On 7/14/2023 4:52 PM, Tony Nance wrote:
> On Thursday, July 13, 2023 at 8:56:24 AM UTC-4, pete...@gmail.com wrote:
>> On Wednesday, July 12, 2023 at 1:51:42 PM UTC-4, pete...@gmail.com wrote:
>>> On Wednesday, July 12, 2023 at 1:36:56 PM UTC-4, Robert Carnegie wrote:
>>>> Apparently I wrote here in 2021 and we didn't get around
>>>> to checking? -
>>>>
>>>> "It may be Joe Haldeman's _The Long Habit of Living_ /
>>>> _Buying Time_ that visits a rotating "2001"-type space station
>>>> (I suppose) where I think the men's room receptacle has
>>>> a target marked /next/ to it, "x <-- Aim Here, Stupid".
>>>> Our hero does so."
>>> It would have be pretty small, and spinning fast, to make a difference,
>>> unless you're going for a long distance shot.
>>>
>>> Fun video:
>>> https://www.youtube.com/watch?v=bJ_seXo-Enc
>> Since no one has posted an answer, I'll reveal it:
>>
>> -----------------
>>
>> The Question:
>> Here's a another fun one: Imagine a hollow sphere the size of the Earth,
>> with a Moon sized spherical void in the center.
>>
>> Assume no rotation, relative to distant stars, and no Sun or other
>> massive bodies nearby.
>>
>> You climb down a shaft from the outer surface to the inner one.
>> How does your weight change as you descend, and what weight
>> do you feel when you reach the inner surface? Which way is 'down'
>> at that point?
>> -----------------------
>>
>> The Answer:
>>
>> Your weight linearly decreases as you go down, and when you
>> reach the void at the center, its zero. The entire central void
>> is at 0 perceived gravity. You aren't attracted to the walls, nor
>> to the center.
>>
>> This seems counter intuitive. I *think* Rudy Rucker got it
>> right, but I can't think of any other 'hollow earth' story that
>> did.
>
> While I would never _expect_ an author to get it right in a
> fictional work, Rucker -- who has a PhD in math -- is way
> high on the list of authors that wouldn't surprise me by
> getting it right.
>
> Tony
>
>> Newton was the first to work this out:
>> https://en.wikipedia.org/wiki/Shell_theorem
>>
>> pt

Rudy Rucker was one of the original programmers for AutoCAD. Incredibly
smart according to John Walker, the founder of AutoDesk.

Lynn

On Friday, July 14, 2023 at 6:19:48 PM UTC-4, Lynn McGuire wrote:
> On 7/14/2023 4:52 PM, Tony Nance wrote:
> > On Thursday, July 13, 2023 at 8:56:24 AM UTC-4, pete...@gmail.com wrote:
> >> On Wednesday, July 12, 2023 at 1:51:42 PM UTC-4, pete...@gmail..com wrote:
> >>> On Wednesday, July 12, 2023 at 1:36:56 PM UTC-4, Robert Carnegie wrote:
> >>>> Apparently I wrote here in 2021 and we didn't get around
> >>>> to checking? -
> >>>>
> >>>> "It may be Joe Haldeman's _The Long Habit of Living_ /
> >>>> _Buying Time_ that visits a rotating "2001"-type space station
> >>>> (I suppose) where I think the men's room receptacle has
> >>>> a target marked /next/ to it, "x <-- Aim Here, Stupid".
> >>>> Our hero does so."
> >>> It would have be pretty small, and spinning fast, to make a difference,
> >>> unless you're going for a long distance shot.
> >>>
> >>> Fun video:
> >>> https://www.youtube.com/watch?v=bJ_seXo-Enc
> >> Since no one has posted an answer, I'll reveal it:
> >>
> >> -----------------
> >>
> >> The Question:
> >> Here's a another fun one: Imagine a hollow sphere the size of the Earth,
> >> with a Moon sized spherical void in the center.
> >>
> >> Assume no rotation, relative to distant stars, and no Sun or other
> >> massive bodies nearby.
> >>
> >> You climb down a shaft from the outer surface to the inner one.
> >> How does your weight change as you descend, and what weight
> >> do you feel when you reach the inner surface? Which way is 'down'
> >> at that point?
> >> -----------------------
> >>
> >> The Answer:
> >>
> >> Your weight linearly decreases as you go down, and when you
> >> reach the void at the center, its zero. The entire central void
> >> is at 0 perceived gravity. You aren't attracted to the walls, nor
> >> to the center.
> >>
> >> This seems counter intuitive. I *think* Rudy Rucker got it
> >> right, but I can't think of any other 'hollow earth' story that
> >> did.
> >
> > While I would never _expect_ an author to get it right in a
> > fictional work, Rucker -- who has a PhD in math -- is way
> > high on the list of authors that wouldn't surprise me by
> > getting it right.
> >
> > Tony
> >
> >> Newton was the first to work this out:
> >> https://en.wikipedia.org/wiki/Shell_theorem
> >>
> >> pt
> Rudy Rucker was one of the original programmers for AutoCAD. Incredibly
> smart according to John Walker, the founder of AutoDesk.

I'll add that Newton's Shell theorem is closely related to the instability of
Nivens's Ringworld. While gravity does work to keep the Ringworld's sun
within the plane of the ring, gravity does not center it.

Pt

On Saturday, July 15, 2023 at 2:43:34 PM UTC+10, pete...@gmail.com wrote:
> I'll add that Newton's Shell theorem is closely related to the instability of
> Nivens's Ringworld. While gravity does work to keep the Ringworld's sun
> within the plane of the ring, gravity does not center it.
>
I believe later books retconned there being an active stabilisation method

In article <e1cdae31-505b-4ec2-bea8-2217c31394f3n@googlegroups.com>,
Hamish Laws <hamish.laws@gmail.com> wrote:
>On Saturday, July 15, 2023 at 2:43:34 PM UTC+10, pete...@gmail.com wrote:
>> I'll add that Newton's Shell theorem is closely related to the instability of
>> Nivens's Ringworld. While gravity does work to keep the Ringworld's sun
>> within the plane of the ring, gravity does not center it.
>>
>I believe later books retconned there being an active stabilisation method

(Hal Heydt)
That would be _Ringworld Engineers_. HOwever, the stabiling
engines had been dismantled and mostly used to power spacecraft.
Getting enough of them re-installed and functioning is part of
the plot.

The neutral stability of the ring itself was the *second* problem
pointed out in the book. The first--pointed out by Karen
Anderson and, probably others--was that Luis Woo went around the
world the wrong way to extend his 200th birthday. That was
corrected in the second edition.

There is a third problem with the entire premise in _Ringworld_
and (especially) _Ringworld Engineers_. That is that, no matter
how impervious to particles and radiation from the core explosion
the ring floor material is, it won't save anyone living on the
ring. The ring rotates. The apparent width of the ring across
it's diameter is trivial compared to the angular with of
the--specified--5000 ly diameter of the core explosion.

On Saturday, July 15, 2023 at 5:25:59 PM UTC-4, Dorothy J Heydt wrote:
> In article <e1cdae31-505b-4ec2...@googlegroups.com>,
> Hamish Laws <hamis...@gmail.com> wrote:
> >On Saturday, July 15, 2023 at 2:43:34 PM UTC+10, pete...@gmail.com wrote:
> >> I'll add that Newton's Shell theorem is closely related to the instability of
> >> Nivens's Ringworld. While gravity does work to keep the Ringworld's sun
> >> within the plane of the ring, gravity does not center it.
> >>
> >I believe later books retconned there being an active stabilisation method
> (Hal Heydt)
> That would be _Ringworld Engineers_. HOwever, the stabiling
> engines had been dismantled and mostly used to power spacecraft.
> Getting enough of them re-installed and functioning is part of
> the plot.
>
> The neutral stability of the ring itself was the *second* problem
> pointed out in the book. The first--pointed out by Karen
> Anderson and, probably others--was that Luis Woo went around the
> world the wrong way to extend his 200th birthday. That was
> corrected in the second edition.
>
> There is a third problem with the entire premise in _Ringworld_
> and (especially) _Ringworld Engineers_. That is that, no matter
> how impervious to particles and radiation from the core explosion
> the ring floor material is, it won't save anyone living on the
> ring. The ring rotates. The apparent width of the ring across
> it's diameter is trivial compared to the angular with of
> the--specified--5000 ly diameter of the core explosion.

The last problem is resolved in the ...of Worlds books.

Pt

On Saturday, 15 July 2023 at 23:29:46 UTC+1, pete...@gmail.com wrote:
> On Saturday, July 15, 2023 at 5:25:59 PM UTC-4, Dorothy J Heydt wrote:
> > In article <e1cdae31-505b-4ec2...@googlegroups.com>,
> > Hamish Laws <hamis...@gmail.com> wrote:
> > >On Saturday, July 15, 2023 at 2:43:34 PM UTC+10, pete...@gmail..com wrote:
> > >> I'll add that Newton's Shell theorem is closely related to the instability of
> > >> Nivens's Ringworld. While gravity does work to keep the Ringworld's sun
> > >> within the plane of the ring, gravity does not center it.
> > >>
> > >I believe later books retconned there being an active stabilisation method
> > (Hal Heydt)
> > That would be _Ringworld Engineers_. HOwever, the stabiling
> > engines had been dismantled and mostly used to power spacecraft.
> > Getting enough of them re-installed and functioning is part of
> > the plot.
> >
> > The neutral stability of the ring itself was the *second* problem
> > pointed out in the book. The first--pointed out by Karen
> > Anderson and, probably others--was that Luis Woo went around the
> > world the wrong way to extend his 200th birthday. That was
> > corrected in the second edition.
> >
> > There is a third problem with the entire premise in _Ringworld_
> > and (especially) _Ringworld Engineers_. That is that, no matter
> > how impervious to particles and radiation from the core explosion
> > the ring floor material is, it won't save anyone living on the
> > ring. The ring rotates. The apparent width of the ring across
> > it's diameter is trivial compared to the angular with of
> > the--specified--5000 ly diameter of the core explosion.
> The last problem is resolved in the ...of Worlds books.

I will guess, a roof?

They're playing tennis in Wimbledon as I type, elsewhere.

On Sunday, July 16, 2023 at 10:33:49 AM UTC-4, Robert Carnegie wrote:
> On Saturday, 15 July 2023 at 23:29:46 UTC+1, pete...@gmail.com wrote:
> > On Saturday, July 15, 2023 at 5:25:59 PM UTC-4, Dorothy J Heydt wrote:
> > > In article <e1cdae31-505b-4ec2...@googlegroups.com>,
> > > Hamish Laws <hamis...@gmail.com> wrote:
> > > >On Saturday, July 15, 2023 at 2:43:34 PM UTC+10, pete...@gmail.com wrote:
> > > >> I'll add that Newton's Shell theorem is closely related to the instability of
> > > >> Nivens's Ringworld. While gravity does work to keep the Ringworld's sun
> > > >> within the plane of the ring, gravity does not center it.
> > > >>
> > > >I believe later books retconned there being an active stabilisation method
> > > (Hal Heydt)
> > > That would be _Ringworld Engineers_. HOwever, the stabiling
> > > engines had been dismantled and mostly used to power spacecraft.
> > > Getting enough of them re-installed and functioning is part of
> > > the plot.
> > >
> > > The neutral stability of the ring itself was the *second* problem
> > > pointed out in the book. The first--pointed out by Karen
> > > Anderson and, probably others--was that Luis Woo went around the
> > > world the wrong way to extend his 200th birthday. That was
> > > corrected in the second edition.
> > >
> > > There is a third problem with the entire premise in _Ringworld_
> > > and (especially) _Ringworld Engineers_. That is that, no matter
> > > how impervious to particles and radiation from the core explosion
> > > the ring floor material is, it won't save anyone living on the
> > > ring. The ring rotates. The apparent width of the ring across
> > > it's diameter is trivial compared to the angular with of
> > > the--specified--5000 ly diameter of the core explosion.
> > The last problem is resolved in the ...of Worlds books.
> I will guess, a roof?

Gur ragver Evatjbeyq gryrcbegf gb cynprf haxabja.

Pt

On Thursday, July 13, 2023 at 5:39:58 PM UTC-4, Lynn McGuire wrote:
> On 7/13/2023 7:56 AM, pete...@gmail.com wrote:
> > On Wednesday, July 12, 2023 at 1:51:42 PM UTC-4, pete...@gmail.com wrote:
> >> On Wednesday, July 12, 2023 at 1:36:56 PM UTC-4, Robert Carnegie wrote:
> >>> Apparently I wrote here in 2021 and we didn't get around
> >>> to checking? -
> >>>
> >>> "It may be Joe Haldeman's _The Long Habit of Living_ /
> >>> _Buying Time_ that visits a rotating "2001"-type space station
> >>> (I suppose) where I think the men's room receptacle has
> >>> a target marked /next/ to it, "x <-- Aim Here, Stupid".
> >>> Our hero does so."
> >> It would have be pretty small, and spinning fast, to make a difference,
> >> unless you're going for a long distance shot.
> >>
> >> Fun video:
> >> https://www.youtube.com/watch?v=bJ_seXo-Enc
> >
> > Since no one has posted an answer, I'll reveal it:
> >
> > -----------------
> >
> > The Question:
> >
> > Here's a another fun one: Imagine a hollow sphere the size of the Earth,
> > with a Moon sized spherical void in the center.
> >
> > Assume no rotation, relative to distant stars, and no Sun or other
> > massive bodies nearby.
> >
> > You climb down a shaft from the outer surface to the inner one.
> > How does your weight change as you descend, and what weight
> > do you feel when you reach the inner surface? Which way is 'down'
> > at that point?
> >
> > -----------------------
> >
> > The Answer:
> >
> > Your weight linearly decreases as you go down, and when you
> > reach the void at the center, its zero. The entire central void
> > is at 0 perceived gravity. You aren't attracted to the walls, nor
> > to the center.
> >
> > This seems counter intuitive. I *think* Rudy Rucker got it
> > right, but I can't think of any other 'hollow earth' story that
> > did.
> >
> > Newton was the first to work this out:
> > https://en.wikipedia.org/wiki/Shell_theorem
> >
> > pt
> "Dark Lightning (A Thunder and Lightning Novel)" by John Varley got it
> right in his six mile long by three mile wide asteroid spaceship
> "Rolling Thunder" rotating at 2 rpm. The kids play a ball game using
> pedaled aircycles that drop in weight as they go higher towards the
> artificial sun on its 24 hour track.
> https://www.amazon.com/Dark-Lightning-Thunder-John-Varley/dp/042527408X

No gravity involved there. It appears that Varley is assuming that the air rotates
as if a solid cylinder (which is questionable), in which case the airbIkes entrained
in it would lose weight as they moved towards the center, or pedaled antispinwise.

Pt

pete...@gmail.com wrote:
> On Thursday, July 13, 2023 at 5:39:58 PM UTC-4, Lynn McGuire wrote:

> > "Dark Lightning (A Thunder and Lightning Novel)" by John Varley got it
> > right in his six mile long by three mile wide asteroid spaceship
> > "Rolling Thunder" rotating at 2 rpm. The kids play a ball game using
> > pedaled aircycles that drop in weight as they go higher towards the
> > artificial sun on its 24 hour track.

> No gravity involved there. It appears that Varley is assuming that the air rotates
> as if a solid cylinder (which is questionable), in which case the airbIkes entrained
> in it would lose weight as they moved towards the center, or pedaled antispinwise.

Shouldn't the air rotate as a whole, if with local disturbances (the proverbial horizontal cyclones)?
I would think with no additional energy input, the air would stabilize as all layers sort of going around together, or bringing the cylinder to a stop.. Although we do have energy input, with an artificial sun, apparently in motion, which a Long Sun wouldn't be.

--
-Jack

On 7/16/2023 11:17 AM, pete...@gmail.com wrote:
> On Thursday, July 13, 2023 at 5:39:58 PM UTC-4, Lynn McGuire wrote:
>> On 7/13/2023 7:56 AM, pete...@gmail.com wrote:
>>> On Wednesday, July 12, 2023 at 1:51:42 PM UTC-4, pete...@gmail.com wrote:
>>>> On Wednesday, July 12, 2023 at 1:36:56 PM UTC-4, Robert Carnegie wrote:
>>>>> Apparently I wrote here in 2021 and we didn't get around
>>>>> to checking? -
>>>>>
>>>>> "It may be Joe Haldeman's _The Long Habit of Living_ /
>>>>> _Buying Time_ that visits a rotating "2001"-type space station
>>>>> (I suppose) where I think the men's room receptacle has
>>>>> a target marked /next/ to it, "x <-- Aim Here, Stupid".
>>>>> Our hero does so."
>>>> It would have be pretty small, and spinning fast, to make a difference,
>>>> unless you're going for a long distance shot.
>>>>
>>>> Fun video:
>>>> https://www.youtube.com/watch?v=bJ_seXo-Enc
>>>
>>> Since no one has posted an answer, I'll reveal it:
>>>
>>> -----------------
>>>
>>> The Question:
>>>
>>> Here's a another fun one: Imagine a hollow sphere the size of the Earth,
>>> with a Moon sized spherical void in the center.
>>>
>>> Assume no rotation, relative to distant stars, and no Sun or other
>>> massive bodies nearby.
>>>
>>> You climb down a shaft from the outer surface to the inner one.
>>> How does your weight change as you descend, and what weight
>>> do you feel when you reach the inner surface? Which way is 'down'
>>> at that point?
>>>
>>> -----------------------
>>>
>>> The Answer:
>>>
>>> Your weight linearly decreases as you go down, and when you
>>> reach the void at the center, its zero. The entire central void
>>> is at 0 perceived gravity. You aren't attracted to the walls, nor
>>> to the center.
>>>
>>> This seems counter intuitive. I *think* Rudy Rucker got it
>>> right, but I can't think of any other 'hollow earth' story that
>>> did.
>>>
>>> Newton was the first to work this out:
>>> https://en.wikipedia.org/wiki/Shell_theorem
>>>
>>> pt
>> "Dark Lightning (A Thunder and Lightning Novel)" by John Varley got it
>> right in his six mile long by three mile wide asteroid spaceship
>> "Rolling Thunder" rotating at 2 rpm. The kids play a ball game using
>> pedaled aircycles that drop in weight as they go higher towards the
>> artificial sun on its 24 hour track.
>> https://www.amazon.com/Dark-Lightning-Thunder-John-Varley/dp/042527408X
>
> No gravity involved there. It appears that Varley is assuming that the air rotates
> as if a solid cylinder (which is questionable), in which case the airbIkes entrained
> in it would lose weight as they moved towards the center, or pedaled antispinwise.
>
> Pt

Nope. The artificial sun is in the middle of the longitudinal axis, the
center of the asteroid. The air does travel with the spin of the
asteroid, otherwise the air would continually knock the buildings down.

Read the book and prove me wrong ! You can still buy the MPPB for $8, a
bargain nowadays. In fact, I cannot remember if the settled area goes
around the total interior of the hollowed out asteroid or just half of
it with a "blue sky" beyond the artificial sun.

Lynn

On Sunday, July 16, 2023 at 9:03:11 PM UTC-4, Lynn McGuire wrote:
> On 7/16/2023 11:17 AM, pete...@gmail.com wrote:
> > On Thursday, July 13, 2023 at 5:39:58 PM UTC-4, Lynn McGuire wrote:
> >> On 7/13/2023 7:56 AM, pete...@gmail.com wrote:
> >>> On Wednesday, July 12, 2023 at 1:51:42 PM UTC-4, pete...@gmail.com wrote:
> >>>> On Wednesday, July 12, 2023 at 1:36:56 PM UTC-4, Robert Carnegie wrote:
> >>>>> Apparently I wrote here in 2021 and we didn't get around
> >>>>> to checking? -
> >>>>>
> >>>>> "It may be Joe Haldeman's _The Long Habit of Living_ /
> >>>>> _Buying Time_ that visits a rotating "2001"-type space station
> >>>>> (I suppose) where I think the men's room receptacle has
> >>>>> a target marked /next/ to it, "x <-- Aim Here, Stupid".
> >>>>> Our hero does so."
> >>>> It would have be pretty small, and spinning fast, to make a difference,
> >>>> unless you're going for a long distance shot.
> >>>>
> >>>> Fun video:
> >>>> https://www.youtube.com/watch?v=bJ_seXo-Enc
> >>>
> >>> Since no one has posted an answer, I'll reveal it:
> >>>
> >>> -----------------
> >>>
> >>> The Question:
> >>>
> >>> Here's a another fun one: Imagine a hollow sphere the size of the Earth,
> >>> with a Moon sized spherical void in the center.
> >>>
> >>> Assume no rotation, relative to distant stars, and no Sun or other
> >>> massive bodies nearby.
> >>>
> >>> You climb down a shaft from the outer surface to the inner one.
> >>> How does your weight change as you descend, and what weight
> >>> do you feel when you reach the inner surface? Which way is 'down'
> >>> at that point?
> >>>
> >>> -----------------------
> >>>
> >>> The Answer:
> >>>
> >>> Your weight linearly decreases as you go down, and when you
> >>> reach the void at the center, its zero. The entire central void
> >>> is at 0 perceived gravity. You aren't attracted to the walls, nor
> >>> to the center.
> >>>
> >>> This seems counter intuitive. I *think* Rudy Rucker got it
> >>> right, but I can't think of any other 'hollow earth' story that
> >>> did.
> >>>
> >>> Newton was the first to work this out:
> >>> https://en.wikipedia.org/wiki/Shell_theorem
> >>>
> >>> pt
> >> "Dark Lightning (A Thunder and Lightning Novel)" by John Varley got it
> >> right in his six mile long by three mile wide asteroid spaceship
> >> "Rolling Thunder" rotating at 2 rpm. The kids play a ball game using
> >> pedaled aircycles that drop in weight as they go higher towards the
> >> artificial sun on its 24 hour track.
> >> https://www.amazon.com/Dark-Lightning-Thunder-John-Varley/dp/042527408X
> >
> > No gravity involved there. It appears that Varley is assuming that the air rotates
> > as if a solid cylinder (which is questionable), in which case the airbIkes entrained
> > in it would lose weight as they moved towards the center, or pedaled antispinwise.
> >
> > Pt
> Nope. The artificial sun is in the middle of the longitudinal axis, the
> center of the asteroid. The air does travel with the spin of the
> asteroid, otherwise the air would continually knock the buildings down.
>
> Read the book and prove me wrong ! You can still buy the MPPB for $8, a
> bargain nowadays. In fact, I cannot remember if the settled area goes
> around the total interior of the hollowed out asteroid or just half of
> it with a "blue sky" beyond the artificial sun.

I'd expect there'd be thermals above hot spots, and perhaps some turbulence..
The flow of fluids is notoriously hard to model, as I'm sure you're aware.

Pt

On 7/16/2023 8:21 PM, pete...@gmail.com wrote:
> On Sunday, July 16, 2023 at 9:03:11 PM UTC-4, Lynn McGuire wrote:
>> On 7/16/2023 11:17 AM, pete...@gmail.com wrote:
>>> On Thursday, July 13, 2023 at 5:39:58 PM UTC-4, Lynn McGuire wrote:
>>>> On 7/13/2023 7:56 AM, pete...@gmail.com wrote:
>>>>> On Wednesday, July 12, 2023 at 1:51:42 PM UTC-4, pete...@gmail.com wrote:
>>>>>> On Wednesday, July 12, 2023 at 1:36:56 PM UTC-4, Robert Carnegie wrote:
>>>>>>> Apparently I wrote here in 2021 and we didn't get around
>>>>>>> to checking? -
>>>>>>>
>>>>>>> "It may be Joe Haldeman's _The Long Habit of Living_ /
>>>>>>> _Buying Time_ that visits a rotating "2001"-type space station
>>>>>>> (I suppose) where I think the men's room receptacle has
>>>>>>> a target marked /next/ to it, "x <-- Aim Here, Stupid".
>>>>>>> Our hero does so."
>>>>>> It would have be pretty small, and spinning fast, to make a difference,
>>>>>> unless you're going for a long distance shot.
>>>>>>
>>>>>> Fun video:
>>>>>> https://www.youtube.com/watch?v=bJ_seXo-Enc
>>>>>
>>>>> Since no one has posted an answer, I'll reveal it:
>>>>>
>>>>> -----------------
>>>>>
>>>>> The Question:
>>>>>
>>>>> Here's a another fun one: Imagine a hollow sphere the size of the Earth,
>>>>> with a Moon sized spherical void in the center.
>>>>>
>>>>> Assume no rotation, relative to distant stars, and no Sun or other
>>>>> massive bodies nearby.
>>>>>
>>>>> You climb down a shaft from the outer surface to the inner one.
>>>>> How does your weight change as you descend, and what weight
>>>>> do you feel when you reach the inner surface? Which way is 'down'
>>>>> at that point?
>>>>>
>>>>> -----------------------
>>>>>
>>>>> The Answer:
>>>>>
>>>>> Your weight linearly decreases as you go down, and when you
>>>>> reach the void at the center, its zero. The entire central void
>>>>> is at 0 perceived gravity. You aren't attracted to the walls, nor
>>>>> to the center.
>>>>>
>>>>> This seems counter intuitive. I *think* Rudy Rucker got it
>>>>> right, but I can't think of any other 'hollow earth' story that
>>>>> did.
>>>>>
>>>>> Newton was the first to work this out:
>>>>> https://en.wikipedia.org/wiki/Shell_theorem
>>>>>
>>>>> pt
>>>> "Dark Lightning (A Thunder and Lightning Novel)" by John Varley got it
>>>> right in his six mile long by three mile wide asteroid spaceship
>>>> "Rolling Thunder" rotating at 2 rpm. The kids play a ball game using
>>>> pedaled aircycles that drop in weight as they go higher towards the
>>>> artificial sun on its 24 hour track.
>>>> https://www.amazon.com/Dark-Lightning-Thunder-John-Varley/dp/042527408X
>>>
>>> No gravity involved there. It appears that Varley is assuming that the air rotates
>>> as if a solid cylinder (which is questionable), in which case the airbIkes entrained
>>> in it would lose weight as they moved towards the center, or pedaled antispinwise.
>>>
>>> Pt
>> Nope. The artificial sun is in the middle of the longitudinal axis, the
>> center of the asteroid. The air does travel with the spin of the
>> asteroid, otherwise the air would continually knock the buildings down.
>>
>> Read the book and prove me wrong ! You can still buy the MPPB for $8, a
>> bargain nowadays. In fact, I cannot remember if the settled area goes
>> around the total interior of the hollowed out asteroid or just half of
>> it with a "blue sky" beyond the artificial sun.
>
> I'd expect there'd be thermals above hot spots, and perhaps some turbulence.
> The flow of fluids is notoriously hard to model, as I'm sure you're aware.
>
> Pt

I don't do CFD in my present software. I did write a CFD program in
college, got an A.

I have measured differential temperatures in an 8 foot diameter cooling
pipe coming out of a very large steam condenser. Actually, four cooling
water pipes with each running about 80,000 gpm of water at 95 F. There
was a 4 F temperature differential across the pipe on the exit of the
steam condenser, I was amazed.

Read the book, you will see that Varley pays extensive care to the
conditions inside the hollowed out asteroid. Especially the thermals
and radiation coming off the artificial sun. Maybe he screwed it up, I
did not analyze it as I enjoyed the book too much.

Lynn

On Monday, July 10, 2023 at 2:55:22 PM UTC-6, Lynn McGuire wrote:
> xkcd: Down
> https://xkcd.com/2800/
>
> Things are so relative. But, gravity is really going to control this one.

If the Earth was flat, we wouldn't have nonsense like this. Up would
be up, down would be down, and there would be nothing relative
about it!

John Savard

On Tue, 11 Jul 2023 09:07:43 -0700, Paul S Person
<psperson@old.netcom.invalid> wrote:

>>because "down" is basically "the way something goes if you drop it" (ok, things get messed up a bit in a moving object)
>>"The enemy's gate is down" worked because there were in weightlessness
>
>Helium balloons also mess that up.

And depending on what the Helium balloon is made of that can be
awhile. We got those foil type balloons for my granddaughter's 1st
birthday in early May and some (but not all) of them are still
touching my ceiling. Others are still 1/2 way between floor and
ceiling. A standard rubber balloon would be empty by now.

On 2023-07-19, The Horny Goat <lcraver@home.ca> wrote:
> On Tue, 11 Jul 2023 09:07:43 -0700, Paul S Person
><psperson@old.netcom.invalid> wrote:
>
>>>because "down" is basically "the way something goes if you drop it" (ok, things get messed up a bit in a moving object)
>>>"The enemy's gate is down" worked because there were in weightlessness
>>
>>Helium balloons also mess that up.
>
> And depending on what the Helium balloon is made of that can be
> awhile. We got those foil type balloons for my granddaughter's 1st
> birthday in early May and some (but not all) of them are still
> touching my ceiling. Others are still 1/2 way between floor and
> ceiling. A standard rubber balloon would be empty by now.

They are impressive! We got one for my mother's birthday last year and
it lasted on the ceiling for over 7 months - looking quite a bit
thinner by the end but still bouyant. Technology continues to improve...

Chris

On 7/19/2023 2:53 AM, The Horny Goat wrote:
> On Tue, 11 Jul 2023 09:07:43 -0700, Paul S Person
> <psperson@old.netcom.invalid> wrote:
>
>>> because "down" is basically "the way something goes if you drop it" (ok, things get messed up a bit in a moving object)
>>> "The enemy's gate is down" worked because there were in weightlessness
>>
>> Helium balloons also mess that up.
>
> And depending on what the Helium balloon is made of that can be
> awhile. We got those foil type balloons for my granddaughter's 1st
> birthday in early May and some (but not all) of them are still
> touching my ceiling. Others are still 1/2 way between floor and
> ceiling. A standard rubber balloon would be empty by now.

Foil balloons are Mylar, a two different material sheet of aluminum and
nylon.
https://balloonideas.com/blog/3-fascinating-facts-about-mylar-birthday-balloons/

Lynn

On Friday, July 14, 2023 at 6:19:48 PM UTC-4, Lynn McGuire wrote:
> On 7/14/2023 4:52 PM, Tony Nance wrote:
> > On Thursday, July 13, 2023 at 8:56:24 AM UTC-4, pete...@gmail.com wrote:
> >> On Wednesday, July 12, 2023 at 1:51:42 PM UTC-4, pete...@gmail..com wrote:
> >>> On Wednesday, July 12, 2023 at 1:36:56 PM UTC-4, Robert Carnegie wrote:
> >>>> Apparently I wrote here in 2021 and we didn't get around
> >>>> to checking? -
> >>>>
> >>>> "It may be Joe Haldeman's _The Long Habit of Living_ /
> >>>> _Buying Time_ that visits a rotating "2001"-type space station
> >>>> (I suppose) where I think the men's room receptacle has
> >>>> a target marked /next/ to it, "x <-- Aim Here, Stupid".
> >>>> Our hero does so."
> >>> It would have be pretty small, and spinning fast, to make a difference,
> >>> unless you're going for a long distance shot.
> >>>
> >>> Fun video:
> >>> https://www.youtube.com/watch?v=bJ_seXo-Enc
> >> Since no one has posted an answer, I'll reveal it:
> >>
> >> -----------------
> >>
> >> The Question:
> >> Here's a another fun one: Imagine a hollow sphere the size of the Earth,
> >> with a Moon sized spherical void in the center.
> >>
> >> Assume no rotation, relative to distant stars, and no Sun or other
> >> massive bodies nearby.
> >>
> >> You climb down a shaft from the outer surface to the inner one.
> >> How does your weight change as you descend, and what weight
> >> do you feel when you reach the inner surface? Which way is 'down'
> >> at that point?
> >> -----------------------
> >>
> >> The Answer:
> >>
> >> Your weight linearly decreases as you go down, and when you
> >> reach the void at the center, its zero. The entire central void
> >> is at 0 perceived gravity. You aren't attracted to the walls, nor
> >> to the center.
> >>
> >> This seems counter intuitive. I *think* Rudy Rucker got it
> >> right, but I can't think of any other 'hollow earth' story that
> >> did.
> >
> > While I would never _expect_ an author to get it right in a
> > fictional work, Rucker -- who has a PhD in math -- is way
> > high on the list of authors that wouldn't surprise me by
> > getting it right.
> >
> > Tony
> >
> >> Newton was the first to work this out:
> >> https://en.wikipedia.org/wiki/Shell_theorem
> >>
> >> pt
>
> Rudy Rucker was one of the original programmers for AutoCAD. Incredibly
> smart according to John Walker, the founder of AutoDesk.
>

Did not know that - thanks. Here's a (short) account of that time
from Rucker himself, just fyi.
https://www.rudyrucker.com/blog/2011/02/06/early-days-of-creative-programming/

Tony

On 7/19/2023 3:38 PM, Tony Nance wrote:
> On Friday, July 14, 2023 at 6:19:48 PM UTC-4, Lynn McGuire wrote:
>> On 7/14/2023 4:52 PM, Tony Nance wrote:
>>> On Thursday, July 13, 2023 at 8:56:24 AM UTC-4, pete...@gmail.com wrote:
>>>> On Wednesday, July 12, 2023 at 1:51:42 PM UTC-4, pete...@gmail.com wrote:
>>>>> On Wednesday, July 12, 2023 at 1:36:56 PM UTC-4, Robert Carnegie wrote:
>>>>>> Apparently I wrote here in 2021 and we didn't get around
>>>>>> to checking? -
>>>>>>
>>>>>> "It may be Joe Haldeman's _The Long Habit of Living_ /
>>>>>> _Buying Time_ that visits a rotating "2001"-type space station
>>>>>> (I suppose) where I think the men's room receptacle has
>>>>>> a target marked /next/ to it, "x <-- Aim Here, Stupid".
>>>>>> Our hero does so."
>>>>> It would have be pretty small, and spinning fast, to make a difference,
>>>>> unless you're going for a long distance shot.
>>>>>
>>>>> Fun video:
>>>>> https://www.youtube.com/watch?v=bJ_seXo-Enc
>>>> Since no one has posted an answer, I'll reveal it:
>>>>
>>>> -----------------
>>>>
>>>> The Question:
>>>> Here's a another fun one: Imagine a hollow sphere the size of the Earth,
>>>> with a Moon sized spherical void in the center.
>>>>
>>>> Assume no rotation, relative to distant stars, and no Sun or other
>>>> massive bodies nearby.
>>>>
>>>> You climb down a shaft from the outer surface to the inner one.
>>>> How does your weight change as you descend, and what weight
>>>> do you feel when you reach the inner surface? Which way is 'down'
>>>> at that point?
>>>> -----------------------
>>>>
>>>> The Answer:
>>>>
>>>> Your weight linearly decreases as you go down, and when you
>>>> reach the void at the center, its zero. The entire central void
>>>> is at 0 perceived gravity. You aren't attracted to the walls, nor
>>>> to the center.
>>>>
>>>> This seems counter intuitive. I *think* Rudy Rucker got it
>>>> right, but I can't think of any other 'hollow earth' story that
>>>> did.
>>>
>>> While I would never _expect_ an author to get it right in a
>>> fictional work, Rucker -- who has a PhD in math -- is way
>>> high on the list of authors that wouldn't surprise me by
>>> getting it right.
>>>
>>> Tony
>>>
>>>> Newton was the first to work this out:
>>>> https://en.wikipedia.org/wiki/Shell_theorem
>>>>
>>>> pt
>>
>> Rudy Rucker was one of the original programmers for AutoCAD. Incredibly
>> smart according to John Walker, the founder of AutoDesk.
>>
>
> Did not know that - thanks. Here's a (short) account of that time
> from Rucker himself, just fyi.
> https://www.rudyrucker.com/blog/2011/02/06/early-days-of-creative-programming/
>
> Tony

I went out to AutoDesk back in 1991 ? 1992 ? to go look at AutoCAD on
the Sun Workstation as we were thinking about basing a new product on
it. During the look, they invited me to come interview with them to
work on AutoCAD. They were incredibly talented programmers. But, I was
not interested in leaving Texas.

Lynn