Rendezvous with Rama

I'm reading this book by Arthur C. Clarke. It involves a spaceship of
sorts, which is a cylinder that rotates about its long axis. The idea is
that a person standing on the inside of the cylinder will experience a
pseudo-'gravity' in the form of a centripetal force that pushes his feet up.
I have a few concerns with this, which are probably relevant to any such
device engineered to create 'gravity' this way.

1. If I'm standing on the inside surface of the cylinder and I jump up,
there is no true 'pull' on me that accelerates me toward the 'floor' like
there is with real gravity. Consequently, if I jump, I will simply float up
and through the long axis, to the other side of the cylinder.

A natural consequence of this is that I can't run on the floor, since this
involves both my feet leaving the floor and not touching again till I hit
the other side. If I fell asleep an area with no roof, I could float away
if I were not strapped down.

2. Also, imagine I were standing on the floor of this cylinder facing the
direction in which it turns. The ground and I are travelling in that same
direction, so I appear to be stationary. However, the ground also slowly
moves 'up' in front of me and also rotates my body 'backwards' slightly.
This would mean that every time I jump I would appear to somersault slightly
in the direction of turn, or alternatively if I turned around 180 degrees, I
would appear to somersault slightly backwards when I jump (or even just
standing there).

This would mean that whatever angle I stand at, my postural reflexes will
have to alter slightly on two sides of my body and I will easily tell which
way the ground am turning.

3. Arthur C Clarke supposes that the air is denser toward the 'floor' than
toward the middle of the cylinder.

This doesn't seem right at all. There is nothing attracting the air to the
floor. Surely the air might be caused to rotate slightly because of the
friction between the floor and the outermost laminar layer, but that would
not be transferred to all the other air molecules. Air is 'slippery' enough
that even two metres above the floor I'd imagine that it would be relatively
motionless and that the gas would evenly distribute itself throughout the
rest of the cylinder.

This means that if I'm standing on the floor, I will feel a breeze.

Am I right in all this?

Testing wrote:

I'm reading this book by Arthur C. Clarke. It involves a spaceship of
sorts, which is a cylinder that rotates about its long axis. The idea is
that a person standing on the inside of the cylinder will experience a
pseudo-'gravity' in the form of a centripetal force that pushes his feet up.
I have a few concerns with this, which are probably relevant to any such
device engineered to create 'gravity' this way.

1. If I'm standing on the inside surface of the cylinder and I jump up,
there is no true 'pull' on me that accelerates me toward the 'floor' like
there is with real gravity. Consequently, if I jump, I will simply float up
and through the long axis, to the other side of the cylinder.

No, that's wrong. Let's choose our coordinate system so that the point
you are standing is at the bottom of the cylinder, and the cylinder
rotates clockwise. Because of this rotationally movement, you have a
speed to the left at this point (seen by an outside observer - you
yourself would say that you are simply standing there and are not moving
at all). If you now jump upwards, you *still* have this speed to the
left - hence you will not go directly "upwards" (towards the center of
the cylinder), but "upwards" *and* to the left (again, as seen by an
outside observer). In other words, you will land on the cylinder again -
and to you, this looks like a force of gravity is pulling you down.


A natural consequence of this is that I can't run on the floor, since this
involves both my feet leaving the floor and not touching again till I hit
the other side. If I fell asleep an area with no roof, I could float away
if I were not strapped down.

Wrong for the reason explained above.


2. Also, imagine I were standing on the floor of this cylinder facing the
direction in which it turns. The ground and I are travelling in that same
direction, so I appear to be stationary.

Right.


However, the ground also slowly
moves 'up' in front of me and also rotates my body 'backwards' slightly.

Huh? No.


This would mean that every time I jump I would appear to somersault slightly
in the direction of turn, or alternatively if I turned around 180 degrees, I
would appear to somersault slightly backwards when I jump (or even just
standing there).
This would mean that whatever angle I stand at, my postural reflexes will
have to alter slightly on two sides of my body and I will easily tell which
way the ground am turning.

False premise, false conclusion.




3. Arthur C Clarke supposes that the air is denser toward the 'floor' than
toward the middle of the cylinder.

This doesn't seem right at all. There is nothing attracting the air to the
floor.

See point 1.


Surely the air might be caused to rotate slightly because of the
friction between the floor and the outermost laminar layer, but that would
not be transferred to all the other air molecules.

Why not? Air molecules collide often.


Air is 'slippery' enough
that even two metres above the floor I'd imagine that it would be relatively
motionless and that the gas would evenly distribute itself throughout the
rest of the cylinder.

I don't think so.


This means that if I'm standing on the floor, I will feel a breeze.

Am I right in all this?

No, sorry.


Bye,
Bjoern

Dear Testing:

"Testing" wrote in message
om.au...
I'm reading this book by Arthur C. Clarke. It involves a spaceship of
sorts, which is a cylinder that rotates about its long axis. The idea is
that a person standing on the inside of the cylinder will experience a
pseudo-'gravity' in the form of a centripetal force that pushes his feet
up.
I have a few concerns with this, which are probably relevant to any such
device engineered to create 'gravity' this way.

A very bright fellow...

I'll only add a little to Bjoern's comments.

....
3. Arthur C Clarke supposes that the air is denser toward the 'floor'
than
toward the middle of the cylinder.

This doesn't seem right at all. There is nothing attracting the air to
the
floor.

"Attract" is not the right word. The air at the outer cylinder is in
contact with the outer cylinder. There are features on the outer cylinder
that tend to keep the air there at similar velocity. Therefore, the bulk
of the air is compressed since it is also being forced to follow a curved
path. Since this air is compressed, the air just "above" (being defined as
closer to tha axis of symmetry) it flows down, and the air above this, and
the air above this... The lowest pressure air in a tornado is the air in
the center.

Surely the air might be caused to rotate slightly because of the
friction between the floor and the outermost laminar layer, but that
would
not be transferred to all the other air molecules.

Blow air out of your mouth onto some scattered flour. You'll see that the
effects of your breath are much wider than your mouth.

Air is 'slippery' enough
that even two metres above the floor I'd imagine that it would be
relatively
motionless and that the gas would evenly distribute itself throughout the
rest of the cylinder.

You are thinking that air is imbedded in something that it can transfer
energy/momentum to. The only thing that can serve this purpose is the
walls of the ship. If the ship is spinning, the air will spin also. When
it spins it is "slung to the outside", just as if it were water. Water
also is 'slippery'. Spin a bucket of water (like it were sitting on a lazy
susan), keep it spinning for a while, and see what shape its upper surface
forms. This shape is indicative of the pressure distribution. It happens
to be a parabola, which is how some mirrors are cast. The pressure is
higher near the outer walls of the container.

This means that if I'm standing on the floor, I will feel a breeze.

No.

Am I right in all this?

You are right to question. Clarke did his homework.

David A. Smith

I'll follow up here owing to newsgroup server problems. Thanks to all
replies.

However, the ground also slowly
moves 'up' in front of me and also rotates my body 'backwards' slightly.

Huh? No.

- I think this is the thing that had me tricked. I forgot that the person
standing on the inside of the cylinder is himself rotating at the same speed
as the cylinder.

- Have experiments confirmed the behaviour of air inside the cylinder?

Dear Testing:

"Testing" wrote in message
om.au...
I'll follow up here owing to newsgroup server problems. Thanks to all
replies.

However, the ground also slowly
moves 'up' in front of me and also rotates my body 'backwards'
slightly.

Huh? No.

- I think this is the thing that had me tricked. I forgot that the
person
standing on the inside of the cylinder is himself rotating at the same
speed
as the cylinder.

- Have experiments confirmed the behaviour of air inside the cylinder?

Yes.

David A. Smith

On Sat, 27 Mar 2004 13:33:13 +1100, "Testing"
wrote:

I'll follow up here owing to newsgroup server problems. Thanks to all
replies.

However, the ground also slowly
moves 'up' in front of me and also rotates my body 'backwards' slightly.

Huh? No.

- I think this is the thing that had me tricked. I forgot that the person
standing on the inside of the cylinder is himself rotating at the same speed
as the cylinder.

- Have experiments confirmed the behaviour of air inside the cylinder?

Yes. That's how a centrifuge works. The only requirement for this is
that air have a non-zero viscosity, which it does.

Al Moore

On Fri, 26 Mar 2004 23:49:23 +1100, "Testing"
wrote:

I'm reading this book by Arthur C. Clarke. It involves a spaceship of
sorts, which is a cylinder that rotates about its long axis. The idea is
that a person standing on the inside of the cylinder will experience a
pseudo-'gravity' in the form of a centripetal force that pushes his feet up.
I have a few concerns with this, which are probably relevant to any such
device engineered to create 'gravity' this way.

1. If I'm standing on the inside surface of the cylinder and I jump up,
there is no true 'pull' on me that accelerates me toward the 'floor' like
there is with real gravity. Consequently, if I jump, I will simply float up
and through the long axis, to the other side of the cylinder.

No, instead, you go straight, and the floor comes up to meet you.

A natural consequence of this is that I can't run on the floor, since this
involves both my feet leaving the floor and not touching again till I hit
the other side. If I fell asleep an area with no roof, I could float away
if I were not strapped down.

Once again, you are mistaken. In the rotating cylinder you are
subjected to a continuous acceleration that provides a good simulation
for weight. The larger the cylinder, the better the simulation.

2. Also, imagine I were standing on the floor of this cylinder facing the
direction in which it turns. The ground and I are travelling in that same
direction, so I appear to be stationary. However, the ground also slowly
moves 'up' in front of me and also rotates my body 'backwards' slightly.
This would mean that every time I jump I would appear to somersault slightly
in the direction of turn, or alternatively if I turned around 180 degrees, I
would appear to somersault slightly backwards when I jump (or even just
standing there).

That's correct. This is referred to as "coriolis force" and was
covered in the novel.

This would mean that whatever angle I stand at, my postural reflexes will
have to alter slightly on two sides of my body and I will easily tell which
way the ground am turning.

How easy it is to tell depends on how large the cylinder is, and how
fast it's spinning.

3. Arthur C Clarke supposes that the air is denser toward the 'floor' than
toward the middle of the cylinder.

This doesn't seem right at all. There is nothing attracting the air to the
floor. Surely the air might be caused to rotate slightly because of the
friction between the floor and the outermost laminar layer, but that would
not be transferred to all the other air molecules. Air is 'slippery' enough
that even two metres above the floor I'd imagine that it would be relatively
motionless and that the gas would evenly distribute itself throughout the
rest of the cylinder.

Once again, Clarke is correct and you are mistaken. Air has viscosity,
and so rotates with the cylinder, and, in consequence becomes denser
at the periphery, and less dense along the axis.

This means that if I'm standing on the floor, I will feel a breeze.

Am I right in all this?

Well, one out of three isn't totally wrong.

Al Moore

Anyone want to comment on Larry Niven's 'Ringworld'?