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July 14

Need help identifying a catapillar

Unknown catapillar

Spotted this little guy as I was working in my garden in Southern Norway, and am at a complete loss for what he is. He was munching away on a young aspen, and is roughly 4-5 cm long. Does anyone know what species he belongs to? WegianWarrior (talk) 13:58, 14 July 2013 (UTC)

Looks a lot like this one,[1] which I found by googling [yellow caterpillar], and which is called a Canadian Yellow Caterpillar. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:08, 14 July 2013 (UTC)

It's had a long swim from Canada to Norway! Agree it looks the same, but caterpillars are generally known by the name of the butterfly or moth that they pupate into. Alansplodge (talk) 14:38, 14 July 2013 (UTC)

Gotcha! It's an Elm sawfly, Cimbex americana. I found it through this forum which reports sightings in southern England, despite it being a native of North America (apologies to Bugs). It is "also know to feed on willow and some other plants" aspen being a member of related to the Willow family. Alansplodge (talk) 15:09, 14 July 2013 (UTC)

Here's a picture of an adult elm sawfly. Alansplodge (talk) 15:19, 14 July 2013 (UTC)

Any idea what the adult stage of the Canadian yellow is? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:17, 14 July 2013 (UTC)

Bugs, please follow my link to the topix.com forum in my post above and read the thread - this is also the source of your photo. Alansplodge (talk) 19:25, 14 July 2013 (UTC)

If I'm reading that correctly, it's not a "Canadian yellow caterpillar", but actually just another photo of the larva of an elm sawfly. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:15, 14 July 2013 (UTC)

Correct. Alansplodge (talk) 07:27, 15 July 2013 (UTC)

Thank you all for helping out - and it certainly explains why I found no references in my Norwegian bug-books. WegianWarrior (talk) 17:31, 14 July 2013 (UTC)

Note that this is not a caterpillar - just looks like one. It's a member of the order Hymenoptera, and as the pictures linked above show, the adult is more like a wasp than a moth. -- Scray (talk) 17:51, 14 July 2013 (UTC)

Right, technically caterpillar is restricted to the lepidoptera, though informally, caterpillar sometimes means "crawly guy with legs" It is definitely a larva, but most people wouldn't call this sawfly larva a grub... so probably just larva is the best term. SemanticMantis (talk) 19:16, 14 July 2013 (UTC)

(Edit conflict) Yes, this blog says "True caterpillars have no more than five (5) pairs of prolegs, the “false legs” along the length of the abdomen that look like suction cups. Sawfly larvae have seven (7) pairs of prolegs." Alansplodge (talk) 19:20, 14 July 2013 (UTC)

As a side point of interest, sawfly larvae are often studied as a way of seeing into Evolution_of_eusociality, because the larvae exhibit some presocial behavior, while the adults are solitary. SemanticMantis (talk) 19:21, 14 July 2013 (UTC)

WegianWarrior, if you could update the details on your image, I can add it to our Sawfly article (there's a space waiting to be filled and it's a great photo). Alansplodge (talk) 09:10, 15 July 2013 (UTC)

Thank you - I just updated the description and requested a rename to a more suitable filename (ie "File:Elm sawfly larva (Cimbex americana).jpg"). WegianWarrior (talk) 11:22, 15 July 2013 (UTC)

It now adorns our article. Alansplodge (talk) 17:09, 15 July 2013 (UTC)

It looks so much like a new variation of Peep, I want to nibble on it. :-) StuRat (talk) 18:40, 15 July 2013 (UTC)

I do hope you are in the habit of frying your peeps first, then. μηδείς (talk) 02:23, 17 July 2013 (UTC)

Heavy legs

A friend said her legs felt heavy, so I was wondering how to measure their mass. I was modelling a leg as a rod with a variable mass distribution joined by a hinge to another rod representing the body also with an unknown mass distribution along it. Assume the axle between has zero mass,, you can have a second equal leg but it doesn't make any difference that I can see. It certainly can't be done by just measuring where the centre of gravity is with the leg in various positions and I don't see that measuring the moment of inertia is any help either.

Anyone like to suggest a way I could measure the mass of a leg in situ or do I have to tell her that unfortunately I really will need to cut off her leg to measure it? ;-) 21:08, 14 July 2013 (UTC)

A simple and approximate way would be to sit relaxed in a chair or lying down with the leg horizontal and rest the heel or calf on a bathroom scale. By relaxing, the leg muscles should neither push down on or lift the leg, and the hip joint should act as a simple hinge. An inaccuracy is that part of the weight is supported at the hip.and the hip and the scale would provide equal support only if the leg were of constant unit mass per unit length, which is not the case. .Edison (talk) 21:37, 14 July 2013 (UTC)

Unfortunately even if all the mass in each rod is concentrated at one point that doesn't work. If one keeps mr constant for each rod where r is the distance from the pivot and keeps the sum of the two weights constant one can vary the masses and not distinguish by those type measurements. One can move a mass over from one rod to the other without making any difference, for example split one in two and move half twice as far away and the other to the pivot. Then amalgamate that mass at the pivot into the massa in the other rod moving both to their common centre of gravity. There's no way to distinguish these two cases by these type measurements. Dmcq (talk) 23:11, 14 July 2013 (UTC)

Alternatively, you could measure the volume of the leg using a bath, and find the density using a CAT scanner, and multiply the two values.--Gilderien Chat|List of good deeds 21:51, 14 July 2013 (UTC)

That does sound like a possibility, not exactly a pure science method but probably very effective. I had a look at body fat percentage and I remember reading a while back about how they measured the volume of the lungs by the percentage of gas in exhaled air but I can't find there, anyway they seemed to do quite complicated things just to do that. I wonder if anyone just uses a scanner for that sort of thing nowadays. Dmcq (talk) 23:30, 14 July 2013 (UTC)

We have an article on Heavy legs, incidentally. Tevildo (talk) 23:01, 14 July 2013 (UTC)

Gosh Wikipedia does have an article on everything. Thanks very much. I'll tell her she's suffering from hypercondria ;-) 23:16, 14 July 2013 (UTC)

No, don't do that. It will serve no purpose and will be seen as a negative comment. Guide her towards the article and let her draw her own conclusion. and its hypochondria. Richard Avery (talk) 06:50, 15 July 2013 (UTC)

Place a large garbage can in a broader, shallower pan that will hold the overflow. Have her slowly get in the garbage can without sloshing. Measure the overflow, and assume she weighs the same as the displaced water. Also, a feeling of heaviness in the legs can be the sign of a severe medical condition. Have her call her doctor. μηδείς (talk) 00:40, 15 July 2013 (UTC)

Here's a reference> An article in a journal which discusses "heavy legs." Edison (talk) 01:49, 15 July 2013 (UTC)

There are even worse medical reasons than edema that can cause such symptoms, so, again, if it is a symptom and not just "do these pants make me look fat" she should contact a doctor immediately. μηδείς (talk) 03:25, 15 July 2013 (UTC)

She's quite healthy no worries - she was dancing and it had been a hot day. It's just me taking what's said literally and wondering about it. Anyway I rather like the one about the large garbage can, I think I'll suggest that one thanks ;-) Dmcq (talk) 07:20, 15 July 2013 (UTC)

A leg could be "heavier" because the volume was constant and the density increased, or because the volume increased at constant density, or some combination. One measurement would be to measure the circumference of ankle and calf when the legs are "heavy" and when they are not, to see if the volume varies. Edison (talk) 18:30, 15 July 2013 (UTC)

Severed legs aren't that hard to come by, either. Accidents, aggravated assault, etc. Those who sever serve in the military run a nonnegligible risk of losing a leg in a war, etc.

Maybe not exactly "not hard" but not extremely rare either. There should be some data on severed legs and their weight. Not sure how "available" , but anonymized data should exist quite abundantly. - ¡Ouch! (^{hurt me} / _{more pain}) 13:21, 16 July 2013 (UTC)

Quite hard to search for. I searched for "severed leg" + weigh, and excepting the three words "RuneScape" (which was the first return), "washed", and "ashore" (we need fresh legs). Still, the returns are usually about the victim's weight, or about items on sale (practical jokes (I hope, had to kill SafeSearch!)) - ¡Ouch! (^{hurt me} / _{more pain}) —Preceding undated comment added 13:30, 16 July 2013 (UTC)

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 [2] 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, July 17, 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 [3]) 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)

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)

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)

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)

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)

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)

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)

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 soild. 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)