Science desk
< July 20	<< Jun \| July \| Aug >>	July 22 >

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

July 21

Iron magnet

Where can I buy a 10kg, magnetized chunk of iron? Thanks, *Max* (talk) 01:26, 21 July 2008 (UTC).[reply]

Why not magnetize iron with a strong rare earth magnet or by making it an electromagnet? --Bowlhover (talk) 10:02, 21 July 2008 (UTC)[reply]

Yeah its going to be much easier to magnetise a large lump of iron your self rather than obtaqin one. Just wind lots of wire round the iron and pass electric current thro it from a car battery say. —Preceding unsigned comment added by 86.130.138.231 (talk) 14:28, 21 July 2008 (UTC)[reply]

That said, you want to take safety precautions like making sure not to short the battery. Theres about a thousand different things that could go wrong in this process. If you are not an expert, please make sure to consult with one before doing anything crazy. In particular, do NOT short the battery in order to get current through the wire. EagleFalconn (talk) 14:56, 21 July 2008 (UTC)[reply]

It's not that likely that someone will be selling one. Firstly for magnets other things often get used in preference including ferrite (iron oxide).

Buying 10 kg of iron is relatively simple though. Was there any particular shape. If you just want a magnet with iron and other things in that should be possible, though 10kg is a big magnet.87.102.86.73 (talk) 19:05, 21 July 2008 (UTC)[reply]

meh, a car battery isn't going to do much harm. Shorting circuits is generally a bad idea, but car batteries don't have enough juice to really do damage. Plasticup ^T/C 19:11, 21 July 2008 (UTC)[reply]

That's dangerously wrong. The amount of energy in a car battery is up in the megajoules, which is plenty to start a fire or make a small object dangerously hot. See http: //www.popularmechanics.com/automotive/how_to/4213127.html for an example. --Anonymous, 22:06 UTC, July 21, 2008.

I know how to magnetize it, but where can I get 10 kg of iron? *Max* (talk) 21:24, 21 July 2008 (UTC).[reply]

Check your phone book for local businesses that do custom metal work. You can get solid square bars of metal in any size you need. ---J.S (T/C/WRE) 21:32, 21 July 2008 (UTC)[reply]

An educational supply business may be able to sell such a magnet. Back in school I remember a U shaped magnet that was pretty strong. When you dropped an aluminum plate between the poles it would only fall about 1 mm per second due to eddy current damping. Graeme Bartlett (talk) 01:46, 22 July 2008 (UTC)[reply]

Consider hiring someone to magnetize a hunk of iron of the specified mass using an electromagnet. That is how magnets are created in recent centuries. Edison (talk) 04:30, 22 July 2008 (UTC)[reply]

To make a powerful electromagnet, you should use a U shape or a disc shape, so that both poles can be applied to the thing you wish to lift, or to the area where you want the powerful magnetic field. The density of Iron is 7.874 g·cm⁻³, so you need a volume of 1270 cm³. If you could find iron bars for sale, you could take three pieces to form the core into a U shape, and bolt them together, allowing three coils to be slipped over the core on the two legs and the top. Any length of core which is not being magnetized by a coil will decrease the pull of the magnet. What you are likely to find comercially available today is not Wrought iron such as Michael Faraday used to create the first strong electromagnets in the 1830's, but Carbon steel. You should review the magnetic properties of the various forms of iron, because they differ in the intensity of magnetization the accept and retain. soft iron, like a nail, quickly loses its magnetisation, while "hard" ferrous materials retain their magnetisation better. If you are building an electromagnet, you need a material which becomes demagnetised when the current is switched off. If you wish to magnetize the iron and create a permanent magnet then a "hard" ferrous material or modern rare earth magnetic materials would create a strong, long lasting magnet. If you just literally want a 10kg chunk of magnetized iron or steel, you might buy a big sledgehammer and magnetize it with a coil which can be slipped aroung the head of the sledge after the handle is removed. A sashweight is another big hunk of iron which could be easily magnetized, but a bar magnet will not be as strong as a pot or U magnet. You could also take an old transformer remove part of the core, and use the rest as an excellent electromagnet, but a weaker permanent magnet, due to the type of iron used. A machine shop might have scrap pieces of iron bar or rod they would sell at a bargain price. An ag=ngle or I beam would be undesirable since a coil would not fit well around it. Edison (talk) 16:50, 23 July 2008 (UTC)[reply]

Microwave oven

Can someone explain briefly (without too much technical or scientific lingo) why you can't place metal / aluminum foil / etc. in a microwave oven ... and what exactly would happen if you do? Also ... why is it that food tastes "different" when cooked in a microwave oven versus a conventional oven? Thanks. (Joseph A. Spadaro (talk) 02:48, 21 July 2008 (UTC))[reply]

See Microwave_oven#Dangers for the answer to your first question. The short-short version is that a piece of metal will act like an antenna, converting the microwaves into electricity. Depending on the shape, size, etc of the metal, that can cause various problems. Metal twist-ties often catch on fire, for example. APL (talk) 03:19, 21 July 2008 (UTC)[reply]

Fixed link. StuRat (talk) 03:26, 21 July 2008 (UTC)[reply]

That's interesting. Hmmmmmm. Do we have any technology that takes advantage of this phenomena of metal turning microwaves into electricity? ScienceApe (talk) 03:37, 21 July 2008 (UTC)[reply]

Sort of. Obviously making microwaves then converting them back to electricity would use more energy than it would produce. However, special metallic foils are used under food to absorb microwaves and turn them into heat, to toast the food from underneath. StuRat (talk) 03:45, 21 July 2008 (UTC)[reply]

There are also various plans (and when I say plans, I mean vague ideas that may or may not have had a 1/10,000 scale prototype made so far) to do things like power spacecraft with microwave lasers, or use microwaves to "transmit" electricity without wires - see microwave power transmission. Confusing Manifestation(Say hi!) 04:16, 21 July 2008 (UTC)[reply]

But a simpler answer to the question of whether we have technology taking advantage of this effect is the antenna used by every radio receiver, every TV set not connected to a cable system, every satellite dish, and so on. Without it, radio and TV broadcasting would be impossible. --Anonymous, 04:21 UTC, July 21, 2008.

A more obscure application of the fact that microwaves heat metal is hobbyist metalworking (see http://home.c2i.net/metaphor/mvpage.html). --Bowlhover (talk) 07:19, 22 July 2008 (UTC)[reply]

We don't have an article on it, but microwave sintering is a way to custom-form metal parts from metal powder and microwaves. --Carnildo (talk) 23:57, 21 July 2008 (UTC)[reply]

As for why foods taste different, there are many reasons. One is that the air doesn't heat up in a microwave oven like in a regular oven. This means the surface of bread doesn't dry out, for example. That's good if the bread was stale already but not so good if it was soggy. Another diff is that foods often cook for different lengths of time. Longer times allow flavors to blend more. StuRat (talk) 03:31, 21 July 2008 (UTC)[reply]

There are some interesting experiments with microwave ovens which I have seen on You Tube that take advantage of the fact that when a match is lit and covered with a glass inside a microwave the burning gases act like a conductor. Placed in a microwave oven the microwaves then react with burning gasses to form a plasma in a very spectacular fashion. -- adaptron (talk) 07:28, 21 July 2008 (UTC)[reply]

See Ball_lightning#Laboratory_experiments subtitle 'Home microwave oven experiments' for more on this. --Ayacop (talk) 07:59, 21 July 2008 (UTC)[reply]

One of the reasons why food tastes different is the lack of 'browning' - microwave ovens use a lot of quite low energy waves - (lower energy than that given off by a heat lamp) - but uses massive ammounts of them - it's a bit like cooking with massive amounts of tepid water (very poor analogy) - because the energy is low it does not cause burning/browning - a bit like steam cooking.

High energy cooking such as using a pan, or oven causes more chemical reactions to occur eg see Caramelization, also maybe look at Maillard_reaction - these reactions cause a change in constitution that gives a different taste.

87.102.86.73 (talk) 09:10, 21 July 2008 (UTC)[reply]

Here is an article detailing the reason microwaved foods taste different. According the to webpage, the temperatures and cooking times involved in microwaving are insufficient for the Millard reaction to occur. Because of this, foods cooked in conventional ovens have greater quantities of volatiles associated with pleasant flavours and less undesirable substances. --Bowlhover (talk) 07:19, 22 July 2008 (UTC)[reply]

Will doing that match thing damage the microwave? 61.69.141.209 (talk) 10:36, 21 July 2008 (UTC)[reply]

Yes, according to the WP link I gave above. Don't try this at home. --Ayacop (talk) 10:39, 21 July 2008 (UTC)[reply]

Apparently, the "plasma" also releases not-too-healthy gases, like NOx, which can be really bad to breathe in. -- Aeluwas (talk) 11:54, 21 July 2008 (UTC)[reply]

Wind vortex experiment

Does any article describe or point to a reference of an experiment in which a large diameter axial fan was setup in the vertical and turned at high speed for the purpose of generating a vortex to serve as a typhoon or a hurricane "seed"? -- adaptron (talk) 07:21, 21 July 2008 (UTC)[reply]

Well, a hurricane is out of the question. Their spin is a consequence of the Coriolis effect, not a requirement for formation -- much less issues of scale. A vertical fan is also the wrong method of formation for a tornado, which originate from horizontally-inclined mesocyclones. Of course, the incorrectness of the approach doesn't preclude somebody from conducting an experiment anyway. 199.209.144.218 (talk) 12:43, 21 July 2008 (UTC)[reply]

Skin Bleaching

Started to read a new trend of anal bleaching but was not able to locate any legitimate medical articles on the procedure and the safety of this. Does anyone have any info or links for me? I don't know exactly what chemicals are used or any long term effects of this? .....you can start laughing now..... --JennaHunter (talk) 13:15, 21 July 2008 (UTC)[reply]

I would certainly expect it to be painful and result in swelling. I'd expect that fasting before the procedure might be in order to reduce the...err..."use" of the area following the procedure. Perhaps only bleaching a bit at a time might be safer, but whole area bleaching is probably done, too. StuRat (talk) 13:37, 21 July 2008 (UTC)[reply]

I've heard of people on the radio talk about adult entertainers getting it done, but other than that, I know nothing about it. --Wirbelwindヴィルヴェルヴィント (talk) 14:40, 21 July 2008 (UTC)[reply]

err....are you sure they're bleaching skin and not hair? --Shaggorama (talk) 14:42, 21 July 2008 (UTC)[reply]

Definitely. Last week there was a report in German TV about a shop in China that offers the service. Of course, their formula is kept secret. --Ayacop (talk) 07:51, 22 July 2008 (UTC)[reply]

There's an article for anal bleaching, but it's just a stub. APL (talk) 14:54, 21 July 2008 (UTC)[reply]

How about a tattoo instead. I suggest one on your butt cheeks that says "If you're close enough to see the color of my anal sphincter, you're too damn close !". StuRat (talk) 21:30, 21 July 2008 (UTC)[reply]

Or "almost close enough", of course, depending on your proclivities. -- Captain Disdain (talk) 08:24, 22 July 2008 (UTC)[reply]

Shallow seas

How deep do a scientist consider shallow seas to be? —Preceding unsigned comment added by 68.11.112.100 (talk) 15:18, 21 July 2008 (UTC)[reply]

Depends on the context. If your talking about a global-view, then anything anything above the contentnal shelf... ~300feet. If your talking about a local ecological view then either (1.) anything above the thermocline (~30-50 feet) or (2.) anything in the zone where sun-light is a major factor (~150feet). Of inteses might be: Intertidal zone, Littoral zone and surf zone. 63.80.111.2 (talk) 17:30, 21 July 2008 (UTC)[reply]

General usage amongst geologists interested in modern and ancient sedimentary environments is that waters are shallow up to about 100m, but it doesn't seem to be something that is rigorously defined. Mostly shallow water is used for areas of the continental shelf as opposed to the continental slope or abyssal plain. Oceanographers may well take a different view. Mikenorton (talk) 17:38, 21 July 2008 (UTC)[reply]

Stability of bikes with different wheel-sizes

My father and one of his oldest friends have been debating an issue of physics ever since they where in their early teens. They both got bikes when they were 13 or 14 and they (naturally) started arguing which one was better. My father's bike had bigger wheels, so he argued that it's more stable. Since the wheel is bigger, the gyroscopic effect of the spinning should be bigger, my father thought. His friend, as young boys are want to do, passionately disagreed. He argued that if the bikes are travelling at the same speed, his wheels will spin faster, thus eliminating any advantage my fathers bike might have had. it's now 35 years later, and the issue still haven't been settled.

He asked me, and I told him only the very basic stuff I know, that the gyroscopic effect depends on the angular momentum of the wheel, which does increase with the size of the wheel. However, I haven't studied physics for years and years, and I can't even come close to figuring out whether the faster rotation of the smaller wheel will be enough to outweigh the longer radius of the larger wheel. I suspect this comes down to an issue of mass, since the larger wheel presumably have more mass, it will win out. But what if the two wheel had the same mass (the smaller one is denser, or something)?

Can you fine folks please settle this long-running dispute? 83.188.199.140 (talk) 16:32, 21 July 2008 (UTC)[reply]

I don't think gyroscopes have anything to do with it. See http://www2.eng.cam.ac.uk/~hemh/gyrobike.htm . 91.143.188.103 (talk) 16:52, 21 July 2008 (UTC)[reply]

I'd say the larger wheeled bike would have a greater rotational inertia, since that's related to the square of the radius, not just the radius. That, in turn should provide more gyroscopic effect. However, I disagree that the gyroscopic effect is all good. While it helps maintain stability while going straight, this also makes turns more difficult, requiring you to slow down more to turn. StuRat (talk) 16:57, 21 July 2008 (UTC)[reply]

We have an article on Bicycle and motorcycle dynamics. -- Coneslayer (talk) 17:36, 21 July 2008 (UTC)[reply]

The moment of inertia, according to StuRat, varies according to r² - since the angular velocity in this circumstance varies according to 1/r, the larger wheeled bike will "win". --Random832 (contribs) 18:44, 21 July 2008 (UTC)[reply]

The larger-wheeled bike will be more gyro-stablilized. That doesn't mean it will be more stable -- gyro-stabilization is a fairly negligible contributor to keeping the bike upright. The more important number to look at is something called trail -- see the article Coneslayer pointed to. --Trovatore (talk) 20:50, 21 July 2008 (UTC)[reply]

A minor point to consider: IMO the moment of inertia should vary as r³, since we can probably assume the mass is concentrated at the circumference and the mass per unit length of the circumference is the same for both sizes of wheel. Therefore, m will vary linearly with r, so mr² will behave, to within the approximations, like r³, so the larger wheel wins by more. —Preceding unsigned comment added by 91.143.188.103 (talk) 15:43, 22 July 2008 (UTC)[reply]

If having bigger wheels is what makes a bike better, how come penny-farthings are so rare? — DanielLC 16:13, 22 July 2008 (UTC)[reply]

They've got other problems. --Carnildo (talk) 20:41, 22 July 2008 (UTC)[reply]

POPCORN EFFECTS ON INDIVIDUALS WITH TYPE 2 DIABETES, INSULIN DEPENDENT?

HELLO;

I'VE CANNOT FIND YES OR NO ANSWERS AS TO, HOW POPCORN EFFECTS TYPE 2 DIEBETICS. IS IT HEALTHY? —Preceding unsigned comment added by 68.10.6.240 (talk) 16:48, 21 July 2008 (UTC)[reply]

[Discussion removed]

Please do not ask for medical advice on the reference desk; consider talking to your doctor. --Random832 (contribs) 17:13, 24 July 2008 (UTC)[reply]

Fan blades and turbine blades

Why are fan blades and wind turbine blades generally very different shapes? Fan blades (such as from a desk fan) are frequently much larger and more "dish" shaped that turbine blades, which are usually thinner and more wing-like.

I would have thought that if both designs were aimed at maximizing efficiency, where efficiency is either most wind per Watt or most Watts per wind, that the two blades would look quite similar. No? — Sam 17:20, 21 July 2008 (UTC)

They are used in different ways. See turbine for more details about why they are shaped the way they are. Also, when your dealing with a desk-fan, the efficiency is much less important then a turbine. ---J.S (T/C/WRE) 17:33, 21 July 2008 (UTC)[reply]

There are two issues with "efficiency". In one case (a desk fan), the most efficient fan is the one which can be produced in mass quantities, very cheaply, and complete the job of moving enough air to make the user feel good. In a wind turbine, the most efficient turbine is the one which moves the most amount of air using the least amount of power (or produces the most amount power given some standard amount of wind). As such, a desk fan usually has blades that are cheaply cut out of sheet metal and cheaply formed into a scoop on a mechanical press. A turbine will use much better materials and designs. -- kainaw ™ 17:37, 21 July 2008 (UTC)[reply]

Seeing as no one has explicity said it - a fan blade and a turbine blade that operate under the same conditions should/could be exactly the same shape.

Turbine blades may be thin because they operate under extreme conditions and so need to be flaw free.. making a continuous fan shape flaw free is harder than making a lot of smaller blades flaw free.

Also using a lot of blades allows the depth of the fan to be reduced - a continuous blade would have more depth - this may be important in enclosed things.

Interestingly the turbines in water generation plants are much more like fans than their counterparts in gas turbines/jet engines eg see Francis turbine, here you might be able to guess why a single piece turbine is favourable (or just easier) over a multibladed one. I particularily like these images:

(Note however that this type of turbine does have linear flow, it's centrifugal..)87.102.86.73 (talk) 18:51, 21 July 2008 (UTC)[reply]

Note that the OP is asking specifically about wind turbines, not turbines in general. -- Coneslayer (talk) 18:58, 21 July 2008 (UTC)[reply]

Oh in that case one of the factors is also that in a fan the air is started from almost zero velocity, and it doesn't have to surive high winds.. Also such a fan could not have the pitch of the blades easily altered. For a wind turbine the opposite is true - the air/wind can be many speeds and so it is useful if the pitch of the blades can be altered - this is easier with narrow blades, it is still possible with thicker blades - but these will also cause more force on the turbine support in high wind - there's a safe limit at how much sideways force can be put up with on the turbine support.

I think it's easier to see why a typical fan would be totallly unsuitable for high winds, rather than explaining exactly why the wind turbines have blades of a certain dimension.87.102.86.73 (talk) 19:11, 21 July 2008 (UTC)[reply]

Fan blades are not the shape they are just because the shape is cheap to make. Aerodynamic studies in the 1930s, for starters, led to redesign to reduce the noise they made. The basic shape of the individual blades was altered and noise was reduced. I am sure that the science of fan making has continued apace to get the most air moved as quietly as possible for the least energy charge, beside the cost of fabrication. Edison (talk) 19:12, 21 July 2008 (UTC)[reply]

Also the long thin shape of wind turbine blades is less succeptable to cross winds than and smaller thicker design. And house fans need to be compact, so a long thin design is impractable.87.102.86.73 (talk) 19:41, 21 July 2008 (UTC)[reply]

Thank you all very much for the great answers! Here's what I'm taking away, correct me if I've misunderstood: Under the exact same conditions, what would be efficient for a fan would also be efficient for a wind turbine. However, 1) The conditions are not the same, and 2) efficiency is not the only factor, and is of much lower importance for desk fans than for turbines. — Sam 20:10, 22 July 2008 (UTC) —Preceding unsigned comment added by 63.138.152.238 (talk)

Recycling, is it a stupid thing to do?

I recently watched an episode of bullshit on recycling and they said it was more expensive and also more environmentally destructive, do you have any data about it? 88.203.106.28 (talk) 19:56, 21 July 2008 (UTC)[reply]

Did you look at the recycling article? It would be interesting to know what examples were given in the show you saw. Recycling#Criticism offers some examples of dubious benefits.

It's cost effective and more environmentally friendly to recycle aluminum cans to obtain aluminum than to mine and smelt aluminum ore to get the same material. Same is true for paper; in fact paper mills recycle their own cuttings when trimming the sheets to size, because it's already paper, not wood pulp that needs mashing and bleaching. The list goes on; it's easier to get glass from other glass than to process raw sand to get glass. Generally, if you need a material and must either make it from raw materials (including the effort needed to mine the raw materials), it's environmentally and financially sound to get what you want from materials that have already been made.

Mind you, there are misguided environmental practices out there. Making ethanol from corn comes to mind as a particularly wasteful practice that consumes more energy than it produces. But that isn't really a recycling issue. ~Amatulić (talk) 20:04, 21 July 2008 (UTC)[reply]

Ethanol fuel energy balance shows disagreement. PrimeHunter (talk) 20:44, 21 July 2008 (UTC)[reply]

Yes, although the studies showing greater than 1:1 efficiency seem to rely on accounting tricks. Nevertheless, perhaps I should have said instead that corn is one of the least efficient sources of ethanol compared to other sources. ~Amatulić (talk) 21:30, 21 July 2008 (UTC)[reply]

My favorite criticism is that corn-based ethanol policies are mass-murdering with intent that borders on genocide. But hey, that's just me. I'll get off this soap box now. Plasticup ^T/C 16:33, 22 July 2008 (UTC)[reply]

I'd say it would depend on what is being recycled and how. Probably the most efficient recycling is composting rotten food to make good soil. All that is required here is to separate out the rotten food, dump it in a pit, and leave it to rot. There are some other things that can be done to speed up the process, like introducing bacteria, worms, and water, stirring the contents periodically, and venting off gases to keep it cool. Since the methane recovered also has value, this can all be done quite cheaply. The least efficienct recycling may be on small electronic devices which must be manually broken down into different components and separated, at great cost, only to produce tiny quantities of reusable material. StuRat (talk) 21:21, 21 July 2008 (UTC)[reply]

Of the 3Rs of environmentalism recycling is the least desirable. Reduce, Reuse and THEN Recycle. ---J.S (T/C/WRE) 21:27, 21 July 2008 (UTC)[reply]

I've read that recycling glass actually does not work out to have an environmental benefit. I can't back that up with science or citations, but I find it plausible. Apparently you need the same amount of energy to remelt glass as you do to make it. Then you have to add in sorting out the trash that comes in with the recycling and the fuel for the truck that drives around to every house picking it up. Of course this neglects that fact that recycling diverts glass from landfills. ike9898 (talk) 22:06, 21 July 2008 (UTC)[reply]

Hmm, Glass recycling contradicts that, as do the sources it uses, and stuff like [1]. So well, meh. But it certainly can be the case that recycling can be uneconomic. I hear plastics recycling is supposed more dubious, though again I can't back that up with science or citations, but I find it plausible. ;) --Fangz (talk) 22:30, 21 July 2008 (UTC)[reply]

It does depend. Recycling glass in the process-engineering sense of recycling is a pretty fantastic thing to do, and one of the best examples is milk bottles if you've got a milkman. The bottles go round and round the system with only a little cleaning required, and this is efficient in terms of energy and raw materials, as well as avoiding sending waste to increasingly unavailable landfill. This is called 'reuse' in lay-speak. Generally 'reusing' things in this way is very good. If the glass has been seperated by colour, and you have someone willing to use the product, then melting broken glass down and making it into new things is also pretty good, but not nearly as good as just using jars and bottles again as jars and bottles. This is reusing the glass, but is referred to as 'recycling' in lay-speak. Not nearly so good is if you've been given a load of different types and colours of glass, some of it broken, and told to deal with it cheaply in a way that doesn't involve landfill. So you crush it down into aggragate and try to sell it to be used as decorative covering for the ground. This takes something which a lot of energy has gone into making into jars and bottles and turns out glass gravel. So these things all depend. 79.66.124.253 (talk) 17:17, 22 July 2008 (UTC)[reply]

Isn't that list supposed to be read in order anyway? Reduce THEN reuse THEN recycle. In other words you reduce usage whenever you can, what you can't you try to reuse and if you really can't reuse it then recycle it. Nil Einne (talk) 21:09, 26 July 2008 (UTC)[reply]

I wonder if instead of newspapers and bottles, it wouldn't be better to have curb-side recycling of items like batteries, and electronics, and fluorescent light bulbs. ie: Things are laden with chemicals we'd rather not have in landfills. APL (talk) 02:31, 22 July 2008 (UTC)[reply]

Here in Bermuda we aren't big enough to support our own recycling plant. We have to ship our recyclables across the Atlantic Ocean to foreign recycling plants. I really have to question whether it is worth it. Plasticup ^T/C 16:35, 22 July 2008 (UTC)[reply]

When figuring out the economic cost-benefit ratios of recycling one should remember to take into account the long-term costs involved with raw material extraction (mining, logging, etc). The costs involved are not only the short-term direct cost to the company doing the extraction, but long-term environmental costs. The latter costs are often ignored in cost-benefit calculations, but over time can, in many cases, grow to large amounts, and frequently after the company that did the extraction and environmental damage no longer exists or is bankrupt, leaving the costs to be paid for by the public. Aluminum is a great example. The cost of cleaning up bankrupt aluminum smelter sites in the US, paid for by taxpayers, is enormous. So don't forget to add such things to the cost side of calculation. Pfly (talk) 07:15, 23 July 2008 (UTC)[reply]

Lifecycle assessment is something we need an article on. Maybe next week... Another thing that's important to bear in mind is what you do with something if you don't recycle it. Certainly in the UK we are physically running out of landfill, so you have to find something to do with your waste. 79.66.124.253 (talk) 19:26, 23 July 2008 (UTC)[reply]

Usually, the way things work is that transporters use waste for recycling to take up empty cargo space on the return leg of their voyages. So it's usually not as bad as you think.--Fangz (talk) 18:10, 25 July 2008 (UTC)[reply]

Sugar water wine

Is it true that one can make wine out of refined sugar and water? I'm not supposing that the result would be any good, I'm just wondering if it would be wine.

Duomillia (talk) 20:30, 21 July 2008 (UTC)[reply]

In my view, no, because it's not made from fruit. (I don't consider sake to be wine, either.) But it's all in how you use the word, I suppose. --Trovatore (talk) 20:32, 21 July 2008 (UTC)[reply]

Not just those two things, no. There needs to be some yeast or other microbes to digest the sugar, and they will need more than just sugar and water to live on, as they can't grow and reproduce without a few other things. Then there is always the question of whether an alcoholic beverage qualifies as "wine" or not. StuRat (talk) 21:11, 21 July 2008 (UTC)[reply]

I assume the OP assumed the use of yeast. The answer is yes, you can make a semblace of "wine" from sugar water and yeast. Try it. That's basically how rum starts out. Or mead in the case of fermenting honey and water. In most western countries it wouldn't qualify as a "wine" but in other countries such as China, the term "wine" has much broader application, and your fermented sugar water would qualify. ~Amatulić (talk) 21:17, 21 July 2008 (UTC)[reply]

If it was relatively pure sugar and water, the yeast would peter out very quickly. They certainly need a nitrogen source and some trace minerals. There would be a little of these carried over in the yeast innoculum, but not enough. ike9898 (talk) 22:02, 21 July 2008 (UTC)[reply]

Perhaps not enough to ferment the wine to completion, but enough to make an unstable, low alcohol sugary wine, yes. If the use of the word "wine" is not legally regulated in your jurisdiction to require the use of grapes (EU). Rmhermen (talk) 23:00, 21 July 2008 (UTC)[reply]

There's a traditional Finnish alcoholic beverage called kilju that's made with sugar, water and yeast, manufactured mostly by teenagers (in secret, naturally) and serious-minded career drinkers conscious of the constant economic pressures they face. Copious vomiting and crapping yourself are only some of the benefits bestowed by this wonderful drink that is usually miraculously foul-tasting. I heartily recommend it to any and all who feel that there just isn't enough embarrassment and diarrhea in their lives. -- Captain Disdain (talk) 08:21, 22 July 2008 (UTC)[reply]

I remember something very similar though I couldn't possibly describe as 'wine'.87.102.86.73 (talk) 08:51, 22 July 2008 (UTC)[reply]

If it is of interest, we have an article on non-grape based wine. Plasticup ^T/C 16:28, 22 July 2008 (UTC)[reply]

Another question about wind farms

Current wind farms show a very small percentage (1%?) of the rotational area being used to generate energy at any time - is there a reason for this? (is noise a factor?)87.102.86.73 (talk) 20:59, 21 July 2008 (UTC)[reply]

Seems to me like 1% is about the ratio of blade area to rotational disc area. In that case, you may as well ask why airplane propellers use such a small fraction of the disc area for thrust? The answer is likely the same: the additional mass and drag from adding more blades has diminishing returns after a point. It's the aspect ratio of the blade that matters to get the most thrust for the least mass and drag. ~Amatulić (talk) 21:22, 21 July 2008 (UTC)[reply]

Lets play a mind-game... imagine the uselessness of a 100% ratio? ---J.S (T/C/WRE) 21:30, 21 July 2008 (UTC)[reply]

Depends on the application; a fanjet's thrust turbine uses 100% of the disc it occupies (i.e. when looking directly at the disc, there are almost no open spaces between the blades). Apparently a higher ratio can be efficient, and the efficiency may depend on the air speed required. Wind turbines and most airplane propellers are comparitively low speed, so mass and drag become important factors. ~Amatulić (talk) 21:33, 21 July 2008 (UTC)[reply]

J.S. : Ok, I'll play your mind game. Here is a photograph of a propeller that uses all 100% of it's circular disk area. [2] While far from ideal for this application, surely you're not suggesting that it would be worthless for power generation in a strong enough wind? APL (talk) 02:26, 22 July 2008 (UTC)[reply]

Similar to a thread above - don't confuse pushing air (or water in re the propeller) with drawing power from air. The two are not symmetrical operations. In the case of the pictured propeller, the Reynolds number will be dramatically different between air and water, so even operation as a propeller could not be expected as equivalent.

And in any case, I think (see thread approx. 1 month ago) that the primary consideration for space-filling on a wind turbine is the strength and cost of the bearings that have to support the load of the blades, and secondarily turbulence effects between the blades. Franamax (talk) 05:50, 22 July 2008 (UTC)[reply]

Plus cost of material used. And it would affect birds more than now. --Ayacop (talk) 07:42, 22 July 2008 (UTC)[reply]

We do of course have an article on this: Wind turbine design. See the Blade count section. --Heron (talk) 19:06, 22 July 2008 (UTC)[reply]

Thank you87.102.86.73 (talk)

Resolved

Charcoal

Can any organism use charcoal as a carbon or energy source? Assuming the answer is no, why not? ike9898 (talk) 21:58, 21 July 2008 (UTC)[reply]

Is there a natural source of it? That would be the first hurdle. --Tango (talk) 22:26, 21 July 2008 (UTC)[reply]

Cellular stuff usually involves absorbing something into the cell by osmosis. The insolubility of base carbon is likely unhelpful for that.--Fangz (talk) 22:49, 21 July 2008 (UTC)[reply]

Burned forests/shrub lands are an excellent source of charcoal. Certain plants are well adapted to growing post forest fire. Slash and burn agriculture is a perfect example of how charcoal can be used to enrich soils (though unusually done in an environmentally unfriendly manner). I can't think of anything of the top of my head that uses charcoal/hydrocarbons as a primary energy source, though if there are any, they would probably be one of those extremophile-bacteria types. 71.77.4.75 (talk) 01:29, 22 July 2008 (UTC)[reply]

Does charred wood from a forest fire count as charcoal? The key feature with producing charcoal is that it's done in the absence of oxygen. I would expect there's plenty of oxygen available during a forest fire, although I don't know for sure. --Tango (talk) 01:48, 22 July 2008 (UTC)[reply]

Yes, there would be a vast natural source of charcoal - forest fires. Within the fire zone and at the unburnt depth of any tree in the fire, there will be high heat and zero oxygen. Terra preta soil is enriched in charcoal (manmade) and provides high fertility, however the charcoal itself doesn't actually provide a source of either carbon or energy (since the carbon levels persist). Rather the charcoal provides a useful medium for growth of beneficial micro-organisms. Per Fangz, the problem would seem to be the insolubility of carbon in charcoal form. This is perhaps mirrored in the wide use that humans make of charcoal to filter everyting else, it is fairly inert. I don't know of any life form that can directly metabolize charcoal. Franamax (talk) 02:01, 22 July 2008 (UTC)[reply]

If you google for coal eating bacteria you'll get a lot of hits, I also remember an article where it was found that abandoned coal mines surprisingly released methane constantly due to those archaea. Of course, they would be able to digest charcoal, too, wouldn't they? --Ayacop (talk) 07:35, 22 July 2008 (UTC)[reply]

I am an organism, and I occasionally use charcoal to prepare my food. The process occurs outside of my body, but is that relevant? Plasticup ^T/C 13:00, 22 July 2008 (UTC)[reply]

Cute, but I don't think that's what the OP is looking for. Technically, most of us use carbon as an "energy source" beyond our gas grills: think power plants. I think the OP wants to know what organisms break down elemental carbon as food. I think Ayacop got it with bacteria and archaea. --Shaggorama (talk) 14:35, 22 July 2008 (UTC)[reply]

Just to clarify, coal and charcoal are more than just carbon. Reading this news release tells me the bacteria are processing the complex molecules in coal, and not the carbon. In fact the (rather non-scientific) article implies they use oil as their nutrient source, and break down impurities as a side effect.-84user (talk) 15:29, 22 July 2008 (UTC)[reply]

OP here. It seems to me that insolubility is an unsatisfying answer. Some fungi do very well on insoluble cellulose; they enzymatically break it into soluble pieces. On a different subject, I think that microorganisms that can use petroleum as an energy source are known. Can anyone say anything about the carbon containing molecules in charcoal that would be relevant to their non-bioavailability? Thx ike9898 (talk) 17:32, 22 July 2008 (UTC)[reply]

But the ubiquity of cellulose in e.g. plant cell walls means there are strong evolutionary pressures to adapt methods of breaking it down. Carbon in charcoal, which I think is mostly in the form of graphite, is not so common. So the ability to break it down should be rare. Though as others have said, probably some bacteria do have that capability.--Fangz (talk) 23:30, 22 July 2008 (UTC)[reply]