From: niklas.holsti@tidorum.invalid   
      
   On 2020-10-25 15:39, Alain Fournier wrote:   
   > Le Oct/25/2020 à 08:32, Niklas Holsti a écrit :   
      
   >> The water bulge that forms a lunar high tide, on the Moon-facing side   
   >> of the Earth, would like, geodesically, to stay directly under the   
   >> Moon. The Earth's rotation, and its drag on the water, tries to force   
   >> the water to rotate with the Earth. This displaces the bulge eastwards   
   >> from the sub-lunar point.   
   >   
   > Yes, but the fact that the bulge is eastward from the sub-lunar point   
   > isn't really important here. Even if the bulge was at the sub-lunar   
   > point we would still have tides. The important point is that Earth's   
   > rotation makes the bulge move around Earth. And that is what allows us   
   > to get energy from tidal power generation.   
      
   With the current length of the day, the bulge could be directly at the   
   sub-lunar point only if there were no coupling (friction or other)   
   between the water and the Earth's surface (including any tidal power   
   plants), in which case it would be impossible for the water to slow down   
   the Earth's rotation, and so no energy could be extracted from that   
   rotation via the tides.   
      
   So while the eastward shift of the bulge is not directly involved in the   
   energy flow, it is an unavoidable aspect of the system.   
      
   It is also the eastward shift of the bulge that is accelerating the   
   Moon's orbital velocity.   
      
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