Wikipedia:Reference desk/Archives/Science/2010 February 27

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February 27

Age of a tree

Is their any way to determine the age of a tree without cutting it? --Extra999 (talk) 11:39, 27 February 2010 (UTC)

From our tree article: "The oldest trees are determined by growth rings, which can be seen if the tree is cut down or in cores taken from the edge to the center of the tree. Accurate determination is only possible for trees which produce growth rings, generally those which occur in seasonal climates; trees in uniform non-seasonal tropical climates grow continuously and do not have distinct growth rings. It is also only possible for trees which are solid to the center of the tree; many very old trees become hollow as the dead heartwood decays away. For some of these species, age estimates have been made on the basis of extrapolating current growth rates, but the results are usually little better than guesswork or wild speculation. White (1998)[25] proposes a method of estimating the age of large and veteran trees in the United Kingdom through the correlation between a tree's stem diameter, growth character and age."--Shantavira|^{feed me} 06:23, 27 February 2010 (UTC)

Yes. It takes many decades for a big tree to get big, so size is one hint. Also, the general condition of the tree, particularly mosses, the bark, and how convoluted the roots and branches are, will also suggest a long history of responding to changing conditions. Vranak (talk) 17:39, 27 February 2010 (UTC)

There have been formula's (formuli?) developed in Britain to estimate the age of oak trees from their diameter I think. There is also a formula to estimate the age of a hedgerow by the number of different species in it. 89.243.151.239 (talk) 18:24, 27 February 2010 (UTC)

Formulae. Apostrophes are never used to pluralise words (but sometimes letters and abbreviations). --Tango (talk) 18:39, 27 February 2010 (UTC)

For some species of trees new branches grow in yearly clumps. This can be used to at least estimate age by counting the vertical 'levels' of tree branches. This really only works with younger trees. APL (talk) 20:53, 1 March 2010 (UTC)

Falling stick

Suppose you were to place a hockey stick near-vertically on (frictionless) ice and let it fall. As the stick falls, would the part of the stick touching the ice (ie the pivot) start moving horizontally? My intuition says yes, but I can't find any force that would cause it to move... —Preceding unsigned comment added by 173.179.59.66 (talk) 08:54, 27 February 2010 (UTC)

If you have a force that moves the stick from being vertical to being horizontal you get a force vector. Part of that is a horizontal force and will have an effect on the pivot point, since there's nothing stopping it. AFAIk. 99.11.160.111 (talk) 08:59, 27 February 2010 (UTC)

But isn't this force vertical, without a horizontal component? —Preceding unsigned comment added by 173.179.59.66 (talk) 09:23, 27 February 2010 (UTC)

That only concerns external forces acting on the stick. There are internal forces that cause the bottom portion of the stick to move to the right. In truth, the stick is simply rotating as it falls; there is no horizontal motion of the stick's center of mass. Someguy1221 (talk) 09:27, 27 February 2010 (UTC)

(edit conflict) There are two sets of forces acting on the stick. There is the normal force which acts vertically upwards through the contact point of the stick with the ice. And there is the force of gravity, which acts on every part of the stick, but which we can treat as if it were a single force acting vertically downwards through the centre of mass of the stick. These two forces are both vertical, but do not act along the same line (because the stick is only almost vertical) so they exert a turning moment on the stick. As there are no horizontal forces on the stick, its centre of mass must fall vertically downwards. Therefore, yes, the end of the stick touching the ice will slide across the ice and the stick will come to rest horizontally with its centre of mass vertically below where it started. No horizontal force is required to move the end of the stick because the stick's net horizontal momentum throughout the motion is zero - as one end moves in one direction, the other end moves in the opposite direction. Gandalf61 (talk) 09:31, 27 February 2010 (UTC)

Right! Obviously, how could I be so dense? Thanks. —Preceding unsigned comment added by 173.179.59.66 (talk) 09:35, 27 February 2010 (UTC)

AUXILLARY questions: 1) what's the value of the normal force? It's obviously not equal to the weight of the stick...so what would it be?

2) if there were friction, what frictional force would be required to keep the pivot in place? 173.179.59.66 (talk) 09:47, 27 February 2010 (UTC)

Nevermind, I think I was able to answer these questions. 173.179.59.66 (talk) 10:51, 27 February 2010 (UTC)

Well you'd have to go down to the microstructure of the stick and the ice, where there would be all sorts of irregularities -- mountains and valleys if you will. The would be a net force one way or the other depending on the initial state of the stick. Of course if it were perfectly vertical it may not fall at all, except through air currents, which is then your horizontal force. Vranak (talk) 17:36, 27 February 2010 (UTC)

Torque and pseudo-forces

Ref: http://discovery.bits-pilani.ac.in/discipline/physics/rishikesh/physics1/prob-40-41-revised.pdf

Towards the bottom of the page, the author takes the torque about the center of mass, which is accelerating. But apparently, because it is the center of mass, any pseudo-forces which do not need to be considered. Why is this true? 173.179.59.66 (talk) 09:33, 27 February 2010 (UTC)

That's because they have a vanishing moment arm.Dauto (talk) 19:43, 27 February 2010 (UTC)

Why are the roofs of factories shaped the way they are?

Why are the roofs of factories shaped like this: http://en.wikipedia.org/wiki/File:Factory.svg  ? —Preceding unsigned comment added by 60.242.27.213 (talk) 09:52, 27 February 2010 (UTC)

To allow the water to run off and light to come in. The vertical parts are typically glass windows, the diagonals are tiled roof. This allows natural light in even for large spaces far from the other walls. --Stephan Schulz (talk) 10:20, 27 February 2010 (UTC)

More specifically, the sloping vertical windows face north (in the northern hemisphere) to admit indirect light while shielding the factory from direct sunlight. There's a good collection of links on uclue.com. P.S. The last article mentioned on that page, in the 1912 Times Engineering Supplement, seems like the clincher, so I added a reference to it in the roof article. --Heron (talk) 10:32, 27 February 2010 (UTC)

Its a pity that high-density houses are not built with a similar design, so that you could have light without loss of privacy or having to look at an ugly view. Although personally I'd prefer a south facing window. 78.149.201.215 (talk) 13:33, 27 February 2010 (UTC)

They are modules placed together to make as big a factory as you need. 86.4.186.107 (talk) 22:03, 27 February 2010 (UTC)

are there any original sound recordings of the moon missions where Houston forgets to wait at least 1 second before answering? (ie "hoax"?)

So the moon is 2.4 seconds (perigee) to 2.7 seconds (apogee) away from Earth at c, round-trip, which is an appreciable amount of time. Now my question is, for the people who propose that the moan landing of 1969 was a hoax, can they point to any original sound recordings from that time recorded e.g. at Houston between Houston and those on the Moon where, for example, Houston asks a mundane question ("how many degrees?") with an answer coming clearly to that question far faster than 2.4 seconds later. It should be an answer clearly to the question asked ("six degress?" - "no, seven") but without the required pause. Also obviously the recording has to be taken at the source, as from the moon side you could record that instantly (" how many degrees?-seven") even though the "how many degrees" had been said 1.2 seconds earlier. From Houston's side, however, it should be "How many degrees.... seven", with the response coming 2.4 seconds later. Is there any example from the original recordings where, assuming for a second this is a hoax, the perpetrators "forgot" to wait for the delay? Thank you. 84.153.244.175 (talk) 12:07, 27 February 2010 (UTC)

If there was, I am sure the good folk over at Moon landing conspiracy theories would be very aware of it and making sure that everybody else knew about it.--Shantavira|^{feed me} 12:45, 27 February 2010 (UTC)

what people forget is that the 'hoax' itself was a hoax - The US had been visiting the moon for decades, but created a soundstage on the moon to fake all that primitive 'spacesuit' stuff, just to keep the Soviet Union from knowing how much contact we had with alien races. see UFO (TV series) --Ludwigs2 15:14, 27 February 2010 (UTC)

Your hypothetical can be anything you want it to be, depending on what you assume (I've always heard that the soundstage was on Mars, because we couldn't get to the moon. Mars is a larger target, you know.). You should be able to find recordings without gaps though, because some TV stations probably edited them out for time and clarity. There are a number of pieces of conspiracy theory evidence that came about this way (some magazine edited together two separate photos to create an impossible situation, for example). Paul Stansifer 17:05, 27 February 2010 (UTC)

If there really was a hoax (I most definitely don't believe there was), there's no reason to presume they were so careless in designing it to rely on people waiting. Even in the pre-digital age, designing a device to delay the audio appropriately can't have been that hard so it seems unlikely anyone was waiting. Rather there would have really been a 2.4s or whatever latency between the two sides of the hoax even if they were in the same building. (That's one of the problems with most conspiracy theorists, they often presume the hoaxers create a brillant deception yet somehow made some major screw up in a very obvious area that was easy to resolve). Nil Einne (talk) 06:53, 28 February 2010 (UTC)

I believe that the Russians used just such a "earthly" timing delay when training the drivers of their lunar rovers in the same era. See Lunokhod programme. Rmhermen (talk) 16:30, 28 February 2010 (UTC)

Standard cassette tape runs at 1 1/8 inch/sec; to build a 4.2 sec delay line using two well spaced tape-heads would be easy even with 1969 technology. One related issue I've heard is that the ground-crew reply to the astronauts immediately. This is, of course, because the tape recorder is beside the ground crew, so what happens is

Astronauts speaks -> 4.2 sec delay -> ground-crew hears; recorder records -> (ground crew thinks) -> crew speaks; recorder records -> 4.2 sec delay -> astronaut hears and replays -> 4.2 sec delay -> recorded

When the tape is replayed, it sounds like the ground crew replies immediately the the astronauts, but there is an 8.4 sec delay to the astronauts replying to the ground crew. CS Miller (talk) 19:54, 2 March 2010 (UTC)

I heard that relativism and quantum mechanics in contradiction with each other

I heard that relativism and quantum mechanics are in contradiction with each other: either one is wrong, the other is wrong, or both are wrong, but they can't both be right in their current form. Is that true? —Preceding unsigned comment added by 84.153.244.175 (talk) 12:22, 27 February 2010 (UTC)

No, not really. quantum electrodynamics for instance is both relativistic and quantum mechanical and give results that match the experimental data better than one part per billion. Dauto (talk) 14:13, 27 February 2010 (UTC)

Relativism has nothing to do with physics. Quantum mechanics and special relativty are perfectly compatible. Quantum mechanics and general relativity are not compatible - see Quantum gravity. DVdm (talk) 14:18, 27 February 2010 (UTC)

There is a difference between saying that we don't have yet a complete theory of quantum gravity and saying that Quantum Mechanica and General Relativity are not compatible. The former is clearly true while I would say that the latter one is necessarily true. Dauto (talk) 17:50, 27 February 2010 (UTC)

(ec) (Relativity, not relativism - specifically, General relativity). See Standard Model#Challenges to the standard model, and Unified Field Theory. "Right" and "wrong" aren't really the best words to use when discussing scientific theories; what matters is if a theory's results are consistent with the experimental data. The results of general relativity are consistent with experimental data on large scales (planets, galaxies), and the results of quantum mechanics are consistent with experiment on small scales (molecules, atoms) - so, both theories are "right". However, there isn't (as yet) _one_ theory that gives us predictions about matter on _all_ scales (from sub-atomic particles to the universe as a whole) - specifically, quantum mechanics doesn't (as yet) include gravity, which is the subject-matter of general relativity. This is the source of the "contradiction" you mention. When the theory which includes both is developed (and it will be, although not perhaps in our lifetimes), its results will be the same as the current theories of quantum mechanics on small scales, and the same as the current theory of general relativity on large scales. Tevildo (talk) 14:20, 27 February 2010 (UTC)

Places to live that never require heating or air conditioning

What places in the world could you live where you would never require either any heating or air-conditioning to be comfortable? Which places in the USA would come closest to this? Thanks 78.149.201.215 (talk) 13:29, 27 February 2010 (UTC)

That depends on the range of temperatures over which one is "comfortable", a subjective criterion if ever there was one. Also, even in the hottest and coldest places on the planet, one doesn't need active heating or air-conditioning to maintain a comfortable temperature, provided one has adequate shelter - see igloo. Tevildo (talk) 14:03, 27 February 2010 (UTC)

Above ground, it would need to be an area of temperate climate. Interpreting 'place' broadly, the most constant comfortable temperatures are found in a below ground dwelling. I am thinking here of Coober Pedy Australia, "famous for most of the residents living below ground" where it can be very hot outside (Average summer high 36.4°C/98°F), while remaining very mild inside. Underground living and Category:Underground_cities may interest —220.101.28.25 (talk) 14:40, 27 February 2010 (UTC)

Would you care to tell us what makes you say it must be on an temperate area? I think Tropical areas would be a better alternative. Dauto (talk) 17:31, 27 February 2010 (UTC)

Overall less highs and lows in temperature. It is supposedly where most people currently live. (though the temperate article gives no references to prove it.) The tropics I think would "require .... air-conditioning to be comfortable". Unless you had a very well designed, passively cooled/heated home, hence my idea of 'underground' living.--220.101.28.25 (talk) 09:28, 28 February 2010 (UTC)

There have been houses built specifically for energy efficiency. These houses usually rely entirely on the benefits of insulation rather than environment. In some cases body and appliance heat must be exhausted even in winter the insulation is so thick. On the other hand Hawaii is generally considered to have the best all-round above ground climate at an average of 72 deg. F per year while the most below ground houses are in New Mexico. Below ground environments, however, offer the most stable temperature stating point from which to decide how much insulation should be used from which to derive the temperature of the living environment. 71.100.5.197 (talk) 15:09, 27 February 2010 (UTC)

I think in the USA the most comfortable place across the entire year would be San Diego, right next to the ocean. You wouldn't be comfortable all year long, but you probably couldn't do any better, unless perhaps somewhere in Hawaii. (I live in the San Francisco Bay area, and never use heating or air conditioning, but I'm not always comfortable.) Looie496 (talk) 17:17, 27 February 2010 (UTC)

Are you comfortable bursting into flame on an annual basis? Someguy1221 (talk) 09:32, 28 February 2010 (UTC)

I could live with very minimal heating here in Vancouver, but I would still want to take hot baths and run the gas fireplace to warm up periodically. If it were up to me the thermostat would be perpetually off, but then I do live with other (cough) people. Oh yeah and air conditioning is unnecessary here. Vranak (talk) 17:31, 27 February 2010 (UTC)

I was thinking about places where you would feel comfortable outdoors, not just indoors. 89.243.151.239 (talk) 18:30, 27 February 2010 (UTC)

The tropics then of course. If you don't mind hurricanes and snakes. Vranak (talk) 18:47, 27 February 2010 (UTC)

There are places on the tropics that are not affected by hurricanes and some islands are also snake free. There are snakes that live on temperate areas as well. Dauto (talk) 19:33, 27 February 2010 (UTC)

I can't think of a single horrible snake that doesn't live in a warm climate. Vranak (talk) 20:36, 27 February 2010 (UTC)

All that tells us is that you personally don't know much about snakes. For example, adder. could you try to provide references when answering on the science reference desk? This would reduce the impression that you're just chatting without feeling the need to know much about the topic at hand. 86.177.121.239 (talk) 01:22, 28 February 2010 (UTC)

An adder is not a horrible snake. Anaconda, Black Mamba, Taipan -- yes. And while we're making petulant requests, why not register a name so you don't look like some anonymous loose cannon that drops in from time to time to make smarmy comments. Vranak (talk) 04:36, 28 February 2010 (UTC)

Hawaii is completely snake free and has been that way since time immemorial. So is Ireland, but it would be too cold to meet the "no heating" criteria. 24.23.197.43 (talk) 07:17, 28 February 2010 (UTC)

I include references in nearly every answer I give, since the purpose of this desk is to lead people to knowledge. You have chosen to change the OP's question from 'air-conditioning and heating' to 'hurricanes and snakes', revising to 'horrible snakes' which apparently don't include snakes that can kill people or (more often) disable them for up to a year. At no point have you provided even a wikilink to support any of your claims, despite several people disagreeing with you. 86.177.121.239 (talk) 12:38, 28 February 2010 (UTC)

Well rightly or wrongly, I have little compunction in sharing a habitat with an adder, but mambas and anacondas, I do. Anything so grievous as to make you think twice about even living in an area is horrible in my books. Vranak (talk) 19:31, 28 February 2010 (UTC)

Madeira has yearly average highs from 19℃ to 25℃, with night temperatures from 13℃ to 19℃. That's pretty comfortable year round, assuming you sleep indoors with a blanket. Gran Canaria is 1-2℃warmer. Hawaii is within 19℃/27℃all year round. In general, subtropical islands have stable temperate climate. --Stephan Schulz (talk) 19:48, 27 February 2010 (UTC)

Many places in the tropics are not affected by tropical cyclones yet, but may be in the future. Also, Madeira is currently recovering from the second wave of the 2010 Madeira floods. ~AH1^(TCU) 23:49, 27 February 2010 (UTC)

Well, the question was "heating and air conditioning", not "umbrella and raincoat" ;-) --Stephan Schulz (talk) 04:53, 28 February 2010 (UTC)

I am late to the party, but was surprised that Key West, Florida was not mentioned. Despite being hurricane prone (and of limited size) it has the most stable temperature of just about any place on Earth (and certainly in the Continental US). As long as you can tolerate high 60s F to high 80s F you would need no supplemental heating/cooling. Most places at a sub-tropical latitude exhibit similar properties, but in the case of Key West, the Gulf of Mexico is not subject to long distance oceanic currents that can bring very warm/very cool water in from time to time. --144.191.148.3 (talk) 15:33, 1 March 2010 (UTC)

Many of the houses in Brisbane Australia had neither heating nor AC when I lived there a few years ago. The house design helped keep the place cool in the summer, but it was a bit chilly during a few "winter" nights. I would most closely equate their climate to that of Miami Florida. Googlemeister (talk) 20:31, 1 March 2010 (UTC)

pulsar

In a NOVA Universe TV program it is illustrated that a pulsar jet 1,000 light years away, if pointed at the Earth, would incinerate a hole in the atmosphere and reek havoc upon the Earth with a beam of Gamma radiation. The animation shows a steady beam about 3/4 the diameter of the Earth lasting for about 10 seconds. Surely this is a false illusion since a beam of any diameter would widen after 1000 light years to millions of more miles than whatever it started as and the Earth's orbit around the Sun and the Sun's orbit around the center of the galaxy and the center of the galaxy's ride on the universe expansion wave would make the Earth a moving target to the extent that its time of exposure would be a great deal shorter or longer than 10 seconds. How wide then could such a beam be and how able to encompass the Earth at a lethal density and for how long under these moving target scenario and would it be anything near to what the NOVA program illustration suggests? 71.100.5.197 (talk) 14:15, 27 February 2010 (UTC)

Perhaps they were talking about SGR_1806-20#Explosion? I believe that starquake was one of the biggest explosions humanity has observed, ever. It could have fried us from 10 lightyears away, but the nearest magnetar is over 10,000 lightyears from us, so we're safe. It was not a beam, of course. I can't analyze your argument about pulsar jets, but I'd like to add that, if you did make an earth-sized beam of laser light (so it didn't widen over distance) and pointed it randomly, the chances of it hitting anything, anywhere are probably negligible. Paul Stansifer 15:10, 27 February 2010 (UTC)

Relativistic jets typically have opening angle of 1-10 degrees (according to theory, we don't have very good ways of measuring this directly), and would cover a huge area after traveling astronomical distances. The NOVA program was probably talking about a gamma ray burst from a supernova and not a pulsar jet. The latter are generally far less powerful and would not pose any risk at those distances. As the beams travel at either the speed of light (gamma rays) or close to it (relativistic particles), the motion of the Earth, Sun, Galaxy, etc. are essentially negligible. Dragons flight (talk) 23:02, 27 February 2010 (UTC)

different locations

What does this mean, "...a number of receivers at different locations in the solar system..." referring to gamma ray and x-ray burst source location detection at slightly differing instances in time? Does this refer to passive reflectors or to active observers which record the pulse and universal time? 71.100.5.197 (talk) 15:41, 27 February 2010 (UTC)

Sounds to be the second choice, actual active receivers with clocks. A reflector for gamma rays on the scale of the solarsystem will be beyond human engineering capability. Graeme Bartlett (talk) 21:14, 27 February 2010 (UTC)

How many stars?

If I were to look straight up at the sky at night and could see stars (light pollution, clouds, etc not factored in), about how many stars would I see without turning my head? A thousand? A million?  ?EVAUNIT^{神になった人間} 16:32, 27 February 2010 (UTC)

The Bright Star Catalogue lists about 9000 stars. Divide that by half because you can only see half the sky and you get 4500. (Interesting sidenote: I once counted the number of stars visible from North York, a suburban area. The result was 110.) —Preceding unsigned comment added by 99.237.234.104 (talk) 16:38, 27 February 2010 (UTC)

Let me give a pointer to some info about this at Answers. Looie496 (talk) 17:06, 27 February 2010 (UTC)

The Bright Star Catalogue goes down to magnitude 6.5, which is extremely optimistic. You need really good eyesight and completely dark skies for that. In a more typical rural, but not wilderness, location you could probably see 2000-3000 stars. If you look straight up, you can see most of the sky without moving your head or eyes. You can probably see the rest just by moving your eyes and keeping your head fixed. If you have good peripheral vision, you'll be able to see at least 180 degrees horizontally, so that's the whole sky in that direction, and maybe 135 degrees vertically, which misses out a little. You can still expect to be seeing something in the low thousands of stars. Light pollution is the main factor, though. In the middle of, say, Tokyo, you would be lucky to spot Jupiter. In a typical suburban area, you might see a few hundred stars. To see into the thousands you need to get into the countryside. --Tango (talk) 18:31, 27 February 2010 (UTC)

You most definitely cannot see even a thousand stars without moving your eyes. For seeing dim objects one should use averted vision, which only works over a narrow range of angles. From experience, I'd say that beyond 20 degrees or so from your center of vision, peripheral vision is only good for stars brighter than magnitude 3. --99.237.234.104 (talk) 22:56, 27 February 2010 (UTC)

I don't have a frame of reference, so I don't know which one would be right: can you link a photo of the night-time sky in which jupiter is visible, however which is NOT zoomed, ie 1:1 the way I would see it. Thank you. 82.113.121.103 (talk) 20:34, 27 February 2010 (UTC)

Cameras don't accurately replicate human vision, so that wouldn't help you. What is it you are trying to understand? --Tango (talk) 21:17, 27 February 2010 (UTC)

Jupiter has an apparent magnitude between -1.6 and -2.94 so it's brighter than any of the stars. The brightest star is Sirius at a mere −1.46 (aside from the Sun of course!). If you can see any stars at all - you'll be able to see Jupiter (assuming it's well above the horizon). The only things in the sky that are brighter than Jupiter are the Sun, the Moon and Venus (which is between -3.8 and -4.6). SteveBaker (talk) 04:31, 28 February 2010 (UTC)

I was ignoring Venus since it is always close to the horizon, so would presumably be behind a building whenever you are in a city centre (unless you are near the top of one of the taller buildings, I suppose). --Tango (talk) 07:12, 28 February 2010 (UTC)

Jupiter: go to the reference desk question above (within the past week) called "Galactic Plane and Rotation" and there's a picture of the milky way. The brightest "star" in the picture is Jupiter, roughly conjoining Antares. I believe the picture is a "normal eyesight from the ground" type picture. 63.17.52.41 (talk) 04:48, 28 February 2010 (UTC)

Sadly, that's not much use - that photo is a 5 hour exposure. SteveBaker (talk) 05:40, 28 February 2010 (UTC)

It is no more or less useful than any other photo. Cameras and eyes are just completely different things. It doesn't even make sense to ask about a photo without zoom - zoom refers to changing the focal length of the camera, it's a relative term, not an absolute one. --Tango (talk) 07:12, 28 February 2010 (UTC)

Believe it or not, a Wikipedia article tells a relevant joke:

“ Sherlock Holmes and Dr. Watson go on a camping trip, and after finishing their dinner they retire for the night, and go to sleep. Some hours later, Holmes wakes up and nudges his faithful friend.

"Watson, look up at the sky and tell me what you see." "I see millions and millions of stars, Holmes" exclaims Watson. "And what do you deduce from that?" Watson ponders for a minute. "Well, astronomically, it tells me that there are millions of galaxies and potentially billions of planets. Astrologically, I observe that Saturn is in Leo. Horologically, I deduce that the time is approximately a quarter past three. Meteorologically, I suspect that we will have a beautiful day tomorrow. Theologically, I can see that God is all powerful, and that we are a small and insignificant part of the universe. What does it tell you, Holmes?" "Watson, you idiot!" He exclaims, "Somebody's stolen our tent!"

”

Cuddlyable3 (talk) 12:23, 1 March 2010 (UTC)

FTL travel

If you have a rod that's over 1 light-year long, and you push and pull it repeatedly to spell out a message in Morse or some other system, someone at the end of the rod could receive the information immediately. But that means that information would travel faster than light, which is impossible. What's wrong with this? --70.245.187.171 (talk) 16:34, 27 February 2010 (UTC)

The information wouldn't be received immediately, in fact the compression/expansion waves would travel far slower than the speed of light. It's basically the same as the reason that an earthquake at one point on Earth takes minutes for even the fastest signs to show up at distant points. (The fastest compression waves travel at about 3 miles per second -- compare that to 186,000 miles per second for light.) Looie496 (talk) 17:00, 27 February 2010 (UTC)

I'd be interested to hear some context on that "fastest == 3 mi/s" thing. I did a quick search on "fastest compression wave" and saw someone claiming (I don't know how reliably) a value of 13 to 17 km/s — I think these were seismic waves. But what about compression waves in, say, a neutron star? Anyone have any idea how fast they go? --Trovatore (talk) 23:25, 27 February 2010 (UTC)

I took my value from our seismic wave article, which gives a speed of 5000 m/s for compression waves in granite. I'm sure there are materials that conduct faster, but unless you go to something bizarre, I doubt that it would be possible to do hugely better. Looie496 (talk) 23:42, 27 February 2010 (UTC)

[1]. Vimescarrot (talk) 18:06, 27 February 2010 (UTC)

Not to mention the weight of the rod! 86.4.186.107 (talk) 22:00, 27 February 2010 (UTC)

A rod floating in space would have no substantial weight. The basic point that people who propose this fail to understand is that rods (and everything else) are made of atoms. You don't move a whole rod. You move some atoms at one end, which move other atoms, which move other atoms, etc... It takes time for a change at one end to propagate to the other end. -- kainaw™ 22:58, 27 February 2010 (UTC)

In context I think it can be assumed that 86 was using the word weight to mean "mass". This is a perfectly fine usage, well-attested over many centuries; it's only on high-school physics tests that you need to be careful about avoiding it. --Trovatore (talk) 23:01, 27 February 2010 (UTC)

If there was substantial compression at only one end, would that not cause part of the rod to heat up? ~AH1^(TCU) 23:44, 27 February 2010 (UTC)

Yes, of course. Basically the information is carried by a sound wave traveling through the medium of the rod. Sound will always lose energy as heat (in fact, at a sufficiently abstract level, heat can be thought of as "random sound"). --Trovatore (talk) 23:49, 27 February 2010 (UTC)

In this case, weight and mass are very different. Claiming it is too heavy to use doesn't make sense because it has no substantial weight. The claim is that it wouldn't be possible to support it with any load-bearing mechanism, which wouldn't be required. Claiming it is too massive to use means something completely different. It is claiming that it would take too much energy to get the rod to move. This is a very good example of weight and mass being used for two completely different arguments. -- kainaw™ 22:37, 28 February 2010 (UTC)

This is a very particular notion of "weight" that is introduced in physics classes specifically to introduce students to the notion that it is not the same as mass. Other than that, this sort of "weight" is not really a physics concept, as it relies on there being a particular gravitational field with respect to which to measure it. In space, it's not at all obvious which one that is supposed to be.

Historically, this physics-class meaning of weight is not the only one; it's not even clear that it's the principal one. In locutions like giving fair weight or Bureau of Weights and Measures, the word weight is clearly being used in the sense of "quantity of matter"; that is, mass. --Trovatore (talk) 22:44, 28 February 2010 (UTC)

Aside from any theoretical constraints (which are entirely correct and valid reasons why this won't work) - if you pulled an actual 1 lightyear-long rod with enough force to make it move with anything but the gentlest imaginable acceleration - it would surely snap. SteveBaker (talk) 04:18, 28 February 2010 (UTC)

Not if it's made out of Structuron-reinforced Arenak. --Stephan Schulz (talk) 05:47, 28 February 2010 (UTC)

Oh god - don't remind me. E. E. "Doc" Smith - possibly the worst of the "golden age" science fiction writers. I hate his work with a passion. SteveBaker (talk) 13:32, 1 March 2010 (UTC)

That just implies that your mind is not of the highest order. You need to study under those eastern masters more. Eventually it will hit you like a blinding flash and deafening report. Inspired by this, I just reread Skylark of Space over the Sunday, and it is really quite horrible - but in a good way ;-) --Stephan Schulz (talk) 20:33, 1 March 2010 (UTC)

LIQUID LATEX

is LIQUID LATEX the same type of latex that they use to make latex surgical gloves? or do they take solid blocks of latex and melt it first? —Preceding unsigned comment added by 67.246.254.35 (talk) 17:12, 27 February 2010 (UTC)

Some sort of liquid dispersion or suspension of latex seems to be used (formulated, no doubt, so as to meet the specifications of the particular gloves), along with a coagulant to make it set up properly. The process doesn't appear to require any melting of latex. For the basics of the manufacturing process, see here; more specific details and variants can be seen by trawling through this search. Deor (talk) 19:21, 27 February 2010 (UTC)

Citation Journals Exercise

What is highest cited peer reviewed exercise science journal? —Preceding unsigned comment added by 72.224.108.36 (talk) 18:20, 27 February 2010 (UTC)

See [2] alteripse (talk) 21:42, 27 February 2010 (UTC)

Detecting blood with light

Is there a name or article which references the technique of finding hard-to-see blood with a shade of light (usually black, blue, or UV), often seen on police procedural dramas shows like NCIS and CSI? I've been searching this in response to my newly-issued flashlight, whish includes a blue light notionally to find blood trails (ref). There is a lot of info at Forensic science and Bloodstain pattern analysis, but nothing about this that I can find. bahamut0013^words_deeds 21:08, 27 February 2010 (UTC)

A flashlight held at an angle can detect blood residue; I don't know whether any specific colour of the flashlight is especially good at this. As an added note, luminol will emit blue light when it contacts the iron found in the red blood cells, specifically in the protein haemoglobin. Intelligentsium 21:15, 27 February 2010 (UTC)

OK, this is quite helpful. Thanks! bahamut0013^words_deeds 21:26, 27 February 2010 (UTC)

I once saw a police officer doing this. He was using a blue flashlight, but he could only see samples glowing if he looked through an orange filter. He also said that they can do the same thing in a large room with a blue laser beam and orange glasses.24.150.18.30 (talk) 02:19, 1 March 2010 (UTC)

You might need to spray the area with Luminol first. Mitch Ames (talk) 04:28, 1 March 2010 (UTC)

can someone help me identify this leaf impression or the material surrounding it?

I think it is a somewhat broad leaf with rounded edges; this means it may be from a warm climate, correct? besides that, can anyone provide any other notable points of interest, like possible geologic period, specie name, or the type of material the leaf was trapped in? I do not know when or where it was found. thank you!Chrisbystereo (talk) 21:45, 27 February 2010 (UTC)

http://i66.photobucket.com/albums/h274/Chrisbystereo/IMG_0330.jpg

http://i66.photobucket.com/albums/h274/Chrisbystereo/IMG_0329.jpg —Preceding unsigned comment added by Chrisbystereo (talk • contribs) 21:44, 27 February 2010 (UTC)

It looks like it's been preserved in a tufa or travertine deposit, which means that it be could relatively recent (a few hundred years) or much older. Of course, if anyone can identify the leaf, that would help. Mikenorton (talk) 22:50, 27 February 2010 (UTC)

I'm not clear whether any of the the leaf margin is visible in the imprint. I get the impression that the margin is rounded rather than toothed, in which case it might be some sort of ficus. But if it could be toothed, it might be a Platanus - see the leaf pictures at London Plane. --ColinFine (talk) 00:11, 28 February 2010 (UTC)

I have the same problem of being unable to identify the leaf margin, if it's there at all. For some reason, the first thing that came to my mind was oak, probably because the venation looks oakish to me. It's not even clear to me whether the remains represent one leaf or two. Deor (talk) 01:31, 28 February 2010 (UTC)

bitter tasting iceberg lettuce

i live in ny why is my iceberg lettuce bitter tasting. i washed it well and i bought it from wegmans. is it safe to eat? —Preceding unsigned comment added by 67.246.254.35 (talk) 22:48, 27 February 2010 (UTC)

Someone once said that iceberg lettuce is not a foodstuff; it's a building material. I have no idea about your particular head of lettuce or its safety, though. As far as taste goes, I think I would prefer bitter iceberg to ordinary iceberg, which has virtually no taste at all.

But seriously. Get some nice spring mix. Much tastier, and much better for you. --Trovatore (talk) 23:14, 27 February 2010 (UTC)

For those who don't live in NY or the area, Wegmans Food Markets is a chain of grocery stores there. Dismas|^(talk) 00:46, 28 February 2010 (UTC)

Its not uncommon for lettuce or cucumbers to taste somewhat bitter. If it is fresh, I would eat it. It may be because it was forced under glass due to being wintertime. 89.243.151.239 (talk) 01:25, 28 February 2010 (UTC)

The reason why lettuce and cucumbers taste bitter is because they haven't been watered enough. They are still perfectly safe to eat though. 24.23.197.43 (talk) 07:21, 28 February 2010 (UTC)

Our article on lettuce notes that some varieties usually taste bitter. Indeed, some leafy vegetables are valued for this taste. Googling for "bitter greens" produced lots of links. BrainyBabe (talk) 12:23, 28 February 2010 (UTC)