h a l f b a k e r yClearly this is a metaphor for something.
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This Idea was inspired by the electrostatic balloon Idea (linked). Note that most things that can be done with electrostatics can also be done with electromagnetics.
A material that is superconductive exhibits a useful property: when a magnetic field tries to penetrate it, some electric current is
induced in the material that opposes that magnetic field, and keeps it from penetrating. (see Meissner Effect link)
Note that this repulsive effect has been used for magnetic levitation of experimental trains (LOTS of repulsive force available!).
So, all we need is a balloon made of superconductive clothlike material, sealed against air pressure AND evacuated, and an extremely powerful (superconductor-based, of course!) magnet in the middle. The clothlike material is repelled away from the magnet, and forces the balloon-shape to appear, against air pressure.
How about THAT method for making a "vacuum balloon"!
The main disadvantage here is that magnetic fields are not spherical. Nevertheless, an appropriately shaped clothlike superconductive material could still be volumous enough, even if magnetic-field shaped instead of being spherical, for this Idea to generate significant lift/buoyancy.
Inspiration
static_20ionized_20air_20balloon
As mentioned in the main text. [Vernon, Dec 08 2012]
Meissner Effect
http://en.wikipedia...iki/Meissner_effect
Superconductive repulsion, as mentioned in the main text. [Vernon, Dec 08 2012]
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The equator will not experience any useful repulsion, but
that could be overcome by spinning the craft.
Congratulations, you have found the missing technology
to make the prayer wheel vacuum blimp work. |
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Great idea, would work rather well as long as the
magnet inside weighed less than the equivalent
amount of hydrogen needed to displace the same
volume inside the balloon. It would have the added
benefits of being electronically adjustable and non-
flammable. Maybe save you a few bucks too. |
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//the missing technology to make the prayer wheel vacuum blimp work// |
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With a remotely controlled electromagnet, this could be adapted for the Hullaballoon, too. |
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I think this runs up against the same problem as
when I posted an idea for a spherical magnetic shell
with the north pole on the outside and the south
pole on the inside, as a synthetic monopole. |
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I was told that, within a closed shell, there is no
magnetic field. |
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Why when it moves? By the same token (all things
being relative), you're arguing that blowing air over
such a balloon would create magnetic fields, which I
doubt. |
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I suspect that you wouldn't see magnetic fields on the outside of the shell, because a superconductor is perfectly diamagnetic - an external magnetic field does not pass into or through it. |
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//I think that only applies for charge within a conductive shell.// I think so too. |
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There should be a force, but it may not be able to sustain a stable configuration. |
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Well, your idea almost certainly won't work, but it's raised some non-trivial questions. |
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I thought the closed field argument applied to
magnetic as well as electrostatic fields - it would be
odd if it applied to one but not the other. |
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There's another problem. If the field *did* work to
cause the skin to repel itself, then the main
forces (by a huge factor) will be between adjacent
pieces of the skin, not opposite ones. |
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To put it another way, inverse cube (for
magnetism, I believe) means that the force
between two pieces of skin 1cm apart will be 10^9
times greater than the force between two pieces
of skin 10 metres apart. |
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Given that the skin has a finite strength, this
means that almost all of the 'restoring force' will
act over short distances. This therefore amounts
to a "skin stiffening" force. The skin stiffness
required to support a hollow shell against
atmospheric pressure is immensely huge, and
becomes immensely huger as the diameter of the
balloon increases (or, equally, as the radius of
curvature increases). |
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So, I think this will fail by a factor of 10^N, where
N is large. However, it will only have to
opportunity to fail in this way if my original
argument about no net field in a closed shell is
wrong. |
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Thus, we have not only a failure mode but a
backup failure mode. |
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Electric and magnetic fields are very different cases; there is no magnetic 'charge' to redistribute on the surface. In any case, this is not a hollow conductor - it's a hollow conductor with a stonking great magnet in it. An empty Faraday cage contains no electric or magnetic field, but your digital watch still works while you're inside one. |
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//we have not only a failure mode but a backup failure mode//
[marked-for-tagline] |
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(+) Loving this discussion. |
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//your digital watch still works while you're inside
one.// Mine doesn't. |
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1 mF (0.001 Farads) is an amount of capacitance. Charge is measured in Coulombs. |
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Superconductors have a magnetic permeability of zero. And the magnet does not move relative to the shell. Thats why I was thinking you wouldn't see magnetic fields on the balloon. |
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//Charge is measured in Coulombs.// |
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I wish. Mine's always in bloody Guineas. |
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My understanding is that the current generated in a superconductor by an external magnetic field lies in an extremely shallow layer. The equal-and-opposite magnetic field is only apparent on that face of the superconductor, and is not apparent on the other side. |
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Thus, it is possible to hide a magnetic field from the rest of the universe inside a superconducting shell. That you can't similarly hide an electric charge is not a paradox; the absence of magnetic monopoles means that the net magnetic charge is always zero, so there is no conservation issue. |
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