Is there proof gravity can not be a energy source?

[e2matrix]

Do you not recognize in your Niagara falls example the two elements -- force (gravity) and displacement -- I pointed out to you, which characterize energy? Gravity acting on still water, even if that water stands still at a height thus having potential energy, does no work. For gravity to do work conditions must be ensured for the second element -- displacement -- to come into play. Gravity itself isn't enough to produce energy. Gravity isn't energy. This isn't semantics but is the essence of this problem.

Just for the sake of argument let's assume for a minute that gravity did not exist.  Or that gravity had zero force and did not cause an object to fall to the ground.  Having taken gravity out of the equation what will happen now with all that water at Niagra Falls?  We could call it 'No Falls' and No Electricity.  And no work being done with the electricity because there is no electromotive force.  It would seem gravity can cause work to be done although in this case it is just capturing the energy the Sun created when it raised water from the ocean to the air which then rains down and once again falls down the river until it reaches Niagra Falls.  So we are using gravity to do work as an object goes from a higher to a lower energy state.  So I say it is semantics as to whether you consider gravity a 'source'.  I say it is a source for energy although ultimately it is the Sun.  You could say water is the source of energy but without gravity it would not be able to turn turbines to generate power.  Is any one thing a true energy source or does it take a combination of things to produce energy?  I'm actually assuming the OP is asking the question to decide if a gravity device can be built to produce usable energy.  I may be wrong but if that is the case then I say yes it can if combined with other natural forces.  I don't recall the name of the device or the inventor at the moment but there is a person selling a device which uses a combination of gravity in air and buoyancy in liquid (counter forces) to generate power.  He has a web site and it has been posted around here.  So if that is the OP's intention in this question I would say yes.  Otherwise I say it's just semantics. 
   

[Omnibus]

Undoubtedly. You're quite right but never forget "combination of things to produce energy". Like I said, combination of force and displacement. That's not at all semantics but is the very essence of things, as I noted already. If you have this in mind then, yes, gravity, provided also there's a construction ensuring spontaneous displacement, can produce energy. Gravity all by itself isn't energy but given the proper conditions to induce displacement of a body, gravity can do work.

[e2matrix]

I was looking for the invention I mentioned in my last post about gravity and buoyancy.  I haven't found it yet but found this very interesting device at this web site.  I've never seen this before but it has patents and claims quite a lot using just gravity in what appears to be a very complex sort of Bessler's wheel.
http://www.karragreenenergy.com/electricity.html

[Omnibus]

Yeah, I've seen that couple of years ago and that's one of the presentations that has really fascinated me only to, sadly, find it has gone into oblivion. I think it was an Armenian invention. So, look what we've got -- Bob Kostoff, Aldo Costa, Sjack Abeling, that Armenian one with claims for self-sustaining run, not to mention Veljko Milkovic or that latest Gravitational Energy Corp. huge one with the 18,000lb bob. And yet, the world is not only hesitant but is ignoring outright this most revolutionary way of producing energy. Who's to blame do you think?

[e2matrix]

I think that one listed Syria as the country origin.  Here is the other one I was referring to:
http://sustainablepowerstation.com/

Ultimately I would say mainstream scientists hold a lot of the blame since investors hesitate on anything not following the traditional laws they have written.  I do believe though that thanks to the Internet the snail pace at which traditional science moves in upgrading it's theories may begin to change as an overwhelming amount of evidence becomes so much easier to find, observe and replicate.