From: fortunati.luigi@gmail.com   
      
   Richard Livingston il 22/02/2023 09:10:09 ha scritto:   
   >>>> What is the difference between the force accelerating the mass (F=ma)   
   >>>> and the force deforming the mass (Hooke)?   
   >>>   
   >>> It's the same force, but applied to two different systems.   
   >>>   
   >>> One system is a point of mass "m" that is not held in position.   
   >>> When we call "F" the force acting on it, then the acceleration   
   >>> of the point is "a".   
   >> I had never heard this one: does F=ma only apply to material points and   
   >> not to bodies?   
   > ...   
   >   
   > You are making this more complex than it needs to be.  Rather than thinking   
   > of two different kinds of force, you need to model the objects (masses).   
   > F=ma is best thought of as applying to point or rigid masses.  If the   
   > situation  requires modeling elasticity of the object, then it is modeled as   
   > an array of point masses with springs (and maybe dampers) between the point   
   > masses.   
   >   
   > Many situations do not require such detailed models of the objects, such as   
   > planets orbiting outside the Roche limit.  However if you are impacting such   
   > a planet with a rock, then you need the elastic model I just described.   
   >   
   > One place where a slightly different model is required is a planet inside the   
   > Roche limit, or when calculating tidal forces.  Then the gravitational   
   > "force" must be applied to each point mass in the elastic model.  As this   
   > "force" will be different for each point, those differences in gravitational   
   > "force" will result is elastic deformation of the body.   
   >   
   > Rich L.   
      
   Ok fine.   
      
   But all this has nothing to do with the question of whether force is   
   relative or absolute.   
      
   I would like to know, for example, why on earth I should specify the   
   "frame of reference" of the force of my weight on the floor if I am   
   always 80 kg-weight whatever the reference.   
      
   This is what interests me to clarify: if the force is not a motion, why   
   should it vary if I observe it from another reference?   
      
   And then, why should I "observe" the force if the force is not an   
   observable quantity?   
      
   There is no "speed" of force, only the "strength" of force.   
      
   I put a dynamometer on it, measure it and that's it!   
      
   Luigi.   
      
   [[Mod. note --   
   It's important not to confuse *weight* and *mass*.  Your *mass* is always   
   the same, but your *weight* is different between [for example] (a) you're   
   standing on a floor attached to the Earth's surface), (b) you're standing   
   on the floor of an Einstein elevator which is current accelerating upwards   
   with respect to the Earth's surface, and (c) you're standing on the floor   
   of a space station in a free-fall orbit.   
   -- jt]]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)