Artificial gravity, a random question.

[Zolgar]

((I hope this is the right forum for this question, it seems to best fit the answers I seek though))

 

We've all seen it in sci-fi movies, the space ship/station, or lunar base, people are walking around just as if they were on earth (because hey, they are). And it's never explained.

 

Well, I'm working on writing a sci-fi story set about 500 years from now. Taking place predominately on a space station and lunar colony. Without rambling too much, I'm trying to figure out ways that one could theoretically produce an artificial gravity.

 

The first one that comes to mind is the rotating space station. Would it actually work?

 

Beyond that, are there any theories for creating an artificial gravitational pull (or increases an exsisting one), that are more or less sound, presuming the technology were availible? Or is it something that is just outright impossible without cracking some matrix-esque code of reality?

 

This is likely only the first of other theoretic questions on technology I'll have. Because frankly, I arn't very smart, but I like my sci-fi to be ... atleast loosely based on science. :rolleyes:

[ronthepon]

The rotating spaceship works on the basis of the 'centrifugal force'. It's what allows you to swing a bucket without the water falling off even when it's moving upside down.

 

Check out about it.

[Zolgar]

The rotating spaceship works on the basis of the 'centrifugal force'. It's what allows you to swing a bucket without the water falling off even when it's moving upside down.

 

 

Yeah, I knew that that was the idea behind it.. I just wasn't sure if contrifugal force would work in weightlessness.

 

After all, here's an interesting thing for you. Fill a balloon with a proper mix of helium (or any other lighter than air gas) and air to make it weigh exactly nothing. It will now not sink or rise, but hover.

 

Place that inside a large spinning wheel (say a giant mouse wheel since we're not actually doing it), will the centrifugal force of the wheel suddenly make the balloon have weight and stick?

 

And if there is no gravity, then there is no weight, things just hover. (this is why if you are in a 0 gravity envirment, it's a very bad thing to be out of reach of any surface, because it's not easy to move yourself.)

 

That's my thought on the centrigifugal force idea of artificial gravity atleast. Hence me asking if it would work.

[CraigD]

… I'm trying to figure out ways that one could theoretically produce an artificial gravity.

 

The first one that comes to mind is the rotating space station. Would it actually work?

As Ron notes, in a word, yes.

 

It’s used routinely on earth to create gravity-like forces greater than the usual m*9.8 m/s/s, in centrifuges from a big, human-carrying one at NASA Ames to small lab centrifuges used to make fluid suspensions (like blood) separate quicker. There were plans to put a small, human-carrying one on the ISS, but they were canceled a couple of years ago.

 

It’s easy to work out the necessary size and angular speed of the centrifuge needed for a spaceship to generate Earth-normal artificial gravity. The basic formula is [math]a = \frac{v^2}r[/math], where a is 9.8 m/s/s, r is the radius of the centrifuge, and v is its speed. Substituting [math]v = 2 \Pi r h[/math], where h is rotational frequency and rearranging gives [math]h = \frac{ \sqr{\frac{a}r}}{2 \Pi}[/math]

 

So, for example, a 1-g centrifuge 10 meters in radius would have to rotate about once every 6 seconds.

Beyond that, are there any theories for creating an artificial gravitational pull (or increases an exsisting one), that are more or less sound, presuming the technology were availible?

Assuming a spaceflight technology with super-high energy density fuels (eg: antimatter), the obvious way to have comfortable, Earth-like conditions on a spaceship is to have its acceleration match that of Earth-surface gravity. There’s always the old standby of just moving a whole, comfortable planet, though obviously the engineering challenge of that is staggering. I’m unaware of any other approaches that don’t require some unanticipated breakthrough in fundamental physics.

 

There’s a lot of discussion of this and other useful scifi ideas in 6352, the hypography thread that launched a collaborative scifi story thread, 6441.

[CraigD]

Fill a balloon with a proper mix of helium (or any other lighter than air gas) and air to make it weigh exactly nothing. It will now not sink or rise, but hover.

 

Place that inside a large spinning wheel (say a giant mouse wheel since we're not actually doing it), will the centrifugal force of the wheel suddenly make the balloon have weight and stick?

No. Since the air and the helium and the balloon are all subject to the same acceleration, they all are subject to equally increased forces, so none is more or less strongly attracted to the outside of the giant mouse wheel.

 

If you’re really talking about a giant mouse wheel, which isn’t airtight, all sorts of strange things will happen, since the wheel will be swirling the air, moving the balloon, striking it, etc.

 

If you spin an airtight mouswheel really fast, you’ll separate the air into it’s component gases, the heavier nitrogen on the outside, causing the balloon to rise to somewhere near the center of the wheel.

[ronthepon]

Yeah, the balloon's weightlessness is different from the weightlessness that you'd associate with space.

 

For the balloon to float, you'll need air outside the balloon. Since you're not gonna make that air outside rotate with the wheel that easily, the balloon will be affected by air friction.

 

Suppose you try in a evacuated chamber, the balloon will fall down, because that air that imparted it the buoyant force is no longer there.

 

Now, *supposing* that air did not offer friction, and you tied the balloon with a string to the wall of the cylinder, the balloon would probably tend to move towards the edge of the wheel.

And if there is no gravity, then there is no weight, things just hover. (this is why if you are in a 0 gravity envirment, it's a very bad thing to be out of reach of any surface, because it's not easy to move yourself.)

Not nessecary though. If the zero G is in a gas, you can 'swim' through the gas.

[ldsoftwaresteve]

the space shuttle, in orbit, is (if standard theory is correct) attached to the earth by the earth's gravitational pull. Do objects in the space shuttle behave any differently than objects that were taken to the moon when we sent men there?

 

I'd think we'd see some kind of difference in the way weightless objects behaved in the two situations. Were there any noticeable differences? If there were, since being meticulous is the order of the day on those craft, I'd have expected to see something said about it.

 

Is anyone aware of anything along those lines?

[CraigD]

the space shuttle, in orbit, is (if standard theory is correct) attached to the earth by the earth's gravitational pull.

I think “attached” is a poor choice of words, better used in phrases like “the ball is attached to the stick with a string” and “the picture is attached to the wall with a nail”.

 

Objects in orbit, like the space shuttle, ones just passing by, like near-Earth objects, or ones sitting on its surface, like me, all experience a force due to our mass and the mass of the Earth. We also experience a force due to our mass and the mass of the Sun, the Moon, the planets, and even stars, planets, dust and debris in our and other galaxies, but near Earth, the Earth’s mass dominates. This is given almost exactly by the famous equation [math]F=\frac{M_1M_2}{d^2}[/math], where F is force, the Ms 2 objects masses, and d is the distance between the objects.

 

Unlike the shuttle or a NEO, the force I experience is almost exactly opposed by a force between me and the surface I’m sitting on, allowing me to be aware of it. If I hold my hand out and relax my muscles, it accelerates toward the Earth, while my butt and the rest of me doesn’t. I don’t have to do this, because I have a good set of musculoskeletal sensory nerves, a very nifty inner-ear, and other sense that tell me I’m being tugged (or rather, alert me when I’m not, as that usually means I’ve stepped off something, and falling, no longer experiencing any differences in force in my various body parts).

 

On the shuttle or a NEO, every part is experiencing almost exactly the same force, unopposed by any other force (unless the shuttle’s firing its thrusters, or something like that), a condition known as free fall. In the case of something in orbit, this “fall” follow a particular elliptical path around it – if not, the path’s a parabola or hyperbola. In any case, the path might intersect the atmosphere and/or surface, causing more complicated things to happen. It’s commonplace to call the free fall condition “zero gravity” or just “zero G”, but deceptive – objects haven’t stopped experiencing gravitational force, they’re just experiencing nearly the same acceleration from it as every nearby object, giving the appearance of the lack of gravity.

 

Free fall wreaks hell on a humans nifty sensory systems, which is why a fair number of astronauts, despite training and preparation, get “space sick” :esick:

Do objects in the space shuttle behave any differently than objects that were taken to the moon when we sent men there?

Yes. On the Moon, objects behaved much like the do on Earth – if you let go of one, it falls to the nearest surface, though, because the moon’s mass is less than the Earth’s, its acceleration is only about 1/6th what it would be on Earth. In the shuttle – or the Apollo spacecraft on its way to or in orbit around the Moon – if you let go of the same object, it doesn’t fall anywhere, but floats roughly where you let go of it.

 

You may note that sticklers for precision often use the term micro gravity in place of free fall or zero G. This is because, inside a spaceship in orbit, released objects don’t always quite stay put. If you release an object near the center of the shuttle, it will stay nearly still. If you release it close to the side of the ship pointing toward Earth, it will slowly fall toward that wall. If you release it close to the side pointing away from Earth, it will slowly fall toward that wall. This is because the rigid body of the shuttle tugs on its “down” side, causing it to move slightly slower than it normally would, and on its “up” side, causing it to move slightly faster than it normally would.

[ldsoftwaresteve]

Wow, that took some work. Thanks.

[ughaibu]

Does this mean that if the Earth stopped rotating we'd be crushed by gravity? If so, as the speed of the Earth's rotation is decreasing, might gravity have been contributive to the excessive size of various extinct animals?

[max4236]

There's an interesting experiment the European Space Agency has been exploring involving rotating superconductors which seems to be generate a small gravitational field. Here's the link: ESA - GSP - Towards a new test of general relativity?

 

Conceivably 500 years from now there might be a meta material multilayered mesh that takes advantage of this phenomenon using sprayed on nanotechnology to create artificial gravity plating. (Much like how we can create strong electromagnets now because of our understanding of Faraday's Law and the use of newly discovered rare earth element alloys in coil cores, or a plasma which can expand the magnetic field out like a gaint balloon)..

[CraigD]

Does this mean that if the Earth stopped rotating we'd be crushed by gravity?

No. If the Earth stopped rotating, we’d just weigh a bit more everywhere except at the poles, where we’d weigh the same.

 

Given how “mushy” any big, gravitationally-made-into-a-near-sphere object like earth is, suddenly stopping its rotation would be a big deal, likely producing earthquakes and volcanism like nothing in billions of years, though, barring some sort of incomprehensible super technology, anything that could suddenly stop the Earth’s rotation would almost certainly do far worse than this.

 

An interesting problem is to calculate how fast the Earth would have to rotate, assuming (unrealistically) that it would remain the same shape at any angular speed, for objects to be weightless at the equator. Left as an exercise to the reader, as I’ve written enough basic mechanics in this thread already, and don’t want to hog all the calculating. :shrug:

[infamous]

Does this mean that if the Earth stopped rotating we'd be crushed by gravity? If so, as the speed of the Earth's rotation is decreasing, might gravity have been contributive to the excessive size of various extinct animals?

Think about it ughaibu, if you were standing on the north pole, centrifugal force created by the rotation of the earth would be nonexistent. So no, we wouldn't be crushed if the earth stopped rotating..........................Infy

[Zolgar]

So all in all my answers are pretty much:

 

For ships/stations, maintaining a specific rotation speed. Or acceleration for ships.

 

Otherwise, theoretic technology in nanomachines. >.> YAY NANOMACHINES! They solve everything.

 

Thanks for all the information folks.

[Janus]

There's an interesting experiment the European Space Agency has been exploring involving rotating superconductors which seems to be generate a small gravitational field. Here's the link: ESA - GSP - Towards a new test of general relativity?

 

 

This experiment deals with a gravitomagnetic field, this is not the same thing as generating an gravitational field.

[InfiniteNow]

This experiment deals with a gravitomagnetic field, this is not the same thing as generating an gravitational field.

 

I read that, and wondered... what is the difference?

[Janus]

I read that, and wondered... what is the difference?

A gravitomagnetic field is to a gravitational field as a magnetic field is to an electric field.

 

The electric field is what is responsible for the Coulomb force ( the force that causes two electric charges to attract or repel.) The magnetic field causes the attraction and repulsion of magnetic poles.

 

If you put a charge into a magnetic field, the charge will not be attracted to or repeled by the magnetic field. This is not to say that a magnetic field can have no efect on a charge. If move the charge through the field, the field will exert a force perpendicular to the direction of movement.

 

In a like way, a gravitomagnetic field will not attract a mass like a gravitational field does. Like above it can effect it though; for instance, an object in freefall near a massive rotating object will begin to rotate itself.