Is artificial centrifugal gravity ever considered?

[stevensfo]

We've all grown up seeing movies with revolving space stations and spaceships with revolving sections that mimic gravity.

In the absence of a StarTrek-like artificial gravity (how would that work anyway?) has a ship or station with revolving habitat rings ever been proposed?

I imagine there must be serious engineering or physical problems associated with navigating a ship with part of it turning all the time.

Just interested. Air and water recycling has improved over the years and fusion power or light sails may come to the aid of propulsion. So doing away with the long-term effects of weightlessness would allow much longer and safer missions.

Steve

[88V8]

I imagine there must be serious engineering or physical problems associated with navigating a ship with part of it turning all the time.

Would it have inertia, like a bicycle wheel? Over and above the inertia it has anyway. That would make it harder to manouevre.

V8

[JohnB]

The space is full of paper studies, all these ideas have been studied to death. The nearest to implementation is having the habitation module one end of a cable, a counterweight the other, and you'd need that most for Mars missions where you don't want a weakened crew leaping onto the surface.

The most important property of a space station is its micro-gravity, and understanding its effect on people, it seems we can get people to live in it for years, a Russian is coming up to his cumulative 3rd year in space. Having a rotating section for crew comfort is likely to send vibration into the stationary section.

Scale is important, you have to rotate quite slowly to avoid coriolis effects which are disorientating, so you need a big habitat, bigger than is currently being planned (unless you are one of the mad space hotel people)

[ReformedCharacter]

Scott Manley 'Can The Human Body Handle Rotating Artificial Gravity?'

https://www.youtube.com/watch?v=nxeMoaxUpWk

At 10.38 an interesting clip of a Soviet cosmonaut throwing a dart in a rotating facility which follows a curved trajectory due to the Coriolis force.

RC

[ReformedCharacter]

NASA experimented with artificial gravity in 1966 by tethering an Agena vehicle with Gemini XI, it wasn't entirely successful but did manage to generate about 0.00015 g:

https://www.nasa.gov/image-article/sept-14-1966-gemini-xi-artificial-gravity-experiment/

RC

[GoSeigen]

Scott Manley 'Can The Human Body Handle Rotating Artificial Gravity?'

https://www.youtube.com/watch?v=nxeMoaxUpWk

At 10.38 an interesting clip of a Soviet cosmonaut throwing a dart in a rotating facility which follows a curved trajectory due to the Coriolis force.

RC

Coriolis force? I don't think so. The dart moves in a straight line as there is no force at all acting on it (ignoring gravity and air resistance). Everything else including the camera is accelerating (rotating) due to the centripetal forces and that is why the dart appears to move in a curve.

GS

[9873210]

Coriolis forces exist in a rotating frame of reference.

Converting between one frame and another is simple math, if you are able to do simple math correctly the results in the two frames are identical, there is no basis for saying one is real and the other is not.

Moreover, we live in a rotating frame, so rotating frames are both real and useful. Try giving your address in an inertial frame.

So many bad physics teachers. Next you'll be saying the pound is a unit of force.

[GoSeigen]

Who cares if Coriolis forces exist in some mathematically modelled frame of reference? Even if we accept them (as conventionally defined) they are not the cause of the arrow's apparent curved path in the video.



GS

[ReformedCharacter]

Who cares if Coriolis forces exist in some mathematically modelled frame of reference? Even if we accept them (as conventionally defined) they are not the cause of the arrow's apparent curved path in the video.
GS

Could you give a better explanation please? Scott Manley seems well informed and has a couple of degrees including one in physics, so I tend to believe he knows what he is talking about. Thanks.

RC

[GoSeigen]

Who cares if Coriolis forces exist in some mathematically modelled frame of reference? Even if we accept them (as conventionally defined) they are not the cause of the arrow's apparent curved path in the video.
GS

Could you give a better explanation please? Scott Manley seems well informed and has a couple of degrees including one in physics, so I tend to believe he knows what he is talking about. Thanks.

I think even well-informed people can be careless and overlook things if they're peripheral to their main focus. I know I often do this even in areas where I should know better.

Coriolis forces are a thing in mathematics but from my reading I have found them extraordinarily badly explained from a physics POV. This arrow is a classic example.

Objects only rotate because they have a roughly constant centripetal (centre-directed) force acting on them. For us on the earth that is gravity. For a child on a turning roundabout that is friction or tension or reaction force depending on how they are positioned on the roundabout.

Considering the arrow: before being released it is constrained in its circular motion by the hand which pulls it around along with the human. The moment it is released however, there is no longer a centripetal force acting upon it. How could there be? Sure enough the air is rotating but the force of the rotating air is tangential, not centripetal. So to my reasoning, from the moment the arrow is released it is no longer rotating, and thus the idea that a "Coriolis Force" (or the equivalent actual physical force) applies to it is nonsense.

Now I don't claim a fraction of the expertise of Scott Manley or some of the contributors here, so it would be no surprise if there is some gotcha lurking in this poor explanation...


GS

[XFool]

It's probably most unwise for me to comment here (but I never learn!) as in this instance I do not feel completely sure of my ground. However...

I think even well-informed people can be careless and overlook things if they're peripheral to their main focus. I know I often do this even in areas where I should know better.

Quite so.

I forces are a thing in mathematics but from my reading I have found them extraordinarily badly explained from a physics POV. This arrow is a classic example.

Objects only rotate because they have a roughly constant centripetal (centre-directed) force acting on them. For us on the earth that is gravity. For a child on a turning roundabout that is friction or tension or reaction force depending on how they are positioned on the roundabout.

Considering the arrow: before being released it is constrained in its circular motion by the hand which pulls it around along with the human. The moment it is released however, there is no longer a centripetal force acting upon it. How could there be? Sure enough the air is rotating but the force of the rotating air is tangential, not centripetal. So to my reasoning, from the moment the arrow is released it is no longer rotating, and thus the idea that a "Coriolis Force" (or the equivalent actual physical force) applies to it is nonsense.

Now I don't claim a fraction of the expertise of Scott Manley or some of the contributors here, so it would be no surprise if there is some gotcha lurking in this poor explanation...

I have a feeling there may well be.

"The moment it is released however, there is no longer a centripetal force acting upon it. How could there be? Sure enough the air is rotating but the force of the rotating air is tangential, not centripetal. So to my reasoning, from the moment the arrow is released it is no longer rotating"

Surely this cannot be true because of inertia? (That "mass" thing again...) If it is in a rotating frame it is in a rotating frame, whether moving through the air, or stationary. If I drop something while on board an aircraft in flight it simply falls straight to the floor of the aircraft (from my pov), it doesn't head to the rear at 600mph because it is no longer being pushed along by the aircraft. In physics, you have to get the frame of reference pinned down. Things can be seen differently inside or outside a particular FoR.

What does happen is that a 'stationary' object let go of in a rotating frame will drop to the floor (or wall, or ceiling) due to the 'pseudo force' acting on it similar to gravity. In a rotating frame this is an inertial force - also called a 'fictitious' force. But the effects are real enough.

https://en.wikipedia.org/wiki/Coriolis_force

But what do I know?

[XFool]

It's probably most unwise for me to comment here (but I never learn!) as in this instance I do not feel completely sure of my ground. However...

I forces are a thing in mathematics but from my reading I have found them extraordinarily badly explained from a physics POV. This arrow is a classic example.

Objects only rotate because they have a roughly constant centripetal (centre-directed) force acting on them. For us on the earth that is gravity. For a child on a turning roundabout that is friction or tension or reaction force depending on how they are positioned on the roundabout.

Considering the arrow: before being released it is constrained in its circular motion by the hand which pulls it around along with the human. The moment it is released however, there is no longer a centripetal force acting upon it. How could there be? Sure enough the air is rotating but the force of the rotating air is tangential, not centripetal. So to my reasoning, from the moment the arrow is released it is no longer rotating, and thus the idea that a "Coriolis Force" (or the equivalent actual physical force) applies to it is nonsense.

Now I don't claim a fraction of the expertise of Scott Manley or some of the contributors here, so it would be no surprise if there is some gotcha lurking in this poor explanation...

I have a feeling there may well be.

"The moment it is released however, there is no longer a centripetal force acting upon it. How could there be? Sure enough the air is rotating but the force of the rotating air is tangential, not centripetal. So to my reasoning, from the moment the arrow is released it is no longer rotating"

Surely this cannot be true because of inertia? (That "mass" thing again...) If it is in a rotating frame it is in a rotating frame, whether moving through the air, or stationary. If I drop something while on board an aircraft in flight it simply falls straight to the floor of the aircraft (from my pov), it doesn't head to the rear at 600mph because it is no longer being pushed along by the aircraft. In physics, you have to get the frame of reference pinned down. Things can be seen differently inside or outside a particular FoR.

What does happen is that a 'stationary' object let go of in a rotating frame will drop to the floor (or wall, or ceiling) due to the 'pseudo force' acting on it similar to gravity. In a rotating frame this is an inertial force - also called a 'fictitious' force. But the effects are real enough.

Actually...

Thinking about this, you have a point. It no longer has a force acting on it to keep it moving in a circle (accelerating) - seen from outside the rotating frame, so it stops doing so. Which is why it now sinks to the floor (ceiling, wall) - seen from inside the rotating frame.

[GoSeigen]

It's probably most unwise for me to comment here (but I never learn!) as in this instance I do not feel completely sure of my ground. However...

Thinking about this, you have a point. It no longer has a force acting on it to keep it moving in a circle (accelerating) - seen from outside the rotating frame, so it stops doing so. Which is why it now sinks to the floor (ceiling, wall) - seen from inside the rotating frame.

Indeed, without any force acting on it (ignoring gravity which is well understood, and air resistance which is negleigible) if flies straight -- straight as an arrow in fact. It is the camera (and other surrounding stuff) which is moving in a curved path.


GS

[XFool]

Thinking about this, you have a point. It no longer has a force acting on it to keep it moving in a circle (accelerating) - seen from outside the rotating frame, so it stops doing so. Which is why it now sinks to the floor (ceiling, wall) - seen from inside the rotating frame.

Indeed, without any force acting on it (ignoring gravity which is well understood, and air resistance which is negleigible) if flies straight -- straight as an arrow in fact. It is the camera (and other surrounding stuff) which is moving in a curved path.

So the Coriolis force would be experience by a moving object ON a moving frame rather than IN a moving frame - as in surrounded by - to which it was not bound?

But, inside the moving frame it would appear that the object was curving and so seem to be acted on by a force. Um... I wonder, would the maths be the same in both cases? Could one tell one from the other?

[9873210]

As I have previously stated the results in an inertial frame of reference with inertial physics and a rotating frame of reference with Coriolis and centrifugal forces are the same. When two things are mathematically equivalent saying "one is real and the other is not" places a lot of work on the word "real".

There is long, dishonourable history of people saying things like zero, negative numbers, imaginary numbers, calculus, Fourier transforms, centrifugal force etc. are not real but some sort of mathematical artifice practiced by witches. You get long convoluted expositions that taking an hour (or a book) to do a 1 minute (or one page) calculation.

Look at the calculations that are needed when you look at how objects in the rotating space station interact.

If you do the calculations in the inertial frame you end up subtracting large, almost equal, numbers to get a small result. This requires high precision and actual arithmetic. Subtracting almost equal numbers is also something you should have been taught to avoid in intro to numerical analysis.

If you do things in the rotating frame the calculations involve small numbers with smaller corrections for the additional forces. If you are doing the arithmetic, you need far less precision. These calculations are also more amenable to rules-of-thumb and similar shortcuts. If you're learning to play tennis in a rotating space station it will be far easier to learn the ball falls to the floor and curves a little to anti-spinward than to try to think it through in the inertial frame.

[GoSeigen]

But, inside the moving frame it would appear that the object was curving and so seem to be acted on by a force. Um... I wonder, would the maths be the same in both cases? Could one tell one from the other?

I don't know to be honest. Reason being I can't really be bothered with the so-called Coriolis Force when it comes to the physics.

The effect is simple enough: we are talking about a force tangentially on a body which is constrained in a rotating motion but nevertheless is moving -- for the sake of simplicity -- along a diameter towards the origin. Think a child's electric toy car driving along the floor towards the centre of the rotating room. The tangential speed of the car is getting smaller (because the tangential speed increases the further you move from the centre), therefore it's clear the car is accelerating in a tangential direction as it moves towards the centre.

To make it easier to figure out imagine a pair of conveyor belts side by side, one moving faster than the other. The slower one represents a position closer to the centre of rotation. If you jump from the faster belt onto the slower belt (moving towards the centre) you experience a force when you land which decelerates you to the speed of the slower belt (or sends you flying if you are not prepared for it!)

That's what is happening with the car, but in a continuous fashion, rather than in discrete jumps. So what exactly is the force that decelerates the car in the tangential direction? It must be its wheels' friction with the floor [with incidentally also provides the perpendicular centripetal force taking the car in a circle].

With the released arrow the situation is different because there is neither a centripetal force, nor a tangential one (well there is air resistance because the air is rotating but I'm assuming that force is much smaller than any "Coriolis force" would be, and negligible for our purposes). So the arrow moves in a straight line -- not parallel with its shaft mind, because it also has a tangential speed due to the rotation as viewed from a stationary frame.

So personally I can't see any Coriolis force here on the arrow. I also don't see the point of having this fictitious Coriolis force except in an abstract mathematical discussion. Similarly I find the notion of a "centrifugal force" bizarre. Yes, maybe that's what the maths looks like in a rotating frame but how is that concept of any use in real life? The actual forces involved are no different to those experienced by a body in rectilinear motion and they are in the centripetal direction, not centrifugal. So why would I want to inhabit an imaginary world, for the particular case of rotation, where everything is back to front and forces are fictitious? It seems equivalent to imagining the Earth is the centre of the universe, which mathematically would also work, but is a mess. Yet as SD hints, this way of thinking seems rather popular over the pond...


GS

[csearle]

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The whole Pound Force sub-discussion moved here - Chris