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2019-09-15, 09:45 AM (ISO 8601)
- Join Date
- Sep 2016
gravity and antigravity calculation question, the floating house
I have a question about the calculation of the results of gravity in a hypothetical situation.
The formula for the gravitational pull is: FG= G*m1*M2/r2.
If an anti-gravity generator would exist ( of relatively small size) and I would anchor it into the ground. My question would then be. Would it be possible to place a then floating house (anchored so it wouldn't drift of place) above it, where you could live relatively normal ( sufficient gravity and right side up). Or would the super-positioning of both gravity wells not provide a point where the pushing of the antigravity well changes back into a attraction (positive force vector).
I have some problems getting the formulas right.
Would the equation allow for something above it to remain in place of would the antigravity well actually push things above it further away indefinitely.
I would think that a constant anti gravity well in between the 2 masses ( earth and house) would actually cause the house to be pushed away.
Is that correct?
(earth)-----(anti grav well)-----(house)
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2019-09-15, 10:30 AM (ISO 8601)
- Join Date
- Feb 2007
- Location
- Manchester, UK
- Gender
Re: gravity and antigravity calculation question, the floating house
The problem here is that anti-gravity does not exist and I'm pretty sure *cannot* exist according to the laws of physics as we know them, so it's pretty much up to you how this works. I would say that if the anti-gravity is affecting everything above it then you have a potential problem with the atmosphere draining off into space because there's nothing holding it down where your house is!
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2019-09-15, 04:07 PM (ISO 8601)
- Join Date
- Jan 2007
Re: gravity and antigravity calculation question, the floating house
Assuming that this antigravity works like negative mass, it can be done
Earth is big and the gravity field around surface is nearly constant (at least for anything the size of a house). A field generated by a small antigravity device would fade with distance just like one generated by mass, so barring any horizontal movement for simplicity an object would indeed float at a set height above the antigravity device (if it goes higher, Earth's pull takes over, if it goes lower, device's push gets stronger). Moreover, above the center of mass of the floating house things would still feel gravity in the regular direction even if diminished (this can be fixed to a degree with good geometrical design of the whole construction).
There is a different problem though: such a construction would be inherently unstable (as far as I can tell) with respect to rotation, since you have a force acting toward the inside and attached to the edge of the house. A bit like trying to balance a pencil on a finger.In a war it doesn't matter who's right, only who's left.
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2019-09-20, 03:17 AM (ISO 8601)
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- Aug 2019
Re: gravity and antigravity calculation question, the floating house
The antigrav field could be easily engineered into shapes. If it has a bathtub shape, you dont even need to anchor the house. With respect to rotation, clever asymmetries in the mass distribution of the house and the field could give a rotational and local stability. Its like floating a ship (=house) on water (=antigrav field). Only that you probably float in your basement or walk upside down there.
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2019-09-20, 03:51 AM (ISO 8601)
- Join Date
- Jan 2007
Re: gravity and antigravity calculation question, the floating house
If antigravity works like antimass (that was my assumption), then no, you cannot shape the field like that. To do a bathtub-like field, it would have to fade with distance quicker then regular gravity. As for the ship analogy, it does not work. What stabilises a ship is that gravity works on mass, but buoyancy works on volume - if you shift the center of mass below the center of volume, you have stability. With antigravity you do not have that, since both forces work on mass.
In a war it doesn't matter who's right, only who's left.
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2019-09-20, 06:10 AM (ISO 8601)
- Join Date
- Aug 2019
Re: gravity and antigravity calculation question, the floating house
Regarding the shape, you'd need several generators distributed under the foundation with varying strength. They'd add up and create basically any regular shape.
You are right that it is trickier with antigravity working just on the mass. But even then you only need a potential field with a local minimum with respect to the mass distribution of the house. Which is doable. My example would be a tripod resting in three indents of a potential field. Its impossible to move or rotate the tripod without leaving the optimal state.
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2019-09-20, 07:30 AM (ISO 8601)
- Join Date
- Jan 2007
Re: gravity and antigravity calculation question, the floating house
Local minimum of gravity field means that in the middle there is a positive mass. If it were possible to immitate positive mass with negative one, then it would also be possible to immitate negative mass with positive one. The easiest way to see the limitation is to consider Gauss law: if there is a local minimum, then the gravity field has locally a non-zero divergence. By Gauss law it means that there needs to be a mass of appropriate sign and magnitude in the middle. So there are strict limiation on the shape of a field.
You can always consider dynamic stabilisation, so that the antigravity generators are adjusting in real time to keep the structure in place. Or have static antigravity generators and some auxiliary thrusters and gyroscope arrays instead.In a war it doesn't matter who's right, only who's left.
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2019-09-21, 10:26 AM (ISO 8601)
- Join Date
- Aug 2019
Re: gravity and antigravity calculation question, the floating house
I think thats only true for strict local minima and point charges. And i said minimum potential field wrt house. You test the sum of gravitational forces on the whole house, not a single point.
Generally with antigravity you should get a surface, where the gravity and antigravity cancel out wrt point charges, thats a minimum in the potential field right there.
I really get what you say, thats instable for points.
The trick is to shape the surface such that a house with its size gets stuck, so to say.
I think I cant explain it better without painting a picture.
Edit: In real life this whole arrangement would be horribly unsafe anyway. Any storm would send the house flying and tumbling, possibly turning your house upside down.Last edited by Rydiro; 2019-09-21 at 10:31 AM.
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2019-09-21, 11:40 AM (ISO 8601)
- Join Date
- Jan 2007
Re: gravity and antigravity calculation question, the floating house
It actually makes little difference, since for stability you need to have the anchor points in actual minima.
Only in the up-down axis, so this is a stationary point but not exactly a minimum. In the horizontal plane at best you would be able to have no forces, or at worse would have forces pushing the house away.
I just realised though that I overestimated the problem of random tumbling - this would happen only if the house has a more vertical distribution of mass. If it is wider rather then higher, it will not flip on its own the same way as rafts or barges ramain stable. Rotation in the vertical axis can actually also be fixed to be honest.
The remaining problem is that it could slide away from the antigravity cushion and here the nature is not as forgiving, but it is nothing active control could not handle.
Now if the antigravity worked like the Meissner effect, then we could also count on flux pinning, which gives excellent stability. This would be neat.In a war it doesn't matter who's right, only who's left.
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2019-09-21, 01:58 PM (ISO 8601)
- Join Date
- May 2007
- Location
- The Land of Cleves
- Gender
Re: gravity and antigravity calculation question, the floating house
If gravity had both positive and negative masses, then it would behave like electromagnetism. It is not possible to create an electrostatic or magnetostatic arrangement that results in anything being supported stably. It is, however, possible to create a system that dynamically adjusts field strengths to hold something in an unstable position, and it is even possible to construct dynamic arrangements that will do so automatically.
But any sort of gravity manipulation that works at all analogously to how we manipulate electromagnetism is going to be phenomenally impractical. We manipulate electromagnetism, fundamentally, by moving charges around. The analogous property for gravity would be to move masses around. But that requires planet-like masses, if you're doing it with matter of ordinary density.Time travels in divers paces with divers persons.
—As You Like It, III:ii:328
Chronos's Unalliterative Skillmonkey Guide
Current Homebrew: 5th edition psionics
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2019-09-22, 04:24 AM (ISO 8601)
- Join Date
- Aug 2019
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2019-09-22, 06:55 AM (ISO 8601)
- Join Date
- May 2007
- Location
- The Land of Cleves
- Gender
Re: gravity and antigravity calculation question, the floating house
Time travels in divers paces with divers persons.
—As You Like It, III:ii:328
Chronos's Unalliterative Skillmonkey Guide
Current Homebrew: 5th edition psionics
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2019-09-23, 02:43 AM (ISO 8601)
- Join Date
- Aug 2019
Re: gravity and antigravity calculation question, the floating house
Last edited by Rydiro; 2019-09-23 at 02:44 AM.