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Physics Experts: Error in 2001 Space Odyssey?

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Physics Experts: Error in 2001 Space Odyssey?

Old 04-29-03, 07:01 AM
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Physics Experts: Error in 2001 Space Odyssey?

I've seen 2001: A Space Odyssey many times, but as I watched it again last night, something struck me as odd. Since Stanley Kubrick is so meticulous to detail and authenticity, I would be surprised if he truly made such a glaring error. Perhaps someone out there can set the record straight.

This is in regards to the concept of artificial gravity produced by a rotating space station. Now first of all, I'm thinking about how gravity is produced by the rotation of the Earth. Because of our planet's spin, we are being pulled toward its center.

In the movie, you have a space station shaped like a wheel, spinning to produce its own gravity. So wouldn't the people inside be walking through the curve of the wheel with their feet pointed towards the center? But instead, if you pay attention to the way the interior of the space station is curving, they are actually walking with their heads pointed towards the center. In my mind, this means they are literally defying gravity and walking on the ceiling.

The same problem exists on the astronauts' ship traveling to Jupiter. Again, if you pay attention to the curve as they walk or jog through the corridor - their heads are pointed to the center which seems to me to be the opposite direction of the force of gravity.

Any physics experts in the house?
Old 04-29-03, 07:18 AM
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Centrifugal Force.

Try this. Get a small bucket and fill it halfway with water. Now, very quickly spin the bucket around. The water stays in the bucket! Same concept when you are going on the loop on a roller coaster.
Old 04-29-03, 07:31 AM
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Ah yes. The old bucket lesson from grade school. Forgot about that one.

So since its centrifugal force we're dealing with, that would actually be different from the force of gravity, correct? I assume the Earth's mass is what creates the force of gravity. But a spinning space station cannot rely on its size to produce true gravity (unless it's the size of the Death Star or something ), so it relies on the concept of centrifugal force. Thanks Groucho - that makes sense.
Old 04-29-03, 08:06 AM
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You are correct in your second post. I wish we would see something like that sooner than later.
Old 04-29-03, 09:15 AM
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You got it. We are held to the Earth not because of its spin, but in spite of it. The huge mass of the Earth more than compensates for the spin, which tends to want to hurl us off into space.
Old 04-29-03, 11:09 AM
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Let's let Einstein explain it:

http://216.239.37.100/search?q=cache...n&ie=UTF-8</a>

That the relation of gravity to inertia was the motivation for general relativity is expressed in an article Einstein wrote which appeared in the February 17, 1921 issue of Nature [28]

"Can gravitation and inertia be identical? This question leads directly to the General Theory of Relativity. Is it not possible for me to regard the earth as free from rotation, if I conceive of the centrifugal force, which acts on all bodies at rest relatively to the earth, as being a "real" gravitational field of gravitation, or part of such a field? If this idea can be carried out, then we shall have proved in very truth the identity of gravitation and inertia. For the same property which is regarded as inertia from the point of view of a system not taking part of the rotation can be interpreted as gravitation when considered with respect to a system that shares this rotation. According to Newton, this interpretation is impossible, because in Newton's theory there is no "real" field of the "Coriolis-field" type. But perhaps Newton's law of field could be replaced by another that fits in with the field which holds with respect to a "rotating" system of co-ordiantes? My conviction of the identity of inertial and gravitational mass aroused within me the feeling of absolute confidence in the correctness of this interpretation."
Old 04-29-03, 11:31 AM
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Originally posted by movielib
Let's let Einstein explain it:
Oh what the f*** does he know?

The real question is how come Dave and Frank aren't weightless when they are in the Pod Bay since there is no artificial gravity there (that part of the ship does not rotate)?
Old 04-29-03, 12:14 PM
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they wear special boots with magnets, I would assume
Old 04-29-03, 12:16 PM
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Originally posted by Pants
The real question is how come Dave and Frank aren't weightless when they are in the Pod Bay since there is no artificial gravity there (that part of the ship does not rotate)?
When you see something like that in a movie, a wizard did it.
Old 04-30-03, 12:21 AM
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Originally posted by Groucho
When you see something like that in a movie, a wizard did it.


Wizards? or HAL?
Old 04-30-03, 02:14 AM
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Originally posted by rennervision
I assume the Earth's mass is what creates the force of gravity.
Correct. According to Newton's law of universal gravitation, every particle in the universe exerts a force of gravity on every other particle that is proportional to the product of their masses and inversely proportional to the distance between them.

Therefore, it is the space station's mass that would produce any gravitational "pull" experiences by the astronauts, not the spin.
But a spinning space station cannot rely on its size to produce true gravity (unless it's the size of the Death Star or something ), so it relies on the concept of centrifugal force.
Technically not size but mass. But yes, it is indeed the centrifugal force that provides the artificial gravity of the space station.

While I'm in my "nerd" mode here, I'd just like to point out a common misconception about centrifugal force. It is often believed that when a person experiences centrifugal force, this force acts on the person, pulling them away from the center. This is not true. It is in fact the person that is exerting this force. What happens is that, in this case, the center of gravity of the space station pulls on the person and, by Newton's third law, the person exerts an equal and opposite force on the center of gravity. This is the force that keeps the person against the back ("the ground") of the space station.

Last edited by Tyler_Durden; 04-30-03 at 02:16 AM.
Old 04-30-03, 09:20 AM
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The explanations all make it seem so basic. Now I'm just disappointed we are building the International Space Station - in the 21st century no less - with no artificial gravity via centrifugal force being implemented!

(Oh wait. Didn't the Mir have that? At least that's how it was depicted in "Armageddon." )
Old 04-30-03, 10:18 AM
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Would the technology shown in 2001 work? Or would it have to be spinning at an unreasonably fast speed to simulate Earth gravity? Or would it just make you barf?
Old 04-30-03, 10:49 AM
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Yes it would work. The rate of spin required to maintain an equivalent of 1g is dependent on the diameter of the station (v^2/r).

And no, you only barf if your inner ear (sense of motion) is scewed from your visual sense of motion.

Part of the problem with such a stations is illustrated nicely in the movie. If the station is too small, you have that curved effect when looking straight (tangent to rotation). If you make the station large enough, you can minimize that, but then it gets expensive.
Old 04-30-03, 11:00 AM
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Originally posted by Pants
Would the technology shown in 2001 work? Or would it have to be spinning at an unreasonably fast speed to simulate Earth gravity? Or would it just make you barf?
Of course it depends on the size of the space station how fast it would have to spin to simulate one gravity at the outer wall.

According to this:

How fast does a space station rotate anyway?

for a space station with a diameter of about 4 miles the outer rim would have to be spinning at about 400 mph.

If the station were only 1000 meters in diameter (1 kilometer, about .62 miles), it would have to spin at about 155 mph.

If it were only 100 meters in diameter it would need only about 50 mph.

(If my calculations are correct. )

Last edited by movielib; 04-30-03 at 11:08 AM.
Old 05-01-03, 04:39 PM
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quote:Originally posted by movielib
Let's let Einstein explain it:

Originally posted by Pants
Oh what the f*** does he know?
Yeah! Doesn't he have Ass Burger Syndrome, anyways???

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