Artificial gravity in spinning space ship conumdrum


by KenJackson
Tags: artificial, conumdrum, gravity, ship, space, spinning
KenJackson
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#1
Apr5-08, 09:31 PM
P: 19
In discussions, and novels, about deep space missions, we frequently read of the plan to spin the space ship to produce artificial gravity. This intuitively makes good sense.

But would it work in a ship that is very, very, very far away from any stars or other matter? That is, if the ship is spinning, relative to what is it spinning?

If the proximity to matter is irrelevant, then does the universe have some inherent sense of direction or "upness"?
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Shooting Star
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#2
Apr6-08, 05:06 AM
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As far as we know, it would work. Also, there is only so far you can be from stars and other matter. The emptiest regions we see is probably between the galactic super clusters or possibly the "voids" between the complexes made by these, the “walls”. But these "empty" spaces, too, contain dark matter. So, if you are trying to invoke Mach’s Principle, it’ll be difficult to conduct any experiment “sufficiently” removed from matter in this universe.

The relevant spinning appears to be with respect to the "distant" matter. Exactly how the distant matter influences the inertia of an object is not known. But according to the qualitative results of Mach’s Principle, nearby masses also should influence inertia locally. This type of phenomenon was investigated by Lens and Thirring in the context of GR, and is known as the rotational frame dragging effect. The effect of local masses on the mass of a test body is also predicted in GR, but the effect is too small to measure with available methods.

Broadly speaking, the universe seems not to distinguish between uniform velocities but between accelerations with respect to the average distribution of matter.
KenJackson
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#3
Apr6-08, 06:46 AM
P: 19
Mach’s Principle

Ah! That is what I was looking for. Thank you.

LURCH
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#4
Apr6-08, 10:38 AM
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Artificial gravity in spinning space ship conumdrum


Quote Quote by KenJackson View Post
In discussions, and novels, about deep space missions, we frequently read of the plan to spin the space ship to produce artificial gravity. This intuitively makes good sense.

But would it work in a ship that is very, very, very far away from any stars or other matter? That is, if the ship is spinning, relative to what is it spinning?

If the proximity to matter is irrelevant, then does the universe have some inherent sense of direction or "upness"?
I would say, no, the universe does not have an inherent sense of direction, nor of "upness," but it does have an inherent sense of inertial and non-inertial reference frames. The same "artificial gravity" effect could be achieved by providing a ship with a form of continuous thrust, resulting in continuous acceleration. It would not matter if the ship were near any massive bodies. The ship does not have to be accelerating "relative to" some other object. It need only be accelerating compared to an inertial frame of reference.
nuby
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#5
Apr6-08, 11:46 AM
P: 364
Is there even any scientific proof of this concept? If a space station is spinning rapidly around an axis in space .. simulated gravity would come from centrifugal force? I've heard lots of talk about this, but where is the proof? Does NASA have a video clip or experiment data?
PatPwnt
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#6
Apr6-08, 01:51 PM
P: 83
Yea there is proof; acceleration is a change in velocity. When you are spining around an axis, you are changing velocity from the centripetal force keeping you from travelling in a straight line. This force can feel just like like gravity, if you are far enough away from the center to where your height towards the center doesn't have a noticable effect on the force distribution on your body. Otherwise, I think your head would feel lighter while standing. But another thing would happen, if you threw a ball with equal velocity of the angular velocity of the ship(times the radius), but in opposite direction, it would just float above the surface as you spun around and it stood still relative to the center of mass of your ship. So, there would be strange things that made it not feel like gravity. If you wanted to toss something to your friend on the other side of the ship, you would have to throw it with a tangeant component to the ship's radius and opposite direction of your real velocity at that point, then it will reach him. So the effects would not be exactly like gravity. If you tried throwing it directly at him, you may just end up spinning around the axis and it landing in your face. Just like if you threw it straight up in gravity. If you were sitting down and stood straight up, you would probably fall over because your body's angular momentum stays the same while your center of mass moves in toward the center.

Have you ever been on one of these?
http://video.google.com/videoplay?do...arch&plindex=0

Notice at the end of the video when he tries to walk towards the camera, he jerks over to his left.
nuby
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#7
Apr6-08, 02:30 PM
P: 364
PatPwnt, Thanks for that video, it was entertaining. But, it proves nothing really.

Please explain why:

1. This simulates the same effects that would occur in outer space.

2. Centrifugal force can't be the 'redirection' of gravity.
Anticitizen
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#8
Apr6-08, 02:46 PM
P: 128
It's not redirection of gravity, it's redirection of motion which happens to behave a bit like gravity to the person being spun.
nuby
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#9
Apr6-08, 02:48 PM
P: 364
Ok. Prove it. A video clip like the previous one (small scale) in space would be great.
Anticitizen
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#10
Apr6-08, 02:53 PM
P: 128
Why do you believe it would happen any differently in space than on land? The centrifuge on land is spinning fast enough (horizontally to the ground) to OVERRIDE the effects of gravity (in the vertical axis to the ground), it'd be the same in space, only easier, because there'd be nothing pulling the person downward.

To prove it to you, I'd have to launch a centrifuge into deep space, which is beyond my current budget I'm afraid.
Anticitizen
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#11
Apr6-08, 03:02 PM
P: 128
Quote Quote by KenJackson View Post
That is, if the ship is spinning, relative to what is it spinning?
To itself, or different parts of itself. If you picture the centrifuge from 'above', that is, your viewpoint in line with the axis of rotation but not rotating with the 'fuge, then you'll see that one side is moving 'left' and the other moving 'right' in regard to each other. I mean that in the same sense that one describes a watch hand moving to the 'right' once it passes the 9 o'clock mark, then curving back 'left' once it passes 3 o'clock.
nuby
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#12
Apr6-08, 10:30 PM
P: 364
Is it safe to say centrifugal existing in outer space is just an assumption?
rbj
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#13
Apr6-08, 10:54 PM
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Quote Quote by KenJackson View Post
But would it work in a ship that is very, very, very far away from any stars or other matter? That is, if the ship is spinning, relative to what is it spinning?
unlike translational velocity, which is completely relative (anyone flying around in a vacuum relative to someone else at a constant velocity has an equal claim to being "at rest" as anyone else at a constant, but different, velocity), rotational velocity is absolute. it's not spinning if the folks in the outer rim of the cylinderical spaceship are experiencing 0g. even if there were no heavenly vistas in which to base one's measurement of spin rate, with an accelerometer at a known location, one can determine the spin rate.
Shooting Star
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#14
Apr6-08, 11:03 PM
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Quote Quote by nuby View Post
Is it safe to say centrifugal existing in outer space is just an assumption?
Not in front of any qualified physicist, especially if he's bigger than you. Here, you have the whole internet shielding you.

What more can we tell you about the existence of centrifugal force? The earth, the Sun, Jupiter, to name a few -- all these bodies which are in "space" -- bulge out at the equator due to centrifugal force. The bulges are visible. These are your large scale experiments in space.

Please don't hijack this thread. If you have so much doubt, start a new one.
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Dear Mentor/Admin,

Doesn't nuby's previous post violate the PF rules/guidelines? Someone may as well question Newton's laws of motion directly, instead of indirectly as member nuby is doing.
nuby
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#15
Apr6-08, 11:27 PM
P: 364
Quote Quote by Shooting Star View Post
What more can we tell you about the existence of centrifugal force? The earth, the Sun, Jupiter, to name a few -- all these bodies which are in "space" -- bulge out at the equator due to centrifugal force. The bulges are visible. These are your large scale experiments in space.
That's not relevant, it's not 'outer space' .. centrifugal force on planets coexist with other forces, gravity, etc.
KenJackson
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#16
Apr7-08, 05:06 AM
P: 19
Quote Quote by rbj View Post
unlike translational velocity, which is completely relative (anyone flying around in a vacuum relative to someone else at a constant velocity has an equal claim to being "at rest" as anyone else at a constant, but different, velocity), rotational velocity is absolute. it's not spinning if the folks in the outer rim of the cylinderical spaceship are experiencing 0g. even if there were no heavenly vistas in which to base one's measurement of spin rate, with an accelerometer at a known location, one can determine the spin rate.
You hit the crux of my original question, but you seem to have answered it based on Newton's classical absolute space argument.

rotational velocity is absolute. it's not spinning if the folks in the outer rim of the cylinderical spaceship are experiencing 0g. This sounds like Newton's bucket argument.

I was pleased that someone mentioned Mach's Principle, which caused me to find the wikipedia discussion on the same. I am content to learn that Einstein grappled with the issue and decided that inertia originates in a kind of interaction between bodies. That is, (as I understand it) the presence of other matter (I guess all matter in the universe) determines what is and is not spinning.
TVP45
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#17
Apr7-08, 05:13 AM
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Quote Quote by nuby View Post
Is it safe to say centrifugal existing in outer space is just an assumption?
No, it is not an assumption. The European Space Agency built a centrifuge for space (obviously not deep space) and a copy was flown by NASA.

Start by Googling NASA JSC. Specifically, you might also look at work done by Scott Wood.
Shooting Star
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#18
Apr7-08, 07:33 AM
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Quote Quote by rbj View Post
... rotational velocity is absolute. it's not spinning if the folks in the outer rim of the cylinderical spaceship are experiencing 0g. even if there were no heavenly vistas in which to base one's measurement of spin rate, with an accelerometer at a known location, one can determine the spin rate.
Absolute with respect to what? The mean of the distant matter? Or Absolute Space?

If there's a germ of truth in Mach's Principle, which the scientific community does believe there is, then a massive rotating shell spinning around you should produce a centrifugal force similar to what is produced by you spinning wrt the background of the distant matter.

Even otherwise, spinning near a massive body gives rise to different effects than spinning in a relatively mass free region, and the accelerometer would show different readings.


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