Wikipedia:Reference desk/Archives/Science/2009 September 2

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September 2

pot handle gives off vapors at high heat

Smells kinda like ammonia. One time (in a dorm kitchen), I was lacking a large enough baking pan, so I stuck a frying pan in the oven with my baked goods in it ... well then it started emitting a strange smell (I was running at about 350-400 F). The funny thing though is that the handle didn't appear to be melting, but I could tell the funny smell (reminded me of burning rubber) was coming from the handle. (must be a ppb detection thing...) Now this time, I made the mistake of switching the wrong burner on, so the burner just below the handle (but not below the pot) turned on for a good 10-20 minutes (I didn't notice until I checked on what I thought should have been boiling food). This time, it smells even stronger -- before I didn't notice its similarity to ammonia, but now I do. (I could tell it was quite hot -- I tried to take hold of the handle with a wet towel and the water became instant steam even after touching it several times.) However, I've tried sticking other pots in other ovens with no problem ... (namely pots with teflon-texture handles) .... does anyone know what sort of handles do this and what the reaction is? John Riemann Soong (talk) 00:14, 2 September 2009 (UTC)

Well, it might be Outgassing - or it might be that the substance making up the handle has a boiling point that's lower than it's melting point so when it gets hot, it goes straight from a solid to a gas (like dry ice turns into gaseous CO2 without ever being a liquid, for example) - or it might be that it's somehow decomposing and giving off reaction products as it does so without actually burning per-se - or it might be that the handle is not made of a single chemical - but a mixture - and one of the chemicals is burning/boiling and the other is not. There are a lot of possibilities here! Pot handles are obviously made to be pretty good insulators with a high specific heat capacity - so they take a long time to get hot - but once they are hot, it takes a lot to cool them off again. But we'll see if some of the resident chemists can't come up with a more specific explanation. SteveBaker (talk) 00:56, 2 September 2009 (UTC)

Possibly melamine . I'm fairly certain the 'teflon' feel handles are either nylon, polypropylene, or maybe ABS or similar - all thermoplastics - they'll melt over 200C (over 400F?) More expensive pans may use much more heat resistant plastics.

If it's melamine prolonged heat will cause it to slowly disintegrate - it tends to lose its strength and eventually disintegrates under any real force or pressure. Here's a link to prove some pans do use melamine [[1]] - it's usually recognisable because it's quite a shiny or glassy plastic as produced (vaguely lacquer like)

On the other hand it might be something completely different.83.100.250.79 (talk) 01:17, 2 September 2009 (UTC)

Thanks! I think melamine is the thing you're describing. It's glossy, kinda light and feels plasticy. Reminds me of the kind of plastics some hard bowls are made out of. Why would it release ammonia gas though? John Riemann Soong (talk) 01:33, 2 September 2009 (UTC)

Also, the handle was still very much intact. In fact, it looked quite identical in strength and feel ... except for temperature and smell of course. Would it be releasing trapped ammonia that couldn't quite be completely removed during manufacture? John Riemann Soong (talk) 01:36, 2 September 2009 (UTC)

I'm not sure - I think the resin may be decomposing a bit - half an hour in the oven probably isn't enough to substantially weaken a big bit of plastic.83.100.250.79 (talk) 02:04, 2 September 2009 (UTC)

Yep - remember, 1 mole of an ideal gas is 22 liters. If it's really ammonia that you're smelling then 17 grams is all it takes to make 22 liters - and you can smell ammonia when there is only a TINY amount of the stuff mixed into the air of a room. Ammonia is really smelly stuff - I'd be surprised if the handle lost even a tenth of a gram of mass in order to fill the room with a pretty powerful stink - a tenth of a gram is about what ten grains of sand weigh...you wouldn't notice so little material lost from the handle.

salty tastes and Cl- and Na+ ions

I came across some chlorine-containing compounds (can't remember if Cl was ionically bonded or not, but I guess the idea is that Cl- gets released) that supposedly tasted very salty, even though there was no sodium in them. This interests me ... because I thought that the salty taste would come purely from sodium cations. On the other hand, seeing as Na+ is already used for the action potential perhaps taste receptors want to use Cl- instead? If I ate a whole bunch of say, sodium acetate (yes I know it's mildly toxic), versus a whole bunch of some other chloride salt, which would taste saltier? (After normalising for moles of Cl- and Na+?) Do Na+ and Cl- have a synergistic effect? John Riemann Soong (talk) 00:48, 2 September 2009 (UTC)

I think one of the compounds that I encountered was potassium chloride. So is Cl- mainly responsible for salty taste? John Riemann Soong (talk) 00:53, 2 September 2009 (UTC)

It's the Na+ or K+ not the Cl-. See taste#Saltiness for more information. I don't know if Cl- has any enhancing effect or is just an inert counterion in this effect. DMacks (talk) 01:25, 2 September 2009 (UTC)

I can confirm that KCl tastes salty, but somewhat less so than NaCl, having tasted both sylvite and halite back in my geology days. The content of Taste#Saltiness looks plausible to me. Deor (talk) 21:48, 2 September 2009 (UTC)

Hmm yes I did read that but apparently google tells me that presence of chlorides in water (without any alkali cations) can result in a salty taste for some people ... and I also looked at this http://www.newton.dep.anl.gov/askasci/gen06/gen06166.htm. Which is more important -- the Na+ or the Cl-? John Riemann Soong (talk) 01:31, 2 September 2009 (UTC)

This is interesting - I think the Cl- is responsible for the some of the taste - the strong bitterness.

The Na is more subtle - though I think it has a saltly taste. You can test this with sodium hydrogen carbonate which is relatively non toxic (in small amounts). Sodium hydroxide has little bitterness at all - but is perceptably saltly in a vaguely 'meaty' way - don't try this at home - sodium hydroxide can burn skin , tongue etc.

There are lots of relatively safe sodium compounds you can try - the citrate, tartrate, and of course monosodium glutamate all should give a good idea of what Na+ actually tastes like.

Personally I associate the description 'salty' with the bitter effect of NaCl, though I believe that the body actually responds to the Na+ (in terms of needing rehydration/remineralisation) rather than the Cl- - in this sense it's the Na+ in salt that is attractive as a taste (instinctively), and not the Cl-83.100.250.79 (talk) 02:00, 2 September 2009 (UTC)

It's probably very conditional on what you actually consider a salty taste.83.100.250.79 (talk) 02:06, 2 September 2009 (UTC)

I've seen iodated salt (which is sodium iodide) being marketed and used as a NaCL substitute, so the salty taste must presumably come from the sodium ions? Zunaid 10:03, 2 September 2009 (UTC)

I think iodate salt contains 99% NaCl, pure NaI would be far too expensive for food use, amongst other things.83.100.250.79 (talk) 10:30, 2 September 2009 (UTC)

iodised salt was the blue linked article, you don't need that much iodine to eat pure NaI. Graeme Bartlett (talk) 11:12, 2 September 2009 (UTC)

Our article says "Two ounces of potassium iodate, costing about USD$1.15". I don't know how that price compares to sodium iodide but if the price is half, that's still US$0.625 for 2 ounces or ~56.7g according to Google. Presuming it's double the price, that's US$2.30. And that's the cost price. While not unusable for food, it's definitely expensive Nil Einne (talk) 20:19, 2 September 2009 (UTC)

~£200 per kilo for the standard NaI stuff[2] , (I can get a kilo of food grade NaCl for £0.26 !) - still not out of the range of things to buy for food - provided it's delicious... LD50 >1g/kg [3] page 5. I'm sure it would do some serious damage long before the lethal does was reached, best not to try it

Anyone know what iodide tastes like (no new original research please)83.100.250.79 (talk) 21:21, 2 September 2009 (UTC)

For KIO3 it's ~£100/kg [4] - that's from Aldrich which isn't cheap - but a long way off the new york times figure of ~$20/kg - it pays to but in bulk obviously :)

83.100.250.79 (talk) 21:29, 2 September 2009 (UTC)

Just to clarify - over 1mg/day of iodide in can cause chronic toxicity [5] 83.100.250.79 (talk) 21:47, 2 September 2009 (UTC)

Do the noble gases taste like anything? (Theoretically since they have approximately the same size as some cations and anions? (Well I suppose slightly smaller than the imitated anion and slightly bigger than the imitated cation...) I suppose without a net charge it might be hard to pass through the ion channel though (if it is made of strongly charged stuff like arginine or something). John Riemann Soong (talk) 12:48, 4 September 2009 (UTC)

I know for sure (from personal experience) that helium and argon don't have any taste whatsoever. FWiW 98.234.126.251 (talk) 05:02, 5 September 2009 (UTC)

Were you tasting the gas, or were you tasting the gas dissolved in aqueous solution? John Riemann Soong (talk) 07:23, 5 September 2009 (UTC)

I was tasting the gas stream from a pressure cylinder. But really, does it make a difference? 98.234.126.251 (talk) 09:08, 5 September 2009 (UTC)

Well the issue is that noble gases are "carrier gases" and so in a gaseous (rather than dissolved) state wouldn't be very prone to entering ion channels. John Riemann Soong (talk) 18:30, 5 September 2009 (UTC)

And I suppose a better solvent for a noble gas would be grease or something oily. Or we could have an aqueous-oily emulsification after tossing some flour in. John Riemann Soong (talk) 05:43, 6 September 2009 (UTC)

anions of -2 charge and higher

Isn't there sort of an inherent kinetic difficulty to making such anions, due to their tendency to self-decompose (and donating electrons to an already formally negative system?) Or does solvation solve (no pun intended) some of these issues? In particular I'm thinking the synthesis of ATP. How do you covalently bind two anions together (via esterification) ... I assume it's kind of hard to perform a nucleophilic attack (even if you're aided by an enzyme) on an anionic center... John Riemann Soong (talk) 04:18, 2 September 2009 (UTC)

I think in a aquous solution the anions negative charges become shielded by water molecules around them. Dauto (talk) 05:10, 2 September 2009 (UTC)

But when the ATP is synthesised by ATP synthase, I imagine that solvation significantly decreases as hundreds of amino acids displace the space where water molecules once were ... (although maybe some of the amino acids might be electropositive and compensate for the lostsolvation). Is it the positive charges that would be located on some of the amino acids? John Riemann Soong (talk) 05:21, 2 September 2009 (UTC)

Sure, water solvation decreases, but the characteristics of the amino acids surrounding the ADP > ATP reaction site makes up for it. Nucleophilic attack in such a situation would be virtually impossible if the molecule were simply in aqueous solution. The enzyme does not simply aid the nucleophilic attack, it is the essential component that allows the reaction to take place. The Seeker 4 Talk 13:56, 3 September 2009 (UTC)

Ions in solution do not repel each-other at a distance, and not at all like classical charged particles. Charges at that scale simply do not work like that; You cannot get real assessments of electro-negativities just from formal charges. Real methods are more complicated (e.g. Mulliken population analysis, and a lot of other related work by Mulliken). --Pykk (talk) 05:17, 2 September 2009 (UTC)

I suppose in solution far away ... they do not. (That is, kinetic energy + solvation allows anions to become reasonably close to each other.) But when you get separation distances of 100-150 pm or smaller... you prolly approach the level of bound quantum mechanical states with bond breaking and bond forming, electron density and whatnot, and I imagine that electron repulsion becomes very important. John Riemann Soong (talk) 05:21, 2 September 2009 (UTC)

Solved Problems in Gauss law & Columbs law

i am an engineering student i need many solved answers in Gauss law & Columbs lawmy branch is Electronics&Telecommunication

You may find the article "Gauss's law" helpful. Axl ¤ [Talk] 07:46, 2 September 2009 (UTC)

Here's one [6] Try searching the same site for coulomb questions.

The best way to find these seems to be to search for "gauss law exam question" or "coulomb law exam question"83.100.250.79 (talk) 09:20, 2 September 2009 (UTC)

Xenon octafluoride and isoelectronic species

It came up Wikipedia:Reference_desk/Science#perchlorate about the possibility of the existence of IF₈^- - I found only one unreference example on the web, and the existence of XeF₈ is also uncertain - one russian journal may have a claim to it's synthesis - but I can't read it..[7] (at least according to the results of this google search http://www.google.co.uk/search?hl=en&q=Xenon+octafluoride+synthesised++sealed+tube&btnG=Search&meta= ) Other sources give good reasons why XeF8 would not exist..

Does anyone know about the more recent discovery of either of these, maybe someone already has access to the journal above, or a big library. Thanks.83.100.250.79 (talk) 12:17, 2 September 2009 (UTC)

for octafluoroiodate there is [8] (High-coordination number fluoro- and oxofluoro-anions ; IF₆O^-, TeF₆O^2-, TeF₇-, IF₈- and TeF₈^2-) by K O Christe et al. Also there is Dictionary of inorganic compounds, Volume 7 By Jane Elizabeth Macintyre on page 503 gives it a mention too on Google books (CsIF₈ NO₂IF₈) (this one does not mention XeF₈ either). Graeme Bartlett (talk) 07:52, 3 September 2009 (UTC)

Thanks!83.100.250.79 (talk) 10:19, 3 September 2009 (UTC)

Lap Tops and Cell Phones in the next 5 years

Will laptops and cellphones merge in the next 5 years? If so, how do you think it will?--Reticuli88 (talk) 12:59, 2 September 2009 (UTC)

Maybe, but once people start getting arthritis in their fingers and especially their thumbs due to all the texting on those tiny keyboards, that might trigger a backlash. Baseball Bugs ^{What's up, Doc?} carrots 13:12, 2 September 2009 (UTC)

There is evidence that cell-phones will continue to become more and more like laptops (see iPhone and all the other various Smartphones already in market) but they are unlikely to replace laptops as they offer and realstically service quite separate functions. The lack of a Full size keyboard is a factor that makes it difficult to perform large-document Word Processing and Spreadsheet work on a mobile phone, and even with a Tablet PC with the best word-recognition software it's still going to be slower to work than anybody who types quickly (unless a form of shorthand becomes popular to increase that speed). Similarly we have seen in the past few years (with the major uptake of wireless networking) that more and more homes are purchasing laptops in place of their old desktop PC. These laptops are not used for their 'portability' in the way that business-laptops are. They are likely to be moved from room-to-room in a house, not from location to location. As a result I would expect this market to focus on features and design more than ultra-portability and battery life/robustness.

Personally I don't envisage carrying a phone the size of a laptop and I have no desire to work on a laptop the size of a phone. That said my wants and that of the general market will be largely different - I don't doubt that the huge success of the iPhone, Blackberry etc. will all increase the amount that mobiles start to perform laptop functions, but I don't see one leading to the demise of the other - just yet more integration of cross-product features/functionality. 194.221.133.226 (talk) 14:28, 2 September 2009 (UTC)

Maybe a full sized keyboard is answerable by a thin plastic keyboard that can be rolled up into a compact form. Bus stop (talk) 14:44, 2 September 2009 (UTC)

The tiny keyboard is one limitation on cell phones or even PDAs. Another is the tiny display. I suppose I could watch my streaming Netflix videos on a cell-phone, but I can't see a postage-stamp-sized picture like that being in any way comparable to one viewed on a full-sized screen. There may be some solutions to these issues, like a pair of high-def virtual reality glasses to display the images and a projection keyboard (but that, or the roll-up keyboard, would still lack the tactile feedback you get from a full keyboard). Given that these issues need to be resolved first, I'd say it will be decades before stand-alone computers begin to be phased out, if ever. StuRat (talk) 14:55, 2 September 2009 (UTC)

We can't predict whether they will converge. However, I will point out that netbooks can already connect to mobile networks. Use Skype (commonly installed as default) and a headset, and you're pretty much there already. AlmostReadytoFly (talk) 15:38, 2 September 2009 (UTC)

It would actually be trivial to install bluetooth-compatable cell phone circuitry into a laptop case and then you could use a bluetooth earpiece, and viola; you have it. I am not certain if anyone has done this, but you could certainly easily build a full-sized laptop with full cellphone capabilities; you would need to actually have your laptop nearby to use the cell phone functions, but it is very feasible... --Jayron32 21:31, 2 September 2009 (UTC)

It's likely they will continue to occupy separate though similar niches for some time. I do imagine that things like iPhones are close to being a bridge; you could imagine having a phone/hard drive that could be plugged into a full-sized keyboard and monitor at a base station, or something like that. With enough base stations in the world you could just carry your computer around with you. But that's an infrastructure thing, not a technology thing (the technology is there, there just aren't base stations all over the place). --98.217.14.211 (talk) 22:55, 2 September 2009 (UTC)

Actually, the technology would require no base stations. If you are looking for a cell-phone sized object with laptop computing capabilities, two pieces of paper would do fine; a white one which acts as a backscreen for a projector, and one with a keyboard layout for you to type on. There is already prototype technology out there to read body movements by camera and detect them; the next generation video game consoles may even incorporate this for true "controlerless" video games. Apply the same technology to your fingers, and it can, by camera, "read" what you are typing in space. A keyboard layout on a piece of paper would be all you would need to type; it wouldn't even need any communication to the cell phone since the camera would be tracking your typing. The basic technology could for such a device could probably be in place in the next decade or so; but I have no idea when a market-ready version may be ready... 20 years? --Jayron32 02:52, 3 September 2009 (UTC)

I think they can (and therefore will) merge. There are three technologies that will allow this to happen:

1. Tiny video projectors. These have already been demonstrated at cell-phone scales - they allow you to project the display onto any handy white-ish surface - such as a sheet of paper - the wall...whatever. This removes the constraint of the laptop screen size - and indeed allows you to project (albeit dimly, initially) at maybe 10' away to make a huge screen.
2. A second video projector could be used to project a picture of a keyboard - or a touch-screen or some other 'virtual' user interface onto another surface - your desktop, say.
3. A stereo camera could double as a keyboard/mouse/touch-screen interface by focussing onto the projected keyboard picture and observing where you tap your fingers. I've seen that very thing demonstrated several years ago - so that's definitely do-able. Since the keyboard is entirely "soft" - it no physical parts whatever, it can adapt to the task you want to do - flipping from a QWERTY keyboard for entering text to an old-fashioned rotary phone dial for dialling numbers - to a touch-screen - to...whatever. Tilt sensors and other gadgets would doubtless permit even weirder interfaces "beyond QWERTY".

The result could be even be much SMALLER than a present cellphone since it would not require any keyboard at all - just one "on/off" button - and no display surface whatever. The two video projectors and the camera could be fitted into a box perhaps an inch on a side - if you can squeeze the battery in that little space. It would use a bluetooth headset interface to avoid the need for a speaker or microphone. If small enough, it could perhaps even be made to clip onto a headset arrangement and project graphics directly into your eyes - using it's camera to aim and stabilize the image. This "heads up" display approach would obviate the need to find a flat surface to display onto. The stereo camera could perhaps even allow you to do simple data entry using something like sign-language when no physical surface is around to conveniently project a keyboard interface.

In the end, I think the battery is the limiting factor.

SteveBaker (talk) 03:17, 3 September 2009 (UTC)

You can get projected keyboards today. They're impossible to type on. If computers are going to ditch physical interfaces like you describe, we're going to have to radically reconsider how we enter textual data. APL (talk) 14:14, 3 September 2009 (UTC)

The crappy ones that don't work well use a single camera. You need a stereo camera to do a good job of it. The one I tried (which was a stereo device) worked - in that it could figure out where I put my finger onto the "key" - the thing that bothered me was that the keys (obviously) don't move - and that made it quite uncomfortable because your fingertips keep hitting this hard, unyeilding surface. However, I think that's something you could get used to. SteveBaker (talk) 18:17, 3 September 2009 (UTC)

The state of the art 2014 cel phone could have the power of an earlier laptop. Typing may become as obsolete as the telegraph key. The input could be by voice, with a greater accuracy than today. Semantic analysis rather than phoneme matching would help vastly. If a bigger display is needed or is a large keyboard is to be used, a fold up/rollup electric paper display could be used, or it could wirelessly couple to a keyboard, screen or printer. It is easier to have one high powered cel phone and couple it to peripherals than to carry a laptop everywhere. A docking station could be a plug-in base which charges the battery while coupling it to printer, keyboard and big screen. It could be the GPS which gives you driving directions as well as directions while you're hiking. Edison (talk) 19:14, 3 September 2009 (UTC)

What's the black stuff in my apple juice bottle?

I waited too long to recycle it. To clean it for recycling would require me to stick my hand in the bottle, but the opening is too small. How else can I get rid of the stuff?Vchimpanzee · talk · contributions · 18:14, 2 September 2009 (UTC)

Pour some boiling water in the bottle, add a squirt of washing up liquid (or a sprinkling of a bio washing powder). Put the top on and shake vigorously. Leave for a while, empty liquid out, rinse under cold tap. --TammyMoet (talk) 18:30, 2 September 2009 (UTC)

That sounds like a lot of resources for recycling one bottle. Just rinse it and recycle it. I'm sure the company has ways of cleaning the bottle that are not so wasteful of resources. 86.4.181.14 (talk) 19:08, 2 September 2009 (UTC)

Boiling water I haven't tried. Soap didn't work. The truth is they'll never know I did it. But there sure are a lot of these bottles now, and they're disgusting.Vchimpanzee · talk · contributions · 19:24, 2 September 2009 (UTC)

If the bottle is actually recycled, it will probably be first shredded and then incinerated, so any mildew will be irrelevant carbon contaminant in the final material. Such contaminants are inevitable, and I suspect your mildewy residue is a negligible contributor to the total contaminant. See Plastic recycling. Nimur (talk) 21:27, 2 September 2009 (UTC)

Usually incineration refers to the process of complete (or near complete) combustion. Plastic which is incinerated wouldn't usually be called "recycled", as it couldn't be re-used as plastic. I'm not overly familiar with the plastic recycling process, but I believe that plastic recycling usually employs melting rather than incineration; although I think there are some places which are looking into pyrolysis and syngas-based proceedures to repurpose waste plastics, however, I doubt those would technically be classed as recycling. -- 128.104.112.102 (talk) 22:35, 2 September 2009 (UTC)

Poor choice of word on my part. I didn't intend to imply anything other than melting. In any case, the residues and impurities will be melted or burned, too. Nimur (talk) 05:30, 3 September 2009 (UTC)

The trick with cleaning out any bottle is to, as TammyMoet says, put in a little soap, some (but not much) water, and to shake vigorously. I've never seen any dirt that could really withstand that kind of treatment. If it is more than that, just throw it out, it's not worth it. --98.217.14.211 (talk) 22:52, 2 September 2009 (UTC)

Well, I guess we need some more information. First, is it a glass or a plastic bottle? Secondly, is it a one-way or a returnable bottle? About the only case I would worry about the dirt is if you directly want to reuse the bottle for something. If it goes back to any commercial recycling company or bottler, they will bombard it with enough heat and chemicals to make it safe enough. --Stephan Schulz (talk) 23:14, 2 September 2009 (UTC)

Can you believe that, in all the many years of Wikipedia, with all the many articles about the intimate affairs of non-canonical Pokemons, that yet we do not have an article about (or a picture of) the humble bottle brush, a simple tubular cleaning brush with stiff tines radiating from a flexible wire rod, suitable for inserting into tight voids such as bottles, and sold in shops near wherever a man has a strange bottle calculus that proves unamenable to soap and bleach and just letting it sit there for a day with hot water in it? -- Finlay McWalter • Talk 23:04, 2 September 2009 (UTC)

The brush article on its own is a bit of a car-crash :( --Tagishsimon (talk) 23:35, 2 September 2009 (UTC)

... and if you don't have a bottle-brush, rice, or even sand, shaken vigorously with some water inside the bottle will remove any deposit. Dbfirs 00:26, 3 September 2009 (UTC)

There doesn't seem much potential for expansion beyond a dictionary entry, and it's already in wiktionary. AlmostReadytoFly (talk) 07:12, 3 September 2009 (UTC)

I suppose that the history of the bottle brush, it's construction, who invented it, different types, etc. could be covered in a WP article, if someone had the inclination to do some research. I've got no idea as to how easy it would be to find any of that stuff out - but I'd imagine that there are at least a few people out there who would be interested in reading about that sort of thing... --Kurt Shaped Box (talk) 07:19, 3 September 2009 (UTC)

I think I'd be dismayed if such a reliable source exists. It sounds worse than Lucky Jim's decision to write a paper so boring and obscure that no peer-reviewer would contradict it. AlmostReadytoFly (talk) 08:41, 3 September 2009 (UTC)

Well, I've now managed to discover that bottle brushes existed prior to 1892, as Anton Zolper's patent on an improved model demonstrates... --Kurt Shaped Box (talk) 09:16, 3 September 2009 (UTC)

This is part of a general problem that I'd sort of like to know as well. I know that in some cases recycling dirty stuff is worse than throwing it away (never recycle greasy pizza boxes, for example — you could ruin a whole batch of pulp). But there are lots of corner cases where I don't know the answer. We don't recycle broken glass because of the danger to the workers, but what about the tops to cat-food cans, which have sharp edges? How much water is it worth to get rid of the last bit of peanut butter in a glass container? That sort of thing. --Trovatore (talk) 07:38, 3 September 2009 (UTC)

Our recycling company here in Australia said don't wash bottles, they don't mind the dirt. They don't mind pizza boxes. Graeme Bartlett (talk) 07:46, 3 September 2009 (UTC)

We (in the UK) keep hearing about consignments of carefully washed recyclable material ending up in landfill sites for various reasons. How common is this? Dbfirs 09:39, 6 September 2009 (UTC)

Rigidity

It seems no matter how strong the material, when you create a long thin rod of it and hold it in the middle then the ends will sag. Is there some equation to determine how much the ends will deviate from the center assuming you know some properties of the material and the length and diameter of the rod?

And is there some super material (maybe carbon nanotubes?) that will remain perfectly rigid? TheFutureAwaits (talk) 21:44, 2 September 2009 (UTC)

They wont sag outside a gravitational fields. Nothing is infinitely rigid. The formula escapes me ATM —Preceding unsigned comment added by 79.75.114.6 (talk) 22:02, 2 September 2009 (UTC)

Would it have anything to do with a strain-stress relationship? (Could it be related to a linear coefficient?) John Riemann Soong (talk) 23:41, 2 September 2009 (UTC)

Isn't it like an upside-down three-point compression/tension relationship? DRosenbach ^{(Talk | Contribs)} 05:11, 3 September 2009 (UTC)

If you are holding two ends of the rod, the equation is the Catenary equation, often given (as in our article), by:

$y=a\,\cosh \left({x \over a}\right)={a \over 2}\,\left(e^{x/a}+e^{-x/a}\right)$

We have a whole section on this. The constant a can be expanded in terms of all the relevant physical parameters - material properties, force of gravity, etc. In this case of a very rigid material, like a short metal rod, the constants in this formulation might be problematic; other formulations can be found which are more suitable approximations for specific material properties. The equation can also be generalized in many ways to deal with (for example) a non-horizontal suspension.

Alternatively, since you asked about suspension from a single point, (holding the rod in the middle), you can model the effect as two symmetric cantilevers; the result is a similar equation but with one free end; constants will again depend on the material properties and force of gravity, etc. Displacement, y, of a cantilever, can often be expressed as a growing exponential:

$y=-Ae^{\frac {x}{\alpha }}$

but this formulation will have obvious physical limitations for sufficiently long cantilevers (i.e. they will snap before they displace by arbitrarily large amounts!) The derivation of this expression is often given in an ordinary differential equation textbook as a "trivial example" of a physical modeling problem in one dimension. Nimur (talk) 06:12, 3 September 2009 (UTC)

See Euler–Bernoulli beam equation. Red Act (talk) 06:31, 3 September 2009 (UTC)

A fairly common question here is "if you had a perfectly rigid rod one light year in length, couldn't you communicate faster than the speed of light by tapping it?", and the answer is yes, but the problem is that nothing can be infinitely rigid. --Sean 14:16, 3 September 2009 (UTC)

Surely it depends upon the speed of sound in your rod; or is that determined by its infinite rigidity? —Preceding unsigned comment added by TimeScience (talk • contribs) 00:40, 8 September 2009 (UTC)

Yes — anything that is perfectly rigid must have an infinite sound speed (so that when you hit it, it can get out of the way fast enough to maintain its shape). Of course, infinite sound speeds are disallowed by special relativity, and so SR disallows rigidity as well (which may be surprising; see also Born rigidity). --Tardis (talk) 20:26, 8 September 2009 (UTC)

impact force from braking

(Relocated from the Miscellaneous Desk. --Anon, 23:00 UTC, Sept. 2/009.)

Although I found lots of calculators and charts for hitting a barrier at various speeds what I am looking for is a calculator or chart that will show the force generated by dropping from one speed to another above zero. In other words if you slam on the brakes in a Volvo at 70 MPH and let off the breaks when your speed hits 30 MPH how much force is generated and is it enough to crash the passenger's head into the windshield? -- Taxa (talk) 18:46, 2 September 2009 (UTC)

Force = mass * acceleration. Acceleration = change in speed / time. So, if you drop 40 miles per hour in speed, it doesn't matter whether the drop is from 70 to 30 or from 50 to 10 or from 40 to 0; its the same acceleration. What needs to be known to do the calculation that you have NOT indicated is the time involved in the slow down. Does it take 10 seconds? 1 second? 0.1 seconds? That is a necessary part of any force calculation. --Jayron32 21:14, 2 September 2009 (UTC)

What you want is the Impulse. Impulse = Force * change in time = mass * change in velocity. That means that we're missing both the time interval and mass of the vehicle in order to calculate the force. ~ Amory (user • talk • contribs) 22:25, 2 September 2009 (UTC)

The force on the vehicle is irrelevant; the question is about the force on its occupants or their body parts, which depends on their own mass. In fact for this sort of thing one usually just uses the acceleration directly: a human in such-and-such a type of restraint can withstand such-and-such an amount of acceleration. Impulse is also irrelevant to the question. But as Jayron said, the time to decelerate is extremely relevant and we weren't given that. However, one would not expect the brakes of a vehicle to provide enough acceleration to smash someone's head into a vehicle unless they were unconscious as well as unrestrained. --Anonymous, 22:55 UTC, September 2/009.

Okay, lets say I'm decelerating at 15 feet per second per second so that it takes 4 seconds to go from 60 MPH to 0 MPH. At 15 FPS then an unrestrained passenger will travel 3 feet in 1/3 second. So what would the impact be (or force) of their head traveling 3 feet in 1/3 second and striking the windshield? In pounds per square inch and with an initial 2 square inches hitting the windshield how much pressure will be generated and would that be enough to cause them to die? -- Taxa (talk) 06:29, 3 September 2009 (UTC)

First of all, you're confusing your units, 60 MPH is 88FPS so an acceleration of 15FPS per second will take closer to 6 seconds to reach 0. When the car decelerates, the passenger is going to continue traveling at 60 MPH(ignoring friction) while the car's speed slowly decreases. So the speed at which the passenger hits the windshield is more complicated than you're making it, but if my back of the envelope calculation is correct the passenger will hit the windshield traveling at 0.6FPS, not enough to be deadly. The amount of force is way way more complicated, it depends on the mass of the person and how much time it takes them to stop when they hit the windshield. -- Mad031683 (talk) 17:08, 3 September 2009 (UTC)

I really think that body mass can be mostly ignored. It's acceleration that's the most important. When a sumo wrestler trips or bumps his head against the doorway I think the net pressure (measured as pain) is roughly the same as when normal people trip or bang heads against doorways. The whole body accelerates, but not all of the body mass is sent against the window. And the human body isn't a rigid object, either... John Riemann Soong (talk) 07:05, 3 September 2009 (UTC)

Two things you've not mentioned are the safety belts and the passenger's location. Is the passenger in the front seat or the back? Is the safety belt fastened; and if so, how strong is it? Nyttend (talk) 00:40, 4 September 2009 (UTC)

No safety belts and passenger in front seat probably crying with head head facing down in hands. Then wham. -- Taxa (talk) 01:30, 4 September 2009 (UTC)

calculating the BPs and MPs of pure perchloric acid

Has this been found out? Google is being really annoying and keeps returning me all these 60-70% solution results. I mean, I imagine measuring the BP or MP of 100% perchloric acid would be dangerous ... but it's something you could do behind a blast screen or with a glovebox. It forms a negative azeotrope with water, right? Could we do various extrapolative techniques? What's the dipole moment of perchloric acid compared to sulfuric acid? (I can't find this easily...) Should we expect that perchloric acid's anhydrous BP be lower or higher than water's? John Riemann Soong (talk) 23:34, 2 September 2009 (UTC)

I can't find the data either.

The way to find the boiling point would be to find the boiling points at low pressures (lower boiling points) - because it seems certain that perchloric acid will decompose before it boils at atmospheric pressure.

The situation may be complicated by this equilibrium [9]

3 HClO4  <<<>>> Cl2O7 + H3O+ClO4-

Basically the anhydrous acid is unstable with respect to the monohydrate and the oxide (the oxide has a low boiling point)

If you know the boiling point at two temperatures (of the heat of vapourisation and one boiling point) - you can use a formula to extrapolate (fairly well) the boiling point at another pressure. There's an equation in Boiling point / Clausius–Clapeyron relation

As a guess the boiling point of the pure acid would be greater than water , just by its mass. Compare anhydrous nitric acid - which has one H for hydrogen bonding, and a lot of oxygens which boils at 83C, I'd expected anhydrous perchloric acid to boil at a higher temperature - maybe 110-120C???

I can't find any dipole moment data (probably because of the difficulties with working with it), it should be similar to sulphuric acid in the overal scheme of things.83.100.250.79 (talk) 10:16, 3 September 2009 (UTC)

Anhydrous perchloric acid appears to be quoted as freezing at -112C http://www.google.co.uk/search?hl=en&q=melting+point+anhydrous+perchloric+acid&start=10&sa=N

Heres one data point for the BP

pure anhydrous compound can be prepared by vacuum distillation as a colorless liquid, which freezes at -112C and boils at 16C at 2.4 kPa (18 mm Hg) without decomposition[10]

Staring at black and gray object for a looong time without blinking

Will desaturation happen if I stare at black and gray object for a day without blinking. Will white surface look differnt color if i look at black and gray stuff for 24 hours? Will whole color system change? Will I not notice black and gray stuff?--69.226.35.110 (talk) 23:51, 2 September 2009 (UTC)

You can't possibly stare at anything for more than a minute or two before you'll reflexively blink. But even in that short period of staring at some colored object, turn away and look at a contrasting surface, and you'll likely see an afterimage of some kind. Baseball Bugs ^{What's up, Doc?} carrots 00:51, 3 September 2009 (UTC)

A basic "Training Drill 0" exercise done by scientologists is to stare without blinking for many minutes, reputedly hours. If you dare blink your watcher calls "Flunk!" and you have to start again. I managed about 5 minutes. Cuddlyable3 (talk) 06:36, 3 September 2009 (UTC)

(ec) IANAD nor an eyesight specialist but, in order: No, No (not for very long), No, Yes. ~ Amory (user • talk • contribs) 00:54, 3 September 2009 (UTC)

You may want to read Color vision and Adaptation (eye). The adaptation processes in the eyes proper happen on the time-scales of milliseconds, seconds, or minutes. Changes on a longer time scale mostly happen on later stages of visual processing, that is, in the brain. Looking at a gray-scale object engages neither the retinal nor the cortical mechanisms of color adaptation or color constancy, so gray stays gray. However, looking at a stationary object and not shifting the gaze (not even by a few arc-minutes) for a sufficiently long time will make the object "invisible" to your brain, even though its image is still captured by the retina; see Stabilized images. This requires a sophisticated setup, though. Simply looking at an object for very long won't make it invisible for you, as your eyes keep moving (head movements, microsaccades, drift, etc...) even as you try to maintain fixation at a certain point. On the other hand, staring at a complete darkness for too long (days or more) will eventually cause your visual cortex to ramp up its gain, trying to pick up the whatever weak signal that may be reaching the retinas. This will result in magnification of the "electric noise" (spontaneous activity) of the retinas and the visual thalamus, and may lead to an effect called "Prisoner's cinema". --Dr Dima (talk) 01:33, 3 September 2009 (UTC)

Well, I don't know about 24 hours - but you've personally stayed in a dark room for 8 to 10 hours with your eyes shut almost every day of your life. Did you notice yourself being unable to see black objects after you woke up? No? I didn't think so. SteveBaker (talk) 12:00, 3 September 2009 (UTC)

Moon to survive without earth

Will sun becomes a giant in 5.5 billion years. if Earth gets swallow up is this possilbe Moon will survive. If moon is moving away from earth, then is this possible for moon to become a planet? moon will just be superheat though--69.226.35.110 (talk) 23:53, 2 September 2009 (UTC)

Sun#Life cycle says that it is likely the Earth will indeed be swallowed by the expanding Sun, so the Moon will likely follow, especially as it is often closer to the Sun than Earth. And yes, it will be superheated. The odds of it becoming a planet are extremely unlikely, but theoretically possible if all the perfect massive interactions happened, presumably with asteroids altering its orbit. ~ Amory (user • talk • contribs) 00:46, 3 September 2009 (UTC)

Not quite, if the earth were swallowed up by the sun, the moon would be too. When the earth is swallowed up it does not cease to exert a large gravitiational force on the moon, and so the moon would be unable to escape without some kind of colossal intervention from an outside body. Elocute (talk) 10:32, 3 September 2009 (UTC)

When the Sun turns into a red giant it will be extremely thinly spread out, so planets that end up inside it won't be instantly destroyed. There will be lots of drag on the Moon as it orbits the Earth so it will pretty soon end up crashing into the Earth. While the Moon is moving further away from the Earth it is doing so very slowly, it won't be a significant distance further away by the time the Sun dies. --Tango (talk) 18:37, 3 September 2009 (UTC)