How does gravity's space time distortion access energy to induce freefall? An observer, standing on top of a building, has a gravity switch (use your imagination) which allows him to turn gravity on and off.  He turns the switch off, then releases a pool ball over the edge of the building at 100' above the street below.  Presumably, both the ball and the earth have a common velocity in some direction and therefore are at rest relative to one another.  The ball hovers at 100'.
Then he turns on the gravity switch.  My understanding is that the gravity will then distort spacetime between the ball and the earth.  This distortion causes a change in the relationship between distance and time, thus inducing motion and acceleration between these two masses, and the ball will go into freefall.
Since Einstein says that gravity is not a force in and of itself, then what is the real source of the potential energy? 
 A: The source of the potential energy is the fact that different observers have a different notion of "stationary", because the curvature of spacetime rotates the time of one observer into the space of another.  We know from classical mechanics that energy is related to time translation symmetry, so it shouldn't be surprising that messing with the definition of time will have an energy associated with it.
Therefore, to this observer, it will look like the infalling object is picking up kinetic energy.  I should add, however, that although this simple example has a notion of energy embedded in it:
1) energy is only conserved for orbits in spacetimes with a time-translation symmetry, like the Schwarzschild or Kerr solutions.  This is true only for particles with a mass so small we can ignore gravitational radiation
2) Generally, only the total energy of spacetime is conserved, and this is true only in a special case of spacetimes known as asymptotically flat (and a few related spacetimes).
3) In these contexts, we really only talk about a total energy, rather than concerning ourselves with dividing it into kinetic and potential energy.
