CaptainPanic

To catch the lightning, a large structure might be a bit of an overkill. I've seen researchers who shot fireworks (rockets) into the clouds, and the lightning then chose the exact path of the rocket to strike the earth. I believe that the relatively high concentration of particles (some of which might be ionic, shortly after the launch) is more conducting than normal air. Alternatively you can attach a thin conducting wire to the rocket.

Engineers, mathematicians, and physicists who work for financial institutions are called economists.

There area already some good answers here... But here's another one. Inflate the balloon, put the neck of the balloon under the cup and let the air out of the balloon. The cup might hover a bit (like a hovercraft).

I think you are pretty right on the numbers and scale. The power used for heating is indeed similar to the power for lights for just a couple of plants. It's a funny reverse idea of combined heat and power. A similar idea is taking off where gas that is used for heating first drives an electricity generator. The waste heat is then used for heating a house. And any surplus of electricity can even be sold to reduce the energy bill. And the idea of your fridge dumping its heat outside to save a few cents on AC: another good idea. One of the best ideas is to heat and cool buildings with a heat pump (a fridge is an example). Some big buildings already have this, but small houses are still heated with gas. A pity really.

The radiation from all the nuclear explosions (both planned tests and Chernobyl) is indeed negligible. Still, I think that it's not just emotions that people don't like to live near test sites or Chernobyl. I think that's because there is a significant difference between local radiation (when you're close to the source) and the average on earth. Personally, I am not worried about Chernobyl or any tests, but some Ukrainians and some people who used to live near Bikini might think different. That one we can calculate. Say that the rocket reaches a speed of 6000 m/s, which is a realistic velocity for reaching orbit. Then due to some error it heads for the surface again. It has a very large mass and relatively small surface area, so that means it will not slow down a lot in the atmosphere. The kinetic energy of 1 kg of material is : [math]E = 0.5\cdot{m}\cdot{v^2} = 0.5*1*6000^2 = 18 MJ. [/math] All of that energy will go into heat: [math]E = Cp*m*\Delta{T}[/math] Let's choose a Cp value of 1000 J/kgK, as most metals have a lower value than that. [math]\Delta{T} = \frac{E}{C_p*m} = \frac{18\cdot{10^6}}{1000\cdot{1}}=18000 K[/math] That means that metals will melt. And that means that you cannot be certain that the storage will survive. Of course we have materials that can withstand airplane crashes (black boxes usually survive). But airplanes have speeds which are an order of magnitude slower. So, now the discussion really is: Do we find it acceptible that sometimes a few pounds of nuclear material (plus a lot of non-nuclear material) come falling down at a random place on earth? Or do we prefer to have only non-nuclear material falling down randomly (from conventional rockets). I'm not sure. I agree that statistics say that it's all safe... but in the unlikely event that a crashing rocket comes down on Manhattan, the effects will be a lot worse than the 2 planes that hit the twin towers. (Ok, that last remark was definitely in the emotional category).

I am not trying to break down your idea. I am merely setting up a risk assessment. Determining the risk is something you must do anyway... so I feel that I am helping here. I feel that your last post is less objective than mine, and that the public opinion is not likely changed by your words, true or not. On topic again: A rocket is meant to go into orbit, and after further acceleration perhaps into the final frontier and beyond. But it's a fact that it will orbit a couple of times, if only to reduce the acceleration so that the astronauts survive. Therefore, it will come over urban areas. Therefore, it is possible that it comes down in an urban area. I have read about safety in the engine. I do believe that nuclear power is safe on the ground. I don't think we'll have another Chernobyl soon in a stationary nuclear facility. I have not yet found a piece of text that described what happens if the Lightbulb Rocket goes from 6000 meters/second to zero in less than 1 second. Does the reactor survive such an impact? I might have overlooked the text describing this. I'd appreciate if you can point out where it is written. Thanks.

Yeah, I figured that both points were not going to cause major problems. I just gave my thoughts on what I thought could possibly go wrong. Then you can go and estimate whether those things are a real risk. It never hurts to come up with possible disaster scenarios to see if you have thought of everything.

The article mentions risk mitigation, and gives two examples: 1. Chernobyl: relatively small, unexpected, at least 40 casualties (probably a few more), area the size of a small country uninhabitable for decades. 2. The Ivy Mike nuclear test, expected, planned, no casualties (that we know of). Let's do a risk assessment: [math]Risk = chance\cdot{impact}[/math] The impact: The thing with a nuclear rocket crash is that I would put it in category 1: unexpected nuclear meltdown possibly in an urban area (wherever the debris comes down). That's what makes accidents totally unacceptable. It would be in the Another-Chernobyl-Category. The chance: As mentioned above by big314mp: we should take into account the amount of rockets that failed during operation. It's pretty high. So, you get: [math]Risk = \text{pretty high chance}\cdot{\text{another Chernobyl}}[/math] The article says that it is not a big danger on a global scale. True. But since the rocket here is also no global project, and does not have 6.7 billion passengers, that is no argument. I think that chapter 9 "But isn't this dangerous?" is flawed.

I believe the main problem with tornado, hurricane and lightning power is that it is much less constant than the already non-constant wind and sun. With the investments you do to capture the energy, you need to design your equipment such that it will not break during operation... so it needs to be designed for 500 km/h winds (or something like that), and for massive currents. So you end up with a huge structure that is virtually unbreakable, but that is not producing 99% of the time. Therefore, I think you should first think of a way to physically move the generator to the storms where the high winds or lightning occurs. Then you can start to think about the device itself after that. Moving the thing around into storms is (I think) going to be the biggest improvement in efficiency. The most obvious would be to build a large ship - at least there is enough space on it to build a large structure. But I'm not sure those are fast enough to catch up with storms. And I am not sure you could make it strong enough to survive. But the problem with sustainable energy is not that we don't have enough of it on earth. There is more than enough wind and sun. We just don't invest enough in it. And any tornado or lightning power is going to face that same problem.

two aspects to this that I can come up with: 1. the first thing I can imaging going wrong is that the CO2 becomes solid after the valve, effectively blocking the exit. This will then suddenly un-block when the CO2 heats up. I don't know how the exit of the lecture bottle looks (the valve, pipes and pressure gauges)... so I don't know how likely this is. 2. Is there any difference between what you want, and the cylinder with internal siphon? I'm breaking my head over this question, but I cannot come up with a good reason why it would be more dangerous than the cylinder with internal siphon, other than that you're not able to put it down easily without turning it back up. The internal siphon cylinder can be put down without turning it around, and is therefore probably easier to handle.

I guess that's the difference between a book and a magazine. A magazine will actually give several titles of several articles on its cover (if only they'd add the page numbers on the cover too, then I could go straight to the good stuff). I believe we should consider ourselves closer to a magazine than to a book. There is just a category of students who are not interested, and will simply copy paste their assignment in the hope of being able to later copy paste the answer and be done with it. That is something we should prevent at all costs... both to protect the students from their own laziness and to protect the forum from being flooded with lazy students who want answers ("because their assignment is due tomorrow, please help!!" ). - (I repeat: no need for a separate subforum for homework - but we should distinguish between homework assignments and curious people with questions).

I would advise you to look into other ways of indentifying your products. Smelling is really the last option you want to use. In case you made something toxic, you probably don't... Why do I even explain this? Nitric, you seem to be totally reckless. I advise you to study things a bit more, and stop trying to kill yourself.

What's FCD?

First of all, we seem to be talking on 2 topics here. For me the "front page" is the one you get when you click "home" at the left top corner. The "index" is the one with all the subforums listed. I personally like the front page (the one you get when you click "home"). It shows the latest posts. Since I visit quite often, it is relevant for me. But I think that a newcomer might not find the "view forums" button easily (because of the wealth of information thrown at you on the front page)... therefore removing it might make sense. I think I like the new index (subforums listing). I have looked at it a couple of times now before answering... I guess I could get used to it. Less scrolling is always a good thing. I think that all the links might be a bit close. Using a little bit more white space between the links might make it more calm to the eyes. As for homework. It would be nice if it remains very obvious that we're dealing with homework... so if the subforum is removed, perhaps a tag of some kind can be introduced to indicate that it's homework? I agree that it makes more sense to keep all questions in their separate subforums rather than having a big mix of questions in a homework forum. [edit] on second thought - I miss something on the new index. The name of the thread with the newest post! I check that all the time on the current index. In one scroll-action, I can see if there is any activity that interests me.

First of all - all that surface area is: We have about 55 meter blades (!), assuming an average breadth of 1.5 meters (just a guess) - that's 55*1.5*3 = 247.5 m2 for all 3 blades. That means you can generate a whopping average power of about 2.5 kilowatts. That would increase the wind turbine's power output from 2 MW to about 2 MW... or in other words: it's totally negligible. Furthermore, the blades are almost never under the perfect angle towards the sun, and because they need to catch wind, there will also never be any design which improves this. In addition, the blades need to withstand massive tensions because of constantly changing wind speeds (at the top and bottom). These things are larger than any aircraft wing, the blade tip has a speed of about 80 m/s. Adding solar panels is not likely to increase the strength of the blades. In stead it just makes them heavier.

Reading the last 6 posts, it's pretty hard to stay on topic, isn't it? No hard feelings for all those who post, I'm sure you all do it with the best intentions. Anyway... I'll just ask my last (on topic) question again, so that it's the last thing somebody reads:

I don't think this should be in the homework section. We're trying to help people to study here. I propose to move it. I think it's a funny game though. Didn't got a really good score, because my olives died. I thought it was a good climate for them, but without warning they perished. I'm not sure what I learned from that.

On the above 3 posts - Why aren't the entire posts deleted? It's pure hijacking and spam... Of course, the pumps and generators of a dam should never be running at the same time. That would be a complete waste. I think that if you want to use a lake as storage, it means that it needs to be able to generate more power during peak hours or hours of low wind/solar energy generation (compared to a normal dam in normal operation), so you'll need more generators. And if you want to store more than currently possible you will need more pumps. I think that it should be fairly easy to introduce a direct current (DC) "culture" in our homes. After all, all battery powered appliances are already DC. Also, in the field of electricity distribution (long distance power cables) there exist several examples of high voltage direct current (HVDC) cables that are hundreds of kilometers of DC cable. I think that storage using batteries is going to be much more expensive than large scale hydro. I think that the raw materials for construction, as well as the life time expectancy are in favor of hydro when compared to batteries (no matter what scale of battery). As an example: most hydro stations are running for periods over 50 years, but my phone's battery is dead after 4 years. I'd have to do a back-of-the-envelope calculation to see the maximum price of a battery to become a good competitor to hydropower for storage. Can anyone comment on the type of control systems needed if a society would introduce a distributed battery storage? And compare that perhaps to a control system for hydro power? (I have very little understanding of how my electricity company even knows when to provide more power - I guess it's measured somehow?)

Many people (including me until 5 seconds ago) were thinking that "buoyancy" is the equilibrium between the actual buoyancy and gravity. But buoyancy is the force of the water pushing on the object's outer surface (force per area = pressure). Gravity is pulling it down. And the equilibrium between the two is what keeps it from either sinking or taking off. - It's the common Archimedes principle, which does take density, volume into account. The picture on wikipedia (as so often) is quite good: http://en.wikipedia.org/wiki/Buoyancy

Oh well... I guess Fox News always tells the truth. Right? But I agree that the Xinhua story is pretty sad (It's easy pointing for me, not many people even know the names of our crappy news agencies).

The final temperature of the metal is not determined by density or specific heat. the final temperature is determined by the equilibrium between the solar radiation (or insolation - the sun shines on the surface, mostly visible light) and thermal radiation (infrared from the metal). Insolation from the sun is about 1000 W/m2 on a nice day. Since metals can be up to 80% reflective, only 20% gets absorbed. So, we can say that: [math]W_{in}=0.2\cdot{1000}=200W[/math] The second effect is the thermal radiation. This is the infrared that is emitted by the metal. It increases a lot when it gets hot (it is a 4th order relation to the temperature!!): [math]W_{out} = \epsilon(T) \cdot \sigma \cdot{A}\cdot T^4 [/math] [math]\sigma[/math] = Stefan–Boltzmann constant = 5.670400×10−8 W·m-2·K-4 [math] \epsilon(T)[/math]= a correction factor because the metal is no perfect "black body". [math]A[/math]=the surface area (1 m2, because we looked at the sun's radiation in W/m2) [math]T[/math]=Temperature - the parameter we're trying to determine [math]W_{in}[/math]=incoming power (insolation from the sun) [math]W_{out}[/math]=outgoing power (infrared radiation from the metal) If we neglect the convective heat transfer (air moving because of temperature differences) - which is quite wrong in fact, but makes explaining a little easier now... we can say that after enough time, the temperature does not increase anymore. So: [math]W_{in}=W_{out}[/math] [math]W_{in}=0.2\cdot{1000}=W_{out} = \epsilon(T) \cdot \sigma \cdot A \cdot T^4 [/math] Which enables the calculation of the temperature. Note that there is no specific heat ([math]C_P[/math]) or density here!! Heat transfer into your hand (when you're stupid, and touch the metal): This is where the mass, specific heat and density come into play... and mostly the conductivity. It goes a bit too far to explain all the theory of heat transfer today. Have a read at the website of wikipedia - it's quite brief, but it's a good start for those who want to learn: http://en.wikipedia.org/wiki/Heat_transfer#Conduction

You're right, and you're right. Check the formula: [math]{\mu}[/math] = viscosity of fluid (water) in Pa s

Just a selection of quotes from the article. There is more background information... I have little to say. I don't want any climate change discussion here. Just numbers of CO2 emissions. People changing the atmosphere's composition. That's a fact. The effects of that can be discussed in other threads. I'll just add this xkcd.com cartoon:

Thanks for giving another example that this way of storing electricity is already wide spread, large scale, and in fact totally normal. I don't want to include environmentalists in this technical discussion. And anyway, I wasn't proposing to build new reservoirs, I was proposing to increase electricity-storage capacity by installing additional pumps at existing reservoirs.

Abbreviations are so great. What's the GD thread? When searching for [GD thread], the forum search comes up with something about diseases and politics. Searching for "superconductors" would probably be the best way to go, ... so I did that too... and voila, it's the "General Discussion forum". Spelling it out would have saved me a good 30 seconds. link: http://www.scienceforums.net/forum/showthread.php?t=35462&highlight=superconductors :D