Wikipedia:Reference desk/Archives/Science/2009 September 7

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September 7

cloth fibers

What is the differenc between polyester and acrylic? —Preceding unsigned comment added by 63.231.111.146 (talk) 01:50, 7 September 2009 (UTC)

Did you read our articles titled Polyester and Acrylic fiber? The main difference is that polyesters are polymers made from compounds called esters (no shit). Acrylics are polymers made from Acrylonitrile. --Jayron32 03:52, 7 September 2009 (UTC)

"Suspension" of a suspension bridge

Emperor Norton Bridge

According to recent news reports (one example), the Emperor Norton Bridge has been closed because of cracks in the cables that support the deck. Is it accurate to say that there's currently a problem with the "suspension" of this suspension bridge, or would that be a bit of a colloquialism? Nyttend (talk) 02:59, 7 September 2009 (UTC)

Did they suspend the suspension bridge because of a broken suspender? --Jayron32 03:28, 7 September 2009 (UTC)

As the driver said when Galloping Gertie collapsed under him, "The suspense is killing me." Baseball Bugs ^{What's up, Doc?} carrots 03:36, 7 September 2009 (UTC)

To answer your question, no you would not be correct, because according to that article they "found a crack in one of the eyebars on the side of the structure." I interpret that to mean the actual bridge part, along where the original work was planned. If there was a crack in the cables, I think you'd be correct in saying it, not like Suspension (vehicle) of cars but rather in the actual hanging of the thing. ~ Amory (user • talk • contribs) 04:19, 7 September 2009 (UTC)

Actually, that wasn't the article I consulted; it was something on the Road Runner website. Here is a story from the San Francisco Chronicle, stating that the link "helps hold up the east span". Nyttend (talk) 03:20, 8 September 2009 (UTC)

I understand an eyebar to be part (or indeed all) of the vertical suspension members of a suspension bridge. Thus I think it would be fine to say that the bridge. Saying there is a problem with the "suspension of this suspension bridge" is probably a bit unhelpful; I'd tend to use the phrase "problem with a vertical suspension link", or somesuch. However, since the eastern span of the bridge, which is where the fault was found, is a combination of "a double-tower cantilever span, five medium-span truss bridges, and a 14-section truss causeway", I'm not convinced that the explanation necessarily relates to suspension at all - though I'm not satisfied that I understand the design of the double-tower cantilever span ... is is cable stayed? --Tagishsimon (talk) 21:27, 8 September 2009 (UTC)

I see that the first image in eyebar explains quite well the space of eyebars in truss sections. So now my view is that although the eyebars are under tension and so can be thought of as suspension members, to describe them as such without more context would probably serve to mislead. --Tagishsimon (talk) 21:31, 8 September 2009 (UTC)

Radioactivity in the early Earth.

From what I know radioactive heating was a major source of heat for the early Earth, and still is today to a lesser extent. My question is, was the radioactivity billions of years ago (when the Earth formed) enough to cause harm to humans if we lived then. Would it be more/less then the fallout from a nuclear blast? —Preceding unsigned comment added by 66.133.196.152 (talk) 06:20, 7 September 2009 (UTC)

From what I know, the sources of radiation were buried deep under the surface (as they are today) and heating the Earth from within. And since ionizing radiation is strongly absorbed by rocks (from what I've heard way back when, a layer of granite just 1 foot thick can absorb gamma rays almost completely), the radiation at the Earth's surface would be negligible, since all of it would've been converted to heat. The heating from the radiation, on the other hand, would be a whole different story -- since it was strong enough to melt rocks, it would surely burn any living creature to a crisp. 98.234.126.251 (talk) 06:35, 7 September 2009 (UTC)

Ehhh, if I lived billions of years ago, I'd be more concerned about the radiation I'd receive from the sun due to a lack of ozone rather than radioisotope decay emerging from the earth's core. Primitive earth was probably devoid of ozone, so heavy amounts of solar radiation would be kill a human pretty quickly.

You should also consider that there's no one set quantity of fallout that's released from any nuclear bomb. The fallout quantity depends on the yield, which can vary. Dougcard (talk) 06:39, 7 September 2009 (UTC)

Much less than a nuclear blast by the time there were humans. That comes trivially from the maths of half lives. Out of interest Rutherford showed without background radiation the world would cool completely in about 10 million years. The fact that the core is still molten etc at 5 billion years is because of radioactive decay generating heat which has nowhere to go. --BozMo talk 09:21, 7 September 2009 (UTC)

It's also worth pointing out that Ernest Rutherford was an atomic physicist, not a geophysicist or planetary scientist. Modern theory have proposed a variety of mechanisms for cooling other than blackbody radiation, including nuclear decay heating and latent heat of fusion from liquid-to-solid crystallization. So, I would take Rutherford's estimate with a grain of salt; modern geophysical theory seems a little more reliable. A common misconception is that all physicists know everything, and are good at back-of-the-envelope calculations. If only we could put the most famous theoretical physicists on the Wikipedia Science Reference Desk to see how their domain-specific expertise translates into general-purpose problem solving skill... Nimur (talk) 15:28, 7 September 2009 (UTC)

If the radiation is hot enough to melt metal and rocks, it is far more radioactive than the radiation in a nuclear blast. Nuclear radiation is bad for humans and other living things (as they say) but it's not much on a geophysical scale. --98.217.14.211 (talk) 20:07, 7 September 2009 (UTC)

Not really true I am afraid. It keeps rocks molten because it heats them incredibly slowly over thousands of years but the heat is locked in. At any instant the level is way less than a nuclear blast--BozMo talk 21:07, 7 September 2009 (UTC)

If we only look at ⁴⁰K, its concentration in potassium was about 12 times as high 4.6 billion years ago. A typical human is about 0.2% potassium by mass, for 75 kg body mass that is 150 g potassium which equals about 3.8 mol. 4.6 billion years ago about 0.14% of the potassium would have been ⁴⁰K, i. e. 0.0055 mol or 3.3*10²¹ atoms. About 89% of the decays of ⁴⁰K is by electron emission (beta decay; the rest of the decays is by electron capture which I will neglect for this calculation), and the half-life is 1.277 billion years, which means the effective decay constant is 1.54*10^-17 s^-1. So there are 1.54*10^-17*3.3*10²¹ = 5.0*10⁴ decays per second, each with an energy of 1.311 MeV, resulting in 1.06*10^-8 W, or 0.33 J/year. This results in 4.5 mSv of equivalence dose per year - that (alone) won't do much harm (it is less than I had hoped for). Do the same calculation for radon (resulting from the uranium (especially ²³⁵U) decay chain) and you should get a more dangerous results as the amount of ²³⁵U was about 93 times of what it is now. Icek (talk) 22:14, 13 September 2009 (UTC)

An additional note on radon: According to this, a human receives 1.4 mSv/year of radon on average today. That means you would have receives 130 mSv/year 4.6 billion years ago, which is already above the limit for nuclear plant workers. Icek (talk) 22:19, 13 September 2009 (UTC)

A further note on the ⁴⁰K calculation: The received radiation power and therefore equivalence dose power would be lower because not all the energy is carried by the electron in beta decay (some by the neutrino). And regarding the electron capture, it causes some X-rays because the electron is captured from an inner shell and an outer electron will fall to the free space on the inner shell, thereby emitting the energy difference as electromagnetic radiation. Icek (talk) 22:24, 13 September 2009 (UTC)

drug/biochemical for feeling refreshed

I understand that adenosine is one of the causative agents of drowsiness and sleepiness. Is there a chemical that gives you the feeling of being refreshed, like after a long nap or a really, really good sleep? And of course I'm not talking about a simple adenosine antagonist like caffeine, since I quite suspect that adenosine antagonism doesn't give you that refreshed feeling.

If this chemical exists, in what natural sources could I find it, and is it capable of passing the blood-brain barrier? If this chemical were say, used as a study drug, would there be any long-term ill effects? John Riemann Soong (talk) 07:52, 7 September 2009 (UTC)

If it exists I think it is probably contained in tea! --TammyMoet (talk) 10:10, 7 September 2009 (UTC)

Tea contains xanthines, which act mainly as adenosine receptor antagonists. Trying to place "feeling refreshed" to one biochemical is almost certainly reductionistic and is the fuel for the pseudoscientific claims of much of alternative medicine. --Mark PEA (talk) 14:38, 7 September 2009 (UTC)

I should also add that these alternative medicines are often labelled as adaptogens. Compounds in conventional medicine which may produce a refreshed feeling are nootropics such as modafinil or the racetams. --Mark PEA (talk) 14:44, 7 September 2009 (UTC)

There is no drug that causes you to feel refreshed in the sense of completely substituting for sleep. There is, however, a wide class of drugs that make you feel awake and energized, including amphetamine, cocaine, and other so-called "psychomotor stimulants". Looie496 (talk) 15:27, 7 September 2009 (UTC)

But those are adenosine antagonists, which I specifically excluded! And I want to exclude compounds that give you a "buzz" or make you feel charged with energy, which is not how I feel when I wake up from a long nap (relaxed). Is the feeling of refreshedness perhaps due to the fact that adenosine is still active (but exiting the system), with various neurostimulants coming in, which induces an interesting competitive effect? John Riemann Soong (talk) 15:57, 7 September 2009 (UTC)

The hypothesis I favor (which comes from Giulio Tononi) says that sleep actually produces structural changes in the brain. While we are awake, synaptic connections get steadily stronger as we store memories, and this change gradually unbalances the brain's activity patterns. During sleep, a process takes place that gradually weakens the synapses. If that's correct, then there is no obvious way for a drug to duplicate the process. (And by the way, psychomotor stimulants are not adenosine antagonists, they are dopamine agonists, a whole different class of drug.) Looie496 (talk) 19:51, 7 September 2009 (UTC)

How much noise do moving cars and other vehicles make?

Cars and other vehicles driving along a road. Measured in dB(SPL) for example, or in sound energy. Thanks 78.146.254.202 (talk) 09:27, 7 September 2009 (UTC)

Obviously it depends, a lot is tyre noise which depends on road surface. http://www.xs4all.nl/~rigolett/ENGELS/vlgcalc.htm looks about right as a calculator --BozMo talk 09:31, 7 September 2009 (UTC)

I was hoping for the noise at say 1 metre. It would be very useful to know the stationary noise or stop-start noise too. 89.242.115.9 (talk) 20:11, 7 September 2009 (UTC)

Also depends heavily on the make of the vehicle. I remember the first time I saw a Prius, it was cruising through a grass parking lot using only its electric motor. It came up behind me and passed slowly by - surprised the hell out of me when a large white object entered my peripheral vision because I hadn't heard a damn thing! 218.25.32.210 (talk) 02:04, 8 September 2009 (UTC)

U,S, and other government websites should have some figures, since in the U.S. associations advocating for blind people are demanding that electric cars make noise so they can hear them coming, and I have read statements by spokesmen for companies planning to manufacture and sell electric cars related to this. See [1], [2],[3]. Maybe they could just require them to put in one of those giant window shaking 200 watt sound systems and play brain thumping noise/music all the time. Edison (talk) 15:50, 8 September 2009 (UTC)

The following web site [[4]] exhibits a scale with the noise level of a wide range of sources, including a car (65-70 dB) and a diesel truck (85-90 dB). I assume that these would be relatively normal, modern vehicles passing by. I have measured levels of the order of 120 dB for a car with a broken exhaust pipe that sounded more like a very loud (and unpleasant) jet engine at a distance of 2-3 m. At that level, noise can be damaging to your ear especially if endured for sustained periods of time. Michel M Verstraete (talk) 20:06, 9 September 2009 (UTC).

Decibels or dB are units of ratio and nothing more so it is meaningless to call a noise level X dB. The cited web site encourages that common error by more or less implying that setting 0 dB = 0.00002 Pa or 0 dB = 10^-12 W is implicit. That is wrong and we should know this as well as the OP who properly quotes a reference for sound levels, as in dB(SPL). Cuddlyable3 (talk) 13:39, 10 September 2009 (UTC)

OK, that's true. Any decibel scale implies the existence of a reference level, so a given number of decibels is never an absolute measure of some intensity but an assessment of how much stronger or weaker that intensity is with respect to the implied or explicit standard. This being said, our own Wikipedia article on Sound pressure states that 'The commonly used reference sound pressure in air is p_ref = 20 µPa (rms), which is usually considered the threshold of human hearing'... Michel M Verstraete (talk) 21:37, 10 September 2009 (UTC).

Bouncing soap bubbles, electrical?

Bubbles colliding with each other in the air typically bounce off of each other -- although they can sometimes hit in a way that causes them to join and assume a more minimal double-bubble configuration and sometimes, more rarely, the two will join as a single larger, and most minimal, sphere.

Soap bubbles typically break if they touch dry wood, metal, stone, plastic or skin. They break if they touch sheer silk fabric or smooth nylon but they typically bounce off of wool and raw silk seems to be excellent for bouncing them as well.

Are these exceptions all examples of electrical repulsion? Is there some other explanation (i.e. the fine hairs of the wool are just not enough contact to pop the bubble, the lanolin in the wool and natural oils in raw silk are a factor?)

I am an entertainer with a show that I call Bubble Magic. I've read C.V. Boys classic work on Soap Bubbles and other science literature but I've never seen a scientific explanation for the apparent repulsion between bubbles and wool or bubbles and other materials. 79.193.226.55 (talk) 10:14, 7 September 2009 (UTC)

What a good set of questions. It is possible for bubbles to bounce off surfaces without contact or electrical forces just from the mechanics of the air between them. Clearly, static and other electrical forces (even van der Waals) could play a part, so could fibre geometry and surface absorbency. I think the film structure of the bubble is fairly well know (with hydro-phobic tails pointing outwards). One thing to try would be to compare dry cleaned wool with natural wool. There is a huge difference in fire resistance (dry cleaned wool is quite hard to burn, natural wool is easy to burn) so I think dry cleaned wool probably has little lanolin. Have you tried other waxy material? --BozMo talk 11:21, 7 September 2009 (UTC)

I have tried other waxy materials including paraffin, bees wax, and even pure lanolin with no success (the bubbles popped) but the lack of "wetting" does seem to be a factor and so it may contribute in some way. Sheer silk (my Hawaiian shirts) seem to grab and quickly drink the drop at the bottom of the bubble ... then it pops. Once a bubble has popped on, even a good wool surface (navy pea coat) that wet spot is no longer a good place to bounce one.

But the two bubbles approaching each other in the air have a very different surface geometry than does the fine-haired wool carpet so it's difficult to see one answer to the question.

The hydrophobic ends of the soap molecules at the surface, I believe, have no great charge to them ... maybe the nearby water molecules attached to those soap molecules that are now all aligned with the same face (charge) aimed outward? What can you say about the "mechanics of the air between them"? 79.193.226.55 (talk) 11:35, 7 September 2009 (UTC) —Preceding unsigned comment added by 79.193.226.55 (talk) 11:34, 7 September 2009 (UTC)

In the complete absence of any electrical forces I do not think that two bubbles would ever be able to squeeze out the thin layer of air between them. They would deform, the air would squash and they would spring apart. Even in classical fluid dynamics the equations suggest a smooth ball cannot touch a flat wall because of the air cushion, only surface irregularities allow it to happen. But I suspect there will always be electrical forces. --BozMo talk 12:08, 7 September 2009 (UTC)

For your show of course you should be able to charge up bubbles positively and negatively. Any static charge would dominate. All that requires is a metal hoop to blow through, standing on a nylon carpet and having one earthed boot. A bit of judicious shuffling should do the trick. --BozMo talk 12:11, 7 September 2009 (UTC)

Thank you for that! Simply compressed air could account for much of what we see with or without electrical forces. I'll take that with me as I continue to watch what they do in various situations.

I have charged bubbles and seen dramatic effects as a result. I often perform in science centers and when I can, I get a hold of a Van de Graff generator. If you blow a stream of bubbles to it they will act as though they are being pulled in ... until ... the first one pops and then, suddenly the others reverse course! They take on the charge (presumably delivered to them by the splash of the first one) that is now the same charge as that of the dome of the Van De Graff ... these retreating bubbles invariably chase me since I'm the closest available place to discharge their excess ... I will sometimes dodge them for a few steps but then they catch me like little kamikazees. I'll try the trick with the carpet and boot ... 79.193.226.55 (talk) 12:53, 7 September 2009 (UTC)

I expect you could get a good effect with a piece of PVC pipe rubbed with a piece of wool. The trick of an uncharged bubble being attracted to the charged object, picking up (or giving up) electrons, then spraying ionized droplets on the other bubbles, which then chase uncharged objects or people, is brilliant. Edison (talk) 21:58, 7 September 2009 (UTC)

Shell vial for prions

Can prions be grown using shell vial tecnique? 87.6.122.44 (talk) 10:20, 7 September 2009 (UTC)

Prions have no genetic material as far as we know, thus, the notion of "growing" is only partially applicable. Prions (specifically, the misfolded prion protein, or PrP^Sc) induce changes in the folding of otherwise normal cellular protein (PrP^C); thus, their propagation in a culture would depend on the abundance and availability (for direct contact) of the PrP^C, and the stability of the PrP^Sc under culture conditions. I don't think anyone has identified an efficient system for detecting PrP^Sc in simple cell culture (in the way that a shell vial assay {is that really a red link??!!} may be used for detecting viruses). Attempts have been made to develop in vitro tests for prions, such as PMCA and various immunoassays (e.g. PMID 19060956). --Scray (talk) 20:24, 7 September 2009 (UTC)

Thanks! 87.10.130.252 (talk) 09:50, 8 September 2009 (UTC)

what is Prohesion

Can any one please define Prohesion.

thank you kindly KAL —Preceding unsigned comment added by 137.44.16.69 (talk) 12:01, 7 September 2009 (UTC)

Not a real dictionary word (yet or probably ever).. But [5] "The test method was developed by British Rail and Mebon Paints and the term Prohesion is derived from a key concept of this development namely Protection is Adhesion."

83.100.250.79 (talk) 13:35, 7 September 2009 (UTC)

Shared Lake

What's the most shared lake (not counting Caspian Sea) in the world? For example, lake Tanganyika is divided between Burundi, Tanzania, Zambia, Congo, or lake Prespa shared by Greece, Albania and Macedonia. --151.51.50.29 (talk) 13:22, 7 September 2009 (UTC)

Looks like you've already found your answer. Vranak (talk) 20:28, 7 September 2009 (UTC)

See List of lakes by volume. According to that list Tanganyika is the largest freshwater lake by volume that borders two nations. APL (talk) 02:09, 8 September 2009 (UTC)

nuclear reactions

does electrons take part in nuclear reactions.while calculating mass of reactants or products the mass of electrons are included or not —Preceding unsigned comment added by Muthu64670858618 (talk • contribs) 15:16, 7 September 2009 (UTC)

Sometimes, and yes, respectively. Beta particles are nothing more than electrons (negative or positive), so beta decay absolutely must consider the mass of the electrons. (The inverse process, electron capture, also involves electrons.) Tables of atomic masses always include the mass of electrons for neutral, ground-state atoms. TenOfAllTrades(talk) 15:27, 7 September 2009 (UTC)

Well, it sort of includes the mass of those electrons. Considering that electrons have roughly 1/1856th (give or take) the mass of a proton, and most atomic masses aren't often reported much past the 4th decimal place, so electrons don't often show up, unless we're dealing with hyper-accurate atomic masses (which are available, but not often used in standard calculations). --Jayron32 18:53, 7 September 2009 (UTC)

I understood the original question somewhat differently... First of all, nuclear forces are relevant only to account for the stability of the nuclei, not to explain the interactions between these nuclei and the electrons of a given atom. Second, there are two main classes of nuclear reactions: fission and fusion. Fission is a process where single individual heavy nuclei (e.g., Uranium, Plutonium, etc) break down in pieces as part of a stochastic process, which can sometime be accelerated by external stimulation (e.g., by neutrons). In some of these cases of disintegration, beta particles (electrons) may be released. Fusion requires multiple light nuclei (e.g., Hydrogen, Helium, etc) to merge together: the old nuclei are now bound together by nuclear forces to form a new, singular nucleus. This process only takes place at very high temperature where materials are already either strongly ionized or in a state of plasma. I am not aware that electrons play any role in stimulating (or hindering) such nuclear reactions. In any case, as already pointed out above, the actual mass of electrons in neutral atoms is minuscule compared to the mass of the nucleus. If these various answers do not answer your question, please clarify or elaborate on what you are looking for. Michel M Verstraete (talk) 19:47, 9 September 2009 (UTC).

What matters in the reaction is not the total mass of the atoms. It is change of mass that is important (At least if what you are trying to do is to calculate the enery released). In that case the mass of the electrons (beta decays and electron capture reactions), is important to get an accurate answer. Dauto (talk) 15:57, 11 September 2009 (UTC)

Insect Identification

I was wondering if anyone would be able to identify this insect. It was squashed and captured on a piece of tape.

(Possibly) Pertinent Information:

I found the insect crawling on my desk.

The body measures approximately 3mm in length, and 2mm in width.

I am located in Toronto, Canada. Today's temperature is 21 Celsius, relative humidity @ 73%.

Images:

I will refrain from embedding the images as they are quite large and may break the page.

View from bottom: http://commons.wikimedia.org/wiki/File:Unknown_bug_back.JPG

View from top: http://commons.wikimedia.org/wiki/File:Unknown_bug_front.JPG

Orange Helium (talk) 16:47, 7 September 2009 (UTC)

Looks like a German cockroach. Mein herzliches Beileid. --Pykk (talk) 19:31, 7 September 2009 (UTC)

First of all, thank you.

However, the body of the German cockroach measures at least 1.3cm long (according to the wikipedia article). The body of the sample I captured measures around 0.3cm long.

Orange Helium (talk) 20:05, 7 September 2009 (UTC)

The lengths quoted in the article are for adults, the one in your pictures looks like a nymph (juvenile), probably 1st or 2nd instar (developmental stage). Mikenorton (talk) 22:34, 7 September 2009 (UTC)

Thanks! Orange Helium (talk) 00:10, 8 September 2009 (UTC)

Impact of the type of cigarettes smoked on the decrease in life expectancy

I have a hard time finding numbers concerning the decrease in human life expectancy caused by smoking which numerically examines the differences between the type of product used. I am particularly interested in the difference between average-yield cigarettes with filters and unfiltered and/or high-yield cigarettes. I found an AP article concerning a study conducted in India which claimed that the decrease was roughly 20 years for long-term smokers of unfiltered "bidi" type cigarettes. One must however consider that bidi smokers usually don't have access to healthcare which as good as that commonly available in countries such as the UK - hence the difference might be much lower in the UK, for example. I suppose that the decrease caused by unfiltered cigarettes in "developed countries" is in the range of 11 to 16 years. Thanks for your help. —Preceding unsigned comment added by Binrapt (talk • contribs) 16:57, 7 September 2009 (UTC)

Careful there. The lack of health care cuts both way. Life expectancy in India is about 10 years below life expectancy in the UK. So people will die earlier even without cigarettes - in other words, any particular harmful custom has less lifespan to take away in the first place. If you die at age 3 from amoebic diarrhea, you cannot die of tobacco-caused vascular diseases at age 60. --Stephan Schulz (talk) 20:13, 7 September 2009 (UTC)

Anemia/obesity connection

Don't worry, this isn't a request for medical advice; I'm just curious. Is there any kind of anemia that is associated with / is exacerbated by / tends to occur with obesity? +Angr 20:29, 7 September 2009 (UTC)

Well, at the risk of sounding as though I'm not taking the question seriously, you do see these 600lb+ guys on talkshows who seem to forget just how much food they consume on a daily basis when asked directly - claiming that they 'don't eat more than anyone else' and that there must be some sort of genetic/glandular cause for their obesity... --Kurt Shaped Box (talk) 22:29, 7 September 2009 (UTC)

And what does that have to do with anemia? +Angr 22:40, 7 September 2009 (UTC)

Oh dear. I'm a complete and utter fool. I read your question as asking about a connection between obesity and *amnesia*. Sorry. --Kurt Shaped Box (talk) 22:45, 7 September 2009 (UTC)

I misread it in exactly the same way... how odd. --Tango (talk) 00:11, 8 September 2009 (UTC)

I also misread it exactly the same way. It is like a magic trick where the audience is misdirected by expectation or "attentional set." Edison (talk) 15:37, 8 September 2009 (UTC)

It's plausible. I vaguely remember reading about malnutrition and obesity, since people who don't manage their diets well probably aren't eating the right stuff either. But you proably knew that already. 98.14.222.125 (talk) 23:39, 7 September 2009 (UTC)

Type II diabetes is associated with obesity. The symptoms can be at least somewhat similar to anemia. Looie496 (talk) 00:43, 8 September 2009 (UTC)

Including too few red blood cells? +Angr 09:23, 8 September 2009 (UTC)

No. Type II diabetes/metabolic syndrome is associated with increased ferritin levels, which is a surrogate marker for iron overload, which is negatively associated (weakly!) with anaemia. See [6]. --NorwegianBlue ^talk 20:31, 8 September 2009 (UTC)

It's been suggested, but it doesn't seem to be the case: "Overweight and obesity were associated with changes in serum iron, TS, and ferritin that would be expected to occur in the setting of chronic, systemic inflammation. However, overweight and obese persons were not more likely to be anemic compared with normal-weight persons."[7] Fences&Windows 04:08, 9 September 2009 (UTC)

Snapping a street light by repeated poking with finger

Is it true that you could snap a street light - I mean a street light on a long mostly vertical pole or tube - by repeatedly pushing it gently with your finger at its resonant frequency? 89.242.115.9 (talk) 20:32, 7 September 2009 (UTC)

No. --Jayron32 21:00, 7 September 2009 (UTC)

Every resonator has some level of damping. Looie496 (talk) 21:14, 7 September 2009 (UTC)

I once saw a group of three college guys "tackling" a sequence of metal light poles by all three simultaneously bumping the pole with their shoulders (one high, one low, one in the middle). This resulted in a wave of energy travelling swiftly up the pole, and a sharp mechanical snap when the weave reached the top, knocking out the light. They scored 4 out of 4 that I saw. There was not a huge amount of force, but the transient shock at the top was impressive. There are legends (doubtful) of Nikola Tesla shattering bridges or buildings with mechanical resonators. I would not rule out the possibility of say a 2 pound force repeatedly applied at a resonant frequency causing resonant motion of a metal light pole, if it is a modern flexible one. An old cast iron one or one on a wooden pole? No way. The designers should have damped out such resonance, to avoid large amplitude resonance in wind, but see Tacoma Narrows Bridge (1940) for a famous example of failure to deal with resonance in a bridge. Edison (talk) 21:56, 7 September 2009 (UTC)

Well, what is "snapping" and what is "gently"? You can certainly excite it to fairly violent movement with repeated pushing with one hand (and if I can do it with my hand, Big Van Vader can do it with a finger). It will not snap the pole, but it may shed some of the glass components on top. --Stephan Schulz (talk) 21:58, 7 September 2009 (UTC)

You can definitely do it by snapping with a put-outer. DRosenbach ^{(Talk | Contribs)} 01:47, 8 September 2009 (UTC)

The idea that you can break anything by gently stimulating it at its resonant frequency is deeply flawed. The biggest problem is that each time you 'poke' the object, you have to put in more energy than the object can dissipate during the next cycle of oscillation. If you don't put in that minimum amount, the oscillation cannot grow. Tesla was a clever guy - but he had a tendency to be taken in by simple ideas and to blow them out of all proportions - then to lie about his results, reporting what he THOUGHT they should be - not what they actually were. He had enough successes to become famous - even revered - but in many ways he was a complete nut-job. His theories on resonance are an excellent example of that. The basic idea is true - there are things that will resonate to destruction (the canonical example being the opera singer shattering a glass with nothing more than her voice)...but that doesn't translate to being able to destroy massive objects with tiny forces. SteveBaker (talk) 02:30, 8 September 2009 (UTC)

Tesla also thought you could transmit electricity through the earth, as I recall. That's not a very practical idea. Edison got a few things wrong too. Both of those guys are examples of the principle that in order to get good ideas, you have to have lots of ideas - some of which will be wrong. Edison, for example, promoted DC while Tesla promoted AC. Guess who won that battle. Baseball Bugs ^{What's up, Doc?} carrots 15:59, 8 September 2009 (UTC)

When I was a kid, we used to knock out lights in parks and playgrounds by kicking the pole behind the maintenance hatch. We didn't know then what exactly was going on, but I suppose there was a relay attached to the inside wall of the pole opposite the hatch, and a sharp kick would break the circuit for just long enough that the mercury vapour lamp would then need to restart, which takes a few minutes.--Rallette (talk) 06:09, 8 September 2009 (UTC)

Hey, that tip might be useful for Special Force commandos who have to operate in cities at night. Thanks a lot! 98.234.126.251 (talk) 06:54, 8 September 2009 (UTC)

Not sure if they had it when Rallette was a kid but don't modern street lights have a collision detection mechanism that cuts the power when it's hit by something (ie. car)? --antilived^{T | C | G} 11:18, 8 September 2009 (UTC)

Here's an alternative they could use.. EasyTarget (talk) 13:37, 8 September 2009 (UTC)

I thought Professor Dumbledore had a patent on that. Or was it Gandalf? :-) 98.234.126.251 (talk) 05:06, 9 September 2009 (UTC)

It would be quite possible to design a metal lamp post which was quite tall, which was strong enough to support itself and a large wind loading, but was underdamped, if that made it a buck cheaper and it was not a specified quality which was tested for by the purchaser. The same folks who put lead in childrens' products, antifreeze in tooth paste, make cribs which strangle babies, build school buildings which collapse in low level earth tremors, and put melamine in pet food, might just market underdamped lightposts. Edison (talk) 15:45, 8 September 2009 (UTC)

Yet another reason to buy American lampposts instead... :-) 98.234.126.251 (talk) 05:03, 9 September 2009 (UTC)

I was thinking of poking the metal pole when it is at the end of its movement, like pushing a child's swing at the end of its swing. The pole would break through metal fatigue, as when you bend a piece of wire such as a paperclip back and forth. 78.147.7.217 (talk) 21:34, 8 September 2009 (UTC)

Possibly, just be prepared to complete 10^7 cycles of fatigue to get a result. Googlemeister (talk) 14:22, 9 September 2009 (UTC)

If you heat said pole, you could decrease the amount of cycles required to induce fracture. John Riemann Soong (talk) 15:44, 9 September 2009 (UTC)