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russ_watters
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Could you quote the passage in the wiki that says putting an object at a Lagrange point will make it spin?thedeester1 said:I got this off of Wikki...
Could you quote the passage in the wiki that says putting an object at a Lagrange point will make it spin?thedeester1 said:I got this off of Wikki...
thedeester1 said:I got this off of Wikki...not the most reliable source I know...But its kinda what i was getting at...Im not a student of astro physics its kinda a hobby for a geek.
http://en.wikipedia.org/wiki/Lagrangian_point
other neutral gravity points must exist between all mass in the solar system and the universe...otherwise fast colapse would be occurring NOW.
russ_watters said:Could you quote the passage in the wiki that says putting an object at a Lagrange point will make it spin?
thedeester1 said:no i cant...sorry...But i think that it will spin. this is my thinking as a novice.. You could try it out place 2 metal ojects on a table then rotate the outer object. given our gravity your going to have to spin the object very quickly.. In space however i don't think that's the case. The passing centrifugal force will spin the said space station...i think
thedeester1 said:no i cant...sorry...But i think that it will spin. this is my thinking as a novice.. You could try it out place 2 metal ojects on a table then rotate the outer object. given our gravity your going to have to spin the object very quickly.. In space however i don't think that's the case. The passing centrifugal force will spin the said space station...i think
tggokulesh said:you are wrong . it is easy to create an artificial gravity.this is what einstein's(actually its mach's) equivalence principle states.if you accelerate upwards it would produce a natural gravity which is induced.to know more read general relativity basics
nismaratwork said:Really? Can you cite a single reference to support that?
dkotschessaa said:Does the inverse square law apply to the the forces created in this way (acceleration or rotation?)
-DaveKA
DaveC426913 said:Well, he's simply saying a ship under constant acceleration (say, 1g) will give its occupants the same effect as gravity. And he's quite right.
Problem is:
1] It's a huge fuel cost, accelerating all the way.
2] The occupants would go floating away every time the ship wanted to stop.
nismaratwork said:Yes, but that's not gravity, but a totally different pseudo-force.
What makes you think this??nismaratwork said:Even if you have massive amounts of fuel and don't want to stop, you eventually start getting close to c, and are no longer able to sustain 1g.
Not totally different; according to the equivalence principle, in a small enough region there's virtually no difference.nismaratwork said:Yes, but that's not gravity, but a totally different pseudo-force.
nismaratwork said:Even if you have massive amounts of fuel and don't want to stop, you eventually start getting close to c, and are no longer able to sustain 1g.
DrGreg said:In relativity, acceleration is relative too. Although all inertial observers agree whether an object is accelerating or not, they disagree over the value of a non-zero acceleration. An inertial observer who is momentarily at rest relative to an accelerating object ("comoving inertial observer") will measure a larger acceleration than observers who have non-zero relative velocity, and the acceleration tends to zero as the relative velocity approaches the speed of light.
The acceleration measured by a comoving inertial observer is called "proper acceleration". It the "g-force" that the object experiences and what is measured by an accelerometer attached to the object.
DrGreg said:If your rocket was accelerating with a constant proper acceleration of 1 g, the acceleration measured by an inertial observer would gradually decrease to zero. So you can continue at 1 g as long as you like, fuel permitting.
DaveC426913 said:In the case of accelerative AG, you will experience the acceleration of the deck toward you, but it will be independent of your distance from the deck.
DaveC426913 said:Granted he then says that "...it would produce a natural gravity..." but I think he's means natural-feeling gravity - as in "indistinguishable from real gravity", which is true (contrarily, rotational AG is experientially quite unlike real gravity.)
DrGreg said:Actually if you were supported at a constant height of h above the deck, you'd experience a proper acceleration of
[tex]a = \frac{g}{1 + \frac{gh}{c^2}}[/tex]
so it's not an inverse square law, just an inverse law.
(This is a consequence of Rindler coordinates.)
cjameshuff said:That may give the wrong impression. It's really no different from the linear case, except for the addition of Coriolis forces and variations in acceleration at different heights. As the radius of rotation increases, these effects become weaker and weaker. Give a constantly-accelerating spacecraft a bit of constant rotation around an axis perpendicular to that of thrust, and it will travel a circular path and give exactly the same appearance of gravity as it would if it were swinging from a tether.
DaveC426913 said:Well, I can show some other rather pronounced differences with rotational AG. Notably, if you could quite easily, through only your own actions, cancel it entirely. Ignoring air friction, you could hover weightless above the surface indefinitely.
cjameshuff said:With the capsule-and-tether approach it's just impossible, you'd splat against the wall. In a fully enclosed 224 meter radius 2 rpm habitat, you would somehow have to change your speed by 47 m/s...that is, about 105 mph or 170 kph. I would not describe this as something a human could easily do through only their own actions...not actions they could reasonably expect to survive, anyway.
DaveC426913 said:Well, that's true if you put constraints on it. You're limiting my freedom to demonstrate how gravity works. If the station were toroidal, I could accelerate antispinward to the point where I could become weightless, at least until air friction spun me up again. If I could do this without having to worry about friction, I could float weightless indefinitely, or at least until a I encountered the first wall to antispinward.
DaveC426913 said:No.
In the case of rotational AG, you won't experience it unless you are in contact with the deck.
In the case of accelerative AG, you will experience the acceleration of the deck toward you, but it will be independent of your distance from the deck.
dkotschessaa said:That's kind of what I thought. Thanks for clarifying. So such gravity isn't really quite "natural."
-DaveKA
DaveC426913 said:Well, that's true if you put constraints on it. You're limiting my freedom to demonstrate how gravity works. If the station were toroidal, I could accelerate antispinward to the point where I could become weightless, at least until air friction spun me up again. If I could do this without having to worry about friction, I could float weightless indefinitely, or at least until a I encountered the first wall to antispinward.
Note that there are several ways of doing this. Another one is simply going up to the space station's attic - quite easy do to through only one's own actions.cjameshuff said:You put constraints on it, by saying "Notably, if you could quite easily, through only your own actions, cancel it entirely.
cjameshuff said:Ignoring air friction, you could hover weightless above the surface indefinitely.". Humans can generally not accelerate themselves to more than a small fraction of the needed velocity in a minimum-sized structure (based on what's needed to achieve 1 g with a comfortable rotation rate). If you were in such a habitat, the most you could do is slightly reduce the apparent gravity.
cjameshuff said:Apart from the added tidal effects on the part of planets and Coriolis effects on the part of rotating structures, the constant upward acceleration exerted by a planet's surface on objects resting on it is indistinguishable from the constant acceleration in one direction of the spaceship or the constant acceleration toward a point of the rotating structure.
DaveC426913 said:Note that there are several ways of doing this. Another one is simply going up to the space station's attic - quite easy do to through only one's own actions.
DaveC426913 said:It comes down to a subjective call as what one considers "similar" to real gravity. I see these things as quite different (possibly alarmingly so, people will surely get injured, or worse, until they get used to it); you do not see them is significant. Neither of us is wrong.
cjameshuff's first law:
If one ignores all the ways two things are different, then those two things are indistinguishable.
I cannot escape that ironclad logic.
I don't know why you insist on dimissing these differences.cjameshuff said:And if you climb a giant space elevator on a planet, gravity drops off as you rise. And if you jump off an accelerating spacecraft , you get left behind in freefall. Neither of these actions affects the fact that the appearance of gravity itself is identical.
No...to be blunt, you are wrong. It is not subjective. The only difference between "centrifugal gravity" and "linear acceleration gravity" is the addition of Coriolis effects. These are not responsible in any way for the impression of gravity, they are simply an artifact of the rotating frame. The impression of gravity is caused in exactly the same way in both cases, and the equivalence of that effect with the effect experienced on the surface of a planet is a rather fundamental principle of relativity.
Coriolis effects and tidal forces are not differences in the nature of the acceleration, they are additional effects that are independent of the acceleration itself...the one resulting simply from being in a rotating reference frame, the other from being in a gravitational field from a spherical body. Both can be experienced in freefall, and both can be made arbitrarily small without affecting the apparent gravitational force, the one by decreasing the rate of rotation (approaching a straight-line acceleration as the radius of rotation approaches infinity), the other by decreasing the density of the sphere.
Yaridovich said:In order to create artificial gravity you would need to have the space station constantly accelerating in one direction so that the people inside would experience a force equal to the rate of acceleration times their body mass. This would create the illusion of weight. This is impractical because the station can't just keep accelerating; it would run out of fuel at some point. Utilizing centripetal acceleration could work, but the space station would need to be orbiting very quickly for any significant effects.
Chronos said:Get a good book on GR, a comfortable bed, and read cjames. You are clueless.
DaveC426913 said:I don't know why you insist on dimissing these differences.
DaveC426913 said:Let me try to reframe it. I think your argument is that, physics-wise, the forces in play are equivalent. If you look at a small enough subset of effects, then that subset is the same in all versions of gravity. (I've captured this, rather facetiously but accurately in cjamehuff's First Law.)
DaveC426913 said:I grant the equivalence principle. But the EP applies academically - in a lab (where you isolate it).
DaveC426913 said:But from a human point of view (which is what we've been talking about), the difference, whether you wish to dismiss them or not, are quite noticeable.
Massive gravity
- has a gradient, lessens as square of distance (not noticeable on any reasonable human scale)
Accelerative artificial gravity
- no gradient (on a hundred mile long ship, g is the same at all points ,also very small effect)
- g-force experiences are intimately tied to ship's motion
Rotational artificial gravity
- pronounced Coriolis forces
--- falling, jumping or any other ballistic motion imparts sideways motion
--- moving spinward increases weight, antispinward deceases weight, to the point of weightlessness
- AG is markedly different on different decks, some decks have micro-g, some have zero-g
Chronos said:Get a good book on GR, a comfortable bed, and read cjames. You are clueless.
cjameshuff said:I don't know why you insist on focusing on extraneous effects, and not just ignoring but outright denying the fact that the resulting appearance of gravity is identical.
Stop this "First Law" nonsense. It's insulting and it reveals that you aren't paying attention to what I'm saying.
Nothing but anti-intellectual nonsense. It applies to everything, everywhere.
You for some reason seem to refuse to consider anything but small radius, high rotation systems. Coriolis effects diminish to nonexistence as rotation rate diminishes to zero...you can not say they are pronounced, only that they exist in rotating frames. They even exist on rotating planets. A space station with a rotation rate of one day, and Coriolis effects no stronger than those you're experiencing right now is entirely physically plausible.
On a structure with a radius of rotation large enough to have a comfortably low rotation rate, a human being simply can not move themselves fast enough to influence the apparent gravity to a notable degree. In human terms, gravity is constant. You make it sound like you'll go careening through the sky if you run in the wrong direction...this is simply false. As for climbing toward the center, if you can insist on decks at all levels of gravity in a rotating structure, I can insist on a giant tower with microgravity at the uppermost levels, or a tunnel to the center of the planet. It's irrelevant.
Once again, take your accelerating spacecraft . Give it a slight rotation perpendicular to the direction of thrust...say once every 24 hours. Your spacecraft is now traveling a circular path, but without special equipment, the occupants have no way of telling that this is the case. Cut the engines...is the rotation the cause of the apparent gravity? The occupants now rattling around in microgravity would not agree with you. Attach it to a counterweight by a long tether so it travels the same circular path it did before...the occupants wouldn't be able to tell the difference. In human terms, no matter how they jump, run, or climb, they wouldn't be able to tell they weren't accelerating in a straight line or resting on a planet's surface. Even with special equipment, they would have to measure other effects associated with rotating frames or gravity wells to determine their situation.
I think you got my posts mixed up with DaveC426913's.
nismaratwork said:re: bold: This is you... http://en.wikipedia.org/wiki/Illusory_superiority
cjameshuff, you're so far from reality I can't tell if you're ignorant of GR as Chronos posits. or a crackpot.
Your application of the EP in this distorted way is just wrong... I don't know another way to put it... you're wrong and if you'd read that book Chronos mentioned you'd know it.
cjameshuff said:A couple people do seem to be suffering from illusory superiority. That you apparently don't even realize that I've barely even mentioned the equivalence principle of GR says something about who that might be. My explanations regarding centrifugal and linear acceleration, which seem to be the main source of DaveC426913's confusion, don't even require any reference to GR to understand. The equivalence principle of GR is more general, equating such accelerating frames with the frame of an object resting on a planetary surface, or otherwise "stationary" with respect to a gravitational field.
Here's another Wikipedia link: http://en.wikipedia.org/wiki/Equivalence_principle
Read it. And perhaps a good book on physics, too. And make sure your criticisms are on target in the future. Maybe give something resembling a counterargument, rather than a blanket "you're wrong!"?
Actually, we have given multiple, carefully-crafted counter arguments. Whether you agree with them or not, to claim we have just said a blanket "you're wrong" is not helping your case.cjameshuff said:Here's another Wikipedia link: http://en.wikipedia.org/wiki/Equivalence_principle
..
Maybe give something resembling a counterargument, rather than a blanket "you're wrong!"?
This is key."local" has a very special meaning: not only must the experiment not look outside the laboratory, but it must also be small compared to variations in the gravitational field, tidal forces, so that the entire laboratory is freely falling.
You have contradicted yourself.cjameshuff said:I don't know why you insist on focusing on extraneous effects, and not just ignoring but outright denying the fact that the resulting appearance of gravity is identical.