From: tjoberts137@sbcglobal.net   
      
   On 3/15/24 3:11 AM, Luigi Fortunati wrote:   
   > In free fall, can you go anywhere freely or are there constraints   
   > that prevent this? Of course you can't fall straight up and you   
   > can't fall sideways.   
      
   As I keep saying, this depends on the meanings of the words you use.   
   Your wishy-washy words are a major part of your failure to   
   understand very basic physics.   
      
   If by the "direction of fall" you mean the 3-velocity relative to   
   ground-based coordinates, that can be pointed in any direction. If you   
   mean the 3-acceleration relative to ground-based coordinates, that can   
   only be pointed straight down. Note the former is the usual meaning for   
   "direction" of any motion, including falling.   
      
   Hint: throw a ball straight up. It is moving upward, it is going upward,   
   and its 3-velocity (relative to ground-based coordinates) is directed   
   upward. It is, of course, in free fall (neglecting air resistance). So   
   one COULD say "it is falling upward", but that is such poor terminology   
   that no physicist would way that.   
      
   > In free fall you can only go in one direction (the vertical one) and   
   > in only one versus (downward).   
      
   This is just plain not true (here you use words with more definite   
   meanings). You can be GOING up or sideways -- that depends on the   
   initial conditions of your trajectory. Because "going" explicitly refers   
   to velocity, not acceleration. Your acceleration (relative to   
   ground-based coordinates) is always downward.   
      
   > The elevator (in free fall) and everything inside it are forced to   
   > fall (always) vertically and (always) downwards.   
      
   Nope. See above.   
      
   > So there is a constraint.   
      
   There is a constraint on the 3-acceleration (relative to ground-based   
   coordinates): downward. There is no constraint on the direction of   
   3-velocity (relative to ground-based coordinates), because this depends   
   on the initial conditions; of course its direction will point   
   increasingly downward as time goes on.   
      
   > And, in free fall, can one move in a straight and uniform motion?   
      
   Yes, RELATIVE TO COORDINATES ACCELERATING DOWNWARD WITH YOU. No,   
   relative to ground-based coordinates.   
      
        [This opens the door to the "local vs. global"   
         distinction in GR. You have no hope of appreciating   
         the subtleties involved until you STUDY.]   
      
   > No, in free fall the motion is always accelerated.   
      
   Again, this depends on what you mean by those words. In Newtonian   
   mechanics this is true. But we live in a post-GR world, and presuming   
   Newtonian mechanics is not appropriate. In GR, of course, an object in   
   free fall follows a geodesic through spacetime, with ZERO proper   
   acceleration.   
      
   > So why call it "free fall" and not "forced fall"?   
      
   Because as the moderator said, it means that no NON-GRAVITATIONAL force   
   acts on the object. "It's a statement about what forces are (not) acting   
   on the body, not about the uniqueness or non-uniqueness of the resulting   
   motion."   
      
   As I keep telling you, your approach of making false statements in this   
   newsgroup is utterly failing to teach you basic physics. You MUST get   
   some good textbooks and STUDY. Better yet, take a college or university   
   course in physics so you'll have an instructor with whom to discuss your   
   confusions.   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)