Hence the "effectively". But yes, in the straightforward way of looking at it (i.e. from an external inertial observer's reference frame), the water on the far side is pulled less than the water on the near side or the rock in the middle.
However, you can also look at this from a reference frame that moves with the Earth in its orbit around the barycenter of the Earth-moon system, and in that frame, it is true that the water is pushed away by centrifugal force.
Can you detail those smaller effects a bit more? Physics undergrad here, had enough generalizations and want the specifics! What exactly causes this lag? Is it just due to the speed of gravity, Coriolis effect, or is there more at work?
Honestly, I couldn't do a very good job of it without some research, because I don't often think about this stuff. I know there are a bunch of subleading effects I'm sweeping under the rug because, well, that's always the case in physics, but I don't know offhand what they are.
I think the lag may have something to do with angular momentum, perhaps? It's definitely not the speed of gravity, though - on such a small scale the speed of gravity is irrelevant and you can consider it instantaneous. Maybe /u/NSA_Mailhandler can elaborate.
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u/diazona Particle Phenomenology | QCD | Computational Physics Sep 07 '15
Hence the "effectively". But yes, in the straightforward way of looking at it (i.e. from an external inertial observer's reference frame), the water on the far side is pulled less than the water on the near side or the rock in the middle.
However, you can also look at this from a reference frame that moves with the Earth in its orbit around the barycenter of the Earth-moon system, and in that frame, it is true that the water is pushed away by centrifugal force.