Wikipedia:Reference desk/Archives/Science/2011 June 10

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June 10

Avian body odour?

Is it a noted fact that birds tend to have little or no body odour? Just something that occurred to me today while my friend's really stinky dog was running around the room in front of me - while accumulations of bird poop do smell bad, I'm yet to encounter a bird that in itself, has an obvious scent. --Kurt Shaped Box (talk) 00:47, 10 June 2011 (UTC)

Feathers don't work very well if they get dirty so birds spend a lot of time preening and keeping themselves clean. Conversly, some dogs seem to take pleasure from rolling around in the foulest substance that can be found. Vespine (talk) 01:10, 10 June 2011 (UTC)

Could the fact that birds lack sweat glands be a significant/more significant factor? I mean, odour-producing bacteria grows in sweat, doesn't it? I know that it's also said that (IIRC) most birds have a poor sense of smell too, so odour-for-the-purposes-of-identification/scent marking would seem to me to be a rather unnecessary. --Kurt Shaped Box (talk) 01:17, 10 June 2011 (UTC)

Yes, but dogs don't sweat either. StuRat (talk) 03:39, 10 June 2011 (UTC)

Dogs don't sweat? Hmmm. Never owned a dog, but I could swear that I've known other people's dogs that've been all sweaty after going for a run (might be wrong). --Kurt Shaped Box (talk) 10:52, 10 June 2011 (UTC)

Overheated dogs have been known to jump into puddles or other water, so a hot, wet dog might be mistaken for a sweaty one. StuRat (talk) 17:35, 11 June 2011 (UTC)

Knowing nothing about this topic, I did a Google search for "odorous birds", and the top hit is a National Geographic article titled BO Attracting Predators to Birds, whose first sentence is "New Zealand's native-bird BO is so pungent, it's alerting predators to the birds' presence, ongoing research shows". The remainder of the article contains some useful information about bird body odor as well. Looie496 (talk) 02:33, 10 June 2011 (UTC)

Doing a casual google also suggests that some birds have fairly highly developed sense of smell, but most do not. So it's not a class wide feature (or more specifically 'lack of' in this case). Vespine (talk) 04:15, 10 June 2011 (UTC)

From what I've smelled of the parrots I've been close to (not that I've been deliberately going around sniffing parrots, mind), they do have a very faint, oily scent. I'd actually theorized that this may be the smell of the preen oil/wax. FWIW, Caiques are supposed to have a distinctive scent, as mentioned in the article. --Kurt Shaped Box (talk) 10:52, 10 June 2011 (UTC)

Penguins have a terrible odour. I couldn't stand being near to them for a long time. But then again those are not "normal" birds. --helohe (talk) 22:30, 10 June 2011 (UTC)

It seems to me that their odor comes from the fish they eat, not from the birds themselves. 67.169.177.176 (talk) 23:30, 10 June 2011 (UTC)

Yeah, is it the penguins themselves that stink - or the accumulated penguin crap, penguin vomit and half-eaten fish in the general area? --Kurt Shaped Box (talk) 00:13, 11 June 2011 (UTC)

Well, those that live in Antarctica do have the problem of all their waste simply freezing and accumulating, rather than decaying. While frozen it's probably not bad, but on the few days warm enough for it to thaw, I imagine there's a horrid stench. One would hope that zoos would clean up after them, but, it they are used to being able to lie on a pile of crap after it freezes in an hour, perhaps they still do that when in a warmer zoo, not realizing that those rules no longer apply there. StuRat (talk) 00:15, 12 June 2011 (UTC)

The mother of a friend of mine raised a few score parrots of various species for commercial sale in her basement. The house smelled a bit dusty, but no more so in the basement than the rest of the house. μηδείς (talk) 01:46, 13 June 2011 (UTC)

Hijacking a ride on a comet

Antoine de Saint-Exupéry aside, has any fiction or pie-in-the-sky proposal ever proposed "hijacking" a comet to use as a generation ship? Presumably the comet's orbit could be changed to eventually leave the solar system instead of continuing, which would mean you'd already be moving at a very healthy clip on top of a big stash of reaction mass and/or in-situ resource utilization raw material. SDY (talk) 01:01, 10 June 2011 (UTC)

I don't know about comets (might be difficult to keep them frozen with livable environment inside), but asteroids have been proposed, to the point where "hollowed asteroid generation ship" pops up as an autocomplete option on Google if you start typing "hollowed as...". There was even a Star Trek (original series) episode with it as a key plot point: For the World Is Hollow and I Have Touched the Sky. -- 174.31.219.218 (talk) 02:48, 10 June 2011 (UTC)

Hollowed asteroid generation ships are a common science fiction theme; see for example Greg Bear's Eon. Hollow comets are little bit harder to come by (there seems to be a certain psychological reluctance to use ice as a building material, even though it would stay quite comfortably frozen on the long journey between the stars). Nevertheless, David Brin offers us Heart of the Comet. Those examples are novels; I strongly suspect that you'll find quite a few examples if you delve into the world of short fiction. (Isaac Asimov's novella The Martian Way introduced the use of chunks of ice from Saturn's rings as cubic-mile-scale spacecraft (but didn't broach the subject of generation ships). TenOfAllTrades(talk) 03:32, 10 June 2011 (UTC)

With out current technology it wouldn't make much sense, as it would take more energy to move that extra mass around, and to catch up to a comet and land on it in the first place, without any corresponding benefit. However, my fave design for an interstellar ship is a massive linear accelerator/nuclear reactor combo (or maybe anti-matter reactor) that clamps onto an asteroid, and hollows it out for material to fling out at the speed of light, while using the asteroid as a shield in the front. StuRat (talk) 03:37, 10 June 2011 (UTC)

Another science fiction example is Jules Verne's Hector Servadac. – b_jonas 14:37, 10 June 2011 (UTC)

Let's not forget that many comets follow a hyperbolic trajectory that takes them out of the Solar System on their own.^[1] While it is unlikely indeed, it is possible to imagine spotting a comet on its way into the Solar System, plotting out a trajectory that comes close to Earth, and seeing that it will go near a planet you want to colonize in a bazillion years or less. So you round up a bunch of idiots astronauts and convince them to take a few tiny, fast ships with just a few basic essentials, confident that they can live off the water and carbon dioxide and other goodies locked away in the cold, dark core of the comet for countless generations before sallying out to claim some barren rock a few parsecs over. (Better bring a lot of mirror foil to concentrate that starlight...) Wnt (talk) 17:12, 10 June 2011 (UTC)

It's obviously still unrealistic, but the only realistic proposals so far in space travel are to extremely local things like the moon or the inner planets, so that it's not immediately feasible isn't surprising. Regardless, my original question was answered. SDY (talk) 17:50, 10 June 2011 (UTC)

You might be interested in the Project Orion (nuclear propulsion). 5BYv8cUJ (talk) 20:14, 10 June 2011 (UTC)

Do pigs have orgasms that last for thirty minutes?

Somebody told me that pigs have orgasms that last for thirty minutes, but I can't find any evidence supporting it. I've already checked the pages about pigs, orgasms, and animal sexual behavior. Additionally, if this is true, is it true for both sexes? — Preceding unsigned comment added by Undercooked (talk • contribs) 04:03, 10 June 2011 (UTC)

Sounds like nonsense to me, and there is an awful lot of nonsense out there. I suggest you ask them to support their claim. Why would you prefer to believe something that someone told you than trust your own researches?--Shantavira|^{feed me} 07:19, 10 June 2011 (UTC)

Simple: No. More details: It's an Internet meme. [2]. Gryllida 09:47, 10 June 2011 (UTC)

This google book page has some details, but I haven't been able to find a scholarly source on the subject.Smallman12q (talk) 11:11, 10 June 2011 (UTC)

A pig told me that it feels like flying. Cuddlyable3 (talk) 22:44, 10 June 2011 (UTC)

It wouldn't surprise me if they have ejaculations that last that long. Dogs and cats do. μηδείς (talk)

Same weight or not?

if 300ml water in liquid state has a weight of say 1 kg, would it have the same weight in solid state(i mean after freezing)? — Preceding unsigned comment added by 175.110.91.49 (talk) 08:44, 10 June 2011 (UTC)

• Yes, it would have same mass. But ice would have different density than water, which means a volume change (water grows, most other substances usually shrink). Please see Crystallization#Process. --Gryllida 09:16, 10 June 2011 (UTC)

(edit conflict) The simple answer is yes, assuming that (1) by "weight" you mean "mass"; (2) the substance you are calling "water" has a density more than 3 times that of ordinary water; (3) we can neglect any small changes in mass due to release or absorbtion of dissolved gases etc; (4) we can neglect the really really small changes in mass due loss of thermal energy. Basically, mass stays the same, but volume and density will change. Gandalf61 (talk) 09:20, 10 June 2011 (UTC)

I'd have to disagree with the first two posters, just on an everyday level, as ice has a lot "heavier" feel to it, from being solid. --188.29.60.182 (talk) 09:35, 10 June 2011 (UTC)

This means: "If you take ice and water of same volume, ice would feel heavier". This is not right for the reason: 1) Unlike other solids, ice is less dense than its liquid state (water). (See Properties of water#Density of water and ice). I have to note that this statement is unrelated to freezing a piece of water in isolated environment and having its mass save due to the law of conservation of mass, which the question is about. :) --Gryllida 09:41, 10 June 2011 (UTC)

"Feels solid" (maybe mentally related to things that are hard and therefore large and/or massive?) and "feels heavier" are separate issues. If you are trying to compare "how heavy" (the question), take a bucket-full of each. Gandalf61 makes an interesting point #2 I'd like to emphasize: though the poster might just be making up numbers for this example, 300 mL of water would actually weigh approximately 300 g and 1 kg of water would be approximately 1000 mL at normal earth conditions. DMacks (talk) 09:53, 10 June 2011 (UTC)

To make things clear: I'll rephrase the question. It can be interpreted in two different manners (I used the first one). --Gryllida 10:04, 10 June 2011 (UTC)

1. "Does water get heavier when it freezes?" --The answer is "no" (see here). --Gryllida 10:04, 10 June 2011 (UTC)

2. "Is a solid of given volume heavier than liquid?" --The answer is "yes" for everything almost everything [updated per reply -Gryllida 13:27, 10 June 2011 (UTC)] other than water (see here). --Gryllida 10:04, 10 June 2011 (UTC)

Not everything other than water. Properties of water#Density of water and ice lists some other examples of substances that expand when they freeze. Red Act (talk) 11:41, 10 June 2011 (UTC)

Thanks, -Gryllida 13:27, 10 June 2011 (UTC)

300ml of water weighs 300g. When frozen into ice, it would weigh the same. 92.24.176.232 (talk) 12:41, 10 June 2011 (UTC)

Yes. It would merely occupy more than 300ml in volume. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:24, 10 June 2011 (UTC)

Right! -Gryllida 13:27, 10 June 2011 (UTC)

The change in volume is an important point to consider, given the distinction between weight and mass. The ice and the liquid water would have essentially the same mass; the state change doesn't affect the amount or type of matter present, and the relativistic effects (associated with different amounts of internal energy) are negligibly small for any reasonable purpose I could imagine.

Whether or not they are the same weight depends on one's definitions, however. If one defines 'weight' to be solely the attractive gravitational force between the ice/water and the earth, then they will have the same weight. If one defines 'weight' as the net apparent force between the water/ice and the earth, then under sensitive measurement conditions the two states will actually show slightly different weights. This latter 'operational' definition represents how most balances and scales tend to work in real life. To consider an extreme example, think about what happens if you tie a helium-filled party balloon to the pan of a balance. Even though we all know the balloon has real mass, it will show up as having a negative weight. The net force exerted by the balloon on the scale is upwards, because the balloon displaces more than its own mass in air: buoyancy.

While this effect is usually only obvious when weighing objects that are comparable in density to (or lighter than) air, it actually comes into play for all objects being weighed in atmosphere. In round numbers, the density of air at sea level is on the order of 1 gram per liter, so 1 kg of liquid water will displace about 1 gram of air. The density of ordinary ice is about ten percent less than that of liquid water; a kilogram of frozen water will displaces about ten percent more air (an extra 0.1 g). This extra volume means extra buoyancy, which means that the measured, apparent weight will be reduced by about one part in ten thousand. That doesn't sound like a lot – it's too small a shift to pick up on a bathroom or kitchen scale, for instance – but it's readily detectable using a good analytical balance (of the sort you'd find in any reasonably-equipped chemical laboratory). That said, buoyancy due to air is something that only has to be explicitly accounted for when making extremely precise measurements of weight. TenOfAllTrades(talk) 14:35, 10 June 2011 (UTC)

Hence the ice would have the same mass as the water, but would weigh slightly less, right? If you take two equal-weight buckets, each containing 300ml of water, as well as plenty of room at the top to expand, you could freeze one of them, and although the one containing ice would weigh measurably less, merely carrying them they should "feel" the same weight. Right? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:42, 10 June 2011 (UTC)

Because the heat of fusion of water is 337 kJ/kg, and the weight of a joule is 11.1 femtograms, a 1 kg block of ice should be 37.2 nanograms lighter than the corresponding amount of water at the same temperature. Additionally, if we suppose that the 1000 cc of water begins as a 1 decimeter cube, and if we constrain the sides and force it to go only upward when freezing, then because ice is 0.9167 the density of water, the center of gravity of the ice will be 4.54% (0.454 cm) higher than that of the water. Since the Earth is 6371 km in radius, at sea level this increases the distance to the center of the Earth by a ratio of 7.13 x 10^-11 - which should decrease the weight by twice as much (i.e. (1 + that) squared), or 142.6 nanograms. In total then (for that shape and manner of freezing) that's 0.18 micrograms - almost a weighable difference! B) Wnt (talk) 16:54, 10 June 2011 (UTC)

You need the change in internal energy here, not the enthalpy; the latent heat is the heat needed to melt ice, which is less than the internal energy change in this case, because you get some energy "free of charge" due to the volume decreasing and the atmosphere performing work on the water. Count Iblis (talk) 18:29, 10 June 2011 (UTC)

If 300ml of water weighed 1 kg then it wouldn't be water on planet Earth. Here the heaviest water we know about is only 10.6% denser than ordinary water. If you freeze heavy water you get heavy ice that actually sinks in ordinary water. I suppose one could make an alloy of ordinary and heavy ice that has exactly the same density as ordinary water (and I think they could coexist at slightly above 0 deg. C.). Cuddlyable3 (talk) 22:34, 10 June 2011 (UTC)

There seems to be a general confusion in several posts here (including the original poster) between mass and weight. 300ml of water has a mass of approximately 300g anywhere in the universe; on Earth it has a weight of approximately 3 Newtons. Gandalf61 (talk) 02:42, 11 June 2011 (UTC)

Following Wnt, if 300 g (or 1000 g) of water gave up energy and froze, consider the mass equivalent of the energy lost, by the formula E=MC² Would this energy loss make the ice have less mass than the water? Granted, no practical measuring device could measure the difference. But theoretically is the ice less massive than the water? I've heard that a car accelerated from zero to 100 km/hr gains a tiny amount of mass, and that a wound up clock gains a tiny amount of mass. Does this energy-mass equivalence extend to freezing/thawing? Edison (talk) 04:10, 11 June 2011 (UTC)

Yes, and there is a very simple way to see this. The center of mass of an object at rest on which no external forces act, cannot change. If you assume that this is always true, then considering a situation where a pulse of light is exchanged between two parts of the object, leads to the conclusion that the transfer of energy was accompanied by a transfer of mass. If there were to exist another hypothetical process in which energy is transferred without a change of mass, the relation E = M c^2 would not be valid; you would be able to transfer arbitrary large amounts of mass from an object of mass M without affecting its internal energy, you could make that mass negative while makig the mass of another object arbitrary large. Count Iblis (talk) 15:46, 11 June 2011 (UTC)

Electric signal

Hi i need what will be output waves form if the input signal were standard test signals(sine, step, square, ramp, triangle,) to the passive components resistor, capacitor and inductor separately and two combined in series and parallel then three combined in series and parallel actually what happens when these combinations are energized with these signals and how they respond (pictures preferred) — Preceding unsigned comment added by Kanniyappan (talk • contribs) 14:45, 10 June 2011 (UTC)

This appears to be homework, but it is hard to tell what level. At the most basic level, a resistor reduces the amplitude of any wave in the direction of 0V (a big enough resistor and you'll pretty much have just 0V). A capacitor allows AC signals to pass, but inhibits DC signals. An inductor allows DC signals to pass, but inhibits AC signals. I know, the idea of a DC "signal" is silly. But, if you are in a higher level, you will be discussing how current and voltage relate to one another as they go through a capacitor/inductor. I was taught "ELI the ICE man" in the Marines. E (voltage) in an L (inductor) precedes I (current). I (current) in a C (capacitor) precedes E (voltage). -- kainaw™ 15:02, 10 June 2011 (UTC)

See RC circuit, RL circuit, LC circuit, RCL circuit.--CookerSock (talk) 18:28, 10 June 2011 (UTC)

Your list of test signals starts with a sinewave, which has a single frequency. The other signals are actually just sets of sinewaves added together. See the article Fourier series. A Resistor is not frequency-sensitive and it passes a current according to Ohm's law. To tackle your circuit questions you need some AC theory. In fact your question looks much like the syllabus of an AC electronics course. This article gives a general introduction: Network analysis (electrical circuits). Cuddlyable3 (talk) 22:12, 10 June 2011 (UTC)

thnx for ur reply these are known by myself what makes me confusion is using resistor and capacitor in parallel when voltage taken across resistor it both act as filter and spike signal generator so that how this is possible — Preceding unsigned comment added by Kanniyappan (talk • contribs) 03:32, 11 June 2011 (UTC)

See RC circuit. Cuddlyable3 (talk) 15:33, 11 June 2011 (UTC)

Question about prisms

Hello. I am a costumer who has been given a very specific request by a client, and I wanted to verify that the client's idea is going to work before I go to the trouble of making the thing.

The client wants a large prism on her costume that will throw rainbows all over the stage. Client's idea is to mount the prism (like a precious stone) on her costume with a mirror backing, on the assumption that light will pass into the prism, bounce off the mirror, and come back out of the prism as rainbows. I was unsure whether rainbows would be created and thrown about the stage without the light being able to pass all the way through the prism and out the other side. So I thought that I'd better try to find a physicist to explain whether this will work or not before I build the thing.

Any assistance would be deeply appreciated. Thanks greatly in advance! Heather (talk) 15:27, 10 June 2011 (UTC)

Light has to pass through a prism in order to bend the light. If it is reflected back by a mirror, any bending will be unbent on the reverse trip. Light would have to pass through the prism and then hit a mirror on the side and not come back through to cause a rainbow. And this will cause just one rainbow per prism, not throw them all over the place. Unless your client is actually wearing little lamps on her body, any such effect is going to be minor and overwhelmed by the amount of white light stage illumination she will need. She'd be better of with a reflective costume of some sort and an experienced lightman with colored lights. μηδείς (talk) 16:07, 10 June 2011 (UTC)

Anyone who has tinkered with a prism knows that getting good rainbows can be problematic. Though with a mirror-backed prism it seemed easier to me. I wonder if you could do better using a diffraction grating, perhaps concealed as the "mirror" in the prism. But still you're up against the solid wall that the light coming out of the prism is no more than what goes in, so if you have a spotlight on her and one little jewel reflecting, it's going to be washed out. If you had the sophistication to use a video camera and image recognition to lock onto the prism and send a 1-inch wide beam straight at it all the time no matter how fetchingly it jigged and danced ... (which I think really could be done with off the shelf technology, but maybe not your shelf or mine!) ... then you'd have something. Wnt (talk) 17:00, 10 June 2011 (UTC)

Oh, and if she has a mirror and a prism, she should also have a lens in homage to Dhalgren. ;) Wnt (talk) 18:33, 12 June 2011 (UTC)

In my opinion, it would be cheaper and easier to use a color-changing LED kit. I've seen color changing LED keychains for around $5. With those, you can get a lot of colors glowing. Keep in mind that with a prism or LED (or anything similar), you will not a rainbow arcing through the air. You will get an array of colors on the floor of the stage, which the audience most likely will not be able to see. You can use smoke to keep the color around the performer but that won't work well. The smoke will appear to glow and make it very difficult to see the performer. -- kainaw™ 17:54, 10 June 2011 (UTC)

I can only see this working if she wears the prism on the top of her head and has a strong spotlight shining at it from behind? Exxolon (talk) 18:02, 10 June 2011 (UTC)

Which will of course, make her look like a person wearing a prism on top of her head. μηδείς (talk) 18:12, 10 June 2011 (UTC)

A mirror ball hat under various coloured spotlights could do. Add Sequins for effect.Cuddlyable3 (talk) 21:55, 10 June 2011 (UTC)

Perhaps it would be better for her to wear a costume with lots of small diffraction gratings sewn in. Or perhaps use diamonds or something -- those can act as prisms without needing any mirror backing. Just my non-expert opinion. -- An American ultranationalist 67.169.177.176 (talk) 23:25, 10 June 2011 (UTC)

On second thought, she could wear a costume that has some kind of small glass prisms (such as rhinestones, etc.) sewn in; their shape could cause them to act as Porro prisms and redirect the light back toward the audience by total internal reflection at the same time as refracting/dispersing it. Her original idea (with the mirror backing) simply will not work. -- An American ultranationalist 67.169.177.176 (talk) 03:23, 11 June 2011 (UTC)

Suggestion: To stick with the prism idea, how about it she has several prisms on her head, with a vertical light between them, and a mirror on the top, like the 3 prisms show here (top view, with mirror removed):

         /\
        /  \
       /    \
      /\    /\
     /  \ °/  \
    /    \/    \

If an electric cord wouldn't work, then a battery pack would be needed to power the light. This light could be either fluorescent or incandescent. The latter requires more energy and creates more heat, but might also make better rainbows. No other light source should be used on stage, as that would wash out the rainbows created. Unless, that is, you want to create additional rainbow light sources to supplement the prisms. StuRat (talk) 08:56, 11 June 2011 (UTC)

Your client may be thinking about the diffraction effect of diamonds, which is supposedly similar to prisms. ~AH1 ^(discuss!) 15:02, 11 June 2011 (UTC)

I think you mean refraction, not diffraction? Although it's common to do x-ray diffraction of diamonds, and there does exist a new technique for cutting diffraction gratings into diamonds that work at visible wavelengths,[3] the wavelength of visible light is normally several orders of magnitude too large to be diffracted by diamonds. The wavelength of visible light is about 400nm or longer, which is much larger than the feature size of the crystal structure of diamond (the carbon-carbon bond length in diamond is 154 pm), so you wouldn't normally get a noticeable diffraction pattern by shining visible light on a diamond. Red Act (talk) 00:18, 12 June 2011 (UTC)

Throwing rainbows wouldn't work that way unless you're using magic. – b_jonas 18:46, 11 June 2011 (UTC)

It would not work. For one thing, you are suggesting that more light comes out of the prism than goes in. If you recall what "slides" were - used to be called the "magic lantern" by the Victorians - then you would need several very powerful slide projectors powered by electricity that project the slide of a rainbow. Unfortunately it could not be made to work in any practical way. Perhaps you could suggest instead having lots of light-bulbs in her costume, like Christmas decorations, although this may be dangerous. A better option would be having her costume covered in small plastic mirrors. 92.24.181.38 (talk) 23:33, 11 June 2011 (UTC)

Or small diffraction gratings, if available -- the diffraction would serve to enhance the rainbow effect. I don't know if those are avialable in small enough sizes, though -- the only diffraction gratings I've ever seen are the ones used in spectrometers, which are typically several inches across. 67.169.177.176 (talk) 01:22, 12 June 2011 (UTC)

I recall reading a Scientific American article long ago where a piece of a CD was used as a diffraction grating. So use pieces of old CDs instead of mirrors, and cover her costume with them. The costume may look irridescent, under powerful focused spotlights you might get possibly get small rainbows. 2.101.1.42 (talk) 11:25, 12 June 2011 (UTC)

Rhinestones would probably work fine too, due to their high refraction and dispersion; so would diamonds, but their cost would probably be prohibitive. FWIW 67.169.177.176 (talk) 01:59, 13 June 2011 (UTC)

It's probably easier to fake it by having a prism on the costume that does nothing, and having a followspot equipped with diffraction gratings to produce rainbows, which follows the actor around the stage.--Srleffler (talk) 17:52, 13 June 2011 (UTC)

Re; Electro Mechanical Spectrum

I have a question: Isn’t it about time the geniuses (et al) call the electromagnetic spectrum what it really is; the ENERGY SPECTRUM? J Hoelz, P.E. Ret (c/q thermo) — Preceding unsigned comment added by 173.69.175.253 (talk) 19:27, 10 June 2011 (UTC)

Er, let me think about it--- NO--CookerSock (talk) 20:18, 10 June 2011 (UTC)

The place on a spectrum doesn't tell you the energy of light. You'd need both a measure of intensity and frequency to determine the overall level of energy in a beam of light. Your idea seems half baked. i kan reed (talk) 20:33, 10 June 2011 (UTC)

The only reason the geniusses of the World haven't done this already is that we can't deduce whether you mean electromechanical or electromagnetic. Cuddlyable3 (talk) 21:43, 10 June 2011 (UTC)

Are you sure it isn't the fault of et al? Nil Einne (talk) 23:07, 10 June 2011 (UTC)

Light has energy, it isn't energy. Plasmic Physics (talk) 08:18, 11 June 2011 (UTC)

The only thing correlating energy and frequency is the fact that photons of shorter wavelengths, higher frequencies generally have greater energy and vice versa. However this breaks down when you start discussing non-photon non-spectrum particles such as beta particles and some cosmic rays. ~AH1 ^(discuss!) 14:59, 11 June 2011 (UTC)

Isotopes

Is there any difference between atoms with the same number of protons and neutrons in the nuclei but with those nucleons arranged differently in the nucleus? --75.40.204.106 (talk) 19:50, 10 June 2011 (UTC)

Yes. See, nuclear isomers. While alternate nuclear configurations are possible, the atom will seeks out the lowest energy nuclear configuration and typically reach it within a nanosecond. As a result such configuration differences only occur very briefly and only under very specific circumstances. They won't generally be observed in everyday experience. Dragons flight (talk) 20:21, 10 June 2011 (UTC)

Maybe not everyday experience, but there are a few important meta-stable nuclear isomers ^180m
₇₃Ta
being the most notable) that are of interest to nuclear physicists and those that would like to use them as high-density energy storage (of course far from being practical with today's technology). The idea is that these isomers, when they return to their ground state, will release an enormous amount of energy, and it may be possible to induce this release by stimulated emission, similar to the way a laser works but on a much more energetic scale.-RunningOnBrains^(talk) 18:26, 12 June 2011 (UTC)

See also Induced gamma emission. Nuclear isomers can potentially be used to produce gamma ray lasers.--Srleffler (talk) 17:57, 13 June 2011 (UTC)

Electron diffraction

The article says that electrons can be diffracted, but how can a single electron be diffracted? --75.40.204.106 (talk) 21:13, 10 June 2011 (UTC)

Wave–particle duality is not easy to imagine, but apparently it's how things work on that scale. APL (talk) 21:52, 10 June 2011 (UTC)

So if a single electron is diffracted into two (or more) parts, what are the resulting parts? Are they both electrons? Doesn't that violate conservation of mass? --75.40.204.106 (talk) 22:04, 10 June 2011 (UTC)

The two blobs are the probability of finding the single electron in either spot. Every atom heavier than Beryllium has split blobs. Hcobb (talk) 22:08, 10 June 2011 (UTC)

It is one electron that goes through both slits. At the receiving screen you will find that each electron arrives at a single unique position, but the distribution of the arrival positions over many electrons is not uniform, and has peaks and valleys caused by the wave-like properties of the electron interfering with itself. Quantum mechanics isn't known for being very intuitive. Dragons flight (talk) 22:54, 10 June 2011 (UTC)

(EC) You can try reading the later parts of Double-slit experiment (look for discussions of single photon or one by one or one photon) and if you're really interested Englert–Greenberger duality relation. These are primarily about photons (although the first article does mention when the first one electron at a time experiment was performed) but I'm pretty sure it's the same for electrons. Nil Einne (talk) 23:01, 10 June 2011 (UTC)

Electron diffraction occurs in the dual-slit experiment (interference pattern) even when electrons are fired and arrive at the detector one-at-a-time. You can model this pattern as a probability distribution of finding any arbitrary individual electron at any point in the diffraction pattern; the deal with wave-particle duality is that the particles, in bulk, obey statistics that give the same results as the wave properties would. Thus, its not that an individual particle behaves as a wave, its that in bulk particles behave as waves, and they do so whether emited in bulk or emitted individually. If you look at discussions at articles like Wave function you see it is full of statistical language, that's because the core of wave-partile duality is probability... --Jayron32 00:27, 11 June 2011 (UTC)

I'm not sure it's quite right to say that an individual particle doesn't behave like a wave. In this experiment the electron is only in a single particular location at the end because we measure it then, which makes the wavefunction collapse. Rckrone (talk) 06:41, 12 June 2011 (UTC)

An individual electron, unobserved, has indeterminate status vis-a-vis wavelike properties. If I fire one electron at the double-slit set up, I get a dot on the detector. I fire another electron. I get another dot. Insofar as no measurement is made of the electron in transit, whether it is behaving like a wave as it passes through the slit, or it behaves like a particle as it passes through the slits, is not only unknown, it is probably unknowable. The explanation of the end results; that of a statistical spread of individual particle hits, OR of an interference pattern created by wavefronts interacting with each other, is entirely moot. Whichever explanation works better for your purposes, you use. But they both work entirely well, and so there's no reason to say definitively that one is right, or one is wrong. The electron is the electron, it does electronish things, and it always does them. That we can't wrap our head around it without forcing it into the "wave" box or the "particle" box isn't really the electron's problem. Its better to think that we can set up some experiments and can interpret the results to mean that it has wavelike properties, and we can use different experiments and different interpretations and say that it has particlelike properties. The whole point is we don't have to actually decide, its neither, but we pick the model for which our application needs it... --Jayron32 03:13, 13 June 2011 (UTC)

Echolocation in cats?

If you have a housecat or watch them stalk birds, then you're probably familiar with the teeth chattering behavior they engage in when they spot a bird. Looking at the popular literature to find out why they do this, I found this site which summarizes the concept.[4] Chattering in cats is considered a "frustrated hunter reflex", usually seen when a cat can't get to a bird and/or the cats way of preparing to bite the bird. Has anyone ruled out animal echolocation as an alternative explanation? Viriditas (talk) 22:19, 10 June 2011 (UTC)

An interesting idea, but a little implausible, I'd think. Cats are basically ground-level hunters, and picking up the echo of prey against the background clutter would be difficult. I'm sure they use their excellent directional hearing to hunt, but passively. Any noise loud enough to produce an echo may alert the prey. For bats, this isn't really a problem, as an insect in free flight has nowhere to hide, but a cat stalking a bird isn't going to have much success. There may be technical difficulties as well, to do with the relative size of the prey and the signal wavelength - but I'll leave that to someone else to clarify... AndyTheGrump (talk) 03:08, 11 June 2011 (UTC)

Apparently, echolocation is used by smaller ground mammals. The last two times my cat has done this, he has had a view of the bird above or below him. Indoors, he was looking down at it from about four meters; outdoors, the bird was about the same distance above him on a small hill. Intuitively I got the sense he was trying to measure the distance to the bird before he could pounce, but that's just my own idea; I have no such evidence. I'm also curious how my cat was generating the chattering and clicking sound, and I wonder if there is a way to record and analyze it. Viriditas (talk) 07:44, 11 June 2011 (UTC)

The only terrestrial mammals our article mentions are shrews and tenrects Animal echolocation#Shrews and tenrecs. For shrews according to both that article and Shrews#Echolocation they only use it to "investigate their habitat rather than additionally to pinpoint food". The article includes a quote:

Except for large and thus strongly reflecting objects, such as a big stone or tree trunk, they will probably not be able to disentangle echo scenes, but rather derive information on habitat type from the overall call reverberations. This might be comparable to human hearing whether one calls into a beech forest or into a reverberant wine cellar.[9]

In other words, it's only used to give broad based info and doesn't give precise location and distance information of small objects.

Echolocation in tenrecs isn't described but as they have poor eyesight it seems likely it's similar to shrews. In other words, echolocation in these animals doesn't seem particularly relevant to the suggested ability of cats to use it to locate or sense the distance of prey. If there are other small mammals with a comparative sense of echolocation to what you suggest in cats, this isn't described. The closest thing is perhaps the learnt human skill Human echolocation.

Nil Einne (talk) 13:13, 11 June 2011 (UTC)

Partially based on [5], some non RS suggest domestic cat chattering is actually a form of mimicry [6]. Of course demonstrating why an animal shows a behaviour is usually fairly difficult. Purring seems to be better studied but is still poorly understood. About how the sound is produced, I believe it may be a combination of vocal chords, lips and teeth, see [7] for example. Nil Einne (talk) 14:03, 11 June 2011 (UTC)

I think they want to "shout" because they see something exciting, but know they can't or will give away their position, and this results in partially suppressed sounds. Compare this to when they dream, but the partial paralysis of sleep makes them move just a little bit. Evolutionarily, I suppose that the suppression in both cases continued to grow stronger as long as doing so increased their chances of survival. However, once it became "good enough", such that further suppression wouldn't increase their survival chances, no further strengthening of this suppression response occurred. StuRat (talk) 08:29, 11 June 2011 (UTC)

Cats chattering at a bird and a

fly (videos). Cuddlyable3 (talk) 15:25, 11 June 2011 (UTC)

I'm surprised a fly is exciting enough for this response. StuRat (talk) 17:26, 11 June 2011 (UTC)

Perhaps this is Mimicry, or more precisely Aggressive mimicry. Perhaps the cat is attempting to lure the prey closer with sounds that might be that of insects or the helpless young of birds, mammals, reptiles, or amphibians. Oh, I see this was already said—my apologies to Nil Einne who said it first. Bus stop (talk) 09:41, 12 June 2011 (UTC)

My cat only chatters at insects out of reach. While he occasionally views the birds outside, he never enters any kind of hunting mode (he's an indoor cat). Based on my lifelong experience with cats, it's always seemed to me a frustration behaviour - they don't do it when they're hunting, only when they're after something that's out of reach. Kind of like a cartoonish "gnashing of the teeth in frustration". Regarding the echolocation hypothesis - it seems quite doubtful. Animals that use echolocation almost always do so due to poor visibility, either due to poor eyesight or atmospheric conditions. You don't need to watch too many cats in the hunt to realize they're primarily reliant on eyesight; hearing gives them a direction for stuff in the underbrush and echolocation wouldn't help with that. Matt Deres (talk) 15:42, 12 June 2011 (UTC)

Given that felines have superb hearing abilities, I would think that an evolved ability to echo-locate is a reasonable hypothesis, and that echolocation would not need to be utilized frequently in their hunting forays for it to have evolved and be useful. It could be advantageous in judging distances wherever there is little or no nearby ground clutter during their nocturnal hunts and other situations where it might serve as a reference system that reveals the ambient acoustic conditions in which any prey, or foe, are generating sound, helping to better locate them. As far as the observed chatter being too noisy, cats certainly have discretion to the extent of its use, so I don't think that would always be a problem, and it wouldn't surprise me if they reserve their loudest echo-locating chatter, should they use it for that purpose, to deliberately startle their prey. There are at least a couple of reasons such a prey flushing technique would be useful. For instance, prey that is moving is easier for a cat to visually see, so a cat may just be attempting to get a better view of a possible bug/bird or whatever. Also, during a hunt, spooking the prey can initiate the prey's escape movements so that a cat can then rapidly plot an intercepting charge upon the animal's intended flight or escape route and thereby improving its chance of capture. .Thus, the chatter may serve any of several different purposes, but I'm unconvinced that the frustration hypothesis or the mimicry hypothesis can adequately explain the cats' chatter. Cats prey on all sorts of critters with different appetites, so I don't think mimicry of a potential meal (which the chatter does not seem to mimic in any case) can explain this particular vocalization. Their chatter also has a very regular quality about it; but should it be produced due to frustration, then I'd expect more irregularity in both its quality and frequency, such as also occurring when the cat is distracted. Instead, these cats are exhibiting their hunting and stalking instincts when they stare at the bird or bug with their ears rotated forward (something that people cannot do) to listen intently (something people should do) while simultaneously chattering. They also can be seen to be literally laidback during their focused chatter, so they seem to be simply exercising one of their innate abilities to target potential prey. Thus, I think their chatter does merit investigation into whether echo-location (and/or the flushing of prey) is occurring. Modocc (talk) 00:34, 14 June 2011 (UTC)

Bookbinding question

What kind of glue is best for binding the spine of a hardcover book? 67.169.177.176 (talk) 23:17, 10 June 2011 (UTC)

I would suggest you find a local art supply store and ask for an acid free or "archival" quality glue. Dismas|^(talk) 02:41, 11 June 2011 (UTC)

PVA glue was recommended to me one for archival stuff, as it does not stain the paper or migrate, and it can be removed readily if needed. Graeme Bartlett (talk) 03:02, 11 June 2011 (UTC)

Thanks for the tip, everyone! 67.169.177.176 (talk) 03:16, 11 June 2011 (UTC)

Binding paste with PVA is good. 76.254.22.47 (talk) 03:21, 11 June 2011 (UTC)