Wikipedia:Reference desk/Archives/Science/2010 July 7

Science desk
< July 6	<< Jun | July | Aug >>	July 8 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

July 7

magictrick banknote in a fruit

I'm looking for how this magic trick works. A magician takes a dollar bill from the audience and makes it appear inside a fruit (orange/lemon). This youtube video demonstrates how it works: http://www.youtube.com/watch?v=cQBrXCcfDyc But I've seen many magicians ask the audience to sign the bill and making it appear in the orange rather than just having a different bill appear inside. Do you know any information on how this one works? I can't seem to find the information anywhere. 69.230.55.21 (talk) 00:19, 7 July 2010 (UTC)

At a guess they probably switch the dollar bill they put in the fruit with the one the audience gave to them at some stage after opening it Nil Einne (talk) 01:04, 7 July 2010 (UTC)

Of course, it is Sleight of hand or हाथ की सफाई as they call it in India. It is an ancient art. Nowadays tricksters tell you that is nothing but art, in India now that is even required by law, though that is not strictly required by law but Rationalist Society people get you otherwise  Jon Ascton  (talk) 01:13, 7 July 2010 (UTC)

Or the "random person from the audience" is in cahoots with the performer. 218.25.32.210 (talk) 01:19, 7 July 2010 (UTC)

ok thanks for the info, but can you give me specific steps in performing this trick? I know that this can be performed with a "random person" not a confederate of the magician. 69.230.55.21 (talk) 01:21, 7 July 2010 (UTC)

Yes, there are always more than one way to do a trick. And a clever magician never repeats a trick before the same audience  Jon Ascton  (talk) 02:24, 7 July 2010 (UTC)

Hey! I just saw the video (after writting my above comments). The magician simply, honestly gives away the trick - that's amazingly easy ! Did'nt ya get it, man ? What happened is this : Before you do the trick you take a dollar, note its serial number on a paper. Then you roll up the note and stick it neatly in an orange, do it in such a way that it does'nt look as if someone's done something to the fruit. Now you are ready for the trick. You ask a guy to come up and give you a dollar, he will give his own dollar of course with it's different serial, but that does'nt bother you because you don't really write it anywhere, but only pretend you do so ! by moving a pen on the paper on which you have already written the number of the dollar which is readily stuffed in the orange. Now you roll the guy's dollar and put the handkerchief on it, this is where you slip the dollar in your other hand or somewhere else he can't see it. He thinks it is there in the handkerchief, but it is some piece of paper rolled in the handkerchief's hem ! Now you unfurl the handkerchief and the dollar "vanishes" (it is already soemwhere else, what the dumb bastard was feeling was the paper in the hem !) Now put the handkerchief out of picture and cut open the orange which has your original dollar whose serial number is safely recoreded on the paper ! Got it ? Cool !  Jon Ascton  (talk) 03:08, 7 July 2010 (UTC)

I used to dabble a lot with magic tricks when my kid was younger. My favorite fruit trick is to hand several members of the audience a banana pulled from an entire bunch I have brought with me. I ask them to inspect their bananas carefully - then without me being anywhere nearby, to peel them. They are all amazed to find that the inside of their banana is neatly sliced into a half dozen pieces - and even after that, they can look at the skin, eat the banana and not see how the trick was done. It's nice because there are so many bananas that I couldn't possibly have that many confederates - and everyone in even a moderately large audience is sitting close enough to one of the bananas to see the trick happen in front of their eyes.

I'll let you figure out how I do that one! SteveBaker (talk) 04:31, 7 July 2010 (UTC)

Hm...I think it's got to do with the art of slicing the inside without damaging the skin ! No ? That can be accomplished either with a sharp needle or a needle and a thread. Right ?  Jon Ascton  (talk) 04:58, 7 July 2010 (UTC)

Yep you use a needle and thread. Pick bananas that are sufficiently ripe to have a few brown speckles and use the needle to pull the thread from one brown spot to another around the banana going back in through the exact same pinhole you came out of. When you've gone all around the banana, come back out of the same hole you started at and then just pull on the thread to slice through the flesh, leaving the skin intact - except for the smallest of pinholes. Then, soaking the entire bunch of bananas in water makes the skin expand slightly, closing the pinholes to the point where they are pretty much invisible. If possible, place your pinholes along the 'seams' of the banana skin so that tearing the banana open helps to destroy the evidence even further. It takes a half hour to prepare an entire bunch of bananas - I like to leave them on the kitchen countertop at work on April 1st. SteveBaker (talk) 03:11, 8 July 2010 (UTC)

I think you're somewhat missing the point. The OP is aware the video shows how it works for that case. What they want is to know how it works when the illusionist shows a bill that was signed by a member of the audience, so you can't just use a different bill. As you and I have said, it would likely be some sort of sleight of hand, swapping the bill inside the fruit for the signed one (alternativing signing the one inside, but this seems far less likely given that the signature could easily be recognised as a fake) but the OP wants more. Nil Einne (talk) 05:18, 7 July 2010 (UTC)

Oops, Nil, you are right, I missed that point ! How stupid of me ! Terribly sorry indeed ! Oh, the OP knows how he did that, my ! I was taking so much pains to tell what he already knew, perhaps better than me ! Sorry, OP man. I overlooked that part - the magician does not explain the whole trick - but leaves a vital loophole - the signature thing. Oh my ! So this is a new way to show magic. You do an easy trick. Explain it is such a way that an asshole like me thinks that all is explained, but when he thinks over he learns there is something he can not get through. Well, there should be a special term for this kind of thing, no ? Yup, Nil man, its good old slieght of hand of course... Jon Ascton  (talk) 07:15, 7 July 2010 (UTC)

...and what do ya think about the SteveBaker's banana ? Like my solution, eh ?

For some reason this trick doesn't show up in my trusty copy of "Cyclopedia of Magic" which is usually my go-to source for when I'm curious about such things.

One way to do it, would be to swap the bills when they're still rolled up. (ie: Cut open the orange, show that it contains a rolled up bill, then use sleight of hand to swap them while you were in the process of unrolling them.) This would probably require the magician to be the one to remove the bill from the orange, which wouldn't have the same effect as letting the spectator do it. APL (talk) 15:21, 7 July 2010 (UTC)

side mirror

what type of glue/ resin do they use to attach a side mirror on a car? i mean attach the actual glass part to the metal part (honda) —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 00:27, 7 July 2010 (UTC)

Are you sure it's glued on? I would have assumed it was bolted on. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:35, 7 July 2010 (UTC)

i think its glued on. mine broke today and there were no bolts —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 00:37, 7 July 2010 (UTC)

Glued onto what? The pivot mechanism? ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:40, 7 July 2010 (UTC)

only the glass part broke not the metal part —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 00:50, 7 July 2010 (UTC)

I don't follow. The glass part has to be attached to a pivot mechanism of some kind so it can be adjusted. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:53, 7 July 2010 (UTC)

No need to interrogate the guy. His question is clear enough. The glass shattered and has to be re-glued to the piece that the mirror itself attaches to. If you don't understand the mechanism, you don't have to answer.

There was a discussion on this very topic here.

Check out Steve's post at the end. If he's right, It looks like what you want is some rubbery adhesive pads specially designed for this purpose. (These two allegedly educational YouTube videos back him up on this : [1][2]) APL (talk) 02:00, 7 July 2010 (UTC)

No need to get snippy. I was asking these questions out of curiosity. Believe it or not, I'm not an expert on everything. :) However, if it were me, I would take it to the dealership and let them figure it out and explain it to me. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:06, 7 July 2010 (UTC)

do they use a formaldehyde resin in the factory to attach it?--Alexsmith44 (talk) 02:08, 7 July 2010 (UTC)

I don't know - but in the previous discussion on this topic, the person said that when they bought the replacement mirror, it came with double-sided sticky foam pads to mount it with. He was skeptical that this would work and glued the mirror on instead - finding that it broke within a very short time later. I deduce that the pads have some role in isolating the mirror from vibration and that when you buy your replacement mirror, you should definitely use them if that's how they come from the auto-parts store.

I asked the previous person this too (but didn't get a response): Did you look to see whether there was signs of glue or sticky pads on the shards of broken mirror glass? That would be a clue at least. SteveBaker (talk) 04:18, 7 July 2010 (UTC)

To reiterate what I mentioned in the aforementioned previous discussion, FWIW, on the several occasions I've had to replace a broken side mirror glass, the replacement glass came with a strong adhesive layer over the whole of the rear surface (covered by a peel-off paper layer): separate glue or adhesive pads was/were unnnecessary. Major UK car component stockists such as Halfords stock a large range of replacement mirrors specific to individual car makes and models, which are generally considerably cheaper than replacements supplied directly by the manufacturers themselves. If Alexsmith44 is not in the UK this information may of course be useless 87.81.230.195 (talk) 09:06, 7 July 2010 (UTC)

Animal Eyes

Why do eyes of animal light up thus when photographed ? And why the same does not happen with humans ?  Jon Ascton  (talk) 01:07, 7 July 2010 (UTC)

They probably have much better night vision than we do. I'm sure there's an article about that phenomenon somewhere. Very noticeable with cats, for example. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:10, 7 July 2010 (UTC)

I don't think that's got something to do with that. Cows are not known for their sight, they can't even discern colours  Jon Ascton  (talk) 01:16, 7 July 2010 (UTC)

Bingo. I looked up night vision and it led me to Tapetum lucidum, a layer of tissue in the eyes of many animals but not in humans. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:13, 7 July 2010 (UTC)

Um...the same does happen with humans. See red-eye effect. Under the right conditions (low light, high sensor sensitivity, subject looking directly at lens), I've seen human eyes glow much brighter than those cow eyes. --Bowlhover (talk) 01:29, 7 July 2010 (UTC)

You don't get that "mirror" effect with humans that you do with animals that have that layer in their retinas. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:32, 7 July 2010 (UTC)

It's of note that red-eye effect and eyeshine are actually two different effects. And notably, red-eye is just seen in photos. Eyeshine you can actually see in nature (shine a flashlight on your dog at night, for example). And note that the cow's photo is in daylight. --Mr.98 (talk) 11:17, 7 July 2010 (UTC)

Goa'uld? -- 58.147.52.199 (talk) 13:33, 7 July 2010 (UTC)

That cow has been to some kind of supermax space prison with Vin Diesel. Googlemeister (talk) 14:16, 7 July 2010 (UTC)

Dragonfly

?

Any idea what this is? --The High Fin Sperm Whale 03:59, 7 July 2010 (UTC)

Should we assume that you took that photo in British Columbia since your user page points out that you live there? Dismas|^(talk) 04:02, 7 July 2010 (UTC)

Yes, you can also assume that since the title says it's in Langley and it has Coordinates. --The High Fin Sperm Whale 04:08, 7 July 2010 (UTC)

If we can't figure it out, you may want to contact the person behind this site. For some reason, their "Gallery" link doesn't actually contain a gallery. Dismas|^(talk) 05:17, 7 July 2010 (UTC)

Looks like a skimmer to me, family Libellulidae. Possibly male Plathemis lydia, not sure at all. --Dr Dima (talk) 06:45, 7 July 2010 (UTC)

Looking at the photos, that is exactly it. You are a genius! Thanks guys. --The High Fin Sperm Whale 16:41, 7 July 2010 (UTC)

An open tube is placed into a container of water

An open tube is placed into a container of water and a vibrating tuning fork placed over the mouth of the tube. As the tube is raised so a greater length of the tube is out of the water, resonance is heard. This occurs when the the distance from the top of the tube to the water level is 12 cm, and again at 50 cm. Determine the frequency of the tuning fork.
The naïve approach would simply evaluate $f={\frac {v}{\lambda }}={\frac {v}{4l}}={\frac {344}{4\times 0.12}}=717Hz$ but this is not correct. hElp?--Alphador (talk) 07:01, 7 July 2010 (UTC)

λ=50cm−12cm? Bo Jacoby (talk) 09:49, 7 July 2010 (UTC).

No, that's λ/2 because the second harmonic occurs at l = 3λ/4 => λ = 0.78 m => f = 441 Hz (a likely correct answer). The reason why 717 Hz is wrong is because of end correction. MER-C 09:58, 7 July 2010 (UTC)

North American bugs

If I find some random strange looking bug in North America, what are the chances that this bug is unknown to biologists? I know that globally the majority of insects have not been cataloged. But is this true in North America as well? Ariel. (talk) 07:04, 7 July 2010 (UTC)

This will depend on where you find it. I know from my own country that bugs and plants are surveyed much better in the vicinity of a major university and in locations that are easily accessible. The chance of it being unknown is also not necessarily larger if it is "strange looking". It is the case with many plants and fungi that they are overlooked by biologists because they are very similar to other species. This could be the case with insects as well. 80.202.238.149 (talk) 10:01, 7 July 2010 (UTC)

Source of stream goes both ways?

The source of the Lawrence Brook is at 40°22′33″N 74°32′32″W. Google Maps shows this coordinate along a stream. One direction is the Lawrence Brook and the other direction is the Devils Brook. Is it a spring that goes both ways? Or are the streams interconnected? Or is the map mistaken and the streams aren't connected at all? Thank you. --Chemicalinterest (talk) 10:59, 7 July 2010 (UTC)

I am not familiar with that stream, but I know of two rivers that have the same source in a marshy area, and on the map they look interconnected. 92.15.27.146 (talk) 20:20, 7 July 2010 (UTC)

Thanks for answering. --Chemicalinterest (talk) 20:42, 7 July 2010 (UTC)

Is it fair to say that the 4th dimension is not time?

When I was younger, it was my understanding that time was the fourth dimension. But this isn't correct is it? I checked out wiki's article on the 4th dimension, and it made no mention of time in it. Just wanted to make sure that time and the 4th dimension are two different things. 148.168.127.10 (talk) 14:48, 7 July 2010 (UTC)

It is mostly a matter of semantics. The debate is a question of what gets to be called the "fourth dimension". Should it be time? Should it be a spacial dimension? Much of modern physics is based on a concept of more than five dimensions (I believe 10 is the current best guess). So, is time the fourth dimension or fifth dimension or sixth dimension? Does it matter? Again, it is a debate that will likely never be resolved. -- kainaw™ 14:51, 7 July 2010 (UTC)

There are indeed physical theories with more than 4 dimensions but they are all speculative. Sticking with what is considered solid knowlege, space-time has three spatial dimensions and one temporal one, so it seems fair to call time the fourth dimension. Dauto (talk) 17:33, 7 July 2010 (UTC)

To clarify something: the "ordinality" of the dimensions is meaningless. That is, there is no particular significance to which dimension you consider "first", which you consider "second", and so forth. While we conventionally refer to time as "the fourth dimension" because we're already used to considering the other three, I put forth that it's more correct to say merely that "time is one of the four dimensions". Note that this can be extended to the higher-dimensional theories, too; I'm just using 4D so as not to write out all the other possibilities. — Lomn 18:03, 7 July 2010 (UTC)

There isn't even a set of dimensions that one could assign an order to. You can't point in three specific directions and say that those are the three dimensions of space. Or rather, you can, but there are many different ways of doing it and no one way is more correct than all the others. Even the division of spacetime into "space" and "time" dimensions is somewhat ambiguous because they mix together. -- BenRG (talk) 19:22, 7 July 2010 (UTC)

There are varying conventions. A lot of authors put time as either the first or the zeroth dimension. --Tango (talk) 21:23, 7 July 2010 (UTC)

So the first three dimensions that we are used to are all spacial dimensions. But time is not a spacial dimension correct? The tesserect exists in a spacial dimension right? 148.168.127.10 (talk) 18:17, 7 July 2010 (UTC)

That's right. Time is not a spatial dimension and a tesseract needs four spatial dimensions, not three of space and one of time. -- BenRG (talk) 19:22, 7 July 2010 (UTC)

If you want to talk about arbitrary assignments in both space and time, note that spacetime can be represented as a metric tensor defining how the dimensions interrelate. In particular, the standard basis of flat spacetime is the simplest, yet still arbitrary, representation of this vector, as we could just as easily choose a basis that mixes in some time components with each of the spatial dimensions. It would be ugly, but it would work just the same. You should also note that in General Relativity, the presence of a gravitational field causes the metric used to change, effectively changing the shape, and thus the metric representation, of spacetime. In conclusion, there is some arbitrariness, but it's not totally haphazard how we choose our dimensions. SamuelRiv (talk) 20:13, 7 July 2010 (UTC)

You can have physical dimensions beyond three that are neither time nor levels of branes. See simplex. ~AH1^(TCU) 21:48, 7 July 2010 (UTC)

Imaginary time can be considered to be a fourth spatial dimension. Count Iblis (talk) 22:33, 7 July 2010 (UTC)

It's entirely arbitary. We could have called time "the first dimension" and the three obvious spatial axes "second, third and fourth". But to me it seems bad to lump such an obviously different measure in with the other three. Basically, it's a (slight) mathematical convenience in some sorts of calculations - beyond that, time just isn't similar enough to the three spatial axes to be usefully treated as a fourth "coordinate". Of course, when we talk about three spatial axes, we don't generally have a particularly good idea of what they are. We tend to think of "left/right", "forwards/backwards" and "up/down" - but you could equally choose "azimuth angle", "elevation angle" and "range" as our three spatial 'dimensions'. We tend not to do that because it's a pain to calculate with and it implies a definite origin...but it's really just as valid. SteveBaker (talk) 23:15, 7 July 2010 (UTC)

Steve Baker claims "Basically, it's a (slight) mathematical convenience in some sorts of calculations - beyond that, time just isn't similar enough to the three spatial axes to be usefully treated as a fourth "coordinate".

Steve Baker is WRONG. Dauto (talk) 12:22, 8 July 2010 (UTC)

Comment (disagree) for a lot of us still using Euclidean space, calling 'time' the fourth dimension, or equating it as equivalent to the three spacial dimensions we use is either a conceit or entirely wrong. 87.102.42.55 (talk) 13:21, 8 July 2010 (UTC)

Sure, but our universe's space ain't euclidian and that's exactly the point. Dauto (talk) 13:40, 8 July 2010 (UTC)

Please remember to link to something that agrees with your opinion, as is expected on reference desk answers. Thanks.87.102.42.55 (talk) 13:49, 8 July 2010 (UTC)

There. Dauto (talk) 13:59, 8 July 2010 (UTC)

See also this. Dauto (talk) 14:06, 8 July 2010 (UTC)

You obviously know what you are talking about, so why don't you make a proper effort to communincate it. Your hidden link to spacetime is an article about the model not physical reality, your hidden link to general relativity gives no indication where in that article can be found the relavent answers to the question. Although I could find it stated that the symmetry of 'spacetime' is different, I couldn't find out why you think it is physically true.87.102.42.55 (talk) 14:15, 8 July 2010 (UTC)

See Tests of general relativity for some of the more important experiments and observations that overwhelmingly confirms the reality of spacetime warping (non-euclidian spacetime) in acordance with the predictions of general relativity. Dauto (talk) 14:27, 8 July 2010 (UTC)

Of course - space is warped and time is warped (and so is mass) - nobody is denying that. However rolling all of those warpages in to a single mathematical object and calling it "spacetime" doesn't mean that space and time are merely aspects of the same thing. They very clearly aren't. For example, it's very easy to find things that are not time-reversible (entropy, for example) - but it's almost impossible to find things that are not space-reversible. You can pick up an object and rotate it through all three spatial dimensions - but you can't rotate it about the time axis. A physical object can have a limited extent in X, Y and Z (imagine a 3 meter cube) - but it can't have a limited extent in time without violating the conservation laws by popping into existence from nowhere, existing for 3 seconds, then popping out of existence again. Spacetime is a mathematical convenience - a handy shorthand, no doubt - but trying to cram what time is into the 'space' mold - or vice-versa isn't a generally workable thing. For a moving object, velocities (dx/dt, dy/dt, dz/dt) are all constrained by the speed of light - but directions (dx/dy, dy/dz and so forth) can take on literally any value without difficulty - time is special and different in that regard.

Time and space are very different things that just happen to share a few common behaviors (like the way they are warped by gravity). Conflating mathematical and descriptive convenience with physical reality is a dumb idea. Sure, in YOUR discipline, it's handy to imagine space and time as a single four-dimensional system...heck, I do computer graphics for a living and sometimes it's convenient for me to work in 6D space (X,Y,Z,Red,Green,Blue) - or sometimes 15 dimensional space with surface orientation adding nine more dimensions. Doing that sometimes produces some nice mathematical insights and shortcuts - but that's not to say that color space and physical space and 'orientation space' are "the same thing" - it's just temporarily useful to treat them as if they were. (eg Take two smoothly colored triangles that share a common edge: ABC and ACD. Can you replace them with the two triangles ABD and BCD and have the result look the same? Yes - but only if ABCD is 'planar' in 6D space!) There are yet higher numbers of dimensions which are mathematically interesting too: Some people like to work in configuration space where every single property of every single fundamental particle is a 'dimension' and you have an insanely large number of dimensions where the entire universe can be represented by a single point and the trajectory of that point as a function of time is all of physics. This seems crazy - but the network protocol for a game I'm writing works like that (although I'm obviously not going down to the level of fundamental particles)! SteveBaker (talk) 21:11, 8 July 2010 (UTC)

Steve, you are clearly a very smart person and very knowlegable as well but you also clearly don't know enough about relativity (you know less than what you think) and should probabily refrain from answering questions about that subject. I'm sorry to say but you are dead wrong. Space and time are indeed different apects of a single thing. This is not just a mathematical convenience. In your example where you use a 6D space that includes color and regular space the two different things never mix. Color always remains color and space always remains space. That is indeed just a mathematical convenience. But in relativity space and time do mix (despite your claims to the contrary). that mixing is what is behind lorentz contraction and time dilation. What is time for one observer may be space for a different observer and vice-versa. That's the crucial point that I'm trying to make, spacetime is a physical reality. The warping of space and time by gravity also mixes them. For instance, inside a black hole the radial direction becomes time-like with the future direction pointing inwards. That's why nothing can lieve a black hole. In order to exit the hole something would have to move back in time which is impossible. Sure, you made many points that show that time and space are clearly different from each other but, despite your efforts, you have not shown that they are not different aspects of asingle thing. Dauto (talk) 03:35, 9 July 2010 (UTC)

In context, I took Steve's remark to be an objection to the old $x_{4}=ict$ convention, which is indeed a mathematical convenience in a few situations, but overall not a particularly helpful way of thinking about spacetime. It tries to make a semi-Riemannian manifold look formally like an ordinary Riemannian manifold, which it just isn't. --Trovatore (talk) 10:34, 9 July 2010 (UTC)

I don't think that's what he meant. May be he should clarify his objection. Dauto (talk) 17:32, 9 July 2010 (UTC)

Dauto - except time mixes with (flat) space with an opposite metric component. Basically (for those watching), the "distance" between event A and event B is the spatial separation minus the time separation (relativistically scaled). That's what Steve means - they are fundamentally different. SamuelRiv (talk) 09:37, 9 July 2010 (UTC)

Yes, obviously time and space are different. We don't need any math to know that. But they are also different aspects of the same thing. They are dimensions of a single manifold known as spacetime continuum. Dauto (talk) 10:27, 9 July 2010 (UTC)

Okay, so we agree. This whole thread is about the math, though, since it's basically addressing what we mean by the fourth dimension, and why it's different from the spatial dimensions. They are the same in that we can make arbitrary rotations of the basis vector, and they are different in that such rotations are not actually arbitrary - there is a bias for time standing alone. SamuelRiv (talk) 19:13, 9 July 2010 (UTC)

Not quite. It is true that spatial rotations always mix two space dimensions and never mix the time with a apatial dimension. On the other hand, a lorentz transformation (due to relative movement between two reference frames) always mix a spatial dimention with time. The lorentz transformation is the equivalent of a rotation involving the time axis. Dauto (talk) 02:53, 10 July 2010 (UTC)

How do they use fusion reactors to make electricity?

The conclusion of the thread above about someone being locked in a fusion reactor was that he'd be fine and wouldn't be killed by heat. So how do they use a fusion reactor to make electricity? I thought they'd use a steam turbine like they do with almost every other method of generating electricity, but it doesn't seem sufficient for that. What do they do?--92.251.137.196 (talk) 15:53, 7 July 2010 (UTC)

The glib answer is that they don't use any existing fusion reactor to generate electricity. Existing experimental fusion reactors are designed to test the principles and demonstrate plasma confinement, rather than to supply the grid with electricity. (I can demonstrate the use of hydrocarbon combustion to generate surplus energy by lighting a candle, but I won't be able to spin a large turbine that way.) Once reactors are built which can sustain high average power output – tens or hundreds of megawatts, at least – for hours or days at a time (rather than seconds or fractions of a second) then the surplus heat will be used for power generation, and you'll see reactors coupled to heat exchangers, steam turbines, and generators.

(As an aside, I would also take the assertions above about the dangers of the interior of an operating fusion reactor with a grain of salt, as they rely on a large number of guesses and few proper sources. One link notes that the JET reactor has sustained a fusion output of 5 MW for 5 seconds, with a heating input power of about 20 MW. That's a non-trivial amount of power floating around — 25 MW for five seconds will do more than warm you slightly....) TenOfAllTrades(talk) 16:19, 7 July 2010 (UTC)

The basic mechanism is that nuclear fusion reactions occur in the plasma. These emit gamma rays, which travel out of the plasma and strike the interior of the reactor vessel, which is lined with blocks of an absorbent material (perhaps vanadium or carbon fibre). The gamma rays are absorbed, which warms the blocks. Around the outside of the blocks (outside the reactor torus itself) are wrapped cooling coils filled with a fluid (say water). The fluid warms, expands, and this expansion causes it to turn a turbine. The turbine in turn turns an electrical generator, which creates the electrical current. -- Finlay McWalter • Talk 16:32, 7 July 2010 (UTC)

I goofed somewhat: depending on the fusion reaction, most of the energy is from fusion neutrons rather than gammas. -- Finlay McWalter • Talk 20:58, 7 July 2010 (UTC)

Hmm why wouldn't a person inside a reactor also heat up?--92.251.236.7 (talk) 23:12, 7 July 2010 (UTC)

It's perhaps worth noting that all of the discussions of humans being cooked at the center of the reactor are focused on JET, which cannot produce electricity. ITER, which could hypothetically produce more energy than it takes to start the reaction, is a much larger beast and presumably has different plasma temperatures and densities. --Mr.98 (talk) 00:56, 8 July 2010 (UTC)

Fusion_power#Subsystems describes a couple of the different ways you could turn fusion power into electricity. --Mr.98 (talk) 22:11, 7 July 2010 (UTC)

According to our fusion power article, the rate at which neutrons deposit energy in the plasma-facing components of a full-scale fusion reactor will be around 10 MW/m². For comparison, the surface power density of direct sunlight at the surface of the Earth is around 100 W/m². So, roughly speaking, the neutrons releasd by the fusion reaction heat the walls of the reaction chamber (and anything within it) with an intensity that is 100,000 times greater than the noon-day sun. Gandalf61 (talk) 11:01, 8 July 2010 (UTC)

Cookie/cake mixes

I was just wondering how when for example Betty Crocker creates a cookie or cake mix in powder form, I see some of the ingredients are or were liquid like corn syrup or milk or oil, even molasses- become in powder form, how can you change a liquid like that into powder or flour form? —Preceding unsigned comment added by 71.137.252.54 (talk) 17:28, 7 July 2010 (UTC)

The simple method is dehydration. That is why you have to add water to the mix. There are many methods of dehydration. It is impossible to know specifically which method the cake mix used to become a powder unless the manufacturer feels like exposing the process. -- kainaw™ 17:31, 7 July 2010 (UTC)

Yes, although oil can't be changed into a powder form, and typically for recipes that use very much, it has to be added by the user. Looie496 (talk) 17:49, 7 July 2010 (UTC)

Actinidain allergies

What % of the US population is allergic to Actinidain? Googlemeister (talk) 20:40, 7 July 2010 (UTC)

Based on a bit of Google-Scholaring, allergies to kiwifruit are relatively common but I couldn't spot any actual numbers. A paper from 1998, PMID 9564807, identified actinidin (the spelling varies) as the major allergen in kiwifruit, but another paper from 2007, PMID 17845415, found that it is not, at least in the UK, and that the major allergen is a different protein, with levels of allergy to actinidin being minimal. So it seems that the story is not completely clear, but that the incidence of allergy in the USA is likely to be quite low. Looie496 (talk) 21:00, 7 July 2010 (UTC)

(Conflict: your Google-fu is stronger than mine!) Actinidain is one of the allergens for those with kiwifruit allergies. I wasn't able to find any exact figures for kiwi fruit allergies, but according to [3] and [4] and [5], in the UK (which isn't all that different from the US), allergies to kiwi fruit are less common than other severe food allergies, but are common enough to be labelled "significant". This study from 2007, however, found that an unidentified 38  kDa protein was the major allergen recognized by 59% of the sample population, and not actinidain. Hope that helps. – ClockworkSoul 21:02, 7 July 2010 (UTC)

beetles

Resolved

Hello Science desk

Tonight I saw several large brownish beetles flying around, their wings making a dull buzzing sound. I've never seen these things before. The time was 9:30pm GMT in the UK. What species might they have been? Thanks 82.43.90.93 (talk) 20:56, 7 July 2010 (UTC)

Sounds like June Bugs Phyllophaga (genus), but I don't recall if those live in the UK? Googlemeister (talk) 21:06, 7 July 2010 (UTC)

Might be the formerly rare but recently burgeoning Cockchafer. Probably wouldn't be hard to catch one of the critters and compare it to the pictures. I'm fairly sure all such large beetles in the UK are harmless! 87.81.230.195 (talk) 21:12, 7 July 2010 (UTC)

The pics look exactly the same as the one I saw. Thanks :) 82.43.90.93 (talk) 21:31, 7 July 2010 (UTC)

Plastic Recycling - Expanding from 1-7 from 1-2 only

For years places typically were only accepting plastic resin codes 1 & 2 for recycling, but now many places in Florida, including my own home town, are beginning to accept 1-7. Is there now a market for the other plastics, and are they actually recycling *all* of the codes, or is it likely that they're only recycling some of the codes but saying 1-7 to avoid the confusion that would occur say if they said 1, 2, 4, and 6? I already know about articles like Plastic recycling. PCHS-NJROTC ^(Messages) 20:59, 7 July 2010 (UTC)

All the plastics listed in Resin identification code can be recycled. They all have monetary value too; from what I've heard/read about the same price as the equivalent weight of oil (not sure what type of oil?) - so it's likely that they want and will recycle all the types.77.86.6.186 (talk) 21:45, 7 July 2010 (UTC)

How hot is hot water?

I don't see a setting on my water heater. I looked at Water heating#Safety but didn't get much help.

I've lived alone for 11 years and since I don't know how to reset it, the setting must have been the same. A plumber replaced a pipe last winter and I'm not aware that he changed anything. I did ask if he thought the water heater should be replaced (though it is making noises like a rodent now when it loads up or starts heating, whatever it's doing). He said no.

It is true, though, that ever since that pipe was replaced the water seems slightly hotter. Before, I could comfortably wet my hands (briefly) to wash them without turning on the cold if I had done something really disgusting, and I could wash dishes without gloves. Now, it seems too hot.

This is important in case I want to replace the water heater.Vchimpanzee · talk · contributions · 21:20, 7 July 2010 (UTC)

The new pipe could easily be shorter and/or better insulated. Either or those would increase the temperature as it comes out of the tap. You don't seem to have asked a question, though (other than the one in the header, to which there is obviously no meaningful answer). What is it you want to know? --Tango (talk) 21:28, 7 July 2010 (UTC)

There will be some sort of temperature control on the heating (to prevent it boiling etc) - but it may or may not be user-adjustable.

However, what and where it is depends on the type of heating you've got - ie is it an immersion heater, integrated gas central heating, wall mounted gas or electrical water heater ?? For increased likelyhood of a workable answer the make and model of the heater will be useful.77.86.6.186 (talk) 21:40, 7 July 2010 (UTC)

Okay, I was really looking for a general answer about how hot water can be and still be comfortable briefly. Now that I think of it, this thing must have an owner's manual somehwre in this house. It is electric and a cylinder in a closet; that much I know.Vchimpanzee · talk · contributions · 21:50, 7 July 2010 (UTC)

Sounds like an immersion heater. All the immersion heaters I've had have been non-adjustable (ie, they're set in the factory). Domestic hot water is usually 60–70 ºC (140–155 ºF) when it comes out the tap. Physchim62 (talk) 22:43, 7 July 2010 (UTC)

According to my mum electric immersion heaters can be adjusted with a screwdriver .. eg don't try this without disconnecting the electricity/know what you're doing etc - I think some versions had a screwdriver adjustable part that could be accessed without removing the top.

I was told that at 50degrees C water causes reflexive pain that makes it impossible to hold your hand in it. Below that it's hot but bearable.. According to http://www.tap-water-burn.com/ the pain threshold is 106-108 F (that's about 41 degrees C). According to this http://www.bre.co.uk/pdf/WaterNews4.pdf the pain threshold is 46.7C or 116F77.86.6.186 (talk) 22:46, 7 July 2010 (UTC)

By the way the standard (in the UK at least) is 60C, which is well above the pain threshold - in every house I've ever lived water from the hot tap on its own was always too hot to touch..77.86.6.186 (talk) 22:55, 7 July 2010 (UTC)

In NZ 60 ºC is recommended for the hot water cylinder. No lower because of the risk of bacterial growth particularly Legionnaires disease but no higher because it's considered just a waste of energy.

However water from sanitary fixtures provided for personal hygiene i.e. sinks for washing hands, taps in the bathroom, the shower etc (the kitchen isn't included obviously) is not supposed (according to the building code) to be any higher then 55 ºC and lower (45-50) is recommended for homes with young children (45 is required for schools and stuff) [6] [7]. Modern systems usually include a tempering valve (which mixes cold water) for this reason (depending on how this is setup it may or may not affect the kitchen, laundry etc).

The temperatures are chosen more for safety then being able to comfortably use the water. At 55 ºC it takes on average 10 seconds for a full thickness burn of a child (22 seconds for an adult), at 50 ºC 40 seconds for a child (5 minutes for an adult), I think 45 ºC is considered fairly safe even for a child for long periods of exposure [8] [9] [10] Nil Einne (talk) 23:10, 7 July 2010 (UTC)

In the UK the recommended standard temperature for hot water has been increased, to avoid Legionarres Disease lurking in the pipes. If it is the same where Vchimpanzee is, then the plumber may have adjusted the thermostat to increase the temperature. 92.29.125.22 (talk) 08:42, 8 July 2010 (UTC)

I doubt that the plumber actually did anything. The pipe may have caused the change because it's a fairly minor change. I'm going with 77.86.6.186, and if I need a new water heater anytime soon, I'll mention those figures. I stayed in a motel where the hot water never reached the point of being uncomfortable.Vchimpanzee · talk · contributions · 17:23, 8 July 2010 (UTC)

If you told us the brand and model of your water heater, someone may be able to find out where the thermostat is and if it is adjustable. 92.24.188.89 (talk) 18:35, 8 July 2010 (UTC)

I'm somewhat surprised by that. I can understand requiring a 60 ºC storage temperature in the cylinder as with NZ. But requiring/recommending 60 ºC coming out from the pipes seems pointless. Since the water isn't continously flowing and isn't continously heated, unless you have very good insulation on the pipes it seems unlikely the water will stay at 60 ºC in the pipes for long, in fact it could easily drop to within the danger range within an hour or so I would guess if you don't have any insulation on the pipes. So if you are worried about Legionarres Disease in the pipes a better bet may be to flush out the pipes regularly. According to some source I read at 50 ºC it takes between 5-6 hours to kill Legionarres Disease so it doesn't even seem occasionally flushing the pipes with 50 ºC is likely to be much more effective in killing anything that is in them then flushing at a lower temperature (it obviously will depend somewhat how long the water stays that high and how often you flush out the pipes). I've looked for some refs, and the best I can find is [11] [12] and various similar refs which suggest a 50 ºC minimum delivery temperature is required in the UK which still surprises me but isn't as extreme as 60 ºC. [13] in fact recognises that the temperature is not going to stay at 50 ºC in the pipes and simply requires it be 50 ºC within one minute (although does at least say the pipework containing water below 50 ºC should be kept to a minumum), which adds to my confusion. Of course since there doesn't seem to be a maximum many may end up with a close to 60 ºC delivery given the 60 ºC required storage and the fact they probably won't bother installing a tempering valve but I haven't yet found any refs mentioning a 60 ºC delivery is required or recommended in the UK. As an aside, I also found [14] which disputes whether the 60 ºC storage is really necessary or 50 ºC is enough. However issues like stratification and thermostat inaccuracy could be one of the reasons why 60 ºC is chosen as 50 ºC even if it is enough doesn't give much leeway for error. Nil Einne (talk) 20:16, 8 July 2010 (UTC)

The U.S. Department of Energy says that 120º F (so 49º C) is a useful and efficient temperature.[15] 75.41.110.200 (talk) 22:25, 8 July 2010 (UTC)

Finger squashing objects

I look at a clock face with one eye closed, holding my index finger upright in front of my face so it appears at the right side of the clock, out of focus. As I move my finger to the left, in front of the clock face, the clock face appears to "squash" or compress a bit while remaining completely in view before it starts to disappear. Why does it appear to "squash#"?--92.251.236.7 (talk) 23:49, 7 July 2010 (UTC)

I'm not sure I get what you mean, i'm trying it out but not really seeing any kind of effect.. how far is the clock and how far is your finger from your face? Arm out stretched or near your face? Vespine (talk) 01:45, 8 July 2010 (UTC)

Even just looking at the text on the computed screen, if a finger is held very near the eye and moved across the text, the letters move a tiny bit, in the blur next to the finger, before they are covered. They also seem slightly sharper. As the finger moves left and right, the letters nearest the finger move a tiny bit in the opposite direction, as if there were a lens. It may be an effect akin to a pinhole image. What would ray tracing of the image imply? Edison (talk) 02:16, 8 July 2010 (UTC)

I don't entirely understand what the original poster means, but it sounds like the phenomenon they're describing is one arising from the pupil not being a pinhole. That is, most of the time we can treat the pupil as being a point hole, but if some object (like the finger) is held near the eye, but the eye is focussed on a distant object like the clock) then some lightpaths from retinal cells will intersect the finger and some will not, producing a blurred image. -- Finlay McWalter • Talk 02:20, 8 July 2010 (UTC)

Well the clock face (or text in Edison's case) actually appears sharper and clearer when "squashed".--92.251.228.73 (talk) 12:25, 8 July 2010 (UTC)

Light does bend a little bit around object. that phenomenon is called diffraction.Dauto (talk) 11:57, 8 July 2010 (UTC)

Your finger is probably acting as a partial pinhole lens. Hopefully the physics of it will be explained at pinhole camera. See also Pinhole occluder and pinhole glasses. 92.24.188.89 (talk) 18:38, 8 July 2010 (UTC)

For anyone who wants a clarification as to the OP's question, a video of head-crushing by Kids In The Hall is quite illustrative. SamuelRiv (talk) 09:41, 9 July 2010 (UTC)