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July 4

Forward-swept wings

How stealthy are forward-swept wings? And would a forward-wing fighter make a good carrier aircraft? And how efficient are they at high speeds? --The High Fin Sperm Whale 00:39, 4 July 2010 (UTC)

(1) Not very, they tend to focus radar waves when viewed from head-on. (2) Forward-swept wings alleviate the boundary layer separation problems associated with swept-back wings, which allows a higher critical angle of attack and thus a lower landing speed. (3) About as efficient as swept-back wings, the reduction in wave drag is a function only of the absolute value of sweep angle without regard as to which way the wing is swept. FWiW 67.170.215.166 (talk) 01:35, 4 July 2010 (UTC)

Stealth: I would have thought that stealth wise it would be much the same as a back sweep, but not as good as 'current' steath aircraft (thinking of the B2 here) where blending the wing/body reduces reflective surfaces. However this site enemyforces.net says of the Sukhoi Su-47 'Berkut', "The forward-swept wing has a lower radar signature from the front hemisphere"

Carrier: What makes a "good carrier aircraft"?. Low take off speed would be one factor, which is why some (F-14 Tomcat) had variable-sweep wings, (though back-swept and which also seem out of fashion now, see [1]) Swept wings have better stall charateristics at high angle of attack, which is relevant for all fighter aircraft. Supposedly, no forward-swept wing(FSW) planes are in production, so I don't think anyone are contemplating Variable forward sweep, yet. Then again, see this at dreamlandresort.com which purports to show a Grumman Northrop design for a FSW with variable sweep! Here too [2] more recently. And Northrop Switchblade on Wikipedia!

This site century-of-flight.net says "Aircraft with forward-swept wings are highly manoeuvrable at transonic speeds". --220.101 (talk) ^\Contribs 01:54, 4 July 2010 (UTC)

Variable FORWARD sweep?! Sounds like a perfect recipe for structural failure! 67.170.215.166 (talk) 05:08, 4 July 2010 (UTC)

Why? I can't see why it would be any more of a problem than variable backward sweep. --Tango (talk) 06:18, 4 July 2010 (UTC)

More twisting loads on the wing pivots, for one thing -- what do you think is the reason why swept-back wings can be made from ordinary aluminum but swept-forward wings require fancy-schmancy composites? 67.170.215.166 (talk) 08:00, 4 July 2010 (UTC)

"More twisting loads on the wing pivots" - I can't see any justification for that statement.77.86.10.42 (talk) 12:18, 4 July 2010 (UTC)

If you experiment with a piece of paper, then you'll see why... 67.170.215.166 (talk) 23:48, 4 July 2010 (UTC)

You know I have absolutely no idea what that means, please read Wikipedia:Reference_desk/Guidelines#Guidelines_for_responding_to_questions - it's quite counterproductive to make unverifyable claims.87.102.23.18 (talk) 01:37, 5 July 2010 (UTC)

What I mean is, take a long, fairly narrow strip of paper and a portable fan, and hold it at an oblique angle to the fan's airflow at the end nearest the fan (as if it were a swept-back wing with the wing root facing into the airflow); the strip of paper should flutter a little about the horizontal, but come back to the horizontal after each oscillation. Got that? Good, now reverse the strip of paper so that you're holding it at the end farthest from the fan (as if it were a swept-forward wing with the wing tip facing into the airflow); now the strip of paper should twist one way (either up or down) as far as it will go, and stay that way. This is such a basic experiment for illustrating the aeroelastic properties of swept-back vs. swept-forward wings that I'm perfectly shocked that the three of you (Tango, 77.86 and 87.102) have no idea about it or about the implications of its results. Seriously, if the three of you had at least a little basic visualization skills between you, then you would've got my point about twisting loads without me having to digest the very basics for you. 67.170.215.166 (talk) 04:38, 5 July 2010 (UTC)

Yes but a wing isn't a completely unrigid structure - in the experiment you describe the strip of paper just bends back completely and flaps about in both cases - there is an article aeroelasticity and I can't see a mention of what you are describing it's not flutter. I originally thought you were talking about up/down (flapping) torsion, but I'm not sure if you mean torsion force that attempts to force the wing back.. (The link to 'responding to questions' was to explain the usefulness of supplying interwiki links or external references to help confirm or explain what you are saying)'.87.102.23.18 (talk) 13:30, 5 July 2010 (UTC)

Doesn't matter- I think Acroteroin has explained it below.87.102.23.18 (talk) 13:35, 5 July 2010 (UTC)

sorry for the inconveinience - it just wasn't clear what you were saying87.102.23.18 (talk) 13:49, 5 July 2010 (UTC)

Yeah, the Goa'uld really loved their death gliders. nerd joke. --mboverload@ 07:12, 4 July 2010 (UTC)

The WP article on FSW makes only passing mention, but FSWs exhibit divergent aeroelastic flutter characteristics which amplify wing twist in certain flight regimes, leading to failure. It can be controlled using composites, but the structure necessary to deal with it increases weight unacceptably in metal construction. Digital flight controls are also helpful. In general, in stealth design, re-entrant angles are avoided, as they focus reflections (think of a headlight's shape) rather than diffusing them. Acroterion _(talk) 16:35, 4 July 2010 (UTC)

Tin allotrope conversion

Why didn't the tin in my pewter spoon change from the beta form to the alpha form when it was in a freezer for a couple weeks? --Chemicalinterest (talk) 12:20, 4 July 2010 (UTC)

Firstly the change doesn't always happen immediately - ie the reaction can be delayed like crystallisation from a supersaturated solution.

Secondly Pewter contains metals that inhibit the allotrope change - see also Tin_pest#Modern_tin_pest_since_adoption_of_RoHS 77.86.10.42 (talk) 12:40, 4 July 2010 (UTC)

Yes it contained antimony and that is one of the substances used to prevent the conversion. --Chemicalinterest (talk) 18:24, 4 July 2010 (UTC)

Only pure tin is subject to tin pest -- that's why these days you always find it alloyed with other metals. 67.170.215.166 (talk) 23:33, 4 July 2010 (UTC)

No. Please stop giving incorrect answers. (Some forms of) Alloyed tin is also subject to tin pest. eg [3] p17/64_{what happened} google books. 87.102.23.18 (talk) 01:38, 5 July 2010 (UTC)

Fine, from now on I will not answer questions about metallurgy, since my knowledge of this subject is admittedly not up to date. As for questions about aerodynamics, I would recommend that you refrain from answering, considering the obvious lack of knowledge about the subject that you demonstrated during the discussion about swept-forward wings. 67.170.215.166 (talk) 10:23, 5 July 2010 (UTC)

Most tin alloys are not subject to tin pest. --Chemicalinterest (talk) 11:56, 5 July 2010 (UTC)

So the tin buttons on the French tunics which caused Napoleon to retreat from the Russian winter (tall story from chemistry teacher that one) were supposed to be pure? Does anyone know if its actually true? --BozMo talk 11:38, 5 July 2010 (UTC)

It would be hard to tell whether that story was true. --Chemicalinterest (talk) 11:58, 5 July 2010 (UTC)

The story is actually not true -- Napoleon had to retreat because his food supplies ran out -- but AFAIK there was a similar incident involving a Russian army unit posted in Siberia (in peacetime) during a winter that was so exceptionally cold (I believe it was some time during the early 19th century, but after the Napoleonic wars) that the tin buttons on their uniforms crumbled and they all had to be issued replacement uniform buttons. I think this was the source of the story about Napoleon. FWiW (OK, no more metallurgy answers from me for the next couple months at least -- I've realized that much of what I learned about the topic way back when has been disproved, and I gotta update the huge database in my cranium with reliable, up-to-date info on this subject.) 67.170.215.166 (talk) 00:17, 6 July 2010 (UTC)

Clarify.. As far as I know nobody makes and sells an alloy that is more susceptible to tin pest than pure tin for obvious reasons (it would be useless). So to say 'tin alloys' don't get tin pest is sort of true - since alloys of tin will be produced with an eye on retarding or eliminating tin pest.94.72.242.84 (talk) 01:54, 6 July 2010 (UTC)

Piano Lid Prop angle

Most modern grand pianos' lid props appear to form a 90º angle where they meet the underside of the piano's lid. It seems logical to me that the lid prop is less likely to slip at that angle because there would be a direct load transfer of the weight of the piano's lid to the support stick. That is, grand piano manufacturers intentionally use a 90º angle for safety reasons. Could someone show me the mathematics, perhaps using vector analysis, to prove my hypothesis? The reader may want to visit http://en.wikipedia.org/wiki/Grand_Piano to see a couple of pianos that do not appear to use the 90º angle. Note the Louis Bas grand piano of 1781 and Walter and Sohn piano of 1805.Don don (talk) 16:52, 21 June 2010 (UTC)

here with an angle less than 90 degrees downward slippage is impossible without raising the mass of the lid

You already asked, [4] as Dmcq might have hinted(?) - your hypothesis is wrong - at 90 degrees the only thing that is stopping slippage is friction. Whereas at more acute angles slippage is impossible since the mass of the lid needs to be raised for the support to be able to fold into the resting position.Sf5xeplus (talk) 13:59, 4 July 2010 (UTC)

Yes, after I posted my question on the mathematics page I thought that it should have been placed in the physics section. How can the original entry be deleted?Don don (talk) 18:25, 5 July 2010 (UTC)

I don't think it's necessary to delete it, I'll add a link to here. [5] 94.72.242.84 (talk) 01:57, 6 July 2010 (UTC)

I assume you didn't mean upward slippage of the support which should be prevented by a block.Sf5xeplus (talk) 13:59, 4 July 2010 (UTC)

Perhaps the most sensible solution would be to have slippage prevention blocks on both sides of support? Sf5xeplus (talk) 14:00, 4 July 2010 (UTC)

Also aren't some fixed and hinged at the lid ? Sf5xeplus (talk) 14:05, 4 July 2010 (UTC)

I know of no piano that has a hinge at point C. (See following paragraph.)Don don (talk) 20:21, 5 July 2010 (UTC)

Perhaps I should clarify the angle to which I am referring in my original question. Looking at the picture of a grand piano found at the right, let point A be the center of the piano lid hinge pin to the left of the pianist; point B is the center of the support stick’s hinge pin; and point C is where the support stick contacts the piano lid. Currently, I have in my possession data (segment lengths AB, BC, and CA) from more than one hundred pianos. Using trigonometry, I have found that the average for angle C is approximately 90 degrees, plus or minus one degree.Don don (talk) 18:45, 5 July 2010 (UTC)

The premise of your question is wrong; most concert grand pianos don't have a fixed angle for the lid. Generally the lid angle can be adjusted either by elongating a telescopic prop (like this one) or by using a replacement prop (this article on recording gives 38° for the long prop and 10° for the short one). The piano lid functions as a reflector for mid- and high-frequency sound; Music, physics, and Engineering by Harry F. Olson shows a 15dB differential of 4kHz volumes horizontally rightward (outward) of the lid vs. the hingeward side. In performance, concern grands have to function well in a variety of settings - on the level with the audience, above them (e.g. on the stage in a multi-use hall where the audience is seated on a flat floor like a basketball court) or below them (e.g. on the stage in a concert hall where the audience on raked seating). So the musician will want the lid adjusted to best present the piano's sound to the audience (further diagrams in Olson suggest this effect is marked for at least the top half of the piano's range). So they'll set the lid angle to suit the performance space. It's not going to slip because it's not relying on flat friction to hold it up (there's a hole, or several). -- Finlay McWalter • Talk 15:34, 4 July 2010 (UTC)

I have been unable to find the "telescopic prop" on the website to which you refer above (beethovenpianos.com). However, I thank you for your comments on angle A. (See my clarifying paragraph above.) Using the data that I have collected so far, angle A is approximately 32 degrees, plus or minus 2 degrees, when the longest lid prop is used on a grand piano. (Some concert grands have as many as four different lid props!) As far as I know, there are only three lid prop sizes readily available commercially, 31", 30" and 22".Don don (talk) 19:01, 5 July 2010 (UTC)

The prop resists the moment of the lid tending to turn on its hinge. The value of the moment is MGR.cosØ where M=mass of lid, G = gravitational constant, R = distance from hinge to center of gravity of lid, Ø = angle of elevation of lid. The force P exerted by the prop on the lid may have two components: P.sine@ and P.cos@ where @ is the angle between the prop and the lid. P.cos@ is a force parallel to the underside of the lid and, if present, it will cause the top of the prop to slide against the lid unless this is prevented by a block, notch or hole. P.sine@ counteracts the lid turning moment which implies that MGR.cosØ = PS.sine@ where S = distance from hinge to prop contact. The situation @ = 90 degrees is interesting because P.cos(90 degrees) = 0 meaning the prop has no tendency to slide against the lid. Nothing here requires R = S so the lid angle Ø can be chosen by the prop length and the OP's hypothesis is not unreasonable. I add the diagram below at request of the OP.

File:Piano lid.png Cuddlyable3 (talk) 13:05, 6 July 2010 (UTC)

Yes angle=90 is a Saddle point Local extrema, but saddle points local extrema aren't really safe at all.77.86.10.42 (talk) 16:50, 4 July 2010 (UTC)

No. It's just a local extremum. Cuddlyable3 (talk) 13:31, 5 July 2010 (UTC)

thanks corrected 87.102.23.18 (talk) 13:38, 5 July 2010 (UTC)

Surely the most logical reason for choosing the angle they do is to best project the sound from the piano towards the audience as it reflects off of the heavy lid. I doubt it has anything whatever to do with the angle of the prop. SteveBaker (talk) 04:46, 5 July 2010 (UTC)

Respond to DonDon - one advantage of having an angle of 90degrees is that it minimises the compressive force in the support making it less likely to break. I still don't entirely agree that it is done for safety reasons since there are safer angles (ie internal angle less than 90) that work in combination with a block stopping the support slipping upwards. Nevertheless your point has a lot of truth in it.94.72.242.84 (talk) 19:31, 5 July 2010 (UTC)

That's possible - but piano lids just aren't that heavy and there is little or no penalty in having a totally over-engineered strut that could comfortably withstand ten times that weight. It's utterly trivial for the piano maker to design a strut that could place the lid at any angle he pleases. Hence the crux of the design here is most certainly not about saving 10 cents worth of wood in the strut and placing at the safest possible angle! It's about getting the lid to the optimum angle for sound reproduction...and all of this stuff about what is the least force and at what angle and slippage versus longitudinal force is totally irrelevant twaddle! SteveBaker (talk) 13:40, 6 July 2010 (UTC)

After the optimum angle of the lid is determined it remains to design the point on the lid where the strut is going to touch, and the angle between the lid and the strut. The tangential component of the force from the strut provides the torque to prevent the lid from closing, while radial and axial components of the force are of no use and can be chosen to be zero. That's why the strut should be perpendicular to the lid. Bo Jacoby (talk) 19:35, 6 July 2010 (UTC).

SI prefixes (redux)

The earlier question about 10²⁷ got me wondering... Among the SI prefixes, why was deca- given the two-letter prefix da? I realize it couldn't be d because that is for deci-, but why couldn't it have been D, just as we have m for milli- and M for mega-? Thank you kindly. — Michael J 16:41, 4 July 2010 (UTC)

Did you spot SI_prefixes#Proposed_changes - it seems they are aware of the inconsistences, but haven't done anything yet.77.86.10.42 (talk) 17:32, 4 July 2010 (UTC)

I saw that. I just wondered why it wasn't done in the first place. — Michael J 17:43, 4 July 2010 (UTC)

I see what you mean. The page Kilo- has the answer - the odd ones out hecto, deca, kilo (and centi, deci, milli) are original Metric system prefixes (year 1795) so they were already introduced and in use when the SI-system was started. I suppose it would have been confusing or impossible to get people to change from lower case prefixes which they had been using for over 100 years

Clearly the original metrix prefixes don't follow the 'same word root/ upper or lower case pattern' as do the later SI type.

In fact the metrix prefixes use a greek derived word for 10,100,1000 and a latin derived word for 0.1,0.01,0.001 .... Metric_system#Prefixes 77.86.10.42 (talk) 18:27, 4 July 2010 (UTC)

Adidas Jabulani

Please see http://commons.wikimedia.org/wiki/Category:Adidas_Jabulani - as far as I can tell all official 'jabulani' balls are the '8 sided' truncated tetrahedron design, yet there are other designs in commons

Can anyone confirm that this is a fake? Thanks.77.86.10.42 (talk) 16:46, 4 July 2010 (UTC)

I can't directly confirm, but I would note the presence of the word "Replique" in the name of the file (replica?), and also the fact that the match balls seem to be smooth, whereas there is distinct stitching on the one shown in the file. --TammyMoet (talk) 16:49, 4 July 2010 (UTC)

The Replique's are the cheaper version for sale to the mass market. See http ://hubpages.com/hub/Which-adidas-Jabulani-World-Cup-2010-official-soccer-ball-is-right-for-you (url split as for some reason that site is on the blacklist) for a truncated list of the different available Jabulani's. Nanonic (talk) 17:35, 4 July 2010 (UTC)

Thanks, the replicas seem to be more expensive than the ones with the new design.. odd

Resolved

Diopters

magnifying lens

magnifying and a diminishing lens

In corrective lenses, what does the unit diopter determine? Is this to do with how curved the lens is, how thick it is? Clover345 (talk) 18:39, 4 July 2010 (UTC)

Please read the article Dioptre. Cuddlyable3 (talk) 18:45, 4 July 2010 (UTC)

Thank you. I read that before I asked but its too scientific for me to understand. Clover345 (talk) 21:26, 4 July 2010 (UTC)

It's a measure of the strength of the lens - a higher value means a more powerful (either magnifying or diminishing lens)

A higher power lens is more curved, and being more curved means it is thicker. For a magnifying lens it's thicker in the middle, for a diminishing lens it's thicker at the edges.

So a higher dioptre lens will be thicker, and more curved than a lower dioptre lens.

I found some useful images at Eyeglass prescription. Note that a negative value is used to denote a diminishing lens.77.86.10.42 (talk) 21:35, 4 July 2010 (UTC)

If it has a positive diopter value you can use a lens as a Burning glass, as some boys discover to the discomfort of a few ants. Cuddlyable3 (talk) 22:15, 4 July 2010 (UTC)

If the sun is bright enough, you can even use a lens to light a campfire (like in The Mysterious Island). 67.170.215.166 (talk) 23:30, 4 July 2010 (UTC)

Though note that in Lord of the Flies, William Golding got it completely wrong by describing the short-sighted Piggy's spectacles being used in this way, even though lenses to correct myopia (such as my own) are diverging, somewhat diminishing my respect for the author when I read the book as a child. I thought I also remembered him describing a crescent Moon rising at sunset, but have subsequently failed to find such a passage - anyone else recall this? 87.81.230.195 (talk) 23:59, 4 July 2010 (UTC)

I've read the Lord of the Flies in high school, but it was a long time ago and I don't remember the details; the one thing I do remember is the conflict between Ralph and Jack, and the gradual transformation of all those civilized schoolkids into savages. 67.170.215.166 (talk) 04:44, 5 July 2010 (UTC)

You (87.81) are right about the crescent moon mistake - I remember it being mentioned in one of Martin Gardner's books. I'll try to find a reference later. AndrewWTaylor (talk) 08:14, 5 July 2010 (UTC)

Reptiles' sense of time

NOTE: I added the above "null" sections so that everyone's links will still work. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:59, 6 July 2010 (UTC)

Reptile's sense of time

Would a reptile, being cold-blooded, subjectively experience a cold day as passing very quickly, but a hot day as going on for much longer? 92.15.12.165 (talk) 19:24, 4 July 2010 (UTC)

There is no reason why it would. Cold-blooded does not mean it has cold blood; it only mean that it is poikilothermic. --Chemicalinterest (talk) 20:07, 4 July 2010 (UTC)

Do I really need to point out to you that "cold-blooded" is a common synonym for poikilothermic and that I and other people using that phrase do not mean that it literally has cold blood?

I'm wondering if, since its body would be hotter on a hot day, therefore its neurones should be faster, therefore its gets more thinking done within a constant time period compared with a cold day. Hence subjectively objective time seems to go more slowly for it on a hot day. 92.15.12.165 (talk) 21:49, 4 July 2010 (UTC)

Haha I thought you meant that since it had cold blood it would see the "good" cold days passing quickly and the "bad" hot days (that heat up his blood) passing very slowly.--Chemicalinterest (talk) 10:59, 6 July 2010 (UTC)

This is an interesting question. We don't fully understand how humans keep time neurally on a minute-to-minute basis, much less reptiles. We do have a good understanding of how circadian rhythms are implemented in the brain, and I believe there is evidence that the day-clocks in cold-blooded animals are temperature-compensated to some degree, but do run a bit slower when body temperature drops. In short, the answer is not known. (And I haven't even addressed whether "subjective" actually means anything for a reptile.) Looie496 (talk) 21:55, 4 July 2010 (UTC)

Right, the question as phrased is about reptiles' qualia, which in principle are not amenable to objective analysis. The only way to know them for sure is to be the reptile in question. --Trovatore (talk) 22:12, 4 July 2010 (UTC)

Yes, but sleep passes very quickly for people (?) and there must be some objective difference in brain activity between the two.. Surely someone must have done a study on 'nerve activity in hot and cold reptiles' for us to be able to draw some sort of conclusion about the 'level of awakeness' or 'quality of experience' in reptiles as they get colder, if not whether times passes quick for them.77.86.10.42 (talk) 22:26, 4 July 2010 (UTC)

Nerve activity certainly slows down as body temperature drops. But there is no guarantee that timekeeping has a simple relationship to neural activity. Circadian timekeeping, for example, doesn't depend on neural activity -- the timekeeping process is driven by gene transcription. As I said, we really don't know at this point what mechanism determines subjective time, even in humans. It is probably neural activity at some level, but there are many types of neural activity, with different temperature dependencies, some of them pretty shallow. Human time estimation is definitely affected by body temperature, but since we are warm-blooded it is possible that there is less evolutionary pressure to counteract this in mammals than in reptiles. Looie496 (talk) 22:52, 4 July 2010 (UTC)

Discussion moved to Wikipedia_talk:Reference_desk#Grammitical_edits_to_question_header_on_science_desk_causing_offence please discuss there, and do not edit the questioneer's section heading further. Thank you.

Is there a behavioral explanation?

Is there a behavioral explanation for why the toilet-trained cat in this video is putting toilet paper in the toilet bowl? Bus stop (talk) 20:03, 4 July 2010 (UTC)

Yes, the cat has probably seen the human "parents" using paper after doing shit. So it has recorded the scene and trained itself to do so though of course it cannot understand why they do this. For the cat it is a ritual that its "parents" (who are humans of course) but to cat they are just big cats who are leaders of the pack who provide the cat food and protection, and what they do must be followed as a sign of respect  Jon Ascton  (talk) 21:57, 4 July 2010 (UTC)

No. It is instinctive behaviour of a cat to scratch earth over its stools. Tame cats try to do this even when there is nothing to scratch, as when the one in the video scratches at the plastic seat. At some point it discovers that a paper roll gives endless scratching satisfaction, that's all. Training a cat this way does not involve the owner performing for the cat to imitate. Cuddlyable3 (talk) 22:08, 4 July 2010 (UTC)

No, I have seen dogs and cats trying to involve the acts they have seen humans doing, and trying to reach out for electric switchs etc for no reason  Jon Ascton  (talk) 23:04, 4 July 2010 (UTC)

I could understand cats and dogs hitting switches for things because there's an immediate "reward" in that some action occurs that they desired. I find it harder, nigh impossible, to believe that a cat would paw at toilet paper just because they had seen a human do it. There's no "reward" for the cat. If the paper is close enough, as in the video, they may paw at that. Notice also that the cat in the video paws all around the seat. It's not unusual for a cat to paw at the walls and other vertical surfaces around a litter box either. (WP:OR warning) Around one of our litter boxes, we have a piece of hard plastic because we found the cats were scratching at the wall and causing damage. They still scratch at the plastic sheet but now it doesn't damage the walls. PS That's a good sized deuce for a cat! Dismas|^(talk) 00:19, 5 July 2010 (UTC)

Maybe pet psychology is different in India than in the West (!) Perhaps the evolutionary relation between human and cat/dog followed a different route to evolve in India, you know due to we-are-spiritual-you-are-materialistic factor  Jon Ascton  (talk) 03:50, 5 July 2010 (UTC)

I very much doubt they do it out of respect. Animals do things to show respect to the alpha, but I've never heard of them doing things to show respect to their parents (unless the parent is the alpha, of course). They probably do it because they have learnt from their parents and assume their parents were doing it for a reason. Animals don't do detailed analyses of the reasons for the things they learn (humans often don't either), they just imitate it when they want the same result (in this case, to not need the toilet any more). It could just be the usual cat instinct to scratch after defecating, as Cuddyable says, though - they certainly will scratch and things other than dirt if there isn't dirt around for no reason other than instinct. --Tango (talk) 19:47, 5 July 2010 (UTC)

Strange beetle

I took a picture of a beetle and uploaded it to Flickr. Can anyone help me identify it?

Americanfreedom (talk) 22:03, 4 July 2010 (UTC)

Reminds me of a Cockchafer, (which is probably isn't) - maybe you could look at the family Scarabaeidae while you wait.. or http://commons.wikimedia.org/wiki/Category:Species_of_Scarabaeidae (there's only 287 to go through..)

I think you need to tell us where you are to aid the indentification, eg region of the country you're in, not your address :) 77.86.10.42 (talk) 22:07, 4 July 2010 (UTC)

And how big is it, _{and what is that thing in the background - a tray with a picture on or something?}77.86.10.42 (talk) 22:10, 4 July 2010 (UTC)

This is definitely not a cockchafer, look at the antennae. Kinda hard to tell from that angle, but my guess would be that this is a fairly large longhorn beetle, maybe Cerambyx sp. or Neocerambyx sp., family Cerambycidae. Some of those guys, although of course not the largest of the beetles in general, tend to get impressively large. Let me know where you took the picture and maybe I can narrow it down to the species. --Dr Dima (talk) 23:08, 4 July 2010 (UTC)

I can't help directly, but here is a site [6] that may help you now or in the future. Caesar's Daddy (talk) 07:27, 5 July 2010 (UTC)

I took a closer look at the longhorn beetle picture you've got, it may be Prionus sp.. --Dr Dima (talk) 08:04, 5 July 2010 (UTC)

Without giving away to much (My dad's worried about security) i live in Northern California.

Americanfreedom (talk) 03:02, 6 July 2010 (UTC)

The beetle is not a security threat :) . Northern California is precise enough, so no need to tell us more than that about your location. I will look up the species tomorrow when the library opens. It does not look like Prionus californicus (AFAIR, P. californicus has prominent spines on the sides of the pronotum, which I can't see in your specimen). Anyway, tomorrow I will probably have a better guess of what it is. All the best, --Dr Dima (talk) 05:40, 6 July 2010 (UTC)

This is probably Prionus lecontei. There are only two Prionus species found in California: P. californicus and P. lecontei. The former has 12 antennal segments, the latter has 13. Looks like your one has got 13 ... --Dr Dima (talk) 03:08, 7 July 2010 (UTC)

abbe or v number

I haven't been able to find a thing on this - I was wondering what would be a typical abbe number (or some other comparative figure at other wavelengths) (whatever measure of chromatic aberration is relevant) for a camera lens assembly - ie is it higher than 59 as per crown or CR39 glass. I was thinking about a mid priced lens rather than super expensive, or super cheap..77.86.10.42 (talk) 23:02, 4 July 2010 (UTC)

Mig-29

Does the Mig-29 require a starter cart to start its engines? Or does it have self-start capability? Thanks in advance! 67.170.215.166 (talk) 23:37, 4 July 2010 (UTC)

This article says it has a "GTDE-117 gas-turbine starter-APU". Moreover this article has a "RD-33 Engine Start" section which says that stored air (from engine bleed) is normally used to start the engines, with the APU or battery-only as fallbacks. I dread to think how quickly you'd flatten your battery starting (presumably just one) engine. -- Finlay McWalter • Talk 00:04, 5 July 2010 (UTC)

Don't know about this Mig thing, but think I heard very interersting thing about the starting-of-engine process of a large propellor (probably a pre WW2 model) aircraft. They put a 12 gauge shotgun cartridge and fire it to start the engine ! Is that true...? Jon Ascton  (talk) 03:20, 5 July 2010 (UTC)

Yep - they really exist. See Coffman engine starter. SteveBaker (talk) 04:37, 5 July 2010 (UTC)

I knew that the Canberra bomber used a cartridge starter; didn't know that piston-engine aircraft also used this system... 67.170.215.166 (talk) 04:48, 5 July 2010 (UTC)

Well, talking of novel uses of 12 gauge shotgun cartridge, is there any machine which exploits the rush of its blast to dig a hole in ground when you have no time for a shovel ? Jon Ascton  (talk) 05:56, 5 July 2010 (UTC)

That would not be very effective, a shovel would work much better. Now if you want to get at water underneath a layer of ice an inch or so thick, maybe you could have more luck with that. Googlemeister (talk) 13:12, 6 July 2010 (UTC)

Submarine aircraft carriers of Japan employed pre-heaters for aircraft engine oil so that minimum time would be spent while vulnerable on the surface for starting and launching floatplanes. Cuddlyable3 (talk) 13:18, 5 July 2010 (UTC)

July 5

Giant isopod-- survival outside of water

Can a giant isopod survive on land? If so, for how long? (I ask because I've seen photos of them on land and apparently alive, such as [this], unless it's fake). 68.123.238.146 (talk) 03:22, 5 July 2010 (UTC)

That photo is definitely a fake. The trilobites vanished in the Permian extinction about 250 million years ago. The ICanHazCheezburger.com site is all about faked photos of one kind or another. Modern isopods are things like wood lice - but there is the Giant isopod Bathynomus - that can grow to a half meter or more in length. They live in very deep ocean areas though - I don't think they'd do well out of water. SteveBaker (talk) 04:35, 5 July 2010 (UTC)

So I can buy realistic plastic Trilobites?

...Excellent... --mboverload@ 04:39, 5 July 2010 (UTC)

I don't think the OP is confused about trilobites. The animals in the picture are clearly giant isopods despite the caption, and the OP asks about the survival of giant isopods out of water. Rckrone (talk) 07:19, 6 July 2010 (UTC)

They're images of giant isopods (which are common enough) who've been exposed to snack foods and Photoshop. Acroterion _(talk) 20:03, 6 July 2010 (UTC)

Considering that our Giant isopod article has a couple of pictures of them out of water (apparently alive), I would imagine that they can live a short time out of water. They're related to crab and lobsters (being crustaceans), which are also known to be able to survive outside of water (in some cases, for extended periods of time). A giant isopod probably couldn't function very well out of water (being used to having water help support its weight), but they might be able to avoid the quick suffocation that most fish would experience. Buddy431 (talk) 23:46, 6 July 2010 (UTC)

On which general topic see Gérard de Nerval. 87.81.230.195 (talk) 09:17, 7 July 2010 (UTC)

I thought most deep-sea creatures couldn't even survive in shallow water, never mind air? Strange.--92.251.137.196 (talk) 15:22, 7 July 2010 (UTC)

Ancient Machines

This site seems to be deliberately laid about yarn. They mention a "University of Chandigarh" which does not exist. The guy who made this up knew that there is a town called Chandigarh in India allright so thought that must have uni too ! There may be other loopholes too that need to be exposed  Jon Ascton  (talk) 03:42, 5 July 2010 (UTC)

Sorry, don't understand your question. Laid about yarn? --mboverload@ 04:13, 5 July 2010 (UTC)

I think he's stringing you along:) Myles325a (talk) 08:10, 5 July 2010 (UTC)

(EC) My guess is that the university is a self-made non-accredited diploma mill, as pretty much no credible scholar would entertain the so-called ancient astronauts theories. Not even the champion of the hypothesis in Chariots of the Gods? has much of anything in the way of credentials. In other words, academia is immune to this nonsense, but the public isn't, especially when this kind of trash appears on National Geographic channel's Is It Real? see critique. Alas, pseudoscience runs strong still, but we can take comfort that cocaine/opium or worse brain tonics aren't sold every which-way in every CVS nowadays, as would be in the late 19th century. SamuelRiv (talk) 04:16, 5 July 2010 (UTC)

Excuse me but there is no need to begin to bad mouth a university or an individual because a 'new-ager' has mentioned it/them in one of their 'new-age' articles. Please do some research before jumping to conclusions, both SamuelRiv and JonAscton. Thank you.87.102.23.18 (talk) 15:28, 5 July 2010 (UTC)

Just to clarify the scholar was Dr. Ruth Reyna who obtained a PhD from University of Poona 1961 , [7] (also written books eg amazon link). The Chandigarh university appears to be Panjab University, and the documents are supposedly held there. I don't know where the documents come from or anything about their authenticity. 87.102.23.18 (talk) 15:23, 5 July 2010 (UTC)

I assume these are the documents [8] ?

Hypothetical Example I have a crackpot theory that the observable universe is explained by tiny silver men inside my eyeballs casting shadows on my retina, and by invisble golden mice jumping up and down on my head to simulate gravity.. In my article I reference Isaac Newton's work on optics and gravity .. Science is not advanced by attempting to discredit the work of Newton, or Cambridge University simply because I mentioned them in my blog..87.102.23.18 (talk) 15:44, 5 July 2010 (UTC)

I don't understand the question here. The "strange artefacts" site is obviously just another conspiracy theory site, not to be read when sober. anything else? Physchim62 (talk) 16:01, 5 July 2010 (UTC)

I think the aim is to show some flaw - I would guess that dating the documents would be one obvious route to disproving the 'ancient astronaut' theory. If the documents prove to be old then that would be a suprise too.87.102.23.18 (talk) 16:08, 5 July 2010 (UTC)

To IP87: fair enough, the fault is mine. Regarding the original question, I hope I answered that with the links in my first response which discuss the whole history of the ancient astronauts kookery. Regarding the "documents" linked, they are actually modern drawings of what are assumed to be descriptions of flying machines in one of the Vedas, if I recall from a badastronomy.com debunking. It's like if I were to draw a picture of Noah's Ark, except I assume beforehand that it's actually a spaceship. SamuelRiv (talk) 16:12, 5 July 2010 (UTC)

Additionally there's no shortage of flying machines/people/creatures in many other ancient texts (along with gold growing rings, cloaks of invisibility etc etc) . Many people require more than just some text describing space travel to make them believe that it's literally true. The usual requirement for a historical document to be taken seriously as containing elements of fact is supporting evidence, usually archaeological remains, or secondary independant documents corroborating (eg such as matches in historical events/people in the bible and in eqyptian historical sources). 87.102.23.18 (talk) 16:47, 5 July 2010 (UTC)

Could you clone a human female from male cells?

As a male cell contains both an X (female) chromosome and a Y (male) chromosome, would it be possible to pair up two of the X chromosomes and create a human female from the male's genome? And if a boy was cloned (XY) as well as a girl (XX), could the two of them theoretically breed and start a population that derives from a single parent? I am supposing that human females can't do this because they do not have a Y chromosome. We are used to thinking that only females can create life, but the whole cloning idea is reminiscent of the Genesis story in which Eve is created from Adam's body, and not vice versa.Myles325a (talk) 08:28, 5 July 2010 (UTC)

I am not used to thinking that only females can create life. Cuddlyable3 (talk) 13:11, 5 July 2010 (UTC)

I suppose it might be possible, in theory, to remove the Y chromosome and duplicate the X chromosome to create a female "clone" from a male cell. But that cell now has two identical X chromosomes, so any recessive genes on the X chromosome have been duplicated, which will reduce the chances of the "clone" developing normally. Similarly, mating clones will result in a population with very low genetic diversity, which leads to low fertility rates. Gandalf61 (talk) 13:27, 5 July 2010 (UTC)

Was it Asimov who sang, "Oh give me a clone, of my own flesh and bone, with its Y chromosome changed to X. And when it is born, my own little clone, will be of the opposite sex."? -- 58.147.52.176 (talk) 12:17, 6 July 2010 (UTC)

Another science fiction reference is that of Lapis Lazuli and Lorelei Lee, daughters by this process of Lazarus Long in Heinlein's Time Enough for Love. -- 58.147.52.176 (talk) 23:40, 6 July 2010 (UTC)

The uniparental disomy article may be of interest, although it does not specifically address this issue. -- 58.147.52.176 (talk) 23:40, 6 July 2010 (UTC)

Strange hydrostatic aroud Australia

Hello dear thinkers. Please excuse my uneasy English, I'm French. For those who prefer the French version, here it is [9].

On this page Australie : nouvel état des lieux du réchauffement climatique they are explainations concerning the rise of water of the oceans linked to the global warming. My question is about a single strange sentence: It's written that "This rise of water is not uniform (all aroud Australia ) : on the south, the sea has risen at a speed of 3 mm per year during the recent years, but has risen at a speed of (from 7 to 10) mm per year on the north coast."

Question : How can the sea rise at a different speed on 2 shores opposite the same island ? (even if this island is a near-continent). With the difference between the 2 speeds (7-3)=4 mmm per year for 10 years long it makes 4 cm (more than 1 inch).

When I asked this question on the Reference desk in French for the 1rst time some months ago I got answers refering to earth gravity changes, but I think it's not conclusive. I also got answers sending me to Geoid but I also think that this geoid doesn't change enough to explain this strange difference between 2 "sea rise speeds".

Sorry for being so long asking my question, thank you very much for your "cogitations". Joël DESHAIES- Rheims-France---90.18.59.162 (talk) 14:07, 5 July 2010 (UTC)

Surprising as it may sound to you, the answers you were given are the correct ones. Dauto (talk) 14:38, 5 July 2010 (UTC)

The mistake you seem to be making is to look at the issue as a problem in hydrostatics, when the oceans are a dynamic system with continual energy input from the Sun. The height of a column of water depends on other factors apart from gravity, for example the temperature and the salinity. Just to give one well known example, the mean sea level (MSL) of the Pacific Ocean at that end of the Panama Canal is 20 cm (8 inches) higher than the MSL of the Atlantic Ocean just 77 km (48 miles) away. Physchim62 (talk) 15:42, 5 July 2010 (UTC)

Yes, there are 'anomalies' in sea level height, but how to explain the anomaly in the rate of sea level rise ?? 87.102.23.18 (talk) 16:28, 5 July 2010 (UTC)

Well, I think the question has a point. It is possible to have different sea level changes at different points, but it clearly isn't possible for the differences to build up continuously at a steady rate for very long. And the explanation wouldn't be in terms of earth gravity changes, but more likely in terms of changes in wind patterns and ocean currents, which push the water from place to place. As Psychim62 pointed out, there is a difference of 20 cm between the Atlantic and Pacific sea levels at Panama, caused by winds and currents. Looie496 (talk) 16:31, 5 July 2010 (UTC)

Perhaps the answer is related to average changes in wind/current direction then , happening at the same time as (and probably related to) the overal sea rise/warming effect. I don't know how to search for such data though.87.102.23.18 (talk) 16:40, 5 July 2010 (UTC)

The Australian tectonic plate[10] moves North (causing seismic activity Java - Indonesia). Might this induce a N-S tilt in Australia? Cuddlyable3 (talk) 18:44, 5 July 2010 (UTC)

Hello, I'm the French OP. Indeed, my title is wrong using "hydrostatic", we have clearly to think in terms of hydrodynamic. As some of you pointed, the hard thing is not the difference of "altitudes" but the difference of "speeds" in rising. After reading your explainations and the French ones hear [11] I'm still at the same point : or I don't understand how it can be possible, or (and it's my opinion now) there's a mistake in the data, according to me it just scientificly impossible. In anycase, I thank you all for helping me understanding sciences. Rheims - France ---90.18.59.162 (talk) 13:28, 6 July 2010 (UTC)

The important part is "in recent years". Obviously the difference can't continue forever, but by your own calculations, it can continue for 10 years without doing anything impossible. Looie496 (talk) 20:11, 6 July 2010 (UTC)

Sea level rise can indeed be higher in some areas than others. Tides, for example, can increase the sea level rise beyond its original levels, but melting of nearby ice caps and shifting of ocean currents can be another factor. A cold current being replaced with a warm current will increase sea level rise, but constant melting from glacial outlets (such as Jakobshavn Isbrae and Pine Island Bay can "channel" the extra water onto a specific swath of the ocean, see here for example. Also, variations in the El Nino Southern Oscillation already causes sea level variations on the scale of several feet between warm and cold anomalies off the coast of South America. Similarly, the drop in sea levels from the 1998 El Nino to the 2008 La Nina is just about enough to almost exactly cancel out the global sea level rise seen in Tuvalu in the same period. Thermal expansion will also be more siginifcant in Arctic regions, meaning the coasts of the Arctic Sea could have more sea level rise than in warm, tropical oceans. ~AH1^(TCU) 15:06, 7 July 2010 (UTC)

There's no reason to suspect a mistake in the data: I have a plot sitting in front of me (possibly from Kang et al., Inhomogeneous Sea Level Rise in the East/Japan Sea, JGR 110 (2005), but I can't find the paper online) that shows average sea level changes from 1992 to 2002 ranging from -4mm/yr to 16mm/yr in the Sea of Japan. Direct measurements and data from TOPEX/Poseidon agree with each other in this area. As others have said, changes in warm/cold currents and areas of upwelling/downwelling could cause this kind of discrepancy (and keep in mind changes of millimetres per year aren't large; static differences in sea level can be in the range of metres). 198.103.39.129 (talk) 18:23, 7 July 2010 (UTC)

Difference between mud and loam

What is the difference between mud and loam, please? I am interested mainly in their use as a construction material.

Wikipedia says that loam consists of sand, silt and clay and that mud consists of soil, silt and clay, but can also contain sand. Thus, to me not being a native speaker both terms seem to have the same meaning. --146.107.3.4 (talk) 14:11, 5 July 2010 (UTC)

In British English, "loam" is used to describe a type of soil (a type that often becomes "muddy" in the British climate): "mud" is a more general term. Physchim62 (talk) 14:31, 5 July 2010 (UTC)

(ec)In agriculture Mud generally refers to ground matter/earth/soil that is clay rich - (ie not really peat, topsoil, humus though they will be described as mud when very wet). it is generally clay like in nature, but may be more liquid. Loam is generally more particulate, and so has better drainage.. though when wet it can be described as mud. It is not as slicky as clay.

In argricultural terms they are different. In building terms they are less distinct see http://www.thefreedictionary.com/loam : "A mixture of moist clay and sand" which is very similar to mud as used in Mudbrick.87.102.23.18 (talk) 14:38, 5 July 2010 (UTC)

You might find this useful http://www.tbe-euro.com/downloads/SustainableBuildingConference-Austria1.pdf : in construction terms I haven't found an example where the two can't be used fairly interchangably.87.102.23.18 (talk) 14:42, 5 July 2010 (UTC)

More Were you thinking of mudbricks and walls or more in terms of groundwork/subgrades? In terms of foundations etc this book makes some useful distinctions [12] 87.102.23.18 (talk) 15:04, 5 July 2010 (UTC)

The difference is a matter of water content mainly. Mud always means soil that is saturated with water enough to be sticky and squishy. If it dries out, it isn't mud any more. Loam is simply a type of soil with no particular implication about water content. If you saturate loam with water, it turns to mud. Looie496 (talk) 16:20, 5 July 2010 (UTC)

Soil classification defines types of soils based on their sand, silt and clay content. Mud usually contains more water than loam. ~AH1^(TCU) 14:55, 7 July 2010 (UTC)

Is it Gun cotton?

This is what we found inside, besides shot itself, when we open a of 12 gauge shotgun cartridge in India. Is it so in the West ? I mean what exactly you find in yours in real life (as opposed to Wikipedia article)? What exactly is the stuff I have shown ? Is it gun cotton, or cordite what ever ? (the scale in centimeter) Jon Ascton  (talk) 17:24, 5 July 2010 (UTC)

I think it is either cordite, or, more likely, Smokeless powder. Guncotton isn't black. --The High Fin Sperm Whale 17:36, 5 July 2010 (UTC)

No, it ain't black either (only seems in pic).It is in fact dark green  Jon Ascton  (talk) 17:42, 5 July 2010 (UTC)

It's not pure gun-cotton nitrocellulose which is white like cotton. Nor cordite (image in article). It's almost certainly a form of smokeless powder. You might find this useful [13] - the powder is similar but slightly lighter. If the cartidge was more full than those in the links with powder then they could be using real gunpowder which is less powerful.87.102.23.18 (talk) 17:53, 5 July 2010 (UTC)

You might find the cutaway shells here [14] [15] interesting to look at.87.102.23.18 (talk) 18:05, 5 July 2010 (UTC)

(edit conflict)In that case, I'd guess smokeless gunpowder (smokeless gunpowder has so many different formulas and ingredients, probably one of them is dark green, or it could even be coloured like that on purpose). --The High Fin Sperm Whale 17:56, 5 July 2010 (UTC)

Yes, this is exactly what I found. The link seems to say that such shot is only meant for bird game, i.e. not in serious ammunition ? What about the standard shotgun ammo in the west ? And what about pistol and revolver etc. ?  Jon Ascton  (talk) 18:26, 5 July 2010 (UTC)

And, the other question, actually I already asked it in another post - talking of novel uses of 12 gauge shotgun cartridge, is there any machine which exploits the rush of its blast to dig a hole in ground when you have no time for a shovel ?

shotgun shell with slug

Erm - shotguns are mostly for bird game, (or firing at rats etc) - the small amount of powder is due to it's high power - shotgun cartridges were originally made for gunpowder - see Shotgun_shell#Construction_of_a_typical_shotshell " Modern smokeless powders are far more efficient than the original black powder used in shotgun shells, so very little space is actually taken by powder" - even the ones for bigger game have a lot of wadding eg see Shotgun slug (image right).

Were you thinking about military use? 94.72.242.84 (talk) 18:40, 5 July 2010 (UTC)

For rifle or pistol cartridges I can't do better than this [16] which has numerous cutaway diagrams of the 'shells'.94.72.242.84 (talk) 18:44, 5 July 2010 (UTC)

cordite in several colours

.--Stone (talk) 20:07, 5 July 2010 (UTC)

A Mythbusters episode tried to reproduce using a gun to cut a circular hole in a floor to escape from the bad guys. I recall that regular firearms were ineffective, and I imagine digging through dirt would be a lot harder. Besides, the dirt would be mostly pushed forward rather than to the side. Clarityfiend (talk) 02:06, 6 July 2010 (UTC)

Yeah - I think the most effective thing you could do to dig a hole with a shotgun shell would be to extract the explosive charge and push it as deep into the soil as you could and then set it off with a fuze. The resulting crater would be the best result you could possibly hope. The energy from the charge would mostly be directed upwards - towards pushing dirt out of the hole - although in soft soil, maybe half of the energy would go to compressing the soil beneath and making it harder to dig the next bit out. But the 'crater' made from a single shotgun shell would be unlikely to be more than a couple of handfuls of dirt...barely one shovel-full, I'd expect. There just isn't that much energy there. People do use small amounts of explosives to break up large rocks while excavating - but the solidity of a rock makes it much more amenable to breaking by explosives than soft, flexible, compressible soil. Furthermore, the goal is generally to break the rock into manageable chunks - not to physically remove it from the hole, which is energetically much more challenging. SteveBaker (talk) 13:30, 6 July 2010 (UTC)

Check out nuclear demolition. There were several plans to blast instant harbours and canals using atom bombs, and the Soviet Union is thought to have actually used bombs to stop gas well fires. Cod Lover Oil (talk) 16:34, 6 July 2010 (UTC)

Yes but there is a tad more energy involved with a nuclear bomb than a shotgun shell. Obviously you can do excavation with explosives - mines and quarries do exactly that all the time. But the puny amount of explosive in a shotgun shell just isn't enough to make much of a hole...even less so if you use that explosive to drive things into the ground rather than lifting stuff out of the hole. SteveBaker (talk) 19:46, 6 July 2010 (UTC)

Bunker buster#Missiles is kinda, sorta close to the concept, although it's job isn't to dig, either. The accompanying image does show some uplift, but I think almost all of it goes back down in roughly the same spot. Maybe Nuclear bunker buster is even closer. These would work better on asteroids, where the gravity is lower. -- JohnWBarber (talk) 00:01, 7 July 2010 (UTC)

Duty or pleasure?

I remember reading in my beginner level Biology books that living things should be able to reproduce. I used to think that all organisms had a sort of 'obligation' to reproduce and hence propagate their species. My current view is that almost all animals copulate due to attraction to the opposite sex and the resulting offspring are not on the parents minds during courtship. Is this natures way of ensuring that species propagate and do not go extinct by hiding duty behind pleasure? Thanks. --119.155.112.195 (talk) 20:08, 5 July 2010 (UTC)

Propagation of Life is the foremost project of evolution, nothing is more important, natural selection is a by-product of the process. Therefore the biological apparatus is designed in such a way that greatest pleasure (enjoyment of sex) can only be achieved by engaging in the process of intercourse. You see, it is a sort of bribe Evolution offers us so that can make the nature work ! By "we" I mean we all, that includes all other species. Interestingly Homo sapiens are the only organisms that can "cheat" mother nature i.e. family planning that is we can have sex for enjoyment alone, I think that Evolutionary Forces will now find some round about to overcome this danger ! Jon Ascton  (talk) 20:30, 5 July 2010 (UTC)

You'd love Idiocracy --mboverload@ 21:45, 5 July 2010 (UTC)

"Almost all animals" is probably too strong. There seems to be a neural "reward" system in all vertebrates, and I believe it is activated by sexual activity in all vertebrates that have been examined. There is also a reward system in insects, but I don't know if it is activated by sex. I don't think there is much information about other types of invertebrates such as molluscs and worms. In any case, there is no requirement for pleasure to be associated with reproduction -- it is theoretically possible for organisms to be hard-wired to give the necessary responses to the appropriate stimuli, without pleasure coming into the picture. Looie496 (talk) 21:30, 5 July 2010 (UTC)

Of course, that's what I meant in other words, in a scientists words (yours) it may sound a bit different, but believe me we are saying the same thing - "pleasure" is a human term," hard-wired to give the necessary responses to the appropriate stimuli" is what I meant if I were you. Perhaps I should not use the word "pleasure"... Jon Ascton  (talk)

I probably didn't explain clearly enough. To say that an animal does something for pleasure means that it is capable of anticipating the consequences of actions, estimating the pleasure expected from each, and choosing the one that is expected to yield the greatest pleasure. Those are sophisticated capabilities, probably beyond the reach of many species. The simplest alternative is to have direct, mechanical connections from certain sensory detectors to certain motor systems, so that detection of the presence of a possible mate leads automatically to performance of the response. I think it would be more reasonable to describe that sort of system as "duty" than as "pleasure" (although neither term is totally accurate). Looie496 (talk) 04:16, 6 July 2010 (UTC)

Both assign too much conscious agency. The essential point is that the evolutionary process leads to drives for reproduction—and if it didn't in some species, they would eventually die out. The mechanisms of those specific drives are not a conscious will to reproduce, even in human beings. Humans are sort of a special case because our understanding of reproductive biology and social consequences are probably much higher than any other animals, and we have rich cultures of reproduction. But our basic drive for sexual intercourse is not motivated by a conscious desire to have babies—it's the other way around. Our gonads say, "do stuff," and we do it, and end up with babies as a result. We see the connection. I'm not sure other animals do. "Pleasure" is probably a better term than "duty" for lots of animals, but "duty" is a bad term even for bugs, who do it not because they feel consciously required to, but because they are programmed to do it. --Mr.98 (talk) 13:03, 6 July 2010 (UTC)

I think you're looking at it backwards. I forget who originally said it - but the truth is that an animal is just a gene's way of making another gene.

From the perspective of a gene, it has to make an animal (or a plant or whatever) that has the highest probability of successfully preserving the gene into the future and spreading as many copies of it as possible. The whole business of animals and plants and mating and all of that stuff is just the way that the gene has found (by evolution) to be most effective in performing that task. The gene had to evolve to make sex pleasurable - or to provide some other 'drive' to do it because that's an effective strategy for ensuring that it'll get propagated.

But this strategy is complicated. If we (as the intermediaries 'caused' by the genes) don't feel an obligation to have kids - if we decide to use birth control through our fertile years...or to become homosexual or to simply abstain from sex altogether - then the gene has failed in it's task to provide that 'sex drive' and will (by definition) be eliminated from the next generation. The gene failed. Do we care that the gene failed? Maybe not. We only care if our genes gave us brains that made us care!

It goes beyond the actual act of creating a child too. If we were genetically 'wired' to have a baby and then abandon it - then those genes would also die out after just one generation. So having kids can be fun - it's definitely rewarding to see your son or daughter go to college and be a success. But the reason why that's a pleasure is because it was to the gene's advantage to have us continue to promote the continued existence of the next generation to the point where it too could propagate the next generation. Why are grandparents suddenly so fixated on their grandchildren? Guess what? Once their child has produced offspring, the most necessary thing for the continued propagation of those genes is to protect the grandchildren - and to hell with the intervening generation!

Hence, the process of evolution has molded the gene to the point where it produces human brains that have instinctual goals to produce offspring and to protect and educate them appropriately.

SteveBaker (talk) 13:20, 6 July 2010 (UTC)

I think your thinking of the Gene-centered view of evolution most notable expressed by Richard Dawkins in The Selfish Gene who I think was the one to coin the phrase ;a whatever is just a gene's way of making another gene'. Nil Einne (talk) 00:02, 7 July 2010 (UTC)

Aha! Thank-you! I was half-suspecting it was Dawkins, but I couldn't remember the precise wording of it so I couldn't search for it and I was side-tracked by wondering if it was Desmond Morris who first said it. Well, whatever. It's an interesting (and entirely valid) way to view the world. SteveBaker (talk) 05:24, 7 July 2010 (UTC)

'Hence, the process of evolution has molded the gene to the point where it produces human brains that have instinctual goals to produce offspring and to protect and educate them appropriately.'

Is it the genes that make a human parent want to send his child to school or the modern norm of good education = good job = respect that has changed the way people think about education? --119.155.11.103 (talk) 15:34, 6 July 2010 (UTC)

Yes, I think so. We have a general, instinctive (and therefore, genetic) drive to want the best for our children. That drive is filtered through intelligence, learned behavior, logic, economics, etc - but in the end, the reason we send our kids to school is that we are instinctually driven to have them perpetuate our genes. Of course, we're using our brains to actively consider how to turn that general 'drive' into actions: "Will sending my kid to school result in him/her getting a better job?"...and..."Will having a better job result in my kids not being hungry, having a roof over their heads?"...those are conscious thoughts - but deep down, it's probably genetics giving us the general drive to want our kids to do well. It's the same with sex, while we only have a rather general drive to reproduce, the precise details of whether to take the girl to the dance or to the movies and whether candy or flowers would make the best impression are coming from our intelligence because we haven't had time to evolve to believe that owning a red convertible with turbochargers and wide tyres will definitely get us laid. (Hmmm - I think I may have just disproven something! :-)

Without genetics, this is a crazily strong drive. Almost all parents would truthfully say that if it came down to it, they would happily lay down their lives to save their kids...and there are plenty of cases where parents have done exactly that. That's an amazing thing - there is really no other instinct that so completely overrides our goal of self-preservation. If not for the pressure of our genes trying to be perpetuated, why on earth would we do that?

The genes provide the "Why" and our intelligence provides the "How".

SteveBaker (talk) 19:34, 6 July 2010 (UTC)

Steve, I agree with all that you say, but I am also puzzled by the fact that some people - including myself and a number of my personal acquaintances (mostly male) - have never felt any desire whatever to have children (as opposed to just having recreational sex should the opportunity arise) and indeed have always actively disliked the idea. Do you think these are examples of individual 'nurture' overriding (genetic) 'nature', or do you know of a genetic explanation that might account for it. (NB: this is not merely a reflection of physical immaturity, as I'm in my 50s!) 87.81.230.195 (talk) 21:36, 6 July 2010 (UTC)

It's complicated (warning: I have an anthropology degree). In very general terms, evolutionary pressures have shaped our desires so as to best leave more of our DNA in the gene pool. It's important for us to eat, drink, pass waste, exercise, and have sex, so these things all make us feel good in various ways. By virtue of their biology, female mammals are much more likely to be responsible for raising the children than the males are - and women are no exception to that rule. But raising kids is no mean feat; it takes a lot of time and energy to carry a baby to term and it then takes even more time and energy to raise the kid enough for them to strike out on their own. That kind of drawn out task is hard to reward with a bribe (like an orgasm); it's rewarding, but nobody has kids so that twenty years later they can look back on the sweat and toil with satisfaction! What's needed instead is a brain that's hard-wired to want to raise kids; it's no accident that young girls play house and put diapers on their teddy bears; their brains are wired to make them instinctively want to do that. They therefore find that kind of play rewarding and are more likely to plunge into the sacrifices needed for the real thing. Men have different drives. We could, in theory, simply enjoy our orgasms with every woman in the area and not think at all about wanting to have a child. If you wanted to look at it cynically, I guess you could say it's because women are forced to care for the child anyway. However you equate it, men can get away with contributing less to the child-rearing, so their brains are not wired in the same way as to find such stuff enjoyable. I'm not saying it's fair, I'm just saying that's how the balance sheet works out. The first complication is that men who have children and stay with the family unit can form extremely strong bonds to their kids. Even men (such as myself) who had little desire for children before parenthood find that switch suddenly turned on. Which makes evolutionary sense as well, of course; children of parents who both care for them have a survival advantage against those that must make do with one parent. This is in contrast to the so-called Cinderella effect, which involves some grim aspects of children being raised by step-parents (see here as well). The most over-arching complication of course, is that people are all individuals and while it's easy to talk in generalizations, specifics will always be cloudy. When I first became a dad, I had no idea I would become a devoted parent, for example; there are an unfortunate number of parents (or either sex) who do not. And not every girl plays with dolls and not every woman has the strong basic urge to "listen to their biological clock". But in general they do; those stereotypes didn't just come out of the blue, they illustrate some of the ways natural selection has worked to shape our desires. Some of this comes from my understanding of parenthood as I've experienced it in, some of it comes from my degree, but it's not entirely OR. You may find the works of Helen Fisher and Desmond Morris to be of interest, for example. Our article on Sexual selection in human evolution also touches on some of this. Matt Deres (talk) 23:19, 6 July 2010 (UTC)

It's worth pointing out that everyone who decides not to have kids, and sticks with that decision, has essentially extinguished his particular genetics, while those who do want kids and are able to have them will pass their genetics along. And since there is no shortage of kids in the world, everybody's happy. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:36, 6 July 2010 (UTC)

Seen from the perspective of the gene, those people who choose not to (or fail to) have healthy, long-lived children have failed in the one single thing that the gene is "trying" to make them do (it's hard not to anthopomorphize!). And from the perspective of the genes of people who do have offspring, it's absolutely wonderful that some people choose not to do that because it leaves more potential mates and more resources for the offspring of those who do...which is a huge win! But I agree - why do we (as humans) have to satisfy our genes? If they fail to compel (or at least sufficiently encourage) us to do what they "need" then it's no big deal so long as we don't somehow suffer as a consequence. In times of old, not having children meant not having anyone to look after you in old age - which would have been a really serious problem for subsistance farmers and hunter-gatherers - but in modern society, we can avoid that issue fairly easily by saving money, buying into pension plans, creating systems of government with welfare, and so forth. In a very real sense, we've managed to cheat our genetics. Evolutionary theory says that sooner or later, the genes will catch on and adapt some clever new strategy...maybe in a few generations, some weird genetic flook will pop up and cause us to gradually suffer more and more horrible pain if we don't have a kid by age 30! Such a mutation would have significantly more breeding success than the lackadaisical gene that let's us get away without reproducing - and would therefore spread rapidly throughout the population, to the general detriment and misery of us humans. SteveBaker (talk) 05:13, 7 July 2010 (UTC)

Identifying a Howitzer

Greetings,

I am trying to identify a howitzer. The photographs were taken at the entrance of the fort of Ouvrage Saint-Gobain; I was told that it is a Skoda 105mm, but I have doubts.

• 
• 

Thank you very much in advance! Rama (talk) 21:23, 5 July 2010 (UTC)

Commons has a couple of pictures of a 105mm howitzer in the Skoda artillery category -- you can compare them. Looie496 (talk) 21:43, 5 July 2010 (UTC)

July 6

I don't get gravity

It's supposed to apply to everything right? Even light. And yet according to the article on helium it was light enough to fly away from the cloud that the early Earth condensed from. Is helium somehow exempt? —Preceding unsigned comment added by 68.69.73.195 (talk) 01:12, 6 July 2010 (UTC)

Helium floats, so it'll always be on top of the atmosphere. Maybe you know that the velocity of a atom of gas depends on its temperature? (See Kinetic theory if not.) The hotter it is the faster it moves. The thing is, this speed is only an average - in any given sample of gas, some are moving faster than this, and some slower. It can happen that the faster ones are moving fast enough to escape the gravity (like a rocket). Ariel. (talk) 01:16, 6 July 2010 (UTC)

I don't think this is actually a question of heat, per se. gravity decreases the farther you get away from the core of the earth. Helium will tend to rise above other gases (it is lighter and less dense), and in the upper reaches atmosphere it will be exposed to the solar wind, which can strip it away from earth's weakened gravity. --Ludwigs2 01:38, 6 July 2010 (UTC)

I'm not sure it could be that, according to the article at weightlessness gravity is only 6% less at 200 km up. Unless the solar winds are really strong anyway. 68.69.73.195 (talk) 01:40, 6 July 2010 (UTC)

No, Helium is not exempt. It's just light and flies away due to a combination of two factors mentioned above. 1.) High thermal speed. 2.) Solar wind. Same thing happens to hydrogen, by the way. Dauto (talk) 02:17, 6 July 2010 (UTC)

According to our atmospheric escape article, atmospheric loss due to solar wimd is not significant for the Earth, on account of our magnetic field. So the primary mechanism for the loss of hydrogen and helium from our atmosphere is thermal loss, also known as Jeans escape. Gandalf61 (talk) 09:57, 6 July 2010 (UTC)

The simple answer is that gravity is weak, weak, weak, as far as the forces go, but acts over a loooonnng distance. Consider that two magnets from your refrigerator can hold themselves together, suspended in the air, and doing so can contradict the gravitational pull of the ENTIRE planet. But their force diminishes quickly with distance, whereas gravity can have effects for hundreds of millions of miles distant. Gravity is good at doing things like keeping the planets aligned, and for roughly keeping heavy things like you and me on the face of the Earth (and even then, with just a little effort we can liberate ourselves from it, at least temporarily). But when you talk about things that are really light—like gases—other forces can be a lot stronger on a local scale, even if gravity rules at planetary and galactic scales. --Mr.98 (talk) 12:59, 6 July 2010 (UTC)

Gravity certainly applies to everything with mass. But lighter things float on denser things just as wood floats on water. Hydrogen and helium (being the least dense gasses) naturally float to the top of the earth's atmosphere. Hydrogen usually doesn't make it that far without running into some oxygen atoms and turning into water - but helium is a noble gas and doesn't react with anything, so it can reach the upper atmosphere fairly easily. The solar wind is a fairly significant force at those altitudes and is quite capable of defeating gravity and gradually blowing away the upper layers of the atmosphere out into space...which makes helium a fairly rare commodity.

The only helium we have is that which is created by radioactive processes and becomes locked underground in natural gas deposits. Ironically, although helium is one of the most abundant substances in the entire universe, it's quite rare down here on earth - and we're actually in danger of running out of the stuff sometime in the next 200 years. SteveBaker (talk) 13:02, 6 July 2010 (UTC)

We can also produce Helium using the Fusion_power#D-T_fuel_cycle. 157.193.175.207 (talk) 13:28, 6 July 2010 (UTC)

So we only need to make our helium stocks hold out for another 50 years? -- 58.147.52.199 (talk) 13:56, 7 July 2010 (UTC)

There's probably still some primordial helium left on Earth, but not much, as evidenced by sources that are rich in helium-3: see this review at p. 735 (p. 53 of the PDF file). Physchim62 (talk) 18:05, 6 July 2010 (UTC)

Yes - but both natural sources and fusion-reactor by-product are truly microscopic quantities compared to industrial needs. A 100MW fusion power plant, operating continuously, would take something like 300 years to produce a kilogram of helium (I hope I got my math right! But that sounds about right to me.) - all of the future fusion power in all of the world wouldn't make enough helium to keep the Goodyear blimp flying...let alone provide inert gasses for welding, birthday balloons for your kids, etc!

Primordial helium is certainly going to be rare because it leaks out into space. Naturally occurring helium is a by-product of natural breakdown of radioactive substances in the ground and ocean - which is indeed being slowly replenished. But think about that for a moment: If it takes just a few hundred years from first human exploitation of helium to when we are likely to run out of the stuff - then it would take a billion years for natural processes to replenish what we use in just a hundred years...and that assumes that the rate of radioactive decay is constant over all time - which it certainly isn't. It's safe to say that when we've used it all up...we're screwed. Other resources (such as copper) are becoming alarmingly scarce too - but at least pretty much every scrap of copper we've ever used is sitting in land-fill someplace waiting to become valuable enough to dig up and recycle. But when you 'consume' helium, it's gone. VERY gone! The nearest place to get more is the Sun...and there are considerable engineering difficulties associated with that! SteveBaker (talk) 19:22, 6 July 2010 (UTC)

The sun might be closer, but I bet it would be easier to harvest the helium from Jupiter, which also has plenty. Could we use tritium to produce light helium (He-3)? I mean tritium is expensive, but is it more expensive then strolling over to Jupiter to pick up some Helium? Googlemeister (talk) 19:43, 6 July 2010 (UTC)

Why does an acidic oxide reacts with water to form an acid?

And why does an acidic oxide reacts with a base to form a salt?

What is the principle behind them? Thank you. 114.247.10.148 (talk) 04:30, 6 July 2010 (UTC)

I assume you mean metal oxides and non-metal oxides. A non-metal oxide consists of a non-metal bonded via covalent bonds to oxygen. The addition of water generally created an oxyacid, which consists basically of hydroxide groups now being attached to the nonmetal. Since the covalent bond to the oxygen withdraws some of the electron density away from the H-O bond, it makes the H very easy to leave. The definition of an acid is something that loses H⁺ ions to solution. Thus, non-metal oxides produce acids. A metal oxide consists of metal ions and oxide (O^2-) ions held together by ionic bonds. When the O^2- ions come into contact with water, it tends to remove one of the hydrogen atoms from the water, producing two hydroxide (OH^1-) ions. The definition of a base is something that produces hydroxide ions in solution. Thus metal oxides produce bases Its basically the difference in reactivity between a covalently bonded oxygen atom, and the oxide ion. --Jayron32 05:07, 6 July 2010 (UTC)

The farther to the left on the periodic table you go, the more basic the oxides are. The farther to the right, the more acidic. Also, higher valence oxides such as chromium(VI) oxide tend to form acidic solution. Lower valence chromium(III) oxide is only very weakly acidic. --Chemicalinterest (talk) 10:51, 6 July 2010 (UTC)

Thank you. I see the reason why non-metal oxides produce acids, not something else. But I start to wonder why non-metal oxides react with water, rather than being nonreactive? Thanks. 114.247.10.133 (talk) 12:44, 6 July 2010 (UTC)

Not all non-metal oxides react with water: take carbon monoxide as an example of a neutral oxide. But that's really something which is in the "character" of each oxide. Physchim62 (talk) 12:55, 6 July 2010 (UTC)

Hmm... Maybe on some of them the bonds are strong between the nonmetal and oxygen so they wouldn't accept a hydrogen and as a result, wouldn't dissolve in water to form an acidic solution. Very few nonmetal oxides are unreactive toward water, though. --Chemicalinterest (talk) 13:10, 6 July 2010 (UTC)

It depends on what you mean by "react". Aldehydes such as formaldehyde for example, are hydrated by water (they form hemiacetals and acetals). It all comes down to whether your compound/element is an electrophile or a nucleophile. Lewis acids tend to be electron-withdrawing / electrophilic; Lewis bases, electron donating / nucleophilic. John Riemann Soong (talk) 16:04, 6 July 2010 (UTC)

You with your organic chemistry again... over my head --Chemicalinterest (talk) 16:31, 6 July 2010 (UTC)

Rifled slug?

"Shotgun slug" - rifled?

Copying the attached pic from a few threads above this one. Why would a shotgun slug be rifled? I didn't think shotguns were rifled. Comet Tuttle (talk) 05:56, 6 July 2010 (UTC)

There are rifled shotguns designed specifically for slugs. 68.69.73.195 (talk) 06:11, 6 July 2010 (UTC)

http://www.rogueturtle.com/articles/shotguns.php

Normal bullets are not rifled. The "rifled" slugs do not, to my understanding, cause significant spin. As mentioned above, modern slug guns often have rifled barrels, but are more often used with sabot slugs. The part of the article at Foster_slug#Foster_Slugs says that these fins on the slug were more about reducing friction than imparting spin. Friday (talk) 15:05, 6 July 2010 (UTC)

I'm no expert but might it be that the 'fins' cause spin due to aerodynamic forces AFTER the slug has left the barrel? That would make sense because you don't need fins to make a bullet spin when the bore is rifled and since so many shotguns are smoothbore, it would make perfect sense to put fins on a shotgun shell for the odd occasions where you want a more accurate shot and less scatter. SteveBaker (talk) 18:48, 6 July 2010 (UTC)

There is no scatter at all from a slug - it is a solid chunk of lead. Rmhermen (talk) 20:40, 6 July 2010 (UTC)

Statistical scatter perhaps (multiple shots?)

Actually the links above note that the centre of gravity of such a slug is close to the tip (like a shuttlecock) so there's (probably) not need for a spin to be imparted to prevent tumbling, since the drag does that. It also claims the fins are there to reduce friction in the barrel, and that there is no spin on the slug in flight. That's what it says, I'm just repeating it.77.86.6.186 (talk) 21:00, 6 July 2010 (UTC)

If the fins are just to reduce friction - surely you'd want them to be parallel to the direction of flight? SteveBaker (talk) 00:12, 7 July 2010 (UTC)

That would increase the edge length for potential abrasion though? from just the leading part of the fin (and to a lesser extent the shallowly angled sides) to multiple circular edges. (Assuming that edge abrasion is a larger contributor to gun fouling than side abrasion - since the sides are more solidly supported - 2pi steradians of support vs pi steradians of support). Spiraling the fins ensures even distribution of support around the circulat cross section of the barrel compared to hypothetical straight fins.

According to book mentioned here the fins impart a slight spin of 1 turn in 24feet - I'm fairly certain this is not effective cf spin distance mentioned in Rifling (though much mass is on the outside so the rotational inertia is greater than a similar solid bullet). There's also an video here [17] (might be a solid slug, not clear).. but it may not convince either way.

Ignoring all the above the reason to have non-circular fins is swaging - see Swage#Firearms_and_ammunition (not that link - doesn't mention gun chokes see [18] instead) - It would be great way to acchieve consistent jamming if the slug wasn't perfectly lined up. So longitudinal fins are needed, and non-twisted longitudinal fins are not the best solution for reasons explained above.

This gives rise to a bullet that looks like it's designed to rifle.. However if you think the description on the page Foster slug is wrong I'd take it up there. It's not difficult to find sources that say they are rifled to make them more stable if you look though; I'm suggesting it's just consequence of other design parameters.

It would be interesting if anyone can be bothered to calculate the stabilisation acchieved from the slow rate of spin that is imparted, and say whether or not it is actually significant.77.86.6.186 (talk) 00:39, 7 July 2010 (UTC)

I'm fairly certain the number one factor behind the design here is making a shell that goes through a Choke (firearms) with no problems.77.86.6.186 (talk) 01:55, 7 July 2010 (UTC)

It's possible to assemble a thousand opinions on this subject. Here's one

"Heavy external "rifling" was cast into these Foster type slugs, allegedly to allow the air they flew through to impart a slow spin that would help stabilize the slug. Like most something for nothing schemes, the rifling proved ineffective, but it did provide some space for some compression if the slug had to squeeze through a tight choke.."[19]

77.86.6.186 (talk) 02:01, 7 July 2010 (UTC)

Duh - just realised that's a Brenneke slug and not a Foster slug - the shuttlecock effect doesn't apply to the brenneke slug.77.86.6.186 (talk) 02:08, 7 July 2010 (UTC)

Seeing as it's a Brenneke slug I can link this:

"The Brenneke design with angular ribs is not to create spin, but to ensure problem-free choke passage" www.brenneke-munition.de

That's the company website, hopefully it can be taken as fact.77.86.6.186 (talk) 02:15, 7 July 2010 (UTC)

Hyrachyus

Hi, I wish to know where lived the Hyrachyus? Because from this two articles I can't find out, where lived this animal.

http://en.wikipedia.org/wiki/Hyrachyus

and

http://en.wikipedia.org/wiki/Rhinocerotidae#Evolution

One say Europe and the other North America. Please answer. —Preceding unsigned comment added by 89.123.165.191 (talk) 13:24, 6 July 2010 (UTC)

Here's a cite for Hyrachyus in North America: [20] (it's in there somewhere). There might also have been Hyrachyus in Europe, not sure. That 1883 report mentions Lophiodon, a European cousin. There's a document here: [21] which I think says "Lopliiodon is limited to Europe; Hyrachyus, Hyracotherium and Pliolophus to Europe and North America" ... but I'm not allowed to read it unless I want to pay thirty quid. I had to extract those words from google in two searches. I think it might be volume III of the same report, which is also available here [22], but I can't find those words in it. However, it does say "Hyrachyus is the American Lophiodon, the difference between them being but slight; both are found in France ; the former in the Lower Parisian, the latter in the Phosphorites." So that's pretty definite: the answer is both. (Not sure how that jives with Laurasia being already separated a million years previously?) 213.122.47.102 (talk) 14:28, 6 July 2010 (UTC)

Thanks anyway! —Preceding unsigned comment added by 92.86.247.63 (talk) 10:30, 7 July 2010 (UTC)

Hawaii

Would Hawaii's climate be considered tropical, or sub-tropical? Googlemeister (talk) 16:45, 6 July 2010 (UTC)

Probably tropical according to File:ClimateMap_World.PNG. --Chemicalinterest (talk) 17:51, 6 July 2010 (UTC)

The state as a whole is tropical, but the actual climate varies quite a bit. Indeterminate (talk) 20:25, 6 July 2010 (UTC)

Cooking Pizza

Not sure if this belongs here or the Misc. desk, but I think this is the best place to start. Buying a pizza from a supermarket and cooking it at home is drastically cheaper than buying one ready-cooked from a pizza takeaway, I don't know why, but it is. However, a pizza cooked at home is never as good as that from a shop - but why? I am sure that the method of cooking is the problem here. When I cook a pizza, the centre is lukewarm but the edges look they've been incinerated but pizzas cooked in a shop are crisp and even.

I know the pizza is slightly thinner towards the edges but we're talking less than a centimetre so I don't see why the difference should be that profound. I also follow the cooking instructions to the letter - put on the top shelf of an oven and cook for 12-14 minutes at 200C. After 12-14 minutes, the outside is just about right but the middle needs at least another 5 minutes (minimum) otherwise it is barely cooked at all. By this time, the edges are hard, dry and burnt. I don't think it's a problem with the oven as I have experienced this with other ovens. I know pizza shops have special ovens but that can't be that much of a factor.

Deep-pan pizzas are just about edible after this cooking ordeal (if you leave the crusts) but thin crust ones? Forget it, the crust is so hard it's virtually inedible.

Is there any way I can cook a pizza more evenly? I would assume I am doing something wrong, due to a. the fact that pizzas for home cooking are available and b. the picture on the box always looks perfectly cooked. Would cooking it more slowly on a lower heat help? Covering up the edges in foil? Anything else? —Preceding unsigned comment added by 94.196.158.83 (talk) 18:01, 6 July 2010 (UTC)

First, frozen pizzas have a number of constraints that make them less than edible (they are usually pre-baked and frozen, and they need to be very cheap. They are also much thicker than real pizza). Fresh pizza is made from unfrozen dough. Secondly, real pizza ovens are a lot hotter than 200°C, and the pizza is placed on a hot stone, cooking from the top and the bottom very quickly. Oh, and thirdly: Do you thaw the pizza before cooking? --Stephan Schulz (talk) 18:19, 6 July 2010 (UTC)

(EC) I must admit, I do not usually have these problems when cooking ready made pizzas except the crusts on the cheap frozen thin crust pizzas does become quite hard, but out of curiosity, are we talking about the frozen ones, or ones that you can find that are refrigerated, which I find are usually higher quality and more expensive? One other possibility, are you at a high elevation (1500+ m)? Googlemeister (talk) 18:22, 6 July 2010 (UTC)

Thanks for the reply. This seems to happen with the shrink-wrapped non-frozen pizzas from the supermarket (which they apparently make in-store from 'fresh' ingredients and yes, they are more expensive) as well as the boxed and shrink-wrapped frozen ones, although the frozen ones seem to cook slightly more evenly than the non-frozen ones for some reason (I usually cook these from frozen as that is usually what the instructions say). I am not at a high elevation, barely above sea level. I thought the frozen ones cooking better might have something to do with humidity (the burnt edges are very dry). 94.196.158.83 (talk) 18:27, 6 July 2010 (UTC)

Pizza stone says you can buy a small one, or use a bunch of unglazed tiles. 213.122.64.116 (talk) 18:33, 6 July 2010 (UTC)

I believe it has more to do with the mode of cooking than with the source of the pizza dough or whether it's frozen, thawed or fresh. My wife (who is an excellent cook) has made pizza completely from scratch and we've had the same disappointing problem of incinerated edges and half-cooked middles. Making 'thin-crust' style pizza seems a little easier than regular or 'deep-dish' styles - but still, it's tough to get it right 100% of the time even with thin-crust.

What seems to help is a proper pizza cooking tray. Ours is a round metal plate with a slightly concave surface and a few hundred half centimeter holes punched in the center third or so. The idea is (presumably) to let the radiant heat from the oven pass through the holes and thereby cook the center of the pizza a little faster than the edges. This seems to be partially succesful...but still, I have to say that it's hard to beat delivery pizza on crispness and crust texture (although it's entirely tivial to do vastly better on taste with fresh ingredients, proper spices and not spending an hour being kept lukewarm in a delivery pouch).

It's frustrating because a combination of the delivery crust style with homemade toppings would be a truly awesome thing to behold.

...and please stop asking these questions on days when I've just missed lunch!

SteveBaker (talk) 18:43, 6 July 2010 (UTC)

Surely the little holes are to allow steam to escape? --Sean 21:19, 6 July 2010 (UTC)

(1) It's a frozen pizza. It is contrary to all the Laws of Science that it will ever (a) taste as good as an average restaurant-made pizza, or (b) look as good as the picture on the box (that would also violate the Laws of Advertising); or (c) cook as good as the instructions lead you to expect -- IIRC, this is the Law of Frozen Pizza Imperfectability (where are those Wikipedia articles when you actually need them?); (2) The old "Red Baron" frozen pizzas had a metalic-like inside cover that customers were told to fold up and under the pizza before putting it in the oven (or maybe the microwave -- maybe it wasn't quite metalic, but it looked like it was -- it's been a long time since I reformed from my evil ways; as I recall, it cooked little mini-pizzas well enough); (3) the hallowed Frank Pepe's Pizzeria, when a new generation of the family ownership decided to do the unthinkable and expand to different locations than the one on Woooster Street in New Haven, Connecticut, arranged to have each new oven built to match the original, ancient oven at Pepe's on the unscientific understanding that you don't mess with success, so that's anecdotal, unscientific evidence that the oven must have something to do with it although this is pretty mystical for a science reference desk, I admit (see Frank Pepe Pizzeria Napoletana#The oven) (3) You do realize, I hope, that there's a special circle in hell reserved for frozen-pizza buyers and sellers? It's in Dante's Inferno somewhere, and I'm told modern translations just don't do it justice. Something about getting shoved inside a brick pizza oven. Or that might have been in The Godfather; (4) try a cookie sheet under the pizza. I encase it with aluminum foil first, shiny side up (at least it's easier to clean). Still doesn't work quite right. Usually, we buy it from a pizzeria; (5) Please realize that scientists all over the world have been working on this problem for decades, and while they haven't solved it yet, side benefits have included the microwave oven, the Tang drink and those diapers that look like blue jeans. Rest assured that while science sometimes progresses slowly (cure for the common cold, anyone?) it does progress. -- JohnWBarber (talk) 18:51, 6 July 2010 (UTC)

By the way, pizza ovens are sold to homeowners. -- JohnWBarber (talk) 18:57, 6 July 2010 (UTC)

The difference is basically in the oven: you can't cook proper pizzas in a domestic oven, and the one's you buy in shops are a compromise that lets you get something edible (and lets remember that pizza, like sex, is often disappointing but only very rarely is it truly bad) The official pizza napoletana is cooked at 485 °C for 60–90 seconds... Physchim62 (talk) 19:04, 6 July 2010 (UTC)

I've never tried his pizza, but Alton Brown has never let me down on anything else. The transcript and recipe from the Good Eats pizza show is here. He uses an unglazed quarry tile to bake on. There are a number of (to me) surprising bits (such as allowing a very long cooled rise for the dough), but he bases his recipes and instructions on food science and tests them empirically before airing them, so I would tend to believe him. As far as fresh/frozen, the problem is likely with the dough being 1) of poor quality and 2) blind baked for too long, making it difficult for the end user to balance the sogginess with the, um, burniness. Matt Deres (talk) 19:38, 6 July 2010 (UTC)

A very long cooled rise is generally the default for people who want to maximise the tastiness of their yeast product. In my experience, you can make good pizza with a short rising too: the only real difference is in the 'grain' taste of the crust, but I'm guessing you eat bread that hasn't been slow-risen, so I don't think you'll notice anything bad. A cool, slow rise also means you can start the dough and leave it overnight or while you go to work: if you don't want to do that, you can rise it in a cool (< 50 C, in a bowl covered with a towel, oven turned off) oven in less than an hour. 86.164.57.20 (talk) 21:00, 6 July 2010 (UTC)

A perpetual motion machine

Gravity is a force, and as such it does work. If I drop a stone from my window, the Earth's gravity will exert a force of roughly 10 newtons per second on it to bring it down.

But then, is gravity really ethernal, or does it eventually run out?

• If gravity lasts forever, that means any piece of rock can exert an infinite amount of force, and thus an infinite amount of energy. Wouldn't it be a perpetual motion machine then?
• If gravity does not last forever, when is it calculated to "run out"?

I'm just having a hard time reconciling the idea of an ethernal gravity with the second law of thermodynamics, and I'd like someone to explain this to me. 88.1.139.43 (talk) 19:18, 6 July 2010 (UTC)

It is not perpetual motion though. Eventually, the rock will stop when it hits something and you would need to exert energy to lift the rock back up to drop it again. Basically, the rock has already stored energy and it is using it up while falling, but it will not fall forever. Googlemeister (talk) 19:31, 6 July 2010 (UTC)

Phrased alternately, this is the distinction in physics between force and energy (or work). You say "...an infinite amount of force, and thus an infinite amount of energy", but this incorrectly equates "force" and "energy". Rather, energy is (roughly) force multiplied by distance. If you want to turn that 10N of force into 10J of energy, you have to move the rock one meter (as the joule is a unit of Newton-meters).

Gravity is a force, but a force in and of itself doesn't do anything. A PM machine, on the other hand, has to be able to do infinite work, that is, the transfer of energy. As Googlemeister has already noted, gravity can cause a rock to fall -- once. Then it reaches a point of equilibrium (the surface of the Earth, the center of the black hole, the center of mass of the combined rock-attractor system, whatever) and it ceases to do any more work until you spend external energy to move it. Gravitational force is still there once the rock stops doing work; it doesn't need to "run out" for useful work to end. — Lomn 19:49, 6 July 2010 (UTC)

Basically agreeing with the other responses but saying it a bit differently: gravity only does work on things that move downward. It can't do infinite work because there isn't an infinite amount of down. If you move the object back up to where it started, gravity does negative work while you're lifting it, so there is no accumulation. Looie496 (talk) 20:15, 6 July 2010 (UTC)

A stone lying on a window ledge has potential energy. While falling the potential energy of the stone is converted to kinetic energy. When the stone has fallen as far as it can go, it hits something and its kinetic energy suddenly converts into sound and heat. Gravity is still there but a stone with no place to fall has no energy at all. I think you mean "eternal". Cuddlyable3 (talk) 21:16, 6 July 2010 (UTC)

Actually, your stone can "fall" forever, achieving a stable orbit around a planet for example (we omit interplanetary dust and solar wind for simplicity). However, this will still not make it a perpetual motion machine: if you try to extract energy out of it, you will slow it down / change its orbit to a lower one.--131.188.3.21 (talk) 23:41, 6 July 2010 (UTC)

Moreover, no orbit is truly "stable", not in terms of thermodynamics. — Lomn 02:24, 7 July 2010 (UTC)

The OP may check the height of their window against the article about Low Earth orbit. Cuddlyable3 (talk) 13:30, 8 July 2010 (UTC)

I'm sorry, we don't stock actual perpetual motion machines, but we do have a fine selection of these other models that might serve your purpose: Gravity can give you practically a perpetual motion machine in the form of a hydroelectric (or mill) dam, as long as the water doesn't run out (Mother Nature brings it uphill for you). Harnessing tidal forces might be more "perpetual". A geothermal pump is practically a perpetual heating/cooling machine (although you have to actually supply some motion for the water or liquid to circulate -- hook it up to your dam), and a solar panel (or other device dependent on energy from the sun) is practically a perpetual electricity-making or heating machine -- in space, anyay -- until you get an eclipse or the sun dies. (I think some utilities use solar and wind power to pump water back up into the reservoir of a hydroelectric dam and there's an idea out there about pumping air into a cave or mine and releasing it later, saving energy until the sun doesn't shine and the wind dies down, a more tenuated "perpetual motion" machine.) Of course, you're simply taking energy from some massive forces of nature (we always are) and these will all die out eventually, but eventually we'll all be dead. But you didn't actually want a machine? You just wanted an explanation of a concept? Sorry, we don't stock those either, but this week our models are all on sale ... -- JohnWBarber (talk) 23:42, 6 July 2010 (UTC)

All of your suggestions only work for very small values of "perpetual", of course! Unless you manage to answer The Last Question. --Stephan Schulz (talk) 08:31, 7 July 2010 (UTC)

The problem here is a confusion between a 'force' and 'energy'. This confusion is so common - and the question comes up here so frequently, that I've written an answer on my personal Wiki HERE so I don't have to keep repeating my answer every couple of weeks! I recommend you go and read that. SteveBaker (talk) 04:58, 7 July 2010 (UTC)

Without having read steve's answer yet where I am quite sure it would be mentioned, magnets is the other thing which is frequently subject to exactly the same confusion. Vespine (talk) 02:07, 8 July 2010 (UTC)

Stellar parallax and the movement of the sun

Stellar parallax is a way to measure distances to stars, comparing their position in the sky when earth is at opposite points in its orbit. This gives a distance of 2 AU. But the solar system is moving at 220 km/s around the galaxy, which is about 46 AU per year.[23] How does this square with the stellar parallax method? Are all nearby stars approximately at rest relative to our sun? EverGreg (talk) 19:38, 6 July 2010 (UTC)

For the most part yes. The fastest star near us, Kapteyn's Star, moves on the order of about 0.001 c relative to the sun and is 13 ly distant. Googlemeister (talk) 19:49, 6 July 2010 (UTC)

Put in perspective, if the solar system is moving with respect to a target star at 46 AU per year, that's less than .000001 c. However, I'm not sure that's really the point here. In the time it's taken the Earth to complete half an orbit (to allow the 2 AU parallax), the solar system has moved about 23 AU, which is to say, 0.00036 light years. On the other hand, we're using data from the Hipparcos satellite to measure stellar distances of up to 1600 light years, a factor difference of about five million. So the motion of the solar system is messing with parallax measurements by thousandths of a percent, which is probably well within the margin of error. Even Proxima Centauri, the closest star, would have its distance mis-measured by only one part in 12000 if we didn't account for the motion of the solar system. So it's not whether nearby stars are at rest relative to us as much as a few dozen AU being insignificant when you're talking light years. — Lomn 19:57, 6 July 2010 (UTC)

Note that it's pretty easy to check on this. All you have to do is repeat the measurement when the Earth comes back to its starting point. If the distant star is moving enough to cause a problem, you will get a substantially different result on the second measurement. Looie496 (talk) 21:07, 6 July 2010 (UTC)

Are all nearby stars approximately at rest relative to our sun? Yes, in fact this 220 km/s frame is called the local standard of rest. -- Coneslayer (talk) 11:25, 7 July 2010 (UTC)

Hmmm - interesting - so I have a followup question: At what time of year does the earth move in the same approximate direction as the sun's motion around the galactic center? SteveBaker (talk) 23:31, 6 July 2010 (UTC)

December. Physchim62 (talk) 23:51, 6 July 2010 (UTC)

So right now, we're moving slower than average relative to the galactic core? Cool! SteveBaker (talk) 04:40, 7 July 2010 (UTC)

Bass energy sucking

Is it possible for a bass drum to suck my bass energy from my bass cab and make it sound bad if they are too close? —Preceding unsigned comment added by 88.104.83.202 (talk) 20:29, 6 July 2010 (UTC)

It would definitely resonate or buzz when bass notes were played, and that sound would likely degrade the quality of sound you heard in the room. So it could easily make the bass cabinet sound different. I just knew that some good would come out of having a bass drum occupying space in the living room. I tried putting a large bass drum in front of a speaker and playing classical or rock music with the bass turned up. I could feel the drumhead vibrating, but couldn't detect much difference in the sound. "Bad" is in the ear of the listener, since musicians often want distortion in a guitar amplifier. Edison (talk) 20:41, 6 July 2010 (UTC)

Yeah, I'd expect that a bass drum could attenuate the sound energy, but not that it would significantly alter the characteristics of that energy. Beyond that, there's no "energy sucking". You might get lousy sound quality, though, if the bass guitar is playing a note that's near, but not at, the note played by the drum -- but that's just being out of tune, not anything specific to these two instruments. Similarly, the room might have lousy acoustics for that frequency range, but again, nothing particular to the instruments themselves. — Lomn 21:22, 6 July 2010 (UTC)

But doesn't a bass drum have a fairly low Q factor, so that it can absorb energy over a reasonably wide frequency range and thus distort the bass from my bass cab? —Preceding unsigned comment added by 88.104.83.202 (talk) 21:52, 6 July 2010 (UTC)

If the bass drum absorbed acoustic energy, should it convert the energy to heat, and either radiate heat or have its temperature rise? Edison (talk) 04:47, 7 July 2010 (UTC)

Ok then, say I had an unenergised bass cab next to my active bass cab, would my bass energy be sucked by the passive cab? —Preceding unsigned comment added by 88.104.91.80 (talk) 00:02, 8 July 2010 (UTC)

What you call energy sucking is just the absence of normal room acoustics. Ways to experience your bass cab (I assume this means "loudspeaker cabinet") without room reflections are to play it outdoors or in an Anechoic chamber. These have far more noticeable effect than a single item such as nearby drum or cabinet. If you noticed a bass loss you would presumably increase your volume to compensate, and would hardly call the effect "bad". However there is another possible effect from a resonator that posesses both high Q and non-linearity. This might buzz at certain frequencies. Cuddlyable3 (talk) 13:51, 8 July 2010 (UTC)

Sprite freezing

Have a question guys. I just took a sprite out of my mini fridge (pretty much a freezer) and when I opened it the liquid froze from top to bottom.

What is this magic?

I thought it might have something to do with the pressure being released, but doesn't high pressure raised a liquid's freezing point. 74.15.137.192 (talk) 22:04, 6 July 2010 (UTC)

Pressure tends to lower the freezing point of a liquid. However, what I think is more likely is that the Sprite was supercooled. In fact, our article notes that Sprite was, at one time, specifically sold in the UK in a supercooled state such that it turned to slush when opened. Supercooled liquids tend to freeze rapidly when they're disturbed, which is why opening the can/bottle caused the freezing -- both the physical shock of opening the can and the pressure change associated with it. A similar, and significantly more dangerous, phenomenon is superheating, which is relatively easy to accomplish with water in a microwave and can lead to severe scalding. As such, it's recommended that you not try to boil water in a microwave unless you've added some rough surface (such as a wooden spoon) to the container so that superheating won't occur. — Lomn 22:18, 6 July 2010 (UTC)

Pressure tends to raise the melting points of liquids – except for the essential exception that is water. Otherwise, I agree completely, the phenomenon seems to be supercooling. As you release the pressure, you get tiny bubbles of carbon dioxide forming, and these act as nuclei for the surrounding liquid to freeze around. Physchim62 (talk) 22:47, 6 July 2010 (UTC)

You're absolutely correct; I should have said "water-based liquid" (as I expect Sprite to be sufficiently water-like for water's general pressure-temperature relationship to hold). — Lomn 02:21, 7 July 2010 (UTC)

Is it possible that the unopened Sprite doesn't freeze because of the dissolved carbon dioxide, and the sudden loss of CO2 upon opening changes the freezing point? I would imagine that this has a small effect, given that there is a ton of sugar dissolved, and still considerable amounts of CO2 remaining in solution, but it may contribute. What if there was a tiny imperfection in one of these supercooled cans? If it was sitting in a store for weeks, wouldn't it be possible to turn to slush before opening?24.150.18.30 (talk) 00:57, 7 July 2010 (UTC)

I would expect that most stuff isn't stored supercooled, though -- generally any soft drinks I buy are at room temperature in the store, and I therefore see no reason that they'd be stored otherwise in the warehouse. In the case of the sold-supercooled link above, I expect that the Sprite was only supercooled once it was in the vending machine, protected from further disturbance. — Lomn 02:21, 7 July 2010 (UTC)

I've seen it happen with bottled water, so dissolved CO2 is not required. (It's a neat trick. Makes you feel like a super hero.) APL (talk) 03:22, 7 July 2010 (UTC)

Unless you didn't want it to go slushy, and just put it in the freezer to cool fast then forgot about it and thought you pulled it out in time but ooops maybe not Nil Einne (talk) 06:04, 7 July 2010 (UTC)

Thanks, everyone, for the quick replies. I've actually always been interested in questions like this. I don't know what the field this would be called (maybe physical chemistry?), but can anyone recommend some books on this subject? Or are there standard university courses that teach material like this? 74.15.137.192 (talk) 02:55, 7 July 2010 (UTC)

This is probably general chemistry; see if the chemistry article has anything good. Also take a look at Portal:Chemistry. Any introductory chemistry course should carry the concepts, including high school and college books. --Chemicalinterest (talk) 20:48, 7 July 2010 (UTC)

I don't understand quantum mechanics!

I was reading the article "uncertainty principle" in an attempt to find out why it is not possible to know a particle's position and its momentum at the same time. The probability that a particle is in a certain position is given by the amplitude of the wave packet at that point (correct?). It also says that to obtain an accurate reading of position, this wave packet must be 'compressed' as much as possible, meaning it must be made up of increasing numbers of sine waves added together (what does this mean?), and that the momentum is proportional to the wavelength of one of these waves, but it could be any of them. —Preceding unsigned comment added by 203.22.23.9 (talk) 22:38, 6 July 2010 (UTC)

First, don't be ashamed you don't understand it. It's genuinely hard and unintuitive when you start. Here is my attempt to break it into relatively easy concepts — it is extremely simplified but hopefully will get the gist across and is, I hope, not so wrong that it will be just laughed at by those who have deeper understandings of it. (Or, if it is as bad as that, hopefully they will write up similarly straightforward corrections!) I am not a physicist but I dabble in its history and concepts.

As for waves. If you combine two waves together, they can either destructively or constructively interfere. See the diagram here. That part is easy. If you add two waves together of different frequencies, you can get interesting results, like so. The bottom sine waves have been added together and constructively/destructively interfere to make the wave packet on top.

Now imagine that we wanted to make that wave packet one infinitely small wave—just a single high point with nothing around it. Well we could keep on adding more and more sines together and we'd get something that looked more and more like a single wave in the middle of calm. A nice illustration of that is figure 7.4 on this page.

Now in QM, the wave packet's amplitude is the probability of finding a particle in a particular region of space. So at the parts of the sine wave that are high, you have a high chance of finding the particular. Now the issue is that if you want that uncertainty to be zero—you want to know exactly where it is—that means you have to add up a very large number of waves, so that you have basically one giant spike in the middle of a bunch of nothing. The more you confine that wavepacket, trying to nail down the position perfectly, the more waves it has to be made up of. As you add more waves to it, you are adding more uncertainty about the momentum of the wavepacket as a whole. So you can get the position down perfectly—no problem. But what do you lose at the same time? You lose the ability to know the frequency of the wave, the more you nail down its amplitude into a tiny space. That's the momentum issue.

Does that help at all, at least with the understanding of what the waves are supposed to indicate? The take-away message of the wavepacket description of UP for me is that UP is not a problem of measurement in and of itself (it is not just that when you physically "touch" one property, it physically modifies the other); it's a fundamental property of the universe, if the various properties of the universe (like a particle's position and momentum) are correctly described as these sorts of wave forms. --Mr.98 (talk) 23:40, 6 July 2010 (UTC)

I struggle, too, but I like Mr 98's explanation. You might be interested in these Wikiquotes. Dbfirs 07:46, 7 July 2010 (UTC)

But how does one "add" waves, in practice, by taking measurements? —Preceding unsigned comment added by 203.22.23.9 (talk) 03:41, 7 July 2010 (UTC)

He refers to the Fourier decomposition of the wavefunction.

Anyway, say we have an electron. To measure its position we can bounce photons off it (i.e. shine a light). The accuracy of the measurement is roughly the photon's wavelength. Photons have energy and momentum, so the resulting collisions destroy information about the particle's momentum. As p = hc/λ for photons, we can only improve precision in position at the expense of momentum. MER-C 10:44, 7 July 2010 (UTC)

Right, but that's actually not a good explanation of UP, because it makes it look like it is just an artifact of the measurement system, whereas the wavepacket model makes it clear it is a fundamental property of the universe. It's not that we don't measure it well—it's that the information is simply not there. (At least in the Copenhagen interpretation.) UP as put forward by Heisenberg was originally a measurement issue; Bohr is the one who said, "ah ha! It's actually about the fundamental limits of physical knowledge." Which is a much more interesting and important interpretation, and the wave approach is the only way I really know how to illustrate that. (It also makes more clear why EPR and Bell's theorem are important, and why it is not just position/momentum that are at issue, but lots of other states as well.)--Mr.98 (talk) 13:17, 7 July 2010 (UTC)

One reason why quantum mechanics is difficult to understand is that several arguments and concepts, which should be kept apart, are put together.

1. The cornerstone of quantum mechanics is that energy $\scriptstyle E$, measured in joule, and frequency $\scriptstyle \nu$, measured in hertz, is the same quantity. The conversion factor is the planck constant $\scriptstyle h$, having the dimension of joule per hertz. So $\scriptstyle E=h\nu$.
2. Now what is frequency? The function $\scriptstyle \psi (t)={\overline {A}}e^{2\pi i\nu t}$ has a well defined frequency $\scriptstyle \nu$. (See Circular motion#Description of circular motion using complex numbers). This function satisfies the differential equation: $\scriptstyle {\frac {d\psi }{dt}}=2\pi i\nu \psi$ or $\scriptstyle \nu \psi ={\frac {1}{2\pi i}}{\frac {d\psi }{dt}}$ . 'Multiplying by the frequency $\scriptstyle \nu$' is thus identified with 'applying the operator $\scriptstyle {\frac {1}{2\pi i}}{\frac {d}{dt}}$'.
3. Fourier series like $\scriptstyle \psi (t)=\sum _{\nu =-\infty }^{\infty }{\overline {A_{\nu }}}e^{2\pi i\nu t}$ (where $\scriptstyle A_{\nu }=\int _{0}^{1}{\overline {\psi (t)}}e^{2\pi i\nu t}dt$), or Fourier integrals like $\scriptstyle \psi (t)=\int _{-\infty }^{\infty }{\overline {A(\nu )}}e^{2\pi i\nu t}d\nu$ (where $\scriptstyle A(\nu )=\int _{-\infty }^{\infty }{\overline {\psi (t)}}e^{2\pi i\nu t}dt$), do not have well defined frequencies. Still the operator $\scriptstyle {\frac {1}{2\pi i}}{\frac {d}{dt}}$ applies to such functions, thus generalizing frequency.
4. Combining these points gives that (multiplying by) the energy $\scriptstyle E$ is identified with (applying) $\scriptstyle {\frac {h}{2\pi i}}{\frac {d}{dt}}$.
5. The differential operator $\scriptstyle {\frac {d}{dt}}$, and the multiplication by $\scriptstyle t$, do not commute: $\scriptstyle {\frac {d(t\cdot \psi )}{dt}}-t\cdot {\frac {d\psi }{dt}}=\psi$, or, isolating the operator: $\scriptstyle ({\frac {d}{dt}}t-t{\frac {d}{dt}})\psi =\psi$, or shortly: $\scriptstyle {\frac {d}{dt}}t-t{\frac {d}{dt}}=1$.
6. So time and frequency does not commute either: $\scriptstyle \nu t-t\nu ={\frac {1}{2\pi i}}$.
7. Nor does time and energy commute: $\scriptstyle Et-tE={\frac {h}{2\pi i}}$.
8. Scaling time up means scaling frequency down: if $\scriptstyle \psi (t)=\int {\overline {A(\nu )}}e^{2\pi i\nu t}d\nu$ then $\scriptstyle \psi (kt)=\int {\overline {A(\nu )}}e^{2\pi i\nu kt}d\nu$$\scriptstyle ={\frac {1}{k}}\int {\overline {A({\frac {\nu }{k}})}}e^{2\pi i\nu t}d\nu$.
9. The argument that the commutation relation $\scriptstyle \nu t-t\nu ={\frac {1}{2\pi i}}$ results in the uncertainty principle $\scriptstyle \sigma _{\nu }\sigma _{t}\geq {\frac {1}{2}}$ is complicated, but scaling up time and scaling down frequency conserves the uncertainty product: $\scriptstyle ({\frac {1}{k}}\sigma _{\nu })(k\sigma _{t})=\sigma _{\nu }\sigma _{t}$.
10. The uncertainty between time and frequency is a mathematical fact dealing with fourier transforms. Only after multiplication by planck's constant does it become the quantum mechanical uncertainty relation between energy and time: $\scriptstyle \sigma _{E}\sigma _{t}\geq {\frac {h}{2}}$.
11. The case $\scriptstyle \sigma _{E}=0,\sigma _{t}=\infty$ describes a stationary state, having well defined energy but not defining a point of time. The case $\scriptstyle \sigma _{E}=\infty ,\sigma _{t}=0$ describes a quantum mechanical starting pistol defining a point of time but having no precise energy.
12. Substituting the differential operators for the physical quantities in the classical mechanical equation $\scriptstyle E=H(p,q,t)$ (where $\scriptstyle E$ is the energy, $\scriptstyle t$ is the time, $\scriptstyle p$ is the momentum, $\scriptstyle q$ is the space coordinate, and $\scriptstyle H$ is the Hamiltonian function), produces a quantum mechanical equation, $\scriptstyle {\frac {h}{2\pi i}}{\frac {d}{dt}}\psi =H({\frac {h}{2\pi i}}{\frac {d}{dq}},q,t)\psi$ , the Schrödinger equation.

Hoping this is helpful. Bo Jacoby (talk) 22:11, 7 July 2010 (UTC).

No offense meant, but how could the above be helpful to someone who doesn't understand how you add waves? I don't mean to be glib but unless you already have extensive understanding of the mathematical methods, formulations, and concepts of QM, the above might as well be in Chinese. It doesn't illuminate anything—unless you already understand everything—and it certainly won't help the original poster. --Mr.98 (talk) 22:24, 7 July 2010 (UTC)

Point taken. The OP had two questions:

1. The probability that a particle is in a certain position is given by the amplitude of the wave packet at that point (correct?). Well, the absolute square of the amplitude, actually.
2. it must be made up of increasing numbers of sine waves added together (what does this mean?). It means that the sound of a starting pistol does not have a well defined frequency.

Bo Jacoby (talk) 08:11, 8 July 2010 (UTC).

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 : [24][25]) 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)

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 [26] and [27] and [28], 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) [29] [30]. 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 [31] [32] [33] 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)

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)

July 8

Dumb question

Where does the latent heat go? I never understood this at school —Preceding unsigned comment added by 88.104.91.80 (talk) 00:17, 8 July 2010 (UTC)

We have an article on latent heat. There are 2 most common forms of latent heat, as the article puts it: latent heat of fusion (melting) and latent heat of vaporization (boiling). The heat, or energy still goes "into" the molecules, it's just doing something to them which isn't increasing their temperature. That's the way I understand it. Vespine (talk) 01:41, 8 July 2010 (UTC)

The way that I understand it, and correct me if I am wrong, but it isn't that heat is temperature, but rather temperature is a byproduct of heat. Different materials in different forms can absorb more heat more readily. That means that they release it more slowly, therefore feeling "cooler" to the touch. Again, I am not a chemist, so tell me if my way of looking at it is incorrect. At any rate, this is not a dumb question. Falconus^{p t c} 02:38, 8 July 2010 (UTC)

If you take a block of ice, and try to crush it with (say) a hammer - break it into tiny little bits, it takes effort to do that. The smaller the bits, the more smashing you have to do, and the more energy it takes. To break it into individual molecules would take even more energy - and when you convert a solid into a liquid, you have to completely pull it apart. So (in effect) the energy is going into breaking the bonds that holds the solid material together. Only when those bonds are broken can the molecules move around enough to start gaining temperature. SteveBaker (talk) 02:52, 8 July 2010 (UTC)

Think of a gram of liquid water at 100 deg C and a gram of steam at 100 deg C. (The liquid water lies in the bottom of a teaspoon, whereas the steam fills a large sealed chamber.) The molecules of steam are widely spaced and moving at very high speed, whereas the molecules of liquid water are much closer spaced and moving at slower speed. Clearly the energy content of the steam is much greater than the energy content of the liquid water, even though they are both at the same temperature. The latent heat is the energy that must be added to the liquid water at 100 deg C to give it sufficient energy to turn into steam at 100 deg C. Dolphin (t) 03:31, 8 July 2010 (UTC)

WTF is that on your ear? AKA fleshy protuberance on the targus?

Here in China I often see people walking around with - for lack of a better word - ``growths`` just in front of their ears - basically just ahead of the targus. Sometimes they're quite small, perhaps 2~3mm tall. Other times they can exceed 1cm in length. Never in my life have I seen these outside of China. I suspect that's because other cultures remove them for cosmetic reasons? In any case, I am VERY curious what causes these growths? what they're called? etc... 218.25.32.210 (talk) 05:21, 8 July 2010 (UTC)

I think the word is tragus 86.4.183.90 (talk) 07:01, 8 July 2010 (UTC)

Is it a Preauricular skin tag? I've noticed them in China, too. Maybe it's more common to remove them at birth in the west? —Preceding unsigned comment added by 128.12.174.253 (talk) 06:10, 8 July 2010 (UTC)

Lego

I have heard that Lego blocks can be used to make even functionable robots that's with motors and all, how i's done ? Jon Ascton  (talk) 10:42, 8 July 2010 (UTC)

You would need additional parts such as motors and bearings and hinges. --Chemicalinterest (talk) 11:17, 8 July 2010 (UTC)

By using the Lego Technics ®/ Lego Mindstorms® kits. CS Miller (talk) 11:37, 8 July 2010 (UTC)

KBr (Potassium Bromide)

Potassium Bromide was called in medical education?--אנונימי גבר (talk) 13:28, 8 July 2010 (UTC)

Do you mean Kalium bromide or Kalii bromidum [34] aka Kalium bromatum or Bromide of Potash ? 87.102.42.55 (talk) 13:56, 8 July 2010 (UTC)

Are you asking "What was it called in medical education?". --Chemicalinterest (talk) 15:22, 8 July 2010 (UTC)

"Shadow Biosphere" life on earth with arsenic DNA backbone?

Last night on the program "Through the Wormhole with Morgan Freeman," this researcher found some cells in Mono Lake that could survive in an environment with arsenic levels thousands of times higher than what most life could stand. The woman sheepishly (to my ears) said it's possible the DNA backbone of the cells in question have arsenic in place of phosphorus, but she just left it at that. Isn't there a way to verify that? (P.S. I read the timesonline article sourced in the Mono Lake article about this exact scientist of whom I am speaking. I'm just surprised it doesn't seem they can verify the composition of a DNA molecule there in their petri dish. I thought we could do that these days.) 20.137.18.50 (talk) 13:53, 8 July 2010 (UTC)

from search of "DNA Arsenate" see [35] quote

The only stumbling block to the idea is that arsenic-based DNA tends to break down quickly. "You don't want to build your DNA out of a compound with a half-life in the order of a couple of minutes," points out Steve Benner of the Foundation For Applied Molecular Evolution in Gainesville, Florida

Yes arsenic can be detected accurately in molecules - but with only a few percent substitution it could be difficult.87.102.42.55 (talk) 14:06, 8 July 2010 (UTC)

ring strain in cyclic adenosine monophosphate

is it present? The skeletal structure looks funny .... does it reflect real life? John Riemann Soong (talk) 15:44, 8 July 2010 (UTC)

Haworth projection - not 3 dimensionally accurate

The Haworth projection exaggerates the angular difference between equatorial and axial bonds on the sugar structure.

The ball and stick picture is more accurate - the 6ring is standard (chair) formation, the 5 ring is standard formation too (envolope)

3d accurate image

If the question was about the ball and stick image - I think the angle chosen and blue heterocyclic structure makes the image look slighly odd- but it's not - note the two sets of rings are at right angles to each other - so the image has been projected at a slightly 'non-aesthetic' angle.87.102.42.55 (talk) 16:41, 8 July 2010 (UTC)

stimulation of exocytosis of nanoparticles by administration of 8-Br-cAMP

8-Br-cAMP is a lipophilic source of intracellular cAMP that can be added to solution. If I added some to epithelial cells (HeLa, lung cancer, etc.), should I expect gold particles trapped in vesicles to be exocytosed faster? Or would it do nothing if they hadn't reached the ER or a lysosome yet? John Riemann Soong (talk) 16:03, 8 July 2010 (UTC)

I have a point-and-shoot digital camera

It came with panasonic alkaline batteries. They used up in a day or two. OK. Then I changed them, and put brand new zinc chloride batteries, it shows "battery exhausted" even though they are brand new. Why ? Or should one only use alkaline batteries ? What's wrong ?  Jon Ascton  (talk) 16:17, 8 July 2010 (UTC)

Take an ohmmeter across the terminals in your camera. Is the resistance unusually low? 20.137.18.50 (talk) 16:38, 8 July 2010 (UTC)

No, man the zinc chloride bat are BRAND NEW, just tore the wrapper ! Jon Ascton  (talk) 16:49, 8 July 2010 (UTC)

Try some alkaline batteries again. If it works, there's your answer. If it doesn't, you've either got yourself a physical fault with the camera (see above with ohmmeter) or a software/hardware fault which would need to be inspected by the manufacturer. Presumably it's still under at least a years warranty? Regards, --—Cyclonenim | Chat  16:53, 8 July 2010 (UTC)

FWIW, I once bought a package of alkaline batteries and one of them was "dead" straight out of the package. -- Coneslayer (talk) 16:54, 8 July 2010 (UTC)