Wikipedia:Reference desk/Archives/Science/2013 March 23

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March 23

Resistance of wire

If a wire is drawn out to 3 times its original length, by how many times excepts its resistance to be increased? Please explain in detail, the answer says it 9 but I got 3? 115.253.134.61 (talk) 06:00, 23 March 2013 (UTC)

Resistance is directly proportional to the wire's length AND inversely proportional to its cross-section. You can figure out the rest on your own -- we're here to explain difficult concepts, not to do your homework for you. 24.23.196.85 (talk) 06:43, 23 March 2013 (UTC)

Agreed, where "cross section" = cross-sectional area. Also note that the volume of the wire stays constant. StuRat (talk) 06:55, 23 March 2013 (UTC)

Do you understand that by "drawn out", they mean "evenly stretched"? -- 41.1.32.203 (talk) 09:52, 23 March 2013 (UTC)

I don't understand this question. First, how you can stretch a wire by this much without it breaking? Second, the volume doesn't stay constant, see Poisson's ratio. Count Iblis (talk) 15:06, 23 March 2013 (UTC)

See Wire drawing, and Poisson's ratio applies only to elastic deformation. Tevildo (talk) 16:33, 23 March 2013 (UTC)

You can easily stretch a wire to three times its length - that's how wire is made! Start with an ingot of a ductile metal like copper or gold. Spool it carefully through staged dies. Use heat and metal lubricant, and pull. Wire drawing is the main article. Very high gauge wire is essentially made by staging and drawing. Here is a nice video, on wire drawing machinery. Evidently the best resources in light metalworking industry are no longer in English; apparently even physicists in the English-speaking world are no longer informed abou basic material processing techniques! Nimur (talk) 16:43, 23 March 2013 (UTC)

I see! I did know about this process to make wires, but it was not something I thought of when reading this question, I was just picturing someone trying to stretch a wire :) . Count Iblis (talk) 16:48, 23 March 2013 (UTC)

exploitation of natural resources on the moon

let's pretend that the cost of transporting material from the moon to earth is negligible. ok now that we are assuming that, is there any natural resources on the moon that we could use to benefit humankind.--There goes the internet (talk) 07:43, 23 March 2013 (UTC)

Cheese. Ya know, bananas in pajamas? ☯ Bonkers The Clown \(^_^)/ Nonsensical Babble ☯ 08:07, 23 March 2013 (UTC)

Helium-3. --Guy Macon (talk) 08:20, 23 March 2013 (UTC)

Ilmenite, zirconium, etc. 24.23.196.85 (talk) 08:52, 23 March 2013 (UTC)

Every kg of the moon has a gravitional potential energy of 56 MJ that is about 50 % more than the combustion heat of a kg gasoline. If the transportation process does not use or discard this energy this represent a significant value. The potential energy of the moon could power our current civilization for 9 000 000 000 years except that the sun will explode before that. The most obvious way to use this energy is to power a system of momentum exchange tethers to transport mass from earth to the moon or other space destinations. Gr8xoz (talk) 21:59, 23 March 2013 (UTC)

Actually, we're already using the Moon's gravity, without even leaving Earth! 24.23.196.85 (talk) 04:13, 25 March 2013 (UTC)

how can ghosts and other magical creatures walk through walls but not fall through the floor

we have no references, please seek an internet forum
The following discussion has been closed. Please do not modify it.
If you can go through solid objects by walking into them, wouldn't gravity pull you straight into the ground and to the center of the earth? Or, alternatively, if gravity had no effect on you, wouldn't you just float away? is there a scientifically coherent explanation why a theoretical ghost would walk on the ground and not fall *into* the ground, but it could still go through walls? i don't beleive in ghosts but it always bugged me that they could walk through walls yet their feet seemed to hit the floor beneath them without going through.--There goes the internet (talk) 08:00, 23 March 2013 (UTC) IF a "ghost" could walk, it would be a matter... And therefore it cannot go through walls. But IF it was made of energy... It could theoretically pass through walls... But it would not be able to walk. Falling through the floor is not a problem in both instances. ☯ Bonkers The Clown \(^_^)/ Nonsensical Babble ☯ 08:06, 23 March 2013 (UTC) I read in a carl Sagan book that it is possible that your car could disappear and reappear in the middloe of your wall at any given time but the likelihood of this happening is like really small. i cant remembere what phenomenon he was talking about... maybe a ghost could go through walls if it were matter. but what if it was like a shapeshifter and it could squeeze through the holes in between the atoms. I don't know anything about science. sorry.--There goes the internet (talk) 08:15, 23 March 2013 (UTC) Maybe the problem is the definition of a "ghost". What if it's not really "there" in a conventional physical sense, but instead is kind of like a "recording" of some past event, via some mechanism unknown to us? ←Baseball Bugs What's up, Doc? carrots→ 08:43, 23 March 2013 (UTC) Or maybe a mental image that you alone can see? Or simply a trick of the eye, like most flying saucers for example? 24.23.196.85 (talk) 08:54, 23 March 2013 (UTC) You are talking about the physical properties of a supposed supernatural entity. If such a supernatural entity exist, it will defy laws of nature, it has its own supernatural properties, it follow its own supernatural laws. So gravity will have no effect on it, because gravity is a natural law. Now, if you want real science, forget thinking about ghost's physical properties. Think about their origin, which lies in the brain of Homo sapiens. See Evolutionary_origin_of_religions#Paleolithic_burials and [1]. Vampire#Origins_of_vampire_beliefs may give you an idea how and why humans construct supernatural entities. --PlanetEditor (talk) 11:08, 23 March 2013 (UTC) "Ghost Rules" as seen in books and movies only really work at all if you assume that the Ghost's mind (or the victim's mind) is making the visuals. APL (talk) 13:40, 23 March 2013 (UTC) Sorry everyone, i think i got everyone fixated on the ghost/supernatural angle. my fault. forget ghosts, and let's get back to physics becuase i dont know much about science. Could a type of physical entity theoretically pass through a wall. like let's say it could voluntarily reshape its matter to somehow fit between the spaces in the molecules of the wall and reform itself on the other side... but would that destroy the wall? because, like, what if the very process of trying to go between the "spaces" in the wall molecules broke the molecular bonds and the wall like dissolved or something. And if such a being could do this let's say the ability somehow became inovluntary and it auotmatically passed through whatever it touched. then i think it would go into the floor and fall into the center of the earth. i'm so confused.--There goes the internet (talk) 14:37, 23 March 2013 (UTC) This isn't a science question, more humanities, but I think here we are seeing a vestige of Aristotelianism. Because ghosts don't really exist in a sciencey way, there is no reason for their theoretical properties to have been updated from what people actually believed controlled the motions of objects in antiquity. I'm not an expert, but as I understand it, they simply thought the place of earth was down, so it tried to go there, and so forth. The reason why a ghost is portrayed walking the battlements is that this is its "place" in the world, so it is naturally drawn there. They can pass through a door or a wall if their "place" was once to walk that path, no matter what its current physical status. Wnt (talk) 15:01, 23 March 2013 (UTC) I remember reading of a haunted pub somewhere in England, where a pair of boots walk across the room, just under the ceiling. The ceiling used to be lower and the ghost doesn't know that it has been changed. (He is walking around in the room above.) --TrogWoolley (talk) 20:05, 23 March 2013 (UTC)

About animals' tolerance of g-force

Are there any researches on this subject? Is it expected to be inversely proportional to body size?--Inspector (talk) 09:42, 23 March 2013 (UTC)

How about "Tolerance of small animals to acceleration"? The abstract concludes "Body weight was inversely related to the threshold G-value at which animals [mice, rats, rabbits, finches, pigeons, and roosters] are resistant to the prolonged acceleration." The author of "Comparative Study on Tolerance to Centrifugal Acceleration in Several Animals" tested dogs, rabbits, guinea pigs, rats, hamsters and frogs. Hamsters did better than the other mammals, but the champs were the frogs. I'm still looking for the elephant study. Clarityfiend (talk) 10:31, 23 March 2013 (UTC)

that study sounds kinda inhumane. i knew a boy who put a mouse in a model rocket and i think it died.--There goes the internet (talk) 14:38, 23 March 2013 (UTC)

See Great Mambo Chicken and the Transhuman Condition: Science Slightly over the Edge. Wnt (talk) 15:04, 23 March 2013 (UTC)

Yes. The first study talks about "50% mortality", and the second "100% lethal time". Clarityfiend (talk) 22:56, 23 March 2013 (UTC)

quadriplegic pregnancies and childbirth

Need information regarding first known childbirth of quadriplegic woman. Information regarding woman's name, year and place of child delivery. Anything prior to 1952 is most helpful. Thank you,Etofbaok (talk) 14:51, 23 March 2013 (UTC)

Do it yourself soil test

"A Simple Do It Yourself Soil Test -- Perform your soil test by placing a sample into two separate cups or containers. Add vinegar to one. If it fizzes your soil is alkaline. If not, add some water to the second cup and stir. Add baking soda. If it fizzes you have acidic soil. If neither have a reaction your soil is somewhat pH balanced."

I copied this advice from the internet. My hunch is that only soils that were highly acidic or highly alkaline would react to this test by bubbling. That for soils in a moderate pH range the test is pretty much useless.

Am I correct or is this test more sensitive than I suspect?

Thanks, CBHA (talk) 18:41, 23 March 2013 (UTC)

The first one is not technically correct. Alkali does not fizz in vinegar. Carbonates fizz in vinegar; while many alkali's which are in soil may be carbonates (limestone or chalk for example) and that may cause fizzing, there are many more alkali compounds which are not carbonates (various hydroxides and oxides for example) which will not fizz in an acid like vinegar. So, fizzing is technically not a pH test, it is a carbonate test (most carbonates will by somewhat alkali). You could have a strongly alkali soil which does not contain a lot of carbonates, which would then fizz in neither test. The baking soda (sodium hydrogen carbonate) test should work well to test for low pH (acid) soil. --Jayron32 19:00, 23 March 2013 (UTC)

But, I agree, this kind of test wouldn't be very accurate. Just get some litmus paper, wet the soil with water, and dip it in. StuRat (talk) 21:41, 23 March 2013 (UTC)

The water should be deionized (distilled or R.O.)--Digrpat (talk) 22:12, 23 March 2013 (UTC)

Trawling vs gillnetting

Which fishing method results in a larger catch?

You would use them for different fish species that live in different areas of the sea. Rmhermen (talk) 00:27, 24 March 2013 (UTC)

Coke in space

The Coca-Cola article says A Coca-Cola fountain dispenser (officially a Fluids Generic Bioprocessing Apparatus-2 or FGBA-2) was developed for use on the Space Shuttle as a test bed to determine if carbonated beverages can be produced from separately stored carbon dioxide, water and flavored syrups and determine if the resulting fluids can be made available for consumption without bubble nucleation and resulting foam formation. What was the result of the test? RNealK (talk) 22:28, 23 March 2013 (UTC)

Experiment was rated as a failure. http://www.spaceline.org/shuttlechron/shuttle-sts77.html CBHA (talk) 22:46, 23 March 2013 (UTC)

Right. NASA's mission summary states: "FGBA-2, a Coca-Cola soft-drink dispenser, required troubleshooting during the flight, and the SEF experiment was declared failed when command problems in the payload could not be repaired". Looie496 (talk) 22:51, 23 March 2013 (UTC)

That was the third attempt. Apparently the second was fairly successful. The first employed can of pop (where the carbonation separated out). The second (FGBA-1) dispensed prepared pop. FGBA-2 was like an Earthly fountain pop machine - with separate CO2, syrup and water - but resulted in two much foaming. Rmhermen (talk) 00:25, 24 March 2013 (UTC)

If that was the two much foaming, what was the one much foaming, and will there be a three much foaming also? Plasmic Physics (talk) 00:52, 24 March 2013 (UTC)

Oh boy! Typo mocking! I was just thinking how much I miss FidoNet... :) --Guy Macon (talk) 01:13, 24 March 2013 (UTC)

There's a difference between a typo and the coincidental combination of bad grammar and homophones. Plasmic Physics (talk) 02:48, 24 March 2013 (UTC)

Zoiks!  - That probably means that beer-in-space also won't work!  ~E:74.60.29.141 (talk) 01:58, 24 March 2013 (UTC)

No, see the followup discussion, it should be doable with the right machine. Nil Einne (talk) 05:28, 24 March 2013 (UTC)

[Warning: detour ahead]  —  I hope you're right. Actually, brewing beer in space would be an interesting experiment (any volunteers?) — For one thing, beers fall into two categories: top-fermenting (ales, etc.) and bottom-fermenting (lagers, etc.). In "zero-G" [a misnomer] there is no up or down, thus no "top" or "bottom". Also I wonder how the natural carbonation process would be affected. ~Cheers, ~E 74.60.29.141 (talk) 07:27, 24 March 2013 (UTC)

Off the top of my having-brewed-occasionally head (there likely being little references available on the subject): probably not much. Although top and bottom-brewing yeasts tend to float or sink somewhat (aspecially when spent), during fermentation they are both spread through the whole of the wort (liquid), so they'd both probably perform fairly well in zero-g. Similarly, they'd still excrete CO₂ which would still dissolve into the ale/lager, with larger gas bubbles coalescing – but not rising or falling – if and when the CO₂ exceeded the soluble capacity of the liquid (which would depend on its temperature and pressure). However, you'd have a major problem venting the excess CO₂ gas (whose volume can be considerable) from a (necessarily) pressurised liquid in zero-g. Perhaps it could be used for propulsion - Poul Anderson wrote the (not entirely serious) novella A Spaceship Built for Brew in which an emergency beer-powered spacecraft was employed. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:26, 25 March 2013 (UTC)

Interesting, that means that two new categories would have to be introduced: outer-fermenting, and inner-fermenting. Plasmic Physics (talk) 09:47, 24 March 2013 (UTC)

Easier to track horizontal lines than vertical lines?

I just noticed while making some measurements with a steel rule that I can focus on the line better when they are horizontal than when they are vertical. When they are vertical, I can't keep track of one line long enough to make a mark at, say, 32 mm, whereas if I change position so that the lines appear horizontal then it becomes much easier. Similarly, I have trouble counting consecutive zeros beyond, say, four zeros - same for other combinations of numbers. Is this a common feature for humans? --78.150.234.51 (talk) 22:44, 23 March 2013 (UTC)

Subitizing is the technical term for "intuitive" counting - the number of things that can be subitized depends on the individual. Different focussing of the vision between horizontal and vertical is astigmatism - you should see an optician if you're worried about your eyesight. Tevildo (talk) 22:49, 23 March 2013 (UTC)

And note that animals can do this type of counting, too, but not the type where you use numbers to represent things. StuRat (talk) 22:52, 23 March 2013 (UTC)

Hey, thanks but I'm not really talking about counting the lines - my issue is tracking a specific line and thereby knowing and distinguishing it from the lines around it. I do have an updated glasses perscription and ordering new glasses is high on my to-do list but things like counting zeros or reading mobile phone numbers that are presenting as a continuous string etc is something I've noticed for a long time. If you're confronted with about 100 zeros, can you easily count them without placing an object on them? Or do you just get lost in them? 78.150.234.51 (talk) 23:45, 23 March 2013 (UTC)

I personally couldn't do more than about five or six without marking them off. Other people are more skillful at such tasks, of course. Tevildo (talk) 00:16, 24 March 2013 (UTC)

Predators have eyes designed to track vertically (for chasing prey): [2], while herbivores have eyes designed for tracking horizontally (to watch for predators): [3]. Human eyes are supposed to be equally good at both. StuRat (talk) 22:58, 23 March 2013 (UTC)

That's interesting. But the lines and numbers etc aren't moving... I'm trying to track a stationary article in among identical articles, also stationary. It can't just be me. 78.150.234.51 (talk) 23:45, 23 March 2013 (UTC)

I believe they're related. That is, the area of optimal vision is spread out vertically for the predators and horizontally for the herbivores, while ours is closer to circular. StuRat (talk) 01:15, 24 March 2013 (UTC)

How many hours a day do you practice tracking a horizontal line without jumping to an adjacent line? (Hint: you are doing it right now) It could be that someone who usually reads vertical text develops the opposite skill. How is your performance when going right to left? The same?

Then again, it might be something as simple as astigmatism. --Guy Macon (talk) 01:10, 24 March 2013 (UTC)

I would tend to go with Sturat. In the early days of television, it was found that horizontal scanning gave a more acceptable picture than vertical scanning - even though, vertical scanning made more sense from the electronic point of view. Both systems contained the same amount of information but our eyes and visual cortex are more receptive to the information in horizontal form. Our Abducens nerve controls this side to side movement. In some alcoholics a loss of this fine control is most noticeable. So, smooth up and down tracking ability is not so evolutionary important as side to side. Therefore, poor horizontal tracking in in the case of the alcoholic -is easier to see. Likewise, our eyes have evolved (well, mine at least) to be side by side- not one over the top of the other). Action before us takes place either side to side ( Abducens nerve) or near to far (convergence and focus). --Aspro (talk) 15:50, 25 March 2013 (UTC)