[calex59]

If you could block the effect of gravity, you could use it to lift a large weight with a small amount of energy, after which you could turn off the device, and capture the energy as the weight fell back down. This cycle could be repeated indefinitely, yielding inexhaustible free energy. That energy could in principle be used to power the device, hence perpetual motion.

The problem with this reasoning is this: The amount of energy required to produce the anti-gravity. The power to lift the object is irrelevant, the power to produce the anti-gravity would have to be less than the power produced by the energy of the falling object. Example denied!:)

[Constantine XIII]

Well, if it takes M x g x h Joules or ft/lbs to move an item up to a height h, then you don't really get any benefit out of using the antigravity. :)