Floating Cities

[Mercury Wells]

While I'm not conversant with Physics as such (barely remember school lesson Phys.).

I have been thinking how would a Floating City (FC from now on) be held up.

The idea I had:- was to use magnets, but how big/many would there have to be to hold up...say a 10 sq mile FC and how high would it float?.

Any thoughts, possible solutions et cetera?

[akumabito]

Hot air. Get a sphere large enough, and even a modest temperature differential will get sufficient lift to get it up in the air. Of course the practicality of a sphere several miles in diameter could be debated, but theoretically possible if you'd have a strong enough building material..

[Narsil]

The problem with magnets is that their distance of action is very short so unless the atmosphere has a very strong electro-magnetic field or some sort they aren't really going to work.

With known technology the only realistic option is buoyancy, as in airships. The downside of that is that you need a very large volume of lifting gas to keep a given mass aloft. Anything else is likely to require large amounts of energy since thrust of some sort would be required.

Simply keeping something suspended doesn't, in itself, require energy since you're not trying to accelerate anything, what is does require, though, is force and there is not much in the way of technology available to apply force over any significant distance.

One possible option would be anti-gravity, which is theoretically at least not impossible although the mechanics of h ow it might work and how much energy it would consume to generate and given anti-gravity field are anybody's guess.

[akumabito]

http://en.wikipedia.org/wiki/Cloud_nine_(Tensegrity_sphere)

[Captain Marcus Stahlsturm]

Who needs technology to make a city float? Maybe there's some rock which at a certain temperature becomes lighter than air? From Mars? Or Venus?  I think the skyships in the Edge Chronicles used something like this.

Or it could use some sort of contraption that harnesses pure moonlight to power hundreds of propellers. Steampunk technology doesn't have to follow the same physics as our world.

[Atterton]

A superconductor would float on a magnetic field, perhaps that could be used. Keeping the balance of the city might be problematic though, perhaps making it spin could help with that.

[von Corax]

A superconductor would float on a magnetic field, perhaps that could be used. Keeping the balance of the city might be problematic though, perhaps making it spin could help with that.

Making it spin would also solve the problems of snow removal, traffic congestion and overcrowding.

[Captain]

There could also be space elevators held up ultimately by centrifugal force generated by the Earth's rotation.  Theoretically this could support a series of platforms at different altitudes. 

[pakled]

Anti-gravitic generators, powered by Zenite. However, the actual mining of the mineral causes violent rages in the miners, and...wait, sorry, wrong genre... (tho it could be 'tweaked' slightly to fit right in)

[chicar]

Maybe something in the line of a hydrogenase.

Warning: article in french

http://slowest.wordpress.com/2010/05/10/hydrogenase-par-vincent-callebaut/

[MWBailey]

A superconductor would float on a magnetic field, perhaps that could be used. Keeping the balance of the city might be problematic though, perhaps making it spin could help with that.

Or, spin two or more supercoductors in opposing planes or in opposing diretctions, helicopter-style. Better yet, make the spins and planar (?) orientations independently adjustable, to compensate for changing conditions.