Artificial gravity in spinning space ship conumdrum

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The discussion revolves around the feasibility of generating artificial gravity in a spaceship through spinning, particularly in deep space where proximity to matter is minimal. It raises questions about what the ship would be spinning relative to and whether the universe has an inherent direction or "upness." While some argue that the effects of spinning could mimic gravity, others point out that without nearby masses, the concept becomes complex and relies on Mach's Principle, which suggests inertia is influenced by distant matter. The conversation also touches on the practical challenges of creating such systems in space, with references to existing experiments and the need for further scientific validation. Ultimately, the concept of artificial gravity through centrifugal force is considered scientifically sound, though engineering it remains a challenge.
  • #31
nuby said:
You are wrong. Unless the astronauts are physically attached to a spinning "centrifuge", or propelling themselves forward (i.e. previous video) they will not experience any sort of "artficial gravity" at all.

As Danger pointed out the "artificial gravity" is just an aproximation of the real thing. If an astronaut managed to avoid the spinning rim for the whole trip then he could avoid being pulled down. (He is actually in a form of internal orbit). But if there is air inside the space station (as there usually is) then the air will gradually be dragged around into synchronisation with the rim and eventually the astronaut too would be dragged by the air and start to "fall".

If he was standing on the spinning rim and let go of a ball, guess where the ball will go?

A) Hover near his hand.
B) Move in an internal orbit like the astonaut before he touched down.
C) Drop towards his feet and stay on the rim after a couple of bounces.


Hint: It's not A or B ;)
 
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  • #32
As long as the astronaut was connected to the rim, the ball would have a curved trajectory toward the ground/rim ..

If the answer is "C" and the ball would drop straight towards his feet. What force would keep the ball adjacent to the floor below?
 
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  • #33
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  • #34
I think perhaps Nuby is looking for an argument rather than an answer.
 
  • #35
I just think "artificial gravity" (walking around in space) is just a myth, and pure science fiction/speculation. And I'm interested in finding out why it should or should not work. If I wanted to argue I would have responded to Shooting Star's previous post.
 
  • #36
When talking about the person dropping a ball dropped inside the "artificial gravity" in reference to the person inside the ring the ball would look like it fell straight down. The ball in question will already have the tangential velocity of the spinning ring that both person and ball are in motion with.

I already asked what your point was, that using rotational acceleration to simulate gravity for one that is in sync with the object that is rotationally accelerating is not artificial gravity, or was your point that rotational acceleration will not even simulate gravity. I think we all agree that it's not real gravity like what we see as a result of mass being present but it's the best approximation we can currently realize.

The problem being, you are stating that it's not artificial gravity but you aren't stating any evidence to back up your claim and then continue to avoid clarifying your statement.
 
  • #37
nuby said:
I just think "artificial gravity" (walking around in space) is just a myth, and pure science fiction/speculation.

Oh, good lord, NUBY, what exactly do you mean by space walking? We hear that astronauts sometimes go for space walks, and that means nothing more than that they are tethered to the ship and have gone out do some work on the ship (EVA). They are essentially just "floating" around in space, though actually they are in free fall around Earth if that vehicle happens to be orbiting earth.

Do you mean that by "artificial gravity"? Also, let me say once more that there is nothing called artificial gravity.

Science fiction and speculation do not share the same status, as you seem to imply in the above post.

If you do want to discuss space walks using artificial gravity, at least open a new thread as I had requested you before.
 
  • #38
Atomsk,

I'm thinking that centrifugal force might behave differently in space than it does on earth, and that 'artificial gravity' (ie 2001: A Space Odyssey) would never work due to the coriolis effect. I'm not arguing the terminology, just the theory.
 
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  • #39
nuby said:
I'm thinking that centrifugal force might behave differently in space than it does on earth...
Be advised that personal speculation is not permitted here.
 
  • #40
Artificial gravity (that is the correct term and needs not to be set off in quotes) is very real, is practical, and is being widely studied (JSC, Cleveland Clinic, Univ. of Texas, Mt. Sinai, etc.). It is not about tossing balls in the air; it is about the physiological effects on humans of living for long periods in microgravity.

In a very large radius ship, as in 2001, one could create an artificial gravity that closely mimics real gravity and a ball would fall almost correctly. A ship that large is out of the question now; it may be built, perhaps within your lifetime, and you'll be able to see demonstrations of that gravity. In the meantime, we all have to be satisfied with short-arm centrifuges.

I earlier posted several links to the work being done at JSC. A centrifuge has been flown, and I mentioned that. There are a ton of links to papers by respected scientists on the sites I gave you. Have you looked at those?

YouTube is fun but not a citation.
 
  • #41
It wouldn't be hard for NASA to demonstrate artificial gravity on a small scale, and there are tons of videos out there with other experiments. Where is the one for artificial gravity?

(27 seconds in) shows a coriolis affect
 
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  • #42
nuby said:
It wouldn't be hard for NASA to demonstrate artificial gravity on a small scale, and there are tons of videos out there with other experiments. Where is the one for artificial gravity?

(27 seconds in) shows a coriolis affect


Are you following any of the links I've suggested? NASA has created artificial gravity hundreds (thousands?) of times. Of course there is a coriolis effect; again, if you look at the sites I've suggested, you'll find a number of papers referencing the problems that creates.
 
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  • #43
TVP45 said:
Artificial gravity (that is the correct term and needs not to be set off in quotes) is very real, is practical, and is being widely studied (JSC, Cleveland Clinic, Univ. of Texas, Mt. Sinai, etc.).

(I think you and I have gone through this before.)

I wanted to avoid that term since there is a lot of confusion going around here. How can somebody confuse "space walks" with "walking in artificial gravity"? Also, "artificial gravity" may suggest something like Star Trek gravity (which would be truly artificial gravity), so I thought I would clarify matters.

The artificial gravity we are talking about here is the effect of inertial forces in any non-inertial frame. I sincerely hope it is clear now.

Let me sum up with what we are dealing here:

Whenever there is an accelerating frame, there are inertial forces, whose effects on a small region and over a short time can be approximated by a uniform gravitational field. (This sounds like the equivalence principle, which it is actually, but all discussions here are within the Newtonian scenario.)

These may be identified as the centrifugal force or the Coriolis force in a uniformly rotating frame. In a uniformly accelerating frame in a straight line, it will be an effective gravitational field in the opposite direction, as in elevators/lifts. If the acceleration of the frame is arbitrary, the inertial forces will be different from these familiar examples. It may be very difficult to calculate and also to predict what effects will be felt by a human being under such arbitrary forces. Also, remember that for a human being to feel anything, he should not be in free fall in that frame, which would just be equivalent to moving with constant velocity wrt some IFR, but has to be stationary wrt the non-IFR. Then only he can feel the effect of inertial forces.

In a very large radius ship, as in 2001, one could create an artificial gravity that closely mimics real gravity and a ball would fall almost correctly.

That is not correct. If you push something from the centre toward the rim, the trajectory will not seem like a straight line in the frame of the ship. We have already discussed this https://www.physicsforums.com/showpost.php?p=1546281&postcount=29".

Similarly, in a small centrifuge, the variations are much more over a short distance, than say, over the Earth for the same distance (due to Earth's rotation).

I earlier posted several links to the work being done at JSC. A centrifuge has been flown, and I mentioned that. There are a ton of links to papers by respected scientists on the sites I gave you. Have you looked at those?

I fail to understand why we have to give an example of something that NASA has built to prove the existence of inertial forces. I know that you are interested in microgravity, but that has nothing to do with the discussion here. (Remember, you can take the horse to the water but you cannot make it drink.)

I don't think you and I have any argument, just some confusion over terminologies. Arguing here about centrifugal forces is just adding fuel to the fire. If you really feel you have to disagree, PM me, as I want to unsubscribe from this thread.
 
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  • #44
I think unsubscribing is a wonderful idea. I'll join you.
 
  • #45
nuby said:
Atomsk,

I'm thinking that centrifugal force might behave differently in space than it does on earth, and that 'artificial gravity' (ie 2001: A Space Odyssey) would never work due to the coriolis effect. QUOTE]

Hold on for a moment. (I was about to unsubscribe when I read this again.) Do I see a glimmer of hope yet?

Nuby, why don't you just explain exactly what you meant when you wrote the above sentence? Did you mean that if I let a ball drop in a big rotating space ship, it will not fall straight toward the rim? Feel free to explain in detail, but just stick to this point.
 
  • #46
nuby said:
As long as the astronaut was connected to the rim, the ball would have a curved trajectory toward the ground/rim ..

If the answer is "C" and the ball would drop straight towards his feet. What force would keep the ball adjacent to the floor below?
The ball would not drop straight toward his feet. "Coriolis" force would make its trajectory curve a little bit. The ball's initial rotational speed would be less than that at the astronaut's feet. That's one difference between "gravity" simulated by spinning and true gravity. That's only noticable in a very large volume.

It is, of course, the "centrifugal force" that would keep it on the floor. Yes, I know that centrifugal force is "ficticious". It is a convenient way of saying that the ball, with its instantaneous velocity parallel to the direction of rotation would attempt to continue in that straight line and is prevented from doing so by the "centripetal" force the floor exerts on it.

There would be no force toward the floor if the astronaut were not on the floor and were not rotating around the axis with the rest of the ship, then there would be no "fake gravity" force. But how would he get there? If he jumped up from the floor, he would still have the floors rotational velocity.

Oh, and to answer the question that was posed in the very first post, "If the ship were very far from any star, what would it be rotating with respect to?", with respect to its own axis, of course. Velocity is relative. Rotation involves an acceleration and is not relative.
 
  • #47
If it sheds any new light, remember that there is Coriolis effect on Earth as well. So, if you drop a ball while standing on the ground, it will not really fall in a perfectly straight line downward, will it? Its path will be slightly curved due to Coriolis, and the fact that your hand is slightly farther from the center of rotation than the ground toward which the ball falls. Even on Earth we are experiencing gravity in a rotating frame, and we have certain effects acting upon us as a result of that rotation. But for the most part, we can ignore these effects because they are vanishingly small.

Likewise, artificial gravity generated by rotation would have some Coriolis effects involved. And, these effects would be greater than we exerience on Earth (because the rotating frame is much smaller). But, for the most part, the effect could still be ignored (just like it is here on Earth). Artificial gravity is, after all, only an approximation of real gravity and, for every-day use, it works perfecty well. You could put your feet on what others would consider the "wall" of the ship, and walk around and feel perfectly normal calling it the "floor." You could put a meal on a plate and it would stay there, and someone outside the ship would say it is stuck to the wall by centrifugal force, but to you it would seem to be sitting on the plate in a perfectly normal way. You could drop a ball and it would fall to the floor at your feet. If you had precise enough instruments, you could measure some curve to that drop, but you could do that on Earth, too.

As for centrifugal force behaving differently in space than it does on Earth, it just doesn't. The scientists on the ISS have been conducting experiments using a centrifuge pretty much since the staion went operational. Centrifugal force works just the same up there as it does down here.
 
  • #48
HallsofIvy said:
It is, of course, the "centrifugal force" that would keep it on the floor. Yes, I know that centrifugal force is "ficticious". It is a convenient way of saying that the ball, with its instantaneous velocity parallel to the direction of rotation would attempt to continue in that straight line and is prevented from doing so by the "centripetal" force the floor exerts on it.

It would be extremely difficult to keep a ball on the outer "floor" of a rotating frame just by centrifugal force alone, as that would be a very unstable situation. It is generally the friction in conjunction with the centrifugal force which will keep the ball stationary wrt the floor, or else the ball would have to be clamped down. As on a horizontal surface of earth, things stay in their places because of friction and gravity, otherwise the rotation of the Earth would cause them to slip. Think of that the next time you are typing and your computer is not sliding off. :smile:


Oh, and to answer the question that was posed in the very first post, "If the ship were very far from any star, what would it be rotating with respect to?", with respect to its own axis, of course. Velocity is relative. Rotation involves an acceleration and is not relative.

Read posts #2 and #18.
--------------------------------------------------------------------
Hey NUBY,

Anticipating an answer from you is the only thing that's keeping me here.
 
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  • #49
Shooting Star, Like other have explained, I think the coriolis effect will be at play in a rotating spaceship (and on earth). But, I'm wondering if the magnitude of the effect is a greater in space, and how it is calculated in space or on land (moon, earth, etc).
 
  • #50
nuby said:
Shooting Star, Like other have explained, I think the coriolis effect will be at play in a rotating spaceship (and on earth). But, I'm wondering if the magnitude of the effect is a greater in space, and how it is calculated in space or on land (moon, earth, etc).

(Nuby, if I have ever seen hijacking, this takes the cake.)

I have this morbid curiosity to know why you think that the Coriolis effect is different in what you call "space"?

You did not answer the question I had asked you in my last post. I am asking you two more.

1. What is "space", according to you?

2. Can we explain all phenomenon happening in the rotating ships without invoking centrifugal or Coriolis force, from the point of view of an IFR?

You can read https://www.physicsforums.com/showpost.php?p=1546281&postcount=29" discussion, which I had mentioned earlier. (It is a simple and very short description of the two points of view.)

Do answer the question in my last post by just saying yes or no.
 
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  • #51
I read that discussion, and almost everything makes sense to me. The thing I see making artifical gravity impractical are the issues astronauts would have with nausea, disorientation, etc. One thing confusing to me is the coriolis effect the astronauts would experience. If an astronaut was standing still in the rotating ship, why would he not experience a coriolis (not sure if this the best term) affect?

It seems since his head and feet would be moving at two different speeds (from an outside reference point), he might experience some sort of (rotating) force from that, even while not moving.

Shooting Star, if you have any more questions for me, send a private message. Since I can't say what I think here.
 
  • #52
nuby said:
I read that discussion, and almost everything makes sense to me.

HEAR THAT, FELLAS? One up for PF.

The thing I see making artifical gravity impractical are the issues astronauts would have with nausea, disorientation, etc.

That has nothing to do with rotating frames and inertial forces, and need not be discussed here. Many people throw up when traveling by car.

One thing confusing to me is the coriolis effect the astronauts would experience. If an astronaut was standing still in the rotating ship, why would he not experience a coriolis (not sure if this the best term) affect? It seems since his head and feet would be moving at two different speeds (from an outside reference point), he might experience some sort of (rotating) force from that, even while not moving.

The Coriolis force is given by -2wXv. This v is wrt the rotating frame, not the "stationary" inertial frame of reference. So, if an astronaut is standing still in the rotating frame, the velocities of all mass points on him is zero wrt the rotating frame. So, v is 0 for all points on his body and the Coriolis force on him is 0.

As you said, his head and feet has two different velocities wrt the IFR, but that has nothing to do with the Coriolis effect. You have to measure velocities wrt the rotating frame.

But the centrifugal force on his head and feet would be different, because they are at different distances from the rotating centre. It may not be noticeable if his distance from the centre is large compared to his height. Even on earth, out head and feet experiences different gravity.

I won't discuss anymore for fear of confusing you with something. Try to understand the Coriolis force. Read that discussion again if you have confusion. Think of something moving with uniform velocity inside a rotating shell, and what you see as st line motion becomes a spiral trajectory wrt the shell. That is what the Coriolis force basically is all about.

Shooting Star, if you have any more questions for me, send a private message. Since I can't say what I think here.

You can PM me any time.

If anybody asks you a question, and you answer honestly without expressing your own opinion, then I believe and hope that you won't get any points any more. I did not unsubscribe because at the last moment I thought you were not able to communicate properly, and also lacked some knowledge. Others will understand that too. But no more comments like in space things are different. Space is the same everywhere, at least for the purpose of our discussion.

And, remember, psychological or even technological issues are not very relevant in theoretical discussions.
 
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  • #53
nuby said:
I read that discussion, and almost everything makes sense to me. The thing I see making artifical gravity impractical are the issues astronauts would have with nausea, disorientation, etc. One thing confusing to me is the coriolis effect the astronauts would experience. If an astronaut was standing still in the rotating ship, why would he not experience a coriolis (not sure if this the best term) affect?

It would have to be a pretty tiny spaceship if nausea was a major problem. Specifically because if they actually employed this method in the design they would increase the ring diameter so that the rotational speed would be less, to create the same centripetal force.
 
  • #54
Maybe this image will chaneg the way things look;

NASA's "Mars Express" plan, to get astronauts to Mars, includes a plan to spool out the capsule, in which they will spend most of the trip, on the end of a long cable. On the other end will be the final booster stage of the rocket. The two objects will be set spinning around each other (the cenetr of thwe cable will eb nearyl staionary). This will provide a downward push to keep the astronauts pressed against the floor, keeping them healthy and making many ordinary tasks easier.

Nuby, when you think of it that way, with the center of rotation outside of the capsule, does it make any difference?
 
  • #55
linton said:
It would have to be a pretty tiny spaceship if nausea was a major problem. Specifically because if they actually employed this method in the design they would increase the ring diameter so that the rotational speed would be less, to create the same centripetal force.
Even in a medium-sized spaceship, the astronaut is still spinning about an axis - it just happens to be an axis that is an arbitrary number of metres over his head. You're going to feel it.
 
  • #56
linton said:
It would have to be a pretty tiny spaceship if nausea was a major problem. Specifically because if they actually employed this method in the design they would increase the ring diameter so that the rotational speed would be less, to create the same centripetal force.

That is one of the most sensible comments I’ve encountered in this thread.

DaveC426913 said:
Even in a medium-sized spaceship, the astronaut is still spinning about an axis - it just happens to be an axis that is an arbitrary number of metres over his head. You're going to feel it.

Is this your feeling or have you got any numbers to show?

Let us take some conservative estimates and do the math.

1. Radius of the rotating space station is 100 m.
2. The angular speed w is such that the centrifugal acceleration equals 9.8 m/s² at the rim.
3. A typical astronaut is, say, 2m tall.
4. He walks at a pace of 5 km/hr = (25/18) m/s.

The difference between the centrifugal acceleration at his feet and head is 0.02 g. This is the “tidal force” when he is not moving wrt the station. I don’t think the human body can sense this variation in g between the head and the foot.

More concern has been shown here about the Coriolis effect. It is maximum when the velocity is perpendicular to the axis of rotation, that is, when he walks along a latitude of the cylinder, and the value turns out to be 0.089 g, which is less than 9/100 than g at earth’s surface. Generally, it will be less than this.

So, when he walks, he may have to compensate for this force. Remember, this is a small space station compared to what people have in minds for the future. (The ISS is around 120 m across, just for the purpose of comparison.) For bigger stations, the Coriolis force will be much less, and people will not notice it or will get habituated to it if it is small but appreciable.

Do not compare the effects of rotations in small or even big centrifuges with effects on a rotating space station.
 
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  • #57
Shooting Star said:
Let us take some conservative estimates and do the math.

1. Radius of the rotating space station is 100 m.

Well we were talking about a spaceship, and a spaceship of 100m diameter is anything but conservative.

That being said, there's no need to belabour it; we'll talk about space stations.
 
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  • #58
Shooting star is the Man! or woman?

ok I'm just a college dropout who found this webpage on a humbug. Artificial graivty, or should I say mechanically produced gravity? would definitely work if the station is spining around fast enough at a steady space, as long as it is a large enough, and on a constant axis(how large I don't know, but i looked at the video link and sure enough, it seemed to be working pretty well!) . It doesn't really matter if gravity is affecting it or not becuase it is going to affect the whole thing including the people equally (unless it's like a black hole or some weird outer space thing I don't know about). Think of the carnival ride once again (I believe there is a link to it up above in this thread). Imagine that, on a giant robotic arm, it doesn't matter if they turn it upside down or sideways those people are still going to stick to that wall. Unless the giant arm turned em upside down and shook em like it was trying to get the last drop of ketchup out of a glass bottle, which i think would be cool, especially if nuby was on it. j/k :-)
 
  • #59


blunt187 said:
would definitely work if the station is spining ... It doesn't really matter if gravity is affecting it or not ... Think of the carnival ride once again (I believe there is a link to it up above in this thread). Imagine that, on a giant robotic arm, it doesn't matter if they turn it upside down or sideways those people are still going to stick to that wall.
Spinning? Who says the carnival ride is spinning and not the Earth? Who nominated the Earth to be the center of the universe?

It's easy to slip into classic absolute space thinking. Though the question isn't absolutely answered yet, I'm still pleased enough by what was said earlier.
KenJackson said:
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.
 

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