Is there proof gravity can not be a energy source?

[spinn_MP]

Hope Stefan follows this exchange and can do something about curbing the spam by @spinn_MB.

Lol, you wish... Idiot!

[Omnibus]

@Alexioco, are you around? Isn't this supposed to be a moderated thread? Who is going to curb @spinn_MP's spamming?

[Karmanaut]

Omnibus is correct. Gravity is not energy.
But Gravity can be used to facilitate the change of one form of energy into another.

Consider "Gravity Assist": a term used in orbital mechanics. Say a spaceship approaches the Earth at a certain velocity. The gravity of the Earth pulls the ship closer. It then loops around the Earth and "slingshots" away. Now, the spaceship experiences no increase in velocity relative to the Earth (because Gravity cannot do work). From our point of view it's not going any faster when it leaves us than when it approached. But because the Earth is traveling at 29,8km per sec around the sun, the spaceship picks up speed relative to the sun. It has, in fact, gained a tremendous amount of energy.

Sounds like a violation of CoE?

No. What has actually happened is that the Earth's gravity has facilitated an "elastic collision" between the spaceship and the Earth. The Earth exerts a force on the spaceship, speeding it up, while the spaceship exerts an equal and opposite force on the Earth (assuming perfect conditions, without friction etc). But since the mass of the spaceship is so tiny compared to the mass of the Earth, the amount the earth slows down is negligible.

It's like shooting a fly with a cannonball. The fly gains kinetic energy, but the cannonball also loses kinetic energy (even if you'd be hard pushed to notice it).

The moon's gravity pulls at our oceans which, when combined with the Earth's spin, causes tides, which can be used an a source of energy. But the moon's gravity creates drag which slows down the Earth's spin. In this case the rotation of the earth is the source of tidal energy, not the moon's gravity. The moon's gravity (and to a lesser extent, the Sun's) merely facilitates the change.

So it is possible to build a machine that utilizes gravity (from the sun and moon) to tap the energy from the rotation of the Earth -- tidal power systems already do this.  But the gravity itself is not the source of the energy.

[exnihiloest]

Gravity is not energy.

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Gravity are conservative. If gravity is acceleration, this acceleration is also conservative. Therfor gravity is not the same as energy, because energy is not conservative
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Vidar

No one pretends that gravity is energy. What is asserted is that there is energy in a gravity field and that gravity could be an energy source (read the thread subject).
Energy is not conservative, but the gravitational force field is conservative because it is the gradient of a scalar potential. The potential energy is path independent.
Therefore the energy in a closed system, including that one in the field, is conserved. To take this fact into account after using the potential energy from a body which fell, there is no other way than to suppose this energy came from a little weakening of the gravity field, due to its topological change in space by the virtue of a new distribution of masses.

[exnihiloest]

I am not wrong about Einstein because his "theory" fails
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Prove it!
Otherwise, the status of people affirming that Einstein is wrong while themselves being unable to oppose by logic arguments, is given there:
http://en.wikipedia.org/wiki/Dunningâ€"Kruger_effect