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A question on magnetohydrodynamics
Posted: 27 June 2010 11:49 AM   [ Ignore ]   [ # 16 ]
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Stormy Fairweather - 27 June 2010 11:17 AM

Providing you could find a fat enough skydiver to cause a signifigant gravity well, any fan would be pushing down with the same force it is pointing up.

In effect, trying to pick yourself up.

Isn’t scaling up the magnets to counteract the increased mass the same problem?  Something has to support and move them to move the plasma mass to move the vehicle, right?

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Posted: 27 June 2010 12:46 PM   [ Ignore ]   [ # 17 ]
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The answer to that is simple enough to verify… suspend something between two magnets on a scale, and see if the wieght of those magnets increases. And it does. Looking at it like that way, it seems likely my idea is not viable.

However plasma acts very differently than most other matter (especially in that its movements seem to be dominated by magnetic fields. Out of the formulas I read and understood, not ONE has gravity as a signifigant variable), which is why I was hoping to get some input from someone familiar with the subject.

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Posted: 27 June 2010 01:05 PM   [ Ignore ]   [ # 18 ]
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So is it your assertion that a 100 pound magnetic containment device containing 10 pounds of plasma does not exert 110 pounds of force on the ground?  That would be surprising to me.  How much plasma mass is involved in the formulas you refer to?  Does the formula continue to correspond with observation as the plasma mass is significantly increased?

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Posted: 27 June 2010 01:18 PM   [ Ignore ]   [ # 19 ]
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As was pointed out early in this thread, so far only minute amounts of plasma have been worked with.

But I am not asking about ten pounds of plasma, I am talking about billions of tons of mass in the space of a dime. And if there is one thing science has shown, is that physics act odd at extremes (quantum functions, special relativity)

Look PC, there are alot of things about this subject I DON’T KNOW. That is why I am ASKING.

When did ‘asking a question’ become an “assertion?”

And responding; ‘well, what do you think/know?’ is not a fucking answer. Not outside of your shrinks office anyway.

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Posted: 27 June 2010 01:26 PM   [ Ignore ]   [ # 20 ]
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Stormy Fairweather - 27 June 2010 01:18 PM

Look PC, there are alot of things about this subject I DON’T KNOW. That is why I am ASKING.

You might as well be asking if the plasma is sentient and can be used to replace DMV clerks.  Seems as productive.

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Posted: 27 June 2010 01:51 PM   [ Ignore ]   [ # 21 ]
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... Why can’t you just say you don’t know?

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Posted: 27 June 2010 01:55 PM   [ Ignore ]   [ # 22 ]
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Oy, no reason for this to get out of hand. My understanding of magnetic levitation generally (e.g. of trains) is that the magnet has to be housed on solid ground, and it supports the thing that floats.

I also recall hearing that if all the atoms in a magnet were lined up in the same direction, the force they would exert would be many, many orders of magnitude greater than we find even from the best magnets. So one thing is to think of a “perfected” solid, and another thing entirely is to think of the solids we actually have around us. Doubtless any plasma will be of the latter kind.

A further question, which I think is germane, is that I doubt a plasma could get dense enough to have strong effects on its surroundings, as proposed. Now, I also don’t know enough to be certain, but if we’re having problems containing thin plasmas, I’m sure that dense ones would be even tougher. I’d further expect that to get a dense material into plasma form it would have to be much hotter than the comparable diffuse one.

So I expect that while this is interesting as a thought experiment, it could never be made workable. But a competent physicist in the right field would of course know much more.

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Posted: 27 June 2010 02:36 PM   [ Ignore ]   [ # 23 ]
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Stormy Fairweather - 27 June 2010 01:51 PM

... Why can’t you just say you don’t know?

Try Physics Forums. You may get better answers there, but try to be polite if you don’t get the answer you want.

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Posted: 27 June 2010 02:36 PM   [ Ignore ]   [ # 24 ]
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Thanks doug… I was starting to lose hope here that anyone would actually contribute.

It is merely a thought experiment of course, as we lack any technologies to make this workable, or testable, likely for a very long time.

But forgetting the whole plasma thing… would it be possible for a gravity well strong enough, and small enough, to move something in a controllable fashion without simply colliding with the nearest object of signifigant mass?

The reason I ask is that gravity is the greatest limitation on human expansion, and it seems the best way to overcome it is to control it.

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Posted: 27 June 2010 10:57 PM   [ Ignore ]   [ # 25 ]
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Stormy Fairweather - 27 June 2010 02:36 PM

But forgetting the whole plasma thing… would it be possible for a gravity well strong enough, and small enough, to move something in a controllable fashion without simply colliding with the nearest object of signifigant mass?

Sure—maglev trains basically do that. But again, the magnets have to be housed on the ground. You can’t lift up the magnet *and* the mass at the same time, unless arguably you’re using the whole Earth as the magnet, but then the force will be very weak.

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Posted: 28 June 2010 03:00 AM   [ Ignore ]   [ # 26 ]
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I been having this idea bouncing around in my cranium for awhile, and really have not put the proper effort in to turn into an actual theory, or even to convey what it is I am speculating about efficiantly (apprently).

My own fault for starting at what should have been the end, the methodology. And I think that clouded your perception on my last question, or I was just unclear (maglev trains do not use a small confined gravitional force to directly counter ambient gravity)

Either way, never mind. I need to refine this idea before pitching it, even as a thought experiment.

I will likely repost on this at some point, but I will have more information included/linked, and hopefully be more concise.

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Posted: 28 June 2010 06:47 AM   [ Ignore ]   [ # 27 ]
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Stormy Fairweather - 28 June 2010 03:00 AM

(maglev trains do not use a small confined gravitional force to directly counter ambient gravity)

Right, they use the electromagnetic force. The same would be true of a confined plasma, levitated inside of a toroidal electromagnetic ring or the like. As of yet there is no evidence for literal “antigravity”, that is, a gravitational force that would ‘counter ambient gravity’.

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Posted: 28 June 2010 12:19 PM   [ Ignore ]   [ # 28 ]
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...

I am in no way whatsoever talking about ‘anti gravity.’ I am talking about controlling the position of a piece of matter massive enough and small enough that its own gravity can be used to move an object.

Using gravity to move stuff. Rather than counter (poor terminology) I should have said overpower. And examples of that abound. The moon for instance is far more immediedly affected by the earth than the sun, despite its much larger and stronger gravity well solely by its proximity to the source. I am simply speculating on the possibility of doing this on a much smaller scale and in a much more deliberate manner.

(I was just gonna drop this for the time being, but the thought that you think I was talking about something as stupid as making antigravity…)

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Posted: 28 June 2010 12:55 PM   [ Ignore ]   [ # 29 ]
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So I’m imagining a device with sufficient energy to contain an enormous amount of plasma mass (which I guess comes from an enormous times the speed of light squared amount of additional energy) that we can turn on and off to gravitationally attract a vehicle of some sort at will.  Where shall we place this device?  Not on or near Earth I hope.  If we’re to attract a relatively small mass vehicle that is relatively far away, imagine the effect of on the nearby large mass Earth - inverse square law and all.

So we have this device way out between planets, solar systems, or even galaxies.  Somewhere where turning it on doesn’t affect the orbits of any planets we might care about.  We’d have to propel the vehicle conventionally toward the device.  I mean, if the gravity of the huge plasma mass is enough to attract a vehicle it would also attract any planet the vehicle was on or near.  So we’ve conventionally moved the vehicle close enough to the device so that we can gradually turn up the mass, gradually turning up the gravitational attraction between the two.  (I’m not sure where we got all the energy needed to create this enormous plasma mass.  It sure would be a lot according to Einstein’s famous formula.)  The vehicle accelerates rapidly toward the device which presumably shuts off just in time to avoid a collision.  Momentum carries the vehicle (with very little loss of velocity through the near vacuum of space) on to its destination.  I gather we turn the plasma mass back into energy at this point too.  That could be spectacular - I mean super-huge-atomic-bomb-spectacular.

But now we have another problem.  How do we slow the vehicle down so that it doesn’t obliterate life on the destination planet?  Either the vehicle uses more conventional propulsion or we modulate the plasma mass as the vehicle passes and seriously slow down the second half of the trip.

Am I close?

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Posted: 28 June 2010 01:00 PM   [ Ignore ]   [ # 30 ]
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That would be a “nope.”

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