From: tjroberts137@sbcglobal.net   
      
   On 5/18/21 8:06 AM, Luigi Fortunati wrote:   
   > [...]   
      
   This depends on what model you use for gravitation. Today the two most   
   common models are Newtonian mechanics (NM) and General Relativity (GR)   
   -- I'll answer for both.   
      
   I presume the man is inside the elevator, nominally standing on its   
   floor, in a building built on the surface of the earth (I stipulate this   
   last so I can distinguiah between a floor of the building and the floor   
   of the elevator).   
      
   Here the elevator is held stopped at some floor of the building.   
      
   > It is correct to say that in the elevator stopped at the floor   
   > (1) an electromagnetic force acts between the man and the elevator   
      
   NM: yes, the elevator floor pushes up on his feet.   
   GR: yes, the elevator floor pushes up on his feet.   
      
   > (2) a gravitational force acts between the Earth and man   
      
   NM: yes, this force is equal and opposite to (1)   
   GR: no, there is no gravitational force, the man is diverted from his   
   geodesic path by the EM force of (1).   
      
   > (3) a gravitational force acts between the Earth and the elevator   
      
   NM: yes, it is equal and opposite to the force on the elevator exerted   
   by the mechanism holding the elevator stopped at the floor of the   
   building.   
   GR: no, there is no gravitational force, the elevator is diverted from   
   its geodesic path by the force from the mechanism holding the elevator   
   stopped at the floor of the building.   
      
   > (3) no gravitational force acts between the elevator and the man?   
      
   NM: no, there is a force, but it is unmeasurably small [#]   
   GR: yes, there is no gravitational force   
      
   [#] if the elevator is appropriately constructed, this minuscule force   
   could be arranged to cancel to zero.   
      
   Now we consider the elevator in free fall.   
      
   > It is correct to say that in the elevator in free fall   
   > (1) a gravitational force acts between the Earth and man   
      
   NM: yes, this force accelerates the elevator down   
   GR: no, there is no gravitational force, the man follows his geodesic   
   path.   
      
   > (2) a gravitational force acts between the Earth and the elevator   
      
   NM: yes   
   GR: no, there is no gravitational force, the elevator follows its   
   geodesic path.   
      
   > (3) no gravitational force acts between the elevator and the man.   
      
   NM: no, there is a force, but it is unmeasurably small [#]   
   GR: yes, there is no gravitational force, both follow their geodesic   
   paths.   
      
   > (4) no electromagnetic force acts between the elevator and the man?   
      
   NM: yes   
   GR: yes   
      
   Note in all cases, in GR the geodesic paths are accelerating downward at   
   9.8 m/s^2.   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)