Wikipedia:Reference desk/Archives/Science/2009 July 9

= July 9 =

Rubbish/Garbage Island
Would it be feasible to create a new island at somewhere like the Dogger bank (which I understand is a large sand bank off the coast of Britain that you can walk on at low tide) merely by dumping the nation's garbage/rubbish there for a few years? If needed, the rubbish could be contained by an earth or sand wall around it. Such an island would be usefull to put things on like wind farms, nuclear power stations, oil refineries, chemical plants, and prisons. I expect it could take a decade or two for the rubbish to stabilise enough to build on, unless you used deep-pile foundations. 78.147.135.194 (talk) 00:09, 9 July 2009 (UTC)
 * The major problem is erosion which could compromise the integrity of the artificial island so maintenance would be expensive since garbage is not exactly as tough as granite. There's also the problem of the garbage contaminating the sea.-- Lenticel ( talk ) 00:55, 9 July 2009 (UTC)
 * It would be feasible to create an island that way but it probably wouldn't be permitted. Garbage in water tends to, um, exude aspects of its essence, so to speak. Looie496 (talk) 00:56, 9 July 2009 (UTC)


 * Landfill is a major method of constructing new land over former waterways. However, garbage (rather, post-consumer waste) has many properties that make it unsuitable for construction of buildings - most notably, it is too squishy for safe construction of building foundations.  A lot of engineering has to go into the landfill design to make sure that the ground is solid enough to use.  Also, there are potential aesthetic (smell) and health issues, depending on the type of garbage used to build it.  However, in some cases, garbage has been used as a fill constituent, properly mixed with other construction materials.  Boston and some parts of the United Arab Emirates are notable examples of this.  In fact, most of the Back Bay is artificial land; the fill is largely imported from elsewhere in the state, but was mostly dry ground (not garbage).  Here is a thorough history from Boston College.  Nimur (talk) 01:32, 9 July 2009 (UTC)


 * Here's our article on the Palm Islands, in Dubai. The fill material is mostly quarried rock and sand; I can not find any indication that post-consumer waste was used anywhere.
 * Also see: Artificial island and List of artificial islands. Nimur (talk) 01:45, 9 July 2009 (UTC)

"Would it be feasible to create a new island... merely by dumping the nation's garbage/rubbish there for a few years?" -- Now why in the world would anyone want to do that? There are other much better options for garbage disposal (reclamation, trash-to-steam incineration, etc., etc.), and if you want to build an artificial island, then gravel would work one hell of a lot better. 76.21.37.87 (talk) 06:28, 9 July 2009 (UTC)


 * A good example of what you'r looking for is Pulau Semakau, the scenic landfill of Singapore. Even referred to as The island paradise built on a garbage dump . The trick appears to be using incinerated trash. EverGreg (talk) 08:54, 9 July 2009 (UTC)
 * Grant Park (Chicago) was extended by waste from the Chicago Fire and elsewhere. It really depends on what kind of rubbish you have available. Brick and stone will work better than banana peels. Rmhermen (talk) 18:46, 9 July 2009 (UTC)


 * What's now the waterfront of San Francisco is built partly on the hulks of abandoned ships; the Embarcadero extension of the N Judah line to Pac Bell Park SBC Park AT&T Park passes through one, and another was partly exposed when a building at Battery and Clay Streets (now four blocks from water) was torn down in 2001. —Tamfang (talk) 18:00, 21 July 2009 (UTC)

What type of tick is this? Is it even a tick?
A friend and I walked through some brush in Nova Scotia yesterday and emerged with many of these on our pants and shoes. We got them off quickly and didn't appear to have been bitten or anything. What is it? Thanks, Kinou (talk) 00:15, 9 July 2009 (UTC)


 * Sure looks like a tick (see pics in tick article). Don't know what kind.  But get in the shower as soon as you can, and check yourself very carefully ALL OVER (scalp, nether regions etc.) for any ticks that may have stuck to you, or any bite marks.  Ticks can spread some pretty nasty diseases. 208.70.31.206 (talk) 00:40, 9 July 2009 (UTC)


 * If you search for images of a wood tick, you'll find a bunch that look just like that. Brown dog tick also looks similar—but I can't decide, and I'm not an expert. Alfonse Stompanato (talk) 00:44, 9 July 2009 (UTC)
 * Thanks for the responses :) Kinou (talk) 06:18, 15 July 2009 (UTC)

Railroad train wheels
After reading most of the references on trains I have nor found the answer to this question. "What keeps a train on the track around curves"?. Cars do it by virtue of a differential, but train axels are solid so both wheels travel at the same speed. I know the answer but I wonder who invented the cone shaped wheel? What are the limitation of speed around curves? I would appreciate all serious answers. Thanks, wsc. —Preceding unsigned comment added by 98.149.228.69 (talk) 00:33, 9 July 2009 (UTC)


 * I see some detailed math related to conical wheels way back in There actually are differentials for railroad wheels available now, for example see  and its cited precedents. DMacks (talk) 01:29, 9 July 2009 (UTC)


 * If I can digress a bit, the top of the rail is somewhat rounded, even on straight runs. Together with the cone shaped wheels, does that help overcome lurching of the carriage? - GlowWorm.


 * The reason I think that will help overcome lurching is that the side of the carriage in the direction of lurch will rise slightly, opposing the lurch. The cone shaped wheel will then ride on a slightly different track on the rail top, hence the rounding. This effect would also help oppose the centrifugal "force" on a curve, like a banked auto race-track. These effects may seem slight, but the wheel rim is actually tapered quiite a bit. - GlowWorm. —Preceding unsigned comment added by 98.21.111.233 (talk) 02:56, 9 July 2009 (UTC)


 * P.S. When one side of the carriage rises, the other side falls. These actions thereby reinforce each other. - GlowWorm. —Preceding unsigned comment added by 98.21.111.233 (talk) 03:16, 9 July 2009 (UTC)


 * P.P.S. The train wheels slide sideways on the rails to bring these effects about. That's no problem. We've all heard a locomotive spinning its wheels when starting to move.- GlowWorm. —Preceding unsigned comment added by 98.21.111.233 (talk) 03:41, 9 July 2009 (UTC)


 * The article about tapered wheels I cited above has information about side-to-side tilt and curved-track issues. DMacks (talk) 06:41, 9 July 2009 (UTC)


 * Tilting train and High speed tilting train (unfortunately only a stub} may help. 71.236.26.74 (talk) 06:08, 9 July 2009 (UTC)


 * The Wikipedia article Wheelset says a bit about conical wheels. But I think it is incomplete and poorly written.. Also, it says "Most wheels have a conical shape of about 1 in 20.", which is unclear. - GlowWorm. —Preceding unsigned comment added by 98.17.35.216 (talk) 04:47, 10 July 2009 (UTC)


 * It means that the conical surface deviates from the angle it would have if it was cylindrical by about 2.86° (I'm sure that's excessive precision) -- because the tangent of that angle is 1/20. In Britain the style "1 in n" is very commonly used to express the inclination of a gradient on a road or railway, so if one of those is rising at 2.86° above the horizontal, that's a "1 in 20 grade".  (In North America we would instead convert the tangent to a percentage and call it a 5% grade.)  --Anonymous, 05:13 UTC, July 10, 2009.


 * The problem I have with a cone angle of "1 in 20" is whether it applies to the angle between the two sides of the cone, or whether it applies to the angle between one side and the axis of the cone. - GlowWorm. —Preceding unsigned comment added by 98.17.35.216 (talk) 05:38, 10 July 2009 (UTC)


 * There's a reasonable discussion in an Institute of Civil Engineers publication on google, Cost-effective maintenance of railway track which tends to corroborate much of this discussion. As to cone angle, if this definition is correct then 98.17's objection does not apply. I should like to know the maths by which 1 in 20 comes to be 2.86°, GlowWorm, if you'd be so kind. --Tagishsimon (talk) 10:43, 10 July 2009 (UTC)
 * I said above: the tangent of 2.86° is 1/20. --Anon, 05:43 UTC, July 11, 2009.


 * Tagishsimon's reference shows another useful function of conical wheels. It is the reduction of "hunting". Figure 3 shows it clearly and simply. - GlowWorm. —Preceding unsigned comment added by 98.17.47.39 (talk) 22:22, 10 July 2009 (UTC)
 * Not quite - hunting is caused by the conical wheelsets, the article Hunting oscillation begins to explain.83.100.250.79 (talk) 15:29, 12 July 2009 (UTC)
 * I thought hunting was caused by hillbillies like myself wanting some red meat... :-D 76.21.37.87 (talk) 09:28, 14 July 2009 (UTC)
 * They have a flange around their inner edge to ensure they don't come off the track. 78.151.124.180 (talk) 23:34, 11 July 2009 (UTC)

Can you legally have hypodermic needles in rochester new york without a perscription?
Can you legally havehypodermic needles in rochester new york without a perscription? —Preceding unsigned comment added by 74.65.3.30 (talk) 01:18, 9 July 2009 (UTC)


 * Wikipedia cannot give legal advice. Nor can we give medical advice.  While we can point you to encyclopedia articles and outside sources which can help inform you, this question is specifically requesting an interpretation of law, which nobody on Wikipedia should be giving. Nimur (talk) 01:35, 9 July 2009 (UTC)

Our article presents several examples of hypodermic uses that are intended for "non-specialists", which suggests that they are commonly used without a medical prescription. Nimur (talk) 01:38, 9 July 2009 (UTC)
 * No it doesn't!! It says nothing of the sort!  It lists a bunch of medical conditions that would require people to inject themselves...but with a prescription syringe - then it says that recreational drug users use them (illegally) - and only in the next section does it point out that the syringe MINUS THE NEEDLE is used in various industrial applications.  Certainly the syringe part is useful without the hypodermic part - and the odds are good that those are perfectly legal.  But the article doesn't give a single legal, non-prescription use for hypodermic needles - which is what our OP actually cares about. SteveBaker (talk) 02:14, 9 July 2009 (UTC)

well apparently they are illigal in ny state but can  i buy them for ear peircing? thats what i need them for —Preceding unsigned comment added by 74.65.3.30 (talk) 02:12, 9 July 2009 (UTC)


 * Needles, like hypodermic needles? Those may be regulated, but they are not what is necessary for ear pearcing.  Why not just head to the piercing kiosk at your local mall.  For the cost of a $10.00 set of cheap starter studs, they'll pierce your ears for free!  --Jayron32. talk . contribs  02:33, 9 July 2009 (UTC)


 * (Please don't start new threads on the same topic - I've moved it back together again) SteveBaker (talk) 03:05, 9 July 2009 (UTC)


 * You can buy a complete ear piercing kit (no illegal hypodermics involved) here for $70. You can buy proper (sterile) ear piercing needles here for about $1.50...they seem very similar to hypodermic needles - but they don't have the fitting to attach to a syringe.  I suppose that's what makes them legal...but who knows?  SteveBaker (talk) 03:13, 9 July 2009 (UTC)
 * I’m not an expert on piercing, and it’s hard to tell for sure from the picture, but my guess is that piercing needles aren’t hollow. There’d be no need for them to be hollow, since no fluid needs to go through them.  So piercing needles would be useless to a drug addict, and there’d be no need to make them a legally controlled device.  Red Act (talk) 03:24, 9 July 2009 (UTC)
 * Years ago someone stole a bunch of analytical-HPLC syringes from a lab where I worked. For those playing along at home, that means the syringes hold a few tens of microliters and the needles are blunt. We figured it'd be easy for the cops to find the druggie who was not high and had a line of bruises instead of needle-tracks up his arm. DMacks (talk) 03:35, 9 July 2009 (UTC)
 * I don't know what's in kits sold to the general public, but Body piercing says hollow needles are used. My WP:OR is "may as well go with a cheap, widely available, sterile existing item" rather than something less common or more special-purpose (i.e., more expensive). DMacks (talk) 03:32, 9 July 2009 (UTC)
 * If they actually are illegal then what do they pack into ink jet cartridge refill kits sold in that state? The one's I've bought so far all contained a hypodermic needle.  I doubt they are sterile, though. (Not a known transmission path for computer viruses :-) 71.236.26.74 (talk) 04:28, 9 July 2009 (UTC)
 * - Hordaland (talk) 11:54, 9 July 2009 (UTC)

Latex vs polyisoprene condoms
A company recently released polyisoprene condoms to the market. Reading that entry says it's natural rubber. How does it compare with latex condoms as far as allergies, strength, and protection? --70.167.58.6 (talk) 01:41, 9 July 2009 (UTC)

Probably the same as latex on all three counts (after all, latex and natural rubber are both isomers of polyisoprene). 76.21.37.87 (talk) 06:38, 9 July 2009 (UTC)


 * So it's just a marketing gimmick? --70.167.58.6 (talk) 01:22, 11 July 2009 (UTC)

Yeah, they just try to come up with all kinds of fancy words for everyday materials to trick customers into thinking that it's something really high-tech (e.g. "anionic detergents" or "alkali-metal salts of trans-fatty-acids" -- any guesses as to what this stuff could be? (Hint: both of these terms describe pretty much the same material.)) 76.21.37.87 (talk) 05:10, 11 July 2009 (UTC)

Purification of fish oil
Does anyone know how fish oil is purified? I've seen a fish oil product which says on its bottle that it is purified by molecular distillation. Is the distillate purified fish oil or is it volatile impurities? What is the effectiveness of the process? Is it able to remove many broad classes of impurities/contaminants, or is it only effective against very specific ones? What level of purity can be expected from fish oil purified by that process? —Preceding unsigned comment added by 98.114.146.41 (talk) 03:01, 9 July 2009 (UTC)
 * Distillation separates the components out by boiling point - therefor it is up to the maufacturer as to which Fraction (chemistry) (s) they put into the final product. In general you should read about distillation to find out about potential limitations of this method.83.100.250.79 (talk) 15:36, 12 July 2009 (UTC)
 * In general distillation can remove many impurities - but if there are impurities with similar boiling point to the product it will be less effective.83.100.250.79 (talk) 15:37, 12 July 2009 (UTC)

oscillators and frequency.
How are oscillators and frequency related to each other?Is constant frequency a compulsion for generating oscillations?please help!! —Preceding unsigned comment added by 210.212.103.10 (talk) 07:20, 9 July 2009 (UTC)
 * Frequency is a measure of the rate of oscillation. DMacks (talk) 07:27, 9 July 2009 (UTC)


 * An Oscillator is something which oscillates, that is, goes back and forth. So when something goes back and forth, each round is called an Oscillation. Now it takes some time to complete each oscillation. This is called Time Period of the oscillation. Now, the inverse of this, that is, 1/t, is called the frequency of oscillation. This need or need not remain constant with time; it is an inherent characteristic of something which oscillates. For more information, please read the relevant articles. Rkr1991 (talk) 08:27, 9 July 2009 (UTC)

Calculating time to full battery recharge
I need a little help calculating how long it would take to charge the battery pack of an electric vehicle with the following parameters:

The vehicle has six 12-volt flooded electrolyte batteries, and an on-board 72-volt DC charger that plugs into a standard 110-volt AC 15-amp outlet.

The manufacturer of this particularly odious Neighborhood electric vehicle (they're all a little odious) doesn't mention the time to full charge in its published specs- a rather telling omission, I think.

I posted this over at the Math desk as well. Thanks Wolfgangus (talk) 08:36, 9 July 2009 (UTC)

Do you know what is the batteries' storage capacity in amp-hours? If you do, then it's a rather easy calculation (for me, at least), but if not, then the calculation becomes absolutely impossible. 76.21.37.87 (talk) 09:06, 9 July 2009 (UTC)


 * I noticed that the on-line calculators I found (before posting this here) were asking for that information, and since I didn't have it, I couldn't use those calculators. But above, I provide all the information that's offered at the company's website. So you're saying that it's impossible to know without the storage capacity in amp-hours.  OK, got it. Thanks for the info. Wolfgangus (talk) 09:15, 9 July 2009 (UTC)
 * Another consideration is that while the charger uses a 15A 110V hookup, that will not likely lead you to the actual charge current of the device (22A if the device is almost 100% efficient, which it likely isn't even close). Knowing the sustained charging current is critical to know how fast those amp-hours will be replenished.--Jmeden2000 (talk) 19:58, 9 July 2009 (UTC)
 * And the other problem (with at least some sorts of battery) is that they can overheat if you charge them at full speed - so you may have to charge them in briefer pulses to keep them from self-destructing. SteveBaker (talk) 04:37, 11 July 2009 (UTC)

Can lightning strike an airplane?
I copied this question from the Newcomer's desk: &mdash; QuantumEleven 09:19, 9 July 2009 (UTC)


 * Is it technically possible for lightning to strike an airplane?
 * Icanhasaccount (talk) 05:59, 9 July 2009 (UTC) Icanhasaccount

Of course it's possible, and had actually happened numerous times (surprisingly, the planes involved usually sustain little if any damage from the lightning strike). 76.21.37.87 (talk) 09:29, 9 July 2009 (UTC)

A simple Google will find a lot of reliable sources discussion this. A frequently made claim is that statistically aeroplanes will be hit by lightning an average of twice a year. You can probably also find a lot of discussion when looking in to the recent Air France crash. Nil Einne (talk) 10:22, 9 July 2009 (UTC)

There is a brief discussion at Air safety. 88.114.222.252 (talk) 10:50, 9 July 2009 (UTC)


 * And do the passangers notice anything?Quest09 (talk) 10:52, 9 July 2009 (UTC)


 * They may hear a loud noise and the lights may flicker - but, as aircraft fuselages are Faraday cages, they won't feel any direct effects. &mdash; QuantumEleven 13:14, 9 July 2009 (UTC)
 * That, as the man said in Men in Black (film), was on Jeopardy! last night"! The current champion, Alyssa McRae, was once in a plane that was hit by lightning, and she talked about it on the show... which, conveniently, I taped. She said: "You look out the window and see a bright flash, and it feels like the plane has hit something, and you just prepare to meet your maker.  And it keeps going, apparently.  I don't know if that's what always happens, but for me that's how it happened."  --Anonymous, 20:08 UTC, July 9, 2009.


 * My knowledge of the issue is that most aircraft are protected/relatively good at withstanding a cloud-to-ground lightning strike. Issues come from different types of lightning such as ground-to-cloud which strike the underside of the plane, and sheet lightning. Some planes aren't quite as well adapted to these types, and it can cause issues. Regards, --— Cyclonenim | Chat 16:17, 9 July 2009 (UTC)
 * I dispute that; Cyclonenim, you're going to have to cite a source on that claim. Tempshill (talk) 18:24, 9 July 2009 (UTC)
 * Sorry, I looked back at the lightning article where I first heard it and it is positive lightning, not ground-to-cloud which causes the issues. The second paragraph which states its danger to most aircraft is cited. See Lightning. Does that help? Regards, --— Cyclonenim | Chat 22:05, 9 July 2009 (UTC)


 * I've actually been in an aircraft that was struck by lightning. It's a lot less dramatic than you might think.  My father used to fly for the flying doctor service in Kenya - which is based in Nairobi (hmm - we don't seem to have an article on the East-African flying doctors) - and on one occasion I went out with him (I was just a kid at the time - maybe 12 years old) and we got caught in a nasty storm.  The meteorology services in Kenya left something to be desired in the mid 1960's - so we didn't know it was in our way until it was too late.  We couldn't get above it because Nairobi is already something like 7,000 feet above sea level and the poor little Cessna doesn't have enough altitude ceiling to get much higher than that - and the plane was somewhat overloaded with land-rover parts that were going out to some back-of-beyond medical center.  My recollection was of an extremely bright flash - followed by some complete confusion as the cockpit instruments went nuts and our eyes gradually adapted to normal light levels - but after not very long, everything settled down and enough of the old mechanical instruments worked to get us back to Nairobi without problems.  The plane was a high-wing nose-wheel Cessna...a Cessna 172 probably.  There was a scorch mark on top and bottom of the wing - maybe an inch or so across and the bulk of the energy seemed to have flowed through a 'stringer' in the wing - melting one of the rivets that held it in place.  The damage was fixed in a matter of hours and the plane was back in service on the following day.  (The way that outfit worked - it would probably have been flying again the next day WITHOUT the damage being fixed!) SteveBaker (talk) 15:34, 10 July 2009 (UTC)

Preparing for war
How well prepared are modern Western democracies? Do governments care about provisions of food, energy, and medicines?

--Quest09 (talk) 10:47, 9 July 2009 (UTC)


 * It varies, country to country, but I expect most are prepared for reasonable wars or warlike scenarios. Independent of warlike scenarios, governments are always concerned with the supply of food, energy, and medicine.  After all, the disruption of such supplies has been a casus belli in the past.  The US' 1940 oil embargo on Japan springs to mind as one such. &mdash; Lomn 12:35, 9 July 2009 (UTC)


 * Several western democracies are involved in wars at the moment (eg. Iraq, Afganistan, although they are often euphemistically called "conflicts"), but I assume you mean wars where fighting takes place nearer to home. Most countries have some kind of contingency plans, but I don't know if there would be anything particularly specific. You generally get some warning of wars. Prior to World War II and during the Cold War there were all kind of preparations going on. At the moment there is no reason to expect any major wars, so there is no need for much preparation. There are all kinds of preparations for major terrorist attacks, though, since those are far more likely. --Tango (talk) 16:39, 9 July 2009 (UTC)


 * Yes, governments care a great deal about provisions of food, energy, and medicines. See Strategic National Stockpile, Strategic Petroleum Reserve, and Defense National Stockpile Center for relevant references.  It doesn't look like there's much detail in the articles about different countries, but I would hope that most well-governed nations have established some form of strategic reserve.  --- Medical geneticist (talk) 17:30, 9 July 2009 (UTC)


 * Few countries have military-quality petroleum reserves. The United States has one of the largest, but it is for mostly economic reasons. No country has more than, IFRC, 60 days' worth of petroleum. Even if regular citizens were cut off, that is simply not enough to sustain modern military operations. See the IEA for more on that point.
 * If every country went to war with every other, only the oil-producing nations would still have airplanes flying and tanks rolling and ships sailing after about a year. Andyo2000 (talk) 19:07, 9 July 2009 (UTC)
 * Assuming they retained the infrastructure to continue to produce their oil perhaps, but such infrastructure is a high priority target, and it would not be likely to escape unscathed. Googlemeister (talk) 19:10, 9 July 2009 (UTC)
 * ...as has twice been demonstrated in recent history. With modern aerial warfare, these longer term considerations of running out of 'stuff' don't apply when a powerful nation attacks a weaker one.  It's usually all over in a matter of days to weeks. SteveBaker (talk) 14:58, 10 July 2009 (UTC)
 * Well, the large-scale fighting is over within days or weeks, getting full control of the newly occupied territory can take far longer. The initial invasion of Iraq, for example, took about 20 days, but the conflict still isn't over. --Tango (talk) 16:46, 10 July 2009 (UTC)
 * True, but under that definition, the Nazis never controlled France. Googlemeister (talk) 18:28, 10 July 2009 (UTC)
 * In any case, as far as petroleum supplies are concerned, it is the initial large-scale fighting that depends critically upon those; the guerilla warfare that (often) follows afterward is mostly infantry warfare that uses lots of ammunition and food supplies but relatively little fuel. FWiW

76.21.37.87 (talk) 05:19, 11 July 2009 (UTC)

Dark skin vs. fair skin
What of both is the evolutionary adaptation?--Quest09 (talk) 10:54, 9 July 2009 (UTC)
 * This answers why dark skin is both an advantage and a disadvantage. Vimescarrot (talk) 11:13, 9 July 2009 (UTC)
 * I believe the question is asking which is the original color and which is an adaptation. It depends entirely on who you want to listen to.  Nobody was around when the first humans were walking around so nobody knows for sure.  Of course, that assumes there was a single group known as the first humans.  There may have been been many groups of so-called humans that, over time, intermixed. --  k a i n a w &trade; 21:56, 9 July 2009 (UTC)
 * Oh. I never thought of that. I thought he was asking what evolutionary advantage each colour inferred, and what pressure there was on it to change. Vimescarrot (talk) 22:04, 9 July 2009 (UTC)
 * The mainstream model of human origins is the Out-of-Africa model. And mean skin color within a population adapts to UV radiation levels from the sun quite rapidly (500-1000 years) on human evolutionary time scales.  So if the mainstream model of human origins is correct, homo sapiens presumably originally had dark skin, due to the advantage of dark skin in Africa, where there is a lot of UV radiation, and light skin arose fairly rapidly among those populations that migrated to parts of the world further from the equator, where lighter skin is an advantage.  Red Act (talk) 00:47, 10 July 2009 (UTC)
 * That is not quite as much a given as it may seem. If the humans that made it out of Africa were still very hairy, their skin underneath might well have been light (like e.g. Chimpanzee) The dark skin might then have developed in Africa as an adaptation later. Not saying that is what happened, just saying it's just as likely. (BTW Polar bears have dark skin.)71.236.26.74 (talk) 10:14, 10 July 2009 (UTC)
 * If the humans that left Africa remained very hairy, that hypothesis would involve widely dispersed populations all evolving from being very hairy to having little hair. It makes more sense to assume that the evolutionary loss of hair occurred while all or at least most humans were in reasonably close genetic contact.  Otherwise, it seems likely that there would be some humans in some isolated parts of the world that retained the thick, chimp-like hair.  Red Act (talk) 11:05, 10 July 2009 (UTC)
 * SeeRobin Williams. Googlemeister (talk) 13:17, 10 July 2009 (UTC)
 * The Ainus of northern Japan are very hairy.76.21.37.87 (talk) 05:24, 11 July 2009 (UTC)
 * The plural "ainu" used as a collective noun is acceptable.83.100.250.79 (talk) 15:42, 12 July 2009 (UTC)
 * Then, we have to make assumptions about how the non-hairy humans got to Africa to start the "out-of-Africa" process. What if they were originally from South America, became ocean creatures, lost much of their hair (as the ocean mammals tend to do), and popped out of the Ocean in Africa?  Then, they could have been rather gray at first and turned black.  The problem is identifying the first "human". --  k a i n a w &trade; 11:11, 10 July 2009 (UTC)


 * According to the Recent African origin of modern humans article, “According to both genetic and fossil evidence, archaic Homo sapiens evolved to anatomically modern humans solely in Africa, between 200,000 and 100,000 years ago ... The recent single origin of modern humans in East Africa is currently the near consensus position held within the scientific community.” I’m just going with the scientific consensus about human origins.  Red Act (talk) 11:25, 10 July 2009 (UTC)
 * I'm not challenging that, however your comment above would rule out any further development of "anatomically modern humans" after the out of Africa movement. The fact there are no pockets of all hairy populations is not conclusive proof.  Parallel development is not unheard of in humans .  There are people with Hypertrichosis, but that condition is poorly understood.  I don't think the exact conditions for humans to have less hair is not yet conclusively known.  (There are indications for genetic causes, but environmental factors are also being considered .) If the genetic or environmental condition that caused less hairiness were encountered equally by all human populations in their development, there is no need for it to have occurred before the split.  "May have happened" is not equal to "must have happened" even if the latter fits nicely with one's assumptions. 71.236.26.74 (talk) 12:26, 10 July 2009 (UTC)
 * Dude, did you even glance at the second reference in your post ? It’s about root hair, a feature of a plant’s roots, and has nothing whatsoever to do with when, where or why our ancient ancestors lost most of their body hair.  Red Act (talk) 14:01, 10 July 2009 (UTC)
 * Oops, late night and too little time to dig up references, sorry. 71.236.26.74 (talk) 14:55, 13 July 2009 (UTC)

Homo sapiens has nothing to do with it. Homo lost its body hair long before that, before 1 million years ago. The "ocean creature" scenario is in fact a respectable theory, known as the aquatic ape hypothesis --dab (𒁳) 13:39, 10 July 2009 (UTC)


 * That is a point I was intending to make... If you say "homo sapien", you have a rather precise point of evolutionary development. If you say "human", it is very fuzzy.  At what point along evolution do you consider the animal to be a "human"?  Then, there is the issue that none of the skin of those pre-homo-sapien creatures is around to take a gander at.  So, we can only consider other mammals that have had almost no adaptation since pre-human times, such as the hedgehog.  A common hedgehog's skin is greyish-pink, but the Algerian hedgehog is almost black.  Again, we have to work out which came first, the pink hedgehog or the black hedgehog.  So, I don't see any means of answering this question with the knowledge available today. --  k a i n a w &trade; 14:09, 10 July 2009 (UTC)
 * Note that my exact original statement above was “…homo sapiens presumably originally had dark skin…”. “Homo sapiens”  and “originally” pins the time I was talking about down to about 200,000 years ago, at which point, according to the most widely accepted theory, all our ancestors had little hair, and were living in Africa.  However, the original question is completely vague about what evolutionary time scale is to be considered.


 * Hedgehog skin is a rather meaningless comparison, since hedgehogs are covered in spines. The environmental factor that appears to determine human skin color in a population is how much exposure the skin gets to UV.  Human skin doesn’t have the UV protection afforded by spines.  Red Act (talk) 14:39, 10 July 2009 (UTC)


 * The questioner did not ask about "homo sapiens". The questioner asked about "skin color".  An answer limited only to homo sapiens is barely a partial answer.  Which came first, light skin or dark skin? --  k a i n a w &trade; 20:49, 10 July 2009 (UTC)
 * That is true. The question exactly as asked isn’t really answerable.  Red Act (talk) 23:32, 10 July 2009 (UTC)
 * In most animals, dark skin is a result of chromatophores; usually neural crest derived melanophores or melanocytes invading the epidermal or dermal layers after they have already formed. Without this process the skin is functional, but light (consider, for example, albinos). Light skin therefore precedes dark skin in ontogeny; if one considers the most parsimonious method of how skin tone evolved, it is most likely that light skin will have preceded dark skin evolutionarily too. Of course, this will all have happened long before humans arrived on the scene. Rockpock  e  t  00:17, 11 July 2009 (UTC)

NH4CL
when ammonium chloride sublimes, it forms nitric acid and hydroclhoric acid. i wanted to ask if this reaction is physical or chemical. cos, this reaction is reversible (in wiki, it's written - "Ammonium chloride sublimes readily but this process involves dissociation into ammonia and hydrochloric acid followed by reforming of the compound." but i know perfectly well that this reaction is also chemical, as it involves chemical changes, and not simple physical changes. please help me! (PHYSICAL OR CHEMICAL?????) thanx!!!!!!! —Preceding unsigned comment added by 122.50.134.64 (talk) 13:10, 9 July 2009 (UTC)


 * When ammonium chloride sublimes, it does NOT form nitric acid and hydrochloric acid. It forms ammonia and hydrochloric acid.  Also, it should be noted that all chemical changes are also physical changes; it is impossible for a chemcial reaction to happen which does also not change some physical property of the materials.  When one says "physical change" they are implying only a physical change; that is one in which the shape, size, or state of matter of a substance is changed without making a change to the composition of the substance.  So the answer here is that this is clearly a chemical change, since the change results in different chemicals being formed after the change than before.  Physical changes would involve such simple things as smashing the ammonium chloride into little bits or dissolving it in water.  --Jayron32. talk . contribs  13:15, 9 July 2009 (UTC)

Isn't the whole division of changes into physical and chemical somewhat artificial?

We say melting is a physical, not chemical, change, but you are changing the bonding situation going from solid to liquid.

Ben (talk) 19:47, 9 July 2009 (UTC)


 * It is artificial, but it is something that is common in beginner-level chemistry textbooks. I honestly can't remember the definitions now, but it was simplified to three or four points.  &mdash;Akrabbimtalk 20:01, 9 July 2009 (UTC)


 * Like many parts of introductory high-school level classes, a big part of the curriculum is about organizing your thinking rather than just presenting actual facts. The idea behind recognizing "chemical" processes vs. "physical" processes is in the first about learning to categorize things.  Secondarily, it is about recognizing what a "chemical" is, and what it means for a chemical reaction to occur.  It is not readily apparent to most people that a process like melting is not a chemical process (but it was "ice" before and "water" after?  Isn't that two different things??? (Ans: no...) ) or that dissolving salt in water is not a chemical process (but, like, the salt dissappears!)  Recognizing what sorts of things can be counted as chemical reactions and which are not requires some training... Which is what this activity is also about.  Usually in the first week of high school chemistry, besides learning this, one also learns basic classification schemes of matter, so that one can recognize the difference between, say, a pure substance and a mixture of substances, or between a heterogeneous mixture and a solution.  --Jayron32. talk . contribs  20:21, 9 July 2009 (UTC)

Indeed. But you can learn how to categorise things without resorting to concepts that are not really important to real scientists.

I guess you could say chemical changes involve breaking and forming chemical bonds. But there are many processes that are traditionally considered physical which do in fact involve bond fission and formation. For example, water boiling. Intermolecular hydrogen bonds are broken as the liquid turns into gas. It all seems a bit pointless to me.

I imagine it would be perfectly possible to avoid classifying things as physical or chemical changes and just talk about what's actually going on at the molecular scale. Dissolving is one of those processes that falls on the border between chemical and physical: Na+···Cl− ionic bonds are broken and ion-water interactions form, energy changes hands (enthalpy change of solution is +3.9 kJ/mol), you can write a chemical equation for the process {NaCl(s) + aq → Na+(aq) + Cl−(aq)}, and the product (NaCl solution) has very different properties from the starting materials (NaCl(s) and water).

Ben (talk) 21:45, 9 July 2009 (UTC)
 * It's a bit late at night, so my interpretation is a bit fuzzy, but from what the last two posts above me have said, it seems they're discussing lies to children - which is a good and necessary thing. The link might be useful to either of them, or to anyone interested in what they were saying. Vimescarrot (talk) 22:02, 9 July 2009 (UTC)


 * Its not really lies; its more of a bridging heuristic. Its not that, several weeks later, we don't teach more details about these things.  Its more of a learning to crawl before you walk thing.  Yes, some kids can walk right away, but many need the extra help crawling first.  They can all get there, but just as you wouldn't teach someone to read Shakespeare before you read Dr. Seuss, generally we teach the simplified stuff first.  --Jayron32. talk . contribs  01:25, 10 July 2009 (UTC)

Plasma weapons
We see plasma weapons in movies and games all the time. I didnt understand what plasma was until I played Halo. The plasma pistol and rifle in the game are powered by batteries and when I fired it on a wall it would show a sort of melting of the wall. I suppose the batteries heat up the plasma. What really is plasma and can such weapons be really made? —Preceding unsigned comment added by 116.71.49.65 (talk) 16:17, 9 July 2009 (UTC)


 * --Shantavira|feed me 16:28, 9 July 2009 (UTC)
 * Weapons in science fiction stories (including games) tend to be based more about looking and sounding good, than any sound scientific principles, so don't expect to see a Type-25 Directed Energy Rifle to look anything like it does in the game, if it's remotely possible to make a weapon on the same principles. Vimescarrot (talk) 18:55, 9 July 2009 (UTC)
 * In almost every case they grossly underestimate the amount of power needed to make such things do what they do in the game. Sure, you could probably make something that sat on the back of a large truck...with another two large trucks full of batteries to power it...but something you could lug around like a machinegun is really not reasonable.  The stored energy for any weapon has to come from somewhere - and there are few sources of energy more 'dense' (in terms of power-to-weight ratio) than explosives.   This is the main reason why we don't see people using laser pistols and rail guns out on real battlefields.  Game designers (and I'm a games programmer - not a designer) don't care to be limited by the bounds of what is realistic - and that's a good thing in many ways because breaking the shackles of reality is what makes most games fun. SteveBaker (talk) 04:34, 11 July 2009 (UTC)
 * "Sure, you could probably make something that sat on the back of a large truck...with another two large trucks full of batteries to power it..." -- I think they actually made a plasma cannon that would just barely fit inside a jumbo jet (the plasma generating equipment and the batteries, plus all the fire-control computers and whatnot, took up most of the fuselage). So that would give you some idea of how big a plasma cannon would be in real life.76.21.37.87 (talk) 05:32, 11 July 2009 (UTC)
 * So perhaps a plasma cannon is a viable weapon for a nuclear powered battleship, but not so much for an individual solider. Googlemeister (talk) 16:39, 13 July 2009 (UTC)
 * My point exactly. 76.21.37.87 (talk) 00:43, 14 July 2009 (UTC)


 * On the other hand, would a plasma cannon fitted on a warship be any more useful in battle than the conventional stuff that you usually find on there already - the main guns, large gattling guns, missiles, etc.? --Kurt Shaped Box (talk) 00:53, 14 July 2009 (UTC)
 * It could be useful for shooting down nuclear missiles... 76.21.37.87 (talk) 01:16, 14 July 2009 (UTC)

Barton's pendulums
Was Barton's Pendulums invented by Arthur W. Barton or his father Edwin H. Barton and does the original experiment apparatus still exist today. Thank you. Clover345 (talk) 16:38, 9 July 2009 (UTC)


 * The source linked from the article says it was E.H. Barton. 71.236.26.74 (talk) 16:48, 9 July 2009 (UTC)


 * The apparatus being a very simple one, but not very manoeuvrable, it was almost certainly dismantled soon after the experiment.--Shantavira|feed me 07:25, 10 July 2009 (UTC)

Freeview (UK) - software updates?
Does Freeview transmit software updates for TVs? I know it sounds unlikely, but I swear my TV (which has an integrated freeview receiver) announced a couple of days ago that a software update was available & did I want to install it. So. Unlikely as it sounds, does Freeview transmit software updates for TVs? --Tagishsimon (talk) 22:06, 9 July 2009 (UTC)
 * You'll have better odds of getting an answer at the Computing Reference Desk. Looie496 (talk) 22:53, 9 July 2009 (UTC)
 * Good point. I'd forgotten we had such a thing. Question now removed. --Tagishsimon (talk) 22:57, 9 July 2009 (UTC)

Milky Way colliding with another galaxy
From a human on earth perspective, what would it be like to witness a galaxy colliding with ours? --Reticuli88 (talk) 22:40, 9 July 2009 (UTC)
 * Well, for one thing, on human time scales, the collision of the galaxies wouldn’t be an event to observe, so much as a very long process, of which only a small portion would be visible within one lifetime. The milky way galaxy has a diameter of 100,000 light-years, and the colliding galaxy would be approaching at sub-light speeds, so the collision process would take perhaps a million years.  Red Act (talk) 23:19, 9 July 2009 (UTC)
 * For one thing, the band of light which is the Milky Way would appear much different, depending on the other galaxy's angle of approach. Red Act is right, though, in saying that we probably wouldn't see much of anything in terms of dynamic movement or astronomical events; the likelihood of even one star colliding with another during this process is minimal. Perhaps the supermassive black hole at the galaxy's center would be a bit more active due to an increase in infalling matter, but that would only be of interest to astronomers. - Running On Brains (talk page) 23:27, 9 July 2009 (UTC)
 * Many earthlings don't see the Milky Way much anyway. Algebraist 23:34, 9 July 2009 (UTC)
 * I remember reading somewhere that when M31 and the Milky Way collide, out of the ~250 billion stars in both galaxies combined, no more than five actual stellar collisions are expected to occur. That's like 2 * 10-9 percent of the stars. J.delanoy gabs adds  23:51, 9 July 2009 (UTC)
 * This is correct. When galaxies collide, essentially none of the stars actually run into each other. But the gas does, causing a massive starburst, which means lots of bright blue stars and spectacular emission nebulae. Plus a whole load of supernovae going off. Of course, the time scale for this sort of thing is on the tens of millions of years. On a rather smaller scale, the Large Magellanic Cloud is currently running into the Milky Way, only one galaxy (the MW) is much more massive than the other (the LMC). If you go to the southern hemisphere, you can easily see the LMC with the naked eye from a dark site - it's much bigger than the full moon and looks like a detached bit of the Milky Way. And you can see the SMC too. Modest Genius talk 03:06, 10 July 2009 (UTC)

That's amazing considering that, from photos of galaxies, they look so dense. thanks.--Reticuli88 (talk) 16:19, 10 July 2009 (UTC)
 * They look dense because the instrument taking the photo doesn't have the resolving power to show just how small stars are compared to galaxies. For that matter, your screen doesn't have pixels small enough for that either. Algebraist 16:21, 10 July 2009 (UTC)
 * Bear in mind that the ratio between the distance to the nearest star to the diameter of the sun is about 30 million to one. there's a lot of empty space. Modest Genius talk 23:08, 10 July 2009 (UTC)