Wikipedia:Reference desk/Archives/Science/2008 September 24

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September 24

Underwater urination

Its easy to pee at sea level, but at what depth below the ocean surface would it become impossible due to the external pressure?--79.76.251.108 (talk) 00:00, 24 September 2008 (UTC)

This is equivalent to asking if a balloon can leak air at under high external pressure. The external pressure pushes on the outside of the balloon (or your bladder) and forces the contents out. So, no, under any pressure in which a human could survive, urination would not be a problem. -- kainaw™ 00:10, 24 September 2008 (UTC)

Agreed, as your question stands, its a simple answer. However, if you were in some sort of vesicle which was at STP (standard temperature and pressure), and you urinated into a system at a different pressure, then plausibly sea water could enter your bladder because of the fluid force being higher on the outside. If your skin was "completely impermeable" then it would be impossible to urinate below a certain depth (and even above this depth, you wouldn't be able to fully empty your bladder, but only an amount less than at STP). Sentriclecub (talk) 03:21, 24 September 2008 (UTC)

I have never had any problem peeing at any depth below the ocean's surface. I don't think it would matter how deep you go. The pressure in the human body (which consists mostly of incompressible liquid) is equal to the pressure of the surrounding environment. Forcing urine out requires no more effort at depth than at the surface.

Now, as Sintriclcub says, if you were in a submarine with an internal pressure of 1 atmosphere, and you wanted to drill a hole through the hull to pee out of, you would have to compete with the water pressure on the outside to force your urine out. ~Amatulić (talk) 20:10, 24 September 2008 (UTC)

True, your urine would be much more compact inside your body. It would be just as easy. Open system, free equilibrium. Sentriclecub (talk) 09:58, 25 September 2008 (UTC)

Death under stress

In a previous question, Kurt Shaped Box said that "If an animal is stressed at the time of death (and strangulation tends to be a stressful experience), various chemicals are released into the bloodstream which (negatively) alter the flavour of the meat and cause it to go off more quickly." Is the same true of humans? Can this be used to determine whether a person died under stress or "peacefully in their sleep"? Is it ever used in court? Plasticup ^T/C 00:53, 24 September 2008 (UTC)

A few years ago, scientists used tissue and blood samples from deceased deer to demonstrate that the practice of hunting with hounds was a stressful experience for the quarry (see [1]). So, yes - I'd imagine that there would be discernible signs, for those who knew where/how to look. --Kurt Shaped Box (talk) 01:47, 24 September 2008 (UTC)

Sadly, I just learned this a week ago, but here it goes anyway. These "various chemicals" are called signals. On the surfaces of cells, there exist various glycoproteins called receptors. Different cells can respond to the exact same signal, in completely different ways! The most cited example is norepinephrine. It will cause different results in different cells because of the physiology of the different tissues comprising massive quantities of similar cells. The main response is the "signals" will cause the vast mega-accumulation of the requested proteins. To answer your question, yes, it could be potentially used in forensic evidence if there are few ambiguities. For example, if a stress hormone causes the same response as a hunger hormone, then if the prosecution argues "look at these protein buildups--the person died in anguish!" the defense would counter "look at these protein buildups--the person died hungry". But yes, as long as there's not much ambiguity, then it could be used as forensic evidence. Remember, the "judge" and "jury" interpret expert testimony. I watched 3 consecutive days of the trial of the accountant who shot up his workplace (famous story, dont know his name) but I think you asked a very good question. It shows that you are creative, and I wish all questions were more like yours that relied on creativity and critical thinking. Its no fun to answer questions that just blue-link to the article, or answer homework questions. Sentriclecub (talk) 03:15, 24 September 2008 (UTC)

An answer and a compliment. What more could I want? Plasticup ^T/C 04:32, 24 September 2008 (UTC)

I'm not so sure. For animals, stress is generally a short-lived matter. The deer gets chased - if it escapes, it's back peacefully nibbling the grass within minutes. We humans can get stressed about (for example) the state of the financial market and remain stressed for days or weeks at a time. Should you happen to "die peacefully in your sleep" during an extreme financial crisis, I think your chemistry might look pretty similar to someone who has been stressed by (say) a burglar. We also deliberately stress ourselves - there are human "adrenaline junkies" who jump out of airplanes, ski down cliffs or drive their cars very fast "just for fun". Those people could be the happiest people in the world and yet show all the signs of high adrenaline in their blood stream. So the chemistry might tell you something about the person at time of death - but because humans are so complicated (behaviorally) - it might be almost impossible to interpret the results in any meaningful or useful way. SteveBaker (talk) 00:25, 25 September 2008 (UTC)

Again, I'm not talking about emotional stress or some other psychological criteria for definition. I'm talking strictly physiological stress, the kind definitively linked to certain molecules which trigger the vast mega-production of proteins inside the cells of various tissue types. Sentriclecub (talk) 10:00, 25 September 2008 (UTC)

Human body

We humans are built to withstand atmospheric pressure and we do not expand or contract. But if we were to go high in the atmoshere would our body expand? Also, if we were to go tho the bottom of the ocean, would our body contract?--GreenSpigot (talk) 01:03, 24 September 2008 (UTC)

Your assumption that humans do not expand or contract is not entirely true. The human body is designed to expand and contract as needed. Just ask anyone who can feel a storm coming as joints (especially knees) react to the change in air pressure. -- kainaw™ 01:19, 24 September 2008 (UTC)

I think he means that humans don't blow up like balloons. The small change in pressure inside joints is negligible. The only part of the body that really adjusts to pressure is the inner ear. Youth in Asia (talk) 03:00, 24 September 2008 (UTC)

Humans do expand and contract. Drive up a mountain with an apparatus attached to your body that disallows your ears to pop, you'll see. But the question you ask is really complicated. Humans are an open system, which means every femtosecond your body adjusts to restore equilibrium. Also, re-think your question in terms of everyday scientific terms. This is a question about volume. At the bottom of the sea, your density would increase. (the water would squish you into a smaller version). You would have the same mass (for simplicity, lets skip the microassumptions), and since your volume decreases, and your mass increases, then viola! your density increases. This is an easy question, but if you try to answer it without science, you may as well discuss evolution vs intelligent design. Hope you find this analogy helpful. Sentriclecub (talk) 03:06, 24 September 2008 (UTC)

(conflict) Excuse me, Youth in Asia, but the human body absolutely blows up like a balloon. It's called breathing, and it affects the chest, abdomen, really the whole torso. Your abdomen also expands to respond to a large meal. The human body is very flexible in terms of changes in volume. As far as the original question goes, the OP may find our articles on Space exposure, Human_adaptation_to_space#Unprotected_effects, and Uncontrolled_decompression#Fallacies enlightening. In short, if exposed to the vacuum of space you will not explode but you may bloat a bit depending on how long you're exposed. If exposure is < 30s you will probably recover completely. Otherwise you will first lose consciousness, then your blood and bodily fluids will begin to boil, resulting in bloating but not rupture of the body because of the strength and flexibility of the skin (see ebullism). CO2 will be released form the blood, resulting in damaging changes in blood pH, and nitrogen will also evolve from the blood forming embolisms. Ultimately, death will result form hypoxia. --Shaggorama (talk) 06:03, 24 September 2008 (UTC)

I'm pretty certain, that if you are talking about extraterrestrial space, then the human body expands well beyond the limits of survivabilitity. Yeah, step out of the spaceship, without your suit, and you will instantly "expand" to about 1,000,000 times your original size. I think the relevant article is about the partial pressures of the organic compounds comprising your skin cells, and then everything else will follow. But I'll let you have the last word, I max 10 edits to this page, then I take a 1-month vacation. Sentriclecub (talk) 06:48, 24 September 2008 (UTC)

Our articles disagree with your expanding hypothesis. --mboverload@ 07:00, 24 September 2008 (UTC)

The difference caused by stepping out of a spacecraft is the same as it caused by rapidly ascending through 10 metres of water. If you try and hold your breath, your lungs might "explode" but most of your body will remain intact - skin is capable of surviving a change of 1 atm. --Tango (talk) 12:47, 24 September 2008 (UTC)

Okay, let's summarise and separate out the hard science from the misinformation and speculation in the above responses:

• High pressure: The human body is, chemically, a dilute solution of proteins and lipids in water. The bulk modulus of water is about 2x10⁹ Pa. So to reduce the volume of a given mass of water by, say, 1% requires a pressure of 2x10⁷ Pa or about 200 atmospheres. In other words, the body's cells and organs are, for practical purposes, incompressible. Saturation divers live and work in pressurised habitats at pressures of more than 5 atmospheres for days at a time. Ultra-deep divers at depths of more than 300 metres experience pressures of 30 atmospheres or more. The most dangerous effects of high pressure on the human body are associated with breathing gases under pressure, not with compression of body parts - see nitrogen narcosis and high pressure nervous syndrome.
• Low pressure: Our article on uncontrolled decompression says "accidents in space exploration research and high-altitude aviation have shown that while vacuum exposure causes swelling, human skin is tough enough to withstand a drop of one atm. This assumes that the person doesn't attempt to hold their breath (which is likely to cause acute lung trauma), the limiting factor on consciousness then being hypoxia after a few seconds". So it is lack of oxygen that kills in vacuum, not the low pressure itself. Soyuz 11 depressurised slowly in orbit, shortly before re-entry, and the crew suffocated, but they did not explode. When Joseph Kittinger's glove seal failed during his Excelsior III balloon ascent, his hand was exposed to a pressure of 1/100 of an atmosphere for several minutes - this caused pain but no long-term damage. Our article on space exposure says that the maximum survivable time for exposure to vacuum is around 90 seconds.
• Rapid decompression: a quick transition from high pressure to a lower pressure is the most dangerous scenario - see uncontrolled decompression. This not due to the expansion of body parts themselves but because of the expansion of gas in various places within the human body. Going from 1 atmosphere to very low pressure in less than half a second does not allow time for the lungs to empty of air, so causes lung damage. The effects of explosive decompression from 9 atmospheres to 1 atmosphere are graphically described in our account of the Byford Dolphin diving bell accident. Divers who surface too quickly can experience decompression sickness, due to the release of gases dissolved in body liquids and tissues.

Hope this help. Gandalf61 (talk) 13:08, 24 September 2008 (UTC)

Addendum to "Low Pressure": Its not just the lack of oxygen in the vacuum that kills you. The low pressure causes your blood to boil and so you lose what little oxygen may already be dissolved in your blood. The low pressure robs you of oxygen you have already inhaled! Also, I think the main article to point to should be space exposure. Otherwise, nice summary --Shaggorama (talk) 02:55, 25 September 2008 (UTC)

the first fortified peanut butter that is not plumpy nut

I am looking for any information on fortified peanut butter. Not the Plumpy Nut, but anything having to do with fortification, enhancement, any additions to etc. —Preceding unsigned comment added by G1963 (talk • contribs) 02:34, 24 September 2008 (UTC)

Density

I feel like this question is like the "which weighs more, 1 lb of bowling balls or 1lb of feathers", but I'm not sure.

"If you were to find the mass of 20 mL of seawater, would it be heavier, lighter, of the same as 20 mL of distilled water? And what does this mean in terms of density?"

I thought that the masses of each would be the same, and that the density of the seawater was more, but my friend told me I had it backwards. Is he right, or am I? —Preceding unsigned comment added by 69.16.88.147 (talk) 02:39, 24 September 2008 (UTC)

Without saying anything about seawater, we can reduce the two questions to one: if the a volume of X has more mass than the same volume of Y, then X is more dense. That's just the definition of density. To decide which substance is denser requires knowledge of the composition of seawater and what that means for density (or else looking it up). The important bit here is that adding a solute (e.g., salt) to a solvent (e.g., water) often increases the density because the molecules of the solvent clump up around those of the solute, reducing their volume. --Tardis (talk) 02:56, 24 September 2008 (UTC)

Agree with the first answer. Furthermore, think of buoyancy. When you lay in salt water, the buoyancy is different. You can float easier. Secondly, mythbusters did a show on quicksand. The result, is that you float extremely well, you have about 30% of your body above quicksand. Also, the ethereal air around us is very non-dense. When a skydiver jumps from a plain, that is like "sinking" because he is more dense than the air around him. Sentriclecub (talk) 03:00, 24 September 2008 (UTC)

Don't skydivers jump onto the plains, rather than from them? (sorry). :) -- JackofOz (talk) 05:38, 24 September 2008 (UTC)

Yeah you caught me, in the language of mathematics, there are no homophones. I'm a regular at the math ref-desk, only came here to post a question, but got too lazy. I'd be happy abolishing letters and using numbers only to communicate in writing. In which case, prime numbers could serve as vowels. I think I goofed because I think of the word plane as a mathematical term, oh well, I goofed, I should enjoy it. Sentriclecub (talk) 06:42, 24 September 2008 (UTC)

8 1, 8 1. -- 10 1 3 11 15 6 15 26.

9 & 7 5 20 & 9 20 Sentriclecub (talk) 10:03, 25 September 2008 (UTC)

I'd really like to see 1 lb of bowling balls! SteveBaker (talk) 23:50, 25 September 2008 (UTC)

Progressivity of electrical loads

If we attach a variable voltage source across a load, we will typically produce a fixed current for each voltage and obtain a current function $i(v)$. With a few exceptions, the function is strictly increasing, and if the load is unpowered clearly $i(0)=0$. For what broad classes of unpowered loads is the function convex, concave, or neither? (A pure resistance/reactance, of course, is the only convex and concave load.) Are there any reasonable components for which the current function is multivalued? DC and AC (considering the magnitude of current; see power factor) both interest me. --Tardis (talk) 03:22, 24 September 2008 (UTC)

A voltage source across a forward biased diode would produce negligible current until a certain voltage was applied (.7 volts for a silicon diode) then sharply increasing current for higher voltages, thus perhaps "concave" although the applicability of "concave" and "convex" is questionable. For a classic resistor it would be linear. Edison (talk) 05:48, 24 September 2008 (UTC)

Im afraid that what you say about diodes is entirely wrong, Edison. A semiconductor diode always has an exponential relationship of current to applied voltage (neglecting the small reverse leakage current). The current is given (approximately) by I= Io exp(qV/kT). This sort of poppycok bandied about by many people about diodes behaving as some sort of voltage dependent switch does nothing to aid understanding of electronics and in fact can lead to many poor designs in circuitry. The article Diode has a grossly misleading diagram of the I V characteristics of a semiconductor diode, implying as it does, that there is some magical transition between ON and OFF. There is NO such transition. (see the equation) It is worth saying also that the equation shows that the voltage across two similar diodes will only be equal if thier currents are equal. Hence the operation of so called bandgap references. Lecture over!--79.76.251.108 (talk) 17:31, 24 September 2008 (UTC)

Things like fluorescent lamps have negative resistance so are convex to a degree. Other things like normal incandescent lamps or real resistive loads have concave function as the higher temperature lead to higher resistance. --antilived^{T | C | G} 08:56, 24 September 2008 (UTC)

Anything with negative resistance is automatically "neither" since it can't have it at $v=0$ and $i(v)$ can't be decreasing forever. The diode and the incandescent lamp are the two examples I had been able to come up with; I should have mentioned them. That the diode is only convex when forward biased reminds me also that positive and negative voltage need to be considered separately (anything unpolarized must have an odd current function and can't be nontrivially convex/concave everywhere). Thanks for the input — any other ideas? --Tardis (talk) 13:26, 24 September 2008 (UTC)

Have you seen our article on Negative resistance. It pretty much covers everything you need to know.--GreenSpigot (talk) 05:01, 25 September 2008 (UTC)

I have; I was just looking for more examples, to get a feel for the most common cases. --Tardis (talk) 23:36, 28 September 2008 (UTC)

Hmm. Have you seen Diac?--GreenSpigot (talk) 22:29, 1 October 2008 (UTC)

Also, what about thermistors?--GreenSpigot (talk) 22:31, 1 October 2008 (UTC)

Lag time and planetary alignment issues regarding laser transimission between Mars and the Moon/Earth

I'm doing research for a web comic, and I'd like to know, roughly:

1- The lag time for laser communications between the Moon/Earth and Mars.

2- The Sun is between Mars and the Moon/Earth for X amount of time. Time of year would be great but not necessary.

Also, I'm assuming that all lasers travel at the speed of light or thereabouts i.e. specific wavelength doesn't matter. Please don't trouble yourself looking for a formula(s) - I'm afraid physics equations are a bit beyond my reach.

Again, I'm looking for general estimates- please don't go through a lot of trouble calculating. Thank you so much!

Sevenzark 7 (talk) 05:36, 24 September 2008 (UTC)sevenzark_7

speed odf light 0.3 million km/s so divide the distances in the Mars and Moon article (normally given in million km) by 3 and you have the seconds. Easy to do it! But for the moon the estimation would be one second for one direction and there and back 2 seconds.--Stone (talk) 06:51, 24 September 2008 (UTC)

For Earth/Mars communication it varies depending on the time of year on both Earth and Mars. If we're both on the same side of the sun, I think it can get as low as three and a half minutes, or if they're on opposite sides of the sun it can get as high as twenty minutes. Roughly. APL (talk) 12:46, 24 September 2008 (UTC)

And starting around the mid-November, NASA will loose communication with the rovers/lander for 2 weeks, while Mars is directly behind the Sun. [2][3] -- MacAddct1984 ^{(talk &#149; contribs)} 13:34, 24 September 2008 (UTC)

I would imagine that laser communication from Earth to Mars would be really tough when they are more or less opposite each other with the Sun in the middle. Imagine pointing your super-sensitive light detector anywhere close to the sun and looking for a bajillionth of a candela of laser light energy. It's worth saying that the speed of light (which is the speed of the laser) and the speed of radio waves is exactly the same - so there is no particular advantage (or disadvantage) in using a laser versus a more conventional radio link. SteveBaker (talk) 00:11, 25 September 2008 (UTC)

(See bit rate :) Saintrain (talk) 01:09, 25 September 2008 (UTC)

The time of year during which the Sun will be directly between Earth and Mars is different every year, so it depends which year your comic story is supposedly happening. You could predict it, though, based on the future date and reasonnably simple calculations and MS excel. Some years the Sun will never be directly between the 2. --Lgriot (talk) 07:09, 25 September 2008 (UTC)

AWESOME! Thank you folks! Thanks SteveBaker I was wondering about radio waves. MacAddct1984 and Lgriot thanks for the date info! Sevenzark 7 (talk) 21:29, 28 September 2008 (UTC)sevenzark_7

Cell phone radiation and hard drives

Does cell phone electromagnetic radiation cause any harm (file corruption, data loss, etc.) to computer magnetic hard drives? If one were to put five cell phones (in use) on top of an external hard drive, would it do anything? —Lowellian (reply) 05:40, 24 September 2008 (UTC)

Short answer--no. Cell phones use low energy electromagnetic waves. If you have ever been in the airport and your computer was passed through a x-ray, that is about 10,000 times more energy per photon. Ionizing radiation is hopefully a blue-link. 99.9999999% of peoples computers survive the x-ray machine. However, the long answer is that my TV got slightly miscolored when I put my cell phone up to it. It needed a degauss button, but its an old tv, like 10 years old. But honestly, I'm supposed to be scientific, but I partly believe that cell phones shouldn't be held up to the ear when talking through them. Afterall, isn't the question about brain cancer the big elephant? I'm 24, and I own no cell phone! Hurray for me. Also, the neat part of your question... put five cell phones, is that electromagnetic radiation is not additive. In other words, if an apparatus is 60% of the energy required to emanate ionizing radiation, then a thousand of these operating concurrently will still not be able to emanate ionizing radiation. In the chemistry of photons... 50 joules + 50 joules + 50 joules + 50 joules does not equal 200 joules, but instead simply equals 50 joules. See photoelectric effect. Don't take my answer literally, I'm just regurgitating stuff from textbooks, i still find it hard to believe, and yet fascinating! Sentriclecub (talk) 06:34, 24 September 2008 (UTC)

I'm still somewhat confused though. I've tried holding up a cell phone in use to a stereo system and a television set, and it produces MAJOR audio and visual distortions, to the point that the audio/video is unlistenable/unwatchable. Considering that it can do so much to a stereo system and a television set, why would it by contrast do so little to a hard drive?

—Lowellian (reply) 07:32, 24 September 2008 (UTC)

That's because the wires in your sound system acted as an antenna, receiving the signal of your cell phone, which is then amplified by your amps and made audible through your speakers. Not sure about video though since I have never experienced that before. Without the amplifier part (which amplified the few milliwatts of power from your cell phone to tens/hundreds of watts to drive your speakers) it simply does not have enough energy to disrupt your hard drive. --antilived^{T | C | G} 08:46, 24 September 2008 (UTC)

But if one's computer speakers are right next to one's computer (since they are, after all, computer speakers), by what you're saying, doesn't this then mean that these speakers will amplify the cell phone radiation right next to the hard drive? —Lowellian (reply) 04:12, 25 September 2008 (UTC)

Computer speakers have amps built into them (notice how they need mains to operate?) as line level signals from your sound card is simply not enough t drive the speakers. Try putting a cell phone next to a proper speaker with no amplification: you won't hear a single thing. --antilived^{T | C | G} 06:08, 25 September 2008 (UTC)

In addition, hard drives are completely encased in thick metal, which has Faraday effect to block a lot of EM radiation you can throw at em. Hard drives are designed to be extremely hard to damage - and very much succeed. They are made from solid aluminum (or something else) and are for all practical purposes dust-proof. They can protect the data they hold even when thrown to the ground or dropped from large heights (I think modern HDD can withstand 300g's of shock). With proper data recovery techniques data can be recovered from hard drives that have been underwater for days or in an intense fire. Running hard drives while open or with fingerprints even work (I've done it - although I wouldn't recommend it) Also, even pretty powerful magnets won't do jack to them. To properly degauss a hard drive you'll need a professional degausser (10 thousand dollars). Some lowly EM radiation isn't going to hurt it. --mboverload@ 06:54, 24 September 2008 (UTC)

I would question whether the thick metal of the average hard drive is effective as a Faraday cage, since it has gaps in it that enable an electromagnetic pulse to easily fry a hard drive.

—Lowellian (reply) 07:28, 24 September 2008 (UTC)

Faraday cage with holes will still block out electromagnetic waves up to a certain frequency. If I'm not mistaken the highest cell phone frequency is 2100Mhz, which has a wave length of roughly 14 centimetres (5 and a half inches). I'm not sure about how small the gap has to be in relation to the wave length in order to block out that wave but unless you have holes 14 cm in size (bigger than your whole hard drive) it's probably blocked by the casing. It's the same principle the screens work in your microwave. --antilived^{T | C | G} 08:46, 24 September 2008 (UTC)

No. [4] - QED! SteveBaker (talk) 00:05, 25 September 2008 (UTC)

No, not quite QED. I actually thought about this particular argument before I asked the question; the reason that cell phones having internal hard drives does not prove that cell phones radiation doesn't affect hard drives is because presumably, even in the case that cell phone radiation did affect hard drives, a manufacturer might still put an internal hard drive inside a cell phone after taking care to specially shield this internal hard drive in a way that normal computer hard drives are not shielded. (I'm not saying that cell phones would harm hard drives; I'm just saying that this particular argument doesn't prove that cell phones wouldn't.) —Lowellian (reply) 04:10, 25 September 2008 (UTC)

Perhaps you should take a phone apart then :p. Compared to the millimetre thick hard drive enclosures the metal sheets inside cell phones for shielding are diminutive (not that thickness matter anyway). --antilived^{T | C | G} 06:08, 25 September 2008 (UTC)

four acceleration

the wikipedia article on 'four acceleration' states that the acceleration felt by an accelerating object is the derivative of proper velocity with respect to proper time. most everything else that I have read including other articles on wikipedia state that it is the derivative with respect to coordinate time. Em3ryguy (talk) 05:57, 24 September 2008 (UTC)

Proper time sounds right to me - then it's the acceleration that the object would actually feel. Can you give an example of an article that defines it wrt coordinate time? --Tango (talk) 12:37, 24 September 2008 (UTC)

thats what I thought too at first. but I did some figuring and the acceleration would indeed seem to be alpha=a*gamma^3. a is regular coordinate acceleration. the derivative of proper velocity (v*gamma) with respect to coordinate time equals alpha (according to the online calculator I used). the article on proper acceleration clearly and unambiguously defines it that way. http://en.wikipedia.org/wiki/Proper_acceleration#Viewed_from_a_flat_spacetime_slice Em3ryguy (talk) 20:07, 24 September 2008 (UTC)

I'm confused, where is the article that disagrees? --Tango (talk) 20:10, 24 September 2008 (UTC)

http://en.wikipedia.org/wiki/Four-accelerationEm3ryguy (talk) 20:21, 24 September 2008 (UTC)

Sorry, what article disagrees with that article? Apart from the strange fact that we have an article on 4-acc and on proper acc when they seem to be defined to be the same thing, I don't see any contradiction... --Tango (talk) 21:53, 24 September 2008 (UTC)

Actually, they're not quite defined to be the same - proper acceleration seems to be defined as a 3-vector, and 4-acc is that 3-vector with a null time component. Is that standard? I would have just called the 4-vector "proper acceleration" and avoided 3-vectors completely... --Tango (talk) 21:56, 24 September 2008 (UTC)

the article on four acceleration clearly states ' four-acceleration is a four-vector and is defined as the change in four-velocity over the particle's proper time'. the article on proper acceleration clearly defines proper acceleration as dw/dt. that is the derivative of proper velocity with respect to coordinate time.(four velocity and proper velocity being more or less the same thing) http://en.wikipedia.org/wiki/Proper_acceleration#Viewed_from_a_flat_spacetime_slice Em3ryguy (talk) 22:16, 24 September 2008 (UTC)

which contradicts the statement at the top of that article that says " The proper acceleration 3-vector, combined with a null time-component, yields the object's four-acceleration" which must be wrong. Em3ryguy (talk) 01:30, 25 September 2008 (UTC)

the article on four acceleration attempts to show that you can use it to calculate the instantaneous (and therefore infinitesimal) change in velocity. but since coordinate velocity, proper velocity, and rapidity are all the same at low speeds then I would think that any of them could do the same. but my math isnt good enough for me to be sure. thats why I'm asking you. Em3ryguy (talk) 20:19, 24 September 2008 (UTC)

if a stationary observer measures A's coordinate velocity to be v and B's velocity to be v+dv and both start at the origin at t=0 then at t=1 B's position is (v+dv,1). simply transform coordinates to A's frame to get (g(v+dv-v),g(1-v(v+dv))). the infinitesimal velocity from A's point of view is therefore g(dv)/g(1-v^2-vdv). which equals dv*gamma^2. divide the infinitesimal velocity by infinitesimal proper time [d(proper time)] to get acceleration from A's point of view. alpha=a*gamma^3.Em3ryguy (talk) 20:44, 24 September 2008 (UTC)

you might also want to know that dgamma/dt=v*a*gamma^3 (again according to the online calculator 1/sqrt[1-((v[t])^2)] http://calc101.com/webMathematica/derivatives.jsp#topdoit).Em3ryguy (talk) 20:58, 24 September 2008 (UTC)

you can also check that the derivative of proper velocity with respect to coordinate time is a*gamma^3. v[t]/sqrt[1-((v[t])^2)] http://calc101.com/webMathematica/derivatives.jsp#topdoit Em3ryguy (talk) 21:19, 24 September 2008 (UTC)

and of course. d(coordinate time)/d(proper time)=gamma. Em3ryguy (talk) 21:19, 24 September 2008 (UTC)

I don't follow what you're trying to show there, however it appears you are making a mistake with your coordinate transform. Relativistic velocities don't add simply like that, you need the velocity-addition formula. --Tango (talk) 21:53, 24 September 2008 (UTC)

I'm not adding velocities. its a coordinate transformation. if the coordinate in one frame is (d,t) then the coordinates (d',t') in a second frame moving at v is (g(d-vt),g(t-vd)). (assuming that their origins coincide at t=0) Em3ryguy (talk) 22:16, 24 September 2008 (UTC)

What is g? And that's not what you wrote, you had "v+dv-v" which is adding velocities (well, subtracting them actually, but that makes no difference). --Tango (talk) 23:55, 24 September 2008 (UTC)

g is gamma for coordinate velocity v. (d',t')=(g(d-vt),g(t-vd)) = (g(v+dv)-v(1),g(1-v(v+dv)) assuming c=1 Em3ryguy (talk) 00:06, 25 September 2008 (UTC)

gamma for velocity v is of course 1/sqrt(1-v^2) assuming c=1 Em3ryguy (talk) 00:52, 25 September 2008 (UTC)

I think I understand now. the 'a' in the article on four acceleration is the coordinate acceleration as measured by the nonaccelerating observer. only if that nonaccelerating observer is moving at the same instantaneous speed of the accelerating object does it equal the acceleration felt by the object (but, I think, thats true of coordinate velocity, proper velocity, and rapidity since they are all the same at low speeds). in all other cases it does not. the article probably isnt wrong but its certainly confusing. Em3ryguy (talk) 22:38, 24 September 2008 (UTC)

the article should read 'Therefore, within that co-moving inertial reference frame the four-acceleration is equal to the proper acceleration that a moving particle "feels"'. —Preceding unsigned comment added by Em3ryguy (talk • contribs) 17:25, 25 September 2008 (UTC)

proper acceleration on the other hand, as I understand it, should always be the same for all observers. just as proper time and proper distance are the same for all observers. Em3ryguy (talk) 22:40, 24 September 2008 (UTC)

the derivative of rapidity with respect to proper time is the proper acceleritaon. that is also clearly defined in the article on proper acceleration http://en.wikipedia.org/wiki/Proper_acceleration#Viewed_from_a_flat_spacetime_slice Em3ryguy (talk) 00:39, 25 September 2008 (UTC)

http://en.wikipedia.org/wiki/Lorentz_factor#RapidityEm3ryguy (talk) 23:35, 25 September 2008 (UTC)

I have edited the pages in question to what I believe is a less confusing form. I would appreciate it if someone would double check my work. Em3ryguy (talk) 01:43, 26 September 2008 (UTC)

Do candles melt when put in a microwave oven?

This question has been bothering me and my roommates during the whole summer while sitting on our balcony. Enjoying a good wine we were contemplating on the candles that were burning on our table: Do candles melt using microwave radiation? I voted for no, because candles are made out of wax and wax is not influenced by microwave radiation. A microwave oven utilizes the polarity of molecules, such was water, to generate heat inside the object that is inside the oven. As I have found out on Wikipedia, candles are made of paraffin wax, meaning a mixture of alkane hydrocarbons with a length between 20-40 C-Atoms. I am not a chemist, but I would guess that those long alkanes do not have a dipole moment? So, is my explanation correct? Ced22 (talk) 08:43, 24 September 2008 (UTC)

Having just put a small tea-light into a microwave oven on full strength for 30 seconds I can report that the candle did not melt nor did it feel any warmer than when it went in. Not very scientific but it's a start. Richard Avery (talk) 11:09, 24 September 2008 (UTC)

On the contrary, that is very scientific. Confronted with a hypothesis (candles heat up in a microwave) you made a prediction (your tea light would heat up in a microwave), tested it (put the candle in the microwave) and used the results to reject the hypothesis. My man, what you did was the definition of science! Plasticup ^T/C 23:45, 24 September 2008 (UTC)

Science is not about ad hoc experimentation. --98.217.8.46 (talk) 14:54, 25 September 2008 (UTC)

Science is all about planned experimentation. Do you mean to imply that Richard Avery's was ad hoc? --Kjoonlee 23:57, 26 September 2008 (UTC)

I think it's just what Karl Popper would have done. William Avery (talk) 20:28, 25 September 2008 (UTC)

Thanks very much for doing the experiment, Richard. We do not own a microwave oven, that's why we have not tried this test. Apparently the results support my theory. I did some further research, apparently alkanes exhibit very low polarity.Ced22 (talk) 11:36, 24 September 2008 (UTC)

Presuming this is an ordinary microwave that you don't wish to break, you might want to be careful with this sort of experiment. If your running your microwave oven with only something which does not absorb microwaves, you're basically running it without anything which as our article mentions, could cause you to burn out the magnetron. While this probably won't happen in 30 seconds, you should try it for too long. The way to avoid this would be to put a glass of water or something similar while doing the experiment Nil Einne (talk) 18:42, 24 September 2008 (UTC)

A microwave can only heat polar compounds, water being ideal. Candles are made mostly of long chain alkanes (see paraffin) that are certainly nonpolar, so they are unaffected by microwaves. Dielectric constant is essentially a measure of polarity. --Russoc4 (talk) 14:02, 24 September 2008 (UTC)

That would be Dielectric constant, or relative static permittivity. jeffjon (talk) 15:29, 24 September 2008 (UTC)

It's probably also worth noting that paraffin wax is, essentially, just a shorter version of the same sort of molecules that make up polyethylene, and polyethylene is widely used as a low-loss dielectric in many electrical applications. "Low loss", in this case, means that it absorbs very little energy from electrical fields.

Atlant (talk) 17:38, 28 September 2008 (UTC)

Thanks for all the clarifications and comments, guys! Ced22 (talk) 08:55, 29 September 2008 (UTC)

Floodwater in the bathroom

There was a big flood in Sueca (Com. Valenciana) last night due to rainfall, and some people said on the TV that they had floodwater coming up through the toilet etc. in the bathroom in flats higher up (not groundfloor). I live in a 3rd floor flat: could floodwater theoretically come that far up through the water system in the case of a flood, where exactly does it comes out and how could you stop it? Thanks for info, --AlexSuricata (talk) 11:00, 24 September 2008 (UTC)

If floodwaters are backing up through the sewers, then the way to shut that off would be to close a sewer valve if one exists or otherwise disconnect your outflow pipes. — Lomn 13:36, 24 September 2008 (UTC)

If you look out the third floor window and notice floodwater above the level of the third floor toilet, then it might be expected to rise out of the toilet. If the flood water is far below the level of the toilet, it's hard to explain why water would rise far above the level of the source (the floodwater) without work being done, and such a phenomenon would allow a perpetual motion machine consisting of a turbine to generate power from the fall of the water back to the level of the floodwater. If the drain were clogged, and the toilet were flushed, it would overflow, with or without a flood. If the building drain were somehow shutoff to prevent floodwater entering the building, and water were entering the drains from the plumbing pipes due to toilets flushing or water going down drains, or if somehow water collecting on the roof were overflowing into floor drains in the top floor, then water could overflow from third floor toilets. Edison (talk) 15:50, 24 September 2008 (UTC)

Floodwater can and does emerge from toilets that are higher than the level of the source. It happens when flowing water creates a surge of pressure in pipes. It has been known to happen from sea tides in the early days of Seattle, when toilets drained directly into the sea. It's the same principle as described in blowhole (geology). ~Amatulić (talk) 19:59, 24 September 2008 (UTC)

I do not believe that tides would cause such a "pressure wave" which would cause water to rise from a thrid floor toilet, presumably many feet above the water level. Consider that building codes (in places I am familiar with) toilets be connected to an upvent as well as a drain, so any pressure wave should go up that upvent to the atmosphere, and the water in the trap should stay in the trap. We have noted here previously, however, that extreme winds have caused pressure variations causing visible level changes in the toilet due to the pressure differential in the bathroom and at the rooftop terminus of the upvent. I just cannot envision the water rising up the drain pipe tens of feet above the level of the floodwater. The system of drains I would expect to dissipate the transient shock of rising water level and prevent the spike of energy required for such a slosh. Edison (talk) 22:22, 24 September 2008 (UTC)

Wouldn't this need to be considered as a momentum problem? Fluid is flowing downward in the sewer pipes from higher areas. That fluid has a definite momentum. At the same time, fluid is backing up from the overload in lower areas, thus flowing backwards with some lower momentum. When these flows meet, the momentum must be dissipated, presumably via a pressure surge upwards in whichever local pipes are handy.

And of course, if it's a rainwater flood and the rain is falling up on the hills and entering the sewer, if you're in the valley, expect the water to seek its own level, which will be above your toilet. Franamax (talk) 15:40, 25 September 2008 (UTC)

'foods that promote cancer and how they promote it'

i would like a detailed analysis of foods that promote cancer and how each of these foods help promote this disease41.219.253.218 (talk) 11:59, 24 September 2008 (UTC)

As in foods that are Carcinogenic#Carcinogens_in_prepared_food? 194.221.133.226 (talk) 12:47, 24 September 2008 (UTC)

You may want read the whole article. Carcinogens act in a variety of ways as mentioned there. And there are so many different carcinogens and potential carcinogens, many of which may occur in food that any complete detailed analysis is liable to be many, many pages long Nil Einne (talk) 18:24, 24 September 2008 (UTC)

Location of seminal vesicles

Is the seminal vesicles located between the rib cage and spine ? —Preceding unsigned comment added by 86.96.226.14 (talk) 12:14, 24 September 2008 (UTC)

Based on the diagrams in our cleverly named seminal vesicles article, I'd say no. --LarryMac | Talk 12:29, 24 September 2008 (UTC)

Rehanrazak (talk) 15:01, 24 September 2008 (UTC)

Whats happens when Global Warming comes to apex?

Does another ice age start on earth? If so, how will that happen? What do you think that most countries (ie. USA, UK, etc) would do? --Anilmanohar (talk) 13:05, 24 September 2008 (UTC)

This is largely beyond the scope of the Reference Desk, as we have no way of knowing what or when the peak of global warming will be. As such, no meaningful prediction of international response can be made. As for ice age trends, it's certainly the case that Earth has historically cycled between warmer and cooler periods. Whether human-affected warming is sufficient to break the cycle is again a question we cannot reliably answer. — Lomn 13:34, 24 September 2008 (UTC)

Venus might be a good model. Plasticup ^T/C 15:48, 24 September 2008 (UTC)

Note that climatically we currently are in an ice age, as there is permanent ice in the Arctic and Antarctic. We are in a slightly warmer interglacial, but the real hothouse mode of Earth is a lot warmer. On the plus side, that means that a complete runaway effect as on Venus is quite unlikely. But on the negative side, that means that we may push Earth into a very much warmer and very different state. --Stephan Schulz (talk) 18:13, 24 September 2008 (UTC)

Global warming doesn't exist. It's all related to sunspots and solar activity. See Maunder Minimum. 31306D696E6E69636B6D (talk) 13:30, 29 September 2008 (UTC)

Isn't it kind of weird that what you said is an opinion? This is science, for god's sakes! Mac Davis (talk) 23:44, 29 September 2008 (UTC)

the charge carried by 100 electrons

write in scientific notation the charge carried by 100 electrons —Preceding unsigned comment added by 76.189.131.73 (talk) 19:24, 24 September 2008 (UTC)

Done. Not sure it helps, since you can't see my notebook. Why don't you try it now? DMacks (talk) 19:32, 24 September 2008 (UTC)

1.2 * 10^-7 steves, this probably won't help either since you didn't specify the units and I just made these units up. (1 steve = 1.2 *10^-9 times the charge of an electron) You might want to try electron -- Mad031683 (talk) 19:48, 24 September 2008 (UTC)

I get about 8.3 × 10¹⁰ steves...are you sure your calculations are correct? :) --WikiSlasher (talk) 11:49, 1 October 2008 (UTC)

a wire carries 2.496E17 electrons

a wire carries 2.496E17 electrons (2.496 x 10^17) determine the charge [c.j] —Preceding unsigned comment added by 76.189.131.73 (talk) 20:04, 24 September 2008 (UTC)

Done. Algebraist 20:09, 24 September 2008 (UTC)

You may wish to read electron, specifically for finding the charge of an electron. —Cyclonenim (talk · contribs · email) 20:34, 24 September 2008 (UTC)

25A fuse

a fuse is rated at 25A.Will it fail if 3600C pass through it in 3 minutes —Preceding unsigned comment added by 76.189.131.73 (talk) 21:17, 24 September 2008 (UTC)

Check out the definition of current. --Tango (talk) 21:26, 24 September 2008 (UTC)

Q=It should be helpful--GreenSpigot (talk) 21:40, 24 September 2008 (UTC)

There is not really enough information to answer the question, if you want to be picky, since it is not specified whether the current flows at a constant rate. Far less charge than 3600 coulombs could blow the fuse if it passed through it in a very short while. If the current source were a large capacitor, most of the 3600 coulombs might flow in the first second. The question is also deficient in not specifying the time/current characteristics of the fuse, since a fuse is not a little magic machine that blows instantly when anything above its nominal rating passes through it. Some 25 amp fuses could carry significantly more than 25 amps for a short while, and others with different time curves would blow quickly at the same current overload. A fuse rated 25 amps should not blow if the current never exceeded 25 amps. If it is an intro science class question, you might just state that for the purposes of the problem solution, you assume the current flows at a constant rate, and that the fuse blows if more than 25 amps flows for a time approaching the 3 minutes. Then calculate the current (charge flowing per second) and compare it to the fuse rating. You will get a clear answer, given the assumptions. Edison (talk) 21:41, 24 September 2008 (UTC)

Is summer vacation over so soon? Plasticup ^T/C 23:38, 24 September 2008 (UTC)

Archie Frederick Collins

I am drafting have moved to main space a biography of this prolific science writer and early radio experimenter (claims to have made voice transmissions in 1899, was a business partner of Nathan Stubblefield) at User:Edison/Archie Frederick Collins Archie Frederick Collins. He used "A. Frederick Collins" as his name in publications. He wrote about 100 books on science, technology and hobbies, numerous encyclopedia articles and over 500 articles in technical magazines and newspapers from about 1900 to 1946. His books often bring handsome prices on Ebay and some are still in print. He wrote the first edition of "The Radio Amateur's Handbook" in 1922, still in print in its 82nd revised edition. He was born in Indiana January 8, 1869, but neither Who's Who (which carried a bio listing and a listing in "Who Was Who") nor the Library of Congress, in its bibliographic index, has a date of death. He seems to have died sometime after 1946, since that was the date of his last book. He was a resident of New York City and of Congers, New York. If anyone has access to New York state vital statistics to find a death certificate, or to any Rockland County, New York or New York City local history sources or probate records , or for an obituary which does not show up online, or any Florida sources (where he once had a residence) I would be grateful. A "real life reference librarian" could not turn up a death date in any bio compendium. His wife was Evelyn (or "Eva Lena") Bandy Collins and they had one son, also an author, Virgil Dewey Collins (born 1898). Thanks. Edison (talk) 21:28, 24 September 2008 (UTC)

Well, I have one teeny-tiny scrap for you:

http://www.daggy.name/cop/bkofdead/obits-co.htm narrows his death date to between 1949 and 1954 and says that he dies in Congers, NY.

The 1954 date is somewhat backed up by http://www.ibiblio.org/ccer/1926a1.htm which points out that the copyright of his book "A Bird's Eye View Of Invention" was renewed by Thomas Y Crowell Co on 20th Jan 1954. The annotation after the renewer's name is "(PWH)" which stands for "Proprietor of a Work made for Hire". There is another annotation for "Proprietor of a Posthumous Work" - so perhaps that is evidence that the author was still alive when his publisher renewed the copyright...but that's pretty thin evidence.

SteveBaker (talk) 23:38, 24 September 2008 (UTC)

The "Daggy" site seems to be guessing. The copyright renewal site might prove something, but it is hard to interpret. I do not see a "PPW" for Collins there, which would at least give a year by which he had died. I believe his publisher was absorbed by other companies, so their records may be unhelpful. I have looked for this information for several decades. The lack of a New York Times obituary for a frequent contributor to that paper suggests that the family wanted to keep it low-key. He was sort of the Mr. Wizard of the pre-television age, with many books on science for children and how to build neat things. Someone of his prominence could easily have had obituaries in papers such as the NY Times, but no joy there. A death certificate from the NY vital statistics office would be ideal. I really need a reliable source for a date of death so I can publish the article in mainspace. Edison (talk) 04:54, 25 September 2008 (UTC)

In the real of copyright renewals, it looks like here [5] and here [6] that A.F. Collins renewed (as author) the copyright of "The book of the microscope" on 7 August 1951, at the age of 82. Agreed? So his demise must have been after that date, if the record is accurate. Edison (talk) 05:18, 25 September 2008 (UTC)

Then 16 December 1955 there is the copyright renewal of a 1928 title "Boys' and Girls' Book of Indoor Games" renewed by Carolyn Collins Vilk, "next of kin," [7] , with the implication he had passed on or was incapacitated by that date. 23 Feb 1955 there is a copyright renewal [8] of "The book of puzzles", a 1927 book, by Myra K. Collins, listed as "executor of the author," so he seems to have died by then. Collins seems to have died circa 1951-1955. That would at least make a vital records search cheaper, since they charge by the time span. .Edison (talk) 05:38, 25 September 2008 (UTC)

Oh! Nice detective work! I didn't think to look for copyright renewals of his other books. But I strongly agree - "next of kin" certainly implies either death or at least a terminal condition. This is strong evidence for a range from 1951 to 1955. It's really bizarre that hundreds and hundreds of Google hits say "1869-" with no death date. Collins sounds like a really interesting guy though - I look forward to reading an article on him. Invented the mobile phone and then went to jail for fraudulantly advertising it - came out of jail and couldn't get a job so he writes dozens and dozens of truly excellent books...an interesting guy evidently. SteveBaker (talk) 23:47, 25 September 2008 (UTC)

I found several books on communications, and on popularized science, which had some discussion of the significance of Collins' research and writing. I have moved the article from my sandbox to main space. I still feel that the combined effort of Wikignomes should be able to find a more precise date of death for such a well known author than "circa 1951-1955." Edison (talk) 22:37, 26 September 2008 (UTC)

Wardenclyffe Tower

It would be great if a few experts in the fields of electronics, physics, Tesla's theories and inventions would look this article over. It certainly seems a most exciting issue, as the size of the article, its content, the strong opinions and some mentioned sources on the talkpage suggest that Tesla's concept of wireless energy transmission of industrial-level electric energy was and remains very feasible, but especially as they all suggest that Tesla obviously knew about stuff such as waves in plasmas, magnetohydrodynamics, the ionosphere, ELF transmission communication, intentional telluric current, Schumann resonances, planet earth's self-capacity and its use as a cavity resonator, and Zenneck waves as far back as around and shortly before 1900, and that his only problem was financial support as soon as his entrepeneur investors found out that he intended to provide free electricity out of thin air for everyone on earth as a quasi-socialist public service; J. P. Morgan asked Tesla, "Where do I put the meter?", but Tesla neither knew nor cared. --80.187.125.4 (talk) 21:31, 24 September 2008 (UTC)

Despite Tesla's major contributions to electrical knowledge such as advances in alternating current motors, robotics, radio, high frequency/high voltage alternating current, and high speed turbines, he had some scientific ideas that have not gained acceptance, or which have been disproved, and is often given credit for understanding issues which he may not in fact have followed, and for having reduced to practice things like "death rays" which were only wild talk in his old age for the benefit of credulous reporters. Edison (talk) 21:47, 24 September 2008 (UTC)

Edison, you're just jealous. Face it, you lost the "current war" - it's an AC world now. ;) Franamax (talk) 12:15, 25 September 2008 (UTC)

I guess I can refute you on at least one call: Tesla's diary entries from as early as 1899 document his understanding of the ionosphere, see Tesla, Nikola, "The True Wireless". Electrical Experimenter, May 1919. It was detailed enough for him to predict the correct ELF frequencies required, half a century before their practical military use, as based upon what's now called Schumann resonances. Note that the radiation Tesla was about to utilize at Wardenclyffe was not Hertzian in nature but in fact Zenneckian, as he was openly saying that he was dismissing Hertzian radiation for far-distance wireless energy transmission and going for Zenneck waves instead, and thus the waves would be propagating basically in plasma, in Tesla's case particularly using air, water, and the planet earth itself as natural media conductors (basically like solar wind plasma). Also remember he'd found a way to draw electric energy from thin air years ago in Colorado Springs already, which was actually the cosmic background radiation, as well as demonstrating wireless eletric energy transmission through the air at a level high enough to fully power head-sized lightbulbs that could be carried by hand hundreds of feet around without glowing any dimmer as early as 1891, as that's the year when he demonstrated it at the American Institute of Electrical Engineers as well as the National Electric Light Association and the Franklin Institute.

And calling his Teleforce design for a particle beam weapon a "death ray" makes it sound more ridicilous than both thes article particle beam weapon as well as teleforce obviously make his device out to be. The basic device you need for particle acceleration is a van de Graaff generator which had been around for half a decade when Tesla started pushing his teleforce design, and contemporary news coverage read that he was either to use a van de Graaff generator or an updated version of his magnifying transmitter. The teleforce obviously was close enough to production that he tried to sell it to several Western governments before WWII.

The other buzzwords mentioned above certainly weren't around by 1900 so it's no surprise that Tesla didn't use exactly these terms back then when explaining what his plant at Wardenclyffe was to be doing. Also, the Wardenclyffe plant certainly isn't much to do with his "later years", as he was still four decades from his death. --80.187.125.4 (talk) 02:14, 25 September 2008 (UTC)

How to store things on an earth floor yet keep them dry

I want to store boxes of books etc. in a small outbuilding which has an earth floor. I have done this before in the past, and I found that neither old carpets or sheets of plastic stopped the moisture from the earth seeping through and making the books damp and subject to insect attack. Can anyone suggest a cheap easy readily available thing to put between the earth floor and the books to keep them dry please? Or some other way of seperating them from the floor that supports them? Aluminium foil for example would be too fragile. Thanks. 78.147.10.10 (talk) 21:58, 24 September 2008 (UTC)

A wooden pallet or plywood supported by thich planks can keep the books up off the ground. If they are on the ground, even on plastic, the coolness of the ground could cause condensation. They still need protection from dust, leaky roof, rodent and bug infestation. A metal clothes cabinet up off the ground might help keep mice and bugs out. There are humidity absorbers available at hardware stores which have a chemical such as calcium chloride in them to absorb moisture. Some can be heated periodically by taking them and plugging them into an electric outlet elsewhere to get rid of the absorbed moisture. Sheets of old carpet or carpet underlayment (as thermal insulation) on top of plastic (as a moisture barrier) could also insulate from the coolness of the ground.Edison (talk) 22:12, 24 September 2008 (UTC)

You could store your books in one of those vacuum-sealed bags (I'm thinking of Space Bags...can you believe we have an article about them?!). These are huge polythene bags - you could store dozens of books in them - with a fitting that lets you hook up a vacuum cleaner and suck out most of the air. Alternatively, you could just stick each book into an individualised 'ziplock' baggie. The result should be pretty much resistant to everything...although if they're going to be there for a long time - you'd want to keep them out of sunlight. SteveBaker (talk) 23:07, 24 September 2008 (UTC)

A pallet would be great. You can sometimes get old or broken pallets for free from large retail stores or transport companies. As for the bugs use insecticide under the pallet. Mieciu K (talk) 23:39, 24 September 2008 (UTC)

I think the important thing is to get them up off the ground, wooden pallets as Edison suggests would be quite good. Once they're off the ground, you can just put them in bin bags. --Tango (talk) 23:47, 24 September 2008 (UTC)

Some plastic container, even a large plastic bin, would be good. Mice and bugs should be kept out, once the moisture problem is solved. Edison (talk) 04:49, 25 September 2008 (UTC)

Raising the books off the floor is key, so that there's air circulation underneath. When I had to store my books for several months, I put them in boxes (from the liquor store, which gives them away free) and bought 4-ounce bags of silica gel. They were rated as giving 3-month protection inside of the sealed unlined cardboard boxes. I would recommend the same approach here, except using hard plastic containers would be better to keep away the critters. Do throw in some desiccant though. Once your books are wrecked, they're wrecked forever. Franamax (talk) 12:05, 25 September 2008 (UTC)

Thanks, I do not think using pallets would be a good idea as the wood would get moist and thus be a magnet for various insects and rots (where I live the soil is moist - perhaps in desert areas in the US it is not). Plastic containers may work but I would need very many of them, which would be expensive. I was hoping someone might suggest some sheeting which is truly waterproof, as polythene is not. Some non-ferrous metal sheeting may be best, if I can get some cheap. 89.243.119.61 (talk) 19:56, 28 September 2008 (UTC)

You are almost dead-wrong here. The key is to allow air circulation between the earth and the books. We don't all live in the desert (or the US) - a skid (pallet) will work fine on dirt, that's what they do, but if you're worried, put the skid on four bricks so it doesn't touch the floor. Metal sheet will provide an equally good condensation surface, you need the air gap. However, if you are proposing to store books unprotected in an enclosed space with a damp-earth floor, you'd best give them away now. You will need all the factors - raised, in plastic boxes, with dessicant. Franamax (talk) 11:44, 30 September 2008 (UTC)

Both the wood of the pallet and its supporting bricks (unless engineering bricks were used) would gradually wick up moisture from the soil. It may be ok if supported off the soil by tin cans, for example. I do not see why a metal sheet would have more condensation that any other surface. Pond-liner may be a truly waterproof sheeting, but I think its quite expensive and not readily available. You are right that ventilation is needed. 78.149.137.49 (talk) 01:24, 1 October 2008 (UTC)

You're on the right track. Minimizing the contact surfaces is important, and airflow is important. The vertical edge of a pallet sitting on a brick will indeed wick some moisture but you are now dealing with only a few square/linear inches as opposed to putting down some carpet right on the dirt. Look at the moisture path - up a brick, to the bottom of the pallet vertical, up the vertical, across the surface of the pallet, into the books/boxes - that's a long path. My point about a metal sheet (or a pond-liner) is that any continuous surface will provide an avenue for moisture creep, the moisture will come out of the damp air and move along the surface.

Those waxy cardboard boxes would also provide a good sealed environment for the books (still should be kept off the ground though), and I'd still recommend a desiccant inside. Sorry for my passion on this subject, I just hate the thought of perfectly good books getting ruined! :) Franamax (talk) 01:41, 1 October 2008 (UTC)

Pluto's sky

DOes anybody know what's the colour of Pluto's sky. Could it be something else besides black like purple-black or dark blue. I thought it has thin atmospher.--57Freeways 22:37, 24 September 2008 (UTC)

According to Pluto, its atmosphere is more than a hundred thousand times thinner than Earth's atmosphere. I would expect the sky to be totally black to the human eye. Algebraist 22:41, 24 September 2008 (UTC)

And even if the atmosphere were denser - the sun is so amazingly dim at that distance that very little light would scatter from it - so yeah - VERY black! On the other hand, the lack of light pollution and the clarity of the atmosphere should make for astoundingly beautiful stars - and that HUGE moon...WOW! SteveBaker (talk) 23:00, 24 September 2008 (UTC)

Given the distance, I'd expect Charon to be pretty dark too, if not completely black.--Fangz (talk) 23:26, 24 September 2008 (UTC)

This artist doesn't think so! Wow. Plasticup ^T/C 23:34, 24 September 2008 (UTC)

Charon's albedo is about 3 times that of our moon and it's more than 10 times closer to Pluto than our moon is to us, so that will compensate a bit. --Tango (talk) 23:50, 24 September 2008 (UTC)

Being nice and shiny can only do so much. Pluto gets 0.06% as much sunlight as the Earth. Dragons flight (talk) 02:48, 25 September 2008 (UTC)

Hmmm - let's toss some numbers around: so Pluto orbits between 30 and 50 AU's from the Sun (the Earth orbits at 1AU). The sunlight will get dimmer as the square of the distance - so the sun appears to be between 900 and 2500 times dimmer on Pluto and Charon than it is here. If Charon is 3 times shinier - then it would look 300 to 800 times dimmer than our moon - although the lack of an atmosphere on Pluto would give that a bit of a boost. Being closer to Pluto won't really make it look brighter because it's not remotely like a "point source" like the sun is at that distance - it's 3 times smaller in diameter than our moon - but it's 10 times closer - so it's going to look about three times bigger than the moon looks from the Earth - that would be quite something to see...but yeah - it would be pretty dim even when it's a "full-moon" (er "full-Charon"?). Pluto and Charon are tidally locked - so if you could see Charon at all from your location on Pluto, it would stay put in the same place in the sky all day and all night. Then, just for fun, you'd have two other teeny-tiny moons (Nix and Hydra) to look at...they are really pretty tiny rocks though - as dim as they are, you might have a hard time spotting them with the naked eye from the surface of Pluto. SteveBaker (talk) 02:51, 25 September 2008 (UTC)

Good point about it being closer not making a difference - I was thinking about the total amount of light you would receive from the moon, rather than the brightness (which is defined as being per unit area). --Tango (talk) 15:07, 25 September 2008 (UTC)

This thread inspired me to do some reading about the planets and moons of the solar system last night. The view from Phobos sounds absolutely stunning. --Kurt Shaped Box (talk) 17:00, 25 September 2008 (UTC)

That is what I love about the Ref Desk. In answering questions and in reading replies, I am taken to parts of the encyclopedia that I might otherwise never visit. Plasticup ^T/C 21:53, 25 September 2008 (UTC)

Yes, indeed. Take a bunch of inquisitive people and the whole of human knowledge in an easy-to-read form and you get something kinda beautiful. I love the part that Phobos will soon (well, within 11 million years) break up due to tidal forces and Mars with have a spectacular (if short lived) low-altitude ring system...followed soon after by 10¹³ tonnes of rock raining down from the sky onto a line precisely around Mars' equator....WOW!....SciFi authors need to know this stuff - stories need to be written! SteveBaker (talk) 23:35, 25 September 2008 (UTC)

Of course, they'll need to change the 11 million years to 11 days, Phobos to our Moon and Mars to Earth, and then remove any resemblance to valid physics. They then need to blow up the Moon with a few nukes (ignoring the fact that the moon breaking up is the problem in the first place giving them extra credit on the valid physics thing) throw in an unrelated romance and it will be a box office hit, for sure! --Tango (talk) 23:54, 25 September 2008 (UTC)

Nice. I'd read an sf book in which Phobos gets crashed into Mars, but I didn't know it could happen naturally. Algebraist 23:58, 25 September 2008 (UTC)

Replying to Fangz, even on a moonless night without cloud cover, the earth is not pitch black (very dark true, but not totally black). Starlight and Zodiacal light surely would count for something, but I agree the artistic picture takes liberties with appearances (perhaps a long camera exposure rather than naked eye). See also Olbers' paradox for why not very bright from starfields. David Ruben ^Talk 19:48, 1 October 2008 (UTC)

Macropenis

How often does this dysfunction happen? How large can a Macropenis be? What are the possible implications other then the inability to have a normal sexual intercourse? Mieciu K (talk) 23:35, 24 September 2008 (UTC)

There is very little information about this in the literature. I think that use of this term is confined to boys who are undergoing puberty or who have not yet reached puberty. See human penis size. Axl ¤ [Talk] 12:09, 25 September 2008 (UTC)