Wikipedia:Reference desk/Archives/Science/2008 March 30

= March 30 =

Tongue rolling genes
From Mendel's list I've looked at that section in the Tongue article and it mentions curling the tongue lengthwise. I know someone who can flex the tongue muscle in three different ways: curling lengthwise, turn it over and fold the tip back flat on itself like folding a piece of paper – all without help from fingers. How common is this – is it genetic and how is it passed along? His parents don't seem to have the knack, but his grandfather could touch the tip of his own nose. Julia Rossi (talk) 02:13, 30 March 2008 (UTC)
 * I don't know much about genes, but I know from Wikipedia that as soon as people discovered genes, they said that genes were responsible for just about every single behavior of the body that was unexplainable. I would personally not believe that being able to move your tongue in certain ways does not come from your genes, but rather something else. Mac Davis (talk) 17:47, 30 March 2008 (UTC)
 * While it is right to criticise a naive view of absoulte genetic determinism, building bodies is an area where genes obviously play a huge role.  I probably wouldn't be able to fold my tongue back as described no matter how much I tried, just like I cant change my eye color, my genes just built my body not to be able to do those things. -- 71.91.127.85 (talk) 19:33, 30 March 2008 (UTC)
 * I believe that certain tongue-rolling abilities are genetic. Edison (talk) 20:23, 30 March 2008 (UTC)
 * I've always believed that tongue (lengthwise) curling was indeed a simple dominant-recessive (it's a common example in text books), well established and understood trait. Evidentally it's not., , , & . Eye colour is mostly genetic, and reasonably well understood but it also not a simple genetic trait (the article has more info). Nil Einne (talk) 18:12, 2 April 2008 (UTC)
 * I'm impressed with all those refs, the intricacies of real genetics, and that there's not only rolling, folding and flipping, but trefoiling! Julia Rossi (talk) 06:29, 3 April 2008 (UTC)

gas molecule unpredictability
If you set up a barometer in a controlled environment with perfectly stable 1 atm air pressure, would you ever see any sort of noticable fluctuation? Would the heat death of the universe occur before you even had a billionth of a percent chance of seeing a 1-second millimeter rise/drop in the mercury, or is it actually quite likely? I'm just looking for very round answers here D\=&lt; (talk) 02:59, 30 March 2008 (UTC)


 * I just realized how absurd that question is.. the part about the perfectly stable air pressure pretty much makes no sense! Let's say the number of gas molecules in the chamber is stable, there's no external influences like heat causing convection, and the average air pressure is 1 atmosphere. D\=&lt; (talk) 03:03, 30 March 2008 (UTC)


 * Wind or pressure/temp changes would cause fluctuations. If there is no wind or pressure/temp change, I wouldn't expect any fluctuations until the mercury evaporation has a noticeable effect. StuRat (talk) 03:07, 30 March 2008 (UTC)
 * Well I just mean from gas molecules not hitting the surface. Like how if every air molecule happened to be bouncing exactly away from your mouth, then your lungs would collapse from lack of air pressure.. except with the surface of the mercury D\=&lt; (talk) 06:49, 30 March 2008 (UTC)
 * Consider a simple approximation: If each particle is approximately independent, then we can pretend that the direction it is moving (e.g. up-down, left-right, etc.) is random. Pressure is created by particles bouncing off a surface.  Under normal conditions ~50% of the particles in any given volume will have a downward component to their motion.  Let's consider, what is the probability that only 45% or less of particles have a downward motion.  This would correspond to a 10% reduction in the downward flux and hence the instanteous pressure.


 * If the motion is random, then the number moving down is governed by combinatorics. Specifically, the probability of $$N_{down} <= \alpha*N$$ is
 * $${1 \over 2^N} {\sum_{i=1}^{\alpha N} {N \choose i}}$$


 * $$= {1 \over 2^N} {\sum_{i=1}^{\alpha N} {N! \over {i!(N-i)!}}}$$


 * $$\approx {1 \over 2^N} {\sum_{i=1}^{\alpha N} {N^N \over {i^i (N-i)^{N-i}}}}$$


 * $$\approx {1 \over 2^N} {N^N \over {{(\alpha N)}^{\alpha N} {((1-\alpha)N)}^{(1-\alpha)N}}}$$


 * $$= {1 \over 2^N} {1 \over {{\alpha}^{\alpha N} {(1-\alpha)}^{(1-\alpha)N}}}$$


 * $$= ({0.5 \over {\alpha}^{\alpha} {(1-\alpha)}^{1-\alpha}})^N$$


 * Where I have used approximations appropriate for large N. If &alpha; = 0.45, then this reduces to $$0.995^N$$.  So with a hundred particles, a 10% fluctuation occurs ≈0.995100 = 60% of the time.  For 2000 particles this reduces to 4 in 105.  For macroscopic ensembles, e.g. 1023 particles, the odds of 10% fluctuation at random is essentially 0 for all practical timescales.  Dragons flight (talk) 08:27, 30 March 2008 (UTC)




 * Simplify your gedankenexperiment by using a J-shaped tube with a vacuum at the tall end and a gas (at one ATM0 at the other. Replace the "mercury" with a perfect theoretical fluid that cannot react with or absorb gas. Now do the math again. -Arch dude (talk) 23:29, 30 March 2008 (UTC)

"japanese algae" keychain
My friend has this keychain, which is a sealed plastic container filled with a liquid and two green spherical puffs which she says are marimo. The liquid looks like green-colored water with oil floating in a layer on top. Could marimo actually survive in this kind of environment, or are they probably just green pom-poms? --Anakata (talk) 03:24, 30 March 2008 (UTC)


 * Another possibility is that it's real, but not alive. It could be preserved in some liquid like formaldehyde. StuRat (talk) 13:45, 30 March 2008 (UTC)


 * Sure its possible, with the right mix of microorganisms, but I am very skeptical. I'd imagine that the smaller the ecosystem, the harder it is to balance and keep healthy. I was poking around for info about ecospheres and people say that they are highly sensitive to changes in light and temperature.  Being repeatedly stuffed into a warm dark pocket does not sound conducive to a stable ecosystem. -- 71.91.127.85 (talk) 19:39, 30 March 2008 (UTC)


 * Wow. Marimo sound cool - thanks to WP, I've learned something else new. Are there any legitimate sports-based applications for these green balls? --Kurt Shaped Box (talk) 19:50, 30 March 2008 (UTC)

Hawaii up from Alaska...?
If you look at Google maps you can see a line of submarine mountains that runs South from Achayvayam, Russia off a jetty, past the West side of Attu Island to a point about 1,800 miles East of Tokyo and then runs South East about 500 miles to Midway Island and then another 1,500 miles or so where it terminates at Hawaii. Does this mean that the hot spot that is still creating Hawaii actually originated in Russia and if so how long ago? —Preceding unsigned comment added by 71.100.0.187 (talk) 05:30, 30 March 2008 (UTC)
 * It looks that way (well, the hotspot stays fixed and the tectonic plates move over it, but same difference). About 80 million years. See Hawaii hotspot and Hawaiian-Emperor seamount chain.
 * Hi. Well, The plate that Hawai'i is situated over is constantly moving northeast, so the islands eventually move, then a new island is remade in its place. The old islands eventually erode and sink underwater. This creates a chain, and it is eventually eaten by the North American place at the destructive boundary. I think I've heard from various places that the Hawai'i chain was nonexistant during the Cretaceous. A new volcano is being created off the coast of the Big Island, and will soon replace it, but it's still got many kilometres and hundreds of thousands of years to go. Hope this helps. Thanks. ~ A H  1 (TCU) 21:19, 30 March 2008 (UTC)

Reversing the effect of Sun tanning on skin colour.
Is it possible to reverse the effect of sun tanning on skin colour ? Does sun tanning permanently change skin colour ? —Preceding unsigned comment added by Shamiul (talk • contribs) 08:33, 30 March 2008 (UTC)

Yes, if you stay out of the sun, your skin will eventually return to its original paler colour. However, you may tan more quickly next time you are in the sun. Also note that persistent overexposure to the sun can permanently damage your skin in a number of ways. See the article Sun tanning.  Sp in ni ng  Spark  12:30, 30 March 2008 (UTC)


 * Hi. I the summertime, I often get a "sandal tan" from wearing sandals. This usually lasts for several months, then fades away around wintertime. It usually redevelopes around late spring. I think it takes about a week to develop, and a few months to fade, although a remnant can still be seen that persists until next summer. Since it becomes darker than usual the next summer, it is often easier to get it again. Hope this helps. Thanks. ~ A H  1 (TCU) 21:23, 30 March 2008 (UTC)

MA and VR Can Opener
How do you calculate how much effort you put on a can opener?

Bzinc (talk) 12:40, 30 March 2008 (UTC)

Would that be Mechanical advantage and Velocity Ratio you would be after? And would this be a homework question? The Lever article might help you.  Sp in ni ng  Spark  12:54, 30 March 2008 (UTC)

What do t hese mean?
I love science, and a lot of the articles have images like on them. I was wondering if anyone would tel me what they mean, because someone (we're brothers) doesn't like me. Thanks! Yamakiri TC    [ §]  03-30-2008 • 14:32:00


 * Ribbon diagram. TenOfAllTrades(talk) 14:59, 30 March 2008 (UTC)


 * Ahhh! My attention span!  It's average!  Nooooooooo! Yamakiri  TC    [ §]  03-30-2008 • 17:14:05


 * OK, we'll try to go easy. Ribbon Diagrams in fifteen sentences or less.  Proteins are special chemicals that exist in all living things.  Every gene is (basically) the set of instructions for building one protein.  So if you've heard of different genes doing different things, it really means that different genes make different proteins that have different functions.  So, it's really, really important, if we're to understand the molecular basis for biology at all, to understand just what those proteins are doing, and how they work.


 * It turns out that you can tell a lot about what a protein does (its function) by looking at its shape (its structure). Imagine that you had to make a chain, the kind you might attach to an anchor or a locked gate.  But imagine that, to make the chain, instead of being given one type of link, you were given twenty similar-looking, but different, links.  That's basically what a protein looks like if you stretch it end-to-end -- a long chain of molecular "links" (called amino acids), twenty different amino acids in all.


 * But a protein isn't very happy stretched end-to-end. It folds in on itself.  Actually, the twenty different links control how it folds.  Let's not worry about that just now.  The important thing is that the folds of that protein determine all of its properties -- whether it will attach to other proteins, whether it will speed up chemical reactions, whether it will make your eyes blue, whatever.  So to really understand what a protein, and therefore what a gene, is doing, you have to look at how it folds.


 * A ribbon diagram is a way of diagramming how a protein chain folds. Each protein gets its own diagram, because it's got its own shape.Vance.mcpherson (talk) 16:22, 1 April 2008 (UTC)

add milk now or later?
I'm about to take a shower and so made an extra-hot coffee to drink when I'm done. I'm going to put some room-temperature milk in it, but should I do so now or when I'm back?

If I do it "now" then the very hot coffee will not have a chance to retain its heat while I shower, since it will be brought a bit right away.

If I do it "later" then the very hot coffee can hold onto its heat a bit, although of course losing some while I shower, only to be brought down a bit later.

It seems the two choices should be identical, but in fact, does heat follow a curve, where the farther from room temperature something is, the faster it loses heat? In this case, I'd better add the milk now, since it will save 15 minutes of heat loss. —Preceding unsigned comment added by 79.122.31.17 (talk) 15:39, 30 March 2008 (UTC)


 * That's correct. Heat flow is proportional to the temperature difference between the two reservoirs (in this case your cup of coffee and the surrounding air). So if your coffee is hotter, it will loose more heat. Of course, other things may come into play - putting milk into very hot coffee may scald the milk, putting the taste off. --Stephan Schulz (talk) 15:51, 30 March 2008 (UTC)


 * Thank you. —Preceding unsigned comment added by 79.122.31.17 (talk) 15:54, 30 March 2008 (UTC)


 * I dispute Stephan Schulz's explanation: If the initial temperature difference (coffee - ambient/milk) is X, and you want to have a fraction p of coffee and a fraction 1-p of milk in what you're going to drink, then you could mix the two now: The temperature difference drops to X*p, and if the heat flow is proportional to the temperature difference, then it will decrease exponentially with some factor a: &Delta;T = X*p*exp(-a*t)
 * where t is the time. If you do it the other way around, it will fall off exponentially to X*exp(-a*t), and then you add the milk, and the outcome is again X*p*exp(-a*t).
 * However, heat transfer by thermal radiation increases with the difference of the fourth powers of the temperatures, and this will make adding the milk "now" superior. Icek (talk) 17:10, 30 March 2008 (UTC)
 * That's strange. You have me completely baffled.  Sticking just with Newtons law of cooling for the moment and ignoring the Stefan-Boltzmann radiation law to keep it simple. The black coffee at every moment up to when the milk was put in is losing heat at a faster rate than the white cup.  After the milk is put in, the two cups are identical composition.  How can the (ex) black cup be at the same temperture when it has lsot more heat.  Sp in ni  ng  Spark  18:27, 30 March 2008 (UTC)
 * Icek is computing with both milk and environment at 0K, I think. --Stephan Schulz (talk) 18:28, 30 March 2008 (UTC)
 * I don't think so, he has used ΔT throughout.  Sp in ni ng  Spark  18:48, 30 March 2008 (UTC)


 * Don't forget that coffee with milk has a lower heat transfer coefficient than black coffee. --Allen (talk) 20:12, 30 March 2008 (UTC)


 * Well that was exactly my point. The white cup is losing heat more slowly so it should end up at a higher temperature.  Anyway, after a monumental struggle with the maths (for me anyway), I've worked out what the difficulty is.  There is a hidden assumption in the Icek analysis that each gram of coffee is losing heat at the same rate (per oC of course).  Since the white cup has more grams of liquid it is losing heat at a faster rate than the black cup at the same temperature.  This precisely cancels the faster rate of heat loss of the black cup.  Happily for the laws of thermodynamics, conservation of energy has been restored and we can all rest easy again.  In a real world cup, the heat loss is not proportional to the mass of coffee, but rather to the surface area of the cup since the internal masses are insulated from the surface.  So I would still go with the white cup, entirely based on Newtons law of cooling, without having to invoke black-body radiation or crackpot ice cream manufactures (and yes, I do know it does work despite sounding crackpot).  Sp in ni  ng  Spark  21:04, 30 March 2008 (UTC)


 * You're right - the constant a will not be the same for both cases in reality. For a cylindrical cup the heat loss should be something like dQ/dt = -(b*m + c)*&Delta;T, the constant c representing the heat loss due to the the nonchanging top and bottom surfaces, the constant b representing the heat loss due to the changing side area, and m being the mass (ignoring different heat capacities and densities). And for the temperature difference it's d&Delta;T/dt = k/m dQ/dt. That makes the final temperature differences for "adding now" p*&Delta;Tinitial*exp(-k*(b + c/(mcoffee + mmilk))*t) which is larger than for adding later: p*&Delta;Tinitial*exp(-k*(b + c/mcoffee)*t). Icek (talk) 12:29, 1 April 2008 (UTC)


 * See Mpemba effect. Gandalf61 (talk) 20:14, 30 March 2008 (UTC)
 * The discussion page there is most interesting, but not that informative!Snorgle (talk) 11:42, 1 April 2008 (UTC)


 * Isaac Asimov wrote that adding the milk early is the best choice if you want the coffee to be hotter later. Edison (talk) 20:21, 30 March 2008 (UTC)

North American bird ID, complex song, PBS "life of birds"
I was just out in my back yard (North Texas, suburban) and noticed some birds presumably doing courtship behavior. The males were dark/black colored, slighlty irridescent and the females more drab and lighter brown. They were approximately the size of a mocking bird. The reason they caught my attention was the complex but short song the males (presumably) would sing. It is a song I remembered from The Life of Birds TV series. It was extremely short, maybe .5 to 1 seconds long but it contained many notes. If I recall, the TV series showed a sonagram of the song and maybe said that it was the fastest (in notes per time unit) song in the bird world. The male would sit next to the female, when she was looking at him he would puff up his feathers and start the song, as he sang he would bow his head down, finishing the song with his head far down. I'm just curious to get an ID of the bird so I can do some more research about it. I have read through the PBS website on the series and tried to do some flowchart-style identification I found on the web but have been unsuccesful. Thanks. -- 71.91.127.85 (talk) 16:44, 30 March 2008 (UTC)


 * I'm looking at the Rusty Blackbird. The song can be heard here at Cornell's excellent site. --Milkbreath (talk) 17:15, 30 March 2008 (UTC)
 * Yeah thats the one, and thanks for the link. -- 71.91.127.85 (talk) 19:03, 30 March 2008 (UTC)

Calculating Mechanical Advantage
How do I know how much force I put on a can opener? and how much force is then put on the can? Bzinc (talk) 16:58, 30 March 2008 (UTC)
 * MA = Output
 * Input
 * but IDK how to find out the can opener thing. Yamakiri TC    [ §]  03-30-2008 • 17:18:07


 * The fulcrum of the lever is where the can-opener rests on the edge of the tin. Measure the distance from the fulcrum to the pointy end of the can-opener where the force is applied to the tin.  Measure the distance from the fulcrum to the end of the handle where you apply the force.  You now have enough data to calculate mechanical advantage.  Work out for yourself how to calculate the MA - I am not going to do ALL your homework for you.  The force applied depends on how much force your arm provides and the mechanical advantage - again, work out for yourself how that would be calculated.  Sp in ni  ng  Spark  18:45, 30 March 2008 (UTC)


 * a can opener is a type of lever. But both the force you apply and the force the can applies to the blade, are on the same side of the "fulcrum" (the hinge). On my can opener, the blade is about one inch from the hinge, and my hand grip applies force at about five inches from the hinge. You must measure your own can opener, and then apply the correct math. If you cannot figure it out, then please come back and ask another question: we will not do your homework, but we will certainly help you with your homework. Here is a bonus question: How is force actually applied to the top of the can, and what is the correct unit of measurement? You know that you cannot push your thumb through the can top, so why does a can opener work? -Arch dude (talk) 23:11, 30 March 2008 (UTC)

Friction
if you wanted to reduce the friction between two objects what would you do —Preceding unsigned comment added by Caseywirth (talk • contribs) 17:58, 30 March 2008 (UTC)


 * Add a lubricant like grease, cooking fats, or graphite etc. Yamakiri TC    [ §]  03-30-2008 • 18:18:11


 * Invent something round which rotates in between the two objects. Let´s call it a wheel? --Cookatoo.ergo.ZooM (talk) 22:43, 30 March 2008 (UTC)


 * Or possibly a ball bearing. Algebraist 23:07, 30 March 2008 (UTC)


 * Or maybe reduce the force holding them together, such as a partial lift on the upper object, loostening screws, expanding a screw top through heat. For example when openeing a jam jar lid, it is easier if you don't force it down as you turn. Graeme Bartlett (talk) 02:37, 31 March 2008 (UTC)
 * That point about jam jars is not necessarily true. If the lid is quite tight (as opposed to, say, glued on by dried jam), each of its screw threads is pressed against the corresponding thread on the jar &mdash; from below, as that is how the lid is drawn against the jar.  Then applying a compressive force may loosen the contact and reduce the friction.  However, in practice one may instead simply deform the lid without the desired effect.  --Tardis (talk) 01:19, 1 April 2008 (UTC)


 * And don't forget sonic lubrication. StuRat (talk) 02:58, 31 March 2008 (UTC)

Would a radio work under 1 foot of water?
Would a radio work under 1 foot of water? Obviously we're assuming its in a waterproof container or something, but would the radio waves penetrate the water? —Preceding unsigned comment added by 79.75.132.81 (talk) 19:06, 30 March 2008 (UTC)


 * Short answer is no. It might be possible to design something that works in only one foot of water but I doubt it.  If it were possible the military would have it already.  Submarines need to surface to use their radio.  Submerged, they use acoustic systems usually.  They can use VLF up to 20 metres in depth but you need something large like a submarine to contain the equipment.  ELF can be used even deeper, but only for reception.  The transmitter would be impractically large for any existing vessel.  There are other problems as well, see Communications with submarines.
 * Devices fitted to animals for scientific tracking only work while the animal is on the surface, or else they are designed to float on the end of a tether - see this picture of a manatee being tracked.  Sp in ni ng  Spark  19:32, 30 March 2008 (UTC)


 * I would expect a radio to be able to receive signals under one foot of water. The dropoff of signal strength with depth would depend on the frequency. Why not put an expendable cheap am/fm radio in a well sealed widemouth gallon jug and push it under the surface of the water for a test, at the beach or in a swimming pool? If your head is under water you can listen for the strength of the sound from the radio. Having headphone leads or a speaker or microphone cord stick up out of the water would invalidate the test. Edison (talk) 20:19, 30 March 2008 (UTC)


 * The attenuation is very severe because of the conductivity of the water. Where ground-penetrating radar is used in geophysics, they can only manage a couple of inches if the soil is wet.  And that is with the antennae right above the surface being surveyed.  If you want to put the remote station some distance away you haven't got a hope of getting it to work at all.  Yes, it does depend on frequency - penetration improves with decreasing frequency (or increasing wavelength).  That is why submarines use VLF.  The wavelength of this band is 10 to 100 km.  You need a big antenna - not suitable for the swimming pool.  With ELF the situation is astronomically worse, a geophysical feature (such as the Rocky Mountains) needs to be used for the antenna.  Even the connection "leads" are around 30 km long.  Sp in ni  ng  Spark  22:14, 30 March 2008 (UTC)


 * Radios work much better in fresh water than in salt water because the salt water is a lot more conductive. This is why remote control submarines always come with warnings not to use them in salt water. Anecdotally, I've read that R/C model submarines that can go four or five (or more) feet down in lakes, lose their signal under only a foot of ocean water.  I have no idea how accurate those numbers are, I've never tried it myself. APL (talk) 13:27, 31 March 2008 (UTC)


 * The article on Evanescent_waves gives the basics. Although its examples are oriented towards optical waves (light), the basic physics is the same for radio waves.  The article points out that the rate of exponential decay (as a function of distance from the surface) depends on wavelength; that is part of the explanation of why ELF can be used by submarines. JohnAspinall (talk) 13:31, 31 March 2008 (UTC)

Drinking water
Some time in the late '70's or early '80's my grandfather showed me a magazine article (I think it was in national geographic but not sure) that refrenced a study concerning drinking water quality. In it, the author stated that "Polar, Wisconsin has the worlds best drinking water." I am doing some research and am having trouble locating this article. I have had other peop[le tell me they remember seeing this article, but no-one can tell me what magazine or exactly when it was published. I would greatly appreciate any help in locating this information. I have tried researching National Geographic archives, Guiness book of records, our local library, and internet searches all with no results, It may be that it is old enough that it isn't cataloged anymore, but someone, somewhere must know where I can find this. Please help! steveg-1960 —Preceding unsigned comment added by Steveg-1960 (talk • contribs) 19:34, 30 March 2008 (UTC)


 * In that same time period Consumer Reports (headquartered in New York City) did a taste test on samples of tap water from different cities around the US. Not surprisingly, they concluded that their local tap water tasted best. Edison (talk) 20:51, 2 April 2008 (UTC)

Slowpitched softball
If I slowpitch a softball with good backspin, does that encourage a ground ball or a fly ball, and why? What are the physics (for dummies) involved? Thanks if you can explain.


 * It's because of Coriolis effect. Basically if you spin a ball a layer of air on the surface of the ball will also spin with it. Say the ball spins clockwise and is traveling to the left. The top of the ball will be going at the same direction as the airflow, while the bottom goes in the opposite direction. When it goes in the same direction, it has very little drag, because the speed difference between the ball's surface and the surrounding air is small, whereas if it goes in the opposite direction it has lots of drag, because the speed difference is much higher. When one side has very little drag while another has lots of drag, it will start to change its trajectory (like when you walk into a pole, if you hit it with your left shoulder you will turn left after you hit the pole, because there's lots of drag on your left side). --antilivedT 05:08, 31 March 2008 (UTC)


 * It's the Magnus effect, not the Coriolis effect, and the direction of the resulting force for a ball with backspin is upwards. Gandalf61 (talk) 12:18, 31 March 2008 (UTC)


 * I would expect that the main effect of strong backspin, at the speed of a softball, would not be anything to do with coreolis but simply the friction when the spinning ball contacts the bat. Which would tend to make the ball fly downwards off the bat. DJ Clayworth (talk) 14:34, 31 March 2008 (UTC)


 * Where are all the physicists? Anyone who has ever played ping-pong knows that a backspin volley makes your opponent hit it off the end of the table, and a topspin volley makes him hit it into the net. This is the way the ball will come off his paddle due to your spin. The mechanics of this are counter-intuitive, them being the same as the motion of the ball in the air. A topspin pitch makes for grounders, and a backspin pitch makes for fly balls, if you only count the movement of the ball off a bat swung along the ball's predicted pitched path in the air and striking the ball in the center when perpendicular to its path. --Milkbreath (talk) 15:00, 31 March 2008 (UTC)


 * Agreed. What happens is that when the spinning ball hits the bat, the friction between ball and bat converts some of the spin into upwards velocity.  You can test the phenomenon yourself by spinning a ball on a table and then barely touching its side with your flat palm.  &mdash; Laura Scudder &#9742; 22:22, 31 March 2008 (UTC)

Global warming
In the last few years, global warming has become an often-discussed issue not only in scientific circles, but also in everyday life. We are warned against it, we have been told about the terrible consequences it could potentially have, and there are groups dedicated to fight climate change. So, I wonder, why is global warming actually so bad?

We are told that mankind is altering Earth's natural state, but our knowledge of the geological history tells us that in fact ice caps are a rare event in our planet's history, happening only in a handful of ice ages. Not only was the Earth devoid of ice caps during most of its history, but also the temperatures in the geologic past were almost always higher. During periods such as the Carboniferous, the Mesozoic and the Eocene, global temperatures were much higher than they currently are, and all of these times were periods in which life thrived and many species radiated – amphibians, dinosaurs and mammals, most notably. On the other hand, since the Azolla event and the break-up of Antarctica and Australia started cooling the planet, the climate has steadily deteriorated and with it, biodiversity has steadily become smaller, especially since the Miocene.

People also seem to equate a hotter climate with a drier climate. Yet the tropical rainforests show that is not (necessarily) true. A huge part of the Earth's species live in the Amazon rainforest, and African and south Asian rainforests are also blooming with life despite their tropical latitudes. The Eocene, with its PETM, was a period in which the Earth was covered in rainforests and other vegetation, showing that there is no necessary correlation between a warmer climate and a drier climate. Rather, the rise of grasses since the Miocene seems to indicate that cooler periods are drier periods.

Let's move to another oft-cited problem of climate change: freak climate episodes become less rare. Hurricanes become more common and heat waves become a greater problem. The sea level rises. Well, IPCC estimates that the current trend of ice melting in the Greenland ice sheet can cause a rise in sea levels of one metre during the next millenium. 1.000 years is more than enough for human civilisation to adapt, and even taking into account other ice sheets around the world, the sea level rise is still far from not being manageable. Adaptations can be made to protect coastal cities, and even paying for developing countries to get those adaptations ready would be costlier than the economic cost of fighting global warming. The fact that heat waves may become more common is compensated for by the fact that cold waves will become rarer: scores of people died in Uzbekistan last winter when temperatures dropped below -40º C, and many people – and animals – have a harsh time in winter.

On the other hand, the benefits would be many: the Northwestern passage open to ships all year long and ice-free; availability of mineral resources currently buried under tons of snow in the poles; an increase in biodiversity... Believing that, without human intervention, the Earth's climate will remain stable is a naive phantasy. We're currently in an interglacial period, so things should be colder in the future – how will we feel when polar caps cover Stockholm, Moscow, Montréal or London? How will we feel when hundreds of tropical species become extinct because cold destroyed their ecosystems? Fighting global warming is like leaping out of the frying pan into the fire: we have a choic between an icehouse world or a greenhouse world, and we are much more suited to the latter.

'''If the so-called ecological dangers of global warming aren't really dangers (biodiversity thrives in the heat!), and the economic cost of fighting it is higher than what it would cost to adapt, why is there so much insistence on global warming being bad? Aren't we against it because we're told it's bad, without even knowing what it means? Aren't we just afraid of changes, even though we're now in a "freak" period of Earth's history and warming would just bring everything back to normal?

So, wouldn't humanity – and life on Earth as a whole – be better off if all the money which is invested in fighting global warming were invested in more urgent and real problems such as desertisation, pollution of water, deforestation, protection of endangered species, etc.?'''

88.1.139.15 (talk) 22:10, 30 March 2008 (UTC)
 * This very much looks like WP:SOAP, not a question. Anyways, there is quite a number of unjustified assumptions in your "question", the major one being that not the absolute temperature is a problem, but the change in temperature. The climate has been quite stable for the last few 1000 years, and human populations and ecosystems are adapted to this stable state. Oak forests will not move North at kilometers per decade (even if there are no humans in the way). For a farmer in Mali whose fields dry up it's little use to know that the season for growing rye has increased by two days in Siberia. Indeed, in the long term the climate will change anyways. But humans live in the short term. The best assessment of the effects of global warming we have is the IPCC Working Group II report.. From the Summary for Policy Makers: "Impacts of climate change will vary regionally but, aggregated and discounted to the present, they are very likely to impose net annual costs which will increase over time as global temperatures increase." --Stephan Schulz (talk) 22:32, 30 March 2008 (UTC)
 * Also, if I'm not mistaken, isn't the main problem with CO_2 not the warming that it has already caused, but the potential future warming. Complex systems take a while to reach a steady state; I have read that if humans stopped emitting all greenhouse gases today, the global temperature would continue to rise (by a few degrees a century) for a few hundred years, to well beyond what has occurred in the past few million years.  Life thrived in periods of warmth because these earth warmed over many many millenia, allowing natural selection to take its course.  Evolution cannot occur fast enough to adapt to the current warming properly. - Running  On  Brains  22:47, 30 March 2008 (UTC)


 * (ec) Please re-read the instructions at the top of this page. The reference desk is here to respond to questions of fact. It is not here to "start debates or to post diatribes." In my opinion, the only further responses to this post will be suggestions of where (other than here) this issue should be discussed. -Arch dude (talk) 22:38, 30 March 2008 (UTC)


 * Agreed, unless the poster has an actual question for the Reference Desk in amongst that rant, in which case could he/she please delete the rant from around the question so we can read it.  Sp in ni ng  Spark  22:49, 30 March 2008 (UTC)


 * (edit conflict)Hi. Well, it's a very complicated issue. True, the climate is rarely stable for very long periods. However, most of us, if we found out that we are living on this borrowed time, would like to prolong this time as much as possible. Now, with sea level rise, the only way I can think of to protect cities all around the world, is to build a massive seawall, along every single coastline around the world, leaving no gaps, and stretching 50 metres high and 100 metres deep. Why? Well, let's say that you build a wall around a coastal megacity. However, if this wall is breached by a major storm or earthquake, or if sea levels rise, say, 5 metres and the highest part of the base of the seawall is 5 metres, the water would flood from the other side.

Global warming would also produce environmental disasters that could destroy cities. How would you feel, if your city became too dry, or under water, and forced to evacuate? We would have to make domed cities, live underground, or in space. Why is hot associated with dry? Well, it's not really. Global warming could make coastal reigons flood, and coastal deserts flood too. However, inland, even in rainforests, places could turn to desert. According to a book I'm reading, "With Speed and Violence: Why scientists fear tipping points in climate change", tropical rainforests, like massive ice sheets, are usually stable but can suddenly collapse. Fires can destroy rainforests, allow billions of tons of methane to be released (like Borneo in that huge El Nino a decade ago), and our deforestation of rainforests is not helping.

Also, global warming will not prevent another ice age. In fact, it can trigger one. Remember the Younger Dryas era? The ice age was in full melt, when suddenly, freshwater was released into the ocean, and boom, ice age for another 1,300 years. Also, although not as quickly as depicted in The Day After Tomorrow, melting water can trigger a disruption in the ocean currents. I suggest you read that book I'm reading. It's up-to-date, too. Some say this could cause a mass extinction worse than the K-T one. Would we want that? I think not. Also, the Greenland ice sheet, as well as the West Antarctic Ice sheet, and perhaps even the East Antarctic ice sheet, are unstable, and can be lubricated from the bottom. Pine Island Bay, for example.

Also, nature prefers slow changes. Also, the statement about "biodiversity thrives in the heat" is not nessicarily true. In the ocean, most plakton, as well as coral, thrive in current temperatures. Turn it up a few degrees, and they die. During El Nino, it becomes overheated off the coast of Peru, plankton die, and so do fish. When you change the sea pressure, temperature, salinity, etc, by a miniscule amount, many species of jellyfish suddenly bloom by the billions, killing off other lifeforms in the ocean and inhabit dead zones (especially the Nomura's jellyfish). Also, some periods, like the late Permian, were hot as well as dry.

Also, have you read about global dimming? This isn't really fighting against climate change, but masking its effects. For 3 days after 9/11, air traffic was grounded. Suddenly, the US experienced unusually sunny and warm conditions. Also, as the Himalayan glaciers melt, and this could happen by midcentury, there will no longer be a constant supply of water, threatening water supplies for 500 million people. The monsoon? It has become erratic and unpredictable over the years. Already, lakes in Nepal and Bhutan are filling with water. Hence: without water, we'd all drown. Also, more flooded areas means hurricanes can travel farther inland. At this rate, even with the melting arctic, oil will likely run out in a few decades and peak immediately. If sea levels rise, Tuvalu will likely be history by midcentury. Also, many species, as well as people, thrive in the arctic.

Global warming is not nessecarily good news for food production. Many species of plants, such as rice, fail to produce good results if you turn up the temperature 1 or 2 degrees. Forests could even go form a carbon sink to a carbon source, with the sun being blocked more often, more trees being pushed into unsuitable territory, and more fires. Also, the forest pine bark beetle is eating many trees in Canada and the United States. If this continues, over half of the pine trees could be damaged or destroyed by midcentury. Also, the dangerous and urgent global warming is already here. Already, towns are drowning below sea level. Have you read a list of possible doomsday scenarios? True, we all choose to deny the truth and live on with our lives, going business-as usual and hoping the worst will never happen in our lifetimes. Yet, it already has, for millions worldwide. So why do we choose to do something? Well, because we can at least do something to delay the parts of climate change caused by our own actions, and hopefully our children will not suffer. That's the reason for many people to help fight climate change, think of the children.

In fact, at this rate the truly poor countries will never be developed. Yet, fighting climate change would only push us back a mere 2 years by 2100, if we start now, that is. Why don't we help more urgent issues? This is an urgent issue, and its long-term implications will be even worse. Also, global warming has been listed as the #2 urgent threat to humanity, second only to a nuclear war, but this is far more likely. Also, global warming might trigger wars as economic instability is pushed to the brink. If we did nothing, civilization would collapse, simple as that. However, although it would probably collapse anyway, don't we at least want a future, for civilization to exist as long as possible, and to help ourselves continue to exist for the time being? Nobody can predict what will happen 1000 or a million years from now. However, this issue is happening right now, and yes we can make a differnece, and it'll be a difference for the better because civilization, the economy, and the environment all prefer stability, even if we can just prolong that stability a little bit.

I already know that climate change will be a reality we will have to face, but if we do something now, then we won't have to face as many horrors later. Also, have you noticed a lot of these urgent issues are somewhat related to global warming? Even disease is spreading, killing off many humans as well as animals, partly owing to global warming. So, it's a very complicated issue, but yes, action on it does help somewhat. Hope this helps. Thanks. ~ A H  1 (TCU) 23:10, 30 March 2008 (UTC)


 * Over geological time scales Human induced global warming could be seen as insignificant as life will adapt to it. Over the period of a human generation the effects of gloabl warming could be seen as nothing short of apocaliptic.

--Shniken1 (talk) 00:41, 31 March 2008 (UTC)

If as you claim, pumping out carbon dioxide to produce global warming may be necessary to avert an 'icehouse world' there is a simple solution, start doing that when we need it. As it stands, there is no evidence we need it at the current time, all the evidence suggests it's harmful and will result in an increase in temperatures, not a stabilisation. Sure once the earth starts to cool, we can consider it. It's not as if it's hard to do. The problem is that the reverse, removing the carbon dioxide that we've already put there, is a lot harder to do therefore it's exceptionally dumb to do it when we don't need it for the sole purpose of preventing a long time in the future 'icehouse world' or ice age Nil Einne (talk) 17:32, 31 March 2008 (UTC)

Mirror, Mirror
If I have room with four walls, floor and ceiling, all made out mirrors--and one wall is a two-way mirror, the material that's a mirror on one side, but see through glass on the other--what would I see if I looked into the room?

I guess my question is--what does a mirror reflect if there is nothing in the room to reflect?NetLace (talk) 22:17, 30 March 2008 (UTC)
 * Assuming that the mirrors aside from the two-way allow no transmission of light, I would think that such an apparatus would act as a blackbody. Unless the room were a few hundred degrees Celsius, you would see nothing. - Running  On  Brains  22:28, 30 March 2008 (UTC)
 * Well, there's no person or thing in it, but that doesn't mean there's nothing at all. Assuming there's a light source, the mirrors would reflect each other as they reflect the corners and joins in the mirror room until you've got that labyrinth or hall of mirrors thing happening. Without a light source there'd be no reflection to track anyway. You could try it on a small scale model to test it. Julia Rossi (talk) 22:33, 30 March 2008 (UTC)


 * Hi. Well, if I understood your question correctly, and there is a light source, it will appear like an endless tunnel. If you have a webcam, for example, and turn on a program that displays what the webcam sees, and the image is inside a rectangular box, then try pointin gthe webcam at that box. What happens is, the box appears like an endless tunnel, and if you shake the webcam, the tunnel shakes. Also, if you could stand between two mirrors, held facing each other, and looked at one of them face-on, yet you are small enough not to be blocking anything yet large enough to see the whole mirror, you'd see an endless tunnel, and maybe endless images of yourself inside it.

The tunnel doesn't really appear endless, however, because as you look farther inwards, the deeper frames are not bright enough to be shown. Hence, if you take two mirrors, and put them at an angle to each other, and shrink the angle, you get more images. Thus, if you turn them towards each other, there should (theoreticly) be an infinity of images. However, many factors prevent us from actually seeing into infinity. Hope this helps. Thanks. ~ A H  1 (TCU) 23:23, 30 March 2008 (UTC)


 * That's right, you'll see an endless tunnel of mirrors, one copy of the room after the next, and getting darker as they are farther away. Just one point needs to be added and that's that the conditions described in the original posting require a light source to be in the room.  A two-way mirror, also called a one-way mirror, is simply a partially silvered mirror that you look through from a darker room into a lighter one.  You can see through it into the light room because there's enough light in there for you to be able to see by even when only a fraction of it gets through the mirror.  In the setup described, you will see a copy of the lamp in each copy of the room.  But because the two-way mirror is partially silvered, the more times the light reflects, the less there is of it, and so the "farther" copies of the room look dark.  --Anonymous, 09:50 UTC, March 31, 2008.


 * The semi-silvered mirror is symmetric, except that one side is subject to higher ambient light, so it's harder to see through from that side. Tangential question- do anisotropic "two-way mirrors" exist?  Specifically, do materials exist with higher reflectivity coefficient in one direction than the other?  (Surely there are materials with variable reflectivity based on the incident angle, but are any known with directionality?  Nimur (talk) 19:24, 31 March 2008 (UTC)


 * I doubt it — at a glance such a mirror would seem to violate the second law of thermodynamics, as it would essentially constitute a Maxwell's demon operating on photons. —Ilmari Karonen (talk) 22:10, 31 March 2008 (UTC)


 * Optical isolator. Someguy1221 (talk) 22:26, 31 March 2008 (UTC)


 * Yes, the Faraday isolator is the interesting answer, for which transmission is asymmetric. But the question as worded was about asymmetric reflectivity, and that can occur in much more mundane circumstances. For instance, consider a symmetric, lossless 50% mirror with an anti-reflection-coated 90% absorber glued to one side. From the mirror side, this device would have a 50% reflectivity, but seen from the absorber side the reflected light would have to travel through the absorber twice, being attenuated by a factor of 10 each way, resulting in a reflectivity of 0.1*0.5*0.1=0.005=0.5%. Transmission on the other hand would be symmetric, at 5% in either direction. --mglg(talk) 02:38, 1 April 2008 (UTC)
 * Interesting. But, this is a composition of different materials.  I guess I was curious if any single material (e.g. unusual crystal structure, or something) could generate that effect.  Thanks for the insights!  Nimur (talk) 14:47, 1 April 2008 (UTC)