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The limitation of flywheel speed mostly depends on the tensile
strength of the material in the wheel and the density.
So if the wheel is enclosed in a vessel which is highly pressurised, say
with air*, the pressure will compress the flywheel and reduce the
apparent tension. That means it should
be able to spin faster without
distruction.
*I originally thought of superfluid Helium (friction-less), but that only
goes up to about 25bar... not enough. And it is only friction free up to a
certain velocity.
[link]
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If the environment is non-frictionless, then the flywheel
will get hotter even before you spin it up to a higher-than-
normal speed. Hotter materials
tend to be less strong than colder materials.... (Colder
materials tend to be more brittle, but that is actually
related to a different thing, "toughness", than "strength".) |
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Wouldn't a fluid be the best for this? |
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This is actually (contrary to my first reaction) not
such a dumb idea. |
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However, you'd need fearsome pressures to have
any
significant effect, and I suspect the greatly
increased
drag would offset any advantages. |
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For instance, the tensile strength of good steel is
something like 1600MPa. If you had a pressure of
160Mpa (1600 atmospheres), you'd get a 10%
increase (and a ~5% increase in maximum speed),
although the liquefaction of the gas would be a bit
of a problem. |
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Instead of pressure from external gas could one use a fixed magnet for a flywheel, with an external fixed magnet around it opposing the field from the wheel? The field from the external magnet should oppose the centrifugal force which wants to pull the wheel apart. It should not slow the rotary motion. |
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Again, the forces you could apply would be very
small compared to the existing tensile strength of a
steel flywheel. As mentioned above, getting only a
10% increase in the effective burst-force of the
flywheel would require applying an external force of
1600 atmospheres, or about 12 tons per square inch. |
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Alternatively, you could use Schrodinger's Flywheel
to store infinite amounts of energy. |
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If the flywheel is utterly isolated from the rest of
the universe, it has no rotational reference.
Hence, it can spin at an infinite rate without
experiencing any centripugal forces, just as a
rocket, when cruising, experiences no
acceleration. |
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Of course, getting energy in and out of the system
would be tricky. |
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Or, just spin the universe really slowly. With its huge inertia it
ought to store a few Joules (x10^alot). |
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One of my old ponderings:
If I fire little thrusters to rotate my spaceship, and set the
frame of reference as my spaceship, then I am rotating the
universe? Since I input so little energy this cannot be so. The
other way to tell is that I am flung to the outside of the
spaceship. How does my spaceship know the universe is
there? |
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//If the flywheel is utterly isolated from the rest of the
universe,// and all the parts of the flywheel are utterly
isolated from each other, even at the sub-atomic level, it
can neither experience any forces nor have the experience
of being a flywheel. |
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//If the flywheel is utterly isolated from the rest of the universe, it has no rotational reference.// |
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I don't think that's true - I think anything anywhere other than on the rotational axis would feel an apparent force ('centrifugal force').
And there's an experiment you can do with a bucket of water as a demonstration. |
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If the parts are isolated from each other I think the essential flywheelness disappears. |
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