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news:434e9f3b$1@news.povray.org...
In other words, to
> simplify things, without extra masses...you weigh less at noon?
>
Don't tides work this way?
Marc
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Anthony D. Baye wrote:
> Alain wrote:
>
>> Anthony D. Baye nous apporta ses lumieres en ce 2005-10-12 20:50:
>>
>>> Mike Williams wrote:
>>>
>>>> Apart from the absence of the plasma tube, I'd say it was Thistledown.
>>>>
>>>> Where does your hollow asteroid get its light from?
>>>>
>>> Wow. Someone else reads what I read.
>>>
>>> A.D.B.
>>>
>>> P.S. Alain, Gravity is based on mass. A sphere the size of earth's
>>> orbit with a shell thick enough to withstand impacts would naturally
>>> have a reasonable amount of gravity on it's inside surface.
>>
>>
>>
>> The gravitational pull from the relatively small but very near region
>> under your feet is exactly countered by that of the extremely large
>> and distant part over your head.
>> That leave you with ONLY the gravity from the sun witch is straight
>> up... NOT a good thing.
>>
> Far be it from me to dislike being proved wrong.
>
> but an interesting factoid: Larry Niven's Ringworld, which was
> conceived as an intermediate step toward a dyson sphere, spun at 770
> mi/h. It was determined that, in order to withstand the shearing forces
> from the spin, the base material which measured 1000' thick would have
> had to have had a tensile strength on the order of the force which holds
> the nucleus of an atom together.
>
> A.D.B.
Still, if it were spun up for gravitational effects, and only the area
around the equator were used for habitation, and the rest was used for
energy collection, storage, life support and suchlike, then there would
still be a massive amount of livable area. f/ex. if the sphere were the
size of earth's orbit, and assuming that the livable area were a million
miles wide, then the total inside surface area (Not accounting for
variations in topography) would be 2(pi)(9.28e6)(1e6) mi^2 that's
several thousand times the surface area of earth.
A.D.B.
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Tim Cook <z99### [at] bellsouth net> wrote:
> Alain wrote:
> > I have a BIG problem with Dyson spheres! Inside an hollow sphere, there
> > is NO gravity, if the sphere is built around a star, everything not held
> > in place will fall in the star. If you make it spin, all the air will
> > collect at the equator, untill the sphere collapses unto itself. The
> > equatorial part goes flying away and the poles plunging into the star.
>
> Why is there no gravity? If you take a sun-sized star and build a
> sphere of Earths around it at 1 AU (dunno where you'd get that many
> Earths), does the now hollow sphere not have gravity on either its
> inside or outside surface?
A spherical shell exerts no gravity on anything within. If you do the math
it turns out that no matter where you are within the shell, the gravity
from the material behind you exactly cancels the gravity from the material
in front of you.
Outside the shell, gravity works like you'd expect.
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Mike Williams <nos### [at] econymdemoncouk> wrote:
> Apart from the absence of the plasma tube, I'd say it was Thistledown.
>
> Where does your hollow asteroid get its light from?
....except that Thistledown was indefinitely long inside. This one appears
to stop.
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"Anthony D. Baye" <Sha### [at] hotmailcom> wrote:
> Mike Williams wrote:
> > Apart from the absence of the plasma tube, I'd say it was Thistledown.
> >
> > Where does your hollow asteroid get its light from?
> >
> Wow. Someone else reads what I read.
>
> A.D.B.
>
> P.S. Alain, Gravity is based on mass. A sphere the size of earth's
> orbit with a shell thick enough to withstand impacts would naturally
> have a reasonable amount of gravity on it's inside surface.
Actually the gravity felt at a distance underground is that due to the
sphere that you are standing on alone. Remove that sphere of material and
you are in free-fall. The easy way to think of this is that a small amount
of material nearby is balanced by a lot at a distance.
Andy
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Wasn't it Marc Jacquier who wrote:
>
>news:434e9f3b$1@news.povray.org...
>In other words, to
>> simplify things, without extra masses...you weigh less at noon?
>>
>Don't tides work this way?
Not at all. If that was how tides worked, there would only be one tide
per day instead of two. Tidal forces also make you lighter when the
extra mass is directly below your feet.
--
Mike Williams
Gentleman of Leisure
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Wasn't it Mack Tuesday who wrote:
>Mike Williams <nos### [at] econymdemoncouk> wrote:
>> Apart from the absence of the plasma tube, I'd say it was Thistledown.
>>
>> Where does your hollow asteroid get its light from?
>
>....except that Thistledown was indefinitely long inside. This one appears
>to stop.
I was thinking of one of the first six chambers. (I had to think for a
while for the term "plasma tube", I knew that I didn't want to say
"flaw").
--
Mike Williams
Gentleman of Leisure
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news:Cra### [at] econymdemoncouk...
> Wasn't it Marc Jacquier who wrote:
> >
> >news:434e9f3b$1@news.povray.org...
> >In other words, to
> >> simplify things, without extra masses...you weigh less at noon?
> >>
> >Don't tides work this way?
>
> Not at all. If that was how tides worked, there would only be one tide
> per day instead of two. Tidal forces also make you lighter when the
> extra mass is directly below your feet.
>
> --
The secon rise is due to a resonnance, an harmonic
Marc
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Marc Jacquier wrote:
> news:Cra### [at] econymdemoncouk...
>
>>Wasn't it Marc Jacquier who wrote:
>>
>>>news:434e9f3b$1@news.povray.org...
>>>In other words, to
>>>
>>>>simplify things, without extra masses...you weigh less at noon?
>>>>
>>>
>>>Don't tides work this way?
>>
>>Not at all. If that was how tides worked, there would only be one tide
>>per day instead of two. Tidal forces also make you lighter when the
>>extra mass is directly below your feet.
>>
>>--
>
> The secon rise is due to a resonnance, an harmonic
>
> Marc
>
No, it's not a resonnance. The way I've heard the two tides explained
is that the ocean is raised by the moon's gravity on that side of the
earth, but it also pulls the _earth_ away from the water on the far
side. So the high tide on the far side is not that the water is higher,
but that the earth is lower.
-=- Larry -=-
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Rick Measham wrote:
> Mike Williams wrote:
>
>> The strength of the force varies with cos(latitude) and the angle to the
>> local vertical is proportional to latitude. So people standing near the
>> poles get very little force, and what force there is would be almost
>> horizontal.
>
>
> Which is where the original argument came from (and I agree) .. the
> poles would implode, thus degrading the structure and causing the
> equator to explode.
>
> One poster (somewhere, not here) suggested a band rather than a sphere.
> The 'band' would be the equatorial region and would (somehow) hold
> together as it spun.
And then some other killjoy did the math and realized that if the ring
were to be moved so that the star was no longer in the center, the
situation would not correct itself naturally; if there were no
artificial corrective measures, the ring would eventually collide with
the sun. Roll the credits.
BTW, Dyson himself did not postulate a solid sphere, but a large number
of small bodies which collectively capture all of the output from a
given star.
Regards,
John
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