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Author Topic: Gravity as a Source of Energy?  (Read 14059 times)

Offline _Stefan_

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Gravity as a Source of Energy?
« on: 14/07/2007 13:47:58 »
What are your thoughts about gravity as an energy source? Are there ways of extracting energy from the Earth's gravity that have been shown to work?


 

another_someone

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Gravity as a Source of Energy?
« Reply #1 on: 14/07/2007 14:22:59 »
Not exactly sure what this means in practice?

To extract energy from something is to imply that it will have less of that energy after you have finished with it than before you started with it.

Gravity is an attribute of mass, and is indivisible from it; thus to reduce gravity is to reduce mass, thus is not extracting energy from gravity the same thing as extracting energy from mass?  If this is this is the case, then the only significant success in this matter to date has been nuclear energy, although it only extracts a very small portion of the available energy.
 

Offline DoctorBeaver

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Gravity as a Source of Energy?
« Reply #2 on: 14/07/2007 17:00:36 »
I can think of a way to indirectly get energy from gravity. If you set up a device near a black hole that will intercept incoming particles, then that could be turned into energy. Whether you'd get enough for it to be practical, I don't know. Maybe Ian or someone of that ilk could tell us.
 

another_someone

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Gravity as a Source of Energy?
« Reply #3 on: 14/07/2007 17:08:56 »
I can think of a way to indirectly get energy from gravity. If you set up a device near a black hole that will intercept incoming particles, then that could be turned into energy. Whether you'd get enough for it to be practical, I don't know. Maybe Ian or someone of that ilk could tell us.

But how would you get that energy back to us without having to climb the same energy gradient that was used to impart kinetic energy into the particle you intercepted (i.e. the net energy gain of an optimal system, once you have got the energy away from the black hole, would still be zero).
 

Offline DoctorBeaver

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Gravity as a Source of Energy?
« Reply #4 on: 14/07/2007 18:07:13 »
I can think of a way to indirectly get energy from gravity. If you set up a device near a black hole that will intercept incoming particles, then that could be turned into energy. Whether you'd get enough for it to be practical, I don't know. Maybe Ian or someone of that ilk could tell us.

But how would you get that energy back to us without having to climb the same energy gradient that was used to impart kinetic energy into the particle you intercepted (i.e. the net energy gain of an optimal system, once you have got the energy away from the black hole, would still be zero).

I'll leave those sort of minor details to other people  :D
 

Offline syhprum

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Gravity as a Source of Energy?
« Reply #5 on: 14/07/2007 19:43:17 »
There is no practical way of extracting energy from a gravitational field but it provides a very convenient way of storing electrical energy when it is cheap and recovering it when it becomes more valuable.




http://en.wikipedia.org/wiki/Energy_storage
 

Heronumber0

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Gravity as a Source of Energy?
« Reply #6 on: 14/07/2007 20:09:45 »
I thought the gravitational potential energy stored in the millions of tonnes of water behind a dam provided an example of the use of the Earth's gravity. What puzzles me -  and I can't understand this -  is why gravity is strong and weak at the same time? We are held on to the Earth by gravity, yet I can easily throw a ball in the air. Or has this been answered by another_s?
 

Offline DoctorBeaver

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Gravity as a Source of Energy?
« Reply #7 on: 14/07/2007 20:20:19 »
Gravity is by far the weakest of the 4 natural forces of nature - electromagnetism, the weak & strong nuclear forces being the other 3.

It has long been a puzzle to physicists why gravity should be so much weaker than the other 3 forces but recent models have suggested reasons. There may be evidence of the models within the next few years from the new LHC collider at CERNE.
 

Offline Soul Surfer

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Gravity as a Source of Energy?
« Reply #8 on: 14/07/2007 23:23:35 »
We regularly extract energy from gravity in hydroeolectric power stations.  This is really energy extracted from the sun because the heat of the sun has eveporated the water from the ocean and sent it inland to rain on a mountaintop whewre the strams run down and are collected in a hydroelectric dam and used to turn a generator.
 

Offline maff

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Gravity as a Source of Energy?
« Reply #9 on: 15/07/2007 12:33:49 »
Besides Hydroelectric dams Scientists have tried to use gravity and Helium filled balloons to try for perpetual motion. The idea is to use the Helium balloons to carry a small mass contained inside a vacuum up to an height then release it. The Helium balloon is not inside the vacuum itself and so rises being lighter than the sourounding air.
When the mass gets to a certain height, the Helium balloon is detached from the mass and it comes to Earth hitting a power generator on the way down. The Helium balloon then has to get back down to Earth to attach itself to the mass again so it can pick it up and lift it to the top again.
This is done by using part of the power generated to deflate the Helium balloon using an electrical decompressor inside the balloon. When the balloon gets back to Earth the electrical device then recompresses the helium inside the balloon using the same helium which it decompressed. It then picks up the mass and starts again.
To drive the generator there are hundreds of these mass-helium devices working in sink.
The idea is a good one but the problem is generating enough force to drive the electrical compressors which they didn't do. But with a tweak to the idea these days you never know!
..maff 
« Last Edit: 15/07/2007 12:36:03 by maff »
 

another_someone

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Gravity as a Source of Energy?
« Reply #10 on: 15/07/2007 13:53:40 »
Hydo dams are not using gravity as a primary source of energy.  As Ian rightly mentioned, the Sun is the ultimate source of energy for them, and gravity is merely a transient storage mechanism.

Besides Hydroelectric dams Scientists have tried to use gravity and Helium filled balloons to try for perpetual motion. The idea is to use the Helium balloons to carry a small mass contained inside a vacuum up to an height then release it. The Helium balloon is not inside the vacuum itself and so rises being lighter than the sourounding air.
When the mass gets to a certain height, the Helium balloon is detached from the mass and it comes to Earth hitting a power generator on the way down. The Helium balloon then has to get back down to Earth to attach itself to the mass again so it can pick it up and lift it to the top again.
This is done by using part of the power generated to deflate the Helium balloon using an electrical decompressor inside the balloon. When the balloon gets back to Earth the electrical device then recompresses the helium inside the balloon using the same helium which it decompressed. It then picks up the mass and starts again.
To drive the generator there are hundreds of these mass-helium devices working in sink.
The idea is a good one but the problem is generating enough force to drive the electrical compressors which they didn't do. But with a tweak to the idea these days you never know!
..maff 

I am trying to understand how this is supposed to work.

The vacuum has to be contained in something, and that thing has to be able to withstand the force of the external atmosphere, and so is likely to be heavy.  But even if you could devise a very strong material with almost zero mass, it seems to be suggesting that the energy required to compress the helium to bring the balloon back to earth would be less than the energy gained by taking the mass up to a given altitude, and I cannot see how this is so.

The vacuum chamber seems to be a bit a red herring, but I am not sure exactly what you expect it to do.  If the idea of the vacuum chamber is to create a place in which to suck in the helium, then the problem still arises that you need energy to create the vacuum (this is no less than the energy required to compress the helium, which will be no less than the energy gained by floating the helium balloon).

 

Offline lightarrow

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Gravity as a Source of Energy?
« Reply #11 on: 15/07/2007 19:47:34 »
What are your thoughts about gravity as an energy source? Are there ways of extracting energy from the Earth's gravity that have been shown to work?
What about earth gravitational field on the Moon? It's possible to extract energy from the sea tidal movement.
 

Offline maff

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Gravity as a Source of Energy?
« Reply #12 on: 15/07/2007 20:12:07 »
I believe the mass was inside a tube where the air had been sucked out creating a vacuum. The helium balloon was on the outside and attached to the mass via magnets. When the mass got to a certain height the magnets became parted via a sheild of somekind on the tubing allowing the mass to drop. The Helium in the balloon was then compressed into a cylinder contained within the balloon (electrically). This allowed the balloon to sink to Earth and attach the magnets again. The compressed Helium in the cylinder was then pushed back into the balloon making the whole job lot rise again. Don't shoot the messenger guys it didn't work because they couldn't generate enough electricity to drive the Helium compressors. But personally I liked the concept.
..maff
 

Offline Barnacle

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Gravity as a Source of Energy?
« Reply #13 on: 16/07/2007 00:30:15 »
water mills do it.
 

another_someone

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Gravity as a Source of Energy?
« Reply #14 on: 16/07/2007 01:34:22 »
What are your thoughts about gravity as an energy source? Are there ways of extracting energy from the Earth's gravity that have been shown to work?
What about earth gravitational field on the Moon? It's possible to extract energy from the sea tidal movement.

The energy is being extracted from the orbital energy of the moon, not from its gravitational field - gravity is merely a means of transmitting the orbital energy.  The tides slow down the orbit of the moon, thus clearly indicating that they are using orbital energy; they do not reduce the gravitational pull of the moon, and so don't consume gravitational energy.
 

another_someone

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Gravity as a Source of Energy?
« Reply #15 on: 16/07/2007 01:34:59 »
water mills do it.

Water mills are no different from hydroelectric plants mentioned above.
 

another_someone

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Gravity as a Source of Energy?
« Reply #16 on: 16/07/2007 01:37:45 »
I believe the mass was inside a tube where the air had been sucked out creating a vacuum. The helium balloon was on the outside and attached to the mass via magnets. When the mass got to a certain height the magnets became parted via a sheild of somekind on the tubing allowing the mass to drop. The Helium in the balloon was then compressed into a cylinder contained within the balloon (electrically). This allowed the balloon to sink to Earth and attach the magnets again. The compressed Helium in the cylinder was then pushed back into the balloon making the whole job lot rise again. Don't shoot the messenger guys it didn't work because they couldn't generate enough electricity to drive the Helium compressors. But personally I liked the concept.
..maff

The point is that if they had generated enough electricity, they would have found the electricity they had to generate exceeded the energy they could extract from the system - hence no perpetual motion, and no extraction of energy from gravity.

Now, if we could ever find a way of receiving those elusive gravity waves, then we might be able to use them for energy.
 

Offline Karen W.

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Gravity as a Source of Energy?
« Reply #17 on: 16/07/2007 05:29:55 »
water mills do it.
Welcome to the forum Lord Tawny! Glad to see you participating! Enjoy!
 

Offline syhprum

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Gravity as a Source of Energy?
« Reply #18 on: 16/07/2007 07:53:55 »
I understand that the Sun converts about 4 million ton of mass into energy per second.
If mass and gravity are equated is this not the extraction of energy from gravity
 

another_someone

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Gravity as a Source of Energy?
« Reply #19 on: 16/07/2007 10:03:38 »
I understand that the Sun converts about 4 million ton of mass into energy per second.
If mass and gravity are equated is this not the extraction of energy from gravity

That is what I suggested earlier, that nuclear energy is the closest approximation we have to date of extracting energy from gravity (and you might I suppose argue that solar energy is nuclear energy by proxy).
 

Offline lightarrow

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Gravity as a Source of Energy?
« Reply #20 on: 16/07/2007 15:28:08 »
What are your thoughts about gravity as an energy source? Are there ways of extracting energy from the Earth's gravity that have been shown to work?
What about earth gravitational field on the Moon? It's possible to extract energy from the sea tidal movement.
The energy is being extracted from the orbital energy of the moon, not from its gravitational field - gravity is merely a means of transmitting the orbital energy.  The tides slow down the orbit of the moon, thus clearly indicating that they are using orbital energy; they do not reduce the gravitational pull of the moon, and so don't consume gravitational energy.
Ok, but slowing down the Moon's orbital speed makes it jump down to a closer orbital distance, that is, the Moon's gravitational energy decreases. So the energy of the tides has actually come from this variation of gravitational energy of the Moon.
 

another_someone

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Gravity as a Source of Energy?
« Reply #21 on: 16/07/2007 19:20:35 »
Ok, but slowing down the Moon's orbital speed makes it jump down to a closer orbital distance, that is, the Moon's gravitational energy decreases. So the energy of the tides has actually come from this variation of gravitational energy of the Moon.

Except that, as I understand it, the Moon is drifting away from us.

In any case, all of the orbital energy of the Moon itself derives from the processes that created the Moon (if the theory that the Moon was created by an impact between the Earth and another body, then the orbital energy of the Moon derives from the kinetic energy of that impact).
 

Offline lightarrow

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Gravity as a Source of Energy?
« Reply #22 on: 17/07/2007 18:30:40 »
Ok, but slowing down the Moon's orbital speed makes it jump down to a closer orbital distance, that is, the Moon's gravitational energy decreases. So the energy of the tides has actually come from this variation of gravitational energy of the Moon.
Except that, as I understand it, the Moon is drifting away from us.
I sincerely don't know if the Moon drifts away or the opposite. If it drifts away, it loses kinetic energy but acquire gravitational potential energy. The sum of the two, that is the Moon's total energy, increases with increasing distance:
T = kinetic energy = 1/2GmM/R
V = potential energy = -GmM/R
E = total energy = T + V = -1/2GmM/R
where G = gravitational constant; m = Moon's mass; M = eart's mass; R = distance Eart-Moon.
So, in that case, the Moon have to subtract energy from Earth in some way (maybe from earth's spinning energy?).
Quote
In any case, all of the orbital energy of the Moon itself derives from the processes that created the Moon (if the theory that the Moon was created by an impact between the Earth and another body, then the orbital energy of the Moon derives from the kinetic energy of that impact).
If you have two bodies with non-zero mass, non-zero tangential relative speed that are approaching, they can form a system planet-satellite where the lighter one orbit around the heavier one. The parameters describing the orbit: distance R and orbital speed V, are defined by the initial parameters of the two bodies: positions and speeds. So you don't need to look for particular ways of generating the orbital kinetic energy.
 

Offline Soul Surfer

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Gravity as a Source of Energy?
« Reply #23 on: 17/07/2007 21:03:32 »
It is not possible for two bodies that are approaching each other from a great distance under their mutual gravitational attraction to go into a stable orbit around each other without the intervention of an additional energy loss in the form of a collision or the inervention of a  third gravitiating object.

All two body orbits from a distance are hyperbolic or at best parabolic like a new comet.
 

Offline lightarrow

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Gravity as a Source of Energy?
« Reply #24 on: 18/07/2007 15:49:34 »
It is not possible for two bodies that are approaching each other from a great distance under their mutual gravitational attraction to go into a stable orbit around each other without the intervention of an additional energy loss in the form of a collision or the inervention of a  third gravitiating object.
Yes, infact it's for this reason I wrote "...they can form a system planet-satellite..." instead of writing "...they form...". Anyway, I would say that the Moon's orbital kinetic energy comes from the Moon's gravitational potential energy in the earth's grav. field and not from the kinetic energy of the impact. Do you agree?
 

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Gravity as a Source of Energy?
« Reply #24 on: 18/07/2007 15:49:34 »

 

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