imagine a man made canal many km wide and many km deep running the full length of one hemisphere at the equator. let one end of the canal be represented at the origin and the other at x=2π. the strength of gravity at any point due to the earth plus tidal forces of the moon should equal a constant plus (I assume) a full sine wave. given enough time the surface of the water should form a sine wave. but as the moon moves across the sky the sine wave representing the force of gravity should move in one direction (at a speed less than the speed of sound in water). if the canal formed a full circle all the way around the earth then the water would simply follow this sine wave. but because it only stretches across one hemisphere its obvious that the water cant possibly follow the sine wave. so what does the water do. how would I solve this? edit:actually maybe it would just follow the sine wave. the water at each point just moves back and forth so I guess it could.