xkcd: Down
https://xkcd.com/2800/

Things are so relative. But, gravity is really going to control this one.

Explained at:
https://www.explainxkcd.com/wiki/index.php/2800:_Down

And I like this comment "Why didn't Orson Scott Card get cowriting props
for this one?" because of this comment "I'm not so sure about the
"relative to gravity in actuality" - there's no objective reason why
"down" must follow gravity. (Take Ender's Game - "The enemy's gate is
down") DownGoer".

Lynn

On Tuesday, July 11, 2023 at 6:55:22 AM UTC+10, Lynn McGuire wrote:
> xkcd: Down
> https://xkcd.com/2800/
>
> Things are so relative. But, gravity is really going to control this one.
>
> Explained at:
> https://www.explainxkcd.com/wiki/index.php/2800:_Down
>
> And I like this comment "Why didn't Orson Scott Card get cowriting props
> for this one?" because of this comment "I'm not so sure about the
> "relative to gravity in actuality" - there's no objective reason why
> "down" must follow gravity. (Take Ender's Game - "The enemy's gate is
> down") DownGoer".
>
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

On Mon, 10 Jul 2023 19:33:00 -0700 (PDT), Hamish Laws
<hamish.laws@gmail.com> wrote:

>On Tuesday, July 11, 2023 at 6:55:22?AM UTC+10, Lynn McGuire wrote:
>> xkcd: Down
>> https://xkcd.com/2800/
>>
>> Things are so relative. But, gravity is really going to control this one.
>>
>> Explained at:
>> https://www.explainxkcd.com/wiki/index.php/2800:_Down
>>
>> And I like this comment "Why didn't Orson Scott Card get cowriting props
>> for this one?" because of this comment "I'm not so sure about the
>> "relative to gravity in actuality" - there's no objective reason why
>> "down" must follow gravity. (Take Ender's Game - "The enemy's gate is
>> down") DownGoer".
>>
>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.
--
"In this connexion, unquestionably the most significant
development was the disintegration, under Christian
influence, of classical conceptions of the family and
of family right."

Hamish Laws <hamish.laws@gmail.com> writes:

> because "down" is basically "the way something goes if you drop it" (ok,
> things get messed up a bit in a moving object)

One of my pet peeves is misconstruing the notional gravity generated
by rotating shells in space. Examples are in Rendezvous With Rama,
Neuromancer and elsewhere.

So I've been entertaining myself, putting myself to sleep at night by
calculating where something you drop goes under these conditions:

+ A Rama-like hollow cylindrical shell far from any planet, without
any architecture or internal structures except as below.

+ Internal diameter 1,000 m

+ Rotating such that if you stand on the inside of the shell, you
have you normal earth weight, i.e. you experience 1 g of
acceleration.

+ There is a tower 500 m tall, standing on the inside of the shell
that is along a radius of the cylinder.

If you stand on top of the tower and drop something (or step off)
where does it (or you) land? At the foot of the tower? If not, how
far from it and in which direction? How fast is it going when it
lands? Does it matter on which side of the tower (turnwise or
anti-turnwise) you drop it?

(Disregard any effect of air movement; the computations are too hard. :-)

--
Mike Spencer Nova Scotia, Canada

On Wednesday, July 12, 2023 at 1:34:49 AM UTC-4, Mike Spencer wrote:
> Hamish Laws <hamis...@gmail.com> writes:
>
> > because "down" is basically "the way something goes if you drop it" (ok,
> > things get messed up a bit in a moving object)
> One of my pet peeves is misconstruing the notional gravity generated
> by rotating shells in space. Examples are in Rendezvous With Rama,
> Neuromancer and elsewhere.
>
> So I've been entertaining myself, putting myself to sleep at night by
> calculating where something you drop goes under these conditions:
>
> + A Rama-like hollow cylindrical shell far from any planet, without
> any architecture or internal structures except as below.
>
> + Internal diameter 1,000 m
>
> + Rotating such that if you stand on the inside of the shell, you
> have you normal earth weight, i.e. you experience 1 g of
> acceleration.
>
> + There is a tower 500 m tall, standing on the inside of the shell
> that is along a radius of the cylinder.
>
> If you stand on top of the tower and drop something (or step off)
> where does it (or you) land? At the foot of the tower? If not, how
> far from it and in which direction? How fast is it going when it
> lands? Does it matter on which side of the tower (turnwise or
> anti-turnwise) you drop it?
>
> (Disregard any effect of air movement; the computations are too hard. :-)

If all the spherical cow type assumptions are in place, ie, all is ideal, then
if you let go of an object along the centerline of the cylinder, it doesn't
drop at all - it just hangs there.

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?

pt

"pete...@gmail.com" <petertrei@gmail.com> writes:
>On Wednesday, July 12, 2023 at 1:34:49=E2=80=AFAM UTC-4, Mike Spencer wrote=
>:
>> Hamish Laws <hamis...@gmail.com> writes:=20
>>=20
>> > because "down" is basically "the way something goes if you drop it" (ok=
>,=20
>> > things get messed up a bit in a moving object)
>> One of my pet peeves is misconstruing the notional gravity generated=20
>> by rotating shells in space. Examples are in Rendezvous With Rama,=20
>> Neuromancer and elsewhere.=20
>>=20
>> So I've been entertaining myself, putting myself to sleep at night by=20
>> calculating where something you drop goes under these conditions:=20
>>=20
>> + A Rama-like hollow cylindrical shell far from any planet, without=20
>> any architecture or internal structures except as below.=20
>>=20
>> + Internal diameter 1,000 m=20
>>=20
>> + Rotating such that if you stand on the inside of the shell, you=20
>> have you normal earth weight, i.e. you experience 1 g of=20
>> acceleration.=20
>>=20
>> + There is a tower 500 m tall, standing on the inside of the shell=20
>> that is along a radius of the cylinder.=20
>>=20
>> If you stand on top of the tower and drop something (or step off)=20
>> where does it (or you) land? At the foot of the tower? If not, how=20
>> far from it and in which direction? How fast is it going when it=20
>> lands? Does it matter on which side of the tower (turnwise or=20
>> anti-turnwise) you drop it?=20
>>=20
>> (Disregard any effect of air movement; the computations are too hard. :-)=
>=20
>
>If all the spherical cow type assumptions are in place, ie, all is ideal, t=
>hen
>if you let go of an object along the centerline of the cylinder, it doesn't=
>=20
>drop at all - it just hangs there.=20
>
>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?

Wouldn't one be effectively weightless with no rotation and no massive bodies nearby?

On 7/12/2023 7:49 AM, Scott Lurndal wrote:
> "pete...@gmail.com" <petertrei@gmail.com> writes:
>> On Wednesday, July 12, 2023 at 1:34:49=E2=80=AFAM UTC-4, Mike Spencer wrote=
>> :
>>> Hamish Laws <hamis...@gmail.com> writes:=20
>>> =20
>>>> because "down" is basically "the way something goes if you drop it" (ok=
>> ,=20
>>>> things get messed up a bit in a moving object)
>>> One of my pet peeves is misconstruing the notional gravity generated=20
>>> by rotating shells in space. Examples are in Rendezvous With Rama,=20
>>> Neuromancer and elsewhere.=20
>>> =20
>>> So I've been entertaining myself, putting myself to sleep at night by=20
>>> calculating where something you drop goes under these conditions:=20
>>> =20
>>> + A Rama-like hollow cylindrical shell far from any planet, without=20
>>> any architecture or internal structures except as below.=20
>>> =20
>>> + Internal diameter 1,000 m=20
>>> =20
>>> + Rotating such that if you stand on the inside of the shell, you=20
>>> have you normal earth weight, i.e. you experience 1 g of=20
>>> acceleration.=20
>>> =20
>>> + There is a tower 500 m tall, standing on the inside of the shell=20
>>> that is along a radius of the cylinder.=20
>>> =20
>>> If you stand on top of the tower and drop something (or step off)=20
>>> where does it (or you) land? At the foot of the tower? If not, how=20
>>> far from it and in which direction? How fast is it going when it=20
>>> lands? Does it matter on which side of the tower (turnwise or=20
>>> anti-turnwise) you drop it?=20
>>> =20
>>> (Disregard any effect of air movement; the computations are too hard. :-)=
>> =20
>>
>> If all the spherical cow type assumptions are in place, ie, all is ideal, t=
>> hen
>> if you let go of an object along the centerline of the cylinder, it doesn't=
>> =20
>> drop at all - it just hangs there.=20
>>
>> 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?
>
> Wouldn't one be effectively weightless with no rotation and no massive bodies nearby?
>
You mean like the one you are climbing into?

--
I've done good in this world. Now I'm tired and just want to be a cranky
dirty old man.

Dimensional Traveler <dtravel@sonic.net> writes:
>On 7/12/2023 7:49 AM, Scott Lurndal wrote:
>> "pete...@gmail.com" <petertrei@gmail.com> writes:
>>> On Wednesday, July 12, 2023 at 1:34:49=E2=80=AFAM UTC-4, Mike Spencer wrote=
>>> :
>>>> Hamish Laws <hamis...@gmail.com> writes:=20
>>>> =20
>>>>> because "down" is basically "the way something goes if you drop it" (ok=
>>> ,=20
>>>>> things get messed up a bit in a moving object)
>>>> One of my pet peeves is misconstruing the notional gravity generated=20
>>>> by rotating shells in space. Examples are in Rendezvous With Rama,=20
>>>> Neuromancer and elsewhere.=20
>>>> =20
>>>> So I've been entertaining myself, putting myself to sleep at night by=20
>>>> calculating where something you drop goes under these conditions:=20
>>>> =20
>>>> + A Rama-like hollow cylindrical shell far from any planet, without=20
>>>> any architecture or internal structures except as below.=20
>>>> =20
>>>> + Internal diameter 1,000 m=20
>>>> =20
>>>> + Rotating such that if you stand on the inside of the shell, you=20
>>>> have you normal earth weight, i.e. you experience 1 g of=20
>>>> acceleration.=20
>>>> =20
>>>> + There is a tower 500 m tall, standing on the inside of the shell=20
>>>> that is along a radius of the cylinder.=20
>>>> =20
>>>> If you stand on top of the tower and drop something (or step off)=20
>>>> where does it (or you) land? At the foot of the tower? If not, how=20
>>>> far from it and in which direction? How fast is it going when it=20
>>>> lands? Does it matter on which side of the tower (turnwise or=20
>>>> anti-turnwise) you drop it?=20
>>>> =20
>>>> (Disregard any effect of air movement; the computations are too hard. :-)=
>>> =20
>>>
>>> If all the spherical cow type assumptions are in place, ie, all is ideal, t=
>>> hen
>>> if you let go of an object along the centerline of the cylinder, it doesn't=
>>> =20
>>> drop at all - it just hangs there.=20
>>>
>>> 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?
>>
>> Wouldn't one be effectively weightless with no rotation and no massive bodies nearby?
>>
>You mean like the one you are climbing into?

A hollow sphere containing a central void would not be a "massive body", nor
would it generate any significant gravitational pull.

I'm assuming 'void' in PT's context is absence of substantial matter.

On Wednesday, July 12, 2023 at 11:50:22 AM UTC-4, Scott Lurndal wrote:
> Dimensional Traveler <dtr...@sonic.net> writes:
> >On 7/12/2023 7:49 AM, Scott Lurndal wrote:
> >> "pete...@gmail.com" <pete...@gmail.com> writes:
> >>> On Wednesday, July 12, 2023 at 1:34:49=E2=80=AFAM UTC-4, Mike Spencer wrote=
> >>> :
> >>>> Hamish Laws <hamis...@gmail.com> writes:=20
> >>>> =20
> >>>>> because "down" is basically "the way something goes if you drop it" (ok=
> >>> ,=20
> >>>>> things get messed up a bit in a moving object)
> >>>> One of my pet peeves is misconstruing the notional gravity generated=20
> >>>> by rotating shells in space. Examples are in Rendezvous With Rama,=20
> >>>> Neuromancer and elsewhere.=20
> >>>> =20
> >>>> So I've been entertaining myself, putting myself to sleep at night by=20
> >>>> calculating where something you drop goes under these conditions:=20
> >>>> =20
> >>>> + A Rama-like hollow cylindrical shell far from any planet, without=20
> >>>> any architecture or internal structures except as below.=20
> >>>> =20
> >>>> + Internal diameter 1,000 m=20
> >>>> =20
> >>>> + Rotating such that if you stand on the inside of the shell, you=20
> >>>> have you normal earth weight, i.e. you experience 1 g of=20
> >>>> acceleration.=20
> >>>> =20
> >>>> + There is a tower 500 m tall, standing on the inside of the shell=20
> >>>> that is along a radius of the cylinder.=20
> >>>> =20
> >>>> If you stand on top of the tower and drop something (or step off)=20
> >>>> where does it (or you) land? At the foot of the tower? If not, how=20
> >>>> far from it and in which direction? How fast is it going when it=20
> >>>> lands? Does it matter on which side of the tower (turnwise or=20
> >>>> anti-turnwise) you drop it?=20
> >>>> =20
> >>>> (Disregard any effect of air movement; the computations are too hard.. :-)=
> >>> =20
> >>>
> >>> If all the spherical cow type assumptions are in place, ie, all is ideal, t=
> >>> hen
> >>> if you let go of an object along the centerline of the cylinder, it doesn't=
> >>> =20
> >>> drop at all - it just hangs there.=20
> >>>
> >>> 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?
> >>
> >> Wouldn't one be effectively weightless with no rotation and no massive bodies nearby?
> >>
> >You mean like the one you are climbing into?
> A hollow sphere containing a central void would not be a "massive body", nor
> would it generate any significant gravitational pull.
>
> I'm assuming 'void' in PT's context is absence of substantial matter.

I specified the parameters- Earth sized body with Moon sized void.

Making the false assumption of uniform density, that leaves a body
with >98% of the Earth's mass.

pt

"pete...@gmail.com" <petertrei@gmail.com> writes:

> If all the spherical cow type assumptions are in place, ie, all is
> ideal, then if you let go of an object along the centerline of the
> cylinder, it doesn't drop at all - it just hangs there.

Yes. I hate making myself look like an moron. I meant to write
"internal RADIUS 1,000 m". You're right: With internal diameter of
1,000 m, it's either an edge case or a trick question, depending on
how you look at it.

For the record, here's what I meant to write:

+ A Rama-like hollow cylindrical shell far from any planet, without
any architecture or internal structures except as below.

+ Internal RADIUS 1,000 m (internal diameter 2 km)

+ Rotating such that if you stand on the inside of the shell, you
have you normal earth weight, i.e. you experience 1 g of
acceleration.

+ There is a tower 500 m tall, standing on the inside of the shell
that is along a radius of the cylinder.

If you stand on top of the tower and drop something (or step off)
where does it (or you) land? At the foot of the tower? If not, how
far from it and in which direction? How fast is it going when it
lands? Does it matter on which side of the tower (turnwise or
anti-turnwise) you drop it?

--
Mike Spencer Nova Scotia, Canada

"pete...@gmail.com" <petertrei@gmail.com> writes:
>On Wednesday, July 12, 2023 at 11:50:22=E2=80=AFAM UTC-4, Scott Lurndal wro=
>te:
>> Dimensional Traveler <dtr...@sonic.net> writes:=20
>> >On 7/12/2023 7:49 AM, Scott Lurndal wrote:=20
>> >> "pete...@gmail.com" <pete...@gmail.com> writes:=20
>> >>> On Wednesday, July 12, 2023 at 1:34:49=3DE2=3D80=3DAFAM UTC-4, Mike S=
>pencer wrote=3D=20
>> >>> :=20
>> >>>> Hamish Laws <hamis...@gmail.com> writes:=3D20=20
>> >>>> =3D20=20
>> >>>>> because "down" is basically "the way something goes if you drop it"=
> (ok=3D=20
>> >>> ,=3D20=20
>> >>>>> things get messed up a bit in a moving object)=20
>> >>>> One of my pet peeves is misconstruing the notional gravity generated=
>=3D20=20
>> >>>> by rotating shells in space. Examples are in Rendezvous With Rama,=
>=3D20=20
>> >>>> Neuromancer and elsewhere.=3D20=20
>> >>>> =3D20=20
>> >>>> So I've been entertaining myself, putting myself to sleep at night b=
>y=3D20=20
>> >>>> calculating where something you drop goes under these conditions:=3D=
>20=20
>> >>>> =3D20=20
>> >>>> + A Rama-like hollow cylindrical shell far from any planet, without=
>=3D20=20
>> >>>> any architecture or internal structures except as below.=3D20=20
>> >>>> =3D20=20
>> >>>> + Internal diameter 1,000 m=3D20=20
>> >>>> =3D20=20
>> >>>> + Rotating such that if you stand on the inside of the shell, you=3D=
>20=20
>> >>>> have you normal earth weight, i.e. you experience 1 g of=3D20=20
>> >>>> acceleration.=3D20=20
>> >>>> =3D20=20
>> >>>> + There is a tower 500 m tall, standing on the inside of the shell=
>=3D20=20
>> >>>> that is along a radius of the cylinder.=3D20=20
>> >>>> =3D20=20
>> >>>> If you stand on top of the tower and drop something (or step off)=3D=
>20=20
>> >>>> where does it (or you) land? At the foot of the tower? If not, how=
>=3D20=20
>> >>>> far from it and in which direction? How fast is it going when it=3D2=
>0=20
>> >>>> lands? Does it matter on which side of the tower (turnwise or=3D20=
>=20
>> >>>> anti-turnwise) you drop it?=3D20=20
>> >>>> =3D20=20
>> >>>> (Disregard any effect of air movement; the computations are too hard=
>. :-)=3D=20
>> >>> =3D20=20
>> >>>=20
>> >>> If all the spherical cow type assumptions are in place, ie, all is id=
>eal, t=3D=20
>> >>> hen=20
>> >>> if you let go of an object along the centerline of the cylinder, it d=
>oesn't=3D=20
>> >>> =3D20=20
>> >>> drop at all - it just hangs there.=3D20=20
>> >>>=20
>> >>> Here's a another fun one: Imagine a hollow sphere the size of the Ear=
>th,=20
>> >>> with a Moon sized spherical void in the center.=20
>> >>>=20
>> >>> Assume no rotation, relative to distant stars, and no Sun or other=20
>> >>> massive bodies nearby.=20
>> >>>=20
>> >>> You climb down a shaft from the outer surface to the inner one.=20
>> >>> How does your weight change as you descend, and what weight=20
>> >>> do you feel when you reach the inner surface? Which way is 'down'=20
>> >>> at that point?=20
>> >>=20
>> >> Wouldn't one be effectively weightless with no rotation and no massive=
> bodies nearby?=20
>> >>=20
>> >You mean like the one you are climbing into?
>> A hollow sphere containing a central void would not be a "massive body", =
>nor=20
>> would it generate any significant gravitational pull.=20
>>=20
>> I'm assuming 'void' in PT's context is absence of substantial matter.
>
>I specified the parameters- Earth sized body with Moon sized void.
>
>Making the false assumption of uniform density, that leaves a body
>with >98% of the Earth's mass.=20
>

Ah, then I misunderstood what you meant by hollow:

' Imagine a hollow sphere the size of the Earth...'

I assumed a diminimis shell surrounding a much smaller
diminimis moon-sized shell.

On Wednesday, July 12, 2023 at 12:59:17 PM UTC-4, Mike Spencer wrote:
> "pete...@gmail.com" <pete...@gmail.com> writes:
>
> > If all the spherical cow type assumptions are in place, ie, all is
> > ideal, then if you let go of an object along the centerline of the
> > cylinder, it doesn't drop at all - it just hangs there.
> Yes. I hate making myself look like an moron. I meant to write
> "internal RADIUS 1,000 m". You're right: With internal diameter of
> 1,000 m, it's either an edge case or a trick question, depending on
> how you look at it.
> For the record, here's what I meant to write:
>
> + A Rama-like hollow cylindrical shell far from any planet, without
> any architecture or internal structures except as below.
> + Internal RADIUS 1,000 m (internal diameter 2 km)
> + Rotating such that if you stand on the inside of the shell, you
> have you normal earth weight, i.e. you experience 1 g of
> acceleration.
>
> + There is a tower 500 m tall, standing on the inside of the shell
> that is along a radius of the cylinder.
>
> If you stand on top of the tower and drop something (or step off)
> where does it (or you) land? At the foot of the tower? If not, how
> far from it and in which direction? How fast is it going when it
> lands? Does it matter on which side of the tower (turnwise or
> anti-turnwise) you drop it?

Not sure I can get all the math right, but....

If you drop it on the side facing into the spin, if collisions
are inelastic, it will roll down the side of the tower to its base.

This helps:
https://www.calctool.org/rotational-and-periodic-motion/centrifugal-force

The cylinder is turning at .945 rpm

At halfway to the center, dropping it off the tower away from the spin
will give it a tangental velocity of 49.5 m/s. You's see it appear to
accelerate away from you as your viewpoint turned away, I cant be
bothered to work out the math as to at what angle and speed it
reaches the cylinder.

pt

On Wednesday, July 12, 2023 at 1:13:23 PM UTC-4, Scott Lurndal wrote:
> "pete...@gmail.com" <pete...@gmail.com> writes:
> >On Wednesday, July 12, 2023 at 11:50:22=E2=80=AFAM UTC-4, Scott Lurndal wro=
> >te:
> >> Dimensional Traveler <dtr...@sonic.net> writes:=20
> >> >On 7/12/2023 7:49 AM, Scott Lurndal wrote:=20
> >> >> "pete...@gmail.com" <pete...@gmail.com> writes:=20
> >> >>> On Wednesday, July 12, 2023 at 1:34:49=3DE2=3D80=3DAFAM UTC-4, Mike S=
> >pencer wrote=3D=20
> >> >>> :=20
> >> >>>> Hamish Laws <hamis...@gmail.com> writes:=3D20=20
> >> >>>> =3D20=20
> >> >>>>> because "down" is basically "the way something goes if you drop it"=
> > (ok=3D=20
> >> >>> ,=3D20=20
> >> >>>>> things get messed up a bit in a moving object)=20
> >> >>>> One of my pet peeves is misconstruing the notional gravity generated> >=3D20=20
> >> >>>> by rotating shells in space. Examples are in Rendezvous With Rama,> >=3D20=20
> >> >>>> Neuromancer and elsewhere.=3D20=20
> >> >>>> =3D20=20
> >> >>>> So I've been entertaining myself, putting myself to sleep at night b=
> >y=3D20=20
> >> >>>> calculating where something you drop goes under these conditions:=3D=
> >20=20
> >> >>>> =3D20=20
> >> >>>> + A Rama-like hollow cylindrical shell far from any planet, without> >=3D20=20
> >> >>>> any architecture or internal structures except as below.=3D20=20
> >> >>>> =3D20=20
> >> >>>> + Internal diameter 1,000 m=3D20=20
> >> >>>> =3D20=20
> >> >>>> + Rotating such that if you stand on the inside of the shell, you=3D=
> >20=20
> >> >>>> have you normal earth weight, i.e. you experience 1 g of=3D20=20
> >> >>>> acceleration.=3D20=20
> >> >>>> =3D20=20
> >> >>>> + There is a tower 500 m tall, standing on the inside of the shell> >=3D20=20
> >> >>>> that is along a radius of the cylinder.=3D20=20
> >> >>>> =3D20=20
> >> >>>> If you stand on top of the tower and drop something (or step off)=3D=
> >20=20
> >> >>>> where does it (or you) land? At the foot of the tower? If not, how> >=3D20=20
> >> >>>> far from it and in which direction? How fast is it going when it=3D2=
> >0=20
> >> >>>> lands? Does it matter on which side of the tower (turnwise or=3D20=
> >=20
> >> >>>> anti-turnwise) you drop it?=3D20=20
> >> >>>> =3D20=20
> >> >>>> (Disregard any effect of air movement; the computations are too hard=
> >. :-)=3D=20
> >> >>> =3D20=20
> >> >>>=20
> >> >>> If all the spherical cow type assumptions are in place, ie, all is id=
> >eal, t=3D=20
> >> >>> hen=20
> >> >>> if you let go of an object along the centerline of the cylinder, it d=
> >oesn't=3D=20
> >> >>> =3D20=20
> >> >>> drop at all - it just hangs there.=3D20=20
> >> >>>=20
> >> >>> Here's a another fun one: Imagine a hollow sphere the size of the Ear=
> >th,=20
> >> >>> with a Moon sized spherical void in the center.=20
> >> >>>=20
> >> >>> Assume no rotation, relative to distant stars, and no Sun or other=20
> >> >>> massive bodies nearby.=20
> >> >>>=20
> >> >>> You climb down a shaft from the outer surface to the inner one.=20
> >> >>> How does your weight change as you descend, and what weight=20
> >> >>> do you feel when you reach the inner surface? Which way is 'down'=20
> >> >>> at that point?=20
> >> >>=20
> >> >> Wouldn't one be effectively weightless with no rotation and no massive=
> > bodies nearby?=20
> >> >>=20
> >> >You mean like the one you are climbing into?
> >> A hollow sphere containing a central void would not be a "massive body", =
> >nor=20
> >> would it generate any significant gravitational pull.=20
> >>=20
> >> I'm assuming 'void' in PT's context is absence of substantial matter.
> >
> >I specified the parameters- Earth sized body with Moon sized void.
> >
> >Making the false assumption of uniform density, that leaves a body
> >with >98% of the Earth's mass.=20
> >
>
> Ah, then I misunderstood what you meant by hollow:
>
> ' Imagine a hollow sphere the size of the Earth...'
>
> I assumed a diminimis shell surrounding a much smaller
> diminimis moon-sized shell.

Having a massy, not-diminimus shell there is what makes the question
interesting.

pt

On Wednesday, 12 July 2023 at 17:59:17 UTC+1, Mike Spencer wrote:
> "pete...@gmail.com" <pete...@gmail.com> writes:
>
> > If all the spherical cow type assumptions are in place, ie, all is
> > ideal, then if you let go of an object along the centerline of the
> > cylinder, it doesn't drop at all - it just hangs there.
> Yes. I hate making myself look like an moron. I meant to write
> "internal RADIUS 1,000 m". You're right: With internal diameter of
> 1,000 m, it's either an edge case or a trick question, depending on
> how you look at it.
> For the record, here's what I meant to write:
>
> + A Rama-like hollow cylindrical shell far from any planet, without
> any architecture or internal structures except as below.
> + Internal RADIUS 1,000 m (internal diameter 2 km)
> + Rotating such that if you stand on the inside of the shell, you
> have you normal earth weight, i.e. you experience 1 g of
> acceleration.
>
> + There is a tower 500 m tall, standing on the inside of the shell
> that is along a radius of the cylinder.
>
> If you stand on top of the tower and drop something (or step off)
> where does it (or you) land? At the foot of the tower? If not, how
> far from it and in which direction? How fast is it going when it
> lands? Does it matter on which side of the tower (turnwise or
> anti-turnwise) you drop it?

Well, what's really happening... practically, gravity doesn't
exist, and the tower is sweeping round in a circle, like the
outer half of a clock's minute hand. How fast, that takes
math, which I'll excuse myself. The top of the tower is
pushing you centripetally into a circular path in the "sky".
Step off, or drop an object, and you just move in a straight
line in space at your previous velocity. Off the back of the
tower, you just fly at one velocity until you hit the shell.
The velocity of an observer standing on the shell is changing,
but they feel like they are standing in one place and you are
accelerating, I want to say initially "straight down" but then
swerving.

If you go off the front of the tower, its lower part initially is
moving in the same direction, and the bottom is accelerating
more than the top. I think the tower is catching you up
and you will slide "down" or along it. I shouldn't have skipped
the math. I think you still reach the shell, but I'm not ruling out
that you ride "down" and "up" and "down" on the tower like a yo-yo?

"pete...@gmail.com" <petertrei@gmail.com> writes:
>On Wednesday, July 12, 2023 at 1:13:23=E2=80=AFPM UTC-4, Scott Lurndal wrot=
>e:
>> "pete...@gmail.com" <pete...@gmail.com> writes:=20
>> >On Wednesday, July 12, 2023 at 11:50:22=3DE2=3D80=3DAFAM UTC-4, Scott Lu=
>rndal wro=3D=20
>> >te:=20
>> >> Dimensional Traveler <dtr...@sonic.net> writes:=3D20=20
>> >> >On 7/12/2023 7:49 AM, Scott Lurndal wrote:=3D20=20
>> >> >> "pete...@gmail.com" <pete...@gmail.com> writes:=3D20=20
>> >> >>> On Wednesday, July 12, 2023 at 1:34:49=3D3DE2=3D3D80=3D3DAFAM UTC-=
>4, Mike S=3D=20
>> >pencer wrote=3D3D=3D20=20
>> >> >>> :=3D20=20
>> >> >>>> Hamish Laws <hamis...@gmail.com> writes:=3D3D20=3D20=20
>> >> >>>> =3D3D20=3D20=20
>> >> >>>>> because "down" is basically "the way something goes if you drop =
>it"=3D=20
>> > (ok=3D3D=3D20=20
>> >> >>> ,=3D3D20=3D20=20
>> >> >>>>> things get messed up a bit in a moving object)=3D20
>> >> >>>> One of my pet peeves is misconstruing the notional gravity genera=
>ted=3D
>> >=3D3D20=3D20
>> >> >>>> by rotating shells in space. Examples are in Rendezvous With Rama=
>,=3D
>> >=3D3D20=3D20=20
>> >> >>>> Neuromancer and elsewhere.=3D3D20=3D20=20
>> >> >>>> =3D3D20=3D20=20
>> >> >>>> So I've been entertaining myself, putting myself to sleep at nigh=
>t b=3D=20
>> >y=3D3D20=3D20=20
>> >> >>>> calculating where something you drop goes under these conditions:=
>=3D3D=3D=20
>> >20=3D20=20
>> >> >>>> =3D3D20=3D20
>> >> >>>> + A Rama-like hollow cylindrical shell far from any planet, witho=
>ut=3D
>> >=3D3D20=3D20=20
>> >> >>>> any architecture or internal structures except as below.=3D3D20=
>=3D20=20
>> >> >>>> =3D3D20=3D20=20
>> >> >>>> + Internal diameter 1,000 m=3D3D20=3D20=20
>> >> >>>> =3D3D20=3D20=20
>> >> >>>> + Rotating such that if you stand on the inside of the shell, you=
>=3D3D=3D=20
>> >20=3D20=20
>> >> >>>> have you normal earth weight, i.e. you experience 1 g of=3D3D20=
>=3D20=20
>> >> >>>> acceleration.=3D3D20=3D20=20
>> >> >>>> =3D3D20=3D20
>> >> >>>> + There is a tower 500 m tall, standing on the inside of the shel=
>l=3D
>> >=3D3D20=3D20=20
>> >> >>>> that is along a radius of the cylinder.=3D3D20=3D20=20
>> >> >>>> =3D3D20=3D20=20
>> >> >>>> If you stand on top of the tower and drop something (or step off)=
>=3D3D=3D=20
>> >20=3D20
>> >> >>>> where does it (or you) land? At the foot of the tower? If not, ho=
>w=3D
>> >=3D3D20=3D20=20
>> >> >>>> far from it and in which direction? How fast is it going when it=
>=3D3D2=3D=20
>> >0=3D20=20
>> >> >>>> lands? Does it matter on which side of the tower (turnwise or=3D3=
>D20=3D=20
>> >=3D20=20
>> >> >>>> anti-turnwise) you drop it?=3D3D20=3D20=20
>> >> >>>> =3D3D20=3D20=20
>> >> >>>> (Disregard any effect of air movement; the computations are too h=
>ard=3D=20
>> >. :-)=3D3D=3D20=20
>> >> >>> =3D3D20=3D20=20
>> >> >>>=3D20=20
>> >> >>> If all the spherical cow type assumptions are in place, ie, all is=
> id=3D=20
>> >eal, t=3D3D=3D20=20
>> >> >>> hen=3D20=20
>> >> >>> if you let go of an object along the centerline of the cylinder, i=
>t d=3D=20
>> >oesn't=3D3D=3D20=20
>> >> >>> =3D3D20=3D20=20
>> >> >>> drop at all - it just hangs there.=3D3D20=3D20=20
>> >> >>>=3D20=20
>> >> >>> Here's a another fun one: Imagine a hollow sphere the size of the =
>Ear=3D=20
>> >th,=3D20=20
>> >> >>> with a Moon sized spherical void in the center.=3D20=20
>> >> >>>=3D20=20
>> >> >>> Assume no rotation, relative to distant stars, and no Sun or other=
>=3D20=20
>> >> >>> massive bodies nearby.=3D20=20
>> >> >>>=3D20=20
>> >> >>> You climb down a shaft from the outer surface to the inner one.=3D=
>20=20
>> >> >>> How does your weight change as you descend, and what weight=3D20=
>=20
>> >> >>> do you feel when you reach the inner surface? Which way is 'down'=
>=3D20=20
>> >> >>> at that point?=3D20=20
>> >> >>=3D20=20
>> >> >> Wouldn't one be effectively weightless with no rotation and no mass=
>ive=3D=20
>> > bodies nearby?=3D20=20
>> >> >>=3D20
>> >> >You mean like the one you are climbing into?
>> >> A hollow sphere containing a central void would not be a "massive body=
>", =3D=20
>> >nor=3D20=20
>> >> would it generate any significant gravitational pull.=3D20=20
>> >>=3D20
>> >> I'm assuming 'void' in PT's context is absence of substantial matter.=
>=20
>> >=20
>> >I specified the parameters- Earth sized body with Moon sized void.=20
>> >=20
>> >Making the false assumption of uniform density, that leaves a body
>> >with >98% of the Earth's mass.=3D20=20
>> >=20
>>=20
>> Ah, then I misunderstood what you meant by hollow:=20
>>=20
>> ' Imagine a hollow sphere the size of the Earth...'=20
>>=20
>> I assumed a diminimis shell surrounding a much smaller=20
>> diminimis moon-sized shell.
>
>Having a massy, not-diminimus shell there is what makes the question
>interesting.
>

Isn't the core significantly denser than the mantle, and thus would
generate a significant fraction of the gravitational pull?

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."

On Wednesday, July 12, 2023 at 1:36:01 PM UTC-4, Scott Lurndal wrote:
> "pete...@gmail.com" <pete...@gmail.com> writes:
> >On Wednesday, July 12, 2023 at 1:13:23=E2=80=AFPM UTC-4, Scott Lurndal wrot=
> >e:
> >> "pete...@gmail.com" <pete...@gmail.com> writes:=20
> >> >On Wednesday, July 12, 2023 at 11:50:22=3DE2=3D80=3DAFAM UTC-4, Scott Lu=
> >rndal wro=3D=20
> >> >te:=20
> >> >> Dimensional Traveler <dtr...@sonic.net> writes:=3D20=20
> >> >> >On 7/12/2023 7:49 AM, Scott Lurndal wrote:=3D20=20
> >> >> >> "pete...@gmail.com" <pete...@gmail.com> writes:=3D20=20
> >> >> >>> On Wednesday, July 12, 2023 at 1:34:49=3D3DE2=3D3D80=3D3DAFAM UTC-=
> >4, Mike S=3D=20
> >> >pencer wrote=3D3D=3D20=20
> >> >> >>> :=3D20=20
> >> >> >>>> Hamish Laws <hamis...@gmail.com> writes:=3D3D20=3D20=20
> >> >> >>>> =3D3D20=3D20=20
> >> >> >>>>> because "down" is basically "the way something goes if you drop =
> >it"=3D=20
> >> > (ok=3D3D=3D20=20
> >> >> >>> ,=3D3D20=3D20=20
> >> >> >>>>> things get messed up a bit in a moving object)=3D20
> >> >> >>>> One of my pet peeves is misconstruing the notional gravity genera=
> >ted=3D
> >> >=3D3D20=3D20
> >> >> >>>> by rotating shells in space. Examples are in Rendezvous With Rama=
> >,=3D
> >> >=3D3D20=3D20=20
> >> >> >>>> Neuromancer and elsewhere.=3D3D20=3D20=20
> >> >> >>>> =3D3D20=3D20=20
> >> >> >>>> So I've been entertaining myself, putting myself to sleep at nigh=
> >t b=3D=20
> >> >y=3D3D20=3D20=20
> >> >> >>>> calculating where something you drop goes under these conditions:> >=3D3D=3D=20
> >> >20=3D20=20
> >> >> >>>> =3D3D20=3D20
> >> >> >>>> + A Rama-like hollow cylindrical shell far from any planet, witho=
> >ut=3D
> >> >=3D3D20=3D20=20
> >> >> >>>> any architecture or internal structures except as below.=3D3D20=
> >=3D20=20
> >> >> >>>> =3D3D20=3D20=20
> >> >> >>>> + Internal diameter 1,000 m=3D3D20=3D20=20
> >> >> >>>> =3D3D20=3D20=20
> >> >> >>>> + Rotating such that if you stand on the inside of the shell, you> >=3D3D=3D=20
> >> >20=3D20=20
> >> >> >>>> have you normal earth weight, i.e. you experience 1 g of=3D3D20=
> >=3D20=20
> >> >> >>>> acceleration.=3D3D20=3D20=20
> >> >> >>>> =3D3D20=3D20
> >> >> >>>> + There is a tower 500 m tall, standing on the inside of the shel=
> >l=3D
> >> >=3D3D20=3D20=20
> >> >> >>>> that is along a radius of the cylinder.=3D3D20=3D20=20
> >> >> >>>> =3D3D20=3D20=20
> >> >> >>>> If you stand on top of the tower and drop something (or step off)> >=3D3D=3D=20
> >> >20=3D20
> >> >> >>>> where does it (or you) land? At the foot of the tower? If not, ho=
> >w=3D
> >> >=3D3D20=3D20=20
> >> >> >>>> far from it and in which direction? How fast is it going when it> >=3D3D2=3D=20
> >> >0=3D20=20
> >> >> >>>> lands? Does it matter on which side of the tower (turnwise or=3D3=
> >D20=3D=20
> >> >=3D20=20
> >> >> >>>> anti-turnwise) you drop it?=3D3D20=3D20=20
> >> >> >>>> =3D3D20=3D20=20
> >> >> >>>> (Disregard any effect of air movement; the computations are too h=
> >ard=3D=20
> >> >. :-)=3D3D=3D20=20
> >> >> >>> =3D3D20=3D20=20
> >> >> >>>=3D20=20
> >> >> >>> If all the spherical cow type assumptions are in place, ie, all is=
> > id=3D=20
> >> >eal, t=3D3D=3D20=20
> >> >> >>> hen=3D20=20
> >> >> >>> if you let go of an object along the centerline of the cylinder, i=
> >t d=3D=20
> >> >oesn't=3D3D=3D20=20
> >> >> >>> =3D3D20=3D20=20
> >> >> >>> drop at all - it just hangs there.=3D3D20=3D20=20
> >> >> >>>=3D20=20
> >> >> >>> Here's a another fun one: Imagine a hollow sphere the size of the =
> >Ear=3D=20
> >> >th,=3D20=20
> >> >> >>> with a Moon sized spherical void in the center.=3D20=20
> >> >> >>>=3D20=20
> >> >> >>> Assume no rotation, relative to distant stars, and no Sun or other> >=3D20=20
> >> >> >>> massive bodies nearby.=3D20=20
> >> >> >>>=3D20=20
> >> >> >>> You climb down a shaft from the outer surface to the inner one.=3D=
> >20=20
> >> >> >>> How does your weight change as you descend, and what weight=3D20> >=20
> >> >> >>> do you feel when you reach the inner surface? Which way is 'down'> >=3D20=20
> >> >> >>> at that point?=3D20=20
> >> >> >>=3D20=20
> >> >> >> Wouldn't one be effectively weightless with no rotation and no mass=
> >ive=3D=20
> >> > bodies nearby?=3D20=20
> >> >> >>=3D20
> >> >> >You mean like the one you are climbing into?
> >> >> A hollow sphere containing a central void would not be a "massive body=
> >", =3D=20
> >> >nor=3D20=20
> >> >> would it generate any significant gravitational pull.=3D20=20
> >> >>=3D20
> >> >> I'm assuming 'void' in PT's context is absence of substantial matter.=
> >=20
> >> >=20
> >> >I specified the parameters- Earth sized body with Moon sized void.=20
> >> >=20
> >> >Making the false assumption of uniform density, that leaves a body
> >> >with >98% of the Earth's mass.=3D20=20
> >> >=20
> >>=20
> >> Ah, then I misunderstood what you meant by hollow:=20
> >>=20
> >> ' Imagine a hollow sphere the size of the Earth...'=20
> >>=20
> >> I assumed a diminimis shell surrounding a much smaller=20
> >> diminimis moon-sized shell.
> >
> >Having a massy, not-diminimus shell there is what makes the question
> >interesting.
> >
> Isn't the core significantly denser than the mantle, and thus would
> generate a significant fraction of the gravitational pull?

It certainly is, but it doesn't affect the answer. Don't worry about it.

The inner core is about 13 kg/liter, while the average for the Earth
is about 5.5.

pt

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

pt

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

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.

Zero gravity at the centre of spherically symmetric object was
a plot point in Banks' "The Algebraist".

William Hyde

On 2023-07-13 12:10, William Hyde 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.
>
> Zero gravity at the centre of spherically symmetric object was
> a plot point in Banks' "The Algebraist".

If you mean at the precise centre, you need to read a little more
closely what the previous poster wrote, because he correctly said that
anywhere inside a spherical shell of uniform density, there is no net
gravitational force from the shell.

<http://hyperphysics.phy-astr.gsu.edu/hbase/Mechanics/sphshell2.html>

William Hyde wrote:
> On Thursday, July 13, 2023 at 8:56:24 AM UTC-4, pete...@gmail.com wrote:
> >
> > 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.
> Zero gravity at the centre of spherically symmetric object was
> a plot point in Banks' "The Algebraist".

You remind me than in Damon Knight's "The World and Thorinn" (1968, for some unknown reason republished in 1981) the title character descended through the Earth, encountering decreasing gravity. The narrator brings up that Thorinn had been observing splashes in water as becoming more and more like those slow-motion films where a water drops form and slowly fall back, so that he is not disconcerted by seeing water form globes in the weightlessness of the center hollow (which I don't remember being too great, possibly just big enough to enjoy this phenomenon).

--
-Jack

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

Lynn

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

On Thursday, July 13, 2023 at 3:10:52 PM UTC-4, William Hyde 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.
>
> Zero gravity at the centre of spherically symmetric object was
> a plot point in Banks' "The Algebraist".
>

Indeed it was! I liked that book for a lot of reasons, and
that is on the list.

Tony