Wikipedia:Reference desk/Archives/Science/2010 May 1

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May 1

Persistent odor

(Note to everyone: This is NOT a request for medical advice)

Just a couple days ago, while testing a sample of refinery wastewater for heavy metals, I accidentally took a whiff of some 5% aqueous ammonia solution (for those who'd never had that happen to them, it feels like a pair of burning matches up your nose). My mucous membranes were burned to a crisp in less than a second, and I had the most horrible itching and sneezing all day long, followed the next day by the worst runny/stuffy nose I've ever had (I've gone through more than two boxes of Kleenex in just one day). All this was stuff that one would expect when one gets ammonia poisoning. What really surprised me, though, was that even after I left the lab, I kept perceiving the stench of ammonia all day long; everything around me -- my hands, my clothes, soap, toothpaste, the food I ate, even the flowers in my yard -- positively reeked of ammonia. (And no, I hadn't spilled any ammonia on myself or my belongings, so the most obvious explanation is out of the question.) Can anyone come up with an explanation for this lingering odor? 76.103.104.108 (talk) 02:45, 1 May 2010 (UTC)

See Sensitization. You could have become rapidly sensitized to the odor of ammonia after your experience. Ammonia is present in LOTS of things. Normally, our brains may not be able to pick the ammonia out of a bunch of compounds that make up the smell profile of something, but given your experience, you may now be hyper-sensistive to ammonia, and can "pick it out" of otherwise complex mixtures of smells, even if it is only present in trace ammounts. Just an idea. --Jayron32 02:52, 1 May 2010 (UTC)

...or you just got a whole lot of it up your nose! 64.69.33.87 (talk) 02:57, 1 May 2010 (UTC)

When you burn your hand, doesn't it kind of feel like you hand is burning constantly until the wound begins to heal? Or when you cut yourself, as if your hand is cut? If there are nerves in your body that know that the smell of ammonia is a hurt smell, I don't see why those nerves wouldn't "throb" after your "injury", thus making you think that you were smelling ammonia. 219.102.220.42 (talk) 03:13, 1 May 2010 (UTC)

Thanks for your answers, everyone. 219 IP, I think your explanation is the most likely, 'cause the smell gradually decreased in intensity through the day, until it finally disappeared the next morning. (And yes, I did get a whole lot of it up my nose, which would explain the intensity and persistence of the smell.) So I can easily see how the nerve endings could continue to tingle for hours afterward, and how this could be perceived as an ammonia smell. As for any possible sensitization, Jayron, maybe I forgot to mention that I've handled ammonia (and smelled it -- it stinks so bad you could smell it from half a mile away) many times in the past -- we use it for a quick-and-dirty test of refinery wastewater for iron, chrome, manganese and vanadium (none of which we're supposed to dump in the river because of toxicity concerns) -- and I've never had a problem until I got a little careless and inhaled the concentrated vapors. Had I become sensitized, it would've happened when I first handled ammonia, wouldn't it? Also, how do you explain the sensitization going away gradually within about 24 hours? 67.170.215.166 (talk) 05:55, 2 May 2010 (UTC)

Sleeping in a chair

I frequently take overnight bus trips and I can never get to sleep on the chair, and I always end up feeling like crap for the rest of the day. Even in bed I can't sleep on my back for some reason, I have to start on my front or else my body never seems to realize that I'm trying to get to sleep. I'm looking for some tips on how to get to sleep sitting in a reclining bus/plane seat, short of taking heavy sleeping pills. I already taken some off-the-counter light pills, but I'm more asking about why I may be having trouble sleeping, and how I can counteract that naturally.

To be honest, I often have the choice to take a bus that will give me two seats, or one that has a fully reclining chair so that I can actually get on my side, but I'm just curious as to why it's so hard for front-sleepers like me to fall asleep on our backs! I guess I also might want to mention that I'm 6'3 (188) so that's also a frequent problem!! 219.102.220.42 (talk) 03:08, 1 May 2010 (UTC)

Part of your answer is sleep hygiene. Much like creating a bedtime routine for children helps them go to sleep, adults often find they need certain 'cues' to get them to sleep. As you say, it is like your body (or brain) doesn't realise you're trying to sleep. People vary in how much this applies to them, but the way you find it easier to sleep is strongly the product of habit. There are also things like sleep apnea, but if you can't even drop off it seems more likely it's just because you don't associate those situations with sleeping. 86.178.225.111 (talk) 16:45, 1 May 2010 (UTC)

Hmmm... practice makes perfect? 210.254.117.185 (talk) 01:27, 2 May 2010 (UTC)

That's actually true when it comes to sleeping in strange places. --Ouro (blah blah) 06:17, 3 May 2010 (UTC)

You need to learn proper relaxation techniques. Let your muscles go slack, your breathing become deeper.. deeper, your body heavier and heavier, you are getting sleepier and sleepier. No?

In a bizarre coincidence, I'm also a 6'3" front-sleeper who has difficulty sleeping on buses and trains. The solution I found was to use a fairly odd sleeping position - put a bag on your lap, cross your arms on it, and sit with your face on your arms. It looks quite silly, but certainly for me it allows me to drop off fairly quickly - i'm apparently enough "on my front" for my brain to decide it's sleep time. Worth a try. ~ mazca ^talk 12:02, 4 May 2010 (UTC)

Yeah, I've done that too on occasion, I'm not sure if I've ever been able to fully fall asleep that way though. A lot of the time though, leaning down on the bus will hit my head against the chair in front! 210.254.117.185 (talk) 21:51, 4 May 2010 (UTC)

Lens-less imaging

I may be misunderstanding some of the fundamentals of optics here, but I was just wondering: if the angle each photon approaches at can be calculated by passing it through a non-focusing surface, would it be possible to resolve an accurate image using those calculations? It seems illogical to me that you could get a "focused" image without a lens, but I don't know why. 219.102.220.42 (talk) 03:36, 1 May 2010 (UTC)

See pinhole camera. Its possible to use diffraction instead of refraction to focus light. Thus, one can make images with tiny holes instead of lenses. --Jayron32 03:58, 1 May 2010 (UTC)

It sounds like you're saying that pinhole cameras work by diffraction. They don't, though you can focus light with a zone plate. -- BenRG (talk) 06:49, 1 May 2010 (UTC)

Sorry, I know what a pinhole camera is, I meant to clump in the pinhole camera with lensed cameras due to the fact it "focuses" the light. I'm asking if it is possible to resolve an image without any directing of the light by calculating the trajectories of individual photons. 210.254.117.185 (talk) 05:28, 1 May 2010 (UTC)

No, photons as particles obey the Heisenberg uncertainty principle, and as such, you cannot know the position AND momentum of a photon simultaneously. In other words, if you can locate a photon's position, you can't tell where it came from before it got there. So it is impossible to assign "trajectories" to photons. Since photons are merely the convenient term we use for the collection of properties that make light kinda-sorta behave like particles, however they are still light; and as such they still obey wave-like properties too, under the right conditions. See Double-slit experiment for a discussion over what happens when you try to assume that a photon is only a particle, and ignore its wave behavior as well. --Jayron32 06:30, 1 May 2010 (UTC)

That's a poor assessment. Heisenberg doesn't say that you can't know them both - it places a limit on the precision with which you can know them both. Since the momentum of the light relates to the color/brightness and the position relates to your ability to focus the image, Heisenberg merely imposes limits on how sharp and color-accurate your photo can be. But that limit is a very tiny one - you can make pretty good photos! SteveBaker (talk) 14:29, 1 May 2010 (UTC)

Photons don't have trajectories; they aren't like the lines of geometric optics. Light is a wave. But you can, in principle, record the electromagnetic field strength at an aperture and computationally simulate the propagation of the light beyond the aperture, through a simulated lens and onto a simulated sensor. Astronomers actually do this at radio frequencies—see Very Long Baseline Interferometry. I don't know whether it's possible at visible frequencies. -- BenRG (talk) 06:49, 1 May 2010 (UTC)

I think the OP is describing something like the compound eye of an insect. There are devices called plenoptic cameras or light-field cameras that attempt to do the same thing. I don't think these cameras are completely lensless, but they chop the light field up into smaller bits rather than passing it all through one humungous lens, which might be what the OP is looking for. --Heron (talk) 09:54, 1 May 2010 (UTC)

Thanks for the answers! I have heard that particles at the quantum level were unpredictable, so that's why I wondered if it would be possible here. In that case I have an expansion to my original question.

Is there any way to make a _surface_ into a camera without using lenses? I specifically want to avoid something like a compound eye, which is really just a lot of small lenses instead of one big one, right? The only way I thought it might be possible is by measuring the photons, but if they can't be measured directly, is there any other way to do this without using a physical lens? I'm thinking of the physical limitations of lenses, in that any camera is only as good as its lens or the corrective measures applied to the lens, but if there were a way to resolve images from sensors, then there wouldn't be this problem. 210.254.117.185 (talk) 10:41, 1 May 2010 (UTC)

No, you can't, actually. The last part of the double slit experiment article discusses this. If you fire photons at a surface individually through the double slits, and let them be detected one at a time, each hitting the detector before the next is fired, you still get an interference pattern; in other words, even if you design an experiment such that light is treated as particle in the most direct way (firing individual photons one at a time) you STILL get wave-like properties. So you can't design a surface which will resolve an image in the way that a lense would, since such a surface would require that the light act solely as a particle. --Jayron32 14:34, 1 May 2010 (UTC)

I recall that the cameras on one of the Mars landers did not have any lenses, and looked slit-like. 92.29.142.124 (talk) 12:22, 1 May 2010 (UTC)

I dunno. According to this, they seem to all have conventional lenses. 210.254.117.185 (talk) 14:30, 1 May 2010 (UTC)

What I was thinking of was static and earlier than the Rovers. Edit: It may have been the earliest lander, when people were concerned about dust storms scouring a lens. Edit2: I was thinking of Viking 1, which shows two slit like things in its photo what may be cameras or imagers. I havnt been able to find anything about these on the internet. 78.151.115.180 (talk) 14:37, 1 May 2010 (UTC)

You should read the papers linked from http://graphics.stanford.edu/projects/lightfield/ - those guys have made a variety of interesting cameras - including a single pixel camera that can take 'normal' photos - a way to transform a photo so you can see it from the perspective of the light source...all sorts of interesting stuff that results from doing numerical analysis of the 'light field'. SteveBaker (talk) 14:29, 1 May 2010 (UTC)

I've heard about those single-pixel cameras - how on earth do they work? 78.151.115.180 (talk) 14:39, 1 May 2010 (UTC)

They slowly scan the thing being photographed, one pixel at a time. The examples I saw take about 15 minutes to take a grainy/blurry photo. -- kainaw™ 14:43, 1 May 2010 (UTC)

Well, you could do it like that - but you'd still need a lens or a pinhole-like aperture - and that's not how the Stanford camera works. Their single pixel camera is an omni-directional detector. What they do is to use 'structured light' - by flashing light on different parts of the scene, the camera builds up a picture from the perspective of the light source. (That's a horrible over-simplification - read their paper to get a more complete answer.) SteveBaker (talk) 16:15, 1 May 2010 (UTC)

Which paper is that please? 92.28.253.63 (talk) 10:56, 3 May 2010 (UTC)

Jayron's answer above is completely wrong. Uncertainty principle applies just the same whether you are using lenses or not. It just turns out that lenses (and mirrors) are the easiest way to disentangle the information contained in the photons into a useful format that allows for an image to form. Dauto (talk) 15:42, 1 May 2010 (UTC)

Yes, exactly. The uncertainty principle imposes strict limits on the ultimate quality of photography - but it says nothing about how you take the photo. Also, the plank constant in the uncertainty principle is a teeny-tiny number! The amount of imprecision that the uncertainty principle causes is utterly negligable in practical photography. What would happen if you tried to take an insanely high resolution image (thereby forcing an accurate position measurement onto the photon) would be that the color and brightness of the image (related to the momentum of the particle) would become less precise. But we're an awful long way from the uncertainty principle imposing limits on the quality of our photography! SteveBaker (talk) 16:15, 1 May 2010 (UTC)

That's not right either. The uncertaity principle does play a role in the optical resolution of a telecope (Assuming high quality lenses). That's in fact the main reason why large telescopes are built. The secondary reason is the increased brightness obtained with larger telescopes. Dauto (talk) 19:36, 1 May 2010 (UTC)

Again, thanks for noting that. I apologize for leading the discussion astray. Of course, we do have surfaces that accurately resolve images without lenses. They are called mirrors. --Jayron32 16:38, 1 May 2010 (UTC)

The uncertainty principle that people have been talking about is already present in classical optics (Maxwell's equations), where it's called the diffraction limit. The classical version of the inequality is Δx Δk ≥ 1/2, where k is the wave number. Quantum mechanically, you can use the de Broglie relation p = ħ k to write it as Δx Δp ≥ ħ/2. Quantization adds shot noise in low-light situations, but aside from that, imaging is governed by Maxwell's equations. When you are limited by shot noise, it does matter how you take the photograph—measurements before and after the light passes through a lens don't commute with each other, meaning that you can't tell from the before-lens measurement what the after-lens result would have been. This problem disappears when the photon count is large because the photons behave as "identically prepared systems" and you can recover complete information about the preparation by doing different measurements on different photons. -- BenRG (talk) 01:06, 2 May 2010 (UTC)

Thanks for the answers and links guys. The digital post-re-focus camera is pretty insane!! So I guess the question is not if images can be resolved from surfaces, but how high resolution they can be. Telescopes are limited by the accuracy of the lenses they use, but the resolution of a surface seems to be restricted by our ability to resolve the properties of photons. I imagined a very long, thin tube with the "sensor" surface on the inside of it, in order to block all the photons from outside of a small patch of sky, but I imagine the wave properties of light will make it impossible to create an image of anything too small/far away. Thanks again! 210.254.117.185 (talk) 01:24, 2 May 2010 (UTC)

If I'm not mistaken, taking a photo by measuring the angle, and without using a lens, is exactly what a hologram does. Ariel. (talk) 02:52, 2 May 2010 (UTC)

Titration curve: part 2

My question is very similar to the one I asked earlier, but it's different enough that I thought I should ask separately.

If I have HCl of a known concentration & volume, being titrated with NaOH of known concentration, and I add x mL of NaOH. How do I determine the exact relationship between pH and x, with no approximations whatsoever? I know that I can use Jayron's method for pH's close to 7 and conventional methods for pH's far from 7, then combine the 3 resulting functions into one, but I can't help but think there has to be an exact mathematical formula for the titration curve. --99.237.234.104 (talk) 04:45, 1 May 2010 (UTC)

You can always use an ICE table. First, react the two species to completion. Then, use those values as the Initial values in the ICE table. This will give you the relationship Kw=([H+]initial + x)([OH-]initial + x). Solve the quadratic equation for x, add that x value to the initial H⁺ concentration, and take the negative log. Note, though, that there are surely some error bars on your amounts of H⁺ and OH^-, so there's little use in getting an "exact" value in this way unless you have very close to equal amounts of acid and base. Buddy431 (talk) 05:31, 1 May 2010 (UTC)

Dry nose when sleeping upright

If I fall asleep during the day, in an upright posture, for instance while sitting on a train or at a desk, I invariably awaken with a very dried-out nose. This never happens if I fall asleep lying down. Why might this be the case? 129.174.184.114 (talk) 06:31, 1 May 2010 (UTC)

I didn't know humans had wet noses. Are you a dog? --TammyMoet (talk) 09:14, 1 May 2010 (UTC)

We do have healthy wet noses, on the inside. This came up on this very desk a month ago, in a question titled "juicy nose". 86.21.204.137 (talk) 12:21, 1 May 2010 (UTC)

I am rather certain that the response then was the same as now: We cannot diagnose how a questioner's nose works without physically inspecting the questioner. -- kainaw™ 14:44, 1 May 2010 (UTC)

Why are people whispering? — Knowledge Seeker দ 17:48, 1 May 2010 (UTC)

You are breathing through your nose and too fast. Try breathing more slowly or prop your mouth open. This will then give you a dry mouth instead.--79.76.230.67 (talk) 21:42, 3 May 2010 (UTC)

name of shooting device

i saw this

http://www.youtube.com/watch?v=fRLCh0Re_LA&feature=PlayList&p=2CA7AB94E58204FB&playnext_from=PL&index=0

what is the name of the shooting device he is using? not the gun but the device that the gun is attached to that makes it have no recoil. its not called a bench rest because thats something else. i want to buy one and need to tell the gun store exactly what im talking about —Preceding unsigned comment added by Tom12350 (talk • contribs) 10:49, 1 May 2010 (UTC)

Please don't post the same question on more than one desk. There is a recoil on the gun, it goes back about two inches. Finally I imagine your gun store has access to You-Tube and can view the vid for themselves. Caesar's Daddy (talk) 13:43, 1 May 2010 (UTC)

The page that video comes from is here, which suggests it's part of a benchrest shooting setup. The Wikipedia article claims that most benchrest shooting setups are custom made. -- Finlay McWalter • Talk 13:57, 1 May 2010 (UTC)

Physics

Hi, please help with these two questions:

1. Estimate what's the difference between cp and cv of chosen metal. (Instruction: Find the temperature coefficient!)
2. Does specific heat of metal have constant value or does it depend on temperature interval? —Preceding unsigned comment added by Atacamadesert12 (talk • contribs) 13:09, 1 May 2010 (UTC)

Please do your own homework.

Welcome to Wikipedia. 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.

Try reading specific heat the answer to half of your problem is right there in the introduction. SteveBaker (talk) 14:13, 1 May 2010 (UTC)

I tried really hard to solve this problem, but all i could do is this: 1. Table of specific heat capacities: it's written that the cp of copper is 0.385 J/(g·K) and cv is 3.45 J/(cm3·K). I just don't understand how to compare them as they have different unities (J/(g·K) and J/(cm3·K)) and what does the temperature coefficient have to do with it? 2. "These quantities are "intensive quantities", meaning they are no longer dependent on amount of material, but capture more directly the dependence on the type of material, as well as the physical conditions of heating."----> So specific heat capacity doesn't depend on mass but it depends on the temperature interval? Actually I had to do 6 pages but this was too tough... —Preceding unsigned comment added by Atacamadesert12 (talk • contribs) 19:09, 1 May 2010 (UTC)

Why would it depend on the interval? Dauto (talk) 21:57, 1 May 2010 (UTC)

Relations between heat capacities might help a little, but honestly you're going to get the best answer for this class by looking at the text and notes you got for this specific class. For example, I know that specific heats of metals do vary with temperature, but rarely enough for it to be an issue for most calculations you'll be doing. Therefore, your class might be expected to say "No, it's constant and doesn't vary with temperature", because that's what you are supposed to assume. But equally, your class might be expected to say "It varies, and here's a table of how the specific heat of ____ varies with temperature". Without being in your class, we can't tell what answer you're expected to learn. 86.178.225.111 (talk) 00:17, 2 May 2010 (UTC)

We could help by pointing out that the unit for Cp is Joules per (gram * degree Kelvin) and for Cv is Joules per (cubic centimtre * degree Kelvin) - so to compare them, all that's needed is to find out how much a cubic centimetre of copper weighs. --Phil Holmes (talk) 09:50, 2 May 2010 (UTC)

Excitation of an atom

Can a an atom in the excited state jump to another higher state when a photon is incident on it? —Preceding unsigned comment added by Rohit.bastian (talk • contribs) 14:26, 1 May 2010 (UTC)

DO you mean the atom itself or do you mean the electrons of an atom? --Jayron32 15:01, 1 May 2010 (UTC)

The answer is yes. Jayron, that's nit picking... Dauto (talk) 15:47, 1 May 2010 (UTC)

He and his brother are in a higher state. Amen. Cuddlyable3 (talk) 16:44, 1 May 2010 (UTC)

Certainly. That's how we get Balmer lines in absorption, amongst many other things. Modest Genius ^talk 20:28, 2 May 2010 (UTC)

Measuring general radio/tv/phone wave strength

For an elementary school science project that is testing how terrain and weather affect wireless communications, what is the best way to measure the "strength" of radio/tv/phone waves? I figure that it will require an extremely wide-band antenna. What circuit could be used to get a general measure of strength (voltage, amperage, whatever)? Can this be completed by elementary school students or is the construction far too difficult? -- kainaw™ 14:31, 1 May 2010 (UTC)

A simple AM receiver can be built using instructions in just about any hobby electronics kit. It doesn't even have to be an amplified circuit. An unpowered AM receiver circuit will pick up radio waves just fine; the early experiments in radio broadcasting used unamplified circuitry. An unamplified circuit would make it easier to quantify the strength of the received signal. You could likely detect the strength of the received signal by hooking the leads from the receiver to a multimeter RATHER than a speaker. History_of_radio#Wireless_experiments_of_the_19th_century discusses some of these experiments. I have seen demonstrations of David E. Hughes's experiments using stuff you can get at a hardware store. At the most basic level, you can demonstrate radio using a speaker and a decently strong spark, without so much as an antenna or receiver circuit. This article at Howstuffworks.com actually contains some pretty good stuff on radio, how it works, and how to build simple transmitters and receivers at home using basic materials. The section titled "The Simplest AM Receiver" shows you how simple such a receiver can be. --Jayron32 15:40, 1 May 2010 (UTC)

Many Mobile phones and PC's equipped for Wireless LAN can display a crude scale of signal strength so no construction is needed to use them. An unamplified Crystal radio will not separate stations well, the voltage you could measure at the output is dc plus large ac variations, and the size of antenna required does not lend itself to portability. An easier choice is a cheap Transistor radio of an older design using discrete components. You can connect a voltmeter to the internal AGC line and the reading will be a (rather non-linear) indication of received signal strength. In principle you could do the same with a car radio but they are harder to open up. However professional equipment is needed to take calibrated measurements over a wide frequency range. Running a Spark-gap transmitter will get you into trouble you can do without.Cuddlyable3 (talk) 16:37, 1 May 2010 (UTC)

I was planning to use old radios, but the goal is to measure as much of the signals out there as possible all at once. There isn't much. There are no local television stations, one FM radio station that sometimes comes in, two AM radio stations, only one cell tower (owned by Verizon), and tons of CB radios. I figured that if necessary, we could measure the strength of the FM station since it fluctuates regularly, but I was hoping to get a better set of reliable data by trying to measure everything that is out there all at once. -- kainaw™ 18:05, 1 May 2010 (UTC)

The trick to making a great science project is not about the equipment - it's about the methodology. I think, in your position, I'd take my cellphone and a paper map of the area. Find out where the cell towers are and pick a suitably large area with hills and other terrain which you have free access to. Then walk around the area methodically writing down the number of bars you're getting on your phone every 100 meters (or whatever). If you can borrow a handheld GPS - or if your phone has GPS, you can get your position from that. If you get it right, you should end up with a map covered with numbers. Now you can look at the contour lines on the map and the locations of the towers and color the map with regions where you got 0, 1, 2, 3, 4 or 5 bars. When you do this, try to hold the phone in the same orientation each time - try to do all of your testing in similar weather condition.

Once you have data - try to form some results - does the number of bars depend on the distance from the cell tower? Do intervening hills make a difference? Did you need to be able to see the tower to get a good signal? Can you form a hypothesis from this data? Perhaps you could test your hypothesis by finding a different area with a different cell tower and predict where you think you'll get good reception and where bad. Then test your hypothesis by actually going to those places and seeing if you get the number of bars you predicted.

SteveBaker (talk) 18:42, 1 May 2010 (UTC)

If you have a budget, you can buy a HAM base (or a standalone receiver) and a VU meter. A VU-meter runs you anywhere from $5 to several hundred dollars (depending on accuracy, digital/software features, etc). Depending on the number of bands you care about, a receiver can run anywhere from $200 to several thousand dollars; at a certain point, you buckle down and buy a mixer too, to expand the frequency capabilities of your receiver. This transceiver unit costs a lot, $2000, but includes a neighborhood spectrum analyzer; or you can use a cheaper but less-interesting Wattmeter display. It operates from 500 kHz to 54 MHz, so if you want to go up to VHF (to listen in on television, commercial radio, and so on), you need to buy a good mixer. Unfortunately, this gear is expensive, technically difficult to use, and requires at least intermediate understanding of radio theory (specifically, how frequencies add when you mix and modulate). The good news is, in receive-only mode, you could train your students to dial in each frequency and record the measured signal level fairly "cook-book"-style. This is really the only way you can sweep out ALL frequencies and get a raw power measurement. If you want to restrict yourself to just a few commercially-used frequencies, such as detecting quality of reception from a commercial AM/FM/UHF/VHF/digital-broadcast television station, your best bet might be to hack up a voltmeter to the inside of a commercial radio or television. Two problems with this: so much stuff is done with an integrated circuit, it might be impossible to locate a place to connect your voltmeter probes. Secondly, so many of these systems have so much signal conditioning, including gain control, that it will be hard to decipher what the actual received radio power is. Nimur (talk) 20:37, 1 May 2010 (UTC)

Boiling

why did water or any liquid comes up when boiled.? —Preceding unsigned comment added by Legend killer harshit (talk • contribs) 14:32, 1 May 2010 (UTC)

The gas form is less dense than the liquid form, so it rises. -- kainaw™ 14:34, 1 May 2010 (UTC)

As the water (or whatever) boils, it turns from a liquid into a gas. If you boil a certain amount of water, the resulting gas (steam) takes up about 800 times more space than the water did. Steam is 800 times lighter than water - so the bubbles formed in the liquid rush to the surface and escape into the air - but between forming and reaching the surface - they take up more space. The combined effect of all of those expanding bubbles forces the level of the liquid in the container to expand.

The answer is actually a little bit more complicated than that. When you boil ordinary tap water, the dissolved air in the water actually comes out of solution at a lower temperature than when the water boils - so you do get small bubbles forming before the water gets hot enough to boil. Those bubbles also increase the volume of the water by a small amount - so the volume of the water starts to increase a little before it actually boils. But the biggest expansion happens (as you say) when the water hits boiling point. SteveBaker (talk) 15:43, 1 May 2010 (UTC)

Question - Helium Canister

Why don't helium canisters float away? —Preceding unsigned comment added by Taratrapie (talk • contribs) 14:56, 1 May 2010 (UTC)

1. The helium is compressed, and so more dense than the air around the canister. 2. The canister is more dense (i.e. has more mass per unit volume) than the air around the canister. This being the case, the canister fails to displace sufficient air to equal its weight, and so sits there unmoved. --Tagishsimon (talk) 15:02, 1 May 2010 (UTC)

In otherwords, the heavy metal that the canister is made out of compensates for the boyant force of the helium given that it is lighter than air. In order to float, the entire container must be lighter than the a chunk of air the same size as the container. For a relatively light and thin balloon, this works. For the heavy metal container, it doesn't. However, if you place a full helium cansiter on a scale, it WILL weigh less than an empty helium canister. --Jayron32 15:15, 1 May 2010 (UTC)

Jayron's answer is incorrect. Remember - the helium is under pressure. Helium is about 7 times lighter than air at the same temperature and pressure. But if you put just 8 cubic feet of helium into a 1 cubic foot tank - then the tank would be heavier than it was when it was full of air. Bottled gas says that a typical gas tank is pressurised to 200 to 400 times atmospheric pressure - so helium at that pressure is between about 30 to 60 times denser than atmospheric-pressure air - so a fully pressurized helium tank will be considerably heavier than an empty one. The tank would have to be about 97% to 99% empty before it would start to weigh less than a tankful of air. SteveBaker (talk) 15:35, 1 May 2010 (UTC)

Correct, of course. (chances are, you can safely ignore any answer I ever give. I am wrong more often than I am right). What I should have said was that a canister of helium would weigh less than a canister of air filled to the same pressure. That would have been correct. What I said above was total bullshit. Just ignore me. --Jayron32 16:00, 1 May 2010 (UTC)

Proving references to back up claims not only helps others find more information on the subject by following the links, but also makes sure what you say is always (or as near as can be) correct :) 82.43.89.71 (talk) 19:20, 1 May 2010 (UTC)

Sky

I was looking at the sky today and then I thought about how the earth is spinning through space at amazing speeds. Why don't the clouds be affected by the spinning of the earth? Or is this exactly how the wind is made? —Preceding unsigned comment added by Goei--inkso (talk • contribs) 15:05, 1 May 2010 (UTC)

One way of thinking about this is to consider that air - gases - have friction. And space has a frictionless vacuum. If an atmosphere of gas is held around a planet by gravity, as our atmosphere is, then it is certain to take more notice of the spin of the glove it is attached to, through the mechanism of friction, than it is to be influenced by the vacuum of space. I'll leave you to read Wind#Cause for more on that subject. --Tagishsimon (talk) 15:08, 1 May 2010 (UTC)

The clouds ARE affected by the spinning of the earth. See Coriolis_effect#Meteorology. The fact that the earth is spinning effects the general path clouds take as they move across the earth. You don't see this standing under them because of the scales involved, but if you watch animations of weather patterns, such spinning effects become clearly visible. --Jayron32 15:13, 1 May 2010 (UTC)

Indeed. And this is explained at Wind#Cause. Sigh. --Tagishsimon (talk) 15:39, 1 May 2010 (UTC)

Modern crystal radio

Would a modern crystal radio with an earpiece be useable for recieving long-wave, medium-wave, or FM broadcasts in the UK? 78.151.115.180 (talk) 16:38, 1 May 2010 (UTC)

I don't know how usable it would be, as you need to be in a silent room to hear anything. StuRat (talk) 16:43, 1 May 2010 (UTC)

(edit conflict)Sort of. The problem with crystal radio is that it is an unamplified circuit, so it needs a pretty strong source. It also cannot directly decode an FM signal, which requires something more advanced than a diode to resolve the signal. However, in principle they can resolve any AM signal, regardless of the wavelength of the source, without any modification. They can resolve FM signals using slope detection, i.e. since FM signals also display AM properties at the boundaries of the bandwidth of the signal, you can "fudge" it by tuning an AM tuner to those boundaries. It produces a noisy, inferior signal, but it can be done. --Jayron32 16:46, 1 May 2010 (UTC)

BBC world service on 648 KHz has a very powerful signal that can easily be picked up with a crystal radio all over Western Europe. This signal so strong that the lack of selectivity of the crystal radio will make it difficult to hear weaker stations like radio Five Live on 693 KHz. Count Iblis (talk) 17:06, 1 May 2010 (UTC)

Thanks. Is there a list anywhere of the wattage of different radio stations, or even what their signal strength may be in various places in the UK? A minature crystal set pernamently tuned to the World Service would not be a bad thing. 89.242.97.110 (talk) 11:09, 2 May 2010 (UTC)

Why do we forget our dreams?

Is it known why, if we don't actively try to remember our dreams as soon as we are awake, we will forget our dreams, even though they might seem vivid just moments ago? --98.114.146.35 (talk) 19:40, 1 May 2010 (UTC)

Its probably not a bad thing to forget your dreams; you have a limited (very large, but still techinically finite) amount of storage capacity in your brain, it makes sense to fill it with stuff that you need on a regular basis (like people's names, how to do stuff, whether or not you left the oven on, where exactly was that bear's den? What was my wife's birthday? etc. etc.), versus dreams, which are pretty much useless when awake (as much as I would like to savor that night I spent with Brooklyn Decker...) That your mind sort-of-automatically knows which stuff to file away as "important" and which stuff to discard is pretty cool. Lucid_dream#Dream_recall and Dream#Recalling_dreams contains some methods for training yourself to remember dreams (caveat emptor, YMMV, etc.). --Jayron32 20:32, 1 May 2010 (UTC)

It is not known why that happens at the physiological level, but I'll tell you my hypothesis. The storage of memory in the brain is thought to depend on a mechanism called long-term potentiation (LTP), which we know quite a bit about. One of the things we know about LTP is that it takes place in two phases. The first phase produces a memory trace that lasts for a few minutes. The second phase, which is dependent on protein synthesis, produces a trace that lasts for hours or longer. My hypothesis is that during the REM sleep stage (when dreams occur) there is an alteration in brain chemistry that disables the second phase of LTP. In order to make a dream memorable it is usually necessary to think about it very soon after waking, before the temporary trace has disappeared bu after awakening has re-enabled the long phase of LTP. I don't know of anything in the literature that contradicts this explanation; but I don't know of anything that proves it is correct either. Looie496 (talk) 23:11, 1 May 2010 (UTC)

This is WP:OR - but I have a compelling hypothesis for dreaming that fits all of the available facts. It appears to me that the brain is doing something akin to 'defragging' the disk drive on your PC. It's rearranging memories for greater efficiency.

If we pursue this 'defragging' analogy, what happens in your computer is that the PC moves blocks of data off of the hard drive, into RAM and then writes them back out to the hard drive in a more "logical" position. Block by block, it rearranges the files on the disk into a more streamlined arrangement that allows the computer to get at the blocks that make up the file very quickly. It used to be the case that you had to make sure that you weren't running any programs at the time you did this - but modern PC's now allow that.

This analogy isn't backed up by much evidence - but it fits the facts perfectly - and is very compelling:

• Dreams (or at least "REM sleep") is very important to us. We can do without it for a while - but if we don't get enough REM sleep over an extended period of time, we get slower, stupider, and ultimately: seriously mentally deranged! If your PC isn't defragged, the files gradually get more and more chopped up and spread all over the disk, like shuffling a deck of cards. Getting at those files starts to take more and more time. Defragging streamlines all of that - puts all the bits of a particular file next to each other...like sorting a deck of cards.

• Our bodies are 'cut off' during REM sleep so we don't 'act out' our dreams while the data is being moved around. This is a good fit for the old "don't run programs while defragging" rule because your software would see temporarily screwed up files while they were being rearranged. Less intelligent animals (dogs, for example) haven't quite mastered this - and when they dream, you can see their feet twitching like they are running - and there are little barks and such. We only move our eyes around under the eyelids.

• If you don't wake up - then the result is that your memories are streamlined and more efficiently accessible - you wake up feeling more alert and refreshed. You don't remember this rearrangement of memories because everything was 'turned off' while they were being moved around.

• If you do wake up - then it's like you stopped the computer midway through 'defragging'. What's in the computer's RAM memory when you do that is just a random collection of bits and pieces of different files you have on the disk. This fits perfectly with the human experience - your short term memory ("RAM") is full of random bits of real long-term memories that were in the process of being re-organized at the moment you wake up.

• If you wake up during a particular dream (and therefore stand a chance of remembering it) - then that section of your memory hasn't been properly 'defragged'. The next time you sleep, the brain has to go back and try to sort that bit out again. If you wake up again, the same stuff is in your short-term memory the next time - and it seems like you had a 'recurring dream'.

But in this hypothesis, your memory doesn't ever contain any kind of "story" - the dream wasn't like a movie playing in your head. It was just random bits of memories, put together in any old order. When you wake up, your short term memory ought to be empty - but it's full of random bits of memories. What is your conscious mind supposed to do with a bunch of completely random bits of old memories that are packed into short term memory just as if they had just happened? That's easy - we think they were true short-term memories - things that just happened to us. We try to put these into a sensible sequence of actions - but it's difficult because it's basically a mess. The brain doesn't put these 'stories' we invent at the moment of waking up into long-term memory unless we specifically concentrate on doing that (eg by writing them down) - so the stories disappear as soon as short term memory expires.

In this hypothesis, the dream didn't actually "happen" at all - it's a bunch of old memories that seem to have just happened if we happen to stop the memory reorganization right in the middle. If that hypothesis is true (and it seems entirely reasonable) - then the issue of 'remembering' wouldn't come up. A dream isn't like a story or a movie unless we wake up while the REM phase is happening. You don't "forget" your dreams - you simply never remembered them in the first place...the dream literally didn't happen unless we woke up.

From what little we know of how memories are stored - there isn't enough storage space for all of our memories to be retained in full detail for life. We forget things that aren't important, we simplify memories where detail is unimportant - some process in the brain must be doing that reorganization on a daily basis - and REM sleep fits the bill perfectly.

I must emphasize that I know of no evidence that this hypothesis is true - but as far as I can tell, it fits all of the facts perfectly. SteveBaker (talk) —Preceding undated comment added 00:47, 2 May 2010 (UTC).

Nice theory, but it doesn't seem to fit with the phenomenon of lucid dreaming. It is possible to realise you are dreaming and take control of the dream - that couldn't happen if the dream never actually happened. --Tango (talk) 00:56, 2 May 2010 (UTC)

Having read Feynman's account of lucid dreaming - I'm inclined to the view that lucid dreams are not REM sleep. He found that when he engaged in this activity, he lost all of the benefits of sleep and he consciously decided not to pursue it because he was concerned for his intellect and state of mental health. That actually fits what I believe. The idea that the brain starts to defrag things - then the conscious mind steps in and starts directing a 'story' (albeit when still "asleep") simply disrupts the memory re-org that's in progress and turns things over to conscious thought. In effect, lucid dreaming isn't the same thing at all. SteveBaker (talk) 13:36, 2 May 2010 (UTC)

Steve's theory has a lot in common with the theory proposed by Francis Crick and Graham Mitchison in 1983, see PMID 6866101. (You can find a pdf online using Google Scholar if you want one.) There isn't a lot of evidence to support it though. There is lots of evidence relating sleep to cleanup of memory, but it mostly points to slow wave sleep rather than dream sleep. Gulio Tononi, in fact, has been pushing a sort of "defragging theory" of the function of slow wave sleep for the past few years, in papers such as PMID 16376591. Also, most sleep researchers favor the idea that dreams play out in real time rather than being stitched together ad hoc on waking. The evidence is somewhat sketchy, mainly involving studies relating eye movements during dreams to the experienced events reported on waking, but it does seem to trend in that direction. Looie496 (talk) 01:08, 2 May 2010 (UTC)

Well, like I said - it's just a hypothesis. The sketchy nature of dream recall seems to me to make correlation with eye movement during REM an 'iffy' piece of evidence at best...but I'm no dream researcher! I originally trained as a cyberneticist (that's what my degree is in) - and cybernetics is all about looking for ways to compare what happens in biological situations and in robotics and computing - so it seems natural to me to look for these kinds of analogies as ways to suggest answers to things that are tough to study in the brain. Sometimes it produces useful insights - sometimes not.

The 'real time' nature of some dreams is certainly a problem for my hypothesis - and it's evident in watching dogs sleep - they seem to lack some of the ability we have to 'turn off' motor control during REM. This gives us a handy way to observe dreams playing out - but unfortunately, not in human subjects. So you see their feet twitching, first one by one like they were walking, then all four together, like they were running, then you hear tiny little barks and sometimes chewing motion with drooling. That's certainly compelling evidence for a real-time dream of squirrel chasing, catching and devouring...but these motions are not long enough to account for the length of dreams that I recall. The entire dog-dream seems to last under a minute - but the evidence (see REM sleep) is that REM lasts for 15 to 20 minutes at a stetch.

So I imagine that what we're seeing is either the recall or the storing of one of the snippets of a memory being pulled into short-term memory in preparation for putting back into long term memory in a different form. The idea that short bits of actual memory have to be replayed in realtime as they are re-organized isn't such a strange idea. After all, the ability to do this stuff had to evolve somehow - and perhaps the ability to re-record short term memory back into long-term requires the memory to be replayed in something like realtime. So this problem isn't necessarily devastating for my hypothesis.

Also, it couldn't be that REM sleep was the whole picture - otherwise, presumably, we'd sleep for only one to two hours a night and have just REM sleep and nothing else. So there are any number of other possibilities. One is that 'long-wave' sleep is a planning process where the brain figures out what needs to be reorganized - and REM is the actual reorganization. That would neatly explain the alternation between the two kinds of sleep. It might also be that long-wave sleep does contain 'real-time dreams' but that the process of erasing all memory of them actually works OK if we're woken up in the middle of them. The fact that dream recall only happens if you wake up during REM (or very shortly afterwards) might well be a failure of the "forget it - it's only a dream" mechanism - or (more likely, IMHO) that REM leaves this 'junk' in our short term memories and we need enough time after that to allow short-term memory to naturally fade away.

The problem I have with other theories is the question of why we dream at all? It's clearly a costly process (in terms of all of this brain activity consuming energy) - and it's clearly essential to our mental health (if you don't dream - you get into a lot of trouble) - so it must have evolved for some rather critical reason. We know that other mammals have 'REM sleep' with dreams (certainly dogs and cats do) - so we can say for sure that it evolved long before big-brained humans needed it. Without the need to dream, why sleep at all? Sleep is pretty dangerous from a perspective of being vulnerable to predators and such like - so it must have a rather massive benefit or we'd evolve to not do it. We know that birds sleep - so the evolution of sleep must go back at least as far as the split between mammals and reptiles - so dinosaurs must have slept. We even know that some birds, whales and dolphins sleep with only one hemisphere of their brains at a time in order that they can stay conscious 24 hours a day. So this is clearly a vitally important bit of what makes brains tick.

The 'defragging' idea seems to be the only idea I've come across that has a compelling explanation of the need for sleep and why we feel so terrible when we don't get it. Arguments that we have to 'rest our bodies' are patently untrue. If I lay still in bed, reading a book all night - I still feel crap in the morning. My body got all the rest it needed - but my brain didn't get to defrag. SteveBaker (talk) 13:36, 2 May 2010 (UTC)

Difficulty remembering dreams is very useful to help you keep track of what really happened and what happened in a dream. If we remembered our dreams perfectly, we wouldn't know if they had actually happened or not. --Tango (talk) 00:56, 2 May 2010 (UTC)

During a dream, our waking sense of logic is often hindered or corrupted. When we wake and logic is slowly restored, the context of the dream may no longer be realistic, rendering the details of the dream as conceptual gibberish. ~AH1^(TCU) 01:10, 2 May 2010 (UTC)

Since this seems to be a thread of original research, I'll say mine as well. I'm of the opinion that we actually do remember every single dream (and indeed almost everything we experience in real life too), but 99% of the time we just can't access it because the brain stores these memories without any links to anything else to trigger the memory. My "proof" is that several times I've suddenly remembered vividly dreams which I had years ago, which I didn't even properly remember at the time I had them. 82.43.89.71 (talk) 13:01, 2 May 2010 (UTC)

I have some questions about your hypothesis:

1. Why would we evolve to store all of that useless information?
2. Why would we evolve to generate it all?
3. What is the point in storing a memory of a dream that we can't subsequently recall?
4. How do you know that you just "remembered" a dream you had years ago - and that your brain didn't just pop a random thought into your head at the instant you "remembered" it rather than at the time you think you remember it from?

You have no means to prove that you had the dream years ago...unless you wrote it down or something - and then you're remembering the thing you wrote - not necessarily the dream itself. Recovered memory is the term for a memory of something that you thought you'd forgotten. As our article points out: "the authenticity of recovered memories has often been challenged; in some cases recovered memories are fictitious". No matter how vividly the memory is suddenly recalled, it can still be completely false. So your "proof" doesn't stand up to careful scrutiny - and unless you can use your hypothesis to explain other things (like why it is that we remember dreams only when we wake up during REM sleep - and what the purpose of all of this complex mechanism is) - then it's not much of a hypothesis. SteveBaker (talk) 15:18, 2 May 2010 (UTC)

Evolution doesn't require everything to be beneficial, as long as it isn't significantly harmful. --Tango (talk) 22:36, 2 May 2010 (UTC)

But if it's not benefecial or harmful then it's just random so how could it become so widespread? Also, storing every single dream (and almost everything else) is harmful to the extent that you would need energy to store that information. Zain Ebrahim (talk) 23:42, 2 May 2010 (UTC)

Football

When a football is tossed into the air, it's usually spinning pretty fast. As the ball travels along its path, the axis of rotation changes and dips with the football. I was wondering what force causes the torque necessary to produce the change in angular momentum. 173.179.59.66 (talk) 20:29, 1 May 2010 (UTC)

Assuming you mean an American football, the answer is that gravity does that. The dynamics of a ball's flight is described by the science of ballistics, sadly our articles on ballistics are weighted towards the forensic aspects of firearms and handguns and bullet trajectories, but strictly speaking ballistics studies the motion of any non-powered flight. The article External ballistics discusses some of the forces at play, in some serious detail, and if you replace any mention of the word "bullet" with "football" you get the basics. Specifically, a football's flight is stabilized by the Magnus effect, which is also discussed at External_ballistics#Magnus_effect. To put it simply, there is a downward force on the football because of the interaction between the spinning ball and the air blowing past it as it sails through the air; this downward force tends to act more on the nose than on the tail. A ball thrown without spin will maintain the same angle in the air; such a ball, if thrown straight and with no other forces acting on it, will tend to land at the same angle thrown (thus, if thrown nose-up, they land nose-up). Spinning balls will tend to land nose down if thrown nose up. --Jayron32 20:43, 1 May 2010 (UTC)

Thanks. 173.179.59.66 (talk) 02:56, 2 May 2010 (UTC)

Coiling microphone cable during use.

Hi, when recording audio using a (battery) powered electret microphone, should I be concerned with the arrangement of the excess cable? Can it be coiled or will this lead to distortion of the audio recording? --84.13.77.150 (talk) 22:43, 1 May 2010 (UTC)

Try it and see. If it leads to distortion that you can't hear, does it really matter? --Tango (talk) 00:58, 2 May 2010 (UTC)

Of greater concern is avoiding laying the microphone cable next to an electric cord carrying AC power. If a mic cable is layed next to a power cord, you can get a mains hum in the mic circuit; if they must cross, always do so at right angles to minimize the effect. However, I am not sure that the mic cable poses too much of a threat to itself. --Jayron32 02:06, 2 May 2010 (UTC)

Jayron beat me to some points, but 84.13 are you thinking of the general practice in the Professional Audio industry to not coil cables? This is very likely to be more applicable to AC mains power cables, where if you do neatly coil up cable, you are effectively forming an inductor.(also see Inductance) Which means that any time the current changes direction, (which is 50/60 times a second) there will be a loss of power as heat. If you have a big pile of cables supplying a bank of power amplifiers at a rock concert, all neatly coiled, there is a risk of overheating, melting, shorts and fire. Though any cable that carries a lot of power where the signal changes continuously ie. audio speaker cables from the power amplifiers to a bank of 'high power' speakers will also experience the heating effect, to a lesser extent. See this website/section, Do not keep your cables coiled about 2/3 of the way down the page. This effect is unlikely to be noticeable with the cable of a battery powered microphone.
The 'inductors' action may also have an effect on the audio, but is unlikely to be noticeable, though as Tango says "Try it and see". And lay cables as per Jayron32 to minimise hum. If you coil your cables you are also more likely to get cross-talk between channels. --220.101.28.25 (talk) 02:52, 2 May 2010 (UTC)

Another source: John Vasey,"Concert sound and lighting systems " 3rd edition, page 10, 1999, Focal Press, ISBN 0-240-80364-7. --220.101.28.25 (talk) 03:49, 2 May 2010 (UTC)