Half a croissant, on a plate, with a sign in front of it saying '50c'
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Gravity pulling equally on all sides of a steel ring canceling each other out creating anti-gravity.
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To do this you would need to put a large ring (steel perhaps) around the moon, or other planet that was parallel to the underlying surface of the planet and several hundred feet above it. If it completely encircled the planet gravity would pull equaly on all sides of the ring making it hover in mid-air.Maybe if someone touched this ring the gravity from the other sides of the planet would effect them causing them to become weightless.
beretboy, Nov 08 2000

Lagrangian Points http://www-spof.gsf...cation/wlagran.html
[jutta, Nov 08 2000]

Dyson Sphere http://www.nada.kth.se/~asa/dysonFAQ.html
[MaxMad, Oct 04 2004]

Earth-Space Web Earth-Space_20Web
As mentioned in an annotation I wrote a long time ago, but somehow didn't think to post a link to it here. [Vernon, Jun 09 2006]


       [sp: equally, affect]   

       The moon is usually not considered a planet, since it doesn't orbit a star.   

       Gravity is not transmitted by touch.   

       In theory, the ring could be made to float, but I don't understand how this is of use to people other than as something weird to look at.   

       The closest concept to what I can make of this that actually makes sense to me is called a "Lagrangian Point" (or "Lagrange Point") - a point (there are five, labelled L1..L5) where gravity from the sun and earth cancel each other out. No rings involved, though.
jutta, Nov 09 2000

       It's true that a solid ring completely encircling a planet would be pulled equally in all directions, and (assuming it were strong enough) remain in place. To an observer on the planet's surface, the ring would indeed appear to be "floating". Unfortunately, the moment the ring got even slightly out of "balance" (and it would always be at least a tiny bit out of balance), the side nearer the planet would be attracted more than the side further from the planet, and the ring would very quickly crash.   

       On the bright side, as long as you don't let it get too far out of alignment, the force needed to keep it aligned is relatively minor. Niven's Ringworld (which circled a star) had ramjets for the purpose.   

       Practical problems abound, however. First of all, planets are not perfectly flat (there are generally mountains and craters and stuff), so you'd have to do something about that. More importantly, this thing would have to be very, very strong, and therefore very, very large. I don't know the relevant equations, but your ring may end up close to the size and mass of the planet itself.   

       Finally, the notion that "gravity from the other sides of the planet would effect them causing them to become weightless" is preposterous.   

       I'm curious; what were you hoping to do with this ring?
egnor, Nov 09 2000

       I now realize that the statement "gravity from the other sides of the planet would effect them causing them to become weightless" is indeed preposterous as egnor pointed out but I do not agree that it would fall because the side nearer to the planet would fall faster.It probably would fall but the gravity on the other side of the planet should balance it out.The only factor I see stopping this from working would be the effect of the sun or earths gravity on the ring throwing it out of balance.As for egnors other comments I stand corrected.I also acknowledge that this would not be antigravity but wieghtlesness.I wonder however if this ring was spun if it would spin considerably long due to it's lack of friction?(probably not but worth thinking about).
beretboy, Nov 09 2000

       A ring of this sort is a significant plot point in Yukito Kishiro's "Gunnm" (aka "Battle Angel" or "Battle Angel Alita").
baf, Nov 09 2000

       Actually, if -- as in egnor's comment -- the ring would be nearly the same mass as the planet, wouldn't that then create a reduced-gravity environment for anyone standing on the planet's surface directly beneath the ring?
PotatoStew, Nov 09 2000

       Note that if you have to hollow out the planet to be in the center of the ring, you might just as well just hollow out the planet, period. (Instant ring!)
jutta, Nov 09 2000

       What grade are you in, Peter "words of one syllable" Sealy?   

       The calculations aren't trivial, but I don't believe a ring will attract objects inside it to its center. I believe a uniform hollow sphere, for example, has absolutely no gravitational effect on objects inside it. Furthermore, he didn't say the ring was "spinning in space". He specifically said it would be "several hundred feet above it" (the planet's surface), and hoped it would hover "in mid-air". If such a ring were spinning, it would in fact suffer air resistance.
egnor, Nov 10 2000

       As noted in my Nov 08 annotation, yup. It might work to shape the ring to the contours of the planet, though accounting for tides would be complex.
egnor, Nov 11 2000

       I believe that all of these thaughts are being wasted here, I see so much effort being put into this and none of you are working together to come up with one answer on how to create any type of antigravity. Have any of you heard about compressing Mercury in a tube connected to 3 bell shaped housing that generate an electromagnetic field inclosed in the underneath of a vessle, also the Mercury is compressed to 5 spheres. This is where the military is going on the newest fighter, which is saucer shaped. Can anyone come up for an answer about this type of antigravity.
davec, Nov 20 2000

       davec: what does mercury have to do with anti-gravity? The military might be better off experimenting with hydrogen (which, no doubt, they are). Can we get a link to the basis of your post?
centauri, Nov 20 2000

       It works just as well to save dew in glass phials, and then be drawn upward with the dew when it rises in the morning.   

       And if the dew should rise in a Web, I may well die a...?
hello_c, Nov 21 2000

       And you can also have everyone on it in freefall...
StarChaser, Jan 07 2002

       Why not completely encompass the moon? Why a ring, when in fact you could make a complete sphere around the moon, which in fact wouldn't be just a sphere, but a space station. This would, in fact, allow us to create a breatheable atmosphere on the moon, by pumping oxygen, nitrogen, and the such into the sphere. Add water, and voila! Plus, scientists and the such could do research within the sphere, providing a great lab for studies, while possibly creating a possible vacation resort on the moon. Imagine sunbathing on the moon (the lights would be fake... like on the Truman Show...)
Salty Ham, Jan 12 2002

       Or just hollow the moon.
dare99, Mar 26 2002

       In regards to egnor's first comment, the ring needn't be massive, nor extremely strong. It would function in much the same way that an arch does, except it would encompass a full 360 degrees. The only force (disregarding everything else for the theoretical model) acting upon it would be the downward force of gravity, which would be translated into compressional forces along the length of the ring. Again, just as with an arch, though this arch would be 25 000 miles long.

       Given, these compressional forces would be immense. However, concrete is already capable of enduring large amounts of compression. If the diameter of the ring is kept down, a composite concrete of a light-enough weight could possibly fufill the requirements. An outer jacket of cables could also further contain any outward expansion of the concrete, much like rebar used in present buildings.

       Though, this would be higly fragile as concrete does not like shearing forces, nor does it like to be bent. This would mean that a person touching the ring would not result in him becoming weightless. Rather, it could result in the destruction of the ring.

       I think...
rapid transit, May 09 2003

       Actually, if you did touch the ring, you would in a sense become weightless; ( or maybe less weighty ) You could grab the ring and hoist yourself up to a new altitude; somehting that is quite impossible in the slippery well we live in here on planet earth. A slippery well means that there are no sides to grab on to. If one could simply step up on to the next rock, it would only be a matter of time before you could climb into space. But there is nothing but air to grap a hold of; hench the term slippery well. But a floating ring! Now there's somehting that can be climbed on to.
sparksd, May 25 2003

       A very very very long rope ladder should also do the trick though I do like better the concept of using monkey-rings for swinging yourself to outer space.
Tiger Lily, May 25 2003

       Fishbone. Kudos for inventing the Dyson circle though.
Jezzie, May 25 2003

       Let me make several technical points here...   

       As egnor points out, a ring exerts no gravitational force on object inside it, at least for objects *in the plane of the ring*, say, people standing at the equator (if that's where the ring were to be built). There *would* be a force exerted on objects not in that plane (i.e. anyone not standing on the equator). That new force would be equatorward at one angle or another. If anything, this would *increase* the experienced gravitational force at the surface of the earth (as it is currently shaped).   

       The surface of the earth is more-or-less at a gravitational equipotential (the shape the ocean would adopt if there were no land in the way). Any variances from this shape (e.g. mountains and valleys) must be supported by the strength of the Earth's crust (which is essentially floating on the liquid mantle). Adding the ring would change the curve of this equipotential, tending to pull the poles of the Earth toward the equator.   

       A ring with a small mass would change the depths of the Earth's oceans in some places, to match the new equipotential. Hopefully, this would not submerge any currently inhabited areas. It would probably also change the rates of subsidence and rising that the various parts of the crust are already engaged in (e.g. due to rebound after the melting of the glaciers from the last ice age, or from tectonic stress).   

       A ring with a large enough mass to put significant stress on the crust can cause increased volcanism. (Constant changes in equipotential is apparently what makes Io, a moon of Jupiter, volcanically active.) Hopefully, the added atmospheric ash and sulfur would not cause widespread crop failures or dangerous climatic cooling (like say, the 1815 eruption of Mount Tambora).   

       A truly massive ring could cause a large enough dislocation to completely liquefy the surface of the planet, both through escape of interior magma and release of tremendous amounts of gravitational potential energy as waste heat.   

       Given that we understand very little about the fluid dynamics of our planet's interior, the addition of even a small ring would have unpredictable consequences. For example, we still don't know why Venus apparently volcanically resurfaced itself about 300-500 million years ago; it might have something to do with interior dynamics. We certainly wouldn't want to trigger that accidentally. It's also unclear to me how a partially constructed ring could be held in place safely.   

       Anyway, enough technical analysis.   

       Hollowing out the planet sounds like a better approach to achieving this dubious goal. Though reducing the gravitational constant might have bad long-term effects on a variety of organisms, including humans. And we'd have to make up for the lost heat source, as well as structurally re-inforce the crust so it won't catastrophically collapse into a ball of molten lava.   

       I think coming up with some kind of locally controllable anti-gravity field would be a lot spluftier.
beland, May 26 2003

       Folks, I will soon be posting an idea that at first glance has some similarities to this one. But it has nothing to do with anti-gravity, and is indeed different (it's also one of those old ideas I've dredged up from a bunch of years ago).
Vernon, Sep 11 2003

       I read a theory about this being possible with diamond supports connected to the planet to keep the gravity freed ring stable....but until we discover how to manufacture solid diamond as a building material, I don't think it's plausible.....would also make the diamond market crash pretty fast, hehe
Half-life below 40yrs, Jun 09 2006

       One time I had an idea to tunnel to the center of a large gravatational object (like a moon), then once your there, gavity would be equal all around you.
BJS, Jun 09 2006

       The ring would still have weight but it would be essentially balanced against itself. It could be lifted if you have a big enough jack, as the only force resisting its collapse is the comprssion strength of the ring. so if you lifted one side of the ring, it would rise and the far side would move closer to the planet. If you spun the ring the same would still be true. however if you then placed a pebble on the ring and the speed was sufficient the pebble would stick to the ringthrough Centripetal force.(like water in a bucket)   

       This is not antigravity at all.
jhomrighaus, Jun 09 2006

       the mass of this ring will have to equal the planet/moon/etc. mass. instead of metal, it may need to be made up of material from a neuton star. Still, the 0-G zone would be between the ring and the surface.   

       Also Salty, if the moon is covered by this space station sphere, holding in air, then how will sunlight get through to the //sunbathing// space tourists? you might as well make underground lunar cities.
the great unknown, Aug 24 2007


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