CaptainPanic

I saw yesterday in a surprisingly decent documentary on National Geographic that pigeons have small rods of magnetic material (ferrite) in their beaks. these rods are really tiny and they're clustered in 3 sites on both the sides of the beak. No clue whether cows resemble pigeons in this matter... But it seemed relevant. [crap]Still, I don't see a big market for homing-cows. Pigeons will probably be faster. Perhaps DHL or UPS are interested in homing cows for larger pieces of mail. [/crap]

That's true... especially for big installations. For the small ones that you use for heating your house, it's less important if the wood isn't completely dry. If it's still fresh, I don't recommend burning it in any case. You came to the scienceforum... expect an overload of technical (and scientific) stuff. (If for some reason you think it's too much, I can recommend the happy campers' forum for cozy campfire discussions... in any case, they'll also recommend dry wood).

The parameters that are of importance are: 1. The heat of combustion (J/kg). This is about 17-19 MJ/kg for dry wood, and it can be as low as 8-10 MJ/kg for wet wood. 2. Cp value of the products. Air has a Cp of 1000 J/kgK, CO2 has a Cp of 0.82 J/kgK and water (gas) has a Cp of 2.0 J/kgK. So, the more water the gas contains, the lower the temperature. With this you can calculate the temperature of the flame, which gives you an efficiency. Simply said: hot fires are more efficient. Take for example a steam engine (considering the efficiency, it is a typical heat engine). It cannot be more efficient than defined by Carnot. It's alright if you don't understand what the formula's on that wiki-page mean... The bottom line is: [math]\eta=\frac{W}{Q_H}=1-\frac{T_C}{T_H} [/math] where η is the efficiency W is the work done by the system (energy exiting the system as work), QH is the heat put into the system (heat energy entering the system), TC is the absolute temperature of the cold reservoir, and TH is the temperature of the hot reservoir. You see: the hotter, the more efficient. The TH here is not the temperature of the fire, it's the temperature of the water in the boiler... so a very hot fire can make really hot steam (and really high pressure, and that's the main problem with high efficiency). And really hot steam will make an efficient system. If you're just considering to heat your house: the only thing that really matters is the fact that you have to evaporate a lot of water. Because this water will not condense in your heating system, it's a pure loss. For the rest, it matters how hot the smoke is coming out of the chimney. The heat produced can only go in 2 "places". It can heat the house, or leave through the chimney. I think that wet wood combustion will result in (relatively) more heat leaving through the chimney. I like the fact that you can just copy paste formula's from wikipedia. Makes life easy

I think that if you're able to make a room temperature superconducting polymer, you'll get the Nobel Prize.

With "Couvier", do you mean "Georges Cuvier" or "Frédéric Cuvier"? Of course, Cuvier died about two decades before Darwin published his work... so the two never had a chance to fight it out together. Cuvier opposed earlier evolution ideas that were indeed based on rather shaky ideas: "[Lamarck's evolution] rested on two arbitrary suppositions; the one, that it is the seminal vapor which organizes the embryo; the other, that efforts and desires may engender organs. A system established on such foundations may amuse the imagination of a poet; a metaphysician may derive from it an entirely new series of systems; but it cannot for a moment bear the examination of any one who has dissected a hand, a viscus, or even a feather." (copy pasted from wikipedia) For the rest, I don't think that the arguments of Bicycle Seat are going to convince a lot of people. Calling Darwin names is not very scientific. But it has some value as entertainment. I enjoy this post more than the shorter ones... It might save you from being banned

I always thought that the process was a bit more gradual: First some other regions on earth become a magnetic north or south (there will be more than 1 magnetic north pole)... This then finally results in flipping the magnetic field completely. I saw this in a documentary. The theory was based on magnetic rocks that were found all over the place (and the direction of the magnetic field in these rocks). The rocks were dated and thus a magnetic history was obtained. What I do not recall is how many rocks, or how many data points, researchers have investigated. I'd say you need lots and lots of data points to make such a claim...

Aaah, a forum is not complete without a good troll. I conclude that trolls also benefit from global warming (discussions).

I believe in Hollywood. I believe that the popular vote will not elect the president. yes, I believe it's all fake. My arguments for this are: 1. There is still debate about how the voting will take place (machines, with paper and a pencil). 2. Machines are known to be insecure. Paper gets lost. 3. The last elections that I recall have all been a close 50-50, while large amounts of the population changed sides. Other countries usually have more outspoken and predictable elections. 99. How is it possible that Bush got re-elected??? Surely that's a sign of fraud. Therefore, I voted YT... because I have more trust in the SFN election than in the USA election.

I find it very funny that in the Netherlands, there exists a political party which is closer to the Republicans than to the Democrats. It favors tax cuts, and is generally considered an employers' party rather than an employees' party. The huge difference is that their primary target seems to be healthy government finances. In the Netherlands, the socialists are being blamed for spending too much. In the US, I read (and I agree) that the republicans are spending too much.

Bicycle Seat, your strong arguments shock me. To people who realize that we've dug up bones of ancestors, and share many genes with other species, there was some kind of evolution... I think the interesting thing is: humans will evolve, slowly, but humans are capable of changing the planet faster than its own genetics (unless we go into the lab, and make some GMO people, which I don't rule out).

What's your best moment today? I was working hard, reading, modeling, writing... and then I looked up and realised my roommate looks and acts a bit like Wallace (from Wallace & Gromit). It really cheered me up. Other days big events might be the highlight, but today this was it (so far). What was your highlight today? (Don't say "the moment I could finally go home", because that's a cliché even before it's written for the first time).

I'm afraid we're going a bit off topic now... I think that combustion is not the right process to study heat transfer differences of gases, because all kinds of other things are also happening, and they all interfere with what we're interested in (at least, in this topic we discuss only heat transfer of wet air compared to dry air... not energy conservation from wood combustion). The water that will evaporate from the wet firewood will perhaps block out oxygen, which makes it harder to introduce enough oxygen. But more importantly, the combustion characteristics are totally different! The temperature of the fire will be different, the rate at which it burns is different, the char production and the exhaust gas composition and aerosol composition will be different. So, not only the concentration of water changes, but everything else as well! This makes it a little hard to look at just the heat transfer from the gas to the solid object. But we can say that dry wood will produce a hotter flame... and probably will give a more complete combustion. Again, I'm afraid it's irrelevant to this discussion... but feel free to open a new topic, and ask more questions about wood combustion.

I have that curiosity for each and every beer in the world. Strange, because not all of them have big bright numbers on their bottles that fuel speculations. A real puzzle, this one!

McCain plans to cut tax for everyone??? That's gonna make him popular with the stupid people... Good thing that American expenses have gone through the roof, and the economy down the drain. The deficit is at a record. And those idiot republicans are planning to cut taxes even more. Mouhaha... Is that graph serious, or is that democrat propaganda? I think Americans already pay ridiculously little tax (and you get ridiculously little in return as well). My top tax level (for the last euro I earn) is 50%! And I don't mind paying it.

Wear the glasses (at home, while watching tv or something), see if you get a headache... if so, then it's the glasses. If that's not it, go in the lab when there are no experiments being done, see if you get a headache. Cancel out each factor one by one like that until you find out. Save the sniffing chemicals (NH3) for last, because that's a guarantee for headaches. Ventilation is important. To check the ventilation of a fume hood, take a piece of toilet paper and attach it with some tape to the edge of the (movable) glass window (the one that goes up and down). Because of the air-flow, it should be at an angle of about 20-40 degrees with respect to hanging straight down. Typical air speeds at the entrance of a fume hood are 0.15-0.4 m/s... depends a bit on the size.

Doh! Im my perfect world, waves are simply a sine (or cosine). I could have know perhaps that the shape of the wave itself can also change. Does anyone know how it's being changed? I'm assuming that the vocal cords do the same trick for both A and O, and that the shape of the mouth then changes the shape of the wave. But that assumption doesn't come with a background or explanation (so it's useless).

I understand sound waves: amplitude and wavelength (or frequency) are rather simple concepts. I understand how sounds travels (in a straight line, and deflected or absorbed by objects). I also read that our vocal cords produce many harmonics, which I suspect is what makes everybody's voice unique. What I don't understand is how you can explain the difference between pronouncing an "A" and an "O", and both at the same frequency. I can see that the mouth makes a different shape, but I fail to understand how the sound waves are affected by the shape of the mouth (amplitude or wavelength of the set of harmonics are changed I guess... since there isn't much else to sound, is there?) I don't think music can be involved in this discussion easily, because I see the differences between instruments more like differences in voices (harmonics) rather than letters Just a question that I cannot answer... for entertainment value

Why would it be a contradiction? It's true and it doesn't sound like a contradiction to me. What still puzzles me however is how 1% water in air can have such an influence.

American politics (and to a lesser extent, European politics) is marketing 24/7, whether it's election year or not. When the primary goal of politicians is to get elected next time again, then their tool cannot be anything else than marketing. It's logical, and it works.

The reversal of the poles would turn around the statistical average orientation of cows. They point north now. http://www.telegraph.co.uk/news/newstopics/howaboutthat/2623809/Cows-point-north-thanks-to-in-built-compasses.html Probably not very important, but funny enough to spam the forum with. [edit] ... And then I spotted the other thread.

A priest and a hunter go out for a walk. A few minutes outside the village, the hunter spots a little bunny. As it's the natural thing for him to do, he immediately takes aim and pulls the trigger of his rifle... Seeing the result he mutters: "Goddamn, I missed". The priest replies: "You shouldn't be saying this, the Lord will not be pleased". They continue their walk, and just a few minutes later, there's a beautiful deer staring at them. The hunter doesn't hesitate and shoots... but he says: "Goddamn, I missed!!". The priest gets annoyed and replies in a firm voice: "You really should watch your mouth, the Lord has ways to make you understand!". They continue their walk in silence, and after some time, there is a large bear... a target that cannot be missed. The hunter aims, shoots, and: "Goddamn, damn, damn, [beep] god, goddamn!! I missed again!!". The priest gets really angry, then sad and says: "Don't say I did not warn you!"... As the priest says this, dark clouds gather, and a blinding bolt of lightning shoots down from the sky. The priest drops dead. A voice from the heaven says: "Goddamn, I missed".

I have not yet found a lot of mistakes on wikipedia. I use it generally for physics and chemistry, as a backup. If it's not important, I just use wikipedia. If it is important, I'll do a double check. It's also great if you need additional keywords to continue a search... Finally I also find it very useful for translations: type the Dutch word, get wiki's page, then click English I agree... but I feel like starting a discussion. Peer reviewed articles in scientific papers are generally accepted as reference. However, because these almost always treat new things, they may contain mistakes. Wikipedia pages are reviewed (anonymously) lots of times, and treat common things. I think that on average wikipedia contains less mistakes than scientific papers. Why not use wikipedia as a reference in science?

Just a guess: all countries that are in the International Atomic Energy Agency? - That's almost all countries in the world (pretty much all countries that are in the UN).

The combined weight of all the world’s ants is equal to that of all the humans on earth… True or False? My guess: false. There are more ants than humans (both in absolute weight and obviously in numbers). What does the “33” represent on bottles of Rolling Rock beer? No clue, but I'm guessing the year of the first production: either 1833 or 1933. The worlds largest flower is nearly 10 feet tall and smells like rotting meat… True or False? True. One just flowered yesterday in the Netherlands, in a botanical garden. I'm sorry to spoil this one... the Dutch media spammed the country with articles about this flower.

Here you have something about acoustics and heat: the acoustic heat engine. It's the same as the first link you posted, but I think it's a better explanation. http://www.aster-thermoacoustics.com/indexeng.html But in any case, heat alone is useless. You'll need a temperature difference. If you have heat, you also need a cold side, or you will go nowhere. Utilize heat: An old proven way to utilize heat is the steam engine. It will run on any kind of heat, and you can make a solar steam engine, although that may have some practical drawbacks. Sterling engines work on heat alone as well. Solar boilers heat up water, although these work on solar power (insolation, rather than pure heat). The Seebeck-effect describes how you can turn a temperature difference straight into electricity (though not very efficiently).