From my poor understanding of Einstein's theory of relativity, gravity is not a force but the consequence of mass curving the space-time continuum. As such, the moon revolving around the earth is actually going straight in the space-time continuum.
The concept of force is very related to the concept of energy. A force is something which changes the energy of a system by doing work on it. In kinematics, work as:
Consider power station using tidal power for example. These stations are creating electricity from potential energy in tides. This energy must comes from somewhere and it is confusing to me how all this water gained potential energy if there was no force caused work on it. I could somehow conceive that the concept of potential energy is an "illusion", just like the concept that gravity is a force but then, it seems surprising that we can convert this "illusion" into electricity!
If gravity is not a force, how come it can produce energy? How to make sense of potential energy under the theory of relativity?