CaptainPanic

m3 is distance to the power 3: it's volume (not mass!). It is meter*meter*meter, or in quantities: length*breadth*height. Multiply volume (in m3) by density (kg/m3, or [math]kg*m^{-3}[/math]) to get mass (kg) There are many quantities which contain all 3 units: m, kg, s. Please distinguish: -"quantity", which is for example mass. -"unit", which is for example kilogram (kg). The quantity mass has the units kg. Also note that when there is a small -1, -2 or -3 in superscript behind a unit, it means to the negative power, which is the same as putting it under the line of division: m/s = ms-1... like in: [math]3*2^{-1} = 3*\frac{1}{2}=\frac{3}{2}[/math] There exist quantities that are made up of 2 units. For example velocity (or: speed): it is in meters per second (m/s). How much distance you travel per time. As mentioned before: density: kilograms per cubic meter (kg/m3). How much weight per volume. But there exist also quantities that have 3 units: Energy: kg*m2/s2 (also known as Joule, 1 Joule = 1 kgm2/s2) This is already becoming harder to understand when you just look at the units. But when you look at some formulas for calculating energy, it makes more sense: E = 0.5*m*v^2 = [kg * (m/2)^2 = kgm2/s2]. Also, force in Newtons: 1 Newton = 1 kgm/s2! So that one can also be broken down into basic units. So why does the gravitational constant have these weird units: volume per mass per time squared (m3/kgs2)?? Well, as many constants, they are just there to relate the other quantities: force (N = kgm/s2), mass (kg) and distance (m). The formula must have the same units on both sides, or else we would be comparing apples and pears (or is that "comparing apples and oranges in the English language? Anyway, comparing two different things). And why does it have the value of 6.67E-11? The world one day kind of arbitrarily chose to use the meter as the measure for distance, kilogram for weight and second for time. We could have chosen this differently. Then the value would have been different.

The one thing that I always add when explaining questions like this is: If you're a little puzzled what a "mol" actually is. It's a number! Just like: Dozen = 12 - used for eggs, apples etc. Gross = 144 - used for eggs, apples etc. Mol = 6.022*10^23 - used for molecules, atoms I remember that it took me a long time to understand this... because the explanation is overly complicated.

Desktop I don't have to consider taking my computer everywhere, while in most cases a piece of paper and a pen (and perhaps a telephone) are sufficient.

What kind of substances had you taken when it was still sounding good? :D I advise you make a small van der Graaff generator. It is safer (much smaller chance of hurting yourself) and it is also much more fun, because it recharges. I love this website: http://scitoys.com/scitoys/scitoys/electro/electro6.html Because it shows how to make a van der Graaff generator from really simple things. I've made one, and (depending on the weather) the sparks are up to 2 cm long.

question already answered. popcorn managed to post this question 4 times... must be the most important question in the frickin' universe. My reply: http://www.scienceforums.net/forum/showthread.php?p=436654#post436654 This thread can be closed.

First: you have created 4 posts about this. I have put time in answering this... what happens when somebody finds the other post, and not this one? Perhaps this other nice person also puts time in it... which is a waste of time. Please post questions only once. I've been searching for a formula in my thermodynamics books... but the short answer is: The excess enthalpy (or heat of mixing) is described as: [math]H^E=S^E\cdot{T}+G^E[/math] The enthalpy change is also: [math]\Delta{H}=C_P\cdot{\Delta{T}}[/math] The values of [math]C_P, G^E, S^E [/math] are all functions of the concentration of the two compounds. The [math]C_P[/math] is linear with the concentration for the ideal case (and [ce]H2SO4[/ce] in water is most certainly not ideal!). So the non ideality is already a reason why it is not linear... But all other properties also aren't linear: [math]G^E=G-\sum_i x_i G_i - RT\sum_i x_i \ln{x_i}[/math] [math]S^E=S-\sum_i x_i S_i - R\sum_i x_i \ln{x_i}[/math] The bottom line, as I understood from my thermodynamics book (Smith, Van Ness, Abbott) is: if you want to know the heat effect of mixing, measure it.

The thrust of a rocket is expressed in N. It's a force, which (if it's larger than the force of gravity) will lead to an acceleration. The trick with a rocket is therefore twofold: 1. Make enough thrust to accelerate (to overcome gravity) 2. Continue to accelerate long enough to get into orbit, meaning you need to reach something like 6-7 km/s (kilometers per second!). [math]\mathbf{T}=\frac{dm}{dt}\mathbf{v} [/math] (source: wikipedia) In that formula, [math]\frac{dm}{dt}[/math] is the amount of mass you push out of the rocket engine. This can be expressed in kg/s. It can be calculated in many ways, but probably the most common is to simply look at how fast you burn the fuel. The harder part is to estimate the exit velocity of the gas. This is described pretty well on wikipedia, on the "De Laval Nozzle" site. Wiki's rocket engine nozzle site gives additional info. The formula you need is: [math]V_e = \sqrt{\;\frac{T\;R}{M}\cdot\frac{2\;k}{k-1}\cdot\bigg[ 1-(P_e/P)^{(k-1)/k}\bigg]} [/math] The only thing not explained on the wikipedia site is how to calculate the pressure that is developed from the propellant. But a little googling got me also a site which seems to explain that one: http://www.nakka-rocketry.net/th_pres.html - search for the "steady-state chamber pressure". That all is needed to calculate the nozzle velocity. From there on it's a matter of [math]F=m\cdot a[/math], and you shouldn't forget to correct for the air-friction that you'll encounter while you are in the atmosphere (it is definitely significant enough to take into account, but since the pressure and velocity is not constant, it is another nasty formula).

swansont, I agree that there are some practical problems if you would allow water levels to drop by 50 meters. I merely wanted to indicate what amount of water you would need for 1 week of continuous power. I should never have written this here... and the moment I posted it, I knew I was asking for a comment. Mental note: when talking about a bigger scheme, make sure that the small details are either well described and without mistakes, or left out altogether... But thanks for the lesson, I need this (I like to illustrate things with numbers, but sometimes I over-simplify it, and that's alright in a conversation with friends, but not alright on a forum full of scientists who do mind each and every detail). So, same idea, different choice of words/numbers: The lake is actually a little larger, and the water level will drop less. Ok? Still totally feasible. This time I propose: 50x25 km, and only a 1 meter water level drop. I hope this is acceptable. and if it is not, please play with the numbers a bit until it is. I would prefer to shift the discussion to the changes in electricity production rather than the size of a lake. (Are there ever periods of 1 week when a major part of a continent has very little wind, no sun? What's the longest such period likely to occur in 100 years? What's the effect of this whole scheme for the income of the wind turbine owners?) And regarding people who live near the lake: In the English channel, people have no problems with a 12 meter water level between high and low tide. So, let's say that my newly proposed 1 meter drop is acceptable. Also, in nature, lake and river levels drop and rise all the time.

Yeah, actually, now that I give it a little more thought... science often suffers from marketing problems. Scientists are often too honest. But this can be easily overcome. Everyone with gas heating has a potential bomb in their homes. Nobody cares. Just a matter of the public getting used to the dangers, and decent marketing when something new is introduced. I love the example of bad science-marketing of the LHC in the question: "Can the LHC create a black hole that can eat the earth"? - Scientists then give it a lot of thought, and are 99.999999999999999% certain that it will not happen, but 100% certain doesn't exist... so they answer the question with "probably not", which is then interpreted by the public as "the scientists think it might go right, but they're not certain at all".) Just keep repeating the good stuff, and brilliant safety records. Airplanes are another great example where a large portion of the public totally ignores possible dangers. Of course, the safety record of airplanes is quite impressive nowadays, and liquid hydrogen superconductors still have a lot to prove.

The most bizarre about the results is that no matter how bad a republican government, a large part of the republicans are as devoted to their party as many believers are to their god(s). That might also go for democrats btw. How can you ever have a functioning democracy with voters like that?

I agree... I think that pumping water uphill should be possible with smaller losses, but I accept your numbers because I lack data, and I am too lazy to search for it today. If we use a wide range of energy generation options, covering all needs, we reduce the need to store energy. This in turn means that the 50% loss is more acceptable... because it will not be 50% of all generated electricity, but rather 50% for all stored electricity. But with a good grid (and the European grid is better than the American) you don't even need to store that much. The Netherlands imports 20-30% of its electricity from France. The total electricity consumption of the Netherlands is about 16 GW. France's nuclear power stations are at least 200 km away (Belgium is in the middle), but probably further away. France exports nuclear electricity to the Netherlands, but stores it in the Alps. This means that the grid capacity and flexibility between the Alps and the Netherlands is sufficient to play with several Gigawatts, which is exactly what is needed. In addition, there exist new power cables that are being built specially for grid flexibility - the European electricity market is opening up, so more cables are needed. One example is a new 700 MW undersea cable from the Netherlands to Norway (another country with good hydropower). The storage capacity of a hydro dam is more than sufficient. A river can dry up, and the station can produce at 100% capacity for weeks. For 1 GW production, for 1 week, at 50 m water level difference, you need 1.23E12 kg of water, or 1.23E9 m3. That means that a lake of 5x5 km and 50 m deep is sufficient. Many lakes are actually much larger than that. The power needs to be increased, because if you want to use the hydroelectricity as storage, you need to be able to produce more electricity than the base output of the hydro station. The "stored" electricity generation is on top of the normal hydro station's output.

That's about the worst argument possible against new developments. but obviously it should be included in the risk assessment. I think you'll find that a bomb attack on this hydrogen-filled superconductive grid will be the same as any leak with an ignition source present. Estimating the chance of it happening is the real tricky part (and it's where many people freak out nowadays, and lose their ability to look at things objectively).

Didn't we discuss practically everything here before? We have the "global warming: salvaging fact from heaps of BS" thread which, with 480 replies and over 12,000 views, should have treated every side of the discussion. In addition, from all the replies here so far, I fear that the opening post might not be based on solid science, but is in stead trying to use a subjective interpretation of pre-selected data. I haven't checked out the link myself. I say we put all this thread in another one, so that we can keep it all together... Opening another thread on this topic is (imho) pointless.

The Bush administration seems to be willing to spend up to 700 billion dollar on this bail out plan. They want to create a fund that can trade in the worst mortgage loans. (Mind you that "The plan would raise the ceiling on the national debt and spend as much as the combined annual budgets of the Departments of Defense, Education and Health and Human Services" - source: see below). We must realize that although this 700 billion fund will not evaporate completely, it will not make any profit - most likely it will actually lose money. Of course it's very noble from the US government to help the economy when it needs it the most. But I wonder, where did they find such huge sums of money? Although it will not evaporate completely, the initial investment sum must come from somewhere... and the losses this fund is likely to make will be paid by someone. Who? Tax payers of course. Is the US government just creating extra money? Printing more money will not solve the problem. Is McCain really planning tax reductions for everyone? That's just retarded with these kinds of plans from his own republican party. What is perhaps even worse is that the Bush administration wants to give the Treasury Secretary Henry Paulson almost absolute control over this fund. (Give absolute control over 700 billion dollar to a guy who is part of a corrupted government does not seem like a good plan to me). source: http://www.bloomberg.com/apps/news?pid=20601087&sid=ae6b6P1L8E_E&refer=home

In retrospect I am not certain that my (2nd) solution is correct in the English language. Seems perfect in Dutch though. Oh well... since I've already been granted the chance to become immortal by posting a good riddle... here's a classic: What can fall through a glass window without breaking it?

Hmm, yeah... I agree that construction of a new hydro dam has serious disadvantages. It destroys ecosystems. But I postulated that you don't need additional dams to increase storage capacity. Electricity transport reduces efficiency, but depending on demand, it is already transported over large distances nowadays.

I've been struggling to understand the whole problem with the storage of electricity. The topic of storage of energy has been treated before, although it was not the main topic in that thread. The popular view is: No wind, no electricity. No sun, no electricity. And storage is a problem, and hydrogen will save the day (eventually). I do not understand why hydro (water) power is no suitable candidate to solve this problem. Is it just not advertised in the right way (marketing problem) or is there a technological disadvantage so serious that we should abandon this idea and continue to wait for other technologies (which are not yet mature)? The Plan The task of storing electricity, and generating it on demand comes on top of the existing power generation of any hydro dam. Therefore, additional pumps and generators (turbines) need to be installed at existing hydro power facilities. No additional dams are needed. The water level in the lake will just fluctuate a little more. Capacity Hydro dams have a typical power capacity of Megawatts or even Gigawatts. And even if the river feeding the storage lake dries up, they can continue to generate power for weeks or months. Therefore, the storage capacity is enough. We can simply add some extra generators for when there is no wind, and build some extra pumps for when there is a lot. No mountains nearby Electricity can be transported over large distances. A thousand kilometers is quite normal in modern grids. So flat coastal regions (with lots of wind) can use storage lakes at inland mountainous regions. Price Hydro power is one of the cheapest forms of energy. Using hydro power for electricity storage would perhaps mean installing additional pumps and generators, but it would not necessarily mean building more dams. Therefore, it is also cheap. Grid capacity Grids to and from a facility are in fact the same cables: current can go in two ways. The grid only needs to be expanded for the additional pumps / generators. Efficiency Losses are found in two places: -The grid (transportation of electricity from power source to the lake's pumps and back from the lake to the consumer). This is typically a small loss of less than 5% (more like 1%). -The pumps and generators (turbines). These operate at 80-90% efficiency. Bigger is better here... and hydro power just happens to be the biggest and therefore the best. Experience Although I find it hard to find links, it's known that France stores its nuclear power in storage lakes in the Alps at night. This is exactly the same technology, on megawatt or gigawatt scale. Therefore, this technology can be called "mature" or "state-of-the-art" or any other term meaning it's not even new. The only decent links in English I found are these: -this one mentions it, but doesn't link to anything itself [ctrl-f storage lakes] -this mentions the increased flexibility in France's electricity production [see: 4.3 critical review: hydropower] Start up times Pumps and generators can be started fast to react on sudden fluctuations on a power-grid. But wind and solar are at least a little predictable (weather forecast). Other solutions - competition for hydro I doubt that any form of storage is going to approach 100% efficiency, and still remain cheap enough. Hydrogen generation is possible at 85% efficiency (in a lab, not yet big scale). Turning that back into electricity will give additional losses, meaning losses are in the same order of magnitude as for hydro. A standard battery can never store the same amount of energy per invested euro/dollar (no source, just a guess). In addition, the expected lifetime of a battery is shorter than that of a hydro dam. Pressurizing gas will come with the same kind of losses as hydro power, possibly larger. In addition, there is no existing large scale facility to pressurize a gas for energy storage. Natural gas technology probably comes closest, but the flow rates are much smaller than needed for megawatt scale electricity storage. The "smart electricity grid" can distribute the load over a larger area... which statistically means that there is always wind and sun. But it's not yet built. So, why does the argument of "storage problems" survive?? This solution is so obvious, that there must be a really good reason why each and every person in the field of sustainable energy is shouting that we have to wait for the development of better batteries and hydrogen storage systems... or that we need a better electricity grid for large areas to distribute the load. But what is that reason??? Or is it just the Dutch in their flat country who don't seem to realize that they are already connected to the European grid (with access to storage lakes)?? My best guess: this solution doesn't need any development, so it's just a marketing problem. There are no scientists shouting that "this is the future!".

I have a short attention span. Haven't read the whole plan. It is a good add. No mud throwing... Obama hasn't even mentioned the other party, nor his opponent. He's just calmly explaining his plan. I consider this a very standard, ordinary, basic political advertisement... totally normal in the part of the world where I come from (the small swamp at the end of the river Rhine).

Better take normal tap water as your base line, and also test diet and zero coke.

The general idea makes sense in a universe that is just full of oscillating phenomena. disclaimer: I'm no expert in quantum stuff

Indeed, and that is based on the electricity output, and the maximum solar insolation available. I'm pretty sure that we can assume that this means that 20% is absorbed. (Or more, if we include that some heat is also produced from additionally absorbed radiation, but that also means that some radiation emanates from the cell in the form of IR). Which means that the whole world is totally puzzled over what the kid means by "If he is right, solar panels with his 3D cells would provide 500 times more light absorption than commercially-available solar cells and nine times more than cutting-edge 3D solar cells." Simply put: I don't believe that the kid really knows what he's talking about. News agencies sent some random journalist, who doesn't know anything about Photovoltaics, and after that the entire world just copied the article. Sure, its a smart kid... graph of solar radiation spectrum: http://en.wikipedia.org/wiki/Image:Solar_Spectrum.png

At the terribly low temperatures, although very serious, I would not consider a leak the main problem. It all goes up in a big mushroom cloud if the insulation breaks off. Heat up the hydrogen until its vapor pressure becomes higher than the breaking pressure of the pipes, and you'll see a very interesting version of the BLEVE (Boiling liquid expanding vapor explosion). The vapor might then produce a secondary explosion when the hydrogen combusts. FYI, the boiling point of hydrogen is 20.28 K (at 1 bar), but at 30 K it is already 10 bars. But my main concern about the whole idea is this: Now we lose energy in the transmission of electricity. In this new plan B, we'd have to cool some hydrogen. Now, unless you make one giant machine capable of cooling to minus-a-lot along the entire length of the grid (probably consuming part of the electricity flowing through it!), you end up pumping around really cold hydrogen. It's rumored that hydrogen might have superfluidity, but the experiment (afaik) was only done at very very small scale. My point is that creating a superconducting grid might end up consuming as much energy as a conventional grid... superconductors might have zero electrical resistance, but the super-insulation is not yet invented, and superfluids were not yet produced on a bulk scale so it's not sure that they show superfluidity at such scale. I wish I knew a bit more about the cooling techniques for liquid hydrogen so I would be able to compare its energy consumption to the "waste" in conventional grids. But answering the question, I think that IF it works, it would require less space than the current grid, although I would consider to build it lower to the ground (like oil and gas pipes), which might interfere with existing infrastructure.

Although most commercial planes all fit the description above (tested, shown to be safe) they do fall out of the sky once in a while. And I don't think a "reasonable flight record" is the kind of flight record I'd like to see for any nucular powered device... especially a device flying over densely populated areas. No matter how good a design, there is always a way to destroy it.

Done.

I probably came closest to thinking about unassociated things when I was very ill, with high fever. My dreams were very abstract and didn't seem to make any sense. But I don't think I can claim that they were unassociated thoughts, because I don't believe that is possible. You will automatically search for associations with anything you see, smell, hear, feel, taste.