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April 24

Energy used in travel

How many joules of energy are expended by each of the following 16 entities? (Additional details for each of the 16 entities: Please deal with entity variations by providing minimum and medium and maximum values; or please specify a typical specimen and provide a value for that specimen. Please assume that there is no wind in the air and no current in the water.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC)
[I am inserting the underlined text. -- Wavelength (talk) 03:34, 24 April 2010 (UTC)]

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.. --Jayron32 03:34, 24 April 2010 (UTC)

None of these questions is a homework question. I am simply curious about all of them. -- Wavelength (talk) 03:39, 24 April 2010 (UTC)

In that case, these are insansely complex problems anyways. The work done by each body in traveling one kilometer. Its a rather complicated problem, since in a perfect frictionless system, the work = 0 if the movement is at a constant velocity. So the work done in traveling one kilometer is the work done overcoming friction. These systems are fantasticly complex; you could calculate joules of energy consumed in traveling that distance for some of these. For example, given a car with a fuel efficiency of 30 km/gallon of gasoline you could calculate the mass of gasoline burned and then the joules of heat released in burning that gasoline from the Heat of combustion value for gasoline. For the human examples, there are ways of calculating "food energy" consumed per minute for various activities, but these are usually pretty inaccurate measurements. Still, you can find calculators online that will do this for you. Then you just need to convert from food calories to joules. --Jayron32 03:49, 24 April 2010 (UTC)

Remember that in both air and water, drag is really important as speed increases (drag increases with the square of the speed). So the speed needs to be known for all the mechanical systems. There are also questions of efficiency. Some engines are more efficient at high speed -- airplane engines are more efficient at the low temperatures of high altitude. The air is also much thinner there. At 1 km altitude, air friction would be quite high and the engines not as good. An aircraft blog I visited earlier gave an economy of ~2.7L/100km/passenger for a Boeing 777-300ER and ~3.1L/100km/passenger for an Airbus A330 and that's overall with most of the flight at ~10km altitude and Mach 0.82 or so (see comment 9 here). -- Flyguy649 ^talk 04:28, 24 April 2010 (UTC)

Also, another difficulty is that airplanes weigh anywhere from a couple hundred pounds to over a million pounds. The An-225 would use an absolutely incredible amount more energy than the CriCri, and the engines are optimized for completely different altitudes. The same (in terms of the weight) goes with automobiles (though not as extreme) and the other things you mention. Even amongst airliners, there will often be a significant difference between types. Falconus^{p t c} 05:02, 24 April 2010 (UTC)

My clarification about "entity variations" applies to all those variations. -- Wavelength (talk) 21:31, 24 April 2010 (UTC)

Extended content

Energy used in travel: by a man walking How many joules of energy are expended by a man walking along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man running How many joules of energy are expended by a man running along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man bicycling How many joules of energy are expended by a man bicycling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man swimming How many joules of energy are expended by a man swimming along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man pedaling a pedal boat How many joules of energy are expended by a man pedaling a pedal boat along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a man rowing a rowboat How many joules of energy are expended by a man pedaling a rowboat along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a horse with a rider How many joules of energy are expended by a horse carrying a rider along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a horse with a carriage How many joules of energy are expended by a horse pulling a carriage along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a motorcycle How many joules of energy are expended by a motorcycle traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by an automobile How many joules of energy are expended by an automobile traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a bus (omnibus) How many joules of energy are expended by a bus traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a ferryboat How many joules of energy are expended by a ferryboat traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a steam locomotive How many joules of energy are expended by a steam locomotive traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a diesel locomotive How many joules of energy are expended by a diesel locomotive traveling along a distance of one kilometer in a straight line on a flat and horizontal surface at sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by an airplane (aeroplane) How many joules of energy are expended by an airplane flying along a distance of one kilometer in a straight line at an altitude one kilometer above sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC) Energy used in travel: by a helicopter How many joules of energy are expended by a helicopter flying along a distance of one kilometer in a straight and horizontal line at an altitude one kilometer above sea level? (Additional details are under the main heading, above.) -- Wavelength (talk) 03:24, 24 April 2010 (UTC)

16 questions from Wavelength collapsed, all identical except for the vehicle. Comet Tuttle (talk) 06:30, 24 April 2010 (UTC)

Could they please be removed? They're screwing up the Table of Contents 82.43.89.71 (talk) 23:41, 24 April 2010 (UTC)

They were not a problem to the Table of Contents until they were collapsed in a recent revision. If they are removed, the discussion will be hanging without the complete context. If the collapsing is not going to be undone, the main heading can be reworded to say "Energy used in travel (collapsed subheadings non-functional in links)", that is to say, including the links in the Table of Contents. But However, I prefer that the collapsing be undone. -- Wavelength (talk) 05:45, 25 April 2010 (UTC)

[I am revising my post of 05:45, 25 April 2010 (UTC). -- Wavelength (talk) 15:31, 26 April 2010 (UTC)]

Are you sure this is what 82.43 is referring to? My guess is the complaint is about the very large TOC due to the 16 additional items (that's aboutmore then the average, and possibly median, of a whole days worth), not the inability to navigate to the individual sub-questions; and that problem occured both before and after the collapsing Nil Einne (talk) 06:35, 25 April 2010 (UTC)

See Bicycle_performance#Energy_efficiency for figures for three of the above. 89.243.216.99 (talk) 13:11, 25 April 2010 (UTC)

You'll be able to find some details for cars, planes etc in Part I of Without Hot Air by David MacKay. 131.111.30.21 (talk) 16:14, 26 April 2010 (UTC)

Thank you, 89.243.216.99 and 131.111.30.21, for your replies and those links. -- Wavelength (talk) 22:10, 26 April 2010 (UTC)

Why no plastic beer bottles?

Why do I never see beer in plastic bottles sold anywhere? Why are they either in aluminum or glass? --70.179.176.30 (talk) 04:09, 24 April 2010 (UTC)

Beer is often sold in plastic bottles at punk/skinhead/metal/etc. gigs. It hurts the singers and band members less when people hurl the bottles at their heads. Also makes it harder to use bottles as weapons when the crowd start beating on each other. :) --Kurt Shaped Box (talk) 04:20, 24 April 2010 (UTC)

(edit conflict) Well, not demonstratably true. For over a decade Anheuser-Busch has sold beer in plastic bottles, and they weren't the first, Miller started some time before they did. Plastic bottles are not as popular as beer sold in cans or glass, tradition being what it is, but they certainly exist. You see them a lot more at major events like ball games or rock concerts, where glass is a concern for safety reasons. However, you can find them in grocery stores and other places where you can buy beer. --Jayron32 04:22, 24 April 2010 (UTC)

I'm pretty sure that I've bought plastic 500ml bottles of Bud in England before, FWIW. --Kurt Shaped Box (talk) 04:29, 24 April 2010 (UTC)

Aye, well, most bottled water is sold in plastic. :) --KägeTorä - (影虎) (TALK) 18:18, 24 April 2010 (UTC)

http://www.packaging-gateway.com/features/feature79/ has some comparisons and consumer info. You can do your own research with Google on beer plastic bottles. PrimeHunter (talk) 04:38, 24 April 2010 (UTC)

Interesting link — it seems to claim the major reason is that more oxygen gets into the bottle while it's on the shelf; but I thought plastic was airtight, and don't particularly see why the cap on a plastic bottle would let in more oxygen than the cap on a glass bottle. Comet Tuttle (talk) 06:28, 24 April 2010 (UTC)

Interesting enough, it also mentions cost. I presume this is in comparison to aluminium cans rather then glass bottles but don't really know. This [1] mentions cost as a factor in 2001. As an aside, plastic bottles are common in stadiums as has been mentioned, but while not as dangerous as glass, they still pose a threat, particularly of course when full and sealed. Stadiums sometimes limit bottle size (even for brought in bottles) as a result. Similarly, tap beer with paper or plastic cups for the beer [2] Nil Einne (talk) 07:24, 24 April 2010 (UTC)

The plastic is not airtight! The plastic allows diffusion of gas, depending on the exact material this diffusion is varying. The oxygen diffuses into the beer and changes the taste by oxidation reactions. There are certain surface treatments necessary for beer bottle to lower this diffusion. There is a book about the properties of polymers which has a good introduction [3] --Stone (talk) 08:12, 24 April 2010 (UTC)

For me, drinking beer from a plastic bottle would be like drinking water from a muddy puddle. It's just not preferred, when inert glass is available. Vranak (talk) 14:25, 24 April 2010 (UTC)

Glass and aluminium cans are much more recyclable than plastic - going to plastic bottles would be a retrograde step. SteveBaker (talk) 18:04, 24 April 2010 (UTC)

To me the Q shouldn't be why beer isn't commonly sold in plastic bottles, but why soda-pop is. It goes flat much faster in plastic, because the plastic isn't airtight, and the bottle may also leach chemicals out of the plastic, into the contents. StuRat (talk) 18:18, 24 April 2010 (UTC)

Similar question: Why in the US is water not sold in 2 liter bottles? This came as a shock to me when I tried to buy it, and had to settle for two 1 liters. Staecker (talk) 22:43, 24 April 2010 (UTC)

Because it comes in gallons. Like milk. How it's decided what is sold in gallons and what is sold in liters is one of the great mysteries of life.

Of course ...while I can understand a single serving, it feels pretty crazy to buy an entire gallon of tap water that someone has put into a bottle. I get that stuff literally piped into my house! APL (talk) 03:15, 25 April 2010 (UTC)

I suspect that the answer is that US manufacturers tend to stick with traditional units (ounces, pints, quarts, and gallons; in this case), until they reduce the size and want to hide this fact from consumers. Then they switch to metric to maximize deception and confusion. This happened with car engines, where a muscle car engine went from 455/460 cubic inches to 5.7 L, so nobody would notice that it was now 3/4 as big. This prevented consumers from trying to pay 3/4 as much. I wonder if any company has then done the reverse, and switched back to traditional units, when they next need to deceive consumers about another decrease in size. StuRat (talk) 07:18, 25 April 2010 (UTC)

Well it's easy to buy 1 liter of water (or soda), even though this is slightly more than a quart. Staecker (talk) 11:59, 25 April 2010 (UTC)

But were the previous bottles a quart (32 ounces), or maybe 36 ounces, slightly larger than a liter ? StuRat (talk) 15:00, 25 April 2010 (UTC)

Catabolic breakdown of muscles

Hello. I've heard many a bodybuilder say that catabolism starts breaking down muscles after about six hours of fasting. However, it seems quite exaggerated to me, so I've come here to seek a scientific answer. For an average person, how much time without eating does it take for the body to start breaking down muscles noticeably to feed itself?

(By "noticeably", I mean to the point that the bodybuilder may lose the muscle mass he has gained by working out during the day, or more). Thank you guys! --95.120.13.224 (talk) 08:35, 24 April 2010 (UTC)

Since they aim to get their fat to muscle ratio to the minim I expect their energy reserves are low. This is an area that the military have long been interested in, maybe another wikipedian knows of a good s reference. You might find of interest some of the things gone into on this site [4]. Fasting adds a complication because metabolism tends to slow down under these conditions.--Aspro (talk) 09:39, 24 April 2010 (UTC)

We may simplify anabolic/catabolic relationships as follows (for an average adult): 1. For about 3-4 hours after a mixed meal, glucose and amino acids and free fatty acids are coming from the gut into the blood; insulin levels are high and glucose is actively moved into liver, kidneys, and muscle, where it is stored as glycogen in all three, and amino acids are moved into muscles and incorporated into protein. From about 4 to 16 hours after a meal, insulin levels fall gradually, and blood glucose levels are maintained by glycogenolysis from liver and kidneys (not muscle), and there is little net uptake or output of amino acids from the muscle. By 16 hours (with wide variation), liver and kidney glycogen is depleted (not entirely gone) and insulin levels are low enough to allow catabolism of both fat and muscle for purposes of making glucose by gluconeogenesis. This is also when ketogenesis from fat breakdown begins. See Cori cycle. This is somewhat oversimplified, as there is considerable overlap between end of glycogenolysis and start of gluconeogenesis, but perhaps is a useful way to think about it for clinical and physical culture purposes. alteripse (talk) 11:13, 24 April 2010 (UTC)

It seems to me that the time frame would change dramatically based on activity levels, with each step taking far longer when asleep than while running a marathon. So, what activity levels were assumed for those values, Alterprise ? Also, doesn't the nature of the last meal matter, with sugars being digested far quicker than fats ? StuRat (talk) 11:19, 24 April 2010 (UTC)

Overnight resting. The major fuel source for muscle activity is muscle glycogen, which is used in muscles during exercise, and not for ordinary between-meal blood glucose maintenance. This partial separation reduces the exercise effect on whole body metabolic balance but amplifies it for in-muscle glycogen balance. Speed of digestion has an early effect which is why I specified mixed meal, but has little effect on the timing of the later stages. We use cornstarch to prolong digestible glucose intake in people whose glycogenolysis and gluconeogenesis is defective but it only adds a couple hours at best. So does a huge high fat meal. alteripse (talk) 11:27, 24 April 2010 (UTC)

Number of cells in a human body

How many (approximately) cells are there in a (an average, adult) human? RJFJR (talk) 13:10, 24 April 2010 (UTC)

Close to 50 trillion cells. However, that conflicts with Human_flora#Gut_flora which declares it to be about 10 trillion cells and Cell (biology) at a 100 trillion. Is this assuming a standard human of 70 kg I wonder? Looks like we will have to do a little proof correcting on these articles. --Aspro (talk) 13:38, 24 April 2010 (UTC)

Do you mean total number of cells, or number of Human cells? I've read somewhere (sorry, no reference yet) that the number of non-human cells (for example, bacteria in the gut and on the skin) out-number the cells that actually have your own human DNA.24.150.18.30 (talk) 15:11, 24 April 2010 (UTC)

The OP's word "in" an average human must include gut flora. Cuddlyable3 (talk) 15:39, 24 April 2010 (UTC)

And do we include dead cells ? A good portion of the skin is dead, so that makes a diff. StuRat (talk) 15:20, 24 April 2010 (UTC)

This must be a harder thing to estimate than it at first appears, as I can't find any references to this in my human physiology text books nor on any of the human genome sites, etc. To give the OP a figure could we say: The average human adult is composed of cells numbering between the magnitude of 1 x 10^13 and 1 x 10 ^14. --Aspro (talk) 16:10, 24 April 2010 (UTC)

Well, Human_flora#Gut_flora and Cell (biology) are compatible, as there are indeed roughly 10 times more non-human than human cells in a human. So Cell (biology) apparently counts all the cells that are inside a person. --Stephan Schulz (talk) 20:06, 24 April 2010 (UTC)

What is strange here is that humans are colonies of cells. So, you have intelligent colonies of cells that have difficulties estimating how many cells they themselves consist of :) . Count Iblis (talk) 20:46, 24 April 2010 (UTC)

Katla

Hi. If Katla were to erupt, how much water vapor would be released into the atmosphere and how much sea level rise would occur from the melted glacier (I previously calculated a figure of 0.3 mm)? Considering both the vapor released into the troposphere and stratosphere, what would be its equivalent CO₂e warming effect as an increase in equivalent carbon dioxide concentrations in ppm? Finally, would the net result from the combination of the ash, sulfur, and vapor ejected from the volcano produce net warming or cooling of the Earth globally in terms of surface temperature, or is this indeterminate? Thanks. ~AH1^(TCU) 13:43, 24 April 2010 (UTC)

I believe volcanoes typically cool the Earth, since the additional sunlight and heat reflected back into space from the ash clouds outweigh all the other factors. StuRat (talk) 15:17, 24 April 2010 (UTC)

I agree. To get a significant warming effect, you need to have an enormous eruption in which huge quantities of CO2 are emitted. Then, because of the long atmospheric lifetime of CO2 (far longer than that of the dust and aerosols), you can get a warming effect. Note that H20 only has a short atmosheric lifetime. I think that even supervolcano eruptions are not large enough; they will still produce a net cooling effect. But large flood basalt eruptions, such as the one that formed the Siberian Traps, will lead to a net warming effect. Count Iblis (talk) 15:52, 24 April 2010 (UTC)

CO2 lives in the upper atmosphere for thousands of years. So I'd expect there to be a short-term cooling effect due to the light colored clouds produced by the volcano - but that effect can't last for more than a year - so the longer term effect can only be to contribute to global warming. SteveBaker (talk) 01:15, 25 April 2010 (UTC)

Stratified Italian soda + cold cream => Salt fingers??

A fluid mechanics professor and myself are a bit stumped on this question:

Go to your local cafe, order an Italian soda. Make sure the barista/server pours the soda in very gently so that the syrup & soda remain as stratified as possible. Now get the carafe of cold half & half & pour in 1-2 tablespoons. The cream is significantly denser than the soda and sinks quickly. However, the syrup is denser than the cream and so the cream is stopped abruptly at the syrup/soda interface. (Side note: the breakdown of large -> small turbulent structures at this point is really cool!)

After ~10 seconds, small fingers of cream appear to drop into the syrup layer ... and look a LOT like salt fingers (see wiki article + links on those). Salt finger theory relies on the lower layer being cold and the upper layer being warm such that thermal diffusivity causes displacement instability (i.e. a bit of warm upper fluid is randomly displaced downward, quickly loses its heat to the ambient cold layer, and continues to fall downward because its density just increased through loss of heat).

In the case of the Italian soda, the cream (upper layer) is COLD and the syrup (lower layer) is warm/room temperature. This SHOULD be a STABLE configuration provided that the syrup is indeed denser than the cream, because any parcel of fluid that falls into the syrup should get warmer, lose density, and rise back to the point of equilibrium. Yet these fingers clearly fall into the syrup.

I thus present this conundrum to the reference desk. I highly recommend you try it!

128.193.45.125 (talk) 20:46, 24 April 2010 (UTC)

I'm afraid I haven't been able to get you a complete answer. Poking around the web, I find these figures for the specific gravity (density) of

• Half and half: 1.031 g/cc at 4.4°C, and 1.024 g/cc at 20.0°C;
• Pure water: 1.000 g/cc at 4°C, and 0.998 g/cc at 20°C;
• The densities for the flavor syrups will depend on the manufacturer and the particular syrup. For Torani brand, there appears to be between 15 and 23 grams of sugar per 30 mL (1 fluid ounce) serving; you'll have to find the tabulated densities for sucrose solutions (the primary contribution to the sugars is cane sugar: sucrose.

Hopefully you'll find what you're looking for. TenOfAllTrades(talk) 21:30, 24 April 2010 (UTC)

Here's my guess: the syrup curdles the cream, creating globules (curds) that are denser and therefore fall into the syrup until the density finds an appropriate equilibrium. Any chemists out there know if syrups are acidic enough to do this?128.193.45.125 (talk) 22:11, 24 April 2010 (UTC)

You might be right - but I suppose there is another possibility. I suspect that the syrup and the cream are very similar in density - with the cream being very slightly the denser. As the cream descends through the liquid, the density gradient will reduce the downward force on the cream to the point where there isn't enough density difference to provide a force that will overcome the viscosity of the liquid. Hence, I'd expect the cream to stop moving just before it's at the right density level. What we have now is a slightly unstable situation - but without enough energy in the overall liquid to overcome the viscosity barrier. But there is still small-scale random motion going on - so it's only a matter of time when two or three streams of liquid flow that happen to be heading in the same direction join and together provide enough energy to overcome the viscosity of the syrup. Hence, the cream breaks through in these "fingers" that appear more or less at random. Once they get started, they can be self-sustaining and will eventually allow the cream to flow to the very bottom.

It would be interesting to get an accurate measure of the densities of syrup and cream...but because either can absorb water and other 'stuff' in this complex mixture, it may be that they absorb other parts of the liquid at different rates. Any system as complex as this is going to be very tough to analyse.

SteveBaker (talk) 00:32, 25 April 2010 (UTC)

Salt fingers require Double diffusive convection. You have to consider both the diffusion of the heat and the diffusion of salt (or sugar in this case). These problems are not trivial even with knowing all the properties of all the components. I went to a course on DDC (and started the Wikipedia article on it) but it was too long ago. --BozMo talk 19:55, 26 April 2010 (UTC)

First human

This may sound oversimplified, but evolutionarily speaking, would the mother of the first homo sapien have been a different species than her offspring? Spellcast (talk) 20:49, 24 April 2010 (UTC)

Strictly speaking no. Because to breed, both parents would need to be of the same species in order to produces fertile offspring. Yet, I have this feeling that some one will post... Yeah But !... --Aspro (talk) 22:14, 24 April 2010 (UTC)

Here is the Yes But bit Neanderthal#Interbreeding_hypotheses. --Aspro (talk) 22:24, 24 April 2010 (UTC)

Yeah but "able to reproduce with fertile offspring" isn't really a satisfactory definition of species. See Species#Definitions_of_species for 14 different definitions of what constitutes a species, of which "fertile offspring" is just one. Most of these definitions would say that the mother was indeed the same species as her child, assuming that she was pretty much like her child in most respects. Which would make the child not the first homo sapien, leading to a paradox. Conclusion: there is no single definition of what exactly constitutes a species, and you have to be comfortable with some blurry boundaries between one species and another. Staecker (talk) 22:41, 24 April 2010 (UTC)

Species is a fuzzy, fluid concept, so there's really no point in trying to establish a final cut-off on who was human and who was just a dirty ape. Vranak (talk)

Interesting argument by Dawkins here Count Iblis (talk) 23:21, 24 April 2010 (UTC)

Ah yes, I'm glad you linked to that interesting article, which I now recall reading years ago. Dawkins' mention of ring species is quite useful in applying here. Spellcast (talk) 01:30, 25 April 2010 (UTC)

Yes, an excellent article by Dawkins. Thanks Count Iblis. It reinforces the notion that a new or different species is identified in retrospect rather than at its first appearance. When a number of creatures are determined to be different to other similar creatures we say they represent separate species of the same genus. It won't necessarily be unambiguous so there is likely to be learned debate about where the boundary lies between the two species. (Genetically, there are millions of differences within any one species.) There is also likely to be speculation about how many thousands of years ago the two species diverged. It certainly won't be possible for the mother of a new-born to say Whoops, I've given birth to the first member of a new species. Dolphin (t) 07:00, 25 April 2010 (UTC)

If we had a solid definition of what is a human - some kind of a bright-line measurement (or set of measurements) - then you could say that the mother of "the first human" was (by definition) not human. However, we don't have a measurement like that. When we look back through the hominid fossil record, we see slow, continuous, change from something that's clearly an ape-like non-human to something that clearly is human with perhaps a couple of million years between those two fossils. We cannot put a stake in the ground and say that at on April 12th on 2123456 BC there was a sudden change between the "obviously not human" and the "obviously human" in the fossil record.

Evolution isn't like that...well, mostly it's not like that. If we look at a specific attribute of what makes us what we are, there are abrupt changes. The one I usually trot out at times like this is the evolution of lactose-tolerance in adults. There is a very specific change on chromosome 2 that flips a switch between lactose tolerance and lactose intolerance - there is no halfway house here. You are either one or the other. So we know for sure that the first lactose-tolerant human child was born of a lactose-intolerant human mother (probably around 4,000 to 6,000 years ago in some part of the world where people started to farm sheep and goats on a large scale).

So if you found some single, special feature of humanity that was controlled by an "on/off" gene like that - then you'd be able to point to that specific baby that had that specific gene and say "definitely human" - and to the mother of that baby and say "definitely not human". But we don't have such a specific gene...if we did, we'd probably be able to point to a specific skull in a long line of them in a museum someplace - and say "that one is human - that one isn't" - but we can't do that, so there is no single gene that we've chosen to mean "human" or "non-human".

That's not to say that we couldn't do that - we could look at our nearest relatives (chimps, gorillas, etc) - find a gene that we have that the chimps and gorillas don't have - and label that "the human gene". But doing that would be extremely controversial. Suppose we picked a particular gene on the long arm of chromosome 7. A child born with a rare genetic condition called "Williams disease" might well be missing that gene. Are we then going to label that child "not-human"? Of course not! But if we picked a bright-line definition of "human" then this kind of thing would happen all the time. I don't think we have the cold-hearted scientific rigor to do something like that.

Our modern definition of "human" is something like "born of a human mother" (although "born from an egg produced by a human mother" might be a better choice if we were to develop artificial wombs or something in the future). But that definition leaves us with a very definite "chicken and egg" problem.

So we have to accept that "humanity" isn't a black-and-white thing. There have been animals around in the past that have been "almost human" and others that are "somewhat human" - but nowhere has there been a step where a "definitely not human" gave birth to a "definitely human" child. What happened was that a "49.9% human" mother gave birth to a "50.1% human" child, the child looked, behaved and performed more or less identically to his/her brothers and sisters - looked like his/her mommy - maybe was slightly better at the "walking upright" thing - maybe fractionally more intelligent - maybe a tad less hairy...but not so much that you'd notice.

In the end, like so many RD:Science questions, this is not about science - it's about the definition of a word. What the OP is asking is a matter of linguistics. I recommend reading Chicken or the egg - an odd article - but actually very meaningful in the context of this question.

SteveBaker (talk) 00:13, 25 April 2010 (UTC)

Since lactose tolerance in adulthood is determined by a single gene, as you say, it probably occurred multiple times spontaneously, which complicates it. --Tango (talk) 01:13, 26 April 2010 (UTC)

The current evidence is unclear but it's possible only one lactase persistence mutation persisted, see Lactose intolerance#History of genetic prevalence and also [5] [6] [7]. Nil Einne (talk) 14:26, 26 April 2010 (UTC)

I think Tango was (pedantically) commenting on Steve's statement that the first lactose tolerant person was born while people were farming goats for milk. Since it (ie lactose tolerance) is determined by a single gene, it quite likely randomly came up at a previous time when there wouldn't have been any selective pressure to support it. 41.213.125.249 (talk) 15:17, 26 April 2010 (UTC)

See http://www.onelook.com/?w=homo+sapiens&ls=a. - Wavelength (talk) 00:25, 25 April 2010 (UTC)

...and in what way does that help? All of those dictionaries say things like "The primate species of mammal to which modern humans belong. Homo sapiens is Latin for knowing man or wise man."...but that completely fails to draw a bright line between this species and other, older species. It also fails in that the word "species" is a totally fuzzy, inadequate term. There is nothing in any of these definitions that would allow you to say "This creature is a human...that one isn't"...and that's what it would take in order to provide a "Yes" answer to our OP's question. Without such a 'bright line' definition (which would undoubtedly have to be genetic in order to be useful) - the answer is a clear "No" - there is no small step along the way from ape to human at which you could say that the mother was non-human and the child was human. SteveBaker (talk) 06:59, 25 April 2010 (UTC)

While there have been good answers, no one has linked to Speciation which discusses the general concept. Nil Einne (talk) 16:29, 25 April 2010 (UTC)

The question is invalid, like the one about chicken and egg (you can find that article on Wikipedia, too). Also consider that the brown bear and the polar bear routinely mate in the wild, when they are obviously on diverging evolutionary paths. Imagine Reason (talk) 11:52, 26 April 2010 (UTC)

Indeed - and if you need an example that's from a pair of animals that have diverged a little further than that, consider the situation with horses and donkeys (which produce mules) and between lions and tigers (which produce tigons and ligars). In those cases, the divergence produces offspring that are generally infertile. (I believe the offspring of brown and polar bears are fully fertile). As divergence increases still further, producing live offspring from mating becomes impossible - and with yet more divergence, even mating becomes impossible. Like so many things in biology, there is a rather smooth/continuous variation between "same species" and "different species" and coming up with useful, firm definitions for words like "human" and "species" is impossible. SteveBaker (talk) 12:36, 26 April 2010 (UTC)

And you have the "humanzee", the mythical human-ape hybrid- In 2008 a Scottish scientist wanted to give it a try [8]. Ethical problems abound. From the last link "The Human Fertilisation and Embryo Bill prohibits the placement of animal sperm into a woman The reverse is not prohibited. It's not even mentioned.".

We don't an article on blynxes, a hybrid of bobcat and lynx: "In 2003, DNA analysis confirmed that five odd-looking felines found in Maine and Minnesota were bobcat-lynx hybrids, dubbed blynxes."[9] --Enric Naval (talk) 15:54, 26 April 2010 (UTC)

A better latter link would be to Canadian lynx (Lynx canadensis), since the bare 'linx' links (ha!) to the Genus, which of course includes the bobcat (Lynx rufus). 87.81.230.195 (talk) 20:15, 26 April 2010 (UTC)

April 25

relation between the expansion of orbits and of the universe

It seems quite reasonable that because orbits like the Moon can expand that such expansion could the explanation for the expansion of the Universe since orbits seem to be a Universal phenomenon, pun intended. Indulging this line of thought consider that somewhere then there must be a center about which everything orbits which probably contains the center of mass as well. What science denies that such a center exists and that orbit is only a local phenomenon and not one that is totally universal? Plain vanilla with chocolate chips (talk) 05:28, 25 April 2010 (UTC)

I'm sorry - but what you are suggesting makes zero sense.

Why would you think that the gradual expansion of the moon's orbit would have anything to do with the expansion of the universe? The gradual increase in the moons' orbit is caused by gradual consumption of the moons' kinetic energy as it raises tides - there is no such mechanism happening in the universe as a whole. You can't just say "Thing A is expanding because of reason B, hence the expansion of thing C must also be because of reason B."

So I'm not going to "indulge this line of thought" - because it's 100% wrong. There doesn't have to be a "center" about which everything orbits or a "center of mass" because this whole orbital theory of yours is not remotely true:

• We know the universe is expanding because we see redshift in light from distant galaxies.
• Einstein field equations of general relativity explain why this is happening in mathematically specific form.
• General relativity is an exceedingly well tried and tested theory.
• Furthermore, many experiments - including the decisive observations of the cosmic background radiation) prove conclusively that space has been expanding ever since the big bang.

To be credible, your "explanation" would have to explain why Einsteins' field equations are somehow incorrect and explain why we observe all of the other effects of general relativity and somehow find another explanation for all of those experiments which you are (in effect) saying must be false.

Science does not allow you to just come up with a mental model that (to you) explains something you don't understand. You also have to tie that in to all of the other aspects of physics that relate to that idea. You won't be able to do that - which is why we know you're wrong.

I suggest you carefully read Metric expansion of space which explains what we know - how we know it - and (crucially) which experiments have been done to show that these theories correctly explain our observations...but "orbits" have nothing whatever to do with that.

SteveBaker (talk) 06:48, 25 April 2010 (UTC)

Gravity is often depicted as an indentation on a grid. How do you express the moon's expanding orbit on this grid? Does the grid become flatter and flatter in the area of the moon's orbit and it so what happens if it becomes entirely flat? Same question for the Universe assuming there is a center around which everything else orbits? Would not this flatter and flatter grid represent the expansion of the Universe as the area of orbit furthest from the center just like we see in galaxies? Plain vanilla with chocolate chips (talk) 09:06, 25 April 2010 (UTC)

The indentation stays the same, since the mass of the Earth doesn't change. Imagine you have a big bowl and roll a marble in it - depending on how fast you roll the marble, it will go around the bowl at different heights (it will gradually move lower due to friction, but that's a limitation of the analogy - there is no significant friction for the moon). The tidal interaction between the Earth and Moon just changes the height of the orbit since it changes the speed of the moon. --Tango (talk) 13:49, 25 April 2010 (UTC)

The moon doesn't move outwards due to consumption of energy, really, (that doesn't make much sense - energy is conserved, so it is just transferred not consumed). It is due to the lag between the moon's current, always moving, position and the tidal bulges it causes (the bulges take time to move, so lag behind the moon). The gravitational interaction between the moon and those bulges results in a transfer of angular momentum between the Earth and moon. --Tango (talk) 13:49, 25 April 2010 (UTC)

Indeed, energy never "goes away" it's just converted to another form. However, we don't usually go around talking about how the batteries in our flashlights transferred all of their energy to this and that form - we say that it ran out of energy and those who care about those kinds of things understand what we're talking about. So, sure, the kinetic energy of the moon is converted into heat and into making the earth rotate a bit faster...both a consequence of tidal effects. But the bottom line is that the moon loses kinetic energy due to tidal effects and that's causing it's orbit to slowly get bigger. SteveBaker (talk) 18:11, 25 April 2010 (UTC)

I would be inclined to agree partially with the original post in that the earth revolves around the sun, the solar system aroung the galaxy and the galaxies around some greater point, what is that point? —Preceding unsigned comment added by 62.172.58.82 (talk) 09:39, 25 April 2010 (UTC)

There is no evidence that the galaxies are rotating around "some greater point". They rotate about their own centers - but precisely because there is no "center" to the universe - there is no larger scale rotation going on. That's yet another reason why this idea is a non-starter. It's tempting to think that because moons orbit planets and planets orbit stars and stars orbit galaxies, that there should be some higher order rotation - but there isn't...so right there (and in a dozen other ways) this theory falls to the ground. It is as I said before - you can't understand the universe by just thinking stuff up in your head - your hypotheses have to fit in with all the other bits of known science - and this hypothesis of yours doesn't do that...not even close! In your mind, this idea "fixes" something you evidently don't understand about the metric expansion of space - but it "un-fixes" a million other things we know with great certainty! SteveBaker (talk) 18:11, 25 April 2010 (UTC)

Some of the larger galaxies do have smaller satellite galaxies orbiting them. The OP might also be interested in the Local Group article, which describes what the Milky Way, and the Andromeda Galaxy etc are doing, the Virgo Cluster and Virgo Supercluster articles, which describes how they are bound to other groups, and the large-scale structure of the cosmos article which describes the situation in general. CS Miller (talk) 22:14, 25 April 2010 (UTC)

See the true expansion of gravity Plain vanilla with chocolate chips (talk) 09:50, 25 April 2010 (UTC)

We can measure the distance to the moon and theorise about what ought to happen to that distance. There is no significant discrepancy between the measurements and the predictions, so we don't need to try and come up with another explanation. --Tango (talk) 13:49, 25 April 2010 (UTC)

(To the question three paragraphs ago about orbits): What is your evidence that "the galaxies" are in orbit around some point? --ColinFine (talk) 14:04, 25 April 2010 (UTC)

I have not read Ismail Kaddah's article at Academia.Wikia. All I have seen is the diagram he uploaded which shows a theoretical (IMHO) center of the Universe around which things that orbit each other orbit so you will have to ask him. Plain vanilla with chocolate chips (talk) 15:58, 25 April 2010 (UTC)

Academia.Wikia is not a peer reviewed journal (their "peer review" process doesn't seem to include any verification of credentials, so cannot be consider to be peer review), so you shouldn't trust any theories posted there. If the theory was likely to have any validity, it would have been published in a real journal. --Tango (talk) 17:54, 25 April 2010 (UTC)

That wikia piece is complete incoherent gibberish. You should ignore it. Wikia is a terrible place to go to find truth and fact. Wikia's policies allow anyone to write anything. I could write an article saying that electricity is carried around by tiny little green men in recycled WalMart shopping bags - and it would be accepted there. Without any kind of control of reliability (such as we have here on Wikipedia) - you simply cannot trust anything that's written there. It truly is a waste of disk space. SteveBaker (talk) 18:11, 25 April 2010 (UTC)

If an object is orbiting below the synchronous rotation orbit height, then it will slow down, and reduce its orbit height until it either enters the atmosphere or collides with the surface, see tidal acceleration. CS Miller (talk) 22:25, 25 April 2010 (UTC)

Someone mentioned that part of the energy drained from the moon is transfered to earth's rotation, speeding it up. That's not correct. The earth is actually slowing down its rotation. Dauto (talk) 15:34, 26 April 2010 (UTC)

Physics-Question regarding Vacuum

What happens when a fan is switched on inside a perfect vacuum? Imagine a glass room that is completely sealed. Perfect vacuum is maintained. A battery is kept in and a fan be connected to it. If we switch it on with any remote controller, will it run or what happens? —Preceding unsigned comment added by Srvnbv (talk • contribs) 06:17, 25 April 2010 (UTC)

It is very easy to answer this question without having to achieve a vacuum. Simply remove the fan blades and run the electric motor. Without a load on the motor it runs at its zero-load speed. Contrary to what you might imagine, the unloaded electric motor doesn't keep accelerating forever. Electric motors have an equilibrium speed determined by their power source and their system of magnetic field and wiring. With no load, the motor will run at its no-load speed. When the motor is loaded, such as with a fan, it runs at a speed somewhat slower than its zero-load speed. Have a look at Synchronous motor. Dolphin (t) 06:25, 25 April 2010 (UTC)

Also, I suspect that the motor may overheat, since it lacks moving air to cool it. Radiation cooling is still possible, as is conduction cooling to the case, but probably wouldn't be sufficient to cool a motor designed to use forced air cooling. StuRat (talk) 07:02, 25 April 2010 (UTC)

If the motor has internal friction (as all "real" motors do) - then the fan would run quite a bit faster than it would in air - but the system would quickly reach an equilibrium at which point all of the electrical energy coming from the battery would go into overcoming friction. If you imagine a totally frictionless motor - then it would either continue to speed up faster and faster so long as you kept a charged battery connected to it...or it would cease to draw power from the battery when it reached a certain maximum speed. (Which of these things would happen depends on the design of the motor). SteveBaker (talk) 07:07, 25 April 2010 (UTC)

There is a limit on how fast the magnetic polarity of the motor's electromagnets can be swapped, which must occur at least twice per revolution (and for most motors, a lot more). This in turn limits the speed of the motor. CS Miller (talk) 09:14, 25 April 2010 (UTC)

If we're talking about the portable battery operated fans that we use in our motor-homes, hobby shacks, etc. then it would be a cheap-an'-cheerful brushed DC motor . It would speed up a bit with no load but the back Electromotive force being generated would limit its maximum speed . As the article Brushed DC electric motor explains As As an unloaded DC motor spins, it generates a backwards-flowing electromotive force that resists the current being applied to the motor. The current through the motor drops as the rotational speed increases, and a free-spinning motor has very little current. It is only when a load is applied to the motor that slows the rotor that the current draw through the motor increases. So it would run a bit cooler without load, but without some gas present to aid cooling, it would get hotter and hotter. The cheap-an'-cheerful bearings are unlikely to be lubricated with vacuum grease (nor employ dry running ceramic ball bearings) so there goes your hope of maintaining a perfect vacuum. The insulating vanish on the windings would start out-gassing with the rising heat too. The plastics would also 'out-gas' and you'd lose perfect vacuum that way too. You would lose vacuum faster than you could pump out the vapours and thus the motor would then start to lose heat. A quick consideration of the tribological effects of the vacuum and one has to ask what happens as the lubrication evaporates and the bearings dry. Without their lubrication (and protective oxide layers) the metal will (or may, depending on different things) start to form many temporary 'micro-welds' creating heat and the micro-weld particles and rough surfaces produced from this, increasing the friction. The carbon brushes will also wear out and fail in a very much sorter time when run in a vacuum. Another phenomena you might witness as the commutator spins: that without the presence of air to quench all those little sparks, a low voltage Corona discharge may lead to speed loss due to shorting. Putting all that together: The fanless fan, would most likely seize first, and if there is no current trip, the windings will (in places) short and glow about 'cherry red' (at which point it will be radiating heat more efficiently), until the conductors sublimate into space/vacuum and an open circuit condition is achieved. If NASA could ignore these problems, it could buy most of its stuff from RadioShack and space exploration would be a lot cheaper. --Aspro (talk) 09:38, 25 April 2010 (UTC)

And why (not) on Earth would NASA want to create a fan capable of functioning in a vacuum ? StuRat (talk) 14:55, 25 April 2010 (UTC)

Say an evil extra terrestrial alien bent on World domination turns up. Do you think we could win with our puny weapons? But it wouldn't matter if this evil little **** hits the fan first :-) --Aspro (talk) 19:37, 25 April 2010 (UTC)

:-) StuRat (talk) 20:50, 25 April 2010 (UTC)

power in watts used when sending a phone text message.

any estimates for this ...sending a text phone message , a tweet, a facbook update? I know the phone powers up as you can hear interference on electrical equipment. —Preceding unsigned comment added by 89.241.1.51 (talk) 11:45, 25 April 2010

According to Mobile phone radiation and health, a GSM phone emits a peak power of 2W, other technologies rather less. The actual power radiated will not depend on the content, but on how accessible the base station is. --ColinFine (talk) 14:15, 25 April 2010 (UTC)

The watts used depends on how far the base station is. But a text message transmits for a very short time - just a chirp, rather than the continuous transmission with voice. Your phone makes these "chirps" anyway, even without a text message, all the time, so that the base station can keep track of it. Ariel. (talk) 08:14, 26 April 2010 (UTC)

I think that the maximum rating set by the FCC and Canada authorities is 1.6W/kg. Normally a phone is less. I don't believe that the radiation emitted by a phone has any effects on the body. --Cheminterest (talk) 20:55, 27 April 2010 (UTC)

What is suprastine

I'm assuming that this was intended to be a separate question, and have made it into a heading. --ColinFine (talk) 14:15, 25 April 2010 (UTC)

I don't know. Wikipedia and Google both say "Do you mean suprastin?". In WP that redirects to Chloropyramine. --ColinFine (talk) 14:15, 25 April 2010 (UTC)

I would agree. Suprastine is a misspelling of suprastin. Ariel. (talk) 08:16, 26 April 2010 (UTC)

Riding a bicycle - reducing energy used per mile

Air resitance increases with the square of speed, but what about rolling resistance? I recall hearing that it decreases with speed, is that correct? My own experience of going on long rides using a conventional bike is that it feels like you are using less energy per mile the faster you go. Is that impression correct please? Is there an ideal speed that balances wind resistance and rolling resitance?

I have always cycled in old jeans and so on. Would I notice any difference in air resistance if I wore the lycra fetish clothes that racing cyclists wear? I probably only cycle at about 10 miles per hour, although I may get fit enough and practiced enough to go faster.

I like going for long rides of say 40 miles through the english countryside. I am not particularly interested in speed, but am very interested in what is best regarding doing long rides without getting very tired on the way home. Thanks 89.243.216.99 (talk) 13:36, 25 April 2010 (UTC)

Hi 89.243, I can't answer your question off the top of my head, but Bicycling Science by D G Wilson is excellent. I think the gist of it is that the most cost-effective way of reducing rolling resistance is making sure your tires are pumped up (and not using knobbly MTB tyres if you're on the road). Bicycling Science also has extensive chapters on energy consumption and air resistance which will be of use to you. Some informed speculation for you: unless you're wearing MC Hammer-style trousers, I don't think switching to lycra will save you much energy: Richard's Bicycle Book (in one of its incarnations at least) says that shaving ones legs will only take about 0.125 seconds off someone's time for a 40km time trial, or there abouts. I would be surprised if the advantage is much more pronounced between jeans and tights. Most people I know find that shorts surpass jeans when it comes to comfort over distance, as there's less to flap about, it's cooler, there's less chafing, your knees are more free to move and if you get wet you don't get stuck in cardboard-like soggy denim! Happy cycling. Brammers (talk) 15:55, 25 April 2010 (UTC)

Thanks, I read parts of the book, but could not see anything about rolling resistance and speed unfortunately. 89.243.216.99 (talk) 17:50, 25 April 2010 (UTC)

Had a rummage for you (would have done it sooner but I left my copy at home and I'm at uni now). This chart shows that although rolling resistance is velocity-dependent, the difference in rolling resistance at two (fairly extreme) speeds decreases sharply with tyre pressure. The data is for car tyres, but I think that since bicycle tyres are pumped to about 5 bar (70 psi) and travel at much slower speeds, the change in rolling resistance with speed would be negligible. Brammers (talk) 10:33, 26 April 2010 (UTC)

One correction - the horsepower required to overcome air resistance increases as the CUBE of the speed - not the square. The power to overcome rolling resistance increases roughly linearly with speed. So from a pure mechanical energy consumption perspective, slow is without doubt better. However, this is a human-powered system - and humans are not simple machines. It takes a certain amount of energy to pump your legs, breathe, maintain body temperature and all sorts of other things that may be completely independent of speed. In that case, getting there quickly has benefit to you - even if you have to apply more power to the bicycle to do it. The trouble is that doing analysis with a human in the loop takes this out of the realm of simple mechanics and into complicated biochemistry stuff...which is the point where I have to shrug and say "I dunno". SteveBaker (talk) 17:46, 25 April 2010 (UTC)

Agreed. But the secret to avoid getting "very tired" on the way home is to eat some carbs while on the bike (or on a break - I'd rather have a nice plate of pasta than the chemical paste used by racers). Once you've run down your glucose levels, the body goes into energy saving mode, and every km hurts. I once rode down from Trento to Lake Garda with a nice backwind, and found out to late that all shops and restaurants were closed. The way back was somewhat less than pleasant... --Stephan Schulz (talk) 20:24, 25 April 2010 (UTC)

Power increases with the cube of speed, but the OP isn't talking about power (which is energy per unit time), but rather energy per unit distance. That cancels one of the speed factors, so turns the cube to a square. Alternative proof: Air resistance, as a force, is proportional to the square of speed (this is well known). Energy=Force x distance (for constant force, which we have), so energy per unit distance is just force. --Tango (talk) 21:20, 25 April 2010 (UTC)

Above ten miles an hour, you're always going to use more energy the faster you go. The most important factor for rolling resistance is your tires -- you want the thinnest, smoothest tires with the highest air pressure. The problem with pushing that to the limit, though, is that with "racing" tires you get a heck of a lot of flats (and keeping them inflated is a bore). The next most important factor is to have good bearings that are well lubricated. The next most important factor, I think, is the frame, and particularly the fork -- a carbon fork is very springy and doesn't absorb much energy from the roughness of the road. Looie496 (talk) 21:56, 25 April 2010 (UTC)

The most important factor is actually getting a well-fitting bike. Bikes are quite efficient machines, so you are bound to lose more energy due to bad ergonomics than due to rolling resistance. And, surprisingly, all other things being equal, a fatter tire has a lower rolling resistance than a slimmer one. Slimmer ones are lighter, have less air resistance, and are faster to accelerate, but at the same pressure, they actually have higher rolling resistance. --Stephan Schulz (talk) 22:20, 25 April 2010 (UTC)

Recumbent bikes have far less air resistance than normal ones, especially the fully enclosed ones. Thus they need less energy to move, or your top speed is far higher. CS Miller (talk) 23:27, 25 April 2010 (UTC)

Would changing from knobbly tires to smooth ones make much difference in the energy required to travel a particular distance please? 78.151.144.28 (talk) 11:30, 26 April 2010 (UTC)

Yes, it makes a noticeable difference, but the pressure in the tires makes even more of a difference (in my experience). Looie496 (talk) 17:21, 26 April 2010 (UTC)

What to do with left over cooking oil?

Is the any way to convert this into electricity (quietly) in a domestic situation? I have a small brick garden shed and a first floor flat with an attic, and it is possible to send a 240 volt cable from shed to my flat. Also, is there any way to power my 36 volt electric bike by the same method? [Trevor Loughlin]80.1.88.25 (talk) 14:28, 25 April 2010 (UTC)

There is a way to use used cooking oil to power an internal combustion generator, basically all you need to do is filter the oil and maybe make a few adjustments to the engine. So, you could power a generator. You would get an odor, but it actually smells good, like fried food. The noise is another problem, as neighbors wouldn't want to hear that at night. You could charge the batteries on the electric bike using such a generator, too. However, you would need large quantities of used cooking oil to make this all worthwhile, which usually means you need to have restaurant(s) willing to donate their oil to the cause. StuRat (talk) 14:48, 25 April 2010 (UTC)

(EC) You can find plenty of homebrew guides for making biodiesel from used/waste vegetable oil online. [10] [11] [12] www.ehow.com/how_5254968_make-biodiesel-out-waste-oil.html www.squidoo.com/Making-Biodiesel-At-Home-Using-Waste-Vegetable-Oil. I presume many diesel generators should work with this either directly or blended with regular diesel. (Generally people do it for cars where the conversions to run on waste vegetable oil are expensive, and damage and problems due to the oil difficult and costly to repair, and the tolerances and conditions required more difficult.) It's a lot of effort if all you have is a small amount of oil from home use however.

A quick search also finds plenty of references to generators that can use the oil directly. E.g. [13] [14] [15] [16].

However most of these look big so I'm guessing cost quite a bit and I somewhat doubt they'll be cost effective unless you want such a big generator for other purposes (e.g. if your house is completely off the grid) particularly if your only supply is from your home, unless you run some sort of home-business where you deep fry stuff and have large amounts of oil. This one for example is targeted to restaurants [17]. (Actually even a say $250 generator is not going to be cost effective but it's less extreme then buying a $5000 generator to use it for 30 seconds.) And getting another supply may not be easy, many restaurants are already selling their waste oil I believe (see Vegetable oil#Waste oil).

You can of course try making or converting a generator yourself [18] [19] but I'm guessing this may be beyond your capabilities.

BTW Vegetable oil fuel may be of interest.

Incidentally, I wouldn't recommend running a mains wire by yourself, especially one that is exposed to the elements.

Nil Einne (talk) 15:15, 25 April 2010 (UTC)

What you need is a diesel generator - these cost between $800 and $1500 (new). You can filter the oil and take measures to remove the water - and use that to power the generator - which in turn can drive electrical appliances - or power the battery charger for your bike. You do need quite a lot of oil to make this worth-while though. If you have just a couple of pints a week - or even a couple of pints per day - then the cost hand hassle of the generator would probably not be worth it. You'll need a diesel generator though - doing this with a regular gasoline powered generator would require converting the oil into gasoline and that requires a lot of complicated chemistry. See: Vegetable oil fuel and Biodiesel SteveBaker (talk) 15:58, 25 April 2010 (UTC)

It's easy to spend more money than your going to get back. The article on Domestic_energy_consumption show more energy is consumed (whether as gas, electric, oil etc.) for heating than for lighting. A Micro combined heat and power unit might be more economical if you are able to do the plumbing yourself. They can use gas (of most types) too, if you run short on oil. You might find Microgeneration a useful article to read for more inspiration. Also, make sure you have your roof fully insulated (there are all sorts of grants available for some of these things) and ask your down-stairs neighbour to turn his heating up in the winter, which will help save on your heating costs.--Aspro (talk) 16:31, 25 April 2010 (UTC)

You could perhaps try a model steam engine with a dynamo or a thermo-electric generator. Burning the oil direct like a candle has a fire risk and may be unhealthy like secondary smoking. 89.243.216.99 (talk) 18:33, 25 April 2010 (UTC)

If you heat with heating oil you might be able to just dump the stuff in your tank. And what do you know, we have an article on that: Bioheat. Ariel. (talk) 08:08, 26 April 2010 (UTC)

Oil won't burn as readily, so it wouldn't be feasible to use it to run an engine, which needs a quick-burning fuel like gasoline to provide the sudden thrust of power.--Cheminterest (talk) 22:24, 26 April 2010 (UTC)

What if I built my own multi-cylinder Stirling Engine to run a generator, with a series of candle-like wicks to heat the bottom of the cylinder, but with the cooking oil instead of wax as the fuel? As for the amount of oil, my own fry-ups already amount to a gallon this month. —Preceding unsigned comment added by 80.1.88.1 (talk) 11:07, 27 April 2010 (UTC)

What!?! You're considering this question for a gallon a month!! OK - I really wish you'd mentioned that at the outset. That's WAY too little to be considering anything fancy. It isn't going to produce enough energy to make it worth-while to build any complicated equipment. Consider that a gallon of diesel fuel (which is rather more energy-dense than cooking oil) costs a couple of dollars (US) - and an equivalent amount of electricity (at 10c per kWh) would run to maybe $4.00 (but bear in mind that your conversion of cooking oil to electricity would be maybe 20% efficient - so you'd maybe get more like $0.80 per gallon in electricity). So using this cooking oil could be saving you maybe $25 a year if you could run your car on it - or maybe $10 a year if you could turn it into electricity somehow. If you consider your personal effort to be worth minimum-wage pay rates then you can't spend much effort on doing this either! Any piece of equipment you might make or buy to use your oil is only likely to run without replacement for (let's be generous) 10 years. So just to break even, you can't spend more than $250 on it (if it's going to make biodiesel) or $100 (if it's going to make electricity) - and it certainly can't take a lot of your time and effort to do it. So sterling engines and generators and things like that are completely out of the question! You're reduced to burning it and using the heat directly - which might require little enough equipment to make it worth-while. If you have an oil fired heating system - then I'd just toss the used cooking oil into the tank...maybe consider filtering it through a coffee filter first to get bits of food out...but that's going to take time and you'd make much more money flipping burgers at McDonalds for one weekend a year than spending an hour a month carefully collecting and filtering your used cooking oil. At the low levels you're doing it at, the heating system wouldn't care about the type of oil. If you have a wood or coal-burning stove - you could certainly pour small amounts of cooking oil onto the fire after every fry-up and get benefit from the oil that way - with no filtering required. Anything else is never going to be cost-effective. SteveBaker (talk) 12:54, 28 April 2010 (UTC)

homoaromaticity in dimedone?

I'm trying to figure out why dimedone is almost as acidic as barbituric acid, compared to other diketones (3 pKa drop). One thing I've been thinking about is homoaromaticity (and the aromaticity-stabilisation for barbituric acid probably is significantly reduced because of the number of heteroatoms and EWGs involved). John Riemann Soong (talk) 17:23, 25 April 2010 (UTC)

Oh the same inquiry especially goes to Meldrum's acid, which would appear to have 6pi electrons. John Riemann Soong (talk) 17:28, 25 April 2010 (UTC)

This is continuation/follwup of Wikipedia:Reference desk/Archives/Science/2009 November 23#acidity of dimedone, barbituric acid and acetylacetone. DMacks (talk) 17:54, 25 April 2010 (UTC)

Anyone? This is a REALLY curious phenomenon. Why is it so ill-studied? John Riemann Soong (talk) 03:01, 26 April 2010 (UTC)

If you draw your ideas out in ChemDraw, I'll happily have a think about them. At the moment it's a bit difficult to see what you're seeing.

Ben (talk) 11:43, 27 April 2010 (UTC)

The anion of Meldrum's acid (deprotonated at the doubly-α position) definitely doesn't look aromatic. When you say "...has 6π electrons" and discussing aromaticity, I assume you are considering primarily the resonance-form of each ester group (oxonium/carbonyl in ring and oxy-anion attached to ring rather than neutral/ether/lone-pair in ring and carbonyl attached to ring)? Regarding barbituric acid, was it ever proven whether the reported thermodynamic pKa is actually for the doubly-α position rather than an amide N-H? That would be a quick'n'easy NMR study. DMacks (talk) 17:19, 27 April 2010 (UTC)

I think it was evident from syntheses involving barbituric acid. You add a little base, some electrophile... boom! I was thinking Meldrum's acid could have weak aromaticity (sort of like aromatic equivalent of paramagnetism) through homoaromaticity. John Riemann Soong (talk) 10:40, 28 April 2010 (UTC)

Hold on, I'm rushing for an assignment right now. I shouldn't even be on RD. I'll get back to you in 3 hours. ;-) John Riemann Soong (talk) 10:42, 28 April 2010 (UTC)

Volcanoes

How do volcanoes make lightning? In the news a few days ago, they showed a picture of that volcano in Iceland with lighting coming out of the ash cloud. Also, the cover of my physics textbook has a picture of Sakurajima with a bunch of lightning coming out of it. --75.34.67.8 (talk) 17:49, 25 April 2010 (UTC)

Somewhat off the top of my head, I believe it is just static electricity generated through friction, similar to 'normal' lighning, though it appears the exact mechanism, as for lightning, is not understood completely. See Dirty thunderstorm, also a mention in the WIkipedia Lightning article. This site might help thunderbolts.info though it seems rather "fringe science" on a quick look (looks like your Sakurajima piccy too). This National Geographic article, Volcanic Lightning Sparked by "Dirty Thunderstorms" and this one New Lightning Type Found Over Volcano? seem more reliable. And this IEEE—Volcanic Lightning article. Try this pic from Chile Chaitin volcano, May 3 2008 Awesome! There is actually a lot on the net, try Googling "volcano lightning cause" for more info.--220.101.28.25 (talk) 19:00, 25 April 2010 (UTC)

Here is a site that has some good technical attempts to explain the phemomena. geology.com --220.101.28.25 (talk) 19:32, 25 April 2010 (UTC)

The ash particles collide and separate into positive and negative charges, similar to the collisions in cumulonimbus clouds involving ice particles and supercooled water droplets. ~AH1^(TCU) 23:17, 28 April 2010 (UTC)

Is this correct?

An atom is moving in the +x direction and a laser beam is headed in the -x direction. The atom absorbs a photon and emits it in the -x direction. What is the photon's energy?

Answer: I think that in the atom's reference frame, the photon's energy is hf*sqrt(1+v/c)/sqrt(1-v/c) before absorption. After emission, the photon's energy is still hf*sqrt(1+v/c)/sqrt(1-v/c) in the atom's reference frame. However, blueshifting this into the lab's frame gives hf*(1+v/c)(1-v/c) = hf*(1+2v/c). Is this correct? --99.237.234.104 (talk) 18:01, 25 April 2010 (UTC)

This is a very tricky question, but I think the energy does not change. Are we assuming the photon is emitted with the same frequency that was absorbed (relative to the atom)? The light is blueshifted relative to the atom when absorbed. The photon is then redshifted relative to the atom when emitted and ends up back where it started. The atom basically did nothing - it picked up the photon, and then let it go. Perhaps the assumption is that any energy absorbed is then emitted? That gives the same result. Are you wondering if the atom can give the photon energy in some way? From the atoms point of view, it's not moving, and has no energy to give the photon. The only way the system as a whole can transfer energy from the atom to the photon, would be to slow down the atom, and speed up (well, "mass up") the photon, but conservation of momentum does not allow that, because a heavier photon would give the atom a larger kick - but then the atom is actually moving faster, not slower. Ariel. (talk) 07:48, 26 April 2010 (UTC)

(OP here) What do you mean by "the photon is then redshifted relative to the atom when emitted"? Assuming that the atom's momentum is much larger than the photon's, the photon should have the same frequency relative to the atom as it did before absorption: in other words, hf*sqrt(1+v/c)/sqrt(1-v/c). However, in the lab frame, moving at speed v relative to the atom, the emitted photon should appear blueshifted: E=hf*sqrt(1+v/c)/sqrt(1-v/c) * sqrt(1+v/c)/(sqrt(1-v/c). This is approximately hf(1+2v/c). I think this should be the answer, but I have an answer key that contradicts this, saying that E=hf if only terms first-order in v are considered. --206.130.23.2 (talk) 16:25, 26 April 2010 (UTC)

You are right, I meant observer not atom. Let me start over. The observer is located at -x. He sees the photon emitted, with no shift. The atom sees the photon with a blueshift, and absorbs it. The atom then emits the same (higher) frequency it absorbed. To the atom this emitted photon in not shifted, but it is at a higher frequency that it started. To the observer the emitted photon is redshifted, because the emitter (the atom) is moving away from the observer. The end result is no change. Ariel. (talk) 20:47, 26 April 2010 (UTC)

If you make your frame of reference the atom, then the atom absorbs and emits the same, unchanged (from it's point of view) frequency. How do you know the atom did not change speed? Because it absorbed momentum by catching the photon, it then lost exactly the same momentum be emitting it. So it could not have changed in speed. No (net) change in speed for the atom means the photon's energy could not have changed. Ariel. (talk) 21:14, 26 April 2010 (UTC)

If you choose the +x observer instead, then you might think that when the photon is emitted from the atom it's blueshifted - since it's heading toward you. But actually, think about it in a different way. The photon is emitted with full speed, but the motion of the atom is away from the direction of the photon, meaning that the photon now is slower (since the motion of the atom robbed it of some speed). Photons are not actually slower, instead it red shifts. This also is correct if the observer is at -x. It's actually correct for all observers. Because the motion of the photon, and atom are opposites, it makes no difference where the observer sits. Ariel. (talk) 21:14, 26 April 2010 (UTC)

That makes perfect sense. I don't know what I was thinking; I was just having another mental block. Thanks. --99.237.234.104 (talk) 21:53, 26 April 2010 (UTC)

Small windmill for electricity

I saw what looked like a home-made windmill recently, about a meter in diameter. It had blades all the way around, like the old fashioned things used on farms for pumping water, so it was not just a propeller. It was turning what may have been a bicycle dynamo. Has anyone any idea how much average power it would provide under average conditions? Thanks 89.243.216.99 (talk) 18:01, 25 April 2010 (UTC)

I don't think a one meter windmill is going to do you much good. A carefully constructed (but homemade) three meter windmill on at least a 20 meter pole (to get it above roof and tree height) will produce about 1kW.hr per day in the right location. Most homes consume 10 to 20 kW.hr per day...so don't get too excited about living off the grid! You can basically use the thing to drive a car alternator and thereby charge a bank of car batteries - and then use an inverter to turn that into mains A/C voltage so you can run things from it. If you have the tools and the DIY expertise, you could probably knock one up for a couple of hundred bucks. People who spent a lot of money (like maybe $15,000) on small, commercially made, windmills have had very mixed results. Some find that they perform no better than the home-built contraptions, on occasion not producing enough energy to run their own electronic control modules! Others seem to be getting maybe 50% of their household power from them. But that's not gonna be remotely cost-effective. If your electricity bill is (let's say) $200 a month - and the windmill is saving half of that - then it's going to take 150 months to pay for itself (well, actually more than that because you could have invested that $15,000 and made interest from it). Will the windmill actually last the 15 to 20 years it takes to pay for itself? I very much doubt it. The trouble with wind power is that it's horribly bad at small-scale installations. If you could get a few hundred neighbors to invest in a one megawatt windmill that you'd all share, then probably it would be worthwhile - but at the scale you can manage by yourself, I don't think windmills are the answer. Solar panels offer much more opportunity for cost-effectiveness - but only if you live somewhere with year-round sunshine. From every angle I've investigated, by far the most cost-effective thing you can do is to conserve energy with better home insulation, energy-efficient appliances and that kind of thing. SteveBaker (talk) 19:26, 25 April 2010 (UTC)

Depends. In the UK the grid companies are now obliged to buy the power back from you at three times the grid price, even if you use the power yourself (ie they have to sell what you use back to you for a lot less than they just paid you for it). They pay about 30p a unit whereas cheap rate night power in the UK is about 5p a unit and peak rate about 10p a unit. Reasonably site gives about 8 years payback on that basis. The societical sense is a bit more arguable but the political argument is that this is the only way to get enough units built to get the cost down. --BozMo talk 19:46, 25 April 2010 (UTC)

That seems ripe for someone to find a cheap way to draw and store as much 5p power as possible and sell it all back for 30p. Dragons flight (talk) 22:14, 25 April 2010 (UTC)

Hmmm... now how does one go about building a pumped storage hydroelectric generator, I'm sure no-one will notice if I flood the abandoned quarry at the top of the hill. I'm going to be rich! 131.111.185.69 (talk) 22:33, 25 April 2010 (UTC)

30p a unit? I wonder if that makes buying a "proper" windmill a good investment.

I have always been intrigued with the idea of having a twelve volt wiring system in a house in addition to the 220v (or 110v) one, and using the fittings designed for caravans, such as 12v lighting, 12v fridges, and 12v TVs. Then you might be able to avoid using mains electricity completely. Since its only 12v, it should be safe for competant non-electricians to do the wiring. Even very inefficient home-made windmills that cost very little could be worth having, and you could have several. Energy-saving lightbulbs only use a few watts, so perhaps they could be run although there would be the problem of stepping up the voltage.

Sometimes old houses have wells in the garden, so I wonder how much money would be saved by going completely off-grid in the Uk or elsewhere? 78.151.144.28 (talk) 09:39, 26 April 2010 (UTC)

You would need some seriously fat wires to run things at 12 volts. You would not save any money at all going off grid - you would spend much more. If people could save money going off grid everyone would be doing it already. Also, if you wire an entire house with 12 volts, you would have a ton of amps going through those wires - any mistake in the wiring and you would have a fire. So, going 12 volts will not let a non-electrician do the wiring. You might not electrocute yourself, but that's not the only hazard available with electricity. Ariel. (talk) 09:54, 26 April 2010 (UTC)

I'm doubtful you would get a "ton of amps" off a 12v car-battery set up. 78.151.144.28 (talk) 10:09, 26 April 2010 (UTC)

Car batteries (lead-acid batteries) have a very low internal resistance and they can pump out hundreds of amps in the case of shorts (which is useful for starter motors, but not for house wiring). --antilived^{T | C | G} 11:24, 26 April 2010 (UTC)

People have been electrocuted and died with as little as 3 volts - and you can easily take a 1,000,000 volt shock from an electrostatic discharge with no ill effects. It's not the voltage that kills you! You can most certainly be killed with the current from a car battery - and you can also start fires that way. SteveBaker (talk) 12:22, 26 April 2010 (UTC)

Best solution for home generation if you are already on or are close to the grid is an inverter so you can use ordinary AC appliances. But you could have one DC socket straight from it, for example to charge an electric car or perhaps to heat water for storage. Itsmejudith (talk) 17:09, 26 April 2010 (UTC)

Mass wrapping around a rod

Mass m is attached to a post of Radius R by a string. Initially it is at a distance r from the center of the post and is moving tangentially with speed v₀, and as the mass moves the string wraps around the rod. What is the final speed of the mass?

That angular momentum is not conserved I understand. But according to: http://physics141.uchicago.edu/2002/hw6.pdf (middle of second page) the total energy is conserved. I don't see why the tension wouldn't do any work. —Preceding unsigned comment added by 173.179.59.66 (talk) 18:05, 25 April 2010 (UTC)

It depends whether how much you your professor wants to simplify, and assume that the string is perfect/ideal/does not stretch or deform. In that case, the string length is exactly constant, and the only change in radius is due to the string wrapping around the pole. If you want to add complexity, you can add two parameters to the string: elastic stretching, which you can model with Hooke's law; and inelastic deformation, which you should model based on an empirical estimate. In any case, angular momentum is always conserved; it is just that you are only considering the rod/string in this problem; those do not constitute a closed system. The angular momentum is transferred outside of that system, to the person holding the rod (or to the Earth, if the rod is planted in the ground); and can be ignored for your considerations.

To estimate a spring constant for the elastic stretching of the string, I would suggest treating the string as an extremely stiff spring (say, thousands of newtons per meter for the spring constant). Of course, this value depends on the type of fiber the string is made of. For the inelastic deformation, we are modeling how much the string permanently degrades (fibres unwinding and changing microscopic position and shape). This is very hard to model, but easy to estimate from measurements. Work is done on the string to deform those fibres; some energy goes into heat, and some goes into the process of changing the material properties of the fibre. How much energy is used will depend on the fibre properties.

You can use the elastic model to simulate dynamics - but you should use a Lagrangian mechanics formulation, because you have multiple variables in an arbitrary coordinate-system (radius, height above ground, and string stretching displacement); each coordinate is described with its own set of kinetic and potential energy terms. Adding the inelastic term will be sort of like adding a "frictional loss" term; it may be best to simply approximate that with an "engineering fudge factor" numerical constant, so that you can match the modeled velocity and wind-up time to experimentally observed times. This is the "work" that is being done by the tension (really, only the inelastic deformation constitutes "work" / energy loss - the elastic stretching will cause a dynamic oscillation, but the net work done by that component is zero). (Well, if you want to be very complicated, you can use a more sophisticated spring law than Hooke's Law; then you could model separate dynamic losses for the oscillation that are distinct from the inelastic deformation; but this adds parameters that you need to experimentally measure, and it is not clear that the oscillatory loss would be caused by a different physical effect than the inelastic deformation anyway - so modeling it separately is dubious).

In any case, you can see that the added complexity may require messier math, more parameters, and (possibly) require a formulation of physics, Lagrangian mechanics, that has not been introduced to you yet (though you could try to do this with strict Newtonian mechanics, the algebra and the integrals will be very ugly and hard). Furthermore, it is reasonable to assume that the string stretching is "small" for most real problems (aside from rubber bungees). So, it may be easier to simplify than to include this added terms. Nimur (talk) 18:37, 25 April 2010 (UTC)

I'm assuming the string is ideal (and based on your answer, I'm glad I am). It's just that...as the mass starts falling in, isn't the tension applying a force which isn't perpendicular to the velocity. If it's pulling in the mass, it seems to me that it must... 173.179.59.66 (talk) 20:52, 25 April 2010 (UTC)

Actually I see it now, thanks. But what force applies the torque??? Is it the contact force between the rope and the string? Because then R and F would be parallel, and so I would expect no torque.173.179.59.66 (talk) 20:59, 25 April 2010 (UTC)

Note that the string pulls on the mass at any given time in the direction of the edge of the pole where the string touches the pole. As the string is winding itself around the pole, that point is changing, but what is important to realize is that the direction of the force is always some point on the edge of the pole and not the center of the pole.

So, you see that the torque relative to the instanteneous contact point of the string on the pole is always zero, but then the torque relative to the center of the pole is not zero. Count Iblis (talk) 21:54, 25 April 2010 (UTC)

Any chance of getting a reactionless drive out of this method?[Trevor Loughlin]80.1.88.1 (talk) 10:59, 27 April 2010 (UTC)

Detonations and the like

I should really know this but if I filled a small plastic fizzy drinks bottle with a liquid and the liquid blew off both ends (classic flower petal each way) does that definitely mean the liquid detonated? I was trying to blow the bottle up (essentially with compressed gas) but I was a bit surprised to see both ends go because I did not think the mixture was detonable. Presumably the drinks bottle are designed with a failure mode and I daresay it got hot but I cannot see why unless the pressure rose significantly on a timescale similar to the acoustic time between the ends one end shouldn't inevitably go first... what am I missing? --BozMo talk 19:41, 25 April 2010 (UTC)

If you slowly raise the pressure, you are likely to get a single point of failure, that's true, but it is still possible to get multiple, simultaneous points of failure, as you also get in an explosion. StuRat (talk) 19:47, 25 April 2010 (UTC)

Hmm. You said the bottle was full of liquid, but then you said you were trying to blow it up essentially with compressed gas. Please clarify. Looie496 (talk) 21:40, 25 April 2010 (UTC)

What did you fill it with? --Dr Dima (talk) 22:39, 25 April 2010 (UTC)

When we work with explosives, we use terminology very carefully (just like everything else). Usually we use detonation to describe the type of exothermic chemical reaction which produces supersonic gas - a shock front or shock wave. It is compared to deflagration, the type of exothermic chemical reaction that produces subsonic gas products. In your case you are not actually creating a chemical reaction at all - you are simply using a pressurized gas to expand explosively - so what you really have is a BLEVE - neither detonation nor deflagration - just rapidly expanding liquid and exploding vapor. Because you are using fizzy soda pop, your BLEVE gas is carbon dioxide, which is actually not ever in liquid state (only dissolved in water) - so the quantity of energy you release is small by comparison (the CO2 never boiled from liquid state, it just came out of solution). Also, carbon dioxide does not burn (in fact, it is a common fire extinguisher ingredient). So, your BLEVE is actually just a "EVE" - expanding vapor explosion. Do not try to create a BLEVE with other gases - some will rapidly combust on contact with atmospheric oxygen if the pressure and shock front conditions are right, and can not be easily extinguished. Nimur (talk) 00:23, 26 April 2010 (UTC)

(nighttime in the UK intervened) I was using the words carefully I thought and was asking about detonation. The mixture I was using was finely powdered mixed citric acid and KMnO4 with a dribble of water. I got banned from Chemistry as a school child for this mixture because of its delightful property of doing nothing for nearly a minute before eruptively evolving CO2 furiously and smothering everything with boiling MnO2 which is very destructive to teacher's clothing, skin etc (sigh, happy memories). But in general it just got hot and evolved gas. With the right proportions (no clues) sealed in a pop bottle it turns out it blows both ends of simultaneously. I am surprised if it is detonable but perhaps with the heat and pressure of the bottle it can be? --BozMo talk 06:25, 26 April 2010 (UTC)

FWIW though I think StuRat is probably right it was probably a coincident failure of the ends. --BozMo talk 10:42, 26 April 2010 (UTC)

I'm no expert, but I am pretty sure that permanganate-acid reactions do not create a shock-front (it is a very slow reaction as you are already aware). All you have done is over-pressure your container, which is not a detonation, properly. High explosive detonates even if uncontained; that is what makes them "high" (dangerous) and subject to legal and logistics controls. If you performed the same reaction without a soda-pop bottle, your reaction would fizz a bunch, but there would be no "exploding." Nimur (talk) 16:14, 26 April 2010 (UTC)

Again, just for the sake of droning, do not play with dangerous chemicals unless you know what you are doing. I mean, we're just random people on the internet and we can't stop you from doing whatever you are doing - but if you were thrown out of chemistry class, it's probably because you did something unsafe. Energetic materials can be a lot of fun, but you need to follow proper, cautious procedures - and the only way to do so is to learn from experts. At the high-school level, those experts are your chemistry and physics teachers. If you satisfy all of their (not so difficult) intellectual and safety criteria, you can move on up to playing with more interesting things - but it doesn't matter what kind of rocket scientist, construction engineer, or military demolition expert you are - people who work with energetic materials do not tolerate recklessness. (This includes splashing even harmless chemicals on lab benches. It sets a bad precedent). Nimur (talk) 16:25, 26 April 2010 (UTC)

In so far as this is directed at me, this is a reasonable remark but a little out of context. A couple of decades ago I spent a few years in industrial research blowing up some fairly major bits of kit (three people working for me had "fit persons" licences for high explosives and we had fun). I am now more interested in bucket chemistry to do with my own kids which is why I would rather avoid possible detonations. Mn2O7 of course detonates and permangate with strong acid is therefore worth avoiding. But as you I am reasonably sure that unlike nitrates etc it is otherwise relatively ok. I made fireworks as a kid myself and am kind of looking for something safer. --BozMo talk 16:37, 26 April 2010 (UTC)

It seems at least theoretically feasible to get an explosion (if not detonation) that way. If the reaction is slow enough that a lot of CO2 dissolves into the liquid, then once the pressure is released by one end of the bottle blowing, the CO2 will start to come out of solution, further raising the pressure. Another factor is that when one end blows off, conservation of momentum will cause the liquid inside to be hurled in the other direction. If the bottle was being held in place by something (not specified here), it seems like this could easily be enough force to blow out the other end. Looie496 (talk) 17:19, 26 April 2010 (UTC)

It is not a permanganate-acid reaction. Any reducible carbon compound (most of them are) such as sugar can be used, but some are better than others. The MnO2 is a staining solid. You could react permanganate with glycerin to produce gas, or just react baking soda with 10M hydrochloric acid. It will probably burst the bottle if you can find a way to detonate it once the lid is closed. It may be considered deflagrating though. --Cheminterest (talk) 22:21, 26 April 2010 (UTC)

This is the reaction that was going on:

12 KMnO₄ + 2 C₆H₈O₇ → 12 CO₂ + 2 H₂O + 12 KOH --Cheminterest (talk) 22:29, 26 April 2010 (UTC)

April 26

Stingray question

Do stingrays make a sound. I have looked extensively and have not found anything about stingrays making noises of any kind. thank you for considering this question. :)174.97.235.163 (talk) 00:45, 26 April 2010 (UTC)pat

Somehow I doubt it, as most fish don't (at least nothing we can hear). StuRat (talk) 00:51, 26 April 2010 (UTC)

Did you have something in mind, particular to a stingray? I used to have an electric catfish as a pet and it made lots of noise at night while electrocuting the minnows. Perhaps a stingray makes a sound (in the most general sense of 'making a sound') when it thrashes it's stinger into predator/prey...I mean, more so than a goldfish, let's say. DRosenbach ^{(Talk | Contribs)} 01:27, 26 April 2010 (UTC)

In this youtube video you can hear a clicking noise and you see a stingray: Octopus Attack - Fuertaventura 2009. Cacycle (talk) 06:53, 26 April 2010 (UTC)

Of course every type of fish makes sound as a result of water sliding over its body. When it comes to other types of sound, I wasn't able to find any reports in a quick Google Scholar search. There are apparently certain types of fish that "vocalize" by vibrating their swim bladders, but elasmobranches (sharks and rays) don't seem to be among them as far as I can tell. Looie496 (talk) 17:10, 26 April 2010 (UTC)

is there an exit valve? what about on the scuba fireman where? and on oxygen tanks in a ambulance or hospital?

Firemens SCBA apparatus.

where does the exhaled air go —Preceding unsigned comment added by Tom12350 (talk • contribs) 01:36, 26 April 2010

This question was answered above. Look for the section about 2-3 days ago labeled "scuba". --Jayron32 02:40, 26 April 2010 (UTC)

no they answered about scuba not scuba fireman where and on oxygen tanks in a ambulance —Preceding unsigned comment added by Tom12350 (talk • contribs) 05:21, 26 April 2010 (UTC)

In a hospital or ambulance oxygen is normally given in two ways. In an emergency where a patient has collapsed and respiration is administered with a mask and pump bag the pump bag apparatus has an exit valve. When oxygen is given over a longer period with a light mask or little tubes at the entrance to the nose then the excess oxygen just dissipates into the atmosphere as there is no closed circuit to contain it. I suspect that the equipment used by firemen is similar in design principle to an underwater scuba, a closed circuit with a one-way exhaust valve. Richard Avery (talk) 07:21, 26 April 2010 (UTC)

On the side of the mask. See if this article helps: Firemens SCBA apparatus and and Oxygen maskAnd see diagram on the right --Aspro (talk) 07:23, 26 April 2010 (UTC)

And again, to be pedantic - the firemans' apparatus is an "SCBA" because the 'U' in "SCUBA" stands for "Underwater". SteveBaker (talk) 12:17, 26 April 2010 (UTC)

you say "light mask or little tubes at the entrance to the nose then the excess oxygen just dissipates into the atmosphere as there is no closed circuit to contain it."

but hows that because isint the mask tight? like is this pic  ?

http://thumbs.dreamstime.com/thumb_54/1145221626xhnGC8.jpg

or this

http://fransonchiropractic.files.wordpress.com/2009/04/oxygen20mask.jpg

or this

http://www.watersafety.com/rescue-and-response-equipment/images/4225023.jpg —Preceding unsigned comment added by Tom12350 (talk • contribs) 22:07, 26 April 2010 (UTC)

milk

can buffered solutions like milk be used to naturalize acids or will it not work cause its buffered. —Preceding unsigned comment added by Tom12350 (talk • contribs) 01:55, 26 April 2010 (UTC)

So long as you don't exceed the buffer capacity of the milk, yes, it can be used to neutralize acid. The property of a buffer is that it works to neutralize BOTH acid and base (more properly, a buffer is something that maintains a constant pH with the addition of either acids or bases). See buffer for more info. --Jayron32 02:39, 26 April 2010 (UTC)

what is the "the buffer capacity of the milk" —Preceding unsigned comment added by Tom12350 (talk • contribs) 05:20, 26 April 2010 (UTC)

Please start signing your posts by using four tildes like this: ~~~~. Please read the Buffer solution article for more info. A buffer is basically an acid and its conjugate base. That is, it consists of a pair of compounds that differ by a hydrogen ion, for example a solution that contained both acetic acid, HC₂H₃O₂, and the acetate anion, C₂H₃O₂^1- would be a buffer. It works because, by adding either acid or base, the conjugate acid/base pair works by reacting with either an added acid OR an added base, and so neutralizes either. Also, because the system is a dynamic equilibrium, the system obeys Le Chatelier's principle such that it resists all changes to return to its initial state. The buffer capacity merely means that the buffer only exists so long as both parts of the conjugate acid/base pair exist in the solution. If you add so much acid that you use up the base part of the buffer, then you no longer have a buffer, and you have exceeded the buffer capacity. --Jayron32 05:27, 26 April 2010 (UTC)

Additionally, you should probably also read up on Brønsted–Lowry acid-base theory which is the basis for understanding how buffers work. --Jayron32 05:30, 26 April 2010 (UTC)

i already read those. what is the "the buffer capacity of the milk" —Preceding unsigned comment added by Tom12350 (talk • contribs) 06:35, 26 April 2010 (UTC)

I just explained that. A buffer consists of an acid and its conjugate base mixed together in water. If you add too much additional acid, you will consume all of the base, and thus destroy the buffer. --Jayron32 12:02, 26 April 2010 (UTC)

I'm not sure but perhaps the OP wants to know what the buffer capacity of milk actually is, not what it means. Having said that I wonder whether the OP actually properly understands buffer capacity or thinks it's a simple value that tells you precisely how 'powerful' a buffer is. In any case, the buffer capacity would vary depending on the type of milk I presume. Edit: These should provide a basic overview on what the buffer capacity of milk actually is [20] [21] [22]. Also [23] if you can find it. Nil Einne (talk) 12:32, 26 April 2010 (UTC)

With a complex solution like milk, it would be quite impossible to calculate directly. You could certainly do an experiment to find the value for yourself. You would need to titrate the milk dropwise with a strong acid, and track the effect of the added acid on the milk's pH. Then you would need to do the same experiment, but with fresh milk and a strong base. The resulting graphs should tell you roughly how much acid or base you can add before exceeding the buffering capacity of the milk. (after edit conflict) It looks like Nil Einne found the results of some of those experiments above. --Jayron32 12:46, 26 April 2010 (UTC)

Yes [24] is probably the most useful but needs a subscription. I have a tendency to reply and then search so often add my results after. I guess I should stop WP:AGF that the OP actually did a simple search before asking the question :-P Nil Einne (talk) 13:18, 26 April 2010 (UTC)

i dont need a exact value just a estimate. anyone know? —Preceding unsigned comment added by Tom12350 (talk • contribs) 21:56, 26 April 2010 (UTC)

From the article that requires a subscription: At pH7, the buffering capacity (dB/dpH) looks like it's around 0.02. It changes a lot depending on pH - eg. at pH 6 it's closer to 0.03. Aaadddaaammm (talk) 13:43, 27 April 2010 (UTC)

hats that mean? how strong a acid can it be used on —Preceding unsigned comment added by Tom12350 (talk • contribs) 21:15, 27 April 2010 (UTC)

"Used on" to do what? Maybe if you rephrase the original question, with more specifics about what you're actually trying to do we could help more. Aaadddaaammm (talk) 10:36, 28 April 2010 (UTC)

Source of pneumonia in bedridden elderly?

From what sources do the elderly often contract pneumonia? I'm thinking of bedridden individuals in nursing homes who are not likely to be able to spread it to other individuals in similar conditions, and who (because they're in the nursing home, not in hospital) by definition can't get hospital-acquired pneumonia. I don't see anything in our article that discusses the question, since it seems unlikely to me that the large number of elderly people who die from it are all infected with fungi, parasites, pneumonia-causing bacteria, or pneumonia-causing viruses when those around them don't have any of these problems. Nyttend (talk) 02:29, 26 April 2010 (UTC)

I think part of the problem is a lack of ability to clear the lungs while bedridden. Thus, any standard cold or flu can cause fluid accumulation in the lungs, which can suffocate the bedridden person. I am pretty sure that is the impression I get from the issue. I could be wrong though. --Jayron32 03:50, 26 April 2010 (UTC)

Also see the short article Aspiration pneumonia, which describes any non-infectious pneumonia caused by the inhalation of material, including one's own saliva and mucus. My guess is that this could explain many of these elderly, bedridden pneumonia cases. There's also Idiopathic interstitial pneumonia, "Idiopathic" being doctor speak for "We haven't the faintest clue what is causing this". --Jayron32 05:37, 26 April 2010 (UTC)

Hubble's "visible spectrum" image of the Carina nebula

I'm wondering what the moon, or the earth would look like if an image were compiled in the same way that the Carina nebula was. (wavelengths detailed here). Is it relatively simple to attempt this? 219.102.220.42 (talk) 02:30, 26 April 2010 (UTC)

If you could obtain the raw images taken at those wavelengths which record those spectral colours then yes. One could easily do the next stage of combining and balancing them in to one image. This image manipulation could be done with GIMP (which I have noticed the Jet Propulsion Laboratories in Pasadena have used) or Photoshop, etc. This web page explains in plain language, the technical bits about what needs to be recorded .Cameras and H-a Emission Nebulas. And what would Earth and the Moon look like? Well I sure: if people were able to mentally work that out, there would be no point using these imaging technique in the first place. However, the United States Geological Survey Spectroscopy Lab has some images of Earth. And the Jet Pro Lab has some images of the moon. [25] As always, Wikipedia has some articles:Imaging spectroscopy, Moon Mineralogy Mapper.--Aspro (talk) 08:00, 26 April 2010 (UTC)

Which elements do you want to use to make your images of the moon/earth? The picture basically shows areas where one element or another are more concentrated. If you use elements in the earths atmosphere, you'll have a white circle and nothing more, since those are basically perfectly mixed. If you choose elements on the ground, you'll see colors showing you where the elements you chose are more/less concentrated. Ariel. (talk) 08:05, 26 April 2010 (UTC)

Those nebula are emission nebulas wich emit light at particular wavelengths in a line spectrum. The earth and moon reflect are much more continuous spectrum, and so are not so easy to establish elemental composition by transition lines. In visible light what you see will be a good clue, eg yellow iron oxide, green chlorophyll. Graeme Bartlett (talk) 09:10, 26 April 2010 (UTC)

Dibenzodiazepines follow-up

I notice all the compounds listed in Category:Dibenzodiazepines are antiaromatic. So it must not be a coincidence. I guess the antiaromaticity destabilisation must not be very large? I'm curious about the relationship between conformation and agonism / antagonism of the target receptors. AFAIK lysergic acid compounds are planar ... right? Or are they? I notice some resonance structures are antiaromatic in LSD too. John Riemann Soong (talk) 03:24, 26 April 2010 (UTC)

What counts most for receptor binding are shape and charge. Antiaromaticity per se does not have a direct effect on binding (whereas aromatic rings allow for specific interactions such as pi stacking). Cacycle (talk) 06:49, 26 April 2010 (UTC)

Regarding LSD, the indole part is definitely aromatic. If you're considering "all the resonance possibilities" (treating them as distinct structures that contribute to the overall "real" average structure), you can mostly disregard antiaromatic ones if there are others that are aromatic. If you have an alkene or lone-pair or something that "maybe could resonate into a ring, but that would make antiaromaticity", that piece of the structure probably does not do that, and thus acts like an independent functional group. DMacks (talk) 08:47, 26 April 2010 (UTC)

Thanks... I was wondering because it doesn't appear to be a factor in LSD, whereas I can envision resonance structures in clozapine that would make it aromatic, not antiaromatic, e.g. by simply drawing benzene a different way. You know what I mean? John Riemann Soong (talk) 20:11, 26 April 2010 (UTC)

If you're interested in stereoelectronics in medicinal chemistry, you might like to get a good book on the topic, like this one, or search the literature. I did a quick Google search for "stereoelectronic QSAR" and found several interesting-looking articles, including Dynamic QSAR: A New Search for Active Conformations and Significant Stereoelectronic Indices.

Further Wikipedia articles of interest:

• Electronic effect
• Pharmacophore
• Quantitative structure-activity relationships

Books you could borrow from a library:

• A. J. Kirby (1996) Stereoelectronic Effects (Oxford Chemistry Primers)

Ben (talk) 19:16, 26 April 2010 (UTC)

Life expectancy of nuclear power plants.

What is the average life expectancy of a nuclear generating station? How do plants built in the US differ from ones overseas in terms of longevity? ataricom (talk) 05:00, 26 April 2010 (UTC)

According to Nuclear power#Economics, a reactor can last as long as 40-60 years. Dismas|^(talk) 07:27, 26 April 2010 (UTC)

Not if they are destroyed by sea level rise. ~AH1^(TCU) 23:14, 28 April 2010 (UTC)

Ant for ID

ID and extermination advice?

Hello! I must catch 10 of this type of ant everyday in my house. Is this a fire ant or a carpenter ant? What is the best way of getting rid of them, sort of calling an exterminator as a last resort? Could they be living outside my house in nests or in my house's foundation? I've found winged ants in my house, as well, which, as I understand, are the ones who help reproduce. Is that a bad sign? Any advice appreciated. Thanks.--el Aprel (^facta-_facienda) 08:17, 26 April 2010 (UTC)

If this was Australia I would say you had a sugar ant. Fill up all the holes they may come in through. You can spray poison around, but may poison you and may not last either. Graeme Bartlett (talk) 09:04, 26 April 2010 (UTC)

I'm not sure, but it does look like Camponotus sayi, red carpenter ant, to me. Red link for the red ant - isn't it ironic? Not really a harmful critter, there are much worse than it; but it can build nests (colonies) in wooden structures which is not something homeowners generally like. This article gives suggestions on how to deal with them, if that ant is really what I think it is. As I said, I am not sure. --Dr Dima (talk) 10:07, 26 April 2010 (UTC)

There are some more photos of Sayi on Wiki Commons [26]--Aspro (talk) 12:50, 26 April 2010 (UTC)

Thanks! Forgot to mention I live in Florida. Are Camponotus sayi ants common here?--el Aprel (^facta-_facienda) 19:30, 26 April 2010 (UTC)

No. Unless of course, their there on vacation. 'Florida' has however, narrowed it down a bit. Here's our next suggestion. Go to | Florida Ants. On the right hand column, under the heading 'Tools” is a link entitled - Florida ants in Google Earth. This link then gives you a map of which ants occur in which localities. I don't know how accurate it is but it looks impressive. In the mean time, see if they like water with some sugar added, because then use could try using borax.--Aspro (talk) 20:43, 26 April 2010 (UTC)

Did you mean to type "THEY'RE there on vacation"? Cuddlyable3 (talk) 23:45, 26 April 2010 (UTC)

• Mix a little jam with borax and smear it inside saucers, jar lids or the like, and leave them near where you find the ants. Replace daily. The ants come and eat the jam, and the borax poisons them. You get borax from places which sell old-fashioned cleaning materials (it's jolly useful stuff). DuncanHill (talk) 22:02, 26 April 2010 (UTC)

You could also get borax (sodium tetraborate decahydrate) at the grocery store. It is normally sold there for laundry freshening and a host of other uses. Are you sure you aren't talking about boric acid though? --Cheminterest (talk) 22:16, 26 April 2010 (UTC)

Not many grocers here sell borax anymore. I get mine at Boots the Chemists, and some old-fashioned hardware shops have it. Yes, I'm sure I mean borax. DuncanHill (talk) 22:32, 26 April 2010 (UTC)

I had a look at the "Florida ants" website, and think this is a Camponotus decipiens ant. I will try the borax solution. I remember treating another ant species, fire ants, with a powder poison that tricked worker ants to take back to their queen as food and exterminate the colony by killing the queen. Is there any poison like this for these carpenter ants? My guess is the borax solution only kills the ants that forage for it.--el Aprel (^facta-_facienda) 22:53, 26 April 2010 (UTC)

I think the powders of which you speak will contain borax or boracic acid. I've used the sweet borax mixture before, and after a few days what had been a steady stream of ants had reduced dramatically. DuncanHill (talk) 23:15, 26 April 2010 (UTC)

You will know if you have made the solution too strong because you will see dead ants. You want them to live long enough to get back and feed the others. The advantage of using borax has been already mention – its useful for so many other things and easier to buy.--Aspro (talk) 23:30, 26 April 2010 (UTC)

It you really want to see dead ants, you can leave out watermelon slices soaked in turpentine. They are highly attracted to the sugar, but the turpentine dissolves their exoskeleton. In the morning, you end up with a lot of black smudges, which clearly identifies the path they were using to get back and forth between the watermelon and their nest. -- kainaw™ 00:41, 28 April 2010 (UTC)

Mold

Is mold killed by pouring boiling water on it? 87.108.22.140 (talk) 09:02, 26 April 2010 (UTC)

Yes if you can heat it to close to 100 degrees. Eucaryotes are not good at surviving high temperatures. You may be left with a stain however. Graeme Bartlett (talk) 09:06, 26 April 2010 (UTC)

Thank you! I knew I could rely on Wikipedia! 87.108.22.140 (talk) 09:10, 26 April 2010 (UTC)

Also remember that mold is not just the blue stuff on the surface, but has hyphae in the material ti is decaying, you have to heat that too. And also mold may make poison in food, so don't just rely on boiling to make it fit for eating (if it is food). Graeme Bartlett (talk) 10:31, 26 April 2010 (UTC)

100 degrees C, right? Also, for what it's worth Aflatoxin is the stuff you still have to worry about even after the mold is dead. --144.191.148.3 (talk) 18:35, 26 April 2010 (UTC)

Yeah 100° F will just make it wet. Graeme Bartlett (talk) 21:44, 26 April 2010 (UTC)

Using a solution of sodium hypochlorite will kill mold too, and turn whatever it is poured on white. --Cheminterest (talk) 22:13, 26 April 2010 (UTC)

CCs?

Are CCs listed on Wikipedia?

eg, 10cc ( or 10ccs )

- 193.61.111.53 (talk) 11:15, 26 April 2010 (UTC)

Try HERE. Dolphin (t) 11:31, 26 April 2010 (UTC)

Unless you mean the music group, 10cc. AlmostReadytoFly (talk) 11:52, 26 April 2010 (UTC)

Also, see our orders of magnitude series entry for examples of things of a given volume: 1 E-5 m³. Paul (Stansifer) 12:17, 26 April 2010 (UTC)

Should I point out that this is probably a student of Loughborough College you're trying to get sense out of!--Aspro (talk) 12:21, 26 April 2010 (UTC)

And what's wrong with Loughborough? I'm from Loughborough, although I never went to college there. FiggyBee (talk) 00:50, 28 April 2010 (UTC)

I'm not referring to the good citizens of your fair town -nor you. Rather, I was err... well... view their talk page and you might get my drift. Now don't you think they could have formulated the question better if they were serious? --Aspro (talk) 19:34, 28 April 2010 (UTC)

Just to be explicit about it, when doctors on television say things like "10 ccs of adrenaline, stat!", the "cc" are an abbreviation for cubic centimeter, which happens to be the same volume as a milliliter. Other senses of the abbreviation can be found, not surprisingly, on the page cc. -- 174.24.208.192 (talk) 15:32, 26 April 2010 (UTC)

"Worst case of ice-cream induced brain freeze I've ever seen, administer 10 cc's of hot fudge, stat !" - Simpsons Ice Cream Social. StuRat (talk) 16:26, 26 April 2010 (UTC)

Another abbreviation for cc is cm³.--Cheminterest (talk) 22:14, 26 April 2010 (UTC)

Kepler mission field of view

Is it true that field monitored by NASA Kepler telescope roughly 24 times bigger then Moon angular diameter (as visible from Earth surface)? 70.52.182.184 (talk) 14:01, 26 April 2010 (UTC)

According to our article section Kepler_Mission#Mission_details its field of view is about 12 degrees. As the moons diameter is about half of one degree that seem to be about right.--Aspro (talk) 14:08, 26 April 2010 (UTC)

(EC) Kepler's field of view is approximately 10 degrees square. The moon subtends an angle of approximately 0.54°. So about 20x or so, yes. --Tagishsimon (talk) 14:10, 26 April 2010 (UTC)

Chromoscope pictures of the galaxy

on the site.. http://www.chromoscope.net/ when we observe the X-ray picture of our galaxy, we can see sumthing like the picture has been struck by a tiger paw or sumthing like that, like torn up in between, where none of the other images show such a thing. what makes it so? Prady —Preceding unsigned comment added by 116.73.242.109 (talk) 15:04, 26 April 2010 (UTC)

It looks like missing data. Dauto (talk) 15:39, 26 April 2010 (UTC)

Yes, it's missing data. This is more of a problem with X-ray telescopes because of their much narrower field of view. Other space telescopes do record the same thing, but over time they record the missing bits with a second or third pass. Why this happens can be understood if one just considers the sinusoidal curved black streak. This was the part of the celestial sphere hidden from the telescope by the sun. If you look at this website you will see an animate representation of the the celestial sphere. [27] Refer to the section: The tilt of the Earth's spin axis with respect to the ecliptic plane results in the Sun tracking out an seemingly sinusoidal path on the celestial sphere when viewed in the projection with the celestial equator horizontal. So, in short, the streaks and other black pixels are due to the fact that it is an incomplete scan of the of the celestial sphere.--Aspro (talk) 17:25, 26 April 2010 (UTC)

Who turns the machine off from a terminally ill patient?

If a decision was taken to turn the machines off, so that a terminally ill patient will die, who does physically push the button (or pulls the cable or whatever)?--Mr.K. (talk) 15:59, 26 April 2010 (UTC)

I'm guessing a nurse would do that. Dauto (talk) 16:00, 26 April 2010 (UTC)

That might make them legally liable, if it's later decided that proper authorization was lacking. For this reason, they may have the family member who requested that they "pull the plug" be the one who actually does it. StuRat (talk) 16:20, 26 April 2010 (UTC)

Do you have a reference for that? Matt Deres (talk) 16:56, 26 April 2010 (UTC)

(ec) Hmm. Do you have a source for that statement? It strikes me as very dubious. Looie496 (talk) 16:58, 26 April 2010 (UTC)

In general, a hospital's legal department would already have reviewed any request to "pull the plug" and certify that the requester has the proper authority and complies with any existing advance directives, etc. Once the lawyers sign off, I'd assume that the nurse is pretty well covered. Dragons flight (talk) 17:07, 26 April 2010 (UTC)

I do also believe that you if it is legally allowed (and it is), there must be a way of doing it without being sued for it. However, I am still not sure that a nurse will do it. Isn't it a huge psychological burden on a nurse, if she has to constantly kill people?Mr.K. (talk) 17:15, 26 April 2010 (UTC)

There are many psychological burdens in nursing. Compared to telling parents that their child has just died, removing a feeding tube from an unconscious person who is shortly going to die anyway is not that high on the list. Looie496 (talk) 17:38, 26 April 2010 (UTC)

I wouldn't say telling parents their toddler went to heaven is a heavier burden than actually killing someone. In the former case you can just use a euphemism and comfort yourself with the thought that it was unavoidable. In the latter case, Jesus, how can you don't think about what you are doing? Mr.K. (talk) 17:51, 26 April 2010 (UTC)

a) It is not up to the nurse/physician to tell parents their child "went to heaven". b) Turning off life support is distinctly different than "killing" someone. c) Don't assume for an instant that the doctors and nurses involved in the care of a terminally ill person do not think deeply about what is happening on a daily basis. Let's keep this discussion about facts and not emotionally charged rhetoric. --- Medical geneticist (talk) 22:59, 26 April 2010 (UTC)

I'm pretty sure you're all looking too much into this. The decision to pull the plug isn't made by the nurse, so they isn't responsible for the death even they did pull the plug physically. In the UK I think you need to have two consultant doctors who permit for life support to be switched off with the next of kin's consent, whereupon the nurse would switch it off. There is no real reason to feel guilt as I'm fairly confident the nurses will be of the same opinion as the doctors--that the person is dead anyway, merely being kept alive on machine. Regards, --—Cyclonenim | Chat  18:02, 26 April 2010 (UTC)

Besides which, there's always the possibility that the patient will stay alive even after the life support is removed... --TammyMoet (talk) 18:35, 26 April 2010 (UTC)

Not really. They go through thorough tests to make sure the person is really dead (which actually include disconnecting the machines for a while to see if the patient tries to breath on their own). While it is always possible that they have a mistake, the probability is negligible. --Tango (talk) 21:24, 26 April 2010 (UTC)

This is a reference desk. Please provide references when you give answers, instead of guessing. Here (page 4) is an article in which someone present at such an event wrote that a doctor and nurse were present, and the nurse switched off the breathing machine. Comet Tuttle (talk) 20:04, 26 April 2010 (UTC)

I second that. The first two answers were "I'm guessing" and sheer speculation. The original poster should look at the list of items under life support. Cessation of medical therapies (inotropes, total parenteral nutrition, dialysis etc.) are ordered by the physician. Feeding tubes and central IVs can be removed by nurses or doctors. Withdrawal of mechanical ventilation is performed by a respiratory therapist. Any of these steps would be discussed in detail with the next of kin or medical power of attorney. Hospital legal or ethical consultation would only be needed if there were a conflict between the medical team and the patient's family. --- Medical geneticist (talk) 23:11, 26 April 2010 (UTC)

According to this source (very small area is visible), the physician may also be the one to flip the switch. The book cited, Sourcebook on death and dying by James A. Fruehling seems like it would also be a good source regarding the possibility of a physician being criminally prosecuted in such an instance, though you'd need to purchase the book to find out for sure. Matt Deres (talk) 22:39, 26 April 2010 (UTC)

According to my wife (who used to be an operating department Nurse many years ago), any of the medical team might actually "flip the switch". The decision is the doctors' - but whoever happens to be standing next to the machine at the time might physically throw the switch - which could be the doctor, a consultant, a nurse, an OR tech or the anesthesiologist. It would be unlikely to be a relative or friend of the patient. She says it's like a prescription - the doctor takes the decision and is responsible - everyone else is just doing what they are told...following instructions...nothing more...it's just like administering any other treatment. Of course the actual making of the decision is an exceedingly complicated and legally 'careful' process involving lots of people. SteveBaker (talk) 02:47, 27 April 2010 (UTC)

No medical person would ever ever ever ask a relative to unplug a respirator. Horrible and cruel idea. Doctors or nurses do it when they are convinced that doing so is not killing the person since they are already dead. Often if any of the care team seem squeamish about it but do not actually oppose doing to, a more senior person will take the responsibility for flipping a switch. It isnt a daily event even in a busy ICU and it is treated seriously by those involved. And all institutions have careful brain death protocols with multiple tests and independent consultations. Been there done that. alteripse (talk) 04:00, 27 April 2010 (UTC)

Reactivity of Na or Ca

Is sodium or calcium more reactive? --Cheminterest (talk) 22:12, 26 April 2010 (UTC)

The elementary answer is at Reactivity series and boils down to "sodium". No doubt others will explain why my GCSE Double Science (which was the last time I heard of that) is inadequate and the question is really rather complicated. 128.232.241.211 (talk) 23:04, 26 April 2010 (UTC)

Yes, sodium is more reactive because it has only one electron in its outer shell, whereas calcium has two. Since sodium only has one, it is much easier to get rid of, making it more reactive. --The High Fin Sperm Whale 00:04, 27 April 2010 (UTC)

That's not actually a good explanation. Having more electrons in your shell increases electron shielding, causes things like spin pairing, etc. which actually makes electrons easier to get rid of -- assuming ENC is constant. The reason why sodium is more reactive than calcium is that calcium has an effective nuclear charge of about 2 while sodium only has an ENC value of around 1. John Riemann Soong (talk) 05:06, 27 April 2010 (UTC)

Both calcium and sodium metal are strong reducing agents: reactive enough to react with water. But compare the reactions: sodium vs. calcium. Buddy431 (talk) 00:41, 27 April 2010 (UTC)

Protein

1) What happens when someone does strength training and doesn't eat much protein afterward? How do the muscles repair themselves? Thanks. --Mudupie (talk) 23:33, 26 April 2010 (UTC)

Difficult to answer absolutely. What do you mean by 'much protein'? Lack of any nutrient will very likely lengthen post exercise recovery time. But more is not necessarily better.
Note that in the early stages at least, strength can increase without increase in muscle mass, as the muscles are learning the new 'skill' of lifting weights.

In the 'west' we tend to eat far more protein than we need. If you have a good all round diet, you may not need any extra protein. Which I cannot judge. This website here has figures that seem consistent with current nutrition standards (Please don't pay too much attention to the ads for 'protein powders' etc!).

This one at (Massachusetts General Hospital) is aimed at adolescents, Weight lifting and training, from which I quote: (my bolding)

"Since adolescents in the United States already eat a diet high in protein, there is no need for most adolescents to take protein supplements during weight training. And scientific studies have not supported any enhancement of muscle growth or strength from protein intake greater than the recommended amounts." para. 7, © 2010 Massachusetts General Hospital

• Recommended 'normal protein' RDA (Recommended Dietary Allowance) is 0.8 grams per kilogram of lean bodyweight (1 kilogram=2.2 pounds).
• If you exercise you need more.(Pregnant women need even more than weight lifters!)
• For muscle building an intake of 1.6-2.2 grams per kilogram of bodyweight is recommended.
  • I think many of us exceed that intake, whether we exercise or not.(see quote above)
• Too much protein can be bad for you (or give no advantage).[28][29]
• As is too little. see Protein-energy malnutrition

See also Body building#Protein, Protein (nutrient), Outline of nutrition, Nutrition, Human Nutrition, Diet (nutrition),and any related articles. This ref Desk question from about 3 day ago may interest breakdown of muscles.

Feel free to ask more questions if I have not fully answered your query --220.101.28.25 (talk) 12:22, 27 April 2010 (UTC)

Addendum: Don't take what is here as 'gospel' truth. I suggest you read the references here, or in the articles I have referred you to yourself. Also, for personalised nutritional advice, consult a nutritionist or dietician. --220.101.28.25 (talk) 13:33, 27 April 2010 (UTC)

American scientists recently advised all but some professional athletes to stop taking protein supplements. They are not necessary. Imagine Reason (talk) 14:27, 27 April 2010 (UTC)

That is one of the the points I was trying to get across, though I was assuming 'normal' amateur training. If you have a link to the data you mention I'd like to read it. :-) --220.101.28.25 (talk) 14:35, 27 April 2010 (UTC)

Thanks! I have a lot of reading to do :) --Mudupie (talk) 17:44, 27 April 2010 (UTC)

Thank you for your thanks, Mudupie. You will find the subject can be rather contentius, as the bodybuilding.com website says at one point. It tends to be weight-lifter/bodybuilders on one vs scientific studies/researchers on the other. (Or perhaps purveyors of supplements vs nutritionists.) Views can be very divided. Educating yourself in this area is very wise, and can be very interesting! But again professional advice should be heeded, not someone with a possible conflict of interest trying to sell you a 'supplement'.! --220.101.28.25 (talk) 21:06, 27 April 2010 (UTC)

Soda Bottle Rocket

In science we are doing a project that involves us making rockets out of ordinary 2 liter soda bottle. We are allowed to modify the bottle in any way that we want. I could not find any information on how to find an ideal nozzle size for a given rocket. The wikipedia article on water rockets says that many people create a nozzle 9mm in diameter. I did not know if there was a means of calculating from chamber diameter, or more likely pressure (around one hundred psi in my case) what an ideal nozzle size would be. Additionally that 9mm nozzle is for a water rocket, and the means of propulsion for our rockets is compressed air. I was also wondering if anybody knew a way to connect two soda bottles, for added chamber volume, that could withstand 100 psi. If so, how should chamber diameter be proportioned to chamber length? —Preceding unsigned comment added by 71.112.13.57 (talk) 23:46, 26 April 2010 (UTC)

I think you need some water in there - it is the water being pushed out by the compressed air that propels the rocket. --Tango (talk) 23:53, 26 April 2010 (UTC)

We've got an article - water rocket, and if you google soda bottle rocket you should find lots of "how to" guides to help you. DuncanHill (talk) 23:56, 26 April 2010 (UTC)

100 psi is pushing it - these bottles are rated at 100psi and tested to 150psi when new...but this site says they may start to deform at 80psi when you have used bottle. So be really careful - stand well back - and FOR SURE don't be tempted to push it over 100psi! I strongly agree with DuncanHill - you need water as propellant if you want to make this thing really fly well. I don't see how using two bottles can help. You double the energy stored in the rocket - but you also double the weight (more than double it, probably because you've got to attach them together somehow. Real world rockets benefit from having multiple thrusters because they have payload other than the motors themselves...and even then, they used a staged approach where they drop the first stage motor before firing the second stage - so the second stage doesn't have to lift the weight of the first stage. Because you can't increase the volume - and you can't (evidently) change the propellant - so the trick is going to be to keep the weight down and to get the nozzle diameter right.

The scientific answer here lies in the "Tsiolkovsky rocket equation". It says that the 'delta-v' of the rocket depends on the log of (the mass of the fully fuelled rocket divided by the empty mass of the rocket) - multiplied by the exhaust velocity. Notice that the heavier the fully-fuelled rocket - and the lighter the empty rocket, the faster it will go. That's why you need some water in there...air at 100psi weighs very little indeed compared to a 2 liter soda bottle...so ln(m1/m2) is only a little bit bigger than zero. So you need a hell of a lot of exhaust velocity...so we're back to that nozzle again. Picking a decent nozzle is probably going to require some experimentation...there are equations, but they are touchy. The shape of the outlet matters in ways that are hard to figure out without supercomputers and such...so experimentation is the answer. SteveBaker (talk) 01:14, 27 April 2010 (UTC)

I second Steve Baker's "experimentation" suggestion. The trick is that you want to fill with enough water, and design the nozzle and air pressure charge, so that the air pressure equalizes at the exact instant that you run out of water. That way, you aren't carrying heavy, useless water around with you as inert mass. At the same time, if you put too little water in, and you have air pressure left over when all the water has already sprayed out, your rocket isn't making the most efficient conversion of potential energy (air pressure) into momentum. Swapping out nozzles is hard - so start with one rocket with a reasonable size nozzle; and vary your experimental parameters: quantity of water, and pressure of air added. Keep in mind that stored energy in this case is equal to pressure times volume - and the water isn't compressing. So, your total stored energy will decrease if you add more water (because you have less volume of air, so the P V product is smaller; but if you add water, your total momentum may increase because you have added mass. So, the question all boils down to: what is the optimum ratio of water to air to maximize the mass of water and its exit velocity, integrated over time? Try changing your parameters and experimenting and recording/graphing the data. When you have a lot of experiments, change the nozzle and see what changes. It's not likely that a mathematical treatment will actually be very useful here, because the messy parameterization details are so uncertain that even a computational solution would be prone to error. Nimur (talk) 14:24, 27 April 2010 (UTC)

April 27

Methanol poisoning

This might sound really dumb, but I thought ethanol was the only alcohol used in, well, alcoholic beverages. Since when is methanol used, or is not actually used at all and this incident rose from an accidental addition of methanol, instead of ethanol? Regards, --—Cyclonenim | Chat  00:30, 27 April 2010 (UTC)

The case you refer to appears to have involved the sale of adulterated Waragi. Methanol is not used, for exactly the reason that it tends to lead to illness and death. --Tagishsimon (talk) 00:37, 27 April 2010 (UTC)

Some people may substitute methanol for ethanol to increase alcohol content. Methanol causes blindness in lower doses (about 10 mL are needed), and death in higher doses. Ethanol is not as toxic. Most alcohols naturally contain a little methanol. --Cheminterest (talk) 20:58, 27 April 2010 (UTC)

Snowflake symmetry

Why do snowflakes form exactly the same on all sides? With billions of molecules between the edges, how does water freezing on one side affect the other side? Thanks in advance, --The High Fin Sperm Whale 01:55, 27 April 2010 (UTC)

Note that all crystals tend to be symmetrical, not just snowflakes. However, many do end up "deformed", too. StuRat (talk) 01:58, 27 April 2010 (UTC)

The edges in a snowflake do not affect one another. Rather the same thing is happening on both sides, so you get the same result on both sides. The shape is determined by things like humidity, wind, temperature, altitude, etc. And all of that is more or less equal on both sides. Ariel. (talk) 02:00, 27 April 2010 (UTC)

Then why don't you get a sphere instead of a crystal? --The High Fin Sperm Whale 02:05, 27 April 2010 (UTC)

You do, sometimes, but water is intrinsically a crystal, so if solidifies slowly enough it will naturally form a six-sided crystal. The exact shape of the crystal depends on temperature, humidity, etc. As the flake falls downwards through the weather, growing, sometimes conditions favor different shaped crystals, so you might wind up with a flake that is simple near the center, but complicated near its outer edge. but the entire flake is always in the same weather conditions, so usually, (but not always) all six sides will have formed the same way. APL (talk) 16:10, 27 April 2010 (UTC)

They are not perfectly symmetrical. There are usually lots of asymmetries (which our pattern-matching human brains tend to ignore because we perceive the similarities as greater). The physics of snowflake formation (and symmetry) is complicated and not fully understood. It is clearly some kind of fractal process, though, which produce lots of (approximately) self-similar objects in nature. --Mr.98 (talk) 02:42, 27 April 2010 (UTC)

You can see pictures of snowflakes at Snowflakes and Snow Crystals. -- Wavelength (talk) 02:49, 27 April 2010 (UTC)

According to our snowflake article, "The sixfold symmetry arises from the hexagonal crystal structure of ordinary ice, the branch formation is produced by unstable growth, with deposition occurring preferentially near the tips of branches." You start with a tiny hexagon, and new water molecules, in order to fit in, have to continue fitting in to the crystal, maintaining the hexagon shape. But this doesn't explain why one end of a snowflake is similar to the opposite end of that snowflake, but different from other snowflakes.

Scientific American has an more complete explanation: the snowflake grows slowly, and at the same speed in all directions. The ambient temperature controls how the crystal forms and changes frequently, but (because the snowflake is very small) is always almost precisely the same over all parts of the snowflake.

Snowflake#geometry covers what effects the various temperatures have. Presumably, snowflakes grown in a lab at a constant temperature would all look boring. The shape of a natural snowflake reflects the history of its formation. If two snowflakes stay near each other throughout their formation, they should have a family resemblance. Very cool! Thanks for making me look this up. Paul (Stansifer) 04:59, 27 April 2010 (UTC)

Here is another SciAm explanation (which also points out that it is not entirely symmetrical)... my understanding (from a talk I saw not too long ago) is that physicists hotly debate this particular question, that it is not totally understood yet in a way that everyone can agree upon. --Mr.98 (talk) 13:33, 27 April 2010 (UTC)

FWIW here's a bigger hexagonal mystery. Cuddlyable3 (talk) 13:04, 27 April 2010 (UTC)

Mechanics of motion sensors

According to Hollywood Sign, the famous sign is surrounded by motion sensors that call the police when triggered. Assuming that this is true (the source doesn't say that), how would such a sensor be able to avoid false alarms from large animals (the source warns readers that if they ignore security and try to reach the sign, they're at risk of being mauled by mountain lions) and yet always catch humans? Nyttend (talk) 03:22, 27 April 2010 (UTC)

Motion sensors only detect motion. They can't distinguish between motion by a person and a large animal. Dolphin (t) 04:36, 27 April 2010 (UTC)

I suppose you could design an infra-red motion sensing system to look for a "mostly vertical heat sources", which are presumably human, since we walk on two legs. However, people could crawl on all fours to fool it. StuRat (talk) 05:45, 27 April 2010 (UTC)

If I were building it, I would attach the motion sensor to a video camera. Then I could look ahead of time before calling the police. Also, you can make barriers that work pretty well against animals, but that humans can defeat. Ariel. (talk) 06:01, 27 April 2010 (UTC)

The article Hollywood sign mentions a 1994 installation of a $100,000 security system featuring video surveillance and motion detection. Cuddlyable3 (talk) 12:41, 27 April 2010 (UTC)

Those that have read Dune (novel) will remember the Thumper which had the same cadence, as the Fremen of Arrakis and so was used to distract the worms. Well, back here on Earth, Remote Intrusion Detection Seismic Sensors can be designed to detect the human cadence (between 1 Hz and 3 Hz), and not the higher cadence of four-legged animals. Find a reasonable flat bit of path where the intruder can walk at a regular step ( flat sections are sometimes created to draw intruders to where you want them) and bury a device along there. You can purchase them with radio senders to report back. WP appears to have missed this application out on Seismometer and yet they are becoming quite widely used. Needless to say, the way to pass by undetected is to employ the same technique that the Fremen taught Paul. Here is an external link with more info: [30]--Aspro (talk) 09:04, 27 April 2010 (UTC)

I fixed your link to the Dune novel and not just a hill of sand. Cuddlyable3 (talk) 12:45, 27 April 2010 (UTC)

Thanks. Aspro (talk) 13:25, 27 April 2010 (UTC)

microbes outside earth

Does the search for life on Mars and other space regions include microbes, especially bacteria which live in any extreme conditions? Or is the search meant for humans? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 04:15, 27 April 2010 (UTC)

They are definitely looking for microbes. There's little hope of finding humans on Mars, so they don't even look for that. StuRat (talk) 05:20, 27 April 2010 (UTC)

They may have found such microbes. The research is still very scanty due to the extremely small samples, and the very sparce evidence in those samples, but there possibility has not been eliminated in as many as three meteorites found on Earth which originated from Mars. See Mars_meteorite#Possible_evidence_of_life. --Jayron32 05:39, 27 April 2010 (UTC)

SETI activities seek life forms with human-like or better intelligence but generally assume they will not be found living on the planets or moons of this solar system. Lack of evidence has not hindered people imagining fictional Martians some of whom are not very nice.Cuddlyable3 (talk) 12:29, 27 April 2010 (UTC)

Eeek! Martians!

There have been perhaps four serious efforts to test directly for life on Mars - The Viking landers, the analysis of Mars rocks that came to the Earth as meteorites - and the recent Phoenix lander and careful analysis of the Martian atmosphere by the Mars Express Orbiter. Both landers scooped soil and analysed it in test cells specifically designed to look for key signs of life. The results are a little odd.

• The Viking lander did it's tests - and the results of one test were positive! (Check out Viking biological experiments.) According to the criteria the craft was designed to test - it "found life on Mars". However, subsequent thinking on the subject has cast doubt on the findings - there are other ways in which the results could have come about - so nowadays, we have to say that the Viking landers didn't "find life"...necessarily. In other words, the experiments were not designed carefully enough.

• Then we had the Mars meteorites: Allan Hills 84001 in particular was first reported to show fossil lifeforms, to have trapped gasses that could only have come from living things, etc. It was announced that life had been found - they even got Bill Clinton on TV to announce it! But, again, more detailed analysis showed that both "fossils" and the gas evidence could come about in other ways...so again, ambiguous results.

• The Phoenix lander results are no better - at one point in the mission, it was reported that the White House had been alerted by NASA to make an important announcement on major discoveries concerning the "potential for life"...which sounded pretty exciting - right up to the point of the announcement when they basically said that they hadn't found anything very exciting.

• Then we have the anomalous nature of methane in the Atmosphere of Mars. This is a gas that would break down in the atmosphere and disappear. Yet it's still there (See: Atmosphere_of_mars#Methane) - and what's more, it comes and goes. There are no good theories as to why this might be - unless there were lifeforms there generating the stuff.

The problem is evidently that while we do really have some things that make it seem a lot like there is (or perhaps was) life on Mars - there is always another plausible explanation. Since we need to try to remain skeptical, we have to say that life has NOT been definitely discovered on Mars...but neither has it been disproved...yet.

However, it's very clear that 'macroscopic' lifeforms (things that might be visible to the naked eye -- or the many Rover & Lander cameras) are not present. If there is still life there - it's tiny stuff like bacteria.

SteveBaker (talk) 04:47, 28 April 2010 (UTC)

An apostrophe carelessly wielded can yield such nonsense as "The Viking lander did it is tests". Cuddlyable3 (talk) 20:18, 28 April 2010 (UTC)

You can let this bother you, or you can adapt, as I have done: Since Mr Baker tends to write relatively long and detailed responses, simply treat an early improper use of it's as a leading hint for the identity of the author, without having to scroll to the bottom of the post ... nearly as reliable as the signature itself. DaHorsesMouth (talk) 00:29, 29 April 2010 (UTC)

You may be interested in this recent discovery of possible organic matter present on Mars.

Sea blue - Sky blue

Why, at times, is sea-blue darker than the sky-blue when it is just a reflection of sky blue by the sea water? - anandh, chennai. —Preceding unsigned comment added by 125.21.50.214 (talk) 04:28, 27 April 2010 (UTC)

Water is not blue because of reflecting the sky, that's wrong. Water actually is blue, by itself, but so slightly that you need a lot of it to see the color. The deeper the water, the deeper blue it will look. Adding salt, as in ocean water, makes it more of a greenish-blue. StuRat (talk) 05:18, 27 April 2010 (UTC)

Thanks. colour of water is an interesting topic. 125.21.50.214 (talk) 05:51, 27 April 2010 (UTC)

THe colour of the sea here in England is usually grey most of the time, blue on sunny summer days, and rarely green. 78.151.102.119 (talk) 09:14, 27 April 2010 (UTC)

I've seen it purple, but that was in Cornwall not England. DuncanHill (talk) 22:45, 28 April 2010 (UTC)

Since we know the colour of the sea isn't a reflection of the sky, but intrinsic to the water, I can only conclude that the bright blue or dull grey sky must affect the intrinsic colour of the sea by some unknown means. 81.131.28.200 (talk) 11:24, 27 April 2010 (UTC)

Well, everything is darker outside on gloomy cloudy days compared to bright sunny days. Is that what you're talking about? Zain Ebrahim (talk) 11:55, 27 April 2010 (UTC)

In a mirror or on the surface of a still lake viewed at a low angle the reflected sky is as bright as the sky. However some of the light falling on a sea surface is refracted into the water so only a part is reflected towards the viewer who perceives a dark and diffused (because of waves) image of the sky. Colour of water is relevant only to seeing a light source deep in the water. Cuddlyable3 (talk) 12:20, 27 April 2010 (UTC)

The ocean color is partially derived from the skies. On a cloudy day, the ocean appears more gray, and on a sunny day, it appears more blue. It also can be green from underwater plankton which colors it. Water also has a very slight color. The molecules of water absorb certain wavelengths of radiation except blue. Needless to say, there are several reasons. --Cheminterest (talk) 21:03, 27 April 2010 (UTC)

"...the color of the sea isn't a reflection of the sky"

"...it is just a reflection of sky blue by the sea water"

This is a

complicated question.

SteveBaker (talk) 04:00, 28 April 2010 (UTC)

Human-Animal perceptions

If human perception varies from that of animal perception, say for example, in case of 'eye sight,' what exactly is the property (like shape, colour etc.,) of the entity (any object). Should we say that the object is rectangular,spherical etc., according to the human view? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 04:33, 27 April 2010 (UTC)

I don't think we particularly care about animal perception, in general. Only animal researchers, trainers, etc., would care, as it affects their jobs. So, if a dog sees a globe, he probably thinks "uninteresting object" and doesn't attempt to classify it further, but so what ? StuRat (talk) 05:27, 27 April 2010 (UTC)

This is an extremely complicated, almost impossible question. The notion of property is a learned, acquired one. You learn what "round" or "straight" or "wavy" means when you see or touch it; you do not know if every human sees it the same way, but every (or almost every) human learn to associate those properties with the same categories. Now, when people study the anatomy and physiology of the eyes, lateral geniculate nucleus, and visual cortex of humans and Old World primates (Catarrhini), it turns out that the structure and function is fairly similar (size and exact shape notwithstanding) across individuals and even across species. This allows one to argue that humans, chimps, and macaques really see those things the same way. Now, cats or rats have eyes and brains that are less similar to ours; birds, reptiles, and fish are further yet; and insects with their compound eyes and ommatidia-lamina-medulla-lobula early visual processing pathway are nothing like the humans at all. Yet bees can be taught to distinguish shapes, and even properties of shapes, such even as the abstract notions of "sameness" and "difference". Do they see the same way as we do? No. --Dr Dima (talk) 07:52, 27 April 2010 (UTC)

An even more puzzling to our hopelessly anthropocentric perception is the question of what qualia (if any) does a rodent have when it "sees" objects with its whiskers (vibrissae); or a pit-viper has when it "sees" objects with its heat sensing organs, or a bat when it "sees" objects with its ears. --Dr Dima (talk) 08:04, 27 April 2010 (UTC)

Well, if you look at the center of a flower you may see a half dome where a bee might "see" a star shape http://en.wikipedia.org/wiki/Bee_learning_and_communication#The_Neurobiology_of_Color_Vision However, that would assume that the bee interpreted the visual information it gets the same way a human with a "bee eye camera" would. IMHO that is highly unlikely. I've linked this story before, but it shows that even an untrained human brain has trouble interpreting shapes. http://nfb.org/legacy/bm/bm02/bm0211/bm021105.htm 99.11.160.111 (talk) 08:57, 27 April 2010 (UTC)

Yes we should OBVIOUSLY say that an object is rectangular, spherical etc., according to our human view. Cuddlyable3 (talk) 12:09, 27 April 2010 (UTC)

"Rectangular" and "spherical" are objective criteria. Even if an optical illusion prevents you from intuiting the shape's true nature, or even if you're blind, you can use tools to measure the shape and determine whether or not it matches the definition of those criteria. APL (talk) 16:03, 27 April 2010 (UTC)

What you describe is not perception; it is measurement and inference. Properties of objects may be, well, objective, but perception is subjective. That is, if you agree with Kant's “Ding an sich” idea. Many philosophers don't, and conclude that fundamentally there is no escape from subjectivity; see e.g. this introduction. Wikipedia, too, has an article on Objectivity (philosophy). --Dr Dima (talk) 18:14, 27 April 2010 (UTC)

Ambidextrous people

how better are ambidextrous people in terms of intelligence, compassion etc.,than a left-hander or a right-hander, while the ambidexterity is obtained either by natural or acquired ways? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 04:50, 27 April 2010 (UTC)

I would suspect you'd find them midway between "right-brain" and "left-brain" individuals, so be able to integrate logic and emotions. StuRat (talk) 05:29, 27 April 2010 (UTC)

While Lateralization of brain function is a real thing (certain tasks predominate in certain areas of the brain) the whole "artsy people are right-brained and scientific people are left-brained" is mostly pseudoscientific bull crap. There's no hard evidence that things like personality or aptitude is connected in this way to "brainedness". --Jayron32 05:36, 27 April 2010 (UTC)

Nope, I'm just as daft as everyone else :-)) 99.11.160.111 (talk) 08:58, 27 April 2010 (UTC)

The Wikipedia article Ambidexterity is mostly about performance in sports. Cuddlyable3 (talk) 12:05, 27 April 2010 (UTC)

Cecil Adams very briefly mentions a study that showed that ambidextrous cats weren't as clever as cats with a definite preference.[31] but without reading the paper he mentions it's tough to say how much Cecil was paraphrasing. APL (talk) 16:01, 27 April 2010 (UTC)

What is this box?

Resolved

There is a large blue metal box in the office in which I work. The footprint is about 8'x3' and it stands about 6' tall. There is a white box on the outside (maybe 2"x6"x10") with two pressure gauges attached. This white box also has a temperature gauge that goes from 50 to 100 degrees F. There is also an electrical junction box on the outside with a big handle type on/off switch. Next to that is a card which is dated from 1999 which lists when various PMs were done. Notes for those PMs include mentions of replacing or checking tension of belts and greasing motors. In black permanent marker, someone has written on the side of the blue box, "CYMER". I have no idea if the writing is in any way related to the box. The only identifying marking is a logo which I've taken a picture of. I ran the image through TinEye and it didn't come up with anything.

The office in which I work used to be a lab of some sort but it was converted to an office years before I got my current job. None of my co-workers know what this box is and we're all kind of curious what it is and/or what it did. I work in the semiconductor industry if that helps. Anyone know what I've described? I'm putting this question on this desk since the room used to be a lab and this box might have been used for something in that lab. Dismas|^(talk) 08:32, 27 April 2010 (UTC)

I don't know what the box is, but you should also take a picture of the whole box from a number of angles. Did you try opening it? Does it make noise ever? Ariel. (talk) 09:37, 27 April 2010 (UTC)

Cymer, Inc.'s website [32] describes the company as a supplier of excimer light sources for photolitography. Pictures of their equipment suggest it fits the general dimensional description you gave, although none of the pictures on their website shows a blue housing. This U.S. patent [33] may provide some clues to the presence of a temperature gauge and a motor. --173.49.9.93 (talk) 09:42, 27 April 2010 (UTC)

It's been powered off ever since I've been in here (about 7 months). So, no, it's never made any noise that I know of. Considering the "L" logo, I don't think it's a Cymer product. There is nothing to open. The outside is just blue sheet metal. I don't see any access panels. One of the blue panels has had a couple screws removed but considering the 8' length and the fact that I don't have any business poking around in the box, I don't feel comfortable trying to pop the panel off if it will indeed come off. My work has nothing to do with it, so it would be rather embarrassing if I couldn't get it back together again. Dismas|^(talk) 10:03, 27 April 2010 (UTC)

Inside you might find a pre-193nm laser with cooling apparatus as it might be cheaper to leave useless technology in place when there is a radical change in node size as it evolves. Currently the plan is to shift to EUV for manufacture below the 17nm node when the power of EVU is able to match that of current 193nm lasers. Your box probably contains a light source for manufacture of older and larger node sizes of very long ago. I would consider it a showpiece in that case like the MARK I computer at Aiken Lab and care for it like a baby and show it off to friends. Plain vanilla with chocolate chips (talk) 11:23, 27 April 2010 (UTC)

Think we need more info. What is the range of the pressure gauges. It sound like it could be a compressor but compressors often run hotter than 100 deg F. Stand on some steps and see if there are any vents or disconnected pipe work on top. Are the pipes iron, stainless steel or copper? If pipe were at one time attached, there may still be the signs of pipe brackets on the ceiling and walls. Are there any vents, what shape? Any more signs on roof of box. Any inspection or access panels up there?. How are they fixed and are lead seals attached (or bits of twisted wire where they once where). Can you follow the cable from the switch box back to the main switchboard for that floor. It maybe that the electrician labelled what piece of equipment was on that circuit. The company you work for will have a department responsible for looking after the building(s) itself. They will have records of all plant and equipment that is permanently installed. I have found a good approach for eliciting a response from such departments in a reasonable time is too say to them: “Is this large equipment cabinet still used or important? Because we are just about to drill a large hole through it!” A manager or executive officer ( or maintenance guy) should know the name and how to contact this department. Maybe their listed in the internal telephone directory under “Site Management or Estates Management or Work Engineering Department, etc. Do however, steer clear, of involving the PHB. Lastly, I would consider that unknown cabinet could well be a safety issue, for one is just trusting someone else did their job properly and ensured that there are no hazardous materials left in side.--Aspro (talk) 11:10, 27 April 2010 (UTC)

The "L" graphic may or may not be the manufacturer's logo. It seems to communicate something about liquid and temperature. Just a guess. --173.49.9.93 (talk) 12:20, 27 April 2010 (UTC)

Wow, what a bit of history! I work for what became of the company that made that. The "L" graphic is actually a really really old Liebert Corp. logo. If you do a google images search you can see what the latest incarnation was (before they stopped using the logo altogether about 2 years ago.) What you are looking at is probably some sort of industrial chiller, installed to provide cooling for the Cymer device that someone else described. --Jmeden2000 (talk) 14:46, 27 April 2010 (UTC)

Could be -well done! The logo symbol does remind me a bit of a Dewar flask with a thermometer stuck in it (the pressure gauges for first and second stage compression maybe). Anything like that (including a compressor) is going to need loads of cooling though. I'm not going to speculate more without more info – it like clutching at straws. After all, it might just be something very obvious; like the new Doctor has almost fixed the Chameleon circuit and the logo is just part of its disguise – but its still suck at blue! --Aspro (talk) 14:57, 27 April 2010 (UTC)

It was colloquially referred to as the "Liebert Drip" since the company was largely in business to make temperature and humidity control products. The 'thermometer inside the water drop' logo (of various forms) was used until the company was bought by Emerson Network Power and internalized. The device in question, if as the OP states it is indoors and has no visible signs of ventilation, is almost certainly a chiller designed to take a water or refrigerant loop from a condenser type device outside the building, and make cool or chilled water for the supported device. These are very common to find in hospitals, cooling MRI machines, but have a multitude of other applications as well. I bet that the front of the device has three covers with horizontal seams. The covers are probably secured with a 3/8" allen key head and if you twist the two on the top cover it will hinge upward. I am *not* advocating taking it apart, this advice is for qualified personnel only! Ah well, enough babbling, back to work. --Jmeden2000 (talk) 17:17, 27 April 2010 (UTC)

Thanks all! I'll take "chiller" as the simple answer. I got on a chair and looked at the top. It's simply a welded wire cage behind which are several air filters. The panels on the front do indeed have horizontal seams. When I checked the top, I found an allen head T-handled wrench which doesn't have the size written on it but looks to be 3/8". Thanks again!! Dismas|^(talk) 08:19, 28 April 2010 (UTC)

Light-straight line; but how many?

It seems to be a ridiculous doubt. Light travels in a straight line. How do we measure/count the total number of 'straight lines' in a particular 'lighted' region? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 10:20, 27 April 2010 (UTC)

Just because something travels in a straight line, does not mean that it is a line. Lux and candela are used to measure light intensity, if that's what you're after, though I don't know much about them. Vimescarrot (talk) 10:55, 27 April 2010 (UTC)

{ec)If I understand our question, the answer is, we do not tend to count such things. An illuminated area is being bombarded by photons. The path of each photon can be considered to be a straight line. If you consider the very smallest point of an area being illuminated, there will be countless straight lines connecting that point to the source of illumination - such as the sun. Trace all of those lines, and you get a solid cone made up of countless lines, with the illuminated point at one end, and, for instance, the sun at the the other end. --Tagishsimon (talk) 10:58, 27 April 2010 (UTC)

The path of each photon is a wave. For example, in the double-slit experiment, the photons each travel through both slits. — DanielLC 14:52, 27 April 2010 (UTC)

The path of each photon is not a wave, it is a straight line. The wave is a time-dependent variation in electric and magnetic field intensities, not a movement in space. --Heron (talk) 17:37, 27 April 2010 (UTC)

I don't think there's any way to argue that photons move in a straight line. Often in special and general relativity people talk about "photons" that are really classical particles moving in straight lines at the speed c. In quantum field theory, though, "a photon" is just a certain amount of energy in the electromagnetic field. Only the total particle number is meaningful. Talking about individual photons is the same as talking about individual liters of water in a river. Do they move in a straight line? It's a meaningless question. -- BenRG (talk) 20:19, 27 April 2010 (UTC)

Is the question "is space infinitely divisible"? 81.131.28.200 (talk) 11:40, 27 April 2010 (UTC)

A true line is an abstract thing with zero cross-sectional area. You could not make holes small enough in two walls some distance apart for a light beam passing through both holes to be reduced to a "line". Questions about how many infinitesimal quantities can add up to a finite quantity, such as how infinitesimal spots lit by lines of light can illuminate an area, are answered mathematically in integral calculus. Before calculus these subjects seemed paradoxical. Cuddlyable3 (talk) 11:47, 27 April 2010 (UTC)

1) Light only travels straight in the absence of gravity. The stronger the gravitational field, the more the path of the light will be bent. (There is an alternate way of looking at it that has the light straight and space-time curved, if you prefer that model.)

2) Light has a dual wave/particle nature. The particle models does have photons of finite size, so there would be a specific, very large, but not infinite, number of photons flying in any given room. StuRat (talk) 13:38, 27 April 2010 (UTC)

Area can theoretically be divided to smallest part up to 2.61223 × 10⁻⁷⁰ m2 (see Plank units). Don't know whether photon in straight line will need more or less than this. - manya (talk) 04:29, 28 April 2010 (UTC)

penury

Is the a mental disease characterized by penury? Plain vanilla with chocolate chips (talk) 10:53, 27 April 2010 (UTC)

No. Mental disease may lead to penury, but is not characterised by it. --Tagishsimon (talk) 11:00, 27 April 2010 (UTC)

penury noun: a state of extreme poverty or destitution. Cuddlyable3 (talk) 11:34, 27 April 2010 (UTC)

It's a pretty inevitable result of schizophrenia in the US. alteripse (talk) 12:06, 27 April 2010 (UTC)

Only if their family won't/can't take care of them. Dauto (talk) 14:30, 27 April 2010 (UTC)

Or if they don't have medical insurance. 76.103.104.108 (talk) 01:52, 28 April 2010 (UTC)

Only if their only option seems to get treatment, and not to be taught to try to fit in socially even with their illness. ~AH1^(TCU) 23:08, 28 April 2010 (UTC)

Spiders

What is the biggest spider found wild in the UK? Is it rare? If so, what would be the largest commonly encountered spider? I'm talking in terms of legspan here, although it would be nice to know the largest in terms of mass also. Thanks —Preceding unsigned comment added by Alaphent (talk • contribs) 14:58, 27 April 2010

Seems you can take your pick between the Raft spider and the Great raft spider as only an expert can tell them apart. --Aspro (talk) 15:45, 27 April 2010 (UTC)

Asystole and CSI: Miami

Calleigh from CSI: Miami was recently rendered unconscious by respiratory distress incident following smoke inhalation. The episode goes on to portray her in ventricular fibrillation with no (perceivable) pulse, followed by asystole. Eric complains they aren't shocking her, which makes sense, because asystole is a non-shockable rhythm, and then the ER physician slams her in the heart area with a syringe, possibly atropine. She then proceeds to jump up with her eyes open. Completely unrealistic, right? People don't just wake up from asystole. And she still has the endotracheal tube in, yet she's not gagging. DRosenbach ^{(Talk | Contribs)} 17:10, 27 April 2010 (UTC)

I generally don't use CSI:Miami as a reliable source for medical information. I assume that every utterance of every word, whether medical, forensic, or anything else, to be complete and utter bullshit made up entirely for advancing the plot of the show, without any hope that any such statements have any connection to actual real medical or scientific truths, except by dumb luck or pure raw coincidence. The same should be said of every single fictional TV show, from House to Lost to Thomas the Tank Engine. They all have an equal level of reliability with regards to medical or scientific information. --Jayron32 18:17, 27 April 2010 (UTC)

No Jayron, Thomas the Tank Engine has origins in the E2 Class designed by Lawson Billinton in 1913 and is a reliable source on matters of Rail transport. Cuddlyable3 (talk) 19:27, 27 April 2010 (UTC)

No, no...It's not like I can't seem to sneak medical advice out of the astute ref desk patrons and seek out CSI to fill that gap :) Rather, I just find it absolutely amazing that so many errors are made when, clearly, many other sorts of routes of medical happenstance could be utilized by the editor team to advance their dramatic agenda. I mean, I laughed when the CSI: NY coroner announced that a bullet had gone through the right occipital bone, when it's clear that the occipital bone is unpaired, and that mistake could have been eliminated without much disturbance to the plot. So when they make Calleigh's dramatic arousal from unconsciousness reliant on silly medicine when they could have made it reliant on actual medicine...I sense a tinge of arrogance on the part of the editorial team to care so little about reality in a show that focuses on reality. It's not the same as Archie Bunker having said, "Let's stop doing CPR because he's dead!" -- but that's what someone told Flack in CSI:NY last year. Can't they just get with the program? DRosenbach ^{(Talk | Contribs)} 18:32, 27 April 2010 (UTC)

It sounds like the doctor watched Pulp Fiction in a med-school course, 'cause it worked for Uma Thurman too. Concidentally, The Economist magazine has an article this week on the "CSI effect", defined as "the phenomenon in which jurors hold unrealistic expectations of forensic evidence and investigation techniques". That's a little more worrisome side effect. Franamax (talk) 19:02, 27 April 2010 (UTC)

Do you mean the CSI effect? WHAAOE. --Jayron32 19:08, 27 April 2010 (UTC)

Actually more than one. Cuddlyable3 (talk) 19:31, 27 April 2010 (UTC)

I dunno about that last one, it was written by someone with an obvious conflict of interest... Also a quick check with an MD confirms that intracardiac injection is never used nowadays; in the past it was likely epinephrine; and the Pulp Fiction scene at least bears no relation at all to medical reality. (Is it medical advice to say that you shouldn't stab your friends in the chest with a honkin' big needle?) Franamax (talk) 20:54, 27 April 2010 (UTC)

The "penny in the fuse" part of the episode was particularly idiotic, along with the notion that the batty neighbor lady could calculate that the penny was needed to prevent the fuse blowing when the plumber was electrocuted through clean water she sprayed on the floor. How did she calculate that more than 15 amperes would be carried through the water, across the floor, through the plumber to the pipe he was touching? I would estimate far less. And sticking an elongated penny into the FRONT of a fuse was not ever a common (but recognized unsafe) practice in the days of fuse boxes. (I will not elaborate on the "to be avoided" practice regarding pennies and fuses, nor should anyone else). What are the writers smoking when they come up with these plot elements? Edison (talk) 04:51, 28 April 2010 (UTC)

In most such cases they're probably performing under the constraint of "We don't need it good, we need it tomorrow!" 87.81.230.195 (talk) 14:57, 28 April 2010 (UTC)

Dropping a potato out of a plane

Yes, it's another of those "Never!" bets again. My friend is an amateur pilot, and through a rather convoluted path we got to the (enthralling) topic of dropping potatoes out of planes. She worried it might kill someone; I said this was unlikely (recalling the coins-off-the-Eiffel-Tower scenario). We promptly set off trying to determine (roughly) what would happen.

Our potato is (for argument's sake) a sphere of diameter 5cm and density of 1.6g/cm³ (it weighs ~105g) and we're dropping it from sufficient height that it will achieve terminal velocity but not so much that it might change during the process (freeze, splinter, gain mass from clouds or whatever). From this, we got a terminal velocity of around 8 m/s. So far, so good.

We now knew everything we needed to about the potato, but transferring this into a living/death thing proved tricky. I'd love to have your thoughts on how to model it - the simpler the better, I suspect the answer is unlikely to only just cause death or just not, so exactitudes don't really matter - we just need an answer! :) Thanks, - Jarry1250 ^{[Humorous? Discuss.]} 18:38, 27 April 2010 (UTC)

What does a potato weigh? About 1/4th to 1/2 of a pound? That's roughly 0.12-0.25 kilograms or so. Will an object, somewhat squishy, moving at 8 m/s and weigh 0.24 kees kill someone? Probably not. It has E = 1/2 mv² = 1/2 * 0.25 * 64 = 8 kilojoules of energy. I can't imagine an object imparting 8 kilojoules of energy actually killing someone, unless it hits just right. It would probably leave a nasty bruise, and that's about it. --Jayron32 18:59, 27 April 2010 (UTC)

Quite. Our imaginary "potato" weighed 0.11kg so slightly less than yours anyway. However, it says at HowStuffWorks (not the most reliable source, I know) that 100 foot-pounds in enough. Wolfram tells me 100 foot-pounds is about 136J (?). Which doesn't seem like much. Which worries me. Where am I going wrong? - Jarry1250 ^{[Humorous? Discuss.]} 19:10, 27 April 2010 (UTC)

Sorry. I mistyped. It should be 8 joules of energy. A joule is a mks unit, and I mistook it for a cgs unit. In that case, a dropped potato of only 0.11 kg should impart about 3.5 joules of energy. This is rougly 2.7% of the energy needed to kill you. In other words, it would need to be a large sack of potatoes to have enough energy to kill you reliably. --Jayron32 19:20, 27 April 2010 (UTC)

Of course. It all makes sense now :) Thanks. - Jarry1250 ^{[Humorous? Discuss.]} 19:30, 27 April 2010 (UTC)

(ec) Got some other figures for you, from Cycle, a national UK cycling charity. It seems that bike helmets need to meet a standard of protecting a head from about 65 joules upon impact with a rounded anvil. I know it's outside the potato/plane box, but I would suppose that realistically, a potato dropped from a great height would be travelling almost straight downwards due to air resistance and so the head would be the most likely impact zone. Cutting it short: it looks like a single spud is an order of magnitude too low to fracture someone's skull. The article states, for comparison, that an estimation of the energy of a fall onto flat tarmac from stationary is about 75 joules. Brammers (talk) 19:37, 27 April 2010 (UTC)

As a pilot myself, I would like to point out that the Federal Aviation Regulations explicitly forbid dropping any object from an aircraft in a manner that creates a hazard to persons or property. The FAA is pretty strict on this one, so it's far better not to drop it at all, as you cannot be 100% sure that there is nobody/nothing in the potential path of the potato. Falconus^{p t c} 19:18, 27 April 2010 (UTC)

Haha, don't worry, we weren't going to try it (although, as my friend rather humorously pointed out, I really ought not to be the one worrying). And we'd be under the CAA anyway, but meh, they probably have the same rules (I'm not a pilot myself). And of course the above omits the small chance it did perchance do serious damage, so not point relying on it. But I'm happy now. - Jarry1250 ^{[Humorous? Discuss.]} 19:30, 27 April 2010 (UTC)

Well they are not suppose to dump stuff out of the aircraft, but sh*t does happen. We hear things like this every now and then. See Blue_ice_(aircraft). --Kvasir (talk) 19:54, 27 April 2010 (UTC)

Impact on the head, pshaw, what sort of imagination is that? How about if it knocks the gun out of a soldier's hand as he's about to ambush an enemy, who hears the noise, turns around, and shoots him? Or it splatters over someone's windshield, blocking the view while they're on a twisty road, and they drift into the oncoming traffic? Or it lands next to a vicious dog or a poisonous snake, which looks around and fatally bites the nearest human? Or it drops into a tornado and is accelerated to 10 times its previous speed and then hits someone on the head? Or it knocks the camera out of someone's hand and breaks it, preventing them from taking the photo which would have been confirmed their testimony which might otherwise have been considered dubious, thus allowing a murderer to plead guilty to a lesser charge and be sentenced to only 15 years in prison, after which he commits another murder? (Insert butterflies here.) What about that, hmmmm??? --Anonymous, 20:55 UTC, April 27, 2010.

I was going to mention those, but decided on "the small chance it did perchance do serious damage" in the end, very much in the spirit of WP:BEANS. Heh. - Jarry1250 ^{[Humorous? Discuss.]} 21:00, 27 April 2010 (UTC)

Mr./Ms. Anonymous, whoever you are, you should be a writer of detective fiction. BTW, why don't you sign your posts so that literary agents would know who you are?  ;-) 76.103.104.108 (talk) 01:57, 28 April 2010 (UTC)

8 ms^-1 for the terminal velocity? That's not all that fast. Gravity is 9.8 ms^-2 - so your potato will get pretty close to that speed in about 2 seconds. You don't have to be all that high up to get that kind of speed - a third floor window would probably be enough. Now all you need is a "human analog" (to use a handy Mythbuster's phrase). I suggest a large watermelon. So find a nice high window - overlooking an enclosed area - stick a handful of representative melons out there and haul a few bags of potatoes up three or four floors. It may take quite a few drops to get a potato on target - but it'll get you an answer in an hour of trying. You can add some other interesting destructible objects too. Tell us what happens! SteveBaker (talk) 03:15, 28 April 2010 (UTC)

Don't forget to invite friends and have a cookout with the potatoes and watermelon. Ariel. (talk) 05:09, 28 April 2010 (UTC)

Railguns on ships

I took the info from this Cracked article, railgun, speed of sound, and a random ship: Spanish aircraft carrier Principe de Asturias.

While discussing the enormous destructive potential of railguns as mentioned in the Cracked article with a buddy, he asked if the sheer force of firing a slug at mach 7 wouldn't roll the ship. Railgun says that the slugs are 3.2kg, and seven times the speed of sound is 5,376 mph. A ship like the Principe de Austurias weighs roughly 16,000 tons, which would be 16,000,000kg, right? Accelerating a mass 5,000,000 times greater than this 3.2 kg slug would accelerate it 5,000,000 times less...meaning...it would accelerate 0.0010752 mph in the opposite direction that the railgun fires.

...Is all of this right? I'm asking on Science not Maths because I imagine most good scientists would be able to think their way through these calculations fairly easily, and I'm also after other factors that I might not have thought of. Vimescarrot (talk) 19:58, 27 April 2010 (UTC)

Note: The gun is not being fired at the ship, it's bolted to the deck and firing from the ship. Ran this scenario past a friend and he didn't realise, so I thought I'd best mention it. Vimescarrot (talk) 20:09, 27 April 2010 (UTC)

Hey, when I model the experiment in my mind, I come up with the complication that you can't simply take the whole weight of the vessel and use it as a denominator to find the ship's acceleration. The question is not 'will the ship move sideways in the water', but 'will the ship roll' (i.e. will the top of the ship move relative to the bottom in the vertical axis'). In this case, you can only use a fraction of the vessel's weight as the denominator. I think the calculation must be complicated but I would suggest that the majority of the ship's weight is low down, to prevent it from capsizing. The weight around the centre of gravity will be accelerated less, but the surface of the ship will be accelerated more because it is lighter and is some distance from the fulcrum. Nonetheless, it's still probably only a fraction of an mph, because you also need displace all that water in order to move the... what's it called... stern? --Seans Potato Business 20:24, 27 April 2010 (UTC)

Err, forget roll for a moment. How are you going to stop the gun's recoil from splinting the vessels structural joints?--Aspro (talk) 20:48, 27 April 2010 (UTC)

Time to break for a photo of the Iowa

An Iowa class battleship fires a projectile of around 1000 kg at about 820 m/s, which (if my dodgy math is right) is a muzzle energy of 336 MJ per projectile, and thus the same amount of recoil energy that has to be dissipated by the vessel. The numbers Vimescarrot quotes amount to 9 MJ for the railgun. And the Iowa has 9 such guns which it seems it can safely discharge simultaneously; that's 3TJ of recoil. -- Finlay McWalter • Talk 21:07, 27 April 2010 (UTC)

Use springs to prevent it from splintering.--Cheminterest (talk) 21:10, 27 April 2010 (UTC)

The 'force' being applied to the projectile is via the use of different principles of physics. So first one need to establish the nature of 'recoil' as it applies to a mass being accelerated in this fashion – yes? --Aspro (talk) 21:20, 27 April 2010 (UTC)

No. A force is applied between two objects, pushing them violently apart. Simplistically, it's an elastic collision, with half the energy used to imply each object with momentum, by Newton's third law. It doesn't matter whether the force comes from an exploding gas or a powerful magnetic field. In practice the process isn't perfect, so the collision is really elastic (stuff gets hot) and with cleverness you can spread the recoil energy around, but it doesn't go away because you're using magnets not cordite. -- Finlay McWalter • Talk 21:38, 27 April 2010 (UTC)

Another concern is resonance. I'd assume they will shoot more than one of those projectiles during a battle, so then the Q is how long they wait between each. If we assume that the rail gun is above the CG for the ship, then the ship should roll somewhat, then roll back the other way, and back again, less with each roll and counter-roll due to frictional effects.

If the time period between firing slugs is the same as a full roll-and counter-roll, then you would get an increase in magnitude with each new shot, due to resonance. I doubt if it would add up to anywhere near enough to roll the ship, but it might be enough to adversely affect accuracy. Of course, all these issues also apply to conventional shells, so I'm sure they already have strategies in place for dealing with the problem. StuRat (talk) 22:30, 27 April 2010 (UTC)

This chapter says that there is a recoil brake (which seems to be a gas cylinder damping arrangement - see fig 5B21) which it likens to a dashpot, which both spreads the recoil impulse delivered to the ship out over time (to lessen the otherwise shattering shock) and to dampen the oscillation. I'd imagine it'll also reduce the noise inside the ship. If they didn't have this, and instead had the gun firmly bolted straight to the main structural members of the ship, I guess it would feel like being inside a giant gong. -- Finlay McWalter • Talk 22:45, 27 April 2010 (UTC)

The scary bit is where they're going to get all the power to run this thing. Railgun#Railguns as weapons talks about a 64MJ muzzle-energy weapon. This General Atomics press release compares the size of the capacitor array to drive a smaller gun, and from that it looks like the whole arrangement (capacitor discharge and railgun operation) is less than 50% efficient (the railgun article also talks about the guns getting very hot due to this inefficiency). So that 64MJ gun will need something like 128MJ in the capacitors to run it, and railgun talks about a fire rate of 10 per minute, which is once every six seconds. To store 128MJ in six seconds they'd need a power supply of 21 MW. The twin Rolls-Royce Marine Trent powerplants they're planning on putting into the (possibly one-day railgun capable) Zumwalt class destroyer put out 78MW, so they'd be using a quarter of the ship's entire power to run one gun (and that assumes they can actually run the generators with the gas turbines at full, and have enough bus capacity to shift that power around). Still, with other power-hungry things like free electron lasers and Electromagnetic Aircraft Launch System (122 MJ) it looks like the US navy is going very capacitor-heavy. -- Finlay McWalter • Talk 23:19, 27 April 2010 (UTC)

So put the railgun on a ship that has a nuclear reactor for power supply. Destroyers are probably too small, but a cruiser could probably have one. Googlemeister (talk) 13:28, 28 April 2010 (UTC)

Sure, you could do that. But a Zumwald already costs getting on for 6 billion dollars, without railguns, nuclear reactors, or death rays. A cruiser like Ticonderoga is about four times the displacement of Zumwald; at that rate the US Navy would be able afford to field only a handful of ships. Railgun has to compete against TLAM for the shore-bombardment role, and while shot-for-shot TLAM is pricey the incremental cost of adding TLAM to existing vessels is pretty moderate and it's flexible enough to fit to Ticonderogas, Iowa, Arleigh Burkes, and submarines. -- Finlay McWalter • Talk 15:21, 28 April 2010 (UTC)

The destructive force of a railgun is given by its energy, which is proportional to the square of velocity. The roll-the-ship effect, however, is given by momentum, which is only linearly proportional to velocity. A 3 kg slug moving at 7 times the speed of sound just doesn't have enough momentum to matter to a thousand-ton ship. You wouldn't feel more than a small shudder. It's curious how poor people's intuition is about things like this -- in movies you often see somebody hit by a bullet who is knocked backward or even stopped in midair. Ridiculous! It happens, I think, because most people's intuition doesn't properly differentiate between kinetic energy and momentum. Looie496 (talk) 05:21, 28 April 2010 (UTC)

I think that pretty much covers everything I was after. Cheers Vimescarrot (talk) 13:03, 28 April 2010 (UTC)

The US Navy has a habit of spending billions on ships who's roles could be filled much more cheaply. For example the new Littoral combat ships fulfill a role that could probably be done better by a tug boat with a Bofors 40 mm. Any big ship could easily handly the recoil from a railgun. They already have fully automatic 5-inch guns that produce about the same recoil yet constatnly--92.251.243.109 (talk) 21:58, 28 April 2010 (UTC)

% of water when raining

How fast would it have to be raining in order for a person to drown from just walking around unprotected? I thought about figuring out what % of the air is replaced by water when it is raining at 1"/hour and then scaling it to a point that a human can not survive, but have not been about to figure out the first. Googlemeister (talk) 21:18, 27 April 2010 (UTC)

It's going to be hard to calculate properly (accurately) because the terminal velocity of rain depends on how much rain there is. According to this, 9m/s seems to be a good number to work with. The equation you want is: 1inch/hour / 9m/s = .000000784 = %.0000784, which is the fraction of the air that contains water. You'd need 1,275,590.55 inches per hour to have the air be solid water (if you convert the units, 9 m/s = 1,275,590.55 inches/hour), but a person may drown in less than that. Ariel. (talk) 22:15, 27 April 2010 (UTC)

it depends on how they face when they breath, too. The rain water in the air isn't randomly distributed, it's in discrete droplets falling downwards. Someone bent over in the rain doesn't inhale much water, but someone staring at the sky might inhale a good deal more. APL (talk) 22:29, 27 April 2010 (UTC)

Is this assuming that it's raining everywhere on Earth at the same time? As the clouds taper to an end, and there is no rain, wouldn't the rainfall adjacent to this circumference run off into the area where it wasn't raining...I mean, does your 1.3M inches an hour take this into account? DRosenbach ^{(Talk | Contribs)} 03:29, 28 April 2010 (UTC)

The 1.3M inch/hour figure is an estimate of how much water would be falling per area if what was falling was solid water coming down at 9m/s. (Of course in that case terminal velocity in air would not really come into play. The velocity would instead be limited by how fast the water on the ground was moving out of the way). Run off isn't an issue until after the water has hit the ground. Otherwise we're just talking about the conditions for flooding, no? Rckrone (talk) 06:05, 28 April 2010 (UTC)

It has to be close to 100% water in the air; if you bend down you will not get the water if it is less. --98.221.179.18 (talk) 19:24, 28 April 2010 (UTC)

If rain is falling down, air must be coming up. Cuddlyable3 (talk) 19:53, 28 April 2010 (UTC)

The relevant experiment is to walk under a waterfall and see how dense it can be before you can't deal with it. If you have any experience with waterfalls you'll probably see that the force of the water will knock you flat long before it gets dense enough to drown you. Looie496 (talk) 20:57, 28 April 2010 (UTC)

extreme human evolution

Assumming that the human race will live to see Pangaea Ultima in 250 million years, what speculations do you have as to how humans will evolve given that amount of time?—Preceding unsigned comment added by CHEMX (talk • contribs) 22:55, 27 April 2010

Since humans have so far been around for maybe 3 million years, and perhaps do not have the stability of cockroaches and trilobites, I would assume that there will be no humans recognizable to us even if the planet has survived that long. alteripse (talk) 23:17, 27 April 2010 (UTC)

Evolution seeks to increase the number of offspring for a given environment, and since humans are doing a fine job of creating offspring, unless the environment changes humans are unlikely to change at all. Except maybe evolution to make birth control impossible. Predicting how the environment will change in 250 million years might be hard. Also, given our intelligence, we are unlikely to allow evolution to do anything at all, but rather we will take control of our DNA on our own. Ariel. (talk) 23:21, 27 April 2010 (UTC)

Respectfully thats just silly. The time scale is nearly 2 orders of magnitude greater than a human history that has already seen changes to the point of speciation. The human birth rate and the rate of the change of the environment means that the only thing we can be sure of is that your prediction, of no real change, is the LEAST likely of all alternatives. alteripse (talk) 23:34, 27 April 2010 (UTC)

Well, the human birth rate suggests we'll see an increase in genetic diversity but for evolution you need a difference in reproductive success (often due to people with certain genes dying before reproducing). Given modern technology and welfare states, your genes don't have much impact on your reproductive success. The amount of evolution we've seen over the last few million years is irrelevant since it is almost all pre-industrialisation and the existence of modern industry cannot be ignored. Evolution due to being a better fit to our environment won't happen much since we tend to alter our environment to suit us rather than the other way around. Evolution due to sexual selection is still possible, I suppose (which some authors have suggested will result in the human race splitting in two [34]). --Tango (talk) 23:46, 27 April 2010 (UTC)

The reference desk isn't for speculation and there is no way to do anything more than guess. Evolution has a large random element. I can make some general comments, though. If humans do change significantly, there won't necessarily be a single human race because we could have undergone speciation, but that seems unlikely due to the ease of travel these days meaning populations won't get isolated (although isolation doesn't have to be geographic). The most rapid evolution tends to happen during times with lots of people dying (especially ones leading to population bottlenecks) and modern technology combined with the near-global spread of humanity means that doesn't happen much any more, so we shouldn't expect much change in the human race. A Google search finds lots of other people's opinions if you don't like mine. --Tango (talk) 23:33, 27 April 2010 (UTC)

There are a lot of speculative, futurology predictions about human genetics. Lee Silver's Remaking Eden has a particularly interesting one regarding the possible long-term effects of "reprogenetics" technology on the human genome. But yeah, 250 million years is a long time. A lot of stuff can happen in that amount of time that would affect things. Even if you imagined that nothing major would happen (which is impossible, really), it's not clear how you'd even extrapolate current trends in a meaningful way. --Mr.98 (talk) 23:48, 27 April 2010 (UTC)

The difficulty here is that humans are able to actively resist the effects of evolution. When someone has a mutation that causes them to be unable to procreate - in steps science and provides a variety of interventions that allow that gene to be passed on. This reduces the tendency for bad genes to be eliminated from the population. We'll get better at this - we'll be able to treat genetic diseases. This could cut out beneficial genes as well as bad ones. Furthermore, we're changing the environment vastly more quickly than evolution can track those changes. Given a few tens of thousands of years of online dating and cellphone texting - we might evolve to take advantage of that...but nobody believes that this technology will still be here, unchanged in 10 years - let alone 100 or 1,000 or the 10,000 it might take for a noticable genetic change. We're also living longer and having children later...that increases the generation length...longer generation length, less genetic change, less evolution. Then there is the possibility of 'designer genetics' - maybe we'll be able to choose the genes of our children? If that happened, evolution could be at the whim of fashion. We might start doing things like copying our brains into computers and becoming immortal, digital beings. No more evolution with an infinite generation time.

With all of those possibilities (and more besides, I'm sure) - the laws of evolution may simply cease to apply to humans. So where we end up in even 1,000 years is totally, fundamentally unpredictable. Most scientists are loath to make technological predictions beyond 25 years - and our lives are increasingly technological beings.

I believe that we are on the brink of a post-genetic era - evolution for us is becoming entirely memetic. Memes (ideas) evolve, mingle, reproduce, survive or die out. They can do it on short genetic timescales and reproduction is cheap in an intercommunication-rich digital world. I could easily imagine a future where ideas are all that's left - humans (and human bodies in particular) become an unnecessary (and difficult) part of the future. We could be out-evolved by our own memetic offspring.

SteveBaker (talk) 02:53, 28 April 2010 (UTC)

Just as an example as to how bad we are at predicting even basic technological advances, consider that the first three books of the Foundation series lacked anything resembling an actual computer. And this is from an author, Isaac Asimov, who was an actual honest-to-god chemistry professor and professional scientist. The first book was written in the early 1940's, before computers even existed, and the series came to be in the early 1950s; at that time computers were basically large devices used to calculate ballistics trajectories and stuff like that. The idea that computers would be as pervasive as they are today didn't even enter into people's mind, even in science fiction. If someone as well versed in the science and technology as Asimov couldn't have predicted something as core to modern life as computers, writing only 60 years ago, how can we meaningfulling make predictions any reasonable time into the future. 60 years from now, will will likely find our lives pervaded by some technology which hasn't even been invented yet and which no one is really even thinking about. --Jayron32 03:40, 28 April 2010 (UTC)

Well, by the early 1950s Asimov was writing about some extremely advanced computers in the form of robots with positronic brains. The thing that pretty much everybody missed until around 1990 was what would happen with the internet. Looie496 (talk) 05:11, 28 April 2010 (UTC)

The difficulty here is that humans are able to actively resist the effects of evolution. - Steve, I'm disappointed that you make such a claim. That's plain wrong. What we do is changing the parameters of the selection - we do nothing about the evolution itself. In fact, we currently select some genetic defects out of the gene pool (without really understanding all implications) by parent screening and pre-natal screening. --Stephan Schulz (talk) 12:41, 28 April 2010 (UTC)

Evolution has effects - we can (and do) resist them. I don't see anything difficult or controversial about that claim. A genetic change that is strongly disadvantageous in our present world would "naturally" have drastically reduced the probability of that individual reproducing successfully. 'Bad' genes may well be retained in the gene pool through artificial reproductive help, or through treatment of the genetic diseases. This is us actively resisting evolution - ensuring survival, not just of the fittest, but also of the profoundly unfit. As a consequence, we may wind up with increasing numbers of people who are accumulating disadvantageous genes who can only continue to survive and breed with advanced medical help. Under those circumstances, we're not evolving to better fit our environment - but developing technology to prevent us from better fitting into our environment by changing the environment to meet whatever genetic weirdness is thrown up by random mutation and recombination. Every time we 'cure' a genetic disease - or help a couple to have children who otherwise could not because of some genetic problem - we're fighting the tide of evolution. Don't get me wrong - I'm not saying we shouldn't do that - but we should be more clearly aware of the magnitude of the effect we're having on our own species by doing that. SteveBaker (talk) 23:46, 28 April 2010 (UTC)

What if humanity is able to finally escape the planet entirely? If it even survives the next 3 million years, it's likely that humanity will leave it's ancestral home. If there are colonies on multiple planets/moons/asteroids, even in our own solar system, there will likely be isolated populations and speciation will occur simply due to the general cost of interplanetary travel. It doesn't help that mutation will be even more likely once you leave the protective cocoon of Earth's magnetosphere. -- JSBillings 13:00, 28 April 2010 (UTC)

Well I don't see us colonizing very far from Earth for a very very long time unless relativity is proven wrong. 25 light years is the point of no return. Would you volunteer to go with a few hundred others to live on a unknown and unexplored, and likely extremely dangerous planet, with no chance of ever seeing the ones you love ever again?---92.251.243.109 (talk) 21:45, 28 April 2010 (UTC)

"The difficulty here is that humans are able to actively resist the effects of evolution"—well, kind of, but not entirely. And in any case, over 250 million years, making that assumption seems wrong. Humans have really only been able to do this well for a few hundred years, maybe a few thousand if you are very generous in your definitions. The idea that we will be extending this capability into the millions seems unjustified to me. (The idea that the species—in any form—will last into the millions seems unjustified to me, as well!) --Mr.98 (talk) 13:51, 28 April 2010 (UTC)

The assumption that the human race will survive millions of years was an explicit part of the question, so it doesn't need to be justified (that is what "assumption" means). --Tango (talk) 14:04, 28 April 2010 (UTC)

I know, that's why I put it in parentheses, because it is a little peripheral. --Mr.98 (talk) 14:32, 28 April 2010 (UTC)

If an advantageous mutation comes along, it has a chance of staying. That's the idea behind natural selection. Imagine Reason (talk) 13:13, 28 April 2010 (UTC)

That's a tautological definition of natural selection; whether a mutation is "advantageous" or not depends on the selective pressures of the environment. --Mr.98 (talk) 13:51, 28 April 2010 (UTC)

Members of the Scientology "Sea Org" who signed a billion-year employment contract with the organization will have only 750 million years left to catch up on their confessionals. Cuddlyable3 (talk) 19:51, 28 April 2010 (UTC)

April 28

Molecular Electronics

I'm a physics undergrad who's starting to appraise his options for a research career, and one field in particular that seemed interesting was molecular electronics. There seems to be elements of both physics and chemistry involved (which I don't mind), but I was wondering if a physics degree would properly prepare me for research in this area. I'm betting that an undergrad program won't matter all that much in the long run anyways, but what should I be looking into for graduate school? Also, while I don't mind chemistry I much prefer physics, so I need to know if such research can be more physics-based than chemistry-based. In other words, will I end up being a chemist or a physicist? Thanks. 173.179.59.66 (talk) 00:41, 28 April 2010 (UTC)

You are right in terms of your undergrad degree being somewhat irrelevent here. Any degree in the hard sciences (Chem, Physics, Bio) or engineering would probably set you up just fine for a graduate program in molecular electronics. What you need to do for grad school is find a professor somewhere in the country who is working in the field you want to work in, and contact them directly, letting them know you are interested in the field. In the sciences, grad school is all about what lab you are working in, and networking with the professor you will be working under is much more important than the school itself. As an undergraduate, things like extracurricular activities, campus life, geography, appearance of the campus, location, dorms, etc. etc. are all important aspects of choosing a school. For a terminal degree (Masters or PhD), its ALL about the program you are interested in. So if you find a well-respected researcher who is working in your field of interest, you should seek him out and ask him if he has any openings in his lab; what sort of work he does, how to go about getting in there. That will make getting into the school much easier. --Jayron32 02:50, 28 April 2010 (UTC)

Warm Sector

All I need to know is the definition of a Warm Sector for a lab titled "Frontal Weather." 74.76.183.139 (talk) 01:26, 28 April 2010 (UTC)

See Air mass and Weather front. A warm sector would simply by the warmer of two air masses that meet at a front. If the cold air is pushing the warm air out of the way, the front is called a cold front. If the warm air is pushing the cold air out of the way, the front is called a warm front. --Jayron32 02:45, 28 April 2010 (UTC)

Usually, the warm sector of a frontal system in the Northern Hemisphere is in its southeast quadrant. ~AH1^(TCU) 23:05, 28 April 2010 (UTC)

Chemistry: Si face and re face

I read the article Si face but I still don't understand how to distinguish a si-face from a re-face. Please explain what they are. —Preceding unsigned comment added by 70.68.120.162 (talk • contribs) 01:46, April 28, 2010

They "are" a formal way of describing the two faces of a flat location (atom in a molecule), defined by the position the things attached to that atom. Consider your right hand: looking at the palm, the fingers in order thumb-first-middle-ring-pinky go around in a counterclockwise direction; looking at the back of your hand, those same fingers in that same order go around in the other (clockwise) direction. The terms "si" and "re" are a way of identifying which face of your flat hand you are looking at, based on clockwise-vs-counterclockwise direction of the things attached. The "order" is the atomic masses of the atoms attached to the one being analyzed. The "direction" is still clockwise (called "re") or counterclockwise (called "si"). DMacks (talk) 06:30, 28 April 2010 (UTC)

Are cars and planes Faraday cages?

If yes, why are we able to use the cell-phone in them? (I assume that a Faraday cage would block a cell-phone wave). If not, why do they protect against a lightning? One possible answer that comes to my mind is that they are good enough to protect us against a lighting, but not good enough to block the cell-phone. Right?--Mr.K. (talk) 11:37, 28 April 2010 (UTC)

Whether a Faraday cage blocks a cell phone signal depends (mainly) in the thickness of the walls and their conductivity. Lightning however, is a discharge which takes to path of least resistance. Here is a photo of a lightning resistant soft-top: [35]--Aspro (talk) 11:55, 28 April 2010 (UTC)

It's also a matter of frequencies - cellphones are up in the GigaHertz range - lighting is basically DC. SteveBaker (talk) 12:08, 28 April 2010 (UTC)

Lightning is an impulse-like burst, and has energy content at most frequencies. There is usually more energy at very low frequency, below 10 kHz, but there is also very strong RF in the VHF and even some energy in the gigahertz range. Lightning is also large and powerful enough to have very nonlinear frequency behavior and is known to couple energy and particles into the ionosphere and magnetosphere. The fact that it doesn't harm people inside airplanes is due the skin effect, not because the plane is (or is not) a Faraday cage. You can be certain that the radio signals can be detected from inside the plane - so it's not effectively shielding all energy. Here is a beautiful video of a lightning research aircraft, the audio includes RF signals detected inside the plane used to analyze the video footage. This video focuses on transient luminous events, which are rare atmospheric/ionospheric electromagnetic phenomena related to lightning. Nimur (talk) 18:07, 28 April 2010 (UTC)

The cell phone signals come in through the windows, which are big holes in the metal screen. Graeme Bartlett (talk) 12:11, 28 April 2010 (UTC)

The newer aircraft made from non-conducting composite material will need thin metal meshes and foil to be included in construction for lightning protection. However, with a cell phone's 800 MHz to 900 MHz frequency (equals wave length of ≈ 33 cm) and with so many gaps in protection it is unlikely that they will block cell phone signals either.--Aspro (talk) 12:17, 28 April 2010 (UTC)

I think you'll find that some cell phone frequencies are 900 MHz, not 900 Hz. And not all are, especially in countries other than the USA, where some of us live. --Phil Holmes (talk) 15:05, 28 April 2010 (UTC)

Thanks --Aspro (talk) 15:42, 28 April 2010 (UTC)

Has anyone mentioned Lightning rod? Pretty good article actually, even has a section on aircraft. Vespine (talk) 23:12, 28 April 2010 (UTC)

EM colours

Looking at this informative diagram, I was wondering about certain crustaceans (shrimps) that can see the UV spectrum (or animals that can see IR) and what colours they can actually see. Then I had a random but intriguing thought - if we could see sound, what colour(s) would it be? How/why did the mechanisms of animals adapt to see higher/lower frequency EM and why can't any animal see sound? Sandman30s (talk) 13:35, 28 April 2010 (UTC)

Animals cannot see sound because sound is MUCH lower in frequency than light. It's like asking why no animal can hear light either. The question if we could see sound, what colour(s) would it be? is meaningless; we could never see sound, and even if we could it would be impossible to describe with the very limited color selection humans have. 99.137.221.37 (talk) 13:42, 28 April 2010 (UTC)

Well, we need to define "see". If we mean perceive sound using eyes, then that's just nonsense, it's not what eyes do. If we mean get information using sound equivalent to that we get from light, then echolocation does something very close to that in some species (eg. bats). There is no concept of colour, though, since it is an active process - the sound is emitted by the animal, so the animal controls the frequency. --Tango (talk) 14:23, 28 April 2010 (UTC)

We don't really have words for the "Colors" you'd see if your vision used different primaries than human vision, if that's what you're asking. APL (talk) 14:07, 28 April 2010 (UTC)

There's a reason that color is the go-to example for the philosophical concept of qualia -- the important characteristic of red, green, and blue is that they are different from each other, nothing more. Philosophers will then argue about whether there is some kind of "essential redness", or if red can be completely described as "the color between 630 and 740mm in wavelength, associated with blood, fire trucks, and stop lights, etc."

Qualia haven't (and pretty much can't) be proved to exist, so questions about "what would it be like to see color differently" are philosophical ones. If you want some fun reading in the area, see philosophical zombie, and try to decide if p-zombies are impossible, possible but non-existent, or everywhere! Paul (Stansifer) 14:15, 28 April 2010 (UTC)

Second question first: It has been proposed by some scientist that bats may perceive their received echoes as visual impressions and in colour, but that's not proven yet. I will leave out people with Sound -colour-synesthesia fascinating as it is. However, to answer your question, it would be better to ask about the advantages of the visual spectrum for our sight and the evolution advantage that favoured it. Basically its down to frequency and the biological limitations of the two sensing organs. The retina evolved from part of the neurone network of the brain. It has many light sensitive nerve endings onto which the image of the external world can be focused. Or put it a different way: it can detect spacial separation of points to form a mental image. Whereas the ear evolved from part of the jaw and other bits of the anatomy into the organ it is today but each ear can only register one scale of frequencies. The two ears can detect differences in loudness and phase. But very often one has to turn one's head to determine the direction of the noise source. Now, this has a limitation that can be understood a little by understanding Information theory. Sound ( in air, S.T.P.) has a narrow bandwidth. Other noise sources easily swamp the 'useful' ( and sometime life preserving) information in such a system. Eyes, don't have that problem. Bats have mitigated this shortfall to some small extent and enough to hunt by, by using higher frequencies, which in effect increases the usable bandwidth well above ours. We evolved ( or so I'm told ) on the ancient, open, savannah. In this environment, it is useful to have astute discrimination for the phase shift of lower frequencies, as made by animals that wanted to eat out ancestors. It is also useful for hunting, as the phase shift give good spacial information as to location of our other hunting companions. It has been suggested that we evolved our ability to run efficiently for extended periods because that way we could run our quarry to exhaustion. The ability to hear as we do, is well suited to this type of pursuit. So, the answer is that visual sight gives animals an evolutionary advantage, which sound alone would not.--Aspro (talk) 15:11, 28 April 2010 (UTC)

If you could see sounds, you would have a seismic image or a sonogram. Sound does not have a color. It has a power spectrum, and can be described as many frequency components, each with their own amplitude and phase. In some ways, this is similar to optics, insofar as light also can be described with a frequency spectrum; both phenomena are waves; but the similarities end there. The type of waves are dramatically different; the scales (of both energy and wavelength) are dramatically different; and therefore, the transducers that can convert the physical effect into usable information are very different (microphones and ears, versus cameras and eyes). If you feel like redefining the word "color" to be equivalent to "frequency", you may consider any frequency-spectrum to contain "color" - but that's a matter of word-choice. In practice, when we generate images using non-visible sources of information, we typically create false color images, where the color in the graph indicates some other property (most often, amplitude, and not frequency). But we can create false color images using any parameter along the color axis. For example, hyperspectral images "compress" many non-visible wavelength spectral channels into the set of printable, visible colors. Nimur (talk) 18:26, 28 April 2010 (UTC)

A peculiar colourisation of Chopin (video) Cuddlyable3 (talk) 19:19, 28 April 2010 (UTC)

Dream Recall

I've tried everything to improve my dream recall. I kept a dream diary, I interrupted the sleep cycle during rem sleep etc, I followed all the guides for dream recall and none of it works. So I was wondering, are there any scientifically proven methods that improve the recollection of memories from dreams? 82.43.89.71 (talk) 14:15, 28 April 2010 (UTC)

I can't see why any scientist would see a need to do a review of the techniques, much less try to develop a protocol. The main use of a dream diary appear to be for indulging in the pastime (or art) of pseudo-psychotherapy dream interpretation. In these modern times (i.e. post Jung, etc), the phenomena known as dreaming is now thought by scientists to serve as a means to consolidate memory. Any 'high emotional' periods from one's past would naturally feature from time to time as links get made from the current day's events but this doesn't mean that they have any meaningful significance (or so I am informed). This seem reasonable to me, as I've known (2 or 3 if you include their spouse ) people get very intrigued by dream interpretation and spent time (after getting their doctorate) to studying it professionally, they all eventual come to the conclusion that it is bunkum. I know this is not a very useful answer but it might save you searching in vain for some scientific work that probably does not exist --Aspro (talk) 18:14, 28 April 2010 (UTC)

I may be wrong here, but it seems that the OP is asking about simply improving his ability to remember his dreams rather than interpret them-- for which things like keeping a "dream diary" can be quite helpful. AlexHOUSE (talk) 18:20, 28 April 2010 (UTC)

His asking is their any scientific proven methods and I'm suggesting probably not and explaining why. Isn't some answer better than non?--Aspro (talk) 18:26, 28 April 2010 (UTC)

Absolutely. Although there's nothing I can find in our articles on oneirology that would suggest scientists are actively plugging away at how to remember your dreams. OP: you might find more tips for dream recall by searching for methods for lucid dreaming-- a field with a little more scientific research put into it. AlexHOUSE (talk) 18:33, 28 April 2010 (UTC)

I don't see how the OP could interrupt their own REM sleep. An effective technique is having an observer wake the subject and record their dream account immediately.Cuddlyable3 (talk) 19:08, 28 April 2010 (UTC)

Alarm clock and notepad? AlexHOUSE (talk) 19:19, 28 April 2010 (UTC)

Alan McGlashan, author of “The Savage and BeautIful Country” said the best way to encourage the Dreaming Mind to facilitate recall of dreams is to respect it and them. Keeping a dream diary would definitely help. Also eating lobsters. Kittybrewster ☎ 20:38, 28 April 2010 (UTC)

Lobsters? Is there some chemical in lobsters that helps remembering dreams? 82.43.89.71 (talk) 20:45, 28 April 2010 (UTC)

Sorry if I wasn't clear with my question. I am indeed trying to remember my dreams more clearly, as currently I have extreme difficulty remembering anything from my dreams. I do understand that scientists aren't actively working on ways to improve dream recall, but I just wondered if there had been any discoveries at all that might improve remembering dreams. Perhaps a chemical that is known to improve dream recollection or something? 82.43.89.71 (talk) 20:45, 28 April 2010 (UTC)

Maybe some dreams just don't want to be remembered. Try to record the dreams when you can remember them clearly, and when you can't then record all the details you do remember before they fade away. ~AH1^(TCU) 23:04, 28 April 2010 (UTC)

Ambient construction

My son is working through a college report on string theory and asked me for help in understanding some key concepts one of which is "ambient construction". I consulted the wiki page as I had no idea what it meant.

I read: "In conformal geometry, the ambient construction refers to a construction of Charles Fefferman and Robin Graham[1] for which a conformal manifold of dimension n is realized (ambiently) as the boundary of a certain Poincaré manifold, or alternatively as the celestial sphere of a certain pseudo-Riemannian manifold."

and I am now more confused then ever. Can someone please explain this to me at a level most adults would understand? TheFutureAwaits (talk) 14:26, 28 April 2010 (UTC)

Not really, no. It is very technical. I've studied quite a lot of topology and even I would have to look up some of those terms (I've never come across the phrase "celestial sphere" in this context). String theory involves a lot of topology. If you don't have the necessary background, you won't be able to understand the more technical areas of the subject. If you want to try and understand it, you should start with manifold, but don't expect it to be quick or easy. Your son should probably ask someone that already knows about the subject (classmates, lecturers, tutors). --Tango (talk) 14:47, 28 April 2010 (UTC)

"Poincaré manifold" means hyperbolic space in this context. The boundary of hyperbolic space (at infinity) is a circle/sphere (it's the boundary of the Poincaré disk model). There's no natural notion of distance on the boundary, because everything is at infinity, but angles and distance ratios make sense: the geometry of the boundary is conformal. You need hyperbolic space, rather than Euclidean space, for this because the conformal boundary of Euclidean space is just a single point (the north pole of the Riemann sphere in the two-dimensional case). "Pseudo-Riemannian manifold" means "curved spacetime as found in general relativity", but in this case they're probably talking about some very specific curved spacetime, like Minkowski space or anti de Sitter space. "Celestial sphere" means the boundary at infinity of the future (or past) light cone at some point in that spacetime (it doesn't matter which point if the spacetime is symmetric enough). The celestial sphere of n+1 dimensional Minkowski spacetime is the same as the boundary of n dimensional hyperbolic space. This isn't exactly "at a level most adults would understand", but maybe it will help somewhat. -- BenRG (talk) 21:42, 28 April 2010 (UTC)

Actually I think that does clear things up a bit. Essentially it's a particular type of model that enables establishing boundries in what would otherwise be infinite space. I still don't get what that would imply but at least I get the basic meaning. TheFutureAwaits (talk) 23:00, 28 April 2010 (UTC)

Ions

Why Hg₂²⁺ is called Mercury(I)?--Mikespedia is on Wikipedia! 14:36, 28 April 2010 (UTC)

It is an example of Stock nomenclature. The Roman numeral in mercury(I) indicates the oxidation state of each mercury atom, whereas the 2+ superscript in Hg₂²⁺ denotes the total charge of the compound ion. TenOfAllTrades(talk) 14:42, 28 April 2010 (UTC)

The symbol Hg is Latinized Greek: hydrargyrum, from "hydr-" meaning watery or runny and "argyros" meaning silver. See the article Mercury (element). Cuddlyable3 (talk) 18:52, 28 April 2010 (UTC)

Since the mercury ion contains two atoms and has a total charge of 2+, each atom has a charge of 1+, making it mercury(i).--98.221.179.18 (talk) 19:21, 28 April 2010 (UTC)

Mercury(I) is also a weird case because it dimerizes. Unlike most metal ions, which are happy to live by themselves, the Mercury(I) ion forms a dimer, much like the neutral Halogens to (hence chlorine gas = Cl₂.) There are reasons for this, but if you are just at the state of learning how oxidation numbers work in your education, you can just take it as a "weird" case. If you are interested in more details on this, Mercury polycations discusses it. --Jayron32 20:46, 28 April 2010 (UTC)

help me please (eating heroin rabbits)

I must be knowing any effect or dangers that would be coming if someone (not being me!) were to be ingesting 5 heroin filled game rabbits. please be helping. This is urgent! —Preceding unsigned comment added by TalipTaste (talk • contribs) 16:02, 28 April 2010 (UTC)

If you think it's urgent, call the emergency services - the operator will at least be able to tell you if it's an emergency or not. Heroin#Effects. I imagine the actual quantity of heroin would need to be known. We can't give medical advice, by the way. Vimescarrot (talk) 17:01, 28 April 2010 (UTC)

Also, see gluttony if you have in fact eaten 5 rabbits in a short time. Googlemeister (talk) 19:03, 28 April 2010 (UTC)

And protein poisoning. AlexHOUSE (talk) 19:08, 28 April 2010 (UTC)

Also, rabbit starvation. ~AH1^(TCU) 23:01, 28 April 2010 (UTC)

(Same thing.)AlexHOUSE (talk) 23:05, 28 April 2010 (UTC)

Naming of a species

The new British moth is named after its discoverer.[36] I thought he was supposed to name it after something other than himself, according to conventions. Imagine Reason (talk) 17:33, 28 April 2010 (UTC)

I think you've misparsed the article. Nowhere does it say HE named it after himself - to quote the article - "In January this year, the moth was officially recognised in the journal Zookeys as a new species, named Ectoedemia heckfordi after its discoverer." - implying it was named in his honour by a third party. Exxolon (talk) 18:21, 28 April 2010 (UTC)

Mass to energy conversion

If One could efficiently (100%) convert mass to energy and v.v., how much mass could you get out of the energy stored in a AA battery? How much mass could a 1GW nuclear reactor produce in an hour? Googlemeister (talk) 19:37, 28 April 2010 (UTC)

E = mc**2, and this page says an AA battery has at most 11050 joules of energy, so:

11050 J = m * c**2
11050 J / c**2 = m
11050 kg*m**2/s**2 / (3*10**8 m/s)**2 = m
11050 kg / 3*10**8 = ~0.00000000000012277778 kg

Similar math applies for the reactor case. --Sean 20:18, 28 April 2010 (UTC)

According to [37], an AA battery contains 1kJ. If we plug that into E=mc², we get a mass of 1000/c²=1.1*10^-14kg. 1 gigawatt-hour is 3.6*10¹²J, or 40 milligrams. --Tango (talk) 20:17, 28 April 2010 (UTC)

If you compress a mass of 6*10^11 kg to within its Schwarzschild radius of 8.9*10^(-16) meters, you'll get a micro black hole that will emit about 1 GW of power in the form of Hawking radiation (at a temeperature of about 200 billon K). Then, as Tango has calculated, it will only lose 40 milligrams per hour, which is 1 kg per 2.85 years. So, we would have plenty of energy and no headaches about what to do with waste! :) Count Iblis (talk) 22:05, 28 April 2010 (UTC)

Now all we have to do is figure out where can we get one of those. Dauto (talk) 23:14, 28 April 2010 (UTC)

Is it normal for men to have a noticeably reducing libido at the age of 50.

Some of my colleagues of a similar age still shout "phwar" when a teenage girl walks past our window. I find I'm thinking "she's younger than my daughter" and only feeling fatherly thoughts. One guy said "what would you like to do if you had a night out with her" when one walked past. Of course I said "cor just imagine", but I was really thinking that if I would probably just treat her like my daughter and take her to the Pizza hut and talk about how her careers going! Is this normal for someone in their early fifties? —Preceding unsigned comment added by 88.107.183.51 (talk) 20:07, 28 April 2010 (UTC)

Congrats, you're one of the few non-perverts in the world. :-) But seriously, male libido starts decreasing from around 18, hence the popularity of Viagra. StuRat (talk) 20:17, 28 April 2010 (UTC)

Yes. You have a daughter and therefore a different reference point. Very healthy and much more grown up. Kittybrewster ☎ 20:20, 28 April 2010 (UTC)

Your colleagues may be doing exactly the same thing you are are just saying it because they thing it's what they should say. --Tango (talk) 20:22, 28 April 2010 (UTC)

As another guy in his 50's (without the daughter) - I doubt it's a matter of libido so much as a matter of maturity and respect. I suspect that (assuming you're otherwise unattached) you'd have no trouble getting sexually interested in an attractive person with the right attributes whom you met under reasonable circumstances. I too don't see the attraction in young women encountered at random like that. Like the majority of people of that age, I find them mostly superficial and uninteresting after not much time spent with them. But reduced libido is another matter entirely. Don't confuse selectivity with disinterest. But all of that bravado from younger guys definitely gets tiresome - and I'm pretty damned sure it doesn't do much for the ladies either. Those of us who have been around the block a few times can more easily tell what's just bullshit and what's not. So don't sweat it...go out and buy yourself a brand new convertible...a red one...with turbo...it's time! :-) SteveBaker (talk) 23:14, 28 April 2010 (UTC)

Chromate formation

Can chromates be formed by reaction of chromium(III) oxide with a hypochlorite. When I react a chemical (formed by the neutralization using ammonia of Nichrome previously dissolved in acid) with sodium hypochlorite, a yellow solution is formed. How could you tell whether it was iron(III) chloride or sodium chromate? I duplicated this reaction with a chromium-containing stainless steel screw and it formed the yellow color too. --Chemicalinterest (talk) 20:41, 28 April 2010 (UTC)

Add thiosulfate to the solution. If Iron(III) is present you will form the blood-red Thiocyanatoiron(III) complex ion. If Iron(III) isn't present, the yellow is probably from Chromate or Dichromate. --Jayron32 20:55, 28 April 2010 (UTC)

Unfortunately I do not have thiosulfate. --Chemicalinterest (talk) 21:13, 28 April 2010 (UTC)

These are the reactions: 2 Ni + 2 Cr + 10 HCl → 2 NiCl₂ + 2 CrCl₃ + 5 H₂ | NiCl₂ + CrCl₃ + 5 NH₄OH → Ni(OH)₂ + Cr(OH)₃ + 5 NH₄Cl | 2 Ni(OH)₂ + 2 Cr(OH)₃ + 4 NaClO + 4 NaOH → 2 Na₂CrO₄ + 4 NaCl + 7 H₂O + Ni₂O₃ --Chemicalinterest (talk) 21:24, 28 April 2010 (UTC)

Iron(III) is a major Lewis acid (in addition to being an oxidant). I don't know as much tests but I am sure there are plenty. Cr(VI) prefers to oxidise over any Lewis acid ability, I think. Also Fe3+ forms many insoluble complexes ... whereas I believe Cr(VI) compounds tend to be more water-soluble. John Riemann Soong (talk) 22:29, 28 April 2010 (UTC)

Btw, Iron(III) chromate forms an insoluble salt. If you didn't observe this, well you probably don't have both ions in there. I would test with some copper (II) chloride (will precipitate copper chromate), sodium sulfide (will precipitate FeS), etc. Your reaction might have just worked because iron(III) hydroxide is very insoluble in water. John Riemann Soong (talk) 22:45, 28 April 2010 (UTC)

Adding a source of phosphate will also precipitate any Fe(III). (Try not to add it in the form of phosphoric acid...monoprotonated or free phosphate is preferred...) John Riemann Soong (talk) 22:51, 28 April 2010 (UTC)

Geology

Recently a large quantity of "river rocks" have been imported to our area to be used in landscaoing. These rocks came from somewhere in Arizona. The rocks appear to be of great variety. some are granite some basesalt etc. They vary in size from one inch to one foot. A few of them are almost perfectly round, but the top and bottom are slightly and equally convex. They are, of course, smoothed by errosion. I do not think, however, that errosion alone explaims there near perfect symmetry. I suspect that they were magma which was blowen into the air by a volcano. As they spun in the air they would have developed into a ball shape. When they struck the ground they would have been flattened like a pancake. But if such were true, one would expect one side to be flatter than the other side. Such is not the case. Can some one explain to me the origin of these beautiful rocks? Thanks, wsc

How about if they just got rounded off by rolling down a stream ? Perhaps one got stuck somewhere and had the top erode more, making it slightly flattened. Then, the next time the river flooded and it rolled, it settled on that flatter side (and then the opposite side eroded the same way). StuRat (talk) 23:11, 28 April 2010 (UTC)

If these have been imported in large quantities, then I think the easiest and most reliable way to find out, is to approach such a home owner with said landscape and inquire. Take a pen and paper for making notes. If your impressed with their garden rock feature, then that is likely to please the owner who may be happy to tell you the supplier, and from them you can find the rock's geological details, formation etc.--Aspro (talk) 23:30, 28 April 2010 (UTC)

Rock that is flung out into the air turns into light stuff like pumice, not into basalt; and granite doesn't form unless cooling is very slow. I'm not aware of any other mechanism that erosion that gives rounded rocks. Looie496 (talk) 00:19, 29 April 2010 (UTC)

Ghost

Is ghost really exist?75.168.119.109 (talk) 23:38, 28 April 2010 (UTC)

Scientists are very sceptical about their existence. Wikipedia has an article about them. Ghost#Scientific_skepticism--Aspro (talk) 23:48, 28 April 2010 (UTC)

Thank You!75.168.119.109 (talk) 00:04, 29 April 2010 (UTC)

No - they don't exist. Aspro: we shouldn't sugar-coat this. I don't know of any scientists who are actually "skeptical" about ghosts. They know ghosts aren't remotely possible - period. Some might come out with some wishy-washy super-formal "we haven't yet proven that they don't exist" statements if forced into it - but nobody in the hard sciences really believes there is even a one in a billion-trillion chance that they could exist. There is absolutely zero solid evidence FOR ghosts - and against that are all of the laws of physics and biology that say they can't exist. The hypothesis that there are ghosts fails the falsifiability test. Occam's razor says the best approach is to assume that they don't exist because that assumption violates no known laws and the guess that they do exist violates many. Russell's teapot asks why you'd believe in ghosts but not the much higher chance that there is a teapot in orbit about Mars (or pink piano-playing aardvarks on the dark side of the moon - or any other crazy thing you might think up on a boring Wednesday afternoon). There are a literal infinity of things one might believe in without any evidence whatever - why pick the ghosts rather than the pink aardvarks? SteveBaker (talk) 00:05, 29 April 2010 (UTC)

Albert Einstein

Who is the next genius, i meant the smartest person, after Albert Einstein's Death?75.168.119.109 (talk) 00:04, 29 April 2010 (UTC)

Tricky: My vote goes to Richard Feynman - but there are a lot of other possibilities. The problem is that the word "smart" is hard to pin down - the concept of "intelligence" and even "IQ tests" is very fuzzy - and the most intelligent people of all sometimes do very badly at those kinds of tests because they are so much smarter than the people who designed them. If you read biographies of Einstein, you tend to come away with the idea that aside from his abilities in the areas of theoretical physics - he was a complete idiot and a general pain in the ass. I don't think I would have liked him - or found him particularly interesting to talk to. Similar complaints may be raised against other possibilities such as Stephen Hawkins. Personally, I respect Feynman precisely because he was brilliant (and funny and talented) in absolutely everything he approached - the sheer breadth of his talent was impressive. But I'm sure we'll have a lot of alternatives put forward. SteveBaker (talk) 00:19, 29 April 2010 (UTC)

You mean nobody is the smartest person? I would agree with that because nobody know everything. I'm sure Albert Einstein didn't know much about other areas beside science and physic like art, genetic, biology...75.73.152.238 (talk) 00:32, 29 April 2010 (UTC)

Cell

I knew all cells come from cell then where the first cell come from?75.168.119.109 (talk) 00:04, 29 April 2010 (UTC)

You should read our article Abiogenesis. The short, honest answer is that we don't know for sure - but we suspect that chemicals that can copy themselves (like, maybe RNA) could come about spontaneously from random chemical reactions in the soil or the oceans - then for such molecules to become trapped inside a lipid bubble and thereby form primitive cells. But we don't know for sure. We're pretty certain it wasn't magic though. SteveBaker (talk) 00:10, 29 April 2010 (UTC)

Aliens

I have heard and read many resources show that aliens are really exist or do not exist. Is alien really exist?75.168.119.109 (talk) 00:07, 29 April 2010 (UTC)

You're aiming for all of the difficult questions today! See our article on the Drake equation which estimates the probability that there is intelligent life on other planets - and comes to the conclusion: "Yes, there probably is". But we haven't found life anywhere - so the answer can only be "probably". On the other hand, aliens visiting Earth...No - that doesn't seem either likely or possible from the evidence we have available. SteveBaker (talk) 00:12, 29 April 2010 (UTC)

I think the aliens have came to Earth before at least one time. If not then how could you explain all the UFO we have seen from the ancient time until today.75.168.119.109 (talk) 00:23, 29 April 2010 (UTC)

I wonder why aliens never try to contact us. Does anyone know?75.73.152.238 (talk) 00:32, 29 April 2010 (UTC)

God

There are many religions in the world. Is god really exist? Or big bang.75.73.152.238 (talk) 00:35, 29 April 2010 (UTC)

If god does exist then who create god?

Black hole

What inside the black hole?75.73.152.238 (talk) 00:42, 29 April 2010 (UTC)

Wormhole

Have we found any of wormhole? does wormhole really allow time travel?75.73.152.238 (talk) 00:46, 29 April 2010 (UTC)

Titration curve: help!

Let's say we have a solution of HCl of known volume and concentration, being titrated by NaOH of known concentration. I want to know what the pH is after x mL of NaOH have been added. According to my book, we can assume that all the OH in HaOH react completely with all the H+ in HCl and neutralize. The obvious problem is, what happens near the equilibrium point? Following the textbook's logic, all the H+ in the solution would eventually react with OH- and disappear, which is obviously impossible because of the self-ionization of water. So, how would I calculate pH's near the equilibrium point? --99.237.234.104 (talk) 00:48, 29 April 2010 (UTC)