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adamskiiix
2010-Jun-22, 08:31 PM
What do you really think people, is artificial gravity really madman's dream? Im a little bit of a sci-fi freak..Star Trek, Battlestar Galactica and the list goes on.. all those starships are equipped with some kind of artificial gravity systems..

And now comes the serious question.Thats what i generally understood,correct me if im wrong: Any object interacts gravitationally with another. Gravity increases with mass. Accelerating object gets heavier.Heavy means larger gravity?

How much would you have to accelerate object, lets say the size of the school bus to create 1g on its surface? Does that make any sense at all?:think:





Second stage of my question: if you place object (dunno about the mass or size) underneath the spaceship and accelerate it magnetically in the loop could that be way to create some kind of gravity?

Dont laugh!
Cheers
adamskiiix

Paul Beardsley
2010-Jun-22, 09:08 PM
If you could accelerate your spaceship (regardless of size) at 9.81 metres* per second per second, then you would experience 1g.

TV Sci-Fi gravity is not based on real science, except for Babylon 5 (which is caused by the space station's spin), and some episodes of The Outer Limits (in which it's caused by acceleration). Generally, gravity exists on spaceships simply because the production team have forgotten that there would be no gravity, or because it's too expensive to do weightlessness so they hope the viewers have forgotten, which they usually have.

*meters in the US

adamskiiix
2010-Jun-22, 09:17 PM
If you could accelerate your spaceship (regardless of size) at 9.81 metres* per second per second, then you would experience 1g.

TV Sci-Fi gravity is not based on real science, except for Babylon 5 (which is caused by the space station's spin), and some episodes of The Outer Limits (in which it's caused by acceleration). Generally, gravity exists on spaceships simply because the production team have forgotten that there would be no gravity, or because it's too expensive to do weightlessness so they hope the viewers have forgotten, which they usually have.

*meters in the US


i know that thing you mentioned about acceleration and i very well know that many ideas of science fiction movies are totally out of the hat but im only wondering whether there is logic in what i thought of and mentioned above;]

ShinAce
2010-Jun-22, 09:20 PM
What do you really think people, is artificial gravity really madman's dream? Im a little bit of a sci-fi freak..Star Trek, Battlestar Galactica and the list goes on.. all those starships are equipped with some kind of artificial gravity systems..

And now comes the serious question.Thats what i generally understood,correct me if im wrong: Any object interacts gravitationally with another. Gravity increases with mass. Accelerating object gets heavier.Heavy means larger gravity?

How much would you have to accelerate object, lets say the size of the school bus to create 1g on its surface? Does that make any sense at all?:think:



Second stage of my question: if you place object (dunno about the mass or size) underneath the spaceship and accelerate it magnetically in the loop could that be way to create some kind of gravity?

Dont laugh!
Cheers
adamskiiix

The occupants of the school bus will never feel a 'surface gravity'. They will always measure their weight as the same, no matter what the stars appear to be doing.

If you accelerate something in a loop below you, where did you get the energy to accelerate it? That energy would have gravity. So you're converting one form of gravity, like a charged battery, into a another form, a spinning mass.

Jens
2010-Jun-23, 03:55 AM
How much would you have to accelerate object, lets say the size of the school bus to create 1g on its surface? Does that make any sense at all?:think:

It's a good question, but the answer is unquestionably, you cannot do that. It may be difficult to explain, but the main point is this. If a spaceship accelerates to close the speed of light, it will appear to have gained mass from the perspective of an observer on the planet where it launched from, but from the viewpoint of those on the spaceship, the mass will be precisely the same. If you are in the starship, you will not notice any change at all, either in the clocks or in the mass or in the length contraction. Everything will appear exactly the way it was before.



Second stage of my question: if you place object (dunno about the mass or size) underneath the spaceship and accelerate it magnetically in the loop could that be way to create some kind of gravity?


The second one is an interesting question. The answer is, I don't know, but it's certainly an interesting idea.

WayneFrancis
2010-Jun-23, 04:18 AM
Artificial gravity is a bit fact bit fantasy topic. By rotating something you can cause a force like gravity due to a centrifugal force. You could also just constantly accelerate in the opposite direction of the desired gravity at 9.8m/s/s as stated but that isn't very practical from an energy point of view.

Use of any object "under" your ship to simulate gravity would in essence be gravity then you have to account for the energy to move said mass. So if you wanted Earth like gravity you'd need an Earth like object in the form of M1M2G/r2

So you could reduce the mass and bring the object closer but its still a big ask to get a good amount of mass under you and then actually accelerate that mass and note the Earth already has a pretty high mass.

There could be some type of exotic matter you could use but I'm afraid that you'd probably have the same issues with accelerating that mass along with your ship.

EDG
2010-Jun-23, 04:26 AM
In my SF settings I tend to define artificial gravity as a pseudoforce - applying only to things on the surface generating the artificial gravity - like the "gravity" generated by centripetal acceleration (of course I have no idea how it'd be generated, I just wave my arms around and say stuff like "superdense elements rapidly rotating in a magnetic field" :) ) - thus, it'd be contained entirely within the ship. It always bugged me that otherwise (a) you'd have a 1g field generated on every single deck of the ship (which struck me as needlessly repetetive and horribly cumulative) and (b) if the ship actually had a 1g gravitational field that fell off with the square of the distance from the ship, then that'd really screw around with the orbits of nearby astronomical objects.

Hungry4info
2010-Jun-23, 04:57 AM
Anyone thought of magnetic boots with tight elastic straps running from those boots to your shoulders? =P

WayneFrancis
2010-Jun-23, 07:06 AM
while this might work some what for moving around on a ship it doesn't help over all...glasses of water are still not feasible

Noclevername
2010-Jun-24, 03:21 AM
The trouble with the rotating-mass "gravity generator" is three things-- one, it would use almost as much energy as accelerating the spaceship, AFAIK. Two, it would produce gravity from a central point, not a "gravity carpet" in the deck. Three, normal matter rotated at near-light speed would tear itself apart-- taking out everything around it, like your ship, for example. The forces needed to hold it together are more sci-fi than artificial gravity. Just call it "a gravity-like pulling force not discovered in the early 21st century" and handwave it, don't go into detail about the mechanism, just the result... it makes more sense to make up your own physics than to mangle existing physics. :whistle:

Jens
2010-Jun-24, 03:45 AM
Just call it "a gravity-like pulling force not discovered in the early 21st century" and handwave it, don't go into detail about the mechanism, just the result... it makes more sense to make up your own physics than to mangle existing physics. :whistle:

I got the impression that the OP meant this as a serious question, i.e. whether this is feasible, not as something for a story. I think the OP was saying he/she is an SF fan, and wonders whether this could be doable in reality.

EDG
2010-Jun-24, 04:43 AM
I got the impression that the OP meant this as a serious question, i.e. whether this is feasible, not as something for a story. I think the OP was saying he/she is an SF fan, and wonders whether this could be doable in reality.

It might become possible in the future, but we just don't know how right now. Or it might never be possible - again, we don't know. With our current knowledge and technology, we can create a force that is like gravity, but that requires a specific configuration or set of circumstances (a rotating wheel/cylinder, or linear acceleration). The only method we know right now for how to create real gravity is to add mass to an object.

WayneFrancis
2010-Jun-24, 06:50 AM
It might become possible in the future, but we just don't know how right now. Or it might never be possible - again, we don't know. With our current knowledge and technology, we can create a force that is like gravity, but that requires a specific configuration or set of circumstances (a rotating wheel/cylinder, or linear acceleration). The only method we know right now for how to create real gravity is to add mass to an object.

I think that is the key point. If our understanding of physics is all wrong then anything is possible but as it stands there isn't even anything on our scopes to do it.

Noclevername
2010-Jun-25, 05:15 PM
I got the impression that the OP meant this as a serious question, i.e. whether this is feasible, not as something for a story. I think the OP was saying he/she is an SF fan, and wonders whether this could be doable in reality.

Given what we currently know of physics, no.

Bearded One
2010-Jun-25, 11:58 PM
(b) if the ship actually had a 1g gravitational field that fell off with the square of the distance from the ship, then that'd really screw around with the orbits of nearby astronomical objects.That's the part of artificial gravity that always makes me scratch my head. Strange how it always seems to stop at the outer hull of the ship in SciFi. :think:

EDG
2010-Jun-26, 01:38 AM
That's the part of artificial gravity that always makes me scratch my head. Strange how it always seems to stop at the outer hull of the ship in SciFi. :think:

That's the beauty of calling it a pseudo-force instead. It's like the "gravity" generated by a spinning space station - it's only there for things inside the station, not outside it :).

dgavin
2010-Jun-26, 02:32 AM
There has been some success scientifically in generating gravitomagnetic fields in some experiments in the UK. While the gravitomagnetic effect was stonger then expected, this has yet have been repeated in experiments since. So while artifical gravity might be possible via gravitomagnetic effects, it's still a long ways off.

eburacum45
2010-Jun-27, 06:38 AM
Since gravity is a distortion in spacetime, you can't just fill a spaceship with it like you can with an atmosphere. A gravity generator under the deck of a multideck spaceship would also create an upside-down gravity field on the ceiling of the deck below; so if the decks were ten feet apart, your feet would be strongly attracted to the floor, your chest region would be in free fall, and your head would be attracted to the floor above.

Obviously that is not an ideal situation.

Basically an artificial gravity generator would create a three-dimensional distortion in space, and objects would be attracted towards that generator from all directions - both up and down, and inside and outside the ship. Switch the artificial gravity generator on and your ship would attract dust and other material from the vacuum of space.

Edg's 'pseudoforce' generator is intriguing- but it is basically a centripetal force generator, and that force is most easily generated by rotation.

EDG
2010-Jun-27, 07:18 AM
Edg's 'pseudoforce' generator is intriguing- but it is basically a centripetal force generator, and that force is most easily generated by rotation.

Well, the way I see it, it'd be like centripetal force, but not actually centripetal force - similar sort of idea, different (armwavy) mechanism. It wouldn't actually generate any distortion in spacetime, either way.

Van Rijn
2010-Jun-27, 07:59 AM
There has been some success scientifically in generating gravitomagnetic fields in some experiments in the UK. While the gravitomagnetic effect was stonger then expected, this has yet have been repeated in experiments since. So while artifical gravity might be possible via gravitomagnetic effects, it's still a long ways off.

The problem with normal matter is that you can't get enough acceleration for a person to notice. I remember the physicist Robert Forward speculated on what someone might manage by properly manipulating a ring of extremely dense material, like a ring of small black holes or alternately, "neutronium" (something with the density you find in a neutron star). You could possibly accelerate something through the center of the ring without it feeling the acceleration (though you'd have to engineer carefully for tidal forces), or if you had something to block passage, you might have something a little like a classical gravity generator. But, nobody knows how to make rings of super-dense material, and if it was possible, the mass of any such ring would be so great that it wouldn't make much sense to use it that way.

Forward also mentioned the idea of taking something like a large asteroid or small planet and squeezing it into a very dense plate. If it was dense enough, you could get a nice 1-g gravity on both the sides of the plate. Again, though, nobody knows how to make a super-dense stable plate like that, and it wouldn't be much use for a ship.

neilzero
2010-Jun-27, 02:07 PM
At present, we don't know why mass produces gravity. If we find out we may be able to make artificial gravity. Your plan won't work without major breakthroughs. You didn't tell us the shape or length of the loop. How about round, 45,000 kilometers long super-orbiting Earth at about 11 kilometers per second? If the ship is attached to the loop a small gravity, perhaps 2% of Earth's surface gravity will occur in the craft. Down will be away from Earth, very slightly cancelled by the mass of the ring. Obviously not what you had in mind. If the same ring is in solar orbit with nothing inside, then about 1.04g occurs if the ship is attached (down is away from the center) but not very useful until the ship is released from the ring after which we get zero gravity at a speed at about 11 kilometers per second (with respect to the ring) which is useful, if the direction is correct.
Near term we can connect two space craft with about one kilometer of tether, and spin them around each other so the more massive craft has 1/6 g and the less massive has 0.38 g. That would be useful to study moon and Mars gravity, and hopefully we will do this soon. Faster spin produces higher artificial gravity, but tether failure becomes likely with the best tethers presently available. Sudden tether failure could be a disaster for the occupants of both craft. Neil

cjameshuff
2010-Jun-27, 11:05 PM
The problem with normal matter is that you can't get enough acceleration for a person to notice. I remember the physicist Robert Forward speculated on what someone might manage by properly manipulating a ring of extremely dense material, like a ring of small black holes or alternately, "neutronium" (something with the density you find in a neutron star). You could possibly accelerate something through the center of the ring without it feeling the acceleration (though you'd have to engineer carefully for tidal forces), or if you had something to block passage, you might have something a little like a classical gravity generator. But, nobody knows how to make rings of super-dense material, and if it was possible, the mass of any such ring would be so great that it wouldn't make much sense to use it that way.

This sounds familiar. IIRC, it was essentially a frame dragging effect, but with toruses each rotating smoke-ring style, around the circular axis of the torus. You could drop a spacecraft through a string of such toruses to accelerate it while its occupants would only feel tidal forces. If a floor was built across the center of the ring, one side would appear to have gravity, while the other would have antigravity.

The requirements of mass, density, and rotation rate make this clearly implausible for real artificial gravity, but it's interesting as a demonstration that the basic effect is not physically impossible....merely uselessly weak at achievable scales.

eburacum45
2010-Jun-29, 08:23 AM
This sounds familiar. IIRC, it was essentially a frame dragging effect, but with toruses each rotating smoke-ring style, around the circular axis of the torus. You could drop a spacecraft through a string of such toruses to accelerate it while its occupants would only feel tidal forces.
We call these 'space time catapults' in OA; here's a nice picture of one by Anders Sandberg.

http://www.orionsarm.com/eg-article/461315d4dbf25

sabianq
2010-Jun-30, 01:17 AM
gravity pulling in one direction is equivalent to an acceleration in the opposite direction..

this means that gravity and acceleration are equivalent..

if this is true, the simply having a constant acceleration on your ship either by rotation of a ring with living quarters or making your spaceship constantly go faster and faster will give you the equivalent of gravity.

sabianq
2010-Jun-30, 01:39 AM
Gravity increases with mass. Accelerating object gets heavier.Heavy means larger gravity?


here is the thing,
mass is not the same thing as weight..
(i am suprised that nobody pointed this out earlier)

weight is how heavy something is due to the gravitational field or an acceleration of that something..

if i weigh 200 pounds and i am in a rocket ship and i am accelerating constantly in one direction at 1.5g, i will weigh 300 pounds, but my mass will still be the same.

mass is defined my volume times my density.. my mass does not change due to an acceleration or a gravity field only my weight will change.

if you want to know your mass, simply step on a typical balance found in a doctors office (where your weight is compared to a set of slidy weights on an amarature)

you can take this balance to the moon and it will still give you your correct "weight" as seen on earth, while a scale (like a bathroom scale that you step on) will show a difference in weight due to the gravitational difference between the moon and earth..

this means that a rotating mass regardless of how fast it is rotating (sans relativistic speeds) will always have the same mass regardless of how "heavy" it gets due to centrifigual forces . since the mass will always be the same, its local gravitational force will not change.

Jens
2010-Jun-30, 03:58 AM
if i weigh 200 pounds and i am in a rocket ship and i am accelerating constantly in one direction at 1.5g, i will weigh 300 pounds, but my mass will still be the same.


The reason nobody pointed that out is that it's actually talking about something different. The increase in mass the person was talking about is the increase in general relativity, which is a real increase (from an outside perspective). So it is a real increase in mass, not just weight.

mugaliens
2010-Jun-30, 06:06 AM
I am 100% (all) for finding a way to accelerate all objects at a distance, regardless of material, at a uniform rate, without having to carry a planet or small moon in one's pocket.

Theoretically, if you were to positively charge a person (or all objects, for that matter) on Deck 7, while the cieling was also positively charged and the floor was negatively charged, they'd be forced towards the floor. The people and objects could be mildly charged, with the insulated decking heavily charged.

The trick is to due this by using something other than electrostatics.