know the mass of the exhaust gas produced then generating 1 kWh. If you know the amount of fuel and fuel type used to produce 1 kWh then that could be used to get a rough estimate. --Gr8xoz (talk) 12:56, 26 February 2011 (UTC)

Victoria waterlily
Why do these have a high raised lip? I presume it isn't for buoyancy, since they seem to stay afloat even when pushed partly underwater (they have some sort of air pockets, don't they?) ... and if it was for buoyancy, what would happen when it rains? Besides, there is a cleft at one point on the circumference (to let rainwater out?), which would be a poor design for a boat. 213.122.25.248 (talk) 14:46, 26 February 2011 (UTC)
 * I think you answer your own question. The lip aids in buoyancy, but the cleft prevents filling with rainwater. SemanticMantis (talk) 16:48, 26 February 2011 (UTC)
 * I guess. I suppose the lip helps a bit, despite the unlikeliness of a human designing a boat with a big hole in the side. It's an odd-looking evolutionary compromise. I'm not even sure it makes logical sense. If, when there is some water inside, the pad is buoyant enough for the water to run out the gap, wouldn't this still be the case with no lip? I can only think its purpose is to prevent sudden flooding, like in the case of being jumped on by one of those giant Amazonian otters ... but the article says the leaves are very fragile, so the leaf would be punctured by the otter's feet anyway. Maybe the point is to protect against being splashed by animals? 81.131.21.81 (talk) 16:57, 26 February 2011 (UTC)
 * Ok, here's a few other things to consider.
 * The leaf doesn't need to be a boat; it doesn't 'want' or need to have much Draft_(hull).
 * Under no load, the 97% rim is quite effective at keeping out all kinds minor slosh/ ripples of water, regardless of the source. This is good for the plant in terms of gas exchange and photosynthesis.
 * If the leaf submerges for any reason, it can more easily drain and resurface due to the gap compared to a full rim.
 * The 97% rim allows allows the leaf to stay afloat under small dry loads, such as frogs, insects, and detritus.
 * A full rim would not be much advantage over 97% rim in most circumstances, and is worse in a the case of submersion.
 * There may be genetic limits to the leaf, wherein a full rim is more difficult to achieve than it's worth. Most traits do indeed strike some sort of balance or trade off, i.e. as described with respect to shade tolerance here.
 * In short, I conclude that the 97% rim is a benefit due it its effects on buoyancy. Also, the cleft is not a big problem, and in fact provides additional benefits. I don't think a trait this distinct is ecologically neutral. Indeed if there are any suggestions for benefits aside from buoyancy issues, I'd be interested to hear them :) SemanticMantis (talk) 17:56, 26 February 2011 (UTC)
 * Oh OK, that's very good, particularly the part about needing to stay dry, rather than avoiding a risk of sinking. Thank you. 81.131.21.81 (talk) 17:59, 26 February 2011 (UTC)
 * It's an interesting question. On the other hand, if the lip is so great, we might wonder why it's not more common among water lilies... SemanticMantis (talk) 18:37, 26 February 2011 (UTC)
 * I did wonder that. It might be a thing which is only needed at large scales for some reason (*waves hands*). It might be that the non-Victoria waterlilies have better water-repelling surfaces (this is achieved by tiny hairs, or some amazing quantum effect and/or goretex). It might be (this is my bet) that there is much more detritus (particularly falling twigs, or falling branches which could cause splashes) in the Amazon than in your typical pond elsewhere in the world. 81.131.21.81 (talk) 18:53, 26 February 2011 (UTC)
 * I think you're on to something with scale. Those leaves are huge. For species with smaller leaves, surface tension plays a relatively larger role in keeping the leaf afloat, so the rim isn't as useful. A small needle can float on surface tension, but a large nail can not. SemanticMantis (talk) 20:06, 26 February 2011 (UTC)
 * This picture of Victoria amazonica would argue against that. Ariel. (talk) 02:28, 27 February 2011 (UTC)
 * While we are speculating wildly, what about preventing the leaves from overlapping? That seems like a simpler explanation; overlapping would have a big impact on photosynthesis, obviously.  -- Scray (talk) 02:02, 27 February 2011 (UTC)
 * Sure, preventing leaf overlap is probably another slight benefit. SemanticMantis (talk) 17:07, 27 February 2011 (UTC)

Electrons circular orbit frequency
Can a electrons circular orbit frequency be changed or altered — Preceding unsigned comment added by Lufc88 (talk • contribs) 18:08, 26 February 2011 (UTC)
 * Do you really expect anybody to know what you are talking about without a little more context?? Dauto (talk) 19:57, 26 February 2011 (UTC)

It is asked in the context of my question above called EM wave and magnetic fields — Preceding unsigned comment added by Lufc88 (talk • contribs) 20:37, 26 February 2011 (UTC)


 * Do you mean Electron cyclotron resonance? If you do, as you can see by yourself in the linked article, the frequency depends on the magnetic field. Dauto (talk) 00:57, 27 February 2011 (UTC)

Thanks sorry about that i did not see that bit — Preceding unsigned comment added by Lufc88 (talk • contribs) 12:44, 27 February 2011 (UTC)

Ruhmkorff lamps
"Finally we had all the necessary chemicals for the Ruhmkorff lamps." -- Jules Verne. Journey to the Centre of the Earth How do you make a Ruhmkorff lamp? I saw the foreign languge links in Heinrich Daniel Ruhmkorff, but I'm looking for some simple step by step procedure. And what chemicals are used? Thanks. -- Uzma Gamal (talk) 20:09, 26 February 2011 (UTC)
 * As the article states, you need a Geissler tube and a source of electricity. Apparently they were powered either by a battery or a portable generator (which maybe fed the battery?). DMacks (talk) 20:27, 26 February 2011 (UTC)


 * The Google link didn't work for me, but from Journey_into_the_Interior_of_the_Earth/Chapter_XI:


 * "Ruhmkorff's apparatus consists of a Bunsen pile worked with bichromate of potash, which makes no smell; an induction coil carries the electricity generated by the pile into communication with a lantern of peculiar construction; in this lantern there is a spiral glass tube from which the air has been excluded, and in which remains only a residuum of carbonic acid gas or of nitrogen. When the apparatus is put in action this gas becomes luminous, producing a white steady light. The pile and coil are placed in a leathern bag which the traveller carries over his shoulders; the lantern outside of the bag throws sufficient light into deep darkness; it enables one to venture without fear of explosions into the midst of the most inflammable gases, and is not extinguished even in the deepest waters. M. Ruhmkorff is a learned and most ingenious man of science; his great discovery is his induction coil, which produces a powerful stream of electricity. He obtained in 1864 the quinquennial prize of 50,000 franc reserved by the French government for the most ingenious application of electricity."
 * The same page says "all the articles needed to supply Ruhmkorpff's apparatus", but doesn't specify what they were. (it lists "a row of phials containing dextrine, alcoholic ether, liquid acetate of lead, vinegar, and ammonia drugs which afforded me no comfort" just before that, but I think these are actually intended for human use???)  I have to assume that the unspecified ingredients are the material needed to supply the Bunsen pile. Wnt (talk) 21:05, 26 February 2011 (UTC)
 * Looking over it, I still can't be sure - probably you'd need zinc anodes, sulfuric acid, and the potassium dichromate mentioned; with the sulfuric acid being used to convert that to chromic acid in the Bunsen pile. Such a pile wouldn't emit NO2 - I'm not sure what sort of chromium salt would come out of it, but I think it would avoid the noxious fumes, hence the "makes no smell" in the text.  Note however that hexavalent chromium has quite a bad reputation nowadays. Wnt (talk) 22:06, 26 February 2011 (UTC)


 * The Ruhmkorff coils would be called "induction coils" in publications from the early 20th century onward. Such a device has a primary coil fed at a low voltage, such as 6 volts, which coil acts as an electromagnet to attract the armature of an interrupter switch, which on being attracted breaks the current for a bit. A spring then recloses the primary circuit. This is the same as how a DC doorbell or buzzer works. Wound around the same magnetic core of a bundle of steel wires is a secondary coil with hundreds of times more turns which produces impulses of several thousand volts every time the primary circuit makes and breaks. The device is a transformer fed by pulsating DC. This is how primitive spark wireless telegraphy got its high voltage in the early Marconi days. The Geissler lamp is like a fluorescent lamp, but without the white phosphorescent coating which generates the nice white light. A basic Geissler coil would have been a dimmer light with less of a broad spectrum than a fluorescent light. Such a coil is rather a current hog, and a substantial and thus very heavy battery would have been needed to run it for extended periods. Short battery life and low light output are arguments against the basic system Verne described. So an induction coil, or a Model T spark coil, would be the "Ruhmkorff" device, and an evacuated tube like a neon sign would be the light emitting element. The battery described would be a complex 19th century wet cell, but as a demo you might use a modern rechargeable battery of the voltage the coil primary is designed for, such as 6  volts. A fluorescent tube, even a "dead" one, will glow brightly when connected to one output terminal of the induction coil. Note: painful and possible dangerous shocks from the high voltage generated are very likely., even from the primary circuit. I found it helpful to ground the primary circuit, a difficult task if the device is carried around.  Further caution: High voltage can produce xrays from the light tube connected to the high voltage, so don't try this at home. A battery powered fluorescent lamp would be a modern and safe analog of the Vern lamp. Edison (talk) 02:36, 27 February 2011 (UTC)
 * Though to be fair, we have altogether lost the artistry of the Geissler tubes depicted in the article, especially as one considers the light such intricate baubles would shed in caves of fantastic minerals in the unknown depths of the Earth. I do concede, however, that whatever Verne said, such a high voltage circuit seems quite likely to involve sparks that would set off firedamp, especially if it truly used a buzzer mechanism.  (though would it possible, in concept, for a well-crafted Bunsen pile to reach the needed voltage simply by using thousands of cells cleverly linked to be filled from common reservoirs?) Wnt (talk) 03:04, 27 February 2011 (UTC)
 * Verne did not suggest that a battery of 2000 cells, like Humphrey Davy's Great Battery of the Royal Institution, circa 1808 was carried on someone's back. Much easier to carry a primary battery which could produce 6 volts at several amps for several hours, and an induction coil with an interrupter to produce 4 kilovolts or so to make the Geissler tube glow. He might also have imagined an incandescent lamp powered by the battery, since one passage in the book says the battery was connected to the "filament" of the lamp. All he needed was an 1860's carbon filament in vacuum lamp, with a late 1870's vacuum pump. Then they would simply have had flashlights. Edison (talk) 06:18, 27 February 2011 (UTC)
 * You're right on this one. I was only speculating at a way to try to avoid the sparks, but among other problems you point out such a massive pile would not use the induction coil Verne specified.  (Alternatively, maybe there's a way to encapsulate the entire relay/transformer mechanism to prevent contact with the air ...?) Wnt (talk) 16:33, 28 February 2011 (UTC)

Tricky physics problem
Dear Wikipedians:

I am working on the following tricky physics problem:

a 0.234 kg shoe is dropped onto a vertically oriented spring with a spring constant of 104 N/m. The shoe becomes attached to the spring upon contact and the spring is compressed 0.117 m before coming momentarily to rest. What work is performed by the weight of the shoe while the spring is being compressed?

My first approach is the gravitational approach:

W = mgh = 0.234×9.8×0.117 ≈ 0.268J

My second approach is the spring approach:

W = ½kx² = ½×104×0.117² ≈ 0.712J

I would tend to the 0.268J answer, but the computer system is rejecting both of my answers as wrong! I have only one more try left and I am desperate to see where I went wrong.

Your help is much appreciated.

174.88.35.131 (talk) 21:02, 26 February 2011 (UTC)
 * The gravitational approach doesn't consider any kinetic energy the shoe had upon hitting the spring. Not sure about the spring method, looks OK to me. Grandiose (me, talk, contribs) 22:18, 26 February 2011 (UTC)
 * The question is a little odd. I can't quite work out what it wants. Since your two answers don't work, the only other thing I can think of is to take the difference between the two. That is, calculate the work done by the resultant force on the shoe. That's not how I would have interpretted the question, but you've already tried my other ideas. --Tango (talk) 23:55, 26 February 2011 (UTC)


 * How many significant digits your answer is required to have? The data of the problem has three significant digits, and given that the average value of earth's surface gravitational acceleration is actually 9.81m/s^2, I'm getting W = 0.269J. If that turns out to be the correct answer to this problem I would say that this computer program is too picky. Dauto (talk) 00:08, 27 February 2011 (UTC)


 * It sounds like the shoe free-falls, then continues to drop as it compresses the spring. Both these things must add up to account for the force that the spring absorbs when compressed.  Hmmm, on second thought, that should simply be the .712 figure, since all the force of the shoe goes into the spring (with typical frictionless assumptions and one-dimensionality it could rebound endlessly).  But the question doesn't ask about the force of the shoe, only the work done by the weight of the shoe.  That's just (F=mg=2.2955) x distance = (0.117 m) = 0.269 after all.  Hmmm... Wnt (talk) 03:07, 27 February 2011 (UTC)

Is there a documented possible link between gender identity to sexual orientation?
Ya know, in a superficial way it seems that indeed there is, i myself don't agree and i think that even if there is, it ain't that robust...

but, what does the research shows to us?, is there a link?, and if there is, how significant it is by this stage of the research?

thanks and blessings,

Beni —Preceding unsigned comment added by 109.66.8.242 (talk) 22:56, 26 February 2011 (UTC)


 * I think it is rather well established that most persons that identifies them self as male primarily are sexually attracted to women and vice versa. I think almost every one agree that this is true in at least 80% of the cases, is it this correlation you want documented or did I misinterpret the question?--Gr8xoz (talk) 23:09, 26 February 2011 (UTC)


 * The question only makes sense if you ask: if my gender identity doesn't match my biological gender, which sexual orientation do I have? Normally that of the biological gender you wish to have... —Preceding unsigned comment added by 212.169.187.124 (talk) 00:08, 27 February 2011 (UTC)
 * Yes, normally but not always. Dauto (talk) 00:58, 27 February 2011 (UTC)
 * My guess is that the intended question is something more like this: If all you know about someone is that they are cisgender, what (if any) information does that give us about the statistical likelihood that they are also heterosexual? And I don't know the answer. --Allen (talk) 08:14, 27 February 2011 (UTC)
 * What does it mean to say that this transgender person is heterosexual? Is that according to his biological or intended gender?Quest09 (talk) 00:11, 28 February 2011 (UTC)
 * Presumably the term "transgender heterotsexual" would apply to person born with male sex characteristics, living as female gender identified, who is attracted to the male gender. Just a terminology note: Biological traits determine sex, but gender is a socio-cultural construct."Intended gender" would probably be considered a loaded term to some. The OP's entry needs clarification if s/he wants more help. SemanticMantis (talk) 00:39, 28 February 2011 (UTC)

I agree with SemanticMantis about what someone would probably mean if they said they were transgender and straight. But either way, that wouldn't change the numbers involved in answering the OP's question, if I'm correct about the interpretation. --Allen (talk) 13:31, 2 March 2011 (UTC)