I understand voltage and current (although looking back, I should have worded my original post better). But I still don't really understand how to think about ground.
To continue with the common water analogy (assuming DC), I get that the water has high voltage at the top of the waterfall. And I get the resistance/rocks. I also understand the current/volume of water flowing down the waterfall. But once the water empties into the pool, it can't just pile up there forever, right? It eventually has to go somewhere or the water level will rise, and it can't rise indefinitely, can it?
Where does the water go? And when it goes, there will be current, right? And you can't have current with zero voltage, can you? I mean, if the water is flowing, then it has to have some energy, even if it is moving very, very, very slowly, doesn't it? Is the point just that the voltage is so minimal it is irrelevant, or is it actually zero?
If we switch over to AC and use the pipe analogy, instead of a waterfall, I think of it as a large pool of water (ground)connected by a pipe (hot/signal wire) to a pump (amp). The pump alternately pumps water through the pipe and into the pool and sucks it out. Over time, the net effect on the volume of water in the pool is zero. Within the pipe, when the pump is actually pushing or sucking (as opposed to the moment when it is switching over from one to the other), the pressure (voltage) is high and there is current.
So far (I think) so good. But I'm having trouble with the idea that there is no effect on the large pool of water (ground) at any given instant (as opposed to over time) when the pump is actively pushing or sucking. Even if the pump and the pipe are moving small amounts of water relative to the pool, there will be some effect on the pool, right? When the pump is sucking, for example, it has to pull some water from the pool into the tube, doesn't it? Won't that create some minimal amount of current and voltage in the pool?
Or do I just need to give up on this water analogy?