From: alain245@videotron.ca   
      
   On Oct/25/2020 at 12:02, Niklas Holsti wrote :   
   > 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.   
      
   You have a circular argument here. If there were no coupling between the   
   water and Earth's surface, as you say the bulge would be directly at the   
   sub-lunar point. But that doesn't mean that you couldn't extract energy   
   from the tides. It means that if you install tidal power generation   
   equipment in such a hypothetical situation then you would create a   
   friction between Earth and the water, and you would thus slow down   
   Earth's rotation.   
      
   > 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.   
      
   Yes.   
      
      
   Alain Fournier   
      
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