OK, so my basic understanding is that GR is all about geometry of space-time. It's all geometry, no other mechanism. This explains why objects change direction due to gravity. But why does the speed increase? How does pure geometry cause a change in speed? Also, where does this kinetic energy come from? I know people will talk about potential energy, but that's just a hand-waving mathematical trick to balance equations. What does geometry have to do with potential energy?