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July 15

"Hearing the wind"

When you crack a whip, you know how you "hear the wind"? If you threw a fastball and "heard the wind", how fast would an estimate be of that pitch? Albacore (talk) 02:45, 15 July 2013 (UTC)

...If you're gonna find the answer anywhere, it'll be at the Physics of Baseball webpage. In fact, you can even apply for a (competitive) fully-funded summer internship to elaborate on these studies! (Here's the summer 2004 final report).

The sound we hear when air rushes past our ears actually has very little to do with the net velocity of the air (or of any object that's moving through the air). Sound is the vibration of air - its volume is determined by the amplitude of the oscillation; and the timbre of the sound is determined by the waveform shape of the oscillation. A "whoosh" is pretty much white noise. Air speed doesn't really enter into things, at least not as a direct first-order term. So, bulk velocity of the air is a secondary concern; and thus velocity of the acoustic transducer (the ball, or the whip) is even further removed from the intensity, volume, and sound we actually hear - it influences the sound in an indirect and subtle way. In practice, you might be able to empirically measure and then deduce a relation between the velocity of a ball and the amplitude of the "whoosh," but that relationship will be a little bit tenuous, because you're essentially trying to be quantitative about a very noisy signal.

In a little bit plainer English: you can make a loud "whoosh" using a slow moving object or a fast moving object. You can also make a quiet "whoosh" using a slow moving object or a fast moving object. The speed of the object is not the main factor in the "whoosh." Nimur (talk) 05:55, 15 July 2013 (UTC)

There are two situations I can think of (which doesn't mean there are only two...) - a reed (instrument) which vibrates due to its own characteristics, creating a sound that depends (among many things) on the speed of the wind, and whipcracking where the object moves at the speed of sound and all that sound emitted piles up into a little sonic boom. Wnt (talk) 15:33, 15 July 2013 (UTC)

I agree that some non-aerodynamic objects make a lot of noise in little wind by creating turbulence and perhaps snapping in the wind like a flag, while other objects create very little noise even in high winds, since they only create laminar flow. However, this Q was about a baseball, so, since we've eliminated the variable of the object type, the relative wind velocity should correspond quite well with the sound level. The only other remaining significant variables should be it's spin, and the air pressure, temperature, and humidity. StuRat (talk) 18:36, 15 July 2013 (UTC)

Why do you assert these speculations as if they are facts? We don't get to arbitrarily decide what should happen in aerodynamics. Just because you think velocity should affect audible noise doesn't mean it does. Turbulent airflow is probably one of the least intuitive, most difficult-to-speculate about, impossible-to-describe-using-simple-first-principles-of-physics subjects known to humans. As an example: one of the papers on the website I linked shows experimental data indicating that the asymmetric flow separation due to the rotation of the ball contributes to turbulent airflow. And sometimes in totally the opposite direction from that which is predicted by ordinary flow separation theory. A small scratch on the ball's surface may have more impact than the net bulk translational or rotational velocity of the ball. In another experiment, the presence of a very tiny "raised wire" on an experimental sphere changed laminar flow into turbulent flow with R=30,000. StuRat, when you assert that velocity is the chief factor - yet you have neither experimental data or theoretical explanation why you believe that should be true, you are conducting pseudoscience. This is worse than being wrong - if your fact was only wrong, we could correct it and move on with our lives. But instead, you are asserting a claim without any evidence. Your methodology is profoundly unscientific. Nimur (talk) 22:34, 15 July 2013 (UTC)

Descriptions of turbulence like this are always so fascinating. If small scratches and extensions have such an impact, why can't we use it? I mean, why can't we fly a few kites per acre on one side of a hurricane at sea to turn it, or have a computer-controlled mesh of thin wires up- or down-wind of a windmill to increase its output by a significant factor? Wnt (talk) 01:43, 16 July 2013 (UTC)

So what's happening with a Bullroarer that produces the sound? HiLo48 (talk) 09:13, 16 July 2013 (UTC)

Bullroarers produce a predominantly humming sound due to the rapid rotation about the long axis as you whirl it round on the end of the string/cord, somewhat like a fan or propellor makes a humming sound. This rapid rotation moves air in pulsations - first towards any point and then away. Bull roarers also produce a bit of shot noise (white noise or "hiss") as does any surface moviing through air, due to the random impact of air molecules on the moving surface. 1.122.182.232 (talk) 13:18, 16 July 2013 (UTC)

(ec) Lots of things are happening, and I can't pretend to list all of them: but here are some interactions that I would pay attention to. Air is rushing over the surface of the object; the object's motion is constrained by a semi-taut vibrating string whose tension varies with the speed of rotation; vibrations of the object and the air couple to the string. When tension changes, the resonant frequency and the acoustic damping change. If you modify the toy, replacing the shaped peg with something else of equal weight, the tension in the string should be identical; if you whirl it at the same speed, you may observe a change in the tone, timbre, and intensity of the sound. If you change the type of string to some other material - say, from an ordinary string to a guitar string, the sound will be totally different! If you spin an object that resonates at a particular frequency, including a tube-shaped peg, you can produce an almost clean, tonal sound - like a whistle or a flute. If you throw the whirling contraption - even if the peg reaches the same airspeed - does it produce the same "roaring" or whistling sound? Does that sound only happen when the string is taut and the object is rotating? How about if you start by whirling and then release the string, allowing the object to fly at the same speed, under its own inertia? How quickly does it stop "roaring"? How would it sound if you got a friend to drive you down the freeway, and you (safely) held the peg out the window at 65 mph?

This apparatus would be a good candidate for some fun experimental acoustics (to be conducted outdoors). The aspiring scientist could even set up a microphone to record the results. How does the sound frequency and volume change when you whirl at different speeds, or throw the object? Does the rotation rate modulate the tone? (It should, that's the basis of vibrato in the old-fashioned Leslie speaker). Just watch out if you're recording with a "smart"-device to analyze the sound - many smart devices now use digital post-processing to "denoise" and normalize the recording to a constant volume. Experimental physicists need to know everything about their measurement-apparatus, to prevent themselves from drawing erroneous conclusions about their data. Nimur (talk) 13:29, 16 July 2013 (UTC)

Noisy ladybirds (ladybugs)

I've just read a technical document which described a component making a noise like a ladybird... I just want to make sure that this is as rediculous as I think it is, since I've never heard them make any noise at all. MChesterMC (talk) 14:32, 15 July 2013 (UTC)

Pretty sure I've heard them [in the UK] make a fluttering sort of buzzing noise when they fly, especially to get off the ground. --Dweller (talk) 14:34, 15 July 2013 (UTC)

Yep, at liftoff, or if they happen to fly right by your ear, you'll hear a whirring buzzing sound. I'd imagine a loose fan or something could make a similar, if much louder, noise. SemanticMantis (talk) 14:52, 15 July 2013 (UTC)

This was a suggestion for an indicator noise, and the other examples given were the chirp of a grasshopper or a cricket, so I'm pretty sure the writer was just not thinking about what they were writing. MChesterMC (talk) 15:59, 15 July 2013 (UTC)

River swelling

What's the physics behind this video: http://www.youtube.com/watch?v=8sEdgHH9F10&feature=youtu.be ? What causes the river to empty and swell like that? 65.92.5.24 (talk) 15:41, 15 July 2013 (UTC)

It's hard to see quite what's going on without a better understanding of the geography, but when a ship moves in a narrow channel it can produce a soliton wave (a solitary wave of compression and then rarefaction which can retain its identity for a remarkable distance). Although solitons occur in all kinds of circumstances, they were first scientifically described when generated by canal boats. -- Finlay McWalterჷTalk 15:48, 15 July 2013 (UTC)

Perhaps Bernoulli effect is helpful? (not sure about that) Wnt (talk) 16:02, 15 July 2013 (UTC)

It's a small tsunami. That article explains the physics. Looie496 (talk) 16:14, 15 July 2013 (UTC)

Similar waves are sometimes created by tidal conditions called a tidal bore; the Severn Bore in England is a great favourite with surfers and kayakers. Alansplodge (talk) 17:14, 15 July 2013 (UTC)

A ship that size displaces an enormous amount of water. I calculate that a "Panamax" sized tanker displaces around four million cubic feet of water - and that one looked much bigger than that. As the tanker moves a distance equal to it's own length, four million cubic feet of water has to move out of it's way and somehow travel around the sides and beneath the vessel to fill in the "hole" it leaves behind the stern. Water is essentially incompressible - so it can't compress and decompress around the ship. So at typical tanker speeds of around 20mph (30 feet per second) - a 950 foot long Panamax ship covers it's own length in about 30 seconds, so the water has to flow around it at about 130,000 cubic feet per second! (Imagine filling and then draining, two olympic-sized swimming pools every second!)

When the vessel is close to land and in relatively shallow water, the water flow will be forced through narrow gaps beneath and on the shoreward side - so the speed of flow will greatly increase. It's not surprising then that water will be forced into (and then sucked out of) side-channels and inlets.

I'm not sure whether the Bernoulli effect is likely to kick in to a significant degree...but imagine if the small river in the video is connected to the larger channel with the ship in it somewhere off to the right of the camera. As the ship moved towards the point where it joins the ocean, the pressure ahead of the ship would build up, causing rapid water flow into the river - and as it passes, would cause a dramatic drop in pressure, causing rapid flow out of the river. At the point in time when the direction of flow reverses, you'd expect lots of turbulance and such - which would explain all of those big waves...but I'm not sure that's what's going on because the water level doesn't go up until after the flow direction reverses.

But if the small river connected to the ocean FAR to the left of the camera - then perhaps the initial flow towards the left is just the natural flow of the river and the temporary reversal is due to the pressure wave from the arrival of the ship - but delayed by a minute or two by the time it took for that wave to travel from the mouth of the river. We might expect an abrupt lowering of the water level sometime later as the pressure drops behind the stern of the ship - but maybe we don't see it because the video ends before that would have happened.

Similar arguments are possible if the camera person is standing on an island with the "river" connected to the ocean at both ends and the water was merely reacting to a build up of pressure before and after the ship.

I think that what we see in the video is consistent with any of the three possible connections between river and ocean...but without knowing exactly how the small river connects - it's hard to know for sure.

SteveBaker (talk) 13:58, 16 July 2013 (UTC)

• It's a wake, although the effect in the canal is similar to a tsunami or a tidal bore. Causing a wake like that is illegal in most costal water in the US. It can be avoided by slowing down, although the pilot will not want to. The gentleman should contact his local coast guard or environmental protection agencies. μηδείς (talk) 21:51, 16 July 2013 (UTC)

This is a small canal (no current) off the St. Clair River in the Great Lakes system. The boat is a 1000-footer. Rmhermen (talk) 02:11, 17 July 2013 (UTC)

Then it's a matter of international treaty. In New Jersey the ship's action would be illegal, and the owners subject to fine. μηδείς (talk) 02:21, 17 July 2013 (UTC)

July 16

Carbon emission

I've had no luck at Talk:Greenhouse gas, so I'm reposting the question here: carbon emission redirects to greenhouse gas, but the article doesn't clearly explain what "carbon emissions" mean. It doesn't seem to refer to emission of elemental carbon, but does it encompass emissions of all compounds of carbon, only gaseous compounds of carbon or some other still? — Kpalion^(talk) 14:08, 16 July 2013 (UTC)

If editors agree on a definition, then the term and the definition can be added to "Glossary of environmental science".

—Wavelength (talk) 14:18, 16 July 2013 (UTC)

From my Google search of glossary environmental terms, I have checked most of the first 50 results and I have found the following.

• http://www.epa.ie/irelandsenvironment/glossary/#C

"In the context of climate change, carbon dioxide released when substances, especially oil, gas, and coal, are burned by vehicles and planes, by factories and by homes."

• http://www.bu.edu/sustainability/reference/glossary-of-terms/

"Polluting carbon substances released into atmosphere: carbon dioxide and carbon monoxide produced by motor vehicles and industrial processes and forming pollutants in the atmosphere"

—Wavelength (talk) 14:59, 16 July 2013 (UTC)

You might wish to consult Wikipedia:List of online reference desks/Science#Ecology (577).

—Wavelength (talk) 15:08, 16 July 2013 (UTC)

• In the context of greenhouse gases, it mainly means CO2 but could also include methane, which is a very potent greenhouse gas but doesn't persist in the atmosphere for very long. Looie496 (talk) 15:11, 16 July 2013 (UTC)

Yes, "carbon emissions" is a little vague. You'll see it in press releases and such, but not usually in serious science writing (or if it is used, the scope is defined in the same article). I don't have time to check right now, but the authoritative/reliable bodies who might have a standard definition would be the IPCC and/or NOAA, who releases several freely-available white papers and technical documents that one could look into. When I'm at conferences that discuss this sort of thing, they usually present e.g. methane and CO2 (and others) in terms of Carbon_dioxide_equivalents. Basically, "tons of carbon" is not always meaningful, because different compounds have very different global warming potentials, even for the same amount of carbon per molecule. To my knowledge, solid carbon, (i.e. soot) is not ever considered an "emission" for the purposes of climate change studies. Soot particles will actually cool the atmosphere when in aerosol form, and when they settle, they become part of soil carbon (and hence are not emitted to the atmosphere). SemanticMantis (talk) 15:33, 16 July 2013 (UTC)

Totally off-topic, but I didn't find where to ask!

Some perpetual-motion believer(s) keep reverting Magnetic motor to represent it as aglorious future solution for humanity. What can be done, and how? Zarnivop (talk) 15:49, 16 July 2013 (UTC)

I have posted the article to the Fringe theories noticeboard, hopefully some editors will take a look at it to make it more neutral. You could also be bold and edit the article yourself! Mildly Mad^T_C 17:36, 16 July 2013 (UTC)

\i did that, but mt edits were reverted. I do not enjoy edit-wars, and it seems in this case the article should be fixed and locked. Thanks for your help! 109.67.255.233 (talk) 20:36, 16 July 2013 (UTC)

When on H. sapiens' evolutionary timeline did the equivalent of the hallux ("thumb" on lower limbs) stop being opposable?

20.137.2.50 (talk) 16:43, 16 July 2013 (UTC)

I think it has not been fully opposable at least since Australopithecus afarensis appeared. Ruslik_Zero 19:15, 16 July 2013 (UTC)

This article [1] in Science says, regarding Ardipithecus ramidus, that "The foot has a widely abducent hallux, which was not propulsive during terrestrial bipedality. However, it lacks the highly derived tarsometatarsal laxity and inversion in extant African apes." I'll let you decide if that counts as "opposable". SemanticMantis (talk) 19:21, 16 July 2013 (UTC)

Yes, the transition seems gradual. See the images at the bottom of Australopithecus sediba. μηδείς (talk) 19:33, 16 July 2013 (UTC)

First embryonic stem cell transplantation in lab rats

I've been looking at the history of embryonic stem cells under the embryonic stem cell page; however it does not specify many of the details of the first transplant in mice which, I assume would have been recorded. Specifically I was wondering whether they transplanted the embryo into one of the two mice who actually parented it; or whether the receiving mouse was completely unrelated to the embryo. Also I am curious how long the scientists waited between the menstrual extraction and the transplantation; and whether prolonged culturing or cryonic freezing was involved in this process. I would say thank you for your assistance in clarifying this matter; however no one is going to answer this question. CensoredScribe (talk) 14:26, 17 July 2013 (UTC)

Energy into matter...

Inspired by the 'Why can't I run an electric heater in reverse to cool a room?' question above...

What's standing in the way of us creating a device that could (just for example) gather the energy from sunlight and convert it into gold? Per Einstein, this should theoretically be possible, correct? Matter can be converted into energy and energy can be converted into matter? --Kurt Shaped Box (talk) 21:14, 16 July 2013 (UTC)

"What's standing in the way"? Entropy !--Aspro (talk) 21:28, 16 July 2013 (UTC)

Well you can collect sunlight and turn it into useful energy in the form of electricity see solar electricity. The next stage of making matter or antimatter can be done in particle accelerators. But note these are very expensive and inefficient. Actually producing gold will need you to assemble protons and neutrons into a nucleus. There is a high level of electric charge in the nucleus that repels other protons, and the nucleus is very small, so it makes it hard to fuse your proton into a smaller nucleus. See synthesis of precious metals and nuclear transmutation. Chrysopoeia is the production of gold, but there is not much content in this article. Graeme Bartlett (talk) 21:30, 16 July 2013 (UTC)

What's standing in the way is the prohibitive cost and extreme inefficiency of such a device. Anyone who can afford to build the device can build a gold mine and get gold much more quickly, at much lower cost. Anyone who can harness huge amounts of solar power can sell it to the grid, instead of using it to produce a few atoms of gold at a time. If gold ever runs out on Earth, mining the asteroids would still be a more economic option. If even the asteroids run out, and humans still haven't colonized other planets, gold would hold the same status as the rare earth elements do today. In other words, the extreme difficulty of obtaining gold would make it useless as a store of value, and nobody would try to obtain gold for economic purposes. --Bowlhover (talk) 23:41, 16 July 2013 (UTC)

Let's run some numbers on this... E=mc^2, so to get 1kg of gold, you need about (3x10^8)^2 =~ 10^17 J of energy, =3x10^10 kWh. A quick googling shows that electricity in the US is about $0.12 per kWh, so this will cost a bit shy of $4x10^9. The price of 1kg of gold on the open market is about $40,000 a kilogram, so around a hundred thousand times less. And that's befor considering the inefficiencies everyone else has highlighted. MChesterMC (talk) 08:11, 17 July 2013 (UTC)

Not a thing stands in the way. Why would you want to create such a device? Plasmic Physics (talk) 08:24, 17 July 2013 (UTC)

Taking the original calculation back to the original 'solar powered' version, it's also worth noting that the mean insolation at the sunniest places on Earth (like the Sahara) is only about 2500 kWh per square meter year—and much less at those places further from the Equator and/or subject to those inconvenient 'cloud' thingies. If you were able to wring every single joule out of every solar photon striking the Earth and apply it to this process with perfect efficiency (it is to laugh), you would still need completely cover 12 square kilometers to get that kilogram of gold in a year. In reality, of course, even the best commercial solar panels are only about 20% efficient at converting sunlight to electricity, so multiply the area required by five. And then note that the nuclear transmutation processes described above will be vastly less energy-efficient than that, since real life isn't always like Star Trek.

Worse still, in 2011, about 2700 tons of gold were mined. At 60 square kilometers per kilogram of gold, that would require 160 million square km of solar panels (all located in the Sahara desert....) The total land surface area of the Earth is only about 149 million square km, much of which is located in less-than-ideal-for-solar-energy locations. TenOfAllTrades(talk) 13:19, 17 July 2013 (UTC)

I didn't focus on the example of generating gold, but matter in general. Plasmic Physics (talk) 13:55, 17 July 2013 (UTC)

Thanks for all the informative answers so far, folks. --Kurt Shaped Box (talk) 18:47, 17 July 2013 (UTC)

So you certainly could do it with enough fancy equipment - but by *FAR* the most efficient way to turn sunlight into gold is to turn sunlight into electricity, sell the electricity to people who need it - and use the resulting cash to buy gold. SteveBaker (talk) 20:24, 17 July 2013 (UTC)

Along those lines (and possibly more efficiently), you could also plant crops, which turn sunlight into food, and sell the food to raise cash for gold. Farmers are ultimately in the solar energy business ;) SemanticMantis (talk) 23:12, 17 July 2013 (UTC)

It is possible to transmute lead into gold, but it's not worth the cost. CS Miller (talk) 21:24, 17 July 2013 (UTC)

This Humpty Dumpty cartoon demonstrates a similar folly, though the device used is far more primitive. And (in case I need to say this), it is only very loosely based on actual science. InedibleHulk (talk) 23:30, 17 July 2013 (UTC)

Sorry to be the party pooper but actually, the question doesn't make sense. Einstein never, ever said that energy could be converted to matter or vice versa. What he did say was there is mass-energy equivalence as denoted by E=MC2 and that mass and energy are always conserved. The difference is subtle but important. Typps (talk) 01:36, 21 July 2013 (UTC)

July 17

How do people sleep during daylight conditions?

Ny-Ålesund at 79°N claims the world's northernmost hotel, which should be able to locate a sleep mask for their guest. If not, try the airport. DreadRed (talk) 11:13, 17 July 2013 (UTC)

I brought dark curtains with me, otherwise I would have gone mad! 83.109.151.51 (talk) 09:54, 17 July 2013 (UTC) (Count Iblis posting from his vacation address)

Maybe this requires more explanation. Are you being forced to sleep during the day and be up at night, or are you maybe posting from very high northern latitudes with a marked lack of darkness? HiLo48 (talk) 10:00, 17 July 2013 (UTC)

The latter, I'm now at the Northernmost hotel on Earth and they don't have decent curtains. 83.109.151.51 (talk) 10:08, 17 July 2013 (UTC)

Everybody's different. Whether it's noon or midnight when I'm sleepy, I just close my eyes and fall asleep. But then, I may have already gone around the bend. Clarityfiend (talk) 10:13, 17 July 2013 (UTC)

After working all night, I find it rather easy. Dismas|^(talk) 10:17, 17 July 2013 (UTC)

Yes, genuine physical tiredness does it for me. HiLo48 (talk) 10:35, 17 July 2013 (UTC)

You can get eye masks or maybe improvise a blindfold. --TammyMoet (talk) 11:04, 17 July 2013 (UTC)

I wonder if the OP was expecting a scientific answer? I sometimes plonk another pillow over my head and if angled correctly can block out most of the light. This also helps to block out barking dogs, screaming children and nagging wives. Sandman1142 (talk) 11:30, 17 July 2013 (UTC)

Yeah, a pillow works fine for me, too. I used to angle it to avoid near suffocation, but now I'm used to breathing straight through it. Actually handy for drowsiness. And yes, works great for muffling sound, too, especially feather pillows (I plug wet toilet paper in my ears, just to be sure). A bit hot some days, but beats laying awake all night (or day). InedibleHulk (talk) 11:36, July 17, 2013 (UTC)

A sleep mask combined with high-quality earplugs will shut out most of the potential interferences. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:10, 17 July 2013 (UTC)

The earplug article warns of health risks which is why I prefer a pillow. As it is, I use headphones far too often, which has a related set of prolonged use dangers such as tinnitus and higher risk of infection. At the risk of asking a medical question, does anyone here have similar concerns? Sandman1142 (talk) 12:53, 17 July 2013 (UTC)

I wouldn't recommend earplugs on a routine basis, no. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:38, 17 July 2013 (UTC)

Every body's different, but in my ten years of regular nightly earplugging, I've had just three occasions where a tiny piece went in too far and some minor swelling, deafness and water-in-the-ear dizziness happened. Lasted about a day and a half each time. I say it's a fair trade. The trick (if you can call it that) is to just get it damp, not soaked. Fold it into a square, and stick it in flat side first. Never a round or bullet shape. I've tried regular foam earplugs, too, but find they're not near as effective. InedibleHulk (talk) 03:04, July 18, 2013 (UTC)

You might want to consider getting some custom-made earplugs. (eg [2]) I know some people in the audio business (who greatly value their hearing) who had their ears scanned and custom-made earplugs produced. The very precise fit they get from that makes the plugs vastly more effective and much more comfortable. But it's not cheap - you're looking at $150 per pair. SteveBaker (talk) 13:48, 18 July 2013 (UTC)

Thanks, but no thanks. Affording the toilet paper is enough of a challenge for me. And at least one audio designer likes that, too. InedibleHulk (talk) 20:21, July 18, 2013 (UTC)

I can certainly understand the expense issue - but none of the earplugs in that review are of the kind that are custom-molded to your ears - so there is no grounds here for saying that they're no better than wadded up TP. The problem with TP is that it doesn't allow for venting (which - as they point out in a couple of those reviews - is important for hearing your own voice and a couple of other reasons), they can also trickle water into your ear and trap it there for extended periods, potentially resulting in swimmers'-ear kinds of infection, and if you use them for long enough, they start to dry out which dramatically reduces their effectiveness at attenuating high frequencies - which is not a good thing if you're trying to protect your hearing. SteveBaker (talk) 02:40, 19 July 2013 (UTC)

It helps to block out blue light from your field of vision for one hour prior to attempting to sleep to increase your serotonin levels. Plasmic Physics (talk) 13:10, 17 July 2013 (UTC)

Around here some people cover the window with black plastic garbage bags or aluminium foil. Or if you are like me you just go to sleep. CambridgeBayWeather (talk) 14:20, 17 July 2013 (UTC)

Stuff like washing machines, people passing by the street, cars, or singing birds doesn't annoy me. For me, it's White noise or random noise, and I can block it out. But I can't sleep when I hear a TV or a prolonged conversation. My brain keeps trying to keep up with the argument, or with the conversation. --Enric Naval (talk) 19:02, 17 July 2013 (UTC)

I'm back. Sleep masks have the problem of causing you to sweat at the parts covered by the sleep mask, that sweat will move into your eyes, causing you to wake up. I know that many people can't sleep during daylight conditions, and yet the hotels (the expensive ones) above the polar circle don't have decent curtains. In my own home I have curtains in the sleeping rooms that block out all the daylight.

During daylingt conditions when I fall asleep, I immediately wake up again. This seems to be caused by rapid eye movement; the light in the room is not uniform, rapid eye movement will cause a strong signal which will wake me up. However, many people can sleep during daylight conditions without problems, so I was wondering why they are not bothered by this effect. Count Iblis (talk) 22:09, 19 July 2013 (UTC)

Measuring rate of rotation by the Doppler effect

Follow-up from this question about the cricket revometer, how can the rate of rotation of an object be detected by the Doppler effect? Apparently this has been done for Venus, does it work for smaller objects - for instance the ball in a sports game? ManyQuestionsFewAnswers (talk) 13:31, 17 July 2013 (UTC)

If your view of the rotating object is somewhat equatorial, one edge is moving toward toward you and the opposite edge away from you (once you've subtracted the net motion of the ball as a whole). But if your aspect is polar then this won't help. Given the small diameter and low rate of rotation of e.g. cricket balls, the Doppler shift differential between the opposite edges is tiny; for galaxies (which have huge diameters and spin at high speeds) it's another matter entirely. -- Finlay McWalterჷTalk 14:49, 17 July 2013 (UTC)

Using optical doppler (ie color shifts) is unlikely for something as small and slowly spinning as a cricket ball - and utterly impossible when using a TV camera to capture the motion as in a cricket revometer (because TV cameras only capture three colors - and not a complete spectrogram). I suppose that if you aimed a focussed beam of sound at the object then acoustic doppler might pick up a different sound reflection from one side of the ball versus the other. SteveBaker (talk) 13:43, 18 July 2013 (UTC)

That's a misunderstanding of how TV cameras work. While TV cameras encode light into three primary colours, red, green, and blue, they detect and resolve any pure spectral colour within a range that approximately corresponds to the range of the human eye. In concept, if a scene contains a wavelength that is half way between red primary wavelength and green primary wavelength, it will be encoded as 50% red and 50% green. If the scene contains a wavelength much closer to green it might (say) be encoded as 25% red and 75% green. If TV cameras only detected and encoded three colours they obviously would be useless - all scenes contain colours ranging from very narrow bandwidths to very wide bandwidths. (The actual coding is a little more complex due to technical reasons.) TV cameras cannot tell the difference between a pure monochromatic colour and a mix of colours occupying a narrow band centred on the same wavelength. But that does not matter, as here we would be interested in the group wavelenth shift. However, Steve is still right to believe that using a TV camera to detect ball rotation speed by doppler effect is quite unlikely as the doppler effect on the red/green/blue ratios is too small to be practial, of the order of some fraction of the speed of the ball surface divided by the speed of light, i.e around 0.001%. And if the axis of rotation points to the camera, there will be no doppler shift at all. Analog electronics is good at resolving to only 0.1% at best. 60.230.221.33 (talk) 15:40, 18 July 2013 (UTC)

(FWIW I'm not sure that Doppler effect is what is used to measure the spin on a cricket ball, it was just one answer in my earlier unresolved question. I was curious how the Doppler effect might be used to measure rotation though - presumably the idea is to use electromagnetic waves rather than sound, but what wavelength would you pick, how would you detect it, and what accuracy would be available? ManyQuestionsFewAnswers (talk) 19:03, 18 July 2013 (UTC))

Well, if you know the size of the object you're measuring (eg for measuring the rotation speed of a planet) then you use doppler shift for the side of the planet that's moving away from us and for the site that's moving towards us - and from the difference between the two, you can figure out the rotational speed. These techniques are fairly precise - astronomers have used them (for example) to measure the wobble induced into a star by a planet orbiting it. Our Doppler spectroscopy article covers much of this. SteveBaker (talk) 19:36, 18 July 2013 (UTC)

When do we call a celestial body a moon?

How are rocks classified as moons? I mean, there are many big and small rocks orbitting planets, but we don't call all of them moons. Yashowardhani (talk) 13:47, 17 July 2013 (UTC)

Natural satellite#The definition of a moon which says there is not an established lower limit on what is considered a "moon" -- Finlay McWalterჷTalk 13:49, 17 July 2013 (UTC)

Presumably it would have to be a naturally-occurring moon or "satellite". What we commonly call a "satellite" is short for "artificial satellite". The countless objects in the rings of Saturn, Jupiter, etc., would qualify as "moons" under a broad definition, but because they are bits of a larger entity they are called "rings" rather than "moons". ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:51, 17 July 2013 (UTC)

So there's a size limit or something? And what do you mean by "naturally occuring"? --Yashowardhani (talk) 15:21, 17 July 2013 (UTC)

"Naturally occuring" means not a man-made satellite, like Mars Reconnaissance Orbiter for example. Gandalf61 (talk) 15:38, 17 July 2013 (UTC)

"Naturally occuring" means the Death Star doesn't qualify. That's no moon. --Onorem (talk) 15:44, 17 July 2013 (UTC)

My go-to reference for such things, de Pater and Lissauer's Planetary Science book, uses the term "moon" and "satellite" mostly interchangeably when describing planet-moon systems within our solar system or discussing the general case of planet-moon system formation. The IAU (who are a sort of well-respected authority on such terminology) made a lot of noise when they re-categorized Pluto in year 2006. IAU and associated researchers released numerous technical papers and news releases for public consumption intended to explain how the word "planet" is defined.

The definition for "planet" needed changing, because over the last ten or twenty years, we've discovered many new objects - extrasolar planets - and the scientific community ought to use consistent terminology to describe new discoveries. The status-quo was changing at an accelerating pace, and the definition needed to be made much more clear than it had ever been before.

Ultimately, the definition for "moon" isn't a problem," because there are really a very small number of known moons; it is very infrequent to discover a new moon-like object; so most planetary scientists who specialize in such things don't get bothered by the semantics. But the recent announced discovery of a previously unknown moon at Neptune is a good example where the terminology is stretched. Here's the long and short of it: such "moons" are so tiny that we know very little about them. Very few people study them and write about them; and so there isn't a large enough community for a standardized terminology to become very strongly entrenched. One could debate whether a 20 kilometer rock is properly termed a moon or a satellite or a dust-speck, but first one would have to find somebody to take an opposing position. Nimur (talk) 18:25, 17 July 2013 (UTC)

But are all the grains of sand in a gas-giant's rings moons? CS Miller (talk) 21:15, 17 July 2013 (UTC)

Actually, that was a topic I started writing about, then deleted, and eventually edit-conflicted with myself. No, and the thing is, there's usually a very clear difference in size between moons and ring particulate matter. But some ring systems have really big particles! So, just like planets and dwarf planets, the boundary is a bit unclear. The key is clearing an orbit - moons almost definitionally do clear their neighborhood, and ring-particulate matter does not - but there aren't enough edge-cases where the terminology is unclear enough to really matter. Again, my favorite planetary science book calls the planet-moon-system relationship a sort of microcosm with a lot of similarities to the sun-planet-system. Nimur (talk) 01:10, 18 July 2013 (UTC)

Energy of Earths Spin

I've noticed a lot of these science questions sound more like science fiction; which bypasses the whole no predictions disclaimer. So I've read that the earths spin creates more energy than several thousand nuclear bombs; most of which I know is just from the mass. But still, why don't we see more spinning half molten iron spheres providing power on a smaller scale if that shape is so effective. You can tell I've never been inside of a power plant before, I would love to know what the name for that part is if it is already in common use. CensoredScribe (talk) 15:14, 17 July 2013 (UTC)

You're referring to dynamo theory - the blanket term describing the geophysical model of semi-molten iron spinning inside Earth and producing a magnetic field. Power plants also have a dynamo, but this term is a little archaic; nowadays, you'll probably hear "generator" or "turbine" or "unit" more commonly spoken in day-to-day operations. Of course, more specific terminology exists for various items in a modern power station. At the "core," all the Earth-Dynamo theory says is that molten iron makes a magnet, and that magnet is spinning around (as a semi-fluid). No new energy is being created. The Earth is just transforming energy from heat and motion into a magnetic field. There are massive quantities of heat and motion inside the Earth, still left over from planetary formation billions of years ago. But no new energy is made by the dynamo.

Spinning molten iron - or any other magnet - doesn't produce energy; it provides a way to transform thermal and kinetic energy into electromagnetic energy, and we can recapture that energy using a coil of wire. In a power station, we already have permanent magnets (or powerful electromagnets made with another coil of wire - a detail that at first seems like a head-scratching perpetual motion machine; but in fact, the energy powering these secondary magnets also comes out of the same thermal or kinetic energy that the plant produces). Making a molten iron core to replace the already very good magnets would introduce new hazards, engineering complexity, and inefficiency.

Even if we consider the giant magnet that we get for free - the Earth - we can't really use it for electric power generation. Very little usable electric energy can be extracted, because Earth's magnetic field is weak - something like a thousand times weaker than a crummy disposable refrigerator magnet. ...And perhaps a hundred thousand times weaker than a refrigerator magnet strong enough to be useful. You'd need an absolutely enormous machine to extract meaningful amounts of energy. Instead, we see that Earth's magnetic field interacts very slowly with very large processes, like the solar wind. A lot of energy is involved, but that energy is not in a usable form for human activities. Nimur (talk) 16:17, 17 July 2013 (UTC)

There are a lot of misapprehensions about this kind of thing. The earth doesn't "produce" energy - it "contains" energy. It might be possible to extract energy from the earth's rotation (by slowing the earth down by a teeny-tiny amount) - but it's not renewable - it's like mining coal: When it's gone, it's gone.

The largest nuclear weapon ever tested released 50Mtons - or about 2x10¹⁷ Joules. That's about the same as the total amount of sunlight striking the surface of the earth in one second...or about 1% of the US's annual electricity consumption. The total rotational energy of the earth is 2x10²⁹ Joules - so about the same as a trillion of our largest nuclear weapons.

The amount of energy contained in the earth's revolution is immense. But it's not because of spinning iron spheres and magnetic fields or weird and wonderful like that...it's just very large, very heavy, and spinning very quickly.

SteveBaker (talk) 19:46, 17 July 2013 (UTC)

... and, of course, we do extract energy from the earth's rotation (and the moon's) when we use tides to generate electricity. If we did this on a much larger scale worldwide, we would possibly notice a minuscule slowing of the earth's rotation (resulting in extra leap seconds) and a minuscule increase in the rate at which the moon is receding from the earth (currently about an inch and a half per year). Other factors such as glacial rebound have a bigger effect. Dbfirs 22:43, 17 July 2013 (UTC)

I'm not sure about us slowing down the earth by using tidal power. We're not actually extracting any extra energy, we're merely directing energy that gets extracted anyway into useful work. 202.155.85.18 (talk) 07:08, 19 July 2013 (UTC)

Yes, most of the energy we capture would otherwise have been dissipated as heat as the tides ebb and flow. I'm not sure what the effects of widespread restriction of tidal flows would be, but I suspect it would be to reduce the slowing. In the back of my mind I had the common practice of pumping water up at high tide and using it to generate extra electricity at low tide (releasing much more energy than the original pumping required). This technique does extract extra energy from the earth-moon system, but it might well be more than offset by the reduction in tidal flow caused by other power-generating techniques. In any case, any effect is swamped by other factors over which we have no control. Dbfirs 07:39, 19 July 2013 (UTC)

• Note the dynamo is powered by radioactive decay in the case of the Earth, and perhaps tides in the case of the Moon, or could briefly be started by energy from a collision; but in any case, the energy in the dynamo is being refilled by some other source, just as in a power station. [3] Wnt (talk) 19:28, 19 July 2013 (UTC)

reaction of amino acids with formaldehyde...a simple way to decarboxylate to form a hetero-diene?

Start at say pH < 4, using a non-acidic or non-basic amino acid (i.e. tyrosine or alanine something). The amino group first becomes an imine group (standard rxn), eliminating water. When the carboxylic group and the amino group are both protonated, what prevents enolization from occuring and attacking the formaldehyd? The enol is stabilized by conjugation with the imine, and after the attack on a second formaldehyde, a hemiacetal is created-- the alkoxide is readily stabilised by the COOH group next to it. When the COOH group is reprotonated, 6-center concerted decarboxylation readily occurs because the hydroxl group is a readily available base, the alpha carbon -COOH bond moves between the alpha-carbon and the formaldehyde-carbon, i.e. water and CO2 are eliminated as a concerted step.

The result is R-(C=CH2)-N=CH2), i.e. a diene. This could be used as a starting point for all sorts of useful Diels-Alder reactions. But I don't see this mentioned very often... it's just a one-step rxn with formaldehyde and some acidity.

This also seems like a good way to turn a carboxylic acid group into a group that can be readily reduced to a methyl group, something that seems sought after.

(I would draw but I don't have access to a scanner or Chemdraw atm.) 76.23.197.50 (talk) 23:11, 17 July 2013 (UTC)

At pH < 4 the alkoxide is already protonated, not likely to be a strong base. If you're under acidic conditions, it would be the (as you say) enol (not enolate) that is present to attack the formaldehyde. And the formaldehyde carbonyl itself may become protonated first (becoming a better electrophile) in order to induce the neutral enol (a not-very-good nucleophile in general, and now also with additional stabilization?) to attack it. I can't envision where you get a hemiacetal structure (especially if it's part of the [carboxylic acid]→[enol]→[β-hydroxy acid (aldol addition product)]→[6-membered-ring decarboxylation].

The overall idea of [enolizeable carboxyl]+[carbonyl]→[alkene]+CO₂ is actually well-known in a variety of malonic ester and related syntheses (aldol condensation#Scope is a similar example). The novel idea in yours is the use of the imine type of reactant (rather than β-carbonyl) to get to the heterodiene structure.

The [amino acid]+H₂C=O→[imine] under acidic conditions is well known, but appears not to proceed further. A few aldol addition reactions of that imine product are popping up in my SciFinder searches to give the Β-hydroxy product but I'm not finding any that give decarboxylation. DMacks (talk) 02:35, 19 July 2013 (UTC)

July 18

19th century medicine on sexual health

In the 19th century, how much onanism did a person have to practice in order to be considered medically an onanist or a person addicted to onanism? Are the physicians referring to masturbation or coitus interruptus or either one or both? Sneazy (talk) 00:55, 18 July 2013 (UTC)

A wise man once said: "Don't be a wanker!" DavidLeighEllis (talk) 01:02, 18 July 2013 (UTC)

On the lines of a classic definition of excessive drinking: more than the diagnosing physician. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:26, 18 July 2013 (UTC)

According to quintessential 19th century physicians such as John Harvey Kellogg, any masturbation was too much. DavidLeighEllis (talk) 15:40, 18 July 2013 (UTC)

Mental inheritance

Are traits like foolishness, psychotic thinking, awkwardness, laziness, aimlessness etc.. genetically inherited ?? — Preceding unsigned comment added by 103.15.60.174 (talk) 08:43, 18 July 2013 (UTC)

It rather depends on the causes of those traits. I suggest you read Biological inheritance.--Shantavira|^{feed me} 10:36, 18 July 2013 (UTC)

I work with teenagers in high schools. I've been in a good cross section of schools. Many of these kids are what most adults would call lazy and aimless, and that's why many of the kids are lazy and aimless. It's very much a peer pressure thing. Those who show high commitment and effort are not conforming with the group ethic, and tend to be isolated from the bulk of students. So those traits for those students are definitely not inherited. HiLo48 (talk) 10:54, 18 July 2013 (UTC)

Nature versus nurture might be another good entry. As far as I can see, and I think this is quite interesting, very few things that matter between humans are mostly one or the other. For instance in HiLo48's observation many children do buck peer group pressure even with the consequences outlined. Dmcq (talk) 11:38, 18 July 2013 (UTC)

It's unlikely to be anything as simple as genetic inheritance - and even if there were genes for (say) "foolishness", I think it's impossible that all people who are foolish became foolish for genetic reasons. All of these attributes are likely to be the result of a complex interplay of many, many genes and wrapped up with how the person lived their early lives. Note also that some traits such as poor education are passed down through a family even without genetics being involved. Poorly educated parents are much less likely to read books to their children or even have books in the house - resulting in their kids being poorly educated too. This is "inheritance" - but not through genetics. But now consider a gene that might cause poor eyesight - if neither parents nor child can see well enough to read - then the child's education might suffer as a result - and then poor education would be inherited genetically but still entangled with environmental factors because with better technology the child could maybe listen to audio books and still get a good education despite a genetic problem.

All of these traits are going to be like that. A mix of genetic and environmental causes.

That said, there are conditions such as Asperger syndrome (which I happen to have) which frequently results in "awkwardness" in social situations and which is thought to have a strong genetic component. But we know that there are plenty of awkward people who don't have Asperger syndrome - so it's not correct to say that "awkwardness is always genetically inherited" - because it's clearly not. But you also can't say "awkwardness is never genetically inherited" because we know that it sometimes is.

This is not a simple question. Your suggested symptoms are far too vague to be pinned to genetics or not-genetics. I'd bet that every single one of those symptoms has some genetic component produced by many, many genes - and some nurture component produced by many, many issues during childhood and beyond.

Worse still, these are complex traits. I'm pretty foolish when it comes to investing money - but razor sharp when it comes to computer programming - do I have a "success-with-money" gene that's defective and a "success-with-computer-programming" gene that's working just great? No. That level of specificity simply isn't possible at the genetic level. Humans only have 20,000 genes (according to Human genome) - there simply aren't enough of them for there to be such specific genes as a "foolishness-with-money" gene. So that trait - even if it were 100% genetic - would come from a subtle blend of hundreds of genes. Tracking down the effect of those genes to behavior with investments would be completely impossible. Hence, there is unlikely to be a scientific answer to this question.

SteveBaker (talk) 13:30, 18 July 2013 (UTC)

Making oil from CO2

If we had enormous amounts of very cheap electricity, for example from nuclear fusion, would it be possible to produce oil (gasoline) from the CO2 in the air plus water (or whatever other byproduct is produced from burning oil), basically reversing the combustion reaction? I found the Synthetic fuel article but that's about converting stuff like coal or natural gas into oil, not CO2. 114.252.96.225 (talk) 13:34, 18 July 2013 (UTC)

Where is our article on reverse combustion? There are these folks who have worked on it. And some have spliced bacterial genes to do the work; Craig Venter mentioned in passing similar work in a TED talk. 88.112.41.6 (talk) 18:05, 18 July 2013 (UTC)

It's been discussed here a few times, I have found an article on the matter, but it's escaping me just now. CS Miller (talk) 19:30, 18 July 2013 (UTC)

The Sabatier reaction will produce methane from water and carbon dioxide (reverse burning). However, most hydrogen is commercially produced by the partial oxidation of methane, so unless you have a very cheap supply of electricity for the electrolysis of water, it's a non-starter. Once you have methane, you can then reverse-crack the methane to longer hydrocarbons (methane reformation). CS Miller (talk) 19:39, 18 July 2013 (UTC)

Plants and green algae do the job of converting CO2+light into plant matter - and there are several techniques out there to turn plant material back into hydrocarbons...not exactly oil or gasoline because those are very complex mixtures of chemicals - but certainly something you could run your car on. Normally, we'd expect to provide the light to the plants using sunlight - but if you truly had vast amounts of cheap electricity, then synthetic light might works out well. You can read about this in our Algae fuel article. SteveBaker (talk) 19:30, 18 July 2013 (UTC)

One thing that has occurred to me is that Iceland has basically 100% of its energy from geothermal, but there hasn't been any way to export it. If Iceland could use the power to synthesize oil from simpler compounds, you might have something. Robert (talk) 20:28, 18 July 2013 (UTC)

Cellulosic_biofuel is all about taking CO2 and making something that can fuel a car. If you do it right, you can even make the whole process carbon negative, meaning that it would tend to reduce the concentration of CO2 in the atmosphere. Big companies like British Petroleum have invested heavily in researching this topic. SemanticMantis (talk) 21:49, 18 July 2013 (UTC)

88.112.41.6's comment deserves a second mention. The first link refers to the recently patented device that catalytically converts carbon dioxide and water directly into hydrocarbons including octane. However, due to a lack in funding for further development, the device remains hopelessly inefficient. Plasmic Physics (talk) 23:23, 18 July 2013 (UTC)

Well, it's never going to be at a point where 100% of the energy you put into generating this fuel comes back out again when you burn it...that's just the laws of thermodynamics. So this is unlikely to be as efficient as (say) an electric car. I doubt that it'll ever be as efficient as just electrolyzing the water to get hydrogen and using that in an internal combustion engine. The business of consuming CO2 and that being useful in reversing global warming is a red herring - sure, you suck out CO2 - but then the exact same amount of CO2 comes right back when you burn the resulting fuel. At best it can only be carbon-neutral. It'll never be better for the environment than using pure electric or hydrogen-power. SteveBaker (talk) 02:29, 19 July 2013 (UTC)

Just a few notes. I did not expect a hundred percent of energy consumed to be extracted, I'm also well aware of the thermodynamic laws; nor did I mention global warming. However, economics determines that as long as there is a demand, there is opportunity for supply -so it does not need to be more efficient than electric or hydrogen-powered cars, or what have you. Plasmic Physics (talk) 03:25, 19 July 2013 (UTC)

What about using photosynthesis to produce ordinary (hydrocarbon) biofuel, using a tiny fraction of that biofuel (or clean energy) to split hydrogen from carbon, and then burying the carbon? It would surely reduce atmospheric CO2, if an efficient reverse mining process is used to dispose of the carbon. I can see that it would lower the useful energy by essentially ignoring the carbon content of the fuel, but why is it not done? Is it too inefficient (because the carbon is either unused or still turned into atmospheric CO2) or just too expensive? 217.88.163.235 (talk) 07:51, 19 July 2013 (UTC)

That would be very inefficient and far too expensive to be viable on a large scale. The efficient way of using photosynthesis is to (a) grow woody plants, (b) turn them into charcoal by letting them dry and then heating them in the absence of oxygen, (c) bury the charcoal. Looie496 (talk) 15:16, 19 July 2013 (UTC)

Right now, just getting people to stop digging up the carbon that's already conveniently buried (we call that "coal") and turning it into CO2 would be a huge win! Until we can stop that from happening - we have no chance of getting carbon put back into the ground any faster than it's being dug up and burned. If you have energy to spare then by far the best use of it is to provide electricity to the grid and thereby shut down some coal-fired power stations (we're still building MORE of those horrible places!!). Doing that is much *MUCH* easier than sequestering the carbon after it's been turned in to CO2! If sequestration is to provide any net benefit at all, it has to be sequestration of the carbon dioxide itself...and we have no good ways to do that. In a future world where CO2 production has been essentially shut off using nuclear, fusion, wind, solar, wave, etc energy - then trying to use some of the spare energy we happen to have just lying around to pull CO2 out of the air might make sense. However, growing large forests over the sahara desert, sustainably harvesting the timber, converting it to charcoal and burying it in disused coal mines is probably the most efficient way to sequester CO2. SteveBaker (talk) 15:14, 19 July 2013 (UTC)

Optimal watering schedule

I recently installed drip irrigation in my vegetable garden and realized that my home's existing lawn irrigation controller wasn't advanced enough to handle seperate schedudules for the lawn and garden. I went overboard replaced it with an industrial controller from the scrap bin where I work. :-) I have it wired up to control the zones, and have the flexibility to schedule it based on pretty much anything. Right now I have it set up so that it can schedule zones based on the sunrise time. I have plenty of inputs to talk to pretty much any sort of sensor you can imagine, but I don't want to spend much. I will attach a thermocouple for measuring the air temperature, and I'll probably at least pick up a cheap rain sensor - they're designed to automatically cut power to sprinkler solenoids for a period after rain, but I can set one up so that the controller knows it rained and can act on that information in any way I want it to.

I live about 1000 ft from Lake Michigan near Holland, MI and have about 6 inches of top soil on top of sand. My front lawn is full sun, and the back is shaded for about half the day. The lawns use impact sprinklers, except for sprayers in some small sections. The garden is raised beds with 6-12" of a 50/50 topsoil/compost mix. The sun varies depending on the bed, but (for now) all the beds are on the same drip irrigation zone.

I'm looking for guidelines on the optimal way to schedule my sprinkler systems to reduce water use. I'll appreciate advice from personal experience, but I would really prefer reliable sources that have information applicable to my region and soil. I'd let the lawn go brown in the summer, but my retired neighbors are meticulous about keeping their lawns perfect, and my kids would probably prefer to play in soft grass anyways. If I do it right, I'm hoping that I can add a maple tree in the front lawn without it growing floating roots. I also plan on adding fruit trees and blueberries to my garden next year, but I can set those up on another irrigation zone if I need to. 209.131.76.183 (talk) 14:02, 18 July 2013 (UTC)

Here's some nice info from the MSU extension service (in the US, these are great resources!) [4], [5]. They have links to calculators, and discuss best practices. Of note, frequent (e.g. daily) light watering is bad for turfgrass. Also, don't sprinkle on your trees, use a soaker hose or Drip_irrigation to get water down deep. SemanticMantis (talk) 14:18, 18 July 2013 (UTC)

You may also be interested in xeriscaping, even though you're not exactly in a dessert. If your soil is that sandy and dry, you might be able to save water with something slightly odd for your area, like bermuda grass. FYI, the extension service will probably also answer specific emailed questions. They are actual experts, try them out :) SemanticMantis (talk) 01:06, 19 July 2013 (UTC)

Anything that involves swapping out my whole lawn is going to be too expensive for now, but I'll keep it in mind. If it were up to me, the whole neighboorhood would be a native habitat - either sand and uncut dune grass with the occasional Pitcher's thistle, or woodlands with sensibly-maintained underbrush. I'll contact the extension service about lawn ideas - they may be able to suggest some native species that will do well as an alternative turf. I'll also have to research township rules in that case. Thanks! 209.131.76.183 (talk) 12:18, 19 July 2013 (UTC)

Here in Austin, TX, we're in the middle of a multi-year drought. Unfortunately, local home-owner's associations (HOA's) are in pretty much every neigbourhood and require residents to have grass and typically dictate how tall the grass is allowed to be and bitch at you if it turns brown (which native texan grasses are quite happy to do - and recover from the next time it rains). Just a few days ago, the city passed a law requiring HOA's to allow xeriscaping - and I'm hopeful that we'll be able to shift to the kind of look you see for the desert homes out in Arizona - earth tones, xeriscape - zero water environments, that kind of thing. Throwing water that's carefully purified to be good enough for human consumption onto grass to make it grow so you have to get out in 100 degree temperatures to cut the stuff sure gets old fast! 15:53, 19 July 2013 (UTC)

My water comes from a well, and I assume that the aquifer gets recharged pretty well from Lake Michigan, but it still seems like a waste. I don't use fertilizer or pesticides on my lawn, but my neighbors definitely do, and I hate the thought of any of that getting into the runoff. We don't have an HOA anymore, but I still have to make sure to follow township rules. I put off sprinkling as long as possible this year, and maybe 10-20% of the grass went dormant and the green stuff is growing really slowly. We've had a 90-100 degree heat wave for at least a week now, but I haven't had to mow in it. 209.131.76.183 (talk) 16:46, 19 July 2013 (UTC)

Is the gravitational lensing caused by Earth measurable?

In theory, couldn't one measure terrestrial lensing of stars or sunlight from a tall tower or airship? I'm thinking something like 50+ miles of viewing radius should provide sufficient enough angle with the horizon to measure such effects, comparing the deflection angles of various wavelengths or some such. Have any experiments of this sort ever been attempted? 70.112.97.77 (talk) 14:39, 18 July 2013 (UTC)

Someone here who knows the math better can probably figure out just how much of an effect to expect, but I know it is going to be very very small. I expect that distortion from the atmosphere will be much greater than what you're proposing measuring. 209.131.76.183 (talk) 14:48, 18 July 2013 (UTC)

When it comes to gravitational lensing, I've seen a lot more mathematical theory than actual observational data. This leads me to the dismal opinion that many publications about gravitational lensing are actually very well-camouflaged professional pseudoscience; they typically consist of very pure and even correct mathematics, but this isn't science when there's almost no physical data to validate specific claims. A few landmark observations of the lensing effect do exist, which provides a little bit of confidence that the general concept is valid; but the famous examples are all very faint deep sky objects, and most of the effects are small perturbations due to massive black holes.

I do not believe any well-known experiment has ever sought to measure gravitational lensing deflection of light due to Earth's gravity. In fact, even deflection effects of the much larger Sun's gravitation are contentious due to the tiny magnitude of the effect and the impact of other experimental error. You will unfortunately find that our article, gravitational lensing formalism, references mostly self-published arXiv pre-prints, rather than peer-reviewed science. Our much better main article, gravitational lensing, lists several famous historical examples, like the Einstein Cross, where the effect and its theory are much better supported by the data. Nimur (talk) 15:21, 18 July 2013 (UTC)

The amount of deflection due to gravitational lensing is

$\theta ={\frac {4GM}{rc^{2}}}$ .

If you plug the Earth's mass and radius into that equation, you get θ=3x10^-9 radians, which is about half a milliarcsecond. It's not uncommon for astronomers to deal with angles that small. Red Act (talk) 15:41, 18 July 2013 (UTC)

For the sake of clarity, I edited my post. Gravitational lensing and deflection of light by gravity are both due to the exact same physics; but astronomers really only use the term "lensing" when the deflection is large enough that the gravity causes light to behave similarly to light passing through a refractive lens. This is probably another reason why you won't find much when you search for "gravitational lensing" by small planet-sized masses - even if the effect exists and is measurable, it isn't lens-like. Nimur (talk) 15:50, 18 July 2013 (UTC)

It looks like my statement above that dealing with an angle of a half a milliarcsecond wouldn't be uncommon for an astronomer was a bit optimistic. I was thrown by knowing that the Gaia space observatory that will be launched this coming October is hoped to measure star positions down to 20 microarcseconds or less. However, ground-based telescopes can only resolve things down to a few hundred milliarcseconds due to atmospheric effects, and even space telescopes like the Hubble which avoid those atmospheric effects are diffraction limited to dealing with angles of about 100 milliarcseconds. Some advanced observatories have been starting to use adaptive optics to get resolutions down to about 50 milliarcseconds, but Gaia's dealing with angles smaller than a milliarcsecond will be quite a breakthrough. In comparison, the gravitational deflection of light by the sun as was measured by Eddington is about 1.75 arcseconds, which is much easier to measure than a half a milliarcsecond. Red Act (talk) 21:30, 18 July 2013 (UTC)

Interesting, thanks all! 70.112.97.77 (talk) 19:59, 18 July 2013 (UTC)

Earth sized planets are routinely detected via gravitational microlensing. Count Iblis (talk) 23:05, 19 July 2013 (UTC)

Is it an example of precipitate reaction?

Here is a simple reaction-
Fe + CuSO₄ ----> FeSO₄ + Cu
Is this an example of precipitate reaction? If yes, then which one is precipitate? Publisher54321 (talk) 15:45, 18 July 2013 (UTC)

Cu (s) for most sulfates dissolve in solution, except barium or lead sulfates. 140.254.227.57 (talk) 15:48, 18 July 2013 (UTC)

No, it is not strictly a precipitation reaction. It can be classified a number of ways, either as a single replacement reaction or as a redox reaction. Precipitation reactions are usually a subcategory of reactions known as double replacement reactions. Classic precipitation reactions involve the mixing of two salt solutions to produce an insoluble salt. Typically, these are reactions like sodium chloride solution mixing with silver nitrate solution (producing silver chloride as a precipitate) or potassium sulfate solution mixing with barium nitrate solution (producing barium sulfate). --Jayron32 16:47, 18 July 2013 (UTC)

Correlation between continuous visible spectrum and the models used in display/detection of red, green, and blue channels

When dealing with color from the point of view of digital monitors, cameras, and so forth we talk about the differing intensity levels of red, green, and blue to describe the perception of the multitude of colors. But in examination of the electromagnetic spectrum of visible light we instead consider a well-defined bandwidth of frequencies with NO regard for intensity. What is the mathematical relationship of these two models? And how does a "pure" signal (peak frequency) of say yellow light "stimulate" intensity levels of red, green, and blue within the eye and optical detectors in the first place? 70.112.97.77 (talk) 15:58, 18 July 2013 (UTC)

I have no idea what the second sentence of your question means; this "we" of whom you speak is considering wrongly. The colour vision article shows the response curves for the three types of colour sensing cone cell found in the human eye, which are non-uniform and which overlap. The arrangement is broadly similar in the CCD detectors found in digital cameras, albeit with different curves. -- Finlay McWalterჷTalk 16:08, 18 July 2013 (UTC)

(edit conflict)The electromagnetic spectrum of visible light pertains to the wavelength at which the light emits. Color itself is the product of our perception, created by our visual pigments in the retina, and is combined from wavelength by the electromagnetic spectrum of visible light, intensity (how bright/dim the color is) and saturation (how much whiteness a color has). According to Hering's theory of color vision, there are three mechanisms, each of which responds in opposite ways to different intensities or wavelengths of light. The Black (-) and White (+) mechanism responds positively to white light and negatively to the absence of light. Red (+) Green (-) responds positively to red light and negatively to green, and Blue (-) Yellow (+) responds negatively to blue but positively to yellow. So, an object that reflects light at the peak wavelength of yellow light may react with the color receptors to fatigue, so that when the color is gone, the opposing color - less fatigued color - appears as an afterimage. The intensity, wavelength, and saturation are in the environment, not created in the eye. We just perceive them a certain way, giving them special characteristics. Sneazy (talk) 16:32, 18 July 2013 (UTC)

To correct our OP a little here - when you get a description of color using the visible spectrum, you still need intensity data. Generally, what you have is a plot of frequency versus intensity. Converting that into an RGB representation entails looking at the frequency response of the Red, Green and Blue sensors and using that to produce a weighted sum of the spectral data under each of the three curves. The reverse operation is impossible - there is insufficient information in the R/G/B intensities to reconstruct the original frequencies unambiguously. SteveBaker (talk) 19:22, 18 July 2013 (UTC)

Thanks for the responses. I still don't get it though: Yellow light has a frequency of 525–505 THz. Red, green, and blue range from 480–400 THz, 575–525 THz, and 670–610 THz respectively. How exactly does varying the intensities of RGB on a display produce what appears to the human eye as a frequency that lies outside the range of these three primary colors (eg: yellow at 525–505 THz)? 70.112.97.77 (talk) 19:53, 18 July 2013 (UTC)

I believe that would depend on the source of the light. Color may be combined together by shining two or more colored lights or mixing two or more colored paints. The former method, shining two or more colored lights, will produce an additive color mixture - all lights are bounced from the wall and into your eye. The latter method, mixing paints, will produce a subtractive color mixture. If a paint reflects long and medium wavelengths and a paint reflects medium and short wavelengths, and you mix them together, they will superimpose on each other, absorbing both long and short wavelength visible light, and therefore you may be left with green - a medium wavelength light. Display screens are just displays of light, not paint. The colors are "mixed" together to create the vast array of colors we see. I put "mixed" in quotes, because display screens have pixels. It is our brains that create the illusion that we are seeing "mixed lights". Think pointillism. Sneazy (talk) 20:47, 18 July 2013 (UTC)

(This is a pet subject of mine!)

The curious thing about "yellow" is that there are two completely different waveforms that both look "yellow" to our eyes and to our cameras - but which are in fact totally different colors when examined spectroscopically. Consider light from a sodium light - which is pretty much entirely composed of light whose frequency is intermediate between red and green. There is no red or green frequencies coming from that lamp at all. Then consider the IDENTICAL-LOOKING light from a TV screen that's showing a picture of a sodium light - which is a mixture of pure red and pure green light with no frequencies in the "yellow" range whatever (because a TV has no means to generate light of the frequencies that the sodium lamp produces)!

Our eyes and our TV cameras simply cannot distinguish between these very different waveforms. They look exactly the same shade of yellow - yet they are in no way similar if examined spectrographically.

I like to think about someone who is colorblind and unable to see green light directly. For those people, the frequency of light midway between red and blue looks identical to a mixture of red and blue...put another way, green and magenta look the same to those people. Well, that says to me that "sodium-lamp-yellow" and "TV-picture-of-sodium-lamp-yellow" are as different as green and magenta...but our eyes can't tell!

If you are unconvinced, try to find a very old orange-colored sodium street lamp and view it's light on a dark night through a prism - or (since you probably don't have one) reflected in a CD-ROM disk. The CD-ROM breaks light up into it's component frequencies like a prism or spectrograph - and all you see is a single patch of yellow light. Now go to your computer screen and set the whole screen to a yellowish orange and in a darkened room, view it the exact same way. When you do that, there is no yellow light reflected on the CD-ROM - only separate patches of red and green.

It's interesting to note that some animals have more than three color receptors - goldfish and some freshwater shrimp actually have a proper yellow receptor in their eyes. They must see sodium lamps and pictures of sodium lamps as wildly different colors...as different as green and magenta in fact!

SteveBaker (talk) 01:59, 19 July 2013 (UTC)

Sorry, I somehow overlooked your response. It makes a lot more sense now. Thanks! 70.112.97.77 (talk) 05:21, 19 July 2013 (UTC)

Steve, every time a question about color vision comes up you post in it, and every time you're wrong and someone has to correct you. Please stop.

The frequency spectrum of RGB subpixels varies widely across displays, but generally there is significant output at the 589nm wavelength of a sodium-vapor lamp, and on plenty of displays (like these) will produce as much yellow as red or green light when displaying an approximation of a sodium lamp's output. Also, the human eye can tell the difference, since the RGB display's approximation of the color is visibly desaturated (mixed with white).

I just thought of something. Consider, for simplicity's sake, three pure sinusoids of specific frequency. Varying the magnitude component any of these might produce a resulting waveform that is a very close approximation some other, non-related frequency (or frequencies). Could this be what is happening when one views a pixel for instance? Up close, distinct bands of red, green, and blue of varying intensity; from afar, an interference pattern that "fits closely" to the shape of say a yellow waveform? 70.112.97.77 (talk) 21:33, 18 July 2013 (UTC)

Amplitude and frequency are two separate things. Amplitude describes "how big" the wave is, and frequency describes "how frequent" the waves come in a period of time. If you change the amplitude, then you just change the size of the wave from hill to trough, not how frequent the waves come in a period of time. That said, the RGB on a display screen is made up of RGB pixels. The reason why we see a wide range of colors on the display screen is that these pixels are extremely tiny, and like pointillism, our brains perceive them as blending together to create various colors of the spectrum. The perception of various colors is real, even though all the colors of the spectrum are not in the pixels. Sneazy (talk) 22:48, 18 July 2013 (UTC)

Well, what I meant was that in varying the amplitude (or even phase) of a single sine wave which is being combined with several other (unchanging) sinusoids, one finds that certain values can actually "deform" the result so dramatically that if one were to say pass it through some sort of smoothing function or whatnot (the "fuzzy logic" of the human brain, for example) one might obtain a waveform that "somehow appears" to contain frequencies not present in the original signal. Seems plausible to me, but then again, maybe I'm way off here... 70.112.97.77 (talk) 04:30, 19 July 2013 (UTC)

No, it doesn't work like that. The three cone types in the eye are all sensitive to a wide, overlapping range of frequencies, and the three phosphor types of an RGB display produce a wide range of frequencies. Since all visible wavelengths are present in the image and all visible wavelengths are detected by your eye, there's no problem of seeing frequencies that aren't there. The three cone types are called L, M, and S, and it's a mistake to think of them as "R, G, and B", since that's not what they detect. The three phosphors on a display are red, green and blue in the psychological sense: they are defined by how they stimulate the cones in the eye of someone with normal color vision, not by their physical spectrum (which varies hugely from one display type to another).

When you look up close at a grid of R and G subpixels, cones in different patches of your retina are being stimulated in different ratios: L more than M in the R regions and M more than L in the G regions (but significant amounts of L and M stimulation in both). When you're farther away, all the cones are getting light from the R and G subpixels, so they are getting the average of the two, which is closer to equal in L and M. These relative ratios translate into psychological red, green, and yellow respectively via the opponent process. -- BenRG (talk) 19:24, 19 July 2013 (UTC)

A positive flame test for sodium has a bright yellow color.

One doesn't need to be a goldfish to see the difference between an actual sodium flame and this picture. The article Gamut explains that no tricolor image can duplicate any of the spectral colours. It's depressing when someone who knows better still exploits the protected forum of the reference desks to promote a spelling deviation that they would find unacceptable in Wikipedia articles. Human vision has evolved its (not "it is") responses to work with the incoherent solar light that is broadband radiation. The retinal cones effectively measure power not phase, and colour sensations do not arise from any particular waveshape. DreadRed (talk) 23:11, 19 July 2013 (UTC)

If Feverfew is poisonous to animal pets

Area Essex England. Is the Feverfew plant poisonous to animal pets? — Preceding unsigned comment added by 80.47.214.143 (talk) 18:47, 18 July 2013 (UTC)

It is not. The Eurasian variety described here is harmless to animals except in large doses; I'm guessing withdrawal symptoms would be similar. The North American variety (parthenium) is toxic to various animals, but you almost certainly have the Eurasian type in Britain. Robert (talk) 20:34, 18 July 2013 (UTC)

Careful, I think this may fall under the category of medical advice with some assumptions thrown in for good measure. — Preceding unsigned comment added by 122.111.254.165 (talk) 03:12, 19 July 2013 (UTC)

Yes, this information would go to a licensed professional in most jurisdictions. μηδείς (talk) 03:36, 19 July 2013 (UTC)

Rules Q: Is "Licensed" advice a valid WP:rule? I only see that neither "medical" nor "legal" advice is to be given. A question if a certain plant is poisonous to pets is neither (veterinary if any).

Can an admin please review this one? 217.255.150.14 (talk) 07:58, 19 July 2013 (UTC) (Not the topic starter.)

We are not supposed to give professional advice, such as medical or legal advice. Click on disclaimer at the bottom of this page: "Not professional advice

If you need specific advice (for example, medical, legal, financial or risk management) please seek a professional who is licensed or knowledgeable in that area." We certainly shouldn't be telling an OP that a plant we cannot see and are not qualified to identify will not poison his pets. μηδείς (talk) 17:08, 19 July 2013 (UTC)

This "ethics" nonsense is a disease. Wouldn't we answer a question about whether benzene is toxic? To humans, that is? Then give sourced data here and move on. If you insist, you can explain you're not giving this information with the intention that somebody is going to feed his cat this herb, not that there's any indication that was the plan. Wnt (talk) 18:58, 19 July 2013 (UTC)

I should note that searching PubMed wasn't very productive for me this time - it yielded up a review [6] of moderate quality which says that its chronic toxicity hasn't been tested, and that the immediate adverse reactions can include mouth ulceration and dermatitis in humans. I didn't find anything about "feverfew" and "dog" or "cat". There is mouse work available, some of which indicates beneficial effect, but extrapolating from those to a more common pet would be as dicey as extrapolating to or from humans. Checking Google Scholar yielded an alleged search hit [7] - it doesn't look very scientific and I have no idea how to get to the part that actually says "feverfew" without reading as much of it as Google cares to serve and see if it's in there somewhere. Ditto [8], probably others. Wnt (talk) 19:42, 19 July 2013 (UTC)

longest-running experiment to reach an unknown conclusion?

So, pretty simple. An experiment can be done where by the time the results are in, nobody knows for sure what these results will be: hence the experiment.

What is the longest such experiment (days/months/years/decades/whatever) that was not simply a demonstration but a genuine experiment? (i.e. specific example). Or, if not the longest, then some candidates for that title . Thanks! 178.48.114.143 (talk) 19:28, 18 July 2013 (UTC)

The Pitch drop experiment is well-known. That article also links to Long-term experiment. 209.131.76.183 (talk) 19:57, 18 July 2013 (UTC)

There has been a very long running test of evolution with bacteria: E. coli long-term evolution experiment - it's been running for 25 years now - but, again, I think the outcome was pretty much expected at the outset =. One thing though - an experiment of such scale that doesn't produce any surprises is still an important experiment...it might have shown up something surprising. Nobody knew.

My vote for longest running experiment with unknown results is the Voyager 1 and Voyager 2 missions (Voyager 2 has been up there longer). It's essentially a range of science experiments - a part of which was to ask what we would measure with it's instruments as it left the solar system. I believe the magnetometer experiment was the first to be activated of the half dozen instruments that are still functioning. Certainly the results it's been producing have been totally unexpected. It launched in 1977 - so 26 years or so - which handily beats the E. coli thing. SteveBaker (talk) 01:44, 19 July 2013 (UTC)

The Domesticated_silver_fox experiment has no known conclusion, and was started in 1959. SemanticMantis (talk) 02:29, 19 July 2013 (UTC)

Oh! Well played! Yes, I forgot about that one...it's an absolute classic - we have a new winner! SteveBaker (talk) 03:27, 19 July 2013 (UTC)

How is that the winner when the pitch-drop experiment outdoes it by 32 years? Also, I am fairly certain there was a break in the continuity of the Silver Fox experiment around the fall of the wall. μηδείς (talk) 03:32, 19 July 2013 (UTC)

Because the OP specifies an experiment with an "unknown conclusion". There is nothing whatever unknown, surprising or unexpected about a pitch-drop experiment. Even if there were, the results were well-known after the first or second drop - which happen about every 10 or 11 years - and would give us some idea of a number for the viscosity of pitch. At this point (after 8 drops) it's a cool demonstration - but could hardly be described as an "experiment". SteveBaker (talk) 14:34, 19 July 2013 (UTC)

But a short-lived victory because... SteveBaker (talk) 03:34, 19 July 2013 (UTC)

I found the Park Grass Experiment has been running since 1856 investigating crop yields and such. Any advance on that? SteveBaker (talk) 03:34, 19 July 2013 (UTC)

Probably. The Morrow_Plots were established soon after, and they are still often used for current research (though there are only a few hundred m^2 left of the original experiement). The Park grass and other stuff at the Rothamsted_Experimental_Station is probably the oldest broadly defined, relatively continuously running extant "experiment". The Oxford Electric Bell is probably more of a "demonstration" in the OP's terms, and it did miss a few days here and there. SemanticMantis (talk) 04:24, 19 July 2013 (UTC)

Yeah - I discounted the bell - it's a demonstration - and nothing unexpected is ever likely to come from it. SteveBaker (talk) 14:34, 19 July 2013 (UTC)

Incidentally, there's recently been some hot news in a Dublin version of the pitch drop experiment. Henry^Flower 03:43, 19 July 2013 (UTC)

There are some fun writeups on all of these (and some others that do not beat the Park Grass record - which this source credits to 1843) here: National Geographic, Atlas Obscura. The one for Vesuvius monitoring goes back to 1841, though I'm not sure that's an experiment, even though the outcome is indeed unpredictable so far. 174.88.9.124 (talk) 17:31, 19 July 2013 (UTC)

Professor William Beal started an experiment 134 years ago in 1879 which is still going on and providing data at Michigan State University. He buried seeds in dry sand in glass jars 20 inches below grade to study the percent germination of the seeds over time. Each of 20 glass jars contained 50 seeds from various plants, and he arranged for his successors to continue the experiment after his demise by digging them up and planting them every so many years. An article from 2000 said "The Beal experiment represents the oldest continuing experiment at the nation's oldest college of agriculture." In 2000 only "Verbascum blattaria, a weed commonly called moth mullein." sprouted, according the the linked publication, but elsewhere it said 2 seeds sprouted. Perhaps they were they same species. The next jar will presumably be opened in 2020. At the present pace of opening jars, the experiment will continue until 2100, for a duration of 221 years. See [9], [10]. According to [11], the Beal experiment is the oldest ongoing one. According the the last publication, Auburn University has been running a crop rotation experiment since 1896. As was mentioned above, the University of Illinois has been running their own agriculture experiment for a long time, the Morrow Plots. which grow corn in one plot of ground every year without crop rotation or fertilization, producing poor quality stunted corn, compared to higher yields in plots with crop rotation and fertilization. It has been an ongoing experiment since 1876. Maybe U of I is considered to have begun new experiments when the conditions changed for the high yield plots. Edison (talk) 18:24, 19 July 2013 (UTC)

Cool, I was not aware of the Beal germination experiments. UI Morrow plots could be ruled out on many technicalities, but I think the main reason is because only 3 of the 10 original plots are left (more info and pictures here [agronomyday.cropsci.illinois.edu/2001/morrow-plots/]). So, although the current plots have been studied since 1876, a purist (or a MSU rival ;) could say the original experiment ended when the first plot was removed. But now I'm wondering why NPR ruled out the Park Grass... SemanticMantis (talk) 19:00, 19 July 2013 (UTC)

'longest-running experiment to reach an unknown conclusion?'

Are we talking about those experiments undertaken by the modern scientific method or in the wider sense of experiments that lead to discovery and new understandings?

Archaeologists might disagree on when mankind first learnt how to control fire yet NASA and many other organisations are still furthering this form of rapid oxidisation experiment to this very day – because they still don't have all the answers.Some primates have been found to be tool users but non so far have been observed preparing a really nice medium rare stake with French fries and sauteed mushrooms.--Aspro (talk) 22:41, 19 July 2013 (UTC)

Laser Magnet

Magnetic fields normally affect their entire surroundings, but it there a way (in today's technology or in theory) to fire a magnetic field at a specific direction, similarly to how lasers emit light? Something that would enable, for instance, to pull a spoon but not a fork that lies next to it. Thanks, 84.109.248.221 (talk) 20:06, 18 July 2013 (UTC)

See this URL: http://www.mushield.com/faq.shtml#q1 . To me, it looks like you couldn't direct the whole force of a magnet in one direction, but if you surrounded the whole thing except for a small gap with shielding material, it would warp the field so it only stuck out the gap. However, apparently magnets can't be shielded from one another. That's as far as I understand what this says. Robert (talk) 20:39, 18 July 2013 (UTC)

Wasn't this question asked and answered on July 5? Nimur (talk) 00:08, 19 July 2013 (UTC)

Good answer there at your link, but now I'm thinking of asking a new question about collimated vs. coherent light :) SemanticMantis (talk) 01:11, 19 July 2013 (UTC)

The short answer is no.

I'm taking your question to be a question purely about magnetostatics, since your question only mentions a magnetic field, not an electric field, and if you wanted to consider electromagnetic fields in general, then a laser beam would be the obvious example of an electromagnetic field that's in the form of a beam like a laser beam.

In magnetostatics, no matter what configuration of magnets and objects of various permeability and susceptibility there are in a system, at large distances the magnetic vector potential due to the system can be written as a multipole expansion which consists of a series of terms which drop off with distance as 1/rⁿ. The smallest n that can have a nonzero term in the multipole expansion is n=2, i.e., the term for the magnetic dipole moment. A magnetic monopole, which would drop off as 1/r, is sometimes theorized to exist, but is not known to exist, much less a term that drops off as 1/r⁰, i.e. a term for a contribution to the field which remains constant independent of distance, like how the intensity of an ideal laser beam is independent of distance from the source. And the magnetic field can't even drop off as 1/rⁿ for some n>=2 but still at least be in the form of a cylinder pointing away from the source (a beam), because that would violate the conservation of magnetic flux (the divergence of B is zero). So there's no such thing as a static magnetic field in the shape of a cylindrical beam. Static magnetic fields always spread out with distance. Red Act (talk) 01:35, 19 July 2013 (UTC)

IMO, lasers are by definition electromagnetic, not magnetic, emitters. However, some amount of "magnetic lensing" is both possible and in use (iron cores, read/write heads of hard disk drives, etc). The July 5 entry has more links on this. 217.255.152.44 (talk) 08:07, 19 July 2013 (UTC)

A magnetic field that's in the middle of an iron core or is a couple microns away from a hard drive head is a lot different from a magnetic beam extending a sizeable distance from the source through air, which is what I read the OP as asking about. The fork and spoon in the OP's example aren't in the middle of an iron core, and simply putting a magnet right next to the spoon isn't what the OP is asking about, either. Red Act (talk) 15:18, 19 July 2013 (UTC)

July 19

Distilled vulcanoids?

Vulcanoids are hypothetical undiscovered asteroids near the Sun between 100 m and 6 km in size. They are believed to lie in a zone with an inner radius imposed by the Poynting-Robertson effect so that they don't get any hotter than 1000K or so. If they get nearer, they slowly spiral into the Sun.

Question: how slowly?

As they get very close to the Sun, they should exceed the 3100 K boiling point of iron, at which point I would expect it to vaporize away, leaving concentrated siderophiles such as rhenium, iridium and tungsten that are key commodities of asteroid mining.

Question: can these asteroids actually become "distilled" to contain only these exotic elements in nearly pure form? Or would alloying produce azeotropes, etc. that would be resistant to distillation?

Now if you have a molten ball of highly valuable metal that is about to fall into the sun, no sense wasting it. I would assume that a missile, encased in high-temperature ceramic and decelerated from Earth orbit, could strike such a blob with extreme force, and if very carefully simulated and very carefully aimed, this could spray gobs of the exotic metal into an orbit so distant it might solidify and be retrievable by specially built mining craft.

Question: would that work?

Last but not least: even as expensive as elements like these are, would they really be worth enough to pay off the energy expended to slow the missile down (even if it uses a fancy slingshot maneuver) and to bring them back? Wnt (talk) 20:11, 19 July 2013 (UTC)

video games

is there a difference in how people with adhd/autism gets influenced by video games, especially violent compared to people without autism/adhd? someone must have done a study about it. --80.161.143.239 (talk) 20:12, 19 July 2013 (UTC)

Aphasia?

Is there a name for the phenomenon where, in a heated argument or under stress, one cannot speak because of overwhelming emotion? --TammyMoet (talk) 20:46, 19 July 2013 (UTC)

Aphonia is the medical term for inability to speak, so it could be called something like "transient iratogenic aphonia" if one wished to sound pretentious about it. (Or if one wished to decieve people into incorrectly informing one that it should be "iatrogenic"). Tevildo (talk) 21:34, 19 July 2013 (UTC)