CaptainPanic

Great post. Exactly what I needed Thanks katmar! (And welcome to the forum!)

The megawatt infrastructure can be built if necessary. In fact, I think that if I have to choose between building a bunch of big fat cables, or carrying tons of highly flammable liquids in trucks and pipes, I would always vote for the cables. Since we've shown we can build the current infrastructure, I am certain we can build a new one as well. I think the bigger problem could be the large fluctuations in the power consumption. With 1-10 minute recharging I doubt that commuters will recharge their vehicles at night (unless there's a financial encouragement). Thousands will recharge it in the morning, causing an even larger peak in the electricity consumption.

Mankind has changed the surface of the entire earth. We are sure as hell capable of covering some significant part of it with solar panels, if we want to. The same thing goes for wind power. Biomass seems to be the only sustainable resource is not capable of powering the whole earth, because there is not enough surface area.

I did (partially) read the links. I tried to read the first post in this topic twice. Usually when I have no answer to a topic, I know which topic is being discussed, and I know I have insufficient knowledge in that particular field. In this case, I don't understand what we're talking about... Can anyone enlighten me?

Perhaps our thread starter meant to say: It's not the factor by which the universe is bigger than something we know, like a house, that we cannot comprehend... it's the fact that this factor is in fact unknown... Or did the threads about the size of the universe have a single constant as an answer? I also feel comfortable with large factors, although like most chemists I think at a small scale. If you really fail to imagine small numbers, thinking not in size, but in terms of dilution might work.

Let's use an example - because I am still confused. If you add 1 liter of ethanol and 1 liter of water, and you mix, the resulting solution will not be exactly 2 liters. 1 liter of water is 0.998 kg. 1 liter of ethanol is 0.789 kg. Mixing would mean that there is 44.2%wt ethanol in the mixture. The density of the resulting solution of 2 liters (if this was linear) would be 0.894 kg/l. However, using Perry's handhook (7th edition), I find that the actual value is 0.92642 kg/l. This means that the 2 liters, upon mixing, were "compacted" to only 1.93 liters. Knowing all this, what is the volume% of the ethanol? (I am just confused about the damned definition - if the answer in this case is 50%, then it means that the definition of %vol. is "the volume percentage after separating all compounds into pure species - if not, then I also don't know what it should be...)

I'm in need of a table or formula (empirical fit) of the conversion of ethanol/water mixtures weight percentage to volume percentage, and back. I know how to calculate the theoretical conversion (ideal mixtures), but I doubt that ethanol/water can be considered ideal. I also found an online conversion tool, but I'd really prefer to have all data neatly in a table. Does anyone have a reference for me? p.s. If the volume percentage is as simple as taking the volume of the pure ethanol and the volume of the pure water, and then dividing the ethanol volume by the sum of the water and ethanol, then I am just a nut. (My results for that don't seem to correspond with the little data I have). [math]Ethanol\ volume\ percentage = \frac{Pure\ Ethanol\ volume}{Pure\ Ethanol\ volume\ +\ Pure\ Water\ Volume}*100\% [/math] Wikipedia says on volume percentage: [math] volume\ percent=\frac{volume\ of\ solute}{volume\ of\ solution}*100\% [/math] which indicates that you do have to take into account the excess volume (the volume change upon mixing)... then again, I am not certain that brewers also use this definition. It's a whole industry, and they might as well have their own conventions. Thanks in advance. p.s. the tool I linked to seems crappy... (Or I completely fail to understand something here). IMHO, 100% ethanol is 100% vol. and also 100% weight... this converter seems to disagree with me.

Doh! Apologies for the mistake, and thanks for correcting it. Apparently I am not able to simply copypaste a 3 digit number.

Recently (on 04-28-2008) we discussed a newly found element: element 118, atomic weight 292. It was reported that it's found in small quantities in nature, and that it's stable. http://www.scienceforums.net/forum/showthread.php?t=32555 In the discussion more links and info are given (so click the link )

I think we're going towards a dog eat dog world, which is why all countries and even regions are increasingly thinking about energy independence and making alliances with resource-rich neighbors. Energy independence can be achieved in any climate, with the right technology. Water is scarce in some regions, so for water, we will need to cooperate (or regions need to desalinate the water, which is quite costly). I think that the problem will eventually sort itself out, whatever the cost. The question is whether we sort it out soon, at a low cost, or sort it out later at a much higher cost. Population control is one of the biggest no-no's in the world. Imho, this is because of religious reasons. Many religions say: "make babies", and "don't use any form of anti conception". And for a politician to go against the mainstream religion is political suicide.

The reaction rate is generally expressed as something that looks like this: [math] Rate = K*e^{-\frac{E_a}{RT}} * [substance A]^a * [substance B]^b [/math] The factors that are of importance are -[math][substance A][/math], Concentration or pressure (which are the same in fact) -[math]T[/math], Temperature -[math]E_a[/math], Activation energy - this is a substance specific energy that says how easy something reacts Other factors are more macroscopic (not molecule scale, but bigger scale), but if you have a perfectly mixed solution, these should have no influence at all. These other factors are the heat and mass transfer, and will become important if you are dealing with heterogeneous systems and catalysis, like the reacting tablet. If something in the tablet should react with the liquid, then the liquid and tablet must be in contact with each other. If you crush the tablet, the liquid can reach the inside of the tablet much faster... Or, in other words: after crushing the tablet, there is much more outside surface of the tablet than before.

Lego? http://mindstorms.lego.com/eng/community/resources/default.asp It uses NQC (Not Quite C) (http://bricxcc.sourceforge.net/nqc/) for programming... and Lego is pretty awesome for building things like robots. - and the price is in the range of toys p.s. I've never used the programming-part myself, but I've heard good things about it. p.s.p.s. They have an online shop, and even sell individual pieces/bricks/parts.

First of all, the fact that your science assignment is due on Monday is not my problem. Second, this should be moved to "homework". We don't give you answers, we usually just help. Finally, searching the internet, using wikipedia, on "manganese dioxide" actually gives you the answer if you read all the page. My advise: read the link, copy paste the relevant text (it's 1-4 lines of text) to show you tried, and if you're still stuck I'll give the answer. I think you're nearly there anyway.

Ah, yes... I feel such an amateur now... I've expressed it better than me. Thanks. Still, I fail to see the major downside of the ion thrusters... The only argument I understood is the costs. When you stay close to earth it's relatively cheap to get something up there... I can imagine that a kg of fuel is more expensive if you have to carry it beyong Mars before using it than when you're talking about merely 200 km. It's probably simply cheaper not to use ion thrusters. Or would the friction on just the ion thruster itself already exert more force than it's thrust? That would be another argument. cool post D H!

So, we've established that the temperature inside a pressure cooker is higher. See it like this: the higher the temperature, the faster molecules are moving. This also goes for the water inside the cooker. So, at 120 deg C, the molecules move faster than in your normal pan. This means that they also penetrate the rice/pasta faster. The food is finished when enough water has entered the food. The faster the water molecules move, the faster this is finished. For potatoes, there is simply the need to warm up. This obviously goes faster at higher temperature.

D H, off topic as it may be, do you have a link or reference to the place where you read about the solar cells? (Personally I always thought that all the pollution actually goes into the cells... rather than being dumped somewhere... of course, this only postpones the problem to the day that the solar cell becomes waste itself).

If the answer is not 42, I am not interested today.

I think it's part of growing up: everyone has a moment where they think that the 1st law of thermodynamics applies only to stupid designers, but not to their stroke of brilliance.

Yeah, ok... so the most (or: the few) ion-thrusters were designed for tiny satellites that were shot into the universe. So, I do understand that a single ion thruster that was built for a 500 kg satellite will not do the job for a 500 ton station. But why not scale it up? Or even more simple: just use more than 1? The whole trick of ion thrusters, as far as I know, is that they have a better power/weight ratio than conventional thrusters. In the end, you carry less stuff into orbit to achieve the same.

Aren't ion-thrusters supposed to be the way to go in case of long and slow burn times?

it's function = reduce cooking time. At 2 bars, the boiling temperature of water is already 120 deg C. http://www.efunda.com/materials/water/steamtable_sat.cfm

An engine is not an engine if you don't have an input of energy (power = energy / time). The most common ones are: Combustion engines: fuel Electric engines: electricity Other alternatives for power can be: Compressed gas (e.g. Air), Muscle power (you or an animal) Please note that things such as a spring, elastic or magnetism are by themselves no source of power. Take the example of a spring: you have to apply power before it will return the power.

For short and perhaps medium range trips I see no problems with the compressed air car. It is a good solution for city traffic, and it reduces the pollution. But I am still skeptic about its overall efficiency (including the compression of the air in "compressed gas stations"). Perhaps the air can be compressed by using the much cheaper coal, rather than using oil for the fuel, which will give an economic benefit. I haven't done any calculations, and I don't intend to do any in the near future, but if anyone has a link or back-of-the-envelope calculation to show these things are at least as (overall) fuel efficient as combustion cars. Personally, I favor the option of the battery + electric engine.

Whaddayamean? The universe is filled with Teh Misterious Dark Mattah! Researchers have discovered everything about it: it's dark, and mysterious! Therefore there is nothing to be discovered anymore. QED (We're basically at the same point as when the earth was flat and the sun was in orbit around us).

I was discussing lightbulbs the other day, and suddenly we realized that we don't know what resistance is. I know the V = I*R laws and other basics. I know that the wire in a lightbulb glows bright because all energy of electrons is lost in the wire because it is thin and therefore has a (relatively) high resistance. Let's look at a DC current in a wire (or any other resistor, they all just heat up to dissipate the energy). So, these electrons entering the wire lose their energy somehow. I'm visualizing it as high energy electrons in the valence band getting too close to another electron in the valance band, pushing the next one forward. That one in turn pushes the next. However, I fail to see where they lose energy in this pushing each other and the ions on the lattice around. These valence electrons must somehow cause increased thermal motion on the ions... Rather disappointingly wikipedia says this (disappointing because don't understand it ):