Wikipedia:Reference desk/Archives/Science/2011 January 9

= January 9 =

Why does any number muliplied by nine add up to nine?
i.e 13times 9=117. 1+1+7=9 and so on.AM radio frequencies in Australia are all multiples of nine. , 9 January 2011 (UTC) —Preceding unsigned comment added by 118.208.93.193 (talk)


 * I removed your e-mail address so that you don't get unwelcome attention from spammers - any answer to your query will appear here. Mikenorton (talk) 00:29, 9 January 2011 (UTC)


 * They add up to nine because they don't add upto 8. See, Numerology, Apophenia, Confirmation bias, and 23 enigma. --Plasmic Physics (talk) 00:55, 9 January 2011 (UTC)


 * It's to do with us using base 10. If you add the digits of an number, in any base, and end up with base-1, then the original number is divisible by base-1. If you end up with a (multiple of a) factor of base-1, then the number is divisible by that factor. For example
 * 123 (= 3 * 41), is 1+2+3 = 6, so 123 is divisible by 3.
 * 32hex (50 in decimal), is 3+2=5. 5 and 3 are the factors of 15 (16-1), so 50 is divisible by 5.
 * There should be an article on this, as WHAAOE, but I don't know what the phenomena is called. CS Miller (talk) 01:09, 9 January 2011 (UTC)
 * BTW, you might have been better asking on the maths desk. CS Miller (talk) 01:11, 9 January 2011 (UTC)
 * See Casting out nines for a related, somewhat more general phenomenon. Buddy431 (talk) 04:22, 9 January 2011 (UTC)


 * Let me first of all rephrase your question more clearly. "Any (positive integer) number multiplied by nine" gives you a (positive integer) number that is divisible by nine. What you asking is, why do all positive integer numbers divisible by nine have their digits, in base 10 notation, adding up to 9. Well, they don't. For example, 99=11*9, 990=110*9, 9900=1100*9, etc. are all divisible by 9, but the sum of their digits is 18. The correct statement is: "In base 10, any positive integer that is divisible by 9 has its sum-of-digits divisible by nine, as well". In the example I just gave, the number 9900 = 1100*9, the sum of digits 9+9+0+0 = 18 = 2*9. A simple, non-rigorous proof -- I am a physicist, not a mathematician :) -- is as follows. Imagine you have a number [ an ... a1 a0 ]. For example, if the number is 3456, a3 = 3, a2 = 4, a1 = 5, and a0 = 6. Incidentally, 3456 = 384*9 and 3+4+5+6 = 18 = 2*9. Since we use base 10, the value of [ an ... a1 a0 ] is x = 1*a0 + 10*a1 + ... + 10n*an. Now, what happens when you divide by 9? Let's divide every term separately. 10*a1 = (9+1)*a1 so residue from this term is 1*a1; the next term 100*a2 = (99+1)*a2 so residue of division of that term by 9 is 1*a2; and so on. When you sum up all the residues you get 1*a0 + 1*a1 + ... + 1*an. This is the sum of digits of your original number! The sum of residues equals the sum of digits. So, if the sum of digits divides by 9, so does the full residue; that means the original number divides by 9, as well. --Dr Dima (talk) 02:08, 9 January 2011 (UTC)


 * The digital root is 9 for all positive multiples of 9. Digital root mentions the generalization to b−1 for base b. PrimeHunter (talk) 02:31, 9 January 2011 (UTC)

Dr Dima in part says the sum of the digits is 18 but as for all whole numbers the digits 1+8 again add to nine.Regardless of how high the number is taken every time the result is added and re-added it wil eventually resolve to 9. I failed maths at school so please be gentle with me.

John Cowell.118.208.9.92 (talk) 03:14, 9 January 2011 (UTC)


 * Can you clarify your question? As you noted, the sum of the digits of any multiple of nine sum to another multiple of nine, eventually summing to nine if you do it long enough (that is, 4617's digits add to 18, and 18's digits add to 9).  This is just as you stated it. &mdash; Lomn 04:09, 9 January 2011 (UTC)
 * Oh, OK, you're referencing this. Dr Dima is being precise about it (in base 10, integer multiple, a formal statement of "might have to repeat to reach 9", etc). &mdash; Lomn 04:12, 9 January 2011 (UTC)
 * See Casting out nines for a more general, related phenomenon. There's an explanation, but it's a bit dense.  One thing to note: whenever you add nine to an integer, you always increase the sum of the digits by zero or by 9.  Check this to see that it works out.  It's intuitively not hard to see why this: if the unit's digit is zero, it becomes a nine, and the rest of the number remains unchanged (for an increase of 9 in the sum).  When the last digit is any other number (1-9), the units digit decreases by one, while the Ten's digit increases by one, for a net increase of zero in the sum of the digits.  Predictably, the reverse is true in subtracting nine: the sum of the digits either decreases by nine, or remains the same. Buddy431 (talk) 04:18, 9 January 2011 (UTC)
 * This is discussed somewhat at our 9 (number) and Digital root articles, and an interesting use of this property is discussed at Casting out nines. It has to do with the fact that in base-10, 9 is the last digit before you have to start reusing digits (ie. the digits "1" and "0" in "10").   WikiDao    &#9775;  11:21 pm, Today (UTC−5)
 * This seems like a fairly decisive and understandable answer that deals a fairly decisive blow against reading too much mysticism into such a thing. Does this mean that the digital root of F in Hexadecimal has the same phenomena associated with it? --Mr.98 (talk) 17:30, 9 January 2011 (UTC)
 * Yes, as I noted above, for base 'n', if the digital root is n-1, then the original number is divisible by n-1. CS Miller (talk) 20:25, 9 January 2011 (UTC)

Ultimately, the reason is that 9 = 10 - 1. --Anonymous, 06:48 UTC, 11/1/11 (or 1/11/11, or...).
 * Regarding the second component of the question: why are AM radio stations broadcast on frequencies that are multiples of 9kHz? Well, you can broadcast on any frequency you like, but the airwaves are a shared channel (and furthermore, they are regulated by the government - specifically, the Australian Communications and Media Authority).  To avoid interference, radio stations need to broadcast on frequencies that are far enough apart that they don't interfere: see frequency allocation for more information.  It happens that for voice (and some music), a frequency band of around 9 kHz is reasonable spacing to preserve quality.  Actually, it's more likely that the ACMA originally allocated a 9 kHz spectrum with the intention of using two side-bands with 4 kHz of signal, and a 1 kHz "spacer"; this was pretty much only suitable for voice; but that more recent AM radio broadcasters use Single-sideband modulation, especially SSB-SC carrier suppression) to expand their signal to fill out 8 kHz with audio signal (suitable for "low-quality" mono music).  So it happens that each frequency is f0 + i×(9kHz), in other words always a multiple of 9 kHz, and f0 = 531 kHz.  This 2006 report, AM radio issues from the official regulatory body in Australia, actually specifies that frequencies are spaced by 9 kHz and may use up to 9 kHz in each sidelobe - meaning that there is potential for frequency overlap.  (AM radio enthusiasts will note that stations with nearby frequencies are laid out to be geographically sparse and are "encouraged" to suppress the "high frequencies" to minimize channel crosstalk).  Nimur (talk) 21:52, 10 January 2011 (UTC)

When and how are 1920s–30s lighthouses lit?
I'm doing research for a painting of the lantern room of a lighthouse. I'm having difficulty finding information on how a lamp is lit and when it is lit. In the "lighthouse technology" section of the lighthouse article, it is mentioned that the Dalén light was used predominantly in the 20th century (up until the 60s), but although I followed through to the sun valve article and its external link, I'm not finding what a Dalén light actually looks like, and where a sun valve would be placed on, or within, the lighthouse. I've also found images of first and second order Fresnel lenses, but not what they look like from above. Are they open at the top to allow heat to escape? (In this example, it almost looks like the answer is "no"). As a mere matter of curiosity, how "hot" was the actual beam of light—could someone stand on the gallery with their back to the lantern room while the light was rotating? Any recommendations for more information on this particular area of the lighthouse would be welcome! –  Ker αun oςc op ia◁ galaxies  01:14, 9 January 2011 (UTC)
 * It was an acetylene lamp, with the "solar valve" which turned it on and off based on the sun shining on the apparatus. Some results are found at Google book search such as . This appears to be a picture of the Fresnel lens and a lamp from a lighthouse, though it may be a different lamp than the Dalen. It went all around and had a vent in the top, naturally to let the combustion gases out. I did not find info on the lightintensity or heat of the lamp. Edison (talk) 02:25, 9 January 2011 (UTC)


 * I found this image, which is the man himself standing next to what is evidently a fresnel, though the caption says it's his sun valve, so I assume the sun valve is attached somewhere (there may even be a Dalén light in there too if you're lucky). Unfortunately I couldn't say which piece of apparatus is which. 213.122.40.179 (talk) 02:31, 9 January 2011 (UTC)


 * I jumped to the Swedish Wikipedia article on the lamp, which linked to an AGA site with some pictures. The solar valve had a bunch of rods which could heat up and turn off the gas when the sun sas shining. See (in Swedish. Google Translate is your friend). Edison (talk) 02:45, 9 January 2011 (UTC)


 * That clarifies the Dalén light perfectly. I was confused because I thought i would actually see it, but the fresnel lens would simply cover it up. A detailed image of the source wouldn't be visible through the lens. Thanks all! –  Ker αun oςc op ia◁ galaxies  03:04, 9 January 2011 (UTC)

Time lapse from brain to tongue.
Any thoughts on the time it takes to make speech from the brain formulating the next word?Think Spoonerisms. John Cowell.118.208.9.92 (talk) 01:20, 9 January 2011 (UTC)
 * It takes perhaps a fifth of a second to voice a known prearranged response when a stimulus is presented, much like pressing a button as a simple reaction time response. If an unknown stimulus letter is presented, the vocal response time is appreciably longer, but still far less than a second. Anecdotally, if one's attention is diverted after an utterance begins, something random and funny may emerge, as if the speech generator were on autopilot and randomly choose a related but unintended word. Certainly the longest time from formulating an utterance to saying it could be many seconds, but the shortest would seem to be a fraction of a second. Mental chronometry researchers have argued for well over a century as to how to determine the time required for internal mental operations, so whether the number you seek is 200 milliseconds or 500 milliseconds or whatever would be open to debate. Edison (talk) 02:10, 9 January 2011 (UTC)

Thinking Spoonerisms maybe I could rephrase in terms of how many words ahead of the tongue is the brain?

Is English spoken more slowly than many other languages e.g.Spanish?

John Cowell.118.208.9.92 (talk) 02:40, 9 January 2011 (UTC)


 * The question can't be answered in any precise way, because the formulation of words is a gradual and distributed process, and "making speech" is an even more gradual process. For a minimal order of magnitude estimate, you could probably take something on the order of 200 milliseconds. Looie496 (talk) 18:45, 9 January 2011 (UTC)


 * The time to start yelling "Stop!" to the driver when a passenger sees a danger ahead of a car, or to yell "Duck!" when some danger is swinging toward people seems less than 500 milliseconds. On TV, there seem to be far more syllables per minute in excited Spanish discourse than in English, but unclear how many words it breaks down into. Some speakers of US English have a very, very slow and drawling mode of speech. Edison (talk) 20:54, 9 January 2011 (UTC)


 * The likely reason Spanish seems to be spoken quicker than English to many English speakers, is quite frankly, because they don't speak Spanish. People often fail to realize how fast they speak in their own language. I'm sure Spanish speakers think English speakers speak fast as well. Also some of this might have to do with the different cadence or rhythm of each language. But if you did a words-per-minute count of English versus Spanish, I doubt they'd be very different. 184.99.113.51 (talk) 01:54, 12 January 2011 (UTC)

electromagnetic waves
How do electromagnetic waves emit? I understand how the elctric and magnetic fields form, but I don't understand how (or why) they move forward. — Preceding unsigned comment added by Sina-chemo (talk • contribs) 09:25, 9 January 2011 (UTC)
 * It is a disturbance in the field that is moving, rather than the field itself. In much the same way, a disturbance on a water surface causes a wave to propagate outwards from the original disturbance without the whole body of water moving anywhere.  Take a look at electromagnetic radiation and come back if you have more questions (the formal mathematical treatment is at the bottom of the article).  Sp in ni  ng  Spark  11:46, 9 January 201it  (UTC)

it was helpful.but it would be better if ther was an image or anything that can help me understand it better.thanks alot.


 * The energy applied to the aerial by the transmitter creates a force field around it -so far so good. As the oscillating voltage reduces to zero, some of the field collapses back into the aerial but  not fast enough for it all to collapse.  What is left of that  force field by the time zero potential is reached,    becomes detached from the aerial. As the voltage builds up in the other direction the old detached field is repelled  and zips off at  the speed of light.  --Aspro (talk) 15:54, 10 January 2011 (UTC)
 * I'm sorry to be pedantic, but "fields" do not experience a force of repulsion or attraction. Electric and magnetic fields cause force on charged particles but they do not induce any force on other fields.  What fields do experience when they interact is superposition.  So it's not quite fair to say the "detached field is repelled." Maxwell's equations are a set of mathematical expressions that describe the way changing fields create new fields; as a group, these expressions provide a way to mathematically describe how electromagnetic waves propagate.  Regarding "why" they propagate, the only real explanation that has physical meaning is something like this: we can observe a set of two related phenomena, called electric force and magnetic force.  We observe that these phenomena can occur in a vacuum; they do not require any medium to "exist" or "reside" in.  It so happens that if we measure carefully, we discover that when either one of these fields changes with time, that causes a new field of the other type to exist.  This interconnected relationship allows waves to propagate, even in empty space.  The mathematical expressions that we use to describe the observed measurements of these fields take the form of a wave equation; this stems from the fact that the defining equations of each physical field can be rearranged as a second order differential equation with relationship to the other field.  Nimur (talk) 22:05, 10 January 2011 (UTC)
 * I should add that we can start one field (or the other) in motion by wiggling around a charged particle according to some pattern. We usually wiggle charges by connecting an antenna up to an electric circuit.  Nimur (talk) 22:06, 10 January 2011 (UTC)


 * ???--Aspro (talk) 22:22, 10 January 2011 (UTC)
 * Can you elaborate about why that was confusing, so that I might explain it better? Nimur (talk) 01:10, 11 January 2011 (UTC)
 * The OP has not indicated that he has any grasp of quantum mechanics. Therefore, I could not see how your reply could bridge over (pons asinorum) from what he could conceptualise to what he couldn't. --Aspro (talk) 20:34, 11 January 2011 (UTC)
 * I don't know what level of previous physics education or intuition the OP has; I am just trying to use terminology that would be consistent with a rigorous physical description, even if it introduces or uses concepts the OP is unfamiliar with. Necessarily, complex questions have complex answers.  Nimur (talk) 21:56, 11 January 2011 (UTC)
 * What's complex about this simple quiry?--Aspro (talk) 21:59, 12 January 2011 (UTC)
 * You can also just say that a radio transmitter produces photons in much the same way that an LED does. 71.198.176.22 (talk) 11:21, 11 January 2011 (UTC)
 * Well, not really, either. LEDs emit photons based on a behavior of semiconductor physics called a band gap; this is a subatomic process and requires a quantum-mechanical explanation; (essentially, you design a semiconducting crystal with certain properties, and then place an electron into a quantum state that forces it to decay to a lower energy level, emitting a photon in the process).  On the other hand, almost all radio transmitters you are familiar with use electronic circuits to move around free electrons as electric current, in a way that is easily explained with classical electrodynamics.  The actual mechanism of causing photon-emission is quite different between an LED and, say, an UHF transmitter/antenna.  Most notably, LEDs tend to emit monochromatic photons, as opposed to a radio circuit (which, though tuned, can emit very broad spectrum of photon energies).  Nimur (talk) 19:54, 11 January 2011 (UTC)
 * Yeah. I was just hoping to get away with band gaps' emission being more similar to electrodynamic emission than thermal filaments, but the three are really all different. Uh, you can just say that it produces photons. 71.198.176.22 (talk) 20:22, 11 January 2011 (UTC)

circular motion
a stunt car makes horizontal circles of radius 20m along the inside surface (with an angle of elevation of 30 degrees) of a vertical cone. the coefficient of static friction between the tires and the road is 0.25. find the possible range of speeds of the car.

i've arrived at these two eqns: n cos 30 =mg+0.25nsin30 and n cos 60 + 0.25nsin60=v^2/20 cos 20. where n is the normal force. how do i continue? — Preceding unsigned comment added by Invisiblebug590 (talk • contribs) 10:17, 9 January 2011 (UTC)


 * In your equations, you are considering the case where the friction force is at its maximum and acting down the slope. This will occur when the car is travelling at its maximum possible speed.  You also need to resolve perpendicular to the slope (where the friction force has zero component) to get "n" in terms of mg.  I read the question to mean that the radius of the circle is 20m  (not 20cos20 as in your equation).  You have also omitted the mass from your second equation.    D b f i r s   12:57, 9 January 2011 (UTC)
 * For the minimum speed, consider the case when the friction force is at its maximum possible value but acting up the slope.   D b f i r s   13:21, 9 January 2011 (UTC)

What did, and will, toilets look like?
I was going to ask this on AOL Answers, but I don't think their users would've been too happy about it, so I asked here instead:


 * 1) What did toilets look like in 1900?
 * 2) What did toilets look like in 1910?
 * 3) What did toilets look like in 1920?
 * 4) What did toilets look like in 1930?
 * 5) What did toilets look like in 1940?
 * 6) What did toilets look like in 1950?
 * 7) What did toilets look like in 1960?
 * 8) What did toilets look like in 1970?
 * 9) What did toilets look like in 1980?
 * 10) What did toilets look like in 1990?
 * 11) What did toilets look like in 2000?
 * 12) What did toilets look like in 2010?
 * 13) What will toilets look like in 2020?
 * 14) What will toilets look like in 2030?
 * 15) What will toilets look like in 2040?
 * 16) What will toilets look like in 2050?
 * 17) What will toilets look like in 2060?
 * 18) What will toilets look like in 2070?
 * 19) What will toilets look like in 2080?
 * 20) What will toilets look like in 2090?
 * 21) What will toilets look like in 2100?
 * 22) What will toilets look like in 2110?

--70.179.178.5 (talk) 12:13, 9 January 2011 (UTC)


 * I'm not sure that we are happy about 22 almost identical questions either, but from the 1800s up to at least 1960, toilets in the area where I live consisted of a thick board with a round or oval hole smoothly carved, and this was set in stone pillars, usually with a stone front, over a deep pit, usually on sloping ground so that it could be cleaned out occasionally from a lower opening. I don't know whether any of these are still in use, but they were standard when I was young.  The variety with two holes side-by-side seemed to fall out of fashion, but my aunt still used one (on her own as far as I know) until about 1970.  We can't predict the future, but perhaps the Composting toilet will become more popular as water becomes more scarce during the next hundred years.    D b f i r s   12:41, 9 January 2011 (UTC)
 * Take a look at this search, many of your questions will be answered by these images - plus a few more such as "what does an elephant toilet look like?"  Sp in ni ng  Spark  13:15, 9 January 2011 (UTC)


 * For your historical toilets, it really depends 1. where you are asking about (India is not the same as, say, England), 2. what income level you are interested in (are you curious about the very poor or the very rich?), and 3. are you looking for the average toilet or the most advanced (though perhaps not used much) toilet? Dividing it up by decade is probably not helpful, because there isn't going to be very rapid change in the design after a point. (If you lift up the top of your current toilet, you can usually see written inside when it was made. A toilet I had in the early 2000s was from the 1960s, and looked like every other toilet I had seen.) Even if we tried to answer, "what does a toilet look like in 2011?", you'd get a wide spread of responses (I have a fairly average toilet, but it looks very different from toilets I have seen in Germany, for example, and certainly is not as high tech as toilets in Japan). And of course we cannot predict the future, much less a century in the future, so those questions are really not going to get useful answers here. --Mr.98 (talk) 15:02, 9 January 2011 (UTC)
 * Part of the geographical variation in toilets is due to whether the location is urban or rural. In general, urban areas get indoor plumbing available earlier than rural areas, so the switch from outhouses to flush toilets in general historically occurs earlier in urban areas earlier than in rural areas.  Red Act (talk) 15:32, 9 January 2011 (UTC)


 * In a given location the toilets will have a variety of styles in a given year. In US cities in 1910, for instance, the wealthy had flush toilets, but the poor had outhouses. In 1960 in the US many rural homes still had outhouses, but virtually all city dwellers had flush toilets. A farm in 1960 in the US might have a flush toilet in the house and the old privy still there by the barn for convenience when working outside. A 1920 flush toilet might still be in use, and hard to distinguish from one a year old. All the internal parts as well as gaskets to connect the tank to the bowl are still readily available for toilets from the 1920's, so it could still be in use through the indefinite future. A friend has a new toilet which will squirt water to the front or rear area of the user, and will blow warm air to dry the bottom. It has a heated seat as well. Edison (talk) 20:43, 9 January 2011 (UTC)
 * You can search at Google Book Search for "flush toilet" or the words without quotes, or "water closet" and restrict the books to a decade. Searching for 1891-1900 I found an 1899 toilet and bathroom. The toilet was much like a modern one, with siphon action, but the tank was elevated on the wall for greater pressure. Anecdotally, this kind worked great. Poorer quality toilets of this period just had "rim flushing," in which water from the mains flowed into the bowl around the rim, with less effective flushing down. As for 1910, "Modern Plumbing Illustrated" (1907) provides some illustrations. Low tanks were replacing high wall mounted tanks in new construction. A larger flush pipe made up for the lower pressure. Here is a description of outhouse at US schools in 1910. Edison (talk) 23:27, 9 January 2011 (UTC)
 * Why does America still use the "flap" type of toilet cistern instead of the better siphon method that's been around for a century or more I expect? 92.15.3.168 (talk) 21:44, 10 January 2011 (UTC)
 * Can you please explain, or link to an example, of what you mean by the siphon method cistern (not to be confused with the siphoning bowl)? Toilet is woefully lacking. -- 119.31.121.84 (talk) 01:11, 11 January 2011 (UTC)
 * 92.15.3.168's comment is puzzling. What is the "flap" toilet you assume is in use presently in the US? By the 1890's toilets which had some flap or pan which opened and closed at the bottom of the bowl were held in disdain in the references I provided. The preferred method in the US 100 years ago was the siphon, in which a deluge of water from the tank flushed out the bowl. Flaps were used on trains in the 1960's, but no longer. They just dumped the poo on the railroad bed. Edison (talk) 03:41, 11 January 2011 (UTC)
 * I was not referring to the bowl, only the cistern. 92.24.190.219 (talk) 22:02, 11 January 2011 (UTC)
 * I understand that American toilets use a "flapper valve" where the water in the cistern is held in place by a flap, shown here http://www.toilettamer.com/htm/toilettamer_media5.htm and is thus likely to be leaking water away all the time, while British toilets use a siphon in the cistern, shown here as the simpler Victorian-style http://www.practicaldiy.com/plumbing/cistern_burlington/cisterns_burlington.php and here in the modern plastic version http://www.practicaldiy.com/plumbing/cistern_syphon/cisterns_syphon.php, neither of which leak. In the British siphon cistern, in its resting state the siphon is empty, but when you turn the handle some water is pushed over the arch of the siphon, which starts it going and rapidly empties the cistern. 92.24.190.219 (talk) 21:53, 11 January 2011 (UTC)

Why is the Washlet hard to penetrate the bathroom fixture market here in the US?
The spray toilets like the Toto Washlet are fairly common in Japan, but why are they hard to enter the market in America? I thought most decent Americans would want the utmost personal hygiene, so why are they still slow to accept the fabled spray-toilet? --70.179.178.5 (talk) 12:13, 9 January 2011 (UTC)


 * I note that the design is based on Japanese rears. Are Americans the same shape?    D b f i r s   13:01, 9 January 2011 (UTC)
 * I'm half-Korean, half-white, and those types of fixtures have worked on me wonderfully! I am a proud owner of a BioBidet 70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)


 * Maybe because the Americans are not so extravagent? --Tyw7 (☎ Contact me! • Contributions)   Changing the world one edit at a time! 16:34, 9 January 2011 (UTC)
 * I still see more Mercedes and other nice European imports than bidet-seats. --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)


 * Bidets are common in many countries, but I don't think I've ever seen one in the United States. I'm not sure there's a concrete reason there other than, "it's not what we're used to."
 * We weren't used to cars for a while, until Henry Ford changed that for us. --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)

I've used them in other countries and, as an American, found them to be extremely odd.
 * We found cars to be quite odd for a little bit. Horses found them even more odd than we did. --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)

That's obviously just because I'm not used to it — my toilet experience has, my entire life, been a "dry" one, and adding water to that just feels exceedingly strange.
 * Attempting to drive a horseless wagon felt exceedingly strange for a time too, and horses thought they were so strange, they'd feel spooked at the sight of a wagon moving without a horse. --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)

Add to the fact that our restrooms are all designed for a single toilet and you have an infrastructure problem. (Not with the integrated bidets, of course. But with bidets in general.) I'm not sure why you'd think that Americans would "want the utmost in personal hygiene" — hygiene is a very culturally relative thing, and most Americans would probably not recognize the bidet as really adding all that much in terms of hygiene.
 * We once didn't recognize soap as being all that necessary for our personal health & hygiene either. For a time, we even thought that any doctor who washed their hands of the so-called "spooks" were "quacks." --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)

My experience is that Americans view the toilet gadgets of the Japanese as an extreme form of using technology to not necessarily useful ends (so to speak) — Americans, from my anecdotal experience, seem to have very little interest in "improving" their toilets, and see the existing models as working pretty well on the whole. --Mr.98 (talk) 17:21, 9 January 2011 (UTC)
 * Skidmarks still strain and even end relationships; the bidet-seats would save them. The water used from the bidet's enema washes would be far cheaper than laxatives. We once thought having a computer in our own homes was an extreme form of technology. We also thought having a GPS navigation aid in our own vehicles were extreme technologies once. The time must come for Americans to realize how useful it would be. --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)


 * Oddly enough, evidently Google has a form of bidets, at least in their women's bathrooms. In this Google YouTube interview with Conan O'Brien, Andy Richter mentions that Conan's assistant is in the bathroom, "front cleansing". (Video time-marked.) –  Ker αun oςc op ia◁ galaxies  18:33, 9 January 2011 (UTC)
 * That's a perk to attract prospective employees, investors, and more business. All other businesses must follow suit if they hope to thrive better, especially in this economy! --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)


 * Living in the U.S. and having avoided such features, I think that my gut reaction when looking at this article is that something is going to go wrong - that feces-tainted water is going to spray off in all directions and shoot out and get all over my pants, etc.
 * The designers of these bidet-seats have considered this in mind, and made adjusting design accommodations to prevent this. --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)

Plus, I think that the nozzle in a public restroom will get sprayed with feces-tainted water from a previous user, opening a potential route of infection.
 * Once the nozzle retracts, it gets sprayed so that all impurities are rinsed off. The water that cleans off the nozzle may be heated, and/or even soaped! --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)

I should further add that the (citation needed) sentence "In order to determine the anal position, 300 male and female employees of Toto were surveyed during development." really raises a red flag, because there's a lot more variety of body shape and size in the U.S. than in Japan. Wnt (talk) 18:39, 9 January 2011 (UTC)
 * Toto is an international corporation. Some of the 300 were foreigners, and they must've used all sorts of body shapes. Possibly, some of the employees were also made to bring their children in for tests to make sure it would work for all ages, body shapes and sizes. Japan has sumo wrestlers too, so some of them may have been test subjects as well. --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)


 * In my limited experience with Googleplex men's bathrooms, the lobby restroom toilets are indeed Washlets, but the employee toilets are ordinary American models. -- BenRG (talk) 21:50, 9 January 2011 (UTC)
 * It's to bring new business and employees to the company, so the lobby must do its utmost to bring prospects the best first impressions. --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)


 * Some good reasons were given so far. Here's some more:


 * 1) Bidets don't make a good gift, since it's just too "icky". So much for it being the latest new Xmas gift.
 * Cars were once too "scary," especially to horses. It was still the latest new Xmas gift for some families. --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)


 * 2) Americans associate dry butts with "clean" and wet butts with "dirty". That perception's not easy to change.
 * I never once thought that. I knew from first learning about these spray-toilets that the water spraying from the nozzle is clean from the get-go, so it rinses off what life throws our way. (My BioBidet BB-i3000 model also has a liquid soap dispenser for extra good measure.) --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)


 * 3) "New technology" toilets have a bad reputation in the US, such as low-flow toilets that leave floaters behind. StuRat (talk) 00:32, 10 January 2011 (UTC)
 * These are seats that can be fitted on most existing toilet bowls. Only the Toto Neorest 600 is a standalone toilet structure. It has options for multiple flow speeds. --70.179.178.5 (talk) 13:01, 10 January 2011 (UTC)

70.179.178.5, please don't break apart other people's posts to you - it makes it very difficult to see who is posting what. Instead, just reply at the end, adding an extra : to the front of your reply to make attributions clear. While I'm sure it's unintentional, your replies read as if you want to start a debate or make a sale. Matt Deres (talk) 14:58, 10 January 2011 (UTC)
 * Agreed. It's really pretty irritating, and trying to counter back endlessly why you think Americans should like these is entirely the wrong approach if you want to understand why they don't like them. --Mr.98 (talk) 23:04, 10 January 2011 (UTC)


 * Americans are creatures of habit. Bidets are some weird European et al. fixation, like the metric system. (!) P ЄTЄRS J V ЄСRUМВА  ►TALK 15:06, 10 January 2011 (UTC)


 * Humans in general are (for the most part) creatures of habit, but there seems to be an additional psychological aversion to, and even disgust of, alien anal cleansing habits (said aversion unaddressed by the article). I remember how strange health faucets seemed when I fist saw them (traveling in Thailand and Malaysia), but now I wouldn't be without one and have installed them in my US home -- and I cringe slightly at the prospect of using only toilet paper at public toilets.  Still, I wouldn't want a washlet's robotic arm doing what I'd rather do myself, not to mention the fact that a washlet may cost a hundred times more.  Likewise, I wouldn't object to using an electric toothbrush, but I don't want a robotic arm moving it around in my mouth. -- 119.31.121.84 (talk) 01:47, 11 January 2011 (UTC)
 * It's not an "arm," it's a nozzle spraying the rinse. Sure, it can move up-down, left-right to make sure every last square millimeter is cleaned off, or it can even vibrate/pulsate to massage you. I've found them to be quite a vast step up from the old way.


 * I haven't tried "health faucets." I hope that when I do, it doesn't give me a bad feeling. --70.179.178.5 (talk) 02:12, 11 January 2011 (UTC)
 * I suspect 70.179.x.x is making a good rebuttal; I should emphasize that, per request, I was giving a simple psychological snapshot of an American perspective, not making an argument that I planned to defend. Though I should point out that from an American perspective no part of the inside of a toilet is generally thought of as clean, even, I suppose, if it is retractable.  For example, the happy bachelor expects that when cleaning a toilet (an action of last resort, typically undertaken only when attempting to recover a security deposit) one will find the underside of the rim covered with fairly thick amounts of feces and/or strange dark aquatic flora which one trepidates to identify. Wnt (talk) 06:58, 12 January 2011 (UTC)

Wet-Bulb Temperature vs Dew Point Temperature
Are these two the same? There are articles on both, with subtle references to each other but to me they seem to describe more or less the same thing. What is the difference between these two? 196.210.162.116 (talk) Eon —Preceding undated comment added 12:50, 9 January 2011 (UTC).


 * I'm no expert on thermodynamics (I am getting all this from just reading our articles) so I might have this wrong but my reading is as follows. To find the thermodynamic dry-bulb temperature the air is cooled by allowing water to evaporate into it until saturation is reached.  This process is adiabatic, ie no heat is input or removed from outside the system.  To find the dew point the air is again cooled (but not necessarily adiabatically) to saturation but no "extra" moisture is injected into the system.  The first conserves heat, the second conserves moisture.  The numerical relationship between these is given at psychrometric chart.  Sp in ni  ng  Spark  21:06, 9 January 2011 (UTC)


 * Brilliant explanation, except you said dry-bulb in one spot where I think you meant wet-bulb. Now that you provide both explanations in the same paragraph I can see the difference. I had actually thought that the two are equivalent even given your explanation. But clearly there is a difference, for example if hot air had 0% relative humidity then it would have a dew point of absolute zero but a wet bulb temperature still somewhere above that. Maybe this is a bad example because water would freeze at those low temperatures but the example sets my mind at ease. 196.211.175.2 (talk) 08:24, 10 January 2011 (UTC) Eon


 * I know the answer, but it will cost you. Short Brigade Harvester Boris (talk) 02:52, 14 January 2011 (UTC)

People in coma
Hi. Is there a list of people in coma? How many living notable people are in coma? Does this deserve a list and a category? Regards. emijrp (talk) 13:51, 9 January 2011 (UTC)


 * The closest I could find is Persistent vegetative state and Category:People with severe brain damage. PrimeHunter (talk) 14:01, 9 January 2011 (UTC)


 * As our coma article explains, the state that neurologists call coma rarely lasts for more than a few weeks -- is almost always resolves either into brain death or a persistent vegetative state. When the broader literature speaks of somebody being in a coma for years, it almost always refers to what neurologists call a persistent vegetative state. (Sorry for the pedantry.) Looie496 (talk) 18:40, 9 January 2011 (UTC)


 * So, are there notable people in vegetative state? I guess so, a list would be interesting. Also, a list with the longest coma states, and people who recovered from them. emijrp (talk) 19:20, 9 January 2011 (UTC)


 * Terry Schiavo springs immediately to mind. -- Jayron  32  20:57, 9 January 2011 (UTC)
 * She's not in a coma. Staecker (talk) 03:50, 10 January 2011 (UTC)
 * She was in a coma, and then in a vegetative state for 15 years (though not currently, of course). Buddy431 (talk) 04:39, 10 January 2011 (UTC)
 * Ariel Sharon is the only one I know of currently. Buddy431 (talk) 00:47, 10 January 2011 (UTC)
 * The request seems to be for notable people presently in a persistent vegetative state. I fear it would include a vast number of folks who have shaped our world; writers, scientists, actors, businessmen and soldiers who are now in their 90's and awaiting death, being spoon fed, and having their diapers changed, not knowing who or where they are. We hear about them only when they die. Edison (talk) 06:00, 10 January 2011 (UTC)
 * Imagine a "List of people who were gaga at the end." Perhaps  Reagan, Churchill, and many more. In most cases, their family pretends they were still alert at the end. Perhaps their handlers use their names to endorse their old favorite causes, despite their senile dementia. A lack of public appearances is one indicator that they have lost it. Edison (talk) 06:04, 10 January 2011 (UTC)


 * The living people at Persistent vegetative state are Haleigh Poutre, Aruna Shanbaug, Ariel Sharon. PrimeHunter (talk) 18:10, 10 January 2011 (UTC)

Balancing of reciprocating masses
See section 22.3 in above reference on balancing of reciprocating masses .the book mentions that only cos component of primary unbalanced force is balanced by the additional ass B. it really dosent looks so,because the sine components of mass m and mass b are also in opposition to each other. kindly clarify my point ,or please pint out where i am making a mistake. Kndly do help me :in which direction is the secondary unbalanced force acting? —Preceding unsigned comment added by 59.93.128.223 (talk) 14:04, 9 January 2011 (UTC)
 * The way I read it, the sine component produces an unbalanced force perpendicular to the line of stroke, and this is indeed not balanced by the mass at B, so the best solution is a compromise but I haven't read the article carefully, and I've never met the theory before, so please forgive me if I have misunderstood!   D b f i r s   17:16, 9 January 2011 (UTC)

Dissolving gases in liquids
I have a system where a gas is added above a liquid (for example methane above water) over a very wide range of possible partial pressures. I need to predict the concentration of the gas in the liquid at equilibrium. Henry's Law tells me that the concentration will be proportional to the pressure at least for relatively low partial pressures. So, this leads me to two questions, A) what is a good reference for Henry's Law constants (for example, the proportionality constant for methane and water at 25 Celsius), and B) is there a way to predict (or at least lookup) when and how the behavior will diverge from Henry's Law at very high partial pressures? For the purposes of this question, one can assume the gases are chemically inert in the liquid. Dragons flight (talk) 14:28, 9 January 2011 (UTC)
 * There's certainly no "one-size-fits-all" solution. You can easily calculate Henry's Law constants for a variety of gases from the data at this site, assuming linear solubility over 0–101.3 kPa (a fair assumption for a sparingly soluble gas like methane, a bad assumption for a reactive gas like chlorine). As for extrapolating those constants to higher pressures, well, you do so at your own risk! If the data are important for an application, they need to be measured. Physchim62 (talk) 02:18, 10 January 2011 (UTC)
 * This system should be well studied, methane clathrate is a type of substance in the phase diagram. Graeme Bartlett (talk) 23:14, 10 January 2011 (UTC)

Mass/Energy
I've watched in a Nova science show that when an object approaches the speed of light, any additional energy that gets put into moving the object changes into mass. (E=mC^2) --Tyw7 (☎ Contact me! • Contributions)   Changing the world one edit at a time! 16:33, 9 January 2011 (UTC)
 * Yes, that is one way of looking at it, though experts tend to frown on the formula that I learnt in the 1960s: $$m = {m_0 \over {\sqrt{1 - \frac{v^2}{c^2}}}} \!$$ because treating the "extra" like normal mass can lead to error. Another way of looking at the situation is to treat the extra as "super-kinetic energy" (since the  ½mv2 of normal kinetic energy is the preceding term in the Taylor Expansion), but the preferred modern approach is to talk about momentum where the relativistic momentum is given by :$$p = {m_0 v \over {\sqrt{1 - \frac{v^2}{c^2}}}} \!$$.  See Mass in special relativity for details.    D b f i r s   17:03, 9 January 2011 (UTC)
 * Excuse me, what was the question? –Henning Makholm (talk) 17:22, 9 January 2011 (UTC)
 * I assumed that the OP was asking about the "energy changing into mass" concept, but I agree that there is no question mark.   D b f i r s   17:50, 9 January 2011 (UTC)

Car battery
If the positive and negative connectors on a standard 12v car battery were connected with a wire, what would happen? 82.44.55.25 (talk) 18:17, 9 January 2011 (UTC)
 * The wire would melt and there is a good chance that you would get a fire or explosion. Looie496 (talk) 18:35, 9 January 2011 (UTC)
 * See Short circuit. Ka renjc 18:37, 9 January 2011 (UTC)
 * Do not try this at home. A new fully charged "12 volt" car battery might have an internal resistance of 0.01 ohms, and a short circuit current of 1200 amps. A 1 foot piece of #12 wire (.205 cm diameter) has a resistance of about .002 ohms, so it would not limit the short circuit current much. The contact resistance of the wire to the battery terminals might limit the current more than the resistance of the wire, since the wire end would spark and melt when the connection was made. A #12 wire would heat up red hot and melt, and the battery might explode. A much smaller wire would also melt or vaporize. A battery  may have hydrogen gas present above the liquid, which  could explode due in a short circuited battery and cause fragments of the battery and the acid to fly around. Edison (talk) 20:34, 9 January 2011 (UTC)
 * In spite of the risk it is not uncommon for a mechanic to dab lightly the tip of a grounded wire to a battery terminal as a test for voltage. The hot arc at the point of contact melts the lead terminal and the wire tip, hopefully breaking the connection before more damage occurs. It is also possible but not recommended to use a car battery for electric Arc welding where the short-circuit arc is deliberately maintained. Cuddlyable3 (talk) 23:50, 9 January 2011 (UTC)
 * Many years ago I was working on a Volkswagen Beetle with a 6V battery. I was using a shifting spanner (adjustable wrench) and inadvertently shorted the two terminals with the spanner.  Big spark and buzzing noise for the half second until I whipped the spanner way!  There was no explosion and the spanner didn't melt.  However, it gave me an unpleasant surprise and since then I have been sufficiently careful that it hasn't happened again.  Dolphin  ( t ) 02:13, 10 January 2011 (UTC)
 * A farmer bought a 4-pronged fork and a tractor battery. He tossed them in the trunk (EN. boot) of his car and they bounced around on the bumpy ride home. When he got home he found a cloud of smoke and a 3-pronged fork. Cuddlyable3 (talk) 04:32, 10 January 2011 (UTC)
 * I never really appreciated electricity, despite sticking my thumb in a 120 volt light socket, until I connected a cliplead incorrectly on a 110 volt DC circuit and saw it light up. Edison (talk) 05:54, 10 January 2011 (UTC)
 * And that, ladies and gentlemen, is how Edison invented the lightbulb! APL (talk) 21:31, 10 January 2011 (UTC)

Bailey bridge girders
Bailey and similar bridge girders are made of sections that are less than about two or three metres long. What is the mechanism that joins these sections together into a single girder? The bottom of the girder, at least, will be in tension. I have not been able to find any photo or diagram of the joining mechanism. Thanks. 92.15.24.111 (talk) 18:33, 9 January 2011 (UTC)


 * Most Bailey bridges are assembled and installed in a matter of days by a small crew. Common hand tools are utilized. All connections are pinned, bolted or clamped. No welding is necessary.. The joins on the bottom girder row can be seen in this picture here and here and here is a diagram. Cuddlyable3 (talk) 23:36, 9 January 2011 (UTC)


 * The 8 15/16" long x 1 27/32" diameter panel pins (which fit into matching holes in each panel) bear the tension between each section and are themselves secured by much smaller safety pins. 71.198.176.22 (talk) 15:40, 10 January 2011 (UTC)

Unfortunately there is no close-up diagram or photo which shows you how the panels lock together, particularly at their base where they will be in tension. The lower locking mechanism is described somewhere as a "knuckle joint" but the only details I have been able to find about a knuckle joint is this: http://www.ejsong.com/mdme/modules/7759G_Mechanical_Design/knuckle_joint/Knuckle_joint.html 92.15.3.168 (talk) 21:00, 10 January 2011 (UTC)
 * Here, in see the inner tab of the knuckle joints on the corners of the upper two of the four panels stacked closest to the camera, and the outer slots on the bottom two of those four. The tabs fit into the slots, the panel pins fit through the matching holes, and then a safety pin goes through the hole in the panel pin. The finished assembly is fairly visible along the right side of . 71.198.176.22 (talk) 11:42, 11 January 2011 (UTC)

Its rather alarming that all the stress in a big bridge with a wide span and a heavy load goes through one not very big pin. 92.24.190.219 (talk) 23:47, 11 January 2011 (UTC)


 * That's why those bridges are supposed to be temporary. A helicopter can hoist a tank from a narrower steel cable, if I'm not mistaken. 71.198.176.22 (talk) 05:58, 12 January 2011 (UTC)

Rotary mechanical toothbrush
Would the rotary mechanical toothbrush shown here http://blog.modernmechanix.com/2006/06/27/hand-cranked-toothbrush/ be good for your teeth according to modern dentistry? It appears that it may be quicker to use and encourage going up and down rather than side to side. Thanks 92.15.24.111 (talk) 18:39, 9 January 2011 (UTC)


 * I'm no dentist, but it strikes me that the apparatus there would be very hard to use to get all of your teeth cleaned sufficiently. You'd have to turn it at some very odd angles to get the ones in the back done well. In general I suspect the rotational angle of a modern electric toothbrush would be much more superior to the simple vertical axis of the one shown. But again, this is just a conjecture on my part. --Mr.98 (talk) 21:19, 9 January 2011 (UTC)

Genealogy
Hi all! I'm not sure if this belongs here or somewhere or else, but here goes. I think I may have found a long-lost cousin, but I'm not sure. She shares my maternal grandmother's maiden name. Apparently, this girl's mother's aunt's sister may be my grandma's sister. What is this girl's relation to me? I checked the cousin article, but I'm still not sure. Thanks for the help! --68.101.253.196 (talk) 20:19, 9 January 2011 (UTC)


 * This all depends on whether the girl's mother's aunt was a blood relative of the girl. It might have been the aunt's husband who was the blood relative, in which case you are not related at all, you just have relatives in common. The sharing of the maiden name doesn't make any difference here unless the girl's mother and grandmother retained their maiden names on marriage (or were unmarried). Assuming that the aunt was not an aunt by marriage, and that there are no half-sister relationships, and that the aunt's sister is also an aunt, it seems possible that you could be second cousins because the aunt's sister could have been your grandmother or another sister in the same family, but you would probably not have explained the situation in such a complex way if this had been the case.  If your mother and the girl's mother had been first cousins (their mothers being sisters), then they would probably have known this (though I actually know two first cousins who don't know each other) .  We need to construct a family tree with names to be sure, but a public forum is perhaps not the best place to do this.    D b f i r s   20:48, 9 January 2011 (UTC)

If I understand your discription right, then your grandmother is their great-grandmother, this would make the relative your first niece once removed. --Plasmic Physics (talk) 20:55, 9 January 2011 (UTC)


 * ... but a "mother's aunt's sister" isn't a "great grandmother" -- or have I mis-read the confusing relationship?   D b f i r s   21:57, 9 January 2011 (UTC)

Sorry, I was confused a bit. I correct myself, the relative would be a second niece, not a first niece once removed. By the sound of it, the aunt, sister and grandmother are all siblings, your mother and the other mother would be cousins. You and ayour second cousin should share a set of great-grandparents. --Plasmic Physics (talk) 22:21, 9 January 2011 (UTC)


 * I've never met the idea of "second niece" before. It seems to imply different generations.    D b f i r s   22:46, 9 January 2011 (UTC)

Replace "niece" with "cousin", wrong use of word. --Plasmic Physics (talk) 00:18, 10 January 2011 (UTC)

Sugar Chirality.
Is it possible to change the chirality of sugar? If so; John Cowell.118.208.9.92 (talk) 22:26, 9 January 2011 (UTC)
 * Would it still taste sweet?
 * Would it be absorbed by the body and still be fattening?
 * If not, could it be used as a dietary aid?


 * The article on L-Glucose answers most of your questions.   D b f i r s   22:53, 9 January 2011 (UTC)

Yes to all of the above except, as one person put it in an article on another site about use of isomers of dangerous drugs in OTC medications (such as nasal inhalers) "there is no magic chirality fairy that will turn L-isomers into D-isomers." You would have to use some form of synthesis. Apparently as per the article above it is an expensive (comparatively) process but is known. 65.29.47.55 (talk) 00:43, 13 January 2011 (UTC)

Tooth Decay/Heat
Since evolution would not have anticipated heating food and drink,have any comparative studies been done on tooth decay of wild primates and other related animals to that of humans?

John Cowell.118.208.9.92 (talk) 23:13, 9 January 2011 (UTC)


 * Don't know about studies, but, since the teeth cool down to body temperature rapidly, the only risk is if the temperature change is so extreme that it actually cracks a tooth, due to uneven thermal expansion. StuRat (talk) 23:30, 9 January 2011 (UTC)


 * If you are heating and cooling your teeth so drasticly that they crack, you're probably setting your face on fire anyways, so I doubt that your cracked teeth are your most pressing concern. -- Jayron  32  01:00, 10 January 2011 (UTC)


 * Actually not so this says it can happen after 3000 cycles. Especially if you drink hot tea then have ice cream. Then there is Jearl Walker who put liquid nitrogen in his mouth (section 4.7) and cracked some teeth. (He's a fun read.) Ariel. (talk) 01:08, 10 January 2011 (UTC)
 * Well there ya go. So a) Don't immediately follow hot tea with ice cream 3000 times in rapid succession, and b) don't gargle with liquid nitrogen, and you should be pretty safe from thermal cracking of your teeth.  -- Jayron  32  01:27, 10 January 2011 (UTC)
 * gasp! medical advice?!? On the reference desk!?! 71.198.176.22 (talk) 14:50, 10 January 2011 (UTC)
 * Shame. If he had used liquid Oxygen, he would have been cleaning his teeth at the same time.  Googlemeister (talk) 17:19, 10 January 2011 (UTC)


 * For the record, our article on Homo ergaster says that species may have been the first to master fire; they lived around 2 million years ago and evolutionary pressure would have had some impact in the time between then and now. Comet Tuttle (talk) 19:33, 10 January 2011 (UTC)