EPTAsk and answer stupid questions here! - Page 284
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ThomasjServo
15244 Posts
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FiWiFaKi
Canada9859 Posts
I'd imagine it's mostly due to cost of always having them emptied out, as well as they don't look good either. If you have a society that's able to put something in a bag, tie it up, and walk with it for a bit, I don't see the problem. It's more an issue with the generic teenager here where they'll throw a cigarette on the ground if there's an ash tray next to them, or throw an empty wrapper on the ground when there is a garbage is few meters into the distance. | ||
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helpman176
128 Posts
How long would it take? | ||
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Oshuy
Netherlands529 Posts
On June 13 2015 20:14 helpman176 wrote: What is the fastest way to bring all the water of the oceans to the moon? How long would it take? Step 1: build a huge ladder that gets to the moon (quite fast, can be ignored) Step 2: give 5billion people a bucket, containing approx. 20dm3 Step 3: everyone fills his bucket, goes up the ladder and empties the bucket on the moon until oceans are dry. Speed on the ladder ~2km/h, distance ~400 000km, round trip in ~45 years. Make that 60 to take time to rest and reproduce. Emptying speed: 5.10^9*0.02/60, approx 1.5 million m3/year. Ocean volume: 1 335 000 000 km3, so 1 335 000 000 000 000 000 m3 Oceans dry in 890 billion years. I guess we need something faster, the sun vaporises them earlier than that. | ||
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Simberto
Germany11906 Posts
For a sensible launch system, we would require some way to generate a lot of energy. From a short look at wikipedia, getting something from earth to the Moon requires a Delta-V of ~16km/s. I am now very much calculating a lower bound because i will assume that it is possible to attach all of that velocity to the mass at the ground, instead of having to fly additional fuel up into space to change the velocity up there. This leads to a required energy per kg of mass that you want to get to the moon of 0.5*16.000²J= 1.28*10^8 J, or 128 MJ. Following the numbers above, to get all of the ocean to the moon you would thus need more than 1.7 *10^26 J According to Wikipedia, the total solar energy absorbed by the earth is ~3.85*10^24 J. So even if we were able to use all of that in an absurdly efficient manner, it would still require ~50 years to transport all of the oceans to the moon. To compare it with another number, the total yearly energy consumption of humanity is ~5.39*10^20 J. So if we were to stop doing anything else, and somehow develop a magic thingy that can use energy to incredibly efficiently transport water to the moon, it would only take us ~300000 years. | ||
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DisaFear
Australia4074 Posts
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Acrofales
Spain18337 Posts
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Simberto
Germany11906 Posts
Basically, the situation is very similar to you having a U-shaped tube filled with water. Both sides will always have the water standing exactly as high as the other. | ||
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killa_robot
Canada1884 Posts
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Simberto
Germany11906 Posts
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juleharen
Norway298 Posts
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Simberto
Germany11906 Posts
Earth's rotation on the other hand is a rather big problem. As you can easily see by the fact that the moon rises and sets, you would need to somehow rotate the base of that string rather quickly around the earth. Another big problem is that the distance is not really consistent, the moons orbit is not exactly circular. | ||
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Acrofales
Spain18337 Posts
On June 14 2015 07:09 Simberto wrote: The moon is tidally locked to the earth (meaning the same side of it always looks towards earth, you can easily notice that by watching its craters, so its rotation is not problematic. Earth's rotation on the other hand is a rather big problem. As you can easily see by the fact that the moon rises and sets, you would need to somehow rotate the base of that string rather quickly around the earth. Another big problem is that the distance is not really consistent, the moons orbit is not exactly circular. The rotation of the earth isn´t a large problem as long as you create it of a material that can coil a bit, and then leave it hanging loose enough that the end can twist around. However, the problem is the material... | ||
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Acrofales
Spain18337 Posts
On June 14 2015 05:32 Simberto wrote: Doesn't work. Water will go exactly as high as the surface of the sea if the tube is filled with air, or ~10m higher than the surface of the seas if empty the tube to a vacuum. Basically, the situation is very similar to you having a U-shaped tube filled with water. Both sides will always have the water standing exactly as high as the other. Damn you and your physics. | ||
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GreenHorizons
United States24059 Posts
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Simberto
Germany11906 Posts
On June 14 2015 07:29 Acrofales wrote: The rotation of the earth isn´t a large problem as long as you create it of a material that can coil a bit, and then leave it hanging loose enough that the end can twist around. However, the problem is the material... Hm, this is quite tricky. I think the best way to "attach" the moon to the earth would be to have basically a space elevator to geosynchronous orbit at the equator, another space elevator to a stationary orbit around the moon, and then attach those two ends together with a very long, flexible rope. Anything else would just lead to instant failure, no matter how durable the rope is, and even in that case i would highly doubt that any of the orbits would remain stable with all of that interference. A big problem would for example be that every part of that rope would tend to try to get into its own orbit with a different orbital speed. | ||
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helpman176
128 Posts
And to address the problem with the lack of atmosphere. How about hollowing out the moon and storing the water there? | ||
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Simberto
Germany11906 Posts
It is currently extremely expensive to put things into orbit, not even speaking about to the moon. | ||
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oGoZenob
France1503 Posts
On June 14 2015 07:40 GreenHorizons wrote: Are 20 oz sodas more expensive than 2-liters around the world or is that an American thing? oz is certainly an american thing^^ I'm guessing it's less than 2 liters, hence your question. And yes, it's probably the case anywhere | ||
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Cascade
Australia5405 Posts
On June 14 2015 17:24 Simberto wrote: A rough guess: Some order of magnitude more often than there is rocket fuel on earth. Fossil fuels will run out MUCH faster. Only possible exception is when you use some other sort of power to separate water into hydrogen and oxygen and use that as fuel. It is currently extremely expensive to put things into orbit, not even speaking about to the moon. So to take another angle again, even assuming that we find some perfect method for moving the water (which has been discussed above), there is a considerable difference in gravitational potential between earth ocean and moon surface, and the oceans are pretty heavy, requiring an enormous amount of energy to move even with near perfect technology. Where to get the energy? - Chemical combustion: I think any chemical combustion you can find on earth (gas, oil, coal, ...) will not be nearly enough before supplies on earth run out. Someone can do the maths, but people keep talking about oil and coal having 100 years left etc. And I think we need many orders of magnitudes higher than earth total yearly energy consumption to move the oceans. - Conventional nuclear fission: I am not sure how much fuel for nuclear fission are available on earth, could be that it would be enough, but could also be that it isn't. Conventional nuclear power may or may not be sufficient, I can't tell myself, but invite people to check up the numbers and the maths. - Fusion: Would do as energy source. Also because you could use the ocean itself as fuel to move it. elegant.  We have huge technological issues today, but this clearly would be a project spanning millenia at the very least, so things may appear.- Renewable: Wind probably won't be enough. Tidal wave energy would be fun, if only as you are using the moons own energy. Not sure how much you would get even with tide-catchers covering all the oceans. Typically tides are a few meters high at most, and involving most of the oceans water. To break free of the earth gravitational field, you need what corresponds to a few thousand km lift I think? Which would mean a few million tidal cycles, which is like 10k years or so, for tidal forces to move the water to the moon (assuming you make perfect use of the energy ofc, which I have no idea how you would do). Hopefully it wouldn't break the moons orbit too much. Solar could probably do as well. Anyone know about effect/area? If you cover a large part of the earth, we would probably get at least as much as tidal I think. Otherwise nothing stops us from having solar catchers/reflectors in orbit using more solar than actually hits earth. So this should be more than sufficient. Earth heat based things could potentially give a lot of energy as well... Anyone dares do a back-of-the-envelope? In summary, for energy source: fusion or solar seems like best bets. | ||
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