Wikipedia:Reference desk/Archives/Science/2008 March 6

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[edit] March 6

[edit] Beer and bowel movements

It never fails: After a long night of beer drinking, you have to pass a bowel movement (or several) the next morning. This happens to many people I know. What causes this? Does beer have some kind of laxative effect? I've searched around on the web and not found a satisfactory answer (various answers contradict each other). Thanks! 210.239.12.85 (talk) 01:28, 6 March 2008 (UTC)

Ethanol has a direct effect on urine output by inhibiting Antidiruetic hormone - with regards to bowel movements however, when you excessively drink that much you are actually creating an osmotic diarrhea effect. Wisdom89 (T / C) 01:31, 6 March 2008 (UTC)
Thanks for the reply, but I'm not sure I understand you. What is an "osmotic diarrhea effect"? Thanks! 210.239.12.85 (talk) 02:34, 6 March 2008 (UTC)
Osmotic diarrhea is diarrhea caused by non-resorbable solutes within the bowel. These solutes pull water into the lumen of the bowel, and diarrhea results. Our article on diarrhea mentions this, but doesn't go into much more detail. - Nunh-huh 02:39, 6 March 2008 (UTC)
D'Oh! Edit conflict. I was going to say much the same thing, but point the dear reader to osmosis and osmolarity to explain how water gets pulled into the bowel. Since its non-resorbable there's only one way for it to go.... grog-bog! Mattopaedia (talk) 02:45, 6 March 2008 (UTC)
Osmotic diarrhea. Just another reason for me not to drink. HYENASTE 21:18, 6 March 2008 (UTC)
Drinking. Just another reason to learn to enjoy osmotic diarrhea. - Nunh-huh 08:00, 7 March 2008 (UTC)

[edit] Quick physics questions

This isn't homework or anything, just stuff that stemmed from a discussion me and a friend were having. So, objects accelerate at the same speed regardless of mass(right??), but will the heavier one eventually gain more speed? —Preceding unsigned comment added by 166.217.186.49 (talk) 01:30, 6 March 2008 (UTC)

Yes, you're right about the acceleration. But, nope, the only time the speed would be different is if the objects you're comparing have a difference in their aerodynamics. Wisdom89 (T / C) 01:33, 6 March 2008 (UTC)
(ec) In general, objects do not accelerate at the same speed. Newton's Second Law of motion states that F=ma, or force equals mass times acceleration. Therefore, for two objects experiencing the same force, the heavier one will accelerate less. Where you're probably getting confused is with gravity. For gravity, the amount of force one body exerts on the other is proportional to their masses. So for gravitational acceleration towards a given object (say the earth), the force exerted on a massive object will be more than that on a lighter object - in fact, it's proportional to the mass. With the force being proportional to mass, and the acceleration due to that force being inversely proportional, the mass terms cancel out, and the acceleration due to gravity is independent of mass. Now acceleration is simply the rate of change of velocity. This relation has no dependence on mass. Two objects starting from the same initial velocity, and experiencing the same acceleration will always have the same final velocity, no matter how long the acceleration lasts. Although they have the same speed, they will have very different energies, though. Kinetic energy (the energy of motion) is equal to 1/2 * m * v2. Although the velocity (v) is the same, the mass (m) of the heavier object is greater, giving it greater kinetic energy. (This is why a bowling ball hurts more than a marble, even when dropped from the same height). -- 128.104.112.47 (talk) 01:45, 6 March 2008 (UTC)
Just a comment, I suppose I just assumed that the user was referring to acceleration due to gravity in his/her question. Wisdom89 (T / C) 02:49, 6 March 2008 (UTC)
Ah, thanks alot, I was indeed referring to gravity. And you actually answered what we were originally discussing, about more massive objects having greater gravity and if that would effect the speed at which they "fall", or are attracted(Gravity works both ways in that sense, right? that both objects are attracted to each other, just the less massive one is the one that moves). —Preceding unsigned comment added by 166.217.186.49 (talk) 03:15, 6 March 2008 (UTC)
In the simplest case, a two-body system, both objects will move towards their combined centre of mass. But, in the case of, say, a system consisting of the Earth and a basketball, said combined centre of mass would be a few millimetres away from the Earth's centre of mass, and the amount the Earth gets accelerated is so small that if you just shift to a frame of reference where the Earth doesn't move, there's no detectable difference. When the two bodies are of similar mass, it becomes more noticeable (this is actually how most planets outside the solar system have been discovered, more or less). Confusing Manifestation(Say hi!) 04:57, 6 March 2008 (UTC)
So the general answer to the question is that, for two geometrically identical bodies differing only in mass, the lighter body will gain the greater speed in free space (without other gravity), but the heavier one will gain greater speed if they fall in air under Earth's gravity (because the identical air resistance is a greater proportion of the weight of the lighter body). Only under Earth's gravity in a perfect vacuum will they fall at the same speed. dbfirs 08:57, 6 March 2008 (UTC)
As a quick reminder of the magnitude of the Earth's mass, the presence of a basketball on the Earth's surface shifts its centre of mass by about one two-thousandth of the radius of a proton. Algebraist 15:40, 6 March 2008 (UTC)

[edit] Horizontal Pressure Gradient

Hello. Why is there a fast wind when the lines of constant (equal atmospheric) pressure are close together? Thanks in advance. --Mayfare (talk) 01:42, 6 March 2008 (UTC)

When isobars are close to each other, that means that a high and low pressure regions are close to each other. Air (like all gases) would prefer to equalize pressure, so the air from the high pressure region rushes toward the low pressure region. The reason you get a faster wind with close isobars versus distant isobars is the same reason water flows faster down a steep hill than down a gentle slope (where you have close topographical lines versus distant topographical lines). Note that even though the air wants to move from high pressure to low pressure, the wind doesn't always make a straight line path, due to the Coriolis effect. -- 128.104.112.47 (talk) 01:54, 6 March 2008 (UTC)

[edit] Bitter chemical in broccoli

I overheard a casual discussion the other day that two fellow students were having in the lounge. Apparently there is a bitter tasting chemical in broccoli and some other foods that is only detectable by ~20% of the population. In their chemistry lab, they had the opportunity to apply this chemical to a stick and press it onto their tongues to see which of them were sensitive to this chemical. Does anyone have an idea what the chemical was? The articles on supertasters and broccoli didn't yield any answers. BigNate37(T) 01:47, 6 March 2008 (UTC)

Does bitter (taste) have the answer? --Tardis (talk) 01:56, 6 March 2008 (UTC)
You know I didn't even read that section, and the first hit of my broccoli-chemical-bitter Googling took me to the taste article where I promptly learned of umami for the first time. Taking a look, it's likely phenylthiocarbamide, although the ratio seems to be the inverse of what I heard. That's easily attributable to a miscommunication of that interesting yet trivial detail, though. Thanks! BigNate37(T) 02:04, 6 March 2008 (UTC)
I don't think its PTC. I can taste PTC, yet I don't find broccoli bitter. HYENASTE 05:27, 6 March 2008 (UTC)
I don't know about you, but broccoli bitterness doesn't taste like PTC. When it's well cooked, I don't taste any bitterness, but when it's badly cooked, I find it unpalatable. PTC on the other hand tastes god-awful. bibliomaniac15 I see no changes 06:03, 6 March 2008 (UTC)
Asparagus has a similar property where it produces methyl mercaptan in everybody's urine, but only a certain percentage of the population can smell it. It's interesting how natural selection allows these kind of sensory deficits on the unimportant margins, but ensures that almost everyone can detect an onrushing sabre-toothed tiger. :) --Sean 13:51, 6 March 2008 (UTC)
Also, Harold McGee's masterful On Food and Cooking says the broccoli harshness comes from isothiocyanates metabolized from glucosinolates (page 321 in this edition). --Sean 14:02, 6 March 2008 (UTC)
Then there's the bitter zucchini (eggplant, cucumbers and varieties of summer squash) thanks to Cucurbitacin E which I take it, is unmissable, not a matter of conditions, but a rogue compound (?) and not nice to the point where local authorities wanted to round them up.[1] Could everyone taste that? Julia Rossi (talk) 22:55, 6 March 2008 (UTC)
Regarding glucosinolates, vegetables, and genetics, here's another article for you to check out: [2] It appears to be what you are referring to. Dforest (talk) 04:58, 7 March 2008 (UTC)

[edit] Chemical compositions of some animal products/byproducts used in early warfare

I am currently working on Early thermal weapons, following a discussion some days back about the use of boiling oil and quicklime during sieges. In my final section I'm trying to show how the weapons were later developed or have modern equivalents (eg Arabic Greek fire had naphtha which is now used in napalm). Anyway, I have discovered some intriguing uses of animal products. Horses' hooves, egg yolks, and pigeon and sheep droppings were used in incendiary mixtures. What chemical/property would these have which is desirable in explosive/incendiary mixtures? (Are pigeon and sheep droppings as useful as guano??) In addition, some folks besieged by the Romans drove them off by burning chicken feathers, producing such a noxious smoke the Romans had to abandon their mining attempts. What's going on here? Gwinva (talk) 03:42, 6 March 2008 (UTC)

Animal dropping may be high in nitrate eg guano - which will cause more vigorous burning, they may also produce an unpleasent smoke when burnt.
Egg yolk i'd guess are there to make the liquid more sticky.
found this http://www.tennessee.gov/environment/tn_consv/archive/PrescribedFire.pdf "Native Americans practiced chemical warfare. Bundles of Poison Sumac or other poisonous plants were burned upwind of the enemy, having severe effects on the attacking force." similar to chemical weapons, I've heard of similar examples using burning plants containing alkaloids to similar effect eg henbane , deadly nightshade
Burning feathers/hair really stinks - as everyone knows - imagine a lot of it - I'd retreat - at least temporarily...compare tear gas87.102.74.217 (talk) 12:19, 6 March 2008 (UTC)
Some may be covered in Chemical_weapons#History87.102.74.217 (talk) 13:40, 6 March 2008 (UTC)
Horse hooves make glue, of course, which is unrefined gelatin. All sorts of excreta would be useful in making potassium nitrate, and I guess that any chemical reaction tending that way would enhance the combustibility of a mixture containing it. --Milkbreath (talk) 20:39, 7 March 2008 (UTC)

[edit] Familiar PTC flavo(u)r

Inspired by the broccoli question from above. Does anyone who can sense phenylthiocarbamide agree that it tastes a lot like earwax? HYENASTE 05:06, 6 March 2008 (UTC)

What does earwax taste like?--Shantavira|feed me 08:42, 6 March 2008 (UTC)
And given what it likely tastes like, do two earwaxes taste the same? Julia Rossi (talk) 12:43, 6 March 2008 (UTC)
There's only one way to find out:
"We have to learn again that science without contact with experiments is an enterprise which is likely to go completely astray into imaginary conjecture." — Hannes Alfven (from Experiment)
AlmostReadytoFly (talk) 15:24, 6 March 2008 (UTC)
Shantavira, surely you have enough ears and fingers to determine this for yourself. HYENASTE 21:22, 6 March 2008 (UTC)

[edit] Aromatic Hydrocarbons and PVC or Polyethylene

I see from the article on polyethylene that "Polyethylene (other than cross-linked polyethylene) usually can be dissolved at elevated temperatures in aromatic hydrocarbons, such as toluene or xylene, or chlorinated solvents, such as trichloroethane or trichlorobenzene." Does anyone know what "elevated temperatures" are meant and whether polyethelene is safe to use as a container for aromatic hydrocarbons (Heptane, Hexane, Toluene, Xylene) at room temperature without degrading the container or contaminating the hydrocarbons? Similarly I'd like to ask the same question in relation to pvc, Polyvinyl chloride and enquire which would be the better to use?

Thanks AllanHainey (talk) 08:34, 6 March 2008 (UTC)

Can't give you the temperatures.
In chemistry PE is not a suitable container for hydrocarbons because of contamination, nor is a PVC container - at least if you wish to keep the liquid free from contamination. This is important for some chemical processes..
However it can be used. The higher the molecular weight of the polymer the better. Some petrol cans are plastic.
You might want to compare high density PE and low density PE87.102.74.217 (talk) 09:56, 6 March 2008 (UTC)
You best choice would be glass, also PVA or similar coatings can act as a hydrocarbon barrier in some cases.87.102.74.217 (talk) 11:26, 6 March 2008 (UTC)
Thanks, I'm asking in relation to a the material a siphon should be made of for siphoning these hydrocarbons - all I've seen available is PE & PVC. AllanHainey (talk) 11:45, 6 March 2008 (UTC)
If you're syphoning for say a car or to be mixed into some paint etc then you should be ok as long as the material you use is specified ok for petroleum. HDPE should be ok, LDPE not ok. PVC is different because it sometimes contains plasticisers which are easily dissolved.
The big problme comes when doing analytical work because even a small amount of dissolved plastic can mess up the process later on.
Even HDPE can swell up when exposed to organic solvents.
I can only suggest you use a pipe that is clearly stated to be safe to use with the liquid you are using87.102.74.217 (talk) 12:13, 6 March 2008 (UTC)

[edit] Ostrich fossil range

What is the fossil range of Struthio camelus? I mean only this species, not the entire Struthio genus. Thanks. -- Leptictidium (mammal talk!) 11:57, 6 March 2008 (UTC)

From Ostrich#Evolution - "The earliest fossil of ostrich-like birds is the Central European Palaeotis from the Middle Eocene, a middle-sized flightless bird that was originally believed to be a bustard. Apart from this enigmatic bird, the fossil record of the ostriches continues with several species of the modern genus Struthio which are known from the Early Miocene onwards." -- MacAddct  1984 (talk • contribs) 14:15, 6 March 2008 (UTC)
Thanks, but that still refers only to the genus Sruthio, not to the species S. camelus. Struthio may date from the Miocene, but S. camelus itself may have appeared later on. -- Leptictidium (mammal talk!) 15:27, 6 March 2008 (UTC)
Oh, I apologize, I read that as "I mean not just this species, the entire Struthio genus." The exact opposite of what you meant.... v_v -- MacAddct  1984 (talk • contribs) 16:35, 6 March 2008 (UTC)

[edit] Atmospheric (unit) vs. Bar (unit)

If bar is barometric pressure, then why is it not equal to atmosperic pressure? A bar = 14.504 psi, but the atmosphere is defined as 101,325 Pa which = 14.696 psi —Preceding unsigned comment added by 160.84.253.241 (talk) 14:21, 6 March 2008 (UTC)

See Bar (unit) it is about the same as atmospheric pressure, not exactly the same..87.102.74.217 (talk) 14:54, 6 March 2008 (UTC)

[edit] Kylstron or RF cavity

What is the large copper ball, I understand that the copper tube is an RF cavity used in particle accelerators, and had assumed therefore that the copper ball was some form of klystron, however, it seems unlike any other klystrons I have seen, and also on Howstuffworks an diagram (thoguh specificalyy of SLAC) implies that some depth of earth is recquired to be between the klystron and the actual RF cavity, this would imply that it having it so close would cause some sort of problem. So is it a klystron, or is it simply some sort of addition to the RF cavity.

Also why is it important that the klystron is seperated from the beam line by such a depth? —Preceding unsigned comment added by 81.140.151.57 (talk) 17:09, 6 March 2008 (UTC)

[edit] Synchrotron radiation

does anyone have some good resources on the maths of Synchrotron radiation, on sorts of things as the energy lost by a certain energy particle when forced through a known radius and length bend, and also the intensity, frequency of the synchrotron light. thanks —Preceding unsigned comment added by 81.140.151.57 (talk) 17:14, 6 March 2008 (UTC)

This topic is woefully under-linked and under-covered in wikipedia. Griffith's Electrodynamics is an excellent textbook reference which has all the answers on this topic. However, there is some information on wikipedia. The article Brehmsstrahlung has some information, but for some reason, no information about radiation due to charges accelerating perpendicularly to their velocities (perhaps I'll try to remedy that in the future). The article Cyclotron radiation (which is radiation specifically from a charge in a magnetic field) is probably closest to what you're looking for, but it isn't very detailed, and there is no derivation. Feel free to come back here if you want more specific help. --Bmk (talk) 17:47, 6 March 2008 (UTC)
One good book is Rybicki & Lightman, Radiative Processes in Astrophysics (ISBN 0471827592). It's ridiculously expensive per ounce, so maybe try a university library. It's a standard text in astrophysics and shouldn't be hard to find. -- Coneslayer (talk) 18:25, 6 March 2008 (UTC)

I found this it is useful, but seems very specific to electrons, it be used for any particles?(what consant is K, is it the invers of the permiability of free space or something) —Preceding unsigned comment added by 81.140.151.57 (talk) 09:13, 7 March 2008 (UTC)

That gives the formula for an electron accelerated perpendicularly to its velocity. It can easily be generalized to any charged particle by taking e to be the charge of the particle. --Bmk (talk) 04:27, 11 March 2008 (UTC)

[edit] Perigee

At what time of year does the moon reach perigee? Autumn? —Preceding unsigned comment added by 71.174.25.42 (talk) 17:33, 6 March 2008 (UTC)

The article Orbit of the Moon has a lot of information about this type of thing. The "anomalistic month" is the time from one lunar perigee to the next. The anomalistic month is only 27.6 days, so the moon reaches perigee just about 12 times a year. Does that answer your question? PS: If you're curious about what perigee looks like, the moon at perigee appears 14% wider than the moon at apogee! --Bmk (talk) 17:54, 6 March 2008 (UTC)
Also, since Earth's solar year and the moon's revolutionary period are not locked into integer multiples of each other, the "season" varies from year to year. Incidentally, this is why some cultures (e.g. Jewish calendar, Islamic calendar) have calendars which do not fit well at all into a 365-day solar year. Nimur (talk) 19:40, 6 March 2008 (UTC)

[edit] What is "Free-space Laser Communication"?

Hi! I want to know about "Free Space Laser Communication". I have tried searching it on the internet, but nothing valuable could come out....I need to know it from scratch....from the very beginning. And please plrovide all details possible of what is it, why do we use it, and how is it done etc. Please help me out. Please. ~~~~

Our article on the subject is Free Space Optics. The key bit of this -- "Free Space" -- indicates that there is no solid medium through which the communications are routed (versus the optical fiber used in fiber optics). — Lomn 19:01, 6 March 2008 (UTC)
You may find the phrase "wireless optical communication" more useful when searching. This textbook appears to be the standard introduction, but it may presume some intermediate level communication theory. Nimur (talk) 19:46, 6 March 2008 (UTC)
I should note that my terminology includes non-laser systems, such as IrDA. If you're not clear on what a laser is, you should read that article too! Nimur (talk) 19:51, 6 March 2008 (UTC)