Wikipedia:Reference desk/Archives/Science/2009 January 11

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 11

Polarisation and magnetisation

In electromagnetism, there is an $\mathbf {E}$ field and a $\mathbf {B}$ field. When there are objects present (as opposed to only vacuum), we often introduce the $\mathbf {D}$ and $\mathbf {H}$ fields, as tools to aid in our calculations. Still I would say $\mathbf {E}$ and $\mathbf {B}$ are the physical fields – the ones charged particles actually respond to.

When an object is penetrated by an electric field, its material can get polarised, which means that inside it, an electric dipole moment density $\mathbf {P}$ arises. This is due to the so called "bound" charge density $\rho _{\mathrm {b} }=-\nabla \cdot \mathbf {P}$ into which the positive and negative charges of the material arrange themselves in response to the felt electric field. The amount of polarisation is typically proportional to this field: $\mathbf {P} =\chi \varepsilon _{0}\mathbf {E}$. The bound charge contributes just like other, "free" charge to the electric field: $\nabla \cdot \mathbf {E} =(\rho _{\mathrm {f} }+\rho _{\mathrm {b} })/\varepsilon _{0}$. Note that this means that the polarisation in a point inside the object depends not only on the external, free charge, but also on the polarisation everywhere else throughout the object. Now, the $\mathbf {D}$ field is defined as $\mathbf {D} =\varepsilon _{0}\mathbf {E} +\mathbf {P}$ so that $\nabla \cdot \mathbf {D} =\rho _{\mathrm {f} }$. Thus, $\mathbf {D}$ is what $\mathbf {E}$ would have been (save for a constant factor) if there were no $\rho _{\mathrm {b} }$, i.e., if there were no object present.

Analogously to polarisation, we get magnetisation $\mathbf {M}$, corresponding to a "bound" current density, when a material is penetrated by a magnetic field. We define $\mathbf {H} =\mathbf {B} /\mu _{0}-\mathbf {M}$, which is what $\mathbf {B}$ would have been (save for a constant factor) in the absence of the object. Finally, and here comes my question, I would expect $\mathbf {M}$ to depend on the actual $\mathbf {B}$, but rather, one writes $\mathbf {M} =\chi _{\mathrm {m} }\mathbf {H}$, as if the magnetisation isn't affected by what happens in other parts of the object. How can this be?

I just now realise that by rearranging, I can get $\mathbf {M} =\mathbf {B} \chi _{\mathrm {m} }/(\mu _{0}(1+\chi _{\mathrm {m} }))$, so now it looks like $\mathbf {M}$ does feel $\mathbf {B}$ (and in my mind therefore can be affected by conditions in other parts of the object). On the other hand, I can also get $\mathbf {P} =\mathbf {D} \chi /(1+\chi )$, losing the nice behaviour of the polarisation. How should all this be interpreted really? —Bromskloss (talk) 01:59, 11 January 2009 (UTC)

1. Only in a steady state with a universal dielectric (or magnetic medium) can D and H be described as (proportional to) "what would be there in vacuum". At interfaces, $\nabla \times \mathbf {D} \not \equiv 0$ and $\nabla \cdot \mathbf {H} \not \equiv 0$, which breaks the analogy with E and B; if anything is changing over time, terms like the displacement current also break the analogy.
2. Any arrangement of free charges and currents, dielectrics, and magnetic materials creates some set of fields, and the constituitve relations like $\mathbf {P} =\chi \varepsilon _{0}\mathbf {E}$ only hold for that "final" arrangement of fields (as opposed to "what would be there"). Therefore it is incorrect to say that an equation like $\mathbf {M} =\chi _{\mathrm {m} }\mathbf {H}$ is somehow "missing out on B"; the H that appears is not independent of B but rather an alternative description of the same underlying pattern.

D and H, as you say, are merely bookkeeping, introduced to simplify analysis of the cases where the interdependence of P and E (and M and B) confuses the issue: "The field's this, so the polarization is that — ooh, but that adds a new field foo, which in turn generates a polarization bar…". Their (imperfect) expression in terms only of (the fixed) free charges and currents is better than nothing because it avoids that circularity and lets you skip straight to the answer you would "eventually" get from the back-and-forth between fields and effects (which I called "final" earlier). --Tardis (talk) 22:45, 12 January 2009 (UTC)

I got a question if water can explode?

Sometimes Im haulin a freight of it and its got hydrogen in it. Just like the Hindenberg,- and that exploded. What if the hydrogen escapes? I got lots of guys sodering around here and dont want no ambulance or clean up bill.--Troy da truck driver (talk) 02:59, 11 January 2009 (UTC)

It takes a lot of energy to separate the hydrogen in water from the oxygen, it's not going to happen accidentally. See Electrolysis of water if you want some details of the work required. --Tango (talk) 03:12, 11 January 2009 (UTC)

Hell, you got to have one of those expensive degrees/toilet paper that I aint got to cut thru that thick fog of nebuloformulas. Please explain the article to me in beer drinking, wife beater English, if you'd be so kind.--Troy da truck driver (talk) 03:30, 11 January 2009 (UTC)

I know you're trying to be funny, but "wife beater" kills the mood. --Scray (talk) 03:48, 11 January 2009 (UTC)

"Wife-beater" is a kind of t-shirt. - Nunh-huh 05:18, 11 January 2009 (UTC)

Simply, the most dangerous thing that is going to happen to water is that it gets very hot and starts to boil. Have many people soldering nearby do you think it requires to heat a freight tank of water enough to get it boiling? Or lets put it another way, if large tanks of water were likely to explode when situated near to heat, do you think fire departments would use water to douse fires? Rockpocket 04:49, 11 January 2009 (UTC)

Water is like the ash you get after you burn a lump of wood. Water is the 'ash' left over after you burn hydrogen. You can't burn ash and you can't burn water - same deal. Ash has no energy left in it - neither does water. You have nothing to worry about. SteveBaker (talk) 05:27, 11 January 2009 (UTC)

OP says he's not hauling water but hydrogen. So I guess the question would be "Can a hydrogen - air mixture explode." I'm also not quite sure we can blow off water exploding quite so fast. See BLEVE. It's not a question whether water can burn but more of whether you get a chain reaction of rapid (heat) expansion AFAIK. I once went to a lecture by a guy who mentioned "anything can explode if you get the distribution of particles fine enough." I've been wondering about that ever since. --76.97.245.5 (talk) 06:06, 11 January 2009 (UTC)

• No, he said he's hauling "it and it's got hydrogen in it"; in other words, "it" is water, as per the question title. --Anonymous, 07:09 UTC, January 11, 2009.

A BLEVE only happens with pressurised, flammable liquids - water isn't flammable and whoever trucks water under pressure? The question is quite clear: "...if water can explode". Our OP realises that water CONTAINS hydrogen - and that's the cause of the concern. Whoever told you that "anything can explode if you get the distribution of particles fine enough." was an idiot. Only combustible things can explode - no matter how fine you get the distribution of particles. A fine mist of particles will increase the RATE of reaction - but it can't conceivably alter the DIRECTION of the reaction. If it did, then you could make a perpetual motion machine by alternately burning water then burning hydrogen. This is a stupid discussion. There is only one possible, conceivable answer and that is a simple, unequivocal "NO!". Let's not muddy the waters for an already confused OP. SteveBaker (talk) 06:53, 11 January 2009 (UTC)

The previous example relating water to ash says it all. Genius! -Pete5x5 (talk) 08:17, 11 January 2009 (UTC)

Just to play devils advocate: Could I use water as the fuel for a nuclear fusion explosion? Of course pressure and temperature would need to be extremely high, and the water would be dissociated already. But would a neutral plasma of two parts hydrogen and one part oxygen start a fusion reaction under the right conditions? For extra points: If yes, how exotic does it have to be, and how efficient would it be compared to pure hydrogen? --Stephan Schulz (talk) 08:33, 11 January 2009 (UTC)

Apparently I misread OP's post. Not wishing to confuse him I'd have to ask him to consider the following as unrelated to his post. I can't agree with Steve's assertions that BLEVE requires flammable liquids. Our article expressly states that that isn't so. As for the "idiot" there seem to be quite a few of them [1] with impressive bits of "toilet paper" on their walls. 76.97.245.5 (talk) 09:38, 11 January 2009 (UTC)

Regarding vapour explosions, water can cause a vapour explosion by boiling in a pressurised environment, but it still needs an energy source to heat the water (seeing as water is not combustible and so cannot release any energy through chemical reactions with natural present chemicals), and seeing as the OP mentioned soldering as the only concerning energy source, I think we are safe, as a soldering is not capable of boiling any significant amount of water at any rate even if it is foolishly left submerged. —Preceding unsigned comment added by 92.16.196.156 (talk) 15:25, 11 January 2009 (UTC)

The oxygen would slow the fusion by being in the way, and would greatly increase the pressure of the plasma (which would make it harder to confine), but would not significantly affect the temperature required (for which see Nuclear fusion#Requirements). It would probably not be too far off to say that it would slow the reaction by a third. --Tardis (talk) 19:14, 12 January 2009 (UTC)

If the water is super-hot, you can of course have a steam explosion. --Sean 18:40, 11 January 2009 (UTC)

For example, today in Boston. DMacks (talk) 20:46, 12 January 2009 (UTC)

There is another way that water can explode, when it freezes in a rigid container, such as glass. Since it increases in volume when it freezes, this can cause the container to rupture. StuRat (talk) 06:09, 12 January 2009 (UTC)

"An explosion is a sudden increase in volume and release of energy in an extreme manner" —Preceding unsigned comment added by 129.67.39.140 (talk) 13:38, 14 January 2009 (UTC)

Audio quality - sampling rate versus bits per sample.

I'm trying to make a Arduino computer board play music and simple sound effects - such as you might find in a computer game. Various trade-offs in the $4 computer hardware(!) mean that I have a choice between higher frequency sampling rates and higher number of bits per sample. The system can't do both high sample rates AND high sample precision. If I want to double the sampling rate - I have to knock off one bit from the sample precision. If I want to add a bit of sample precision, I have to halve the sampling rate.

I can have 8kHz sampling rate with 10 bits of precision - or 16kHz with 9 bits or 32kHz with 8...and so on.

How do I make the trade-off to get the best quality of sound to the human ear? Does it make a difference whether I want to play sound, voice or sound effects? I also have an RC audio filter on the output - and I can choose the resistance and capacitance to do whatever filtering is needed.

SteveBaker (talk) 07:05, 11 January 2009 (UTC)

One thing to consider is Nyquist frequency: for example, if you care about sound components with frequencies >8kHz, you really need >16kHz sampling but if you can convince yourself that you only care about somewhat below 8kHz, you can probably get away with 16kHz sampling. O'Reilly's Web Design in a Nutshell has this to say about sample-rate: "As a general guideline, audio files that are voice-only can be reduced down to 8 KHz. Sound effects work at 8 Khz or 11.025 KHz. Music sounds acceptable at 22 Khz." Here is a breakdown of ranges of some sound types. Or get a CD of some representative types of sounds and fiddle with the equalizer to see what range cutoff doesn't sound crappy. DMacks (talk) 07:41, 11 January 2009 (UTC)

This is the ENTIRE computer!

Yeah, yeah - I understand all of that. I want 22kHz (roughly the upper limit of human hearing) and that needs >44kHz (because of Nyquist). I'd also like to have at least 12 bits of precision per sample. But I simply can't have that much because this project is engineered down to a price - not up to a quality-bar. I know I can't get what I want - and the music is going to sound pretty bad. But what I need is to do the very best I can with what I have in a $4 Atmel AVR computer! What I'm really looking for is the relationship between "perceived sound quality" and the sampling rate AND (importantly) the number of bits per sample....perhaps "dynamic range" is the thing I need to think in terms of...but I'd like some science. SteveBaker (talk) 16:47, 11 January 2009 (UTC)

Perhaps the best way to find out the answer is through experimentation. Start with a high-quality audio file of the type of music you want to play, reduce the sampling rate and/or precision, and see what combination gives you the best compromise. Not actually having tried it myself, my inclination is to go with 32 kHz at 8 bits. Having way too little bandwidth leads to very noticeable reduction in quality. Compare, for example, FM radio's 15 kHz audio bandwidth against AM radio's less than 5 (IIRC); the difference is dramatic. --98.114.98.136 (talk) 17:24, 11 January 2009 (UTC)

Again, the link I posted breaks down different types of sounds (including "voice" and "piano", which seem representative of two of your three areas of interest) and what quality various eq bands contribute. Seems to support 98's 32kHz sample-rate thought, given that up to 8kHz sound components look pretty important, therefore 16kHz sample would probably distort badly there. DMacks (talk) 19:31, 11 January 2009 (UTC)

Is the limit in RAM or CPU speed? If it's RAM (or for that matter, flash memory, EEPROM or IO pins), try the Sanguino instead ? If 4K isn't enough, wait 3 months and you may have 16k [2]. BTW, while I'm not an audio engineer I strongly suspect for speech only 8k with 10 bits might be better. Most speech codecs are 8kHz, even say G.711's μ-law algorithm and A-law algorithm which in terms of perceived quality are still some of the best telephony codecs around (admitedly that's because all of the other ones have concentrated on bandwidth). I'm sure there most be some listening tests out there that will offer some help. You may want to try the Hydrogen Audio forums (people who really understand audio and science hang out there and do double blind tests etc, not the junk OMG my $200 cable has so much better air or OMG fibre optic gives so much better quality for my digital audio then coax or other mumbo jumbo kind) Nil Einne (talk) 21:35, 11 January 2009 (UTC)

No - it's not exactly RAM or CPU that's the problem here. The ATmega chips don't have a 'real' digital-to-analog converter. They use a technique called PWM (Pulse-Width Modulation) whereby there is an internal hardware counter that counts up to some specified value then turns on a digital output pin - then it counts up to a different specified value and flips it back to a zero again - the resulting digital signal is then integrated with a simple RC low-pass filter to make a true analog waveform. The ratio between the "on" and "off" time is therefore the "analog" value. So we have a '1' bit emitted for 'A' clock cycles and a '0' but emitted for 'B' clock cycles - and my software can set A and B as frequently as is reasonably necessary to maintain the sample rate (I could certainly update those numbers at 20kHz - maybe at 40kHz if I don't need much CPU time to do everything else). So here are the 'givens':

• A+B must equal the clock-rate divided by the desired audio sampling rate.
• A/B gives the voltage.
• A and B are both integers
• The underlying clock ticks at 8MHz (I can't change that - it's the clock frequency of the chip).

So if I make the sample rate be (say) 8kHz - then A+B=1000 clock ticks and I can vary A from 0 to 1000 and B from 1000 to 0 and end up with A/B having values from 0 to 1 in steps of 1/1000 - ie a 10 bit sample precision. If I make the system run at 16kHz then A+B=500 clock ticks - so A can be anywhere between 0 and 500 and B anywhere from 500 to 0 - and now A/B is accurate to only 9 bits. So there is a straight trade between sample frequency and sample precision.

I could do this experimentally - but there are several reasons why not:

1. I'm getting a little deaf and at 54 years old my high frequency hearing is crap. 16kHz might sound OK to me...but not to anyone else!
2. The software for replaying audio on such a horribly limited machine is a bitch to write - there is all sorts of ugly trickery involved and changing the sample frequency and precision is FAR from a matter of changing a command line parameter and running it again! It takes me HOURS to write the code because each precision trick requires different data compression and byte alignment.
3. I'd like to understand the relationship that's underlying this. These two numbers are GENERALLY completely unrelated in terms of performance - but here they are tightly (and annoyingly) coupled!

SteveBaker (talk) 23:15, 11 January 2009 (UTC)

Steve, Would your system allow for "subband processing" with variable bit-allocation ? Say, using 12 bits/sample for 0-500Hz range (sampled at 1000 samples/s), 11 bits for 500-2000Hz and so on. The system design problem will be significantly more complicated but it will permit a better quality/processing-power tradeoff - at least if you were designing a system from scratch. Abecedare (talk) 21:47, 11 January 2009 (UTC)

I'm not outputting simple sine waves - these are things like short audio samples or waveforms made by 'FM-synthesis' and driven with MIDI-like note-on/note-off data for music with four note polyphony. So I don't really know what frequencies are present in the music signal - but for sample data, I could probably do some offline processing to extract two bands of frequencies. I could certainly do something different for speech than for music if that helps. I suppose I could use multiple PWM outputs (I might have one or two to spare) added together off-chip...but splitting my audio into bands in realtime is a bit 'ikky'. It's worth thinking about though - that's definitely food for thought - thanks! (However, I'd STILL like to understand the relationship between sample frequency and sample precision in terms of how they affect perceived quality. SteveBaker (talk) 23:15, 11 January 2009 (UTC)

To address your last point (understand the relationship between sample frequency and sample precision in terms of how they affect perceived quality) on a completely theoretical level:

1. Essentially, you are looking for the bandwidth B vs (quantization) noise Q tradeoff. As a starting point, you can compute the information theoretic channel capacity, making the usual AWGN modelling assumption, to see whether (8kHz, 10 bits) is "better" than (16kHz, 9 bits).

2. However the channel capacity results are likely to be quite irrelevant to your problem, since they ignore all a priori information about the source (voice, music) and receiver (human ear). So here is another strategy:

• For large enough number of bits M, one can confirm that the quantization noise is white and compute its noise level (power spectral density) Q,
• Now analyze the spectrum of your "typical" audio signal. We would expect this spectrum to level off or start decreasing for higher frequencies.
• Roughly speaking, there is no point in preserving the spectral components of the audio signal that are not "significantly" larger than the noise at that frequency. So this provides an upper bound on the largest "useful" sampling frequency corresponding to number of bits B. Now we play around with different choices of B's to try to get the useful sampling frequency and achievable sampling frequencies to "match" as closely as possible.
• This scheme is likely to be better than (1), since it at least takes some account of the properties of the signal source. But it is still has several problems, such as (a) it ignores any properties of the human ear, (b) the optimal scheme will depend upon the audio source (voice vs music vs type of music, say samba vs classical :) ) and (c) even for a fixed audio source (i.e., fixed spectral shape) the optimal scheme will depend upon the volume ( at which the audio is played dynamic range), since playing the music at half the volume is equivalent to reducing the number of "true" encoding bits used by 1, or doubling the quantization noise level.

Absolute thresholds of hearing by age in males and females.

3. One can further extend the above scheme to account for at least some information about the hearing system. For example, we know that the ear is less sensitive to higher frequencies (see adjoining image). So before comparing the audio spectrum with the noise source in (2) above, we can "weigh" it by the hearing sensitivity (see noise shaping, for a related though non-equivalent idea). Of course, this scheme too is completely heuristic and far from perfect, since, in addition to the problems noted in (2), the sensitivity curves are derived by playing a single tone at a time, and ignore effects like frequency masking.

In summary, the question you pose has a far from straightforward answer! Note: I know you have a information theory background, so I have not bothered to explain or even wikilink all the techical terms or write down the formulas for computing channel capacity, converting between number of bits B and noise level Q etc. And the problem of defining the terms written in quotes ("weigh", "useful" ," better", "match" etc.) is left as an exercise for the student. :) Abecedare (talk) 01:15, 12 January 2009 (UTC)

I thought about the "channel bandwidth" thing and dismissed it. The nature of my replay system hardware is that in order to double the sample rate - I have to drop 1 bit of sample precision. When I do that, with (say) a 10 bit system, I drop to 9 bits (a 10% reduction in channel capacity) and double the sample rate (a 100% increase in channel capacity) - so I'm getting about 180% of the bandwidth I had with a 10 bit system...every time I do that, I win. That says that I should push the sample rate out 512 or 1024 times what it is now and drop the bits per sample to 2 or even 1 bit. That gives me the maximum number of bits per second. But I know that 2 bit audio is incomprehensible...so channel capacity can't be everything. Information theory falls apart when we apply human cognition to the results! For (2) and (3) - I need to think about it some more. Thanks - this is definitely more the kind of thing I'm looking for. SteveBaker (talk) 15:49, 12 January 2009 (UTC)

Well, technically, it's fully possible. Super Audio CD uses a 1-bit delta-sigma modulation, however, with a far higher sampling rates (~2.8 MHz). Clearly, such a sampling rate is not possible on the AVR, not even closely. So my recommendation would be to go with 32 kHz, 8 bit, assuming you need that frequency range. TERdON (talk) 01:21, 18 January 2009 (UTC)

Another point to note: Typically for music we care about (perceived) fidelity, while for noise voice the goal is often intelligibility. That means, that in order to do a real good job we need to consider not only the different spectral properties of these two sources, but also worry about how these sources are processed cognitively. Incidentally, all these issues arise not only in the field of audio compression but also in the design of hearing aids/cochlear implants, where the design engineers have to work under severe physical size and power consumption constraints. Abecedare (talk) 01:23, 12 January 2009 (UTC)

Yes - although this is not 'easy listening' music - this is a little jingle at the start and end of a game...and the voice output is stuff like "Game Over" and "You Win"...not stuff you really have to think much about. The rest is beeps, sounds of gunshots, the sound that an unrealistically large velociraptor might reasonably make...(they evolved into birds - but somehow "tweet tweet" ain't gonna cut it!)...it's not the Sidney Opera or the BBC Radio 4...it's a crappy handheld game. I just want to do the best job I can within the limitations of what I've got (which is pretty much the definition of what a "game programmer" does every day!). A previous colleague of mine once said (of computer graphics) "If it looked real, we wouldn't call it 'simulation'."...and that applies here too. SteveBaker (talk) 15:49, 12 January 2009 (UTC)

Getting Younger Every Day

A 50-year-old Arctic explorer is 10 feet from the North Pole. He walks around the Pole, moving from West to East. As he does that, he crosses the International Date Line and the date moves back one day. He walks around the Pole again, and the date moves back again. How many times does he have to walk around the Pole to beome 25 years old? – GlowWorm —Preceding unsigned comment added by 174.130.253.174 (talk) 09:59, 11 January 2009 (UTC)

Assuming what you're saying works, 25*365 times. (But it doesn't work)124.169.223.172 (talk) 10:10, 11 January 2009 (UTC)

Not enough - you forgot the leap years. Since the number of leap years in 25 years varies depending on when you start walking - we can't give a single answer. (And it's a silly question - so I'm not going to bother working it out.) SteveBaker (talk) 16:07, 11 January 2009 (UTC)

This is one of those questions like how many eggs does a Leghorn rooster lay in a week? The effect of crossing the International Date Line is not cumulative. If it's Friday 10:00 on one side and Thursday 10:00 on the other that difference still persists after you've spent 14 min walking around the pole and crossing from Friday 10:14 into Thursday 10:14. The time line separates "locally observed" times. If you wanted to follow the time zones you'd have to adjust your watch every minute, half-minute or three quarter-minute till you get back to the dateline (not quite accurate because there is some odd stuff in the Pacific for 2 hrs every day.) Your explorer could always invent a new calendar that counts years differently. As a positive side effect he can do that in his tent while sipping hot cocoa instead of having to walk around in the cold. 76.97.245.5 (talk) 10:52, 11 January 2009 (UTC)

It doesn't work (aside from the obvious reasons) because as the explorer walks around the pole, he crosses 23 other time zones. If he's following the rules, he puts his watch ahead one hour every time he crosses a time zone - then puts it back 23 (not 24!) hours when he crosses the International date line. Hence he "ages" 23 hours and then "gets younger" by 23 hours on every loop. Overall - no gain! SteveBaker (talk) 16:07, 11 January 2009 (UTC)

Why 23? UTC-12 does exist.See also File:Timezones2008 UTC-12.png Nil Einne (talk) 20:58, 11 January 2009 (UTC)

The time zones don't have such a simple structure. There aren't 24 wedge-shaped zones converging at the poles. I know they use New Zealand time "throughout Antarctica" (i.e. at the few research stations in Antarctica), so you won't cross any time zone boundaries walking around the pole down there. I doubt the north pole is in any defined time zone; polar explorers can set their watches however they want. Also, there are a lot more than 24 times zones. Many nations and parts of nations are a half-integral number of hours from UTC, like India at UTC+9½. The Chatham Islands are at UTC+12¾! Even the integral offsets from UTC range from UTC−12 to UTC+13 (26 choices, not 24). Here's the map I extracted most of these factoids from: [3]. Then there's daylight saving time. Different regions might use the same time for some parts of the year and a different time for other parts because their DST start and end dates are different or one of them doesn't have DST. And DST goes in opposite directions in the northern and southern hemispheres.

But none of this matters because it's trivially true that the total time change around any closed loop will be zero, regardless of the nature of the zones. -- BenRG (talk) 21:20, 11 January 2009 (UTC)

Actually a few research stations (in Antartica but not the South Pole) do use different timezones, see [4], [5] and [6]. Sometimes a research station belonging to a specific country will use that countries timezone but others use the timezone of their supply base which is commonly NZ Nil Einne (talk) 08:55, 12 January 2009 (UTC)

On the plus side, if he does try it he'll never have to fret at turning 51 years old. (He probably won't even survive a day) Nil Einne (talk) 20:54, 11 January 2009 (UTC)

Why do you think that? Sure, it's cold, but it's not going to kill him just by him walking around for a bit. Our article has a related bit of information about a performance artist named Guido van der Werve who used the north pole in a slightly similar, but much more clever way. Matt Deres (talk) 16:21, 13 January 2009 (UTC)

I don't think walking ~25*365 times in a cirle counts as 'a bit'. Even if you only walk in a circle with a radius of 10 feet (as the OP mentioned) that's still 19.1511488 meters [7] circumference. Times that by 25*365 [8] gives you ~ 174.75 kilometers. Thats more then 4 marathons. And while yes, people have run marathons near the North Pole and Antartica before, I'm pretty sure they come well prepared and with support teams in case anything goes wrong. It sounds unlikely our explorer did likewise given that they were dumb enough to try such a pointless endeavour. And I don't know of any that did try to run 4 x marathon distance in the North Pole. Indeed the OP specifically mentioned walking, so it's liable to take a lot longer then (I presuming mostly running) a marathon. (Indeed the running is likely to help keep the body temperature up I would suspect.) Did Guido van der Werve really walk ~174.75 km around the North Pole non stop? For that matter, is there anyone who has survived a day alone in the North Pole not staying in shelter? Nil Einne (talk) 19:20, 14 January 2009 (UTC)

Yes, it has to do with time zones. There are 24 time zones around the earth. As the explorer exits each time zone, he sets his watch forward 1 hour. When he crosses the International Date Line he sets his calendar back 1 day. When he exits a time zone at 11:xx a.m. he sets his watch to 12:xx p.m. The date does not change. But when he exits a time zone at 11:xx before midnight, he sets the watch to 00:xx a.m., and he must also set his calendar forward 1 day. He then completes his walk to his starting point, setting his watch forward as he exits each remaining time zone. When he gets back to his starting point, he will be older by the time it took to walk around the Pole. Briefly put, he sets his watch forward by 1 hour 24 times in his walk around the Pole. That counteracts setting the date back 1 day when he crossed the International Date Line. – GlowWorm. —Preceding unsigned comment added by 174.130.253.174 (talk) 20:53, 11 January 2009 (UTC)

Apparent Size of the Moon

One night driving somewhere I noted that the moon appeared very large. This brings a few questions to mind. Does the apparent size of the moon change with season? Does the apparent size of the moon change with variations in the atmosphere? Finally, does the atmosphere cause any permanent shift in apparent angular size of objects outside the atmosphere? Noodle snacks (talk) 12:24, 11 January 2009 (UTC)

The apparent size of the moon is a psychological phenomenon. Ses [9]. - Nunh-huh 12:36, 11 January 2009 (UTC)

• Nevertheless, the OP's observation is correct. The full moon yesterday night was the largest we'll see in 2009, according to this source and others. --NorwegianBlue ^talk 13:04, 11 January 2009 (UTC)
• Yes, a part of of the effect is psychological. But the moon also is an an elliptical orbit. Since it moves around the sun with the earth, the full moon sometimes will be further from the earth (when the long axis coincides with the line earth-sun at the time of the full moon, and the longer part of hat axis is away from the sun, or in show-off lingo, when apogee and full moon coincide), and sometimes will be closer to the sun (again, the extreme case is the alignment of the axes and the longer part of the long axis pointing towards the sun). At the moment, we are in the "close moon" scenario, and a number of newspaper have reported on this. See [10] and [11]. --Stephan Schulz (talk) 13:17, 11 January 2009 (UTC)

The Moon appearing larger when it is close to the horizon compared to when it is high in the sky (the Moon illusion) is almost completely psychological.

As for optical phenomena due to Earth's atmosphere, there is atmospheric refraction which causes objects close to the horizon to appear higher up than they really are (and also causes obects slightly below the horizon to appear above the horizon). This has a very small effect upon the apparent size of the Moon near the horizon: It is smaller than higher in the sky, but only in the vertical direction; this is because the atmospheric refraction is smaller at the upper limb than at the lower limb, and this difference is larger closer to the horizon.

And regarding the distance of the Moon from Earth, it does vary, as NorwegianBlue and Stephan Schulz already mentioned. But because the Moon's orbit ellipse itself rotates (the period is somewhere between 8 and 9 years), the largest full Moon doesn't always occur in the same season.

Icek (talk) 16:09, 11 January 2009 (UTC)

There certainly ARE some very small, very subtle effects due to distortion by the atmosphere and the nature of the moon's orbit - but those effects are negligable compared to what we're discussing here. The practical problem with the moon is purely an optical illusion. When the moon is high in the sky - away from terrestrial objects - you have nothing to use to estimate it's "size" - so your perception of the size "goes into free-fall". Interestingly - I recently managed to prove this theory quite conclusively using computer graphics. In my flight simulator graphics system (where the image is projected onto the inside of a 30 foot dome using lasers!), there is no atmospheric distortion (or any other kind of distortion for that matter). The number of pixels covered by the moon on the screen didn't change AT ALL - yet people STILL claimed that the moon changes size! I noticed this because one of my managers spotted the "change in the size of the moon" as I moved it around in the sky - and complemented me on having gone to the trouble of writing software to simulate the "atmospheric effect"!! Hey - I'll take all the credit I can get OK? SteveBaker (talk) 16:18, 11 January 2009 (UTC)

Also, the biggest full moon anytime in either 2008 or 2009 was on December 12, 2008. So if you saw the moon then, there's a good chance you might have noticed a larger-than-usual moon. It was also brighter than normal, some people in Florida reported the moon to be "pulsating". ~AH1^(TCU) 18:39, 11 January 2009 (UTC)

How satisfying. Last night (Sat 10th) my wife commented that the moon looked bigger and brighter than normal, and she was right (for once). [12] Rockpocket 19:47, 11 January 2009 (UTC)

What are recent developments in Internal Combustion Engines?

(SB: Added this title) SteveBaker (talk) 15:55, 11 January 2009 (UTC)

what is the recent development in IC engines? —Preceding unsigned comment added by Just.chintu (talk • contribs) 13:21, 11 January 2009 (UTC)

6 stroke ICs. For one. —Preceding unsigned comment added by 92.16.196.156 (talk) 16:11, 11 January 2009 (UTC)

There are so many to choose from! Gasoline direct injection is pretty cool - it's what lets my MINI Cooper'S get 35 to 40 mpg and still push the car from 0-60 in under 7 seconds with a top speed around 140mph! SteveBaker (talk) 16:23, 11 January 2009 (UTC)

It's not very new, but I believe the Wankel engine has recently become more widespread. --Sean 18:46, 11 January 2009 (UTC)

What IS relatively new about the Wankel that's made is more useful is the bearings used at the tips of the rotors. As the rotor (the only moving part!) spins, the tips rub against the cylinder walls and that wear made for short engine life. Evidently the folks at Mazda have found a way around that - which makes their Wankel look pretty attractive. SteveBaker (talk) 22:39, 11 January 2009 (UTC)

One neat trick I liked in the '08 MINI Cooper is the idea of using the starter motor to accelerate the car from stationary to a few miles per hour before the spark is turned on an the engine fires. Sadly, for some bizarre legal reason, this isn't allowed in the USA - so the US variant (that I have) doesn't do it. But the idea is clever: An IC engine doesn't run at all well at very low RPM - and even in first gear, you're "lugging" the engine as you pull away from a standing start which is very bad for it - so this trick increases engine life. Secondly, IC engines have very poor torque at low RPM - and electric motors have the same torque at all RPM - so they do well at getting the car rolling and that saves you fuel. Finally, in stop-start traffic, you are effectively driving an electric car. It's a cheap way to get hybrid-like performance without all that fancy extra 'stuff'. Aside from a slightly more robust starter motor, all it takes is a little extra software in the computer. It's really annoying that this isn't legal in the USA - some stupid law that could be 'fixed' at the stroke of a pen would save a lot of gasoline and engine wear. I believe BMW will be putting this feature in all of their new cars this year. SteveBaker (talk) 22:39, 11 January 2009 (UTC)

tingling in the chin

(Question removed)

Sorry - we are not allowed to diagnose medical conditions on the WP:RD. If you (or anyone else you know) is concerned about their health - they should seek immediate medical advice. Sorry. SteveBaker (talk) 17:21, 11 January 2009 (UTC)

Levitation - frogs or otherwise.

The article Orders of magnitude (magnetic field) says:

1.25 T - strength of a modern neodymium-iron-boron (Nd2Fe14B) rare earth magnet. A coin-sized neodymium magnet can lift more than 9kg.

...and...

16 T - required strength to levitate a frog

I've seen the Discovery-channel show that demonstrates the levitating frog - and there is a reference in our article that backs up the 16T number...does this mean I can levitate a frog with just a dozen or so coin-sized Neodymium magnets? Seems like I'd be able to feel that kind of a pull on my finger...which seems kinda unlikely. There has to be something wrong here...but what?

SteveBaker (talk) 17:19, 11 January 2009 (UTC)

Magnetic fields can't possibly be cumulative like that. Otherwise why would 100T be so hard to obtain, if you could just stack up 100 coin-sized magnets? (I'm not saying this as someone who knows much about magnetic fields, but it's clear from the article that even "just" 45T is pretty freakin' difficult to obtain, and so it can't be just a matter of stacking up magnets.) --98.217.8.46 (talk) 18:00, 11 January 2009 (UTC)

Yes - that's kinda what I was thinking - I just wanted to understand the physics of it. SteveBaker (talk) 22:24, 11 January 2009 (UTC)

Don't the magnetic field lines have to be coherent? Using 16 different magnets would result in crossing lines of magnetic force (which go from pole to pole). The diamagnetic repulsion then wouldn't have a single vector. (See also Magnetic levitation) Franamax (talk) 22:48, 11 January 2009 (UTC)

Here's some physics for you: [13][14]. All you have to do now is figure out how the B fields of 16 magnets combine. ;) Franamax (talk) 22:56, 11 January 2009 (UTC)

Maybe another way of looking at it is that magnetic materials can only hold so much magnetic flux, at which point they become saturated (it says so somewhere in WP). If you put two saturated magnets together, they can't reinforce each other any further, so the flux just bulges outwards away from the magnets. Perhaps if you put two 50% saturated magnets together then they would combine to make one 100% saturated magnet with double the flux density, but then why would anyone bother to make a 50% saturated magnet? Presumably these rare earth magnets are already at 100%. --Heron (talk) 20:54, 12 January 2009 (UTC)

Phosphate pit

What exactly is a phosphate pit? Thank you. (Joseph A. Spadaro (talk) 17:57, 11 January 2009 (UTC))

Do you have context? I could refer to the hole left after open-pit mining for phosphate ore. [15] Rockpocket 19:39, 11 January 2009 (UTC)

Thanks. The context is the following news story, in which a murder victim's body was found floating in a phosphate pit: [16]. At first when I read the story, I imagined that the murderers stored / hid their victim's body in a type of drum (or some such). After reading the story, it sounds like the victim was swimming in some type of open water (river, lake, pond, or whatever). That is the context. The story left me confused. Thanks. (Joseph A. Spadaro (talk) 19:45, 11 January 2009 (UTC))

I expect thats what it is, then. Mulberry, Florida, where the event took place, is the "Phosphate Center of the World." [17]

I still don't "get it". Per the above reply, there's an open hole left after mining for phosphate ore ... OK. But, then what? What was the murder victim swimming in? This open hole just gets filled with water from the rain, etc.? And forms a lake or pond? I am still not "getting it". What exactly did the murder victim jump into and swim away in? Any clarification? Thanks. (Joseph A. Spadaro (talk) 20:00, 11 January 2009 (UTC))

Any open hole without sufficient drainage from the bottom is obviously going to get filled with water over time (well unless it's in a desert). This happens with tin mines in Malaysia [18] File:Taiping lake gardens with hills behind.jpg [19] [20] [21] and is bound to happen with open-pit phosporus mine too. These things are usually very deep so would probably be a convient place to hide a body. Nil Einne (talk) 20:33, 11 January 2009 (UTC)

See our article on Quarry. You will see several pictures of quarries (i.e. open pit mines) which have been filled in by rain water. When I was a kid, there was an old abandoned granite quarry where we used to go diving. It looked a lot like this pic: File:SandersQuarryIndiana.JPG. --Jayron32.talk.contribs 20:35, 11 January 2009 (UTC)

OK ... thanks ... I basically "get it" now. So, the headline of the news article could just as easily (and accurately) have stated that the murder victim's body was found floating in a lake (instead of using the term "phosphate pit") ... is that correct? Or did I miss something there? Thanks. (Joseph A. Spadaro (talk) 20:41, 11 January 2009 (UTC))

This was a local newspaper, so I presume they expected most people to understand the term. It's obviously more descriptive and accurate then simply 'lake' which could be any number of things and doesn't really convey the same meaning to me Nil Einne (talk) 20:46, 11 January 2009 (UTC)

Yeah, a phosphate pit or a quarry is definately different than a lake. If the local paper reported a body found in a phosphate pit, I would understand exactly what it meant, and a lake is something different. The problem is exactly as Nil Einne describes; the local paper is written for the local audience, which understands that phosphate pits will fill in with water, and so have no problem understanding the intent of the writer. For people who do not live in areas with these structures, it makes less sense. --Jayron32.talk.contribs 22:09, 11 January 2009 (UTC)

For purposes of hiding a body, the typical abandoned open pit is a much better choice than the typical natural lake. In general, a natural lake is a lot shallower than an man-made pit, although there are many exceptions. If you are careful to carefully attach weights, the body is much less likely to be found in the pit than in a lake. -Arch dude (talk) 02:26, 12 January 2009 (UTC)

Thanks for all of the input. This was very helpful. I agree with the points made about local newspapers being written for their local audiences ... in which case, some things get "lost" for the non-local readers. Thanks. (Joseph A. Spadaro (talk) 16:52, 18 January 2009 (UTC))

light

is it true or false that mirages are due to the effects of refractions —Preceding unsigned comment added by 82.38.52.19 (talk) 19:14, 11 January 2009 (UTC)

See mirage. 62.128.252.85 (talk) 19:42, 11 January 2009 (UTC)

Briefly: true. SteveBaker (talk) 22:21, 11 January 2009 (UTC)

"Super greens" pills

Hi all,

Is there any value to those "super greens" or "super foods" pills they sell in health food stores or Whole Foods, those packed with spirulina, greens (wheat grass, broccoli, spinach, etc.), probiotics and so on? Are there any studies even suggesting that they might improve one's health? Can they really provide the "equivalent of a full day's serving of fruits and vegetables?"

I eat pretty healthy -- all home-cooked, lots of veg -- but I'm wondering whether adding these on top of my regular meals is silly or might be healthy.

Thank for any thought (I know -- not medical advice), — Sam 146.115.120.108 (talk) 21:47, 11 January 2009 (UTC)

Just to note... Drop the "I eat pretty healthy..." part of your question and it is a request for reference material, not a request for medical advice. As for studies, I assume you want unbiased scientific studies. The companies manufacturing these products do studies. Basically, they pop a pill or whatever they are marketing. Then, they wonder if they feel better. Of course. So, the pill must make everyone feel better. The lack of scientific studies by these companies leads to injunctions like this. -- kainaw™ 22:15, 11 January 2009 (UTC)

How can you pack a pill with all that stuff? Either it contains such small amounts that it's pointless or it actually contains certain things extracted from them (and is probably just like standard dietary supplements like multivitamins and iron supplements). There have been lots of studies on whether dietary supplements actually help (eg. see Multivitamin#Scientific assessment) and they have differing results. If you have a poor diet or are otherwise at risk (pregnant women, for example), then supplements can certainly help (although they obviously aren't a complete replacement to good food). If you are eating well and aren't at risk, then it is less clear, but if there is a difference it is probably small. With regards to the particular pills you mention, you need to read the packet and find out what is actually in them and in what quantities - if it doesn't break it down into different vitamins and minerals and whatever then you can guarantee that it is completely worthless. --Tango (talk) 22:19, 11 January 2009 (UTC)

Doing X will "flush the toxins out of your body"?

Hi all,

There are plenty of things that health websites and experts talk about that are supposed to remove toxins from the body -- drinking lots of water, fasting, sweating, exercise, detox diets, etc. etc.

Have there been any studies at all that show that doing any of the above things actually leads to a measurable decrease in the quantity of toxins in the body?

Thanks, Sam 146.115.120.108 (talk) 21:58, 11 January 2009 (UTC)

You must define what you mean by "toxins". Whenever I hear that term used in any advertisement for any service or product, its with 100% certainty that the product or service being sold to you is pure bullshit. There are many processes which the human body uses to filter waste materials from itself, generally the liver converts the offending material into something somewhat less offending, and the kidneys remove the material from the bloodstream and send it to the bladder, from whence it is eliminated by urination. If the material is genuine waste (i.e. material that is part of normal metabolic processess, but which must be removed from the body) this is the most common way for removal of it from the body. If you believe that this process doesn't work right for you, and have a genuine medical problem, please seek the advice of qualified medical professionals and not random strangers on teh interwebz. --Jayron32.talk.contribs 22:06, 11 January 2009 (UTC)

To the best of my knowledge, no. At least, not in relation to detox diets and the like - keeping hydrated, getting plenty of exercise and eating a healthy diet are all good things and may well help reduce toxin levels. For example, not drinking large amounts of alcohol is going to reduce the amount of alcohol in your system, but there's no need to stop eating completely in order for your liver to process alcohol (in fact, there's a good chance it would harm the liver's ability to function). If you want advice on how to stay healthy, go see a doctor, the internet is full of misinformation on such matters. --Tango (talk) 22:10, 11 January 2009 (UTC)

There was an interesting BBC New article on this just the other day. [22] Rockpocket 22:47, 11 January 2009 (UTC)

Please correct me if I am wrong, but there is some evidence that milk thistle and NAC might be helpful to your liver[23]. A Quest For Knowledge (talk) 01:00, 12 January 2009 (UTC)

Plenty of plants have medicinal uses, a very large number of our medicines have their origins in plants. If milk thistle does work then scientists will find out by doing trials and studies and will isolate the substance in it that does the job and then work out how to turn it into a drug. That's how pharmacology works. --Tango (talk) 01:53, 12 January 2009 (UTC)

Tango, you are quite correct. Unfortantly, an entire industry has sprung up selling alterative suppliments, some of which might work and some of which might not. But which ones are which? How does the average consumer know how to make such a decision? Until science conducts exhaustive studies of alternative suppliments, we don't really know which ones are which are legit and which ones are complete nonesense. These companies are making billions of dollars while science catches up to their claims.

In fact, I've thought about this problem a few times. I wish I was a billionaire philanthropist so I could create a legitimate scientific institute for the sole goal of examining (either confirming or debunking) the claims of the alternate medicine and alternate sumplement industries to find out which ones (if any) actually work. For years, we've had thousands and thousands of kids lifting weights and eating creatine because they think they it help them become stronger. But does creatine actually work? If so, how much? There does appear to be some evidence for creatine's effectiveness, but off the top of my head, I don't think that there has ever been any exhaustive, third-party, double-blind, peer-reviewed studies of creatine. Some of us have seen the so-call 'male enhancment' (a euphemism for penis enlargement) products on late night TV which are obviously bullshit, but are there any double-blind, peer-reviewed studies that actually make this conclusion? (There's only one product that I am aware of that can actually increase the size of the human penis but you rarely hear about it.) The two I referenced earlier, milk thistle and NAC have some scientic evidence to believe that they might actually be beneficial. Pardon my soapbox, but I guess what I am saying is that science moves too slowly and it would be nice if some effort was made to confirm/debunk the supplement industry. A Quest For Knowledge (talk) 05:26, 12 January 2009 (UTC)

I've had similar thoughts myself, although my solution is government funding of university studies to separate the wheat grass from the chaff. I would tend to trust the results of such studies, as long as those who benefit from sales of the supplements were not allowed to fund or otherwise influence them. Yes, this would be an additional tax burden on the public, but I feel there are a large number of potentially useful and inexpensive products out there, and once we knew what they were, we could benefit enormously. I'd also like to see cooperation between different nations and universities to divvy up the work load, much like the Human Genome Project. StuRat (talk) 05:44, 12 January 2009 (UTC)

To my knowledge, the above is absolutely correct regarding detox diets and detox footpads and suchlike. In the case of heavy metal poisoning, we have chelation therapy, but that is something you would prefer to avoid absent an urgent medical problem. On the issue of study, there is in the US a National Center for Complementary and Alternative Medicine. It has numerous problems, mostly related to quality of evidence and undue credulity, but there is serious study of alternative medicine. - Eldereft (cont.) 12:50, 12 January 2009 (UTC)

Check this site,[24] it has a number of links and for me makes a lot of sense. Richard Avery (talk) 14:48, 12 January 2009 (UTC)

Some of the adverts for these things are just crazy though. The detox footpads have to be the biggest scam - and I notice that my local HEB and WalMart stores now carry them in the same aisle as asperin and ibruprofen! Their advert says that they work "just like a tree draws toxins out of the air and pushes them out of it's root system!!! Er...excuse me? Doesn't a tree suck things UP through it's roots and expel the resulting byproducts out of the leaves? That right there tells you just how much science went into these pads. A couple of years ago, I made a point of closely watching every advert that played during an hour of the "Discovery Channel" - which is mostly talking about science and stuff like that. In that entire hour - I was unable to find a single advert that wasn't some kind of lie or deceitful thing. Not one advert was promoting a product or service that anyone with a still-functioning brain cell should be touching. Between adverts for "free" things where you "just pay shipping and handling" ($6.99 for an envelope with a prepaid postage stamped on it? Yeah - right.)...adverts for things that can't possibly work (penis enhancers, detox footpads)...things that are claimed to cost $50 in stores - but are yours for only two payments of $19.99 (plus shipping)...things where "You can try it risk-free and just return it to us for the cost of shipping" - but are in reality just a bunch of random garden herbs in pill form and worth maybe $2 - so that the company can easily make a good profit on the inflated shipping charges even if 100% of people return them. Several adverts claim "our weight loss program is so good, the US goverment has granted us a patent on it"...failing to mention that any patent for anything is likely to pass without scrutiny if it doesn't contain the phrase "perpetual motion machine". In many adverts, the announcer is loudly asserting "X is true" while the small print at the bottom of the screen clearly says "X is false". "You can earn $130,000 in one month with our easy work from home program!"...well, if so, why aren't the company paying people minimum wage to do the work and collecting the resulting $128,000 profit per month themselves instead of wasting all that money advertising it on TV? There are coins that have all of these fancy claims of rareness and value that are not even really coins at all - you're spending $20 on an utterly worthless piece of metal that costs less than $0.05 to produce and will have PRECISELY zero value the nanosecond after you take it out of the envelope! "We'll take your old jewellery - just post it to us, we'll assess how much it's worth and send you back a cheque for the full value!"...so wait - you'll accept any amount they decide it's worth? $1 is OK for that antique gold wedding ring? Is that REALLY a good idea?

The level of dishonesty is quite chilling - and the level of gullibility on behalf of the general public MUST be stunning in order for these companies to be able to afford that level of advertising.

We don't need people to research these products and determine which ones are scams - they are ALL scams of one sort or another. What we need is to teach "critical thinking skills" in schools. Without critical thinking - you are the potential victim of every junk product, scam and hoax out there. Problems like email spam and junk mail are other consequences of this lack of skepticism in the community.

<sigh> SteveBaker (talk) 15:06, 12 January 2009 (UTC)

But Steve, gold chains that are "just tangled in my closet" can't possibly have any value, can they ? :-)

I agree that we need to teach better critical thinking skills, but also don't think companies should be able to just outright lie in their ads and make a profit doing so, which seems quite common in the US. A sizable portion of TV ads also seem to be for something that will likely work, to some extent, but is overpriced. Vacuum cleaners and cooking devices are typically in this category. One of the new scams seems to be "take this product home and try it out, then, if you're not 100% satisfied, return the UNOPENED container for a full refund". Now if you can only figure out how to try it without opening the container, everything will be great. Then there are those which only want to bill your credit card $1, so they have you're credit card info and can then ship you worthless crap, bill you at an exorbitant rate, and claim you ordered it or failed to cancel their "convenient automatic shipment plan" (meaning convenient for them, of course).

One simple legal step to take is to require that all "investments" list the average rate of return, much as stock market investments must do. Instead, they are able to put a small group of people on TV who claim they made lots of money, and may very well be lying in any case, to trick people into sending them money. If they were required to contract a third party to survey all of their "clients" to determine their real financial gains (or, more likely, losses), then this type of scam would pretty much disappear. StuRat (talk) 16:57, 12 January 2009 (UTC)

We do have articles on toxins and detoxification. A Quest For Knowledge (talk) 16:45, 12 January 2009 (UTC)

Assuming no genetic or health condition that would dictate otherwise, doing the classic things to stay as healthy as possible (eat & drink appropriately, exercise, avoid undue exposure to environmental contaminants) is plenty enough to allow your body's normal metabolic and filtration systems to keep you in fine working condition. Millions of years of evolution have created many effective processes to eliminate waste products and most low-level environmental toxins. There are some notable exceptions (industrial heavy metal exposure, for example) that require real medical intervention.

It is worth noting that adverts for "detox" products rarely indicate what supposed "toxin" are removed, and almost never indicate a rational mechanism through which this would be achieved. Chelation therapy is an interesting beast--it's used in real medicine to treat life-threatening heavy metal exposure, but quacks the world over have taken this treatment (which can be very dangerous) and convinced many, many people that chelation therapy is necessary to treat autism (zOMG! mercury in vaccines!) and other conditions. Generally, "detox" is just a meaningless buzzword. The only thing detox products have been shown to effectively remove is money from one's wallet. — Scientizzle 18:14, 12 January 2009 (UTC)

Ah, but money has been shown to contain all sorts of nasty critters, from bacteria and viruses to chemicals and drugs, so they really are improving your health by taking that away from you, right ? :-) StuRat (talk) 19:52, 12 January 2009 (UTC)

True - but if you do feel an urgent need to get rid of all your cash - I'm sure there are many better alternatives! (Hint: Look at the banner at the top of this page!) SteveBaker (talk) 21:58, 12 January 2009 (UTC)

Psssst, the drive ended several days ago. It's safe to look at the top of the screen again. Dragons flight (talk) 22:38, 12 January 2009 (UTC)

Ah - then send the money to me directly and I'll "look after it" until the next drive comes around. :-) SteveBaker (talk) 16:20, 13 January 2009 (UTC)

When one drinks alcohol (a known toxin), it gets metabolized in the liver and otherwise by enzymes, as well as by exhalation in the breath. The rate of flushing this toxin from the body varies among individuals based on their genetics and general health. Food consumption affects the rate of removal of the toxin, as does gender and body mass. Edison (talk) 03:41, 13 January 2009 (UTC)

Radar turns on a radio?

I was reading in Wikipedia:Reference_desk/Archives/Science/2009_January_5#Ray_that_stops_internal-combustion_engines and one person claimed tha radar directed at a radio will turn it on and make it play music. Google can't find anything relevant ot his topic, but is it true if you direct a powerful radar wave at a radio, suddenly the radio turns on and plays music with the radio unplugged? Thing is in ghost haunting stories, usually the ghost will turn on the radio with the radio unplugged. Are you ready for IPv6? (talk) 23:14, 11 January 2009 (UTC)

I can't see why it would play music, but it might play a single tone or something. It would be playing the radar wave itself. The radio only needs to be plugged in so that it can amplify the signal, if the radar is powerful enough then it wouldn't need amplification to be audible. --Tango (talk) 00:07, 12 January 2009 (UTC)

I guess the theory is that the radar would somehow induce enough voltage into the radio to power it even though the On/Off switch is in the Off position. Then it would simply power up as usual - and if it happened to be turned to a music station - it would play music. However - it's hard to imagine so much voltage induced in JUST the right place - without it also being induced somewhere undesirable and blowing up some critical component. So it all sounds a bit 'iffy'. Certainly not ALL radios would magically do this - most would do nothing, some would fail disasterously...MAYBE one in a thousand would play music. SteveBaker (talk) 00:28, 12 January 2009 (UTC)

Don't radios, like any other piece of electronics, require a positive power rail and a negative/ground power rail to function properly? How would a radar induce such a thing? Just having current randomly flowing in the wires isn't going to do anything useful. --Tango (talk) 00:41, 12 January 2009 (UTC)

If the radio contains a transformer and rectifier to produce DC power, then if the radar resonates with the transformer coil, it could power the radio. --Carnildo (talk) 23:36, 12 January 2009 (UTC)

Or if it was plugged in the radar might be picked up by the leads going to the "on" button, and switch the radio on. Depending on the type of switch. I'm not sure how likely that is, though. APL (talk) 00:14, 12 January 2009 (UTC)

If it was an electronic switch, then maybe, but I think most radios have mechanical switches (you press a button and it makes or breaks a physical connection). It could happen if the radio wasn't off but was actually just on standby, I guess. --Tango (talk) 00:26, 12 January 2009 (UTC)

I guess this is theoretically possible, but I think there would need to be an antenna/coil connected in a different way (to the power supply of the radio?) to actually generate any power. Very unlikely if at all possible. -Pete5x5 (talk) 05:14, 12 January 2009 (UTC)

I have no touble believing it happened. For one thing, it was Kainaw, who is neither a liar nor insane. For another, it's one of those things where the very act of pronouncing it impossible renders it almost inevitable, sort of like the Infinite Improbability Drive. For a third thing, high-frequency AC could induce current in the set's power supply that would be rectified just like any other AC, powering the radio some. --Milkbreath (talk) 16:41, 12 January 2009 (UTC)