59c738db   
   XPost: sci.math   
   From: relativity@paulba.no   
      
   Den 13.11.2025 13:16, skrev Maciej Woźniak:   
   > On 11/13/2025 12:10 PM, Paul.B.Andersen wrote:   
   >> Den 12.11.2025 22:31, skrev Maciej Woźniak:   
   >>> On 11/12/2025 9:56 PM, Paul.B.Andersen wrote:   
   >>>> Den 12.11.2025 18:13, skrev Maciej Woźniak:   
   >>>>> On 11/11/2025 8:58 PM, Paul.B.Andersen wrote:   
   >>>>>>   
   >>>>>> A force is what makes a mass m accelerate at a. F = ma   
   >>>>>>   
   >>>>>   
   >>>>> "A force is what makes a mass m accelerate at a. F = ma"   
   >>>>> Do you  accelerate on orbit or not?   
   >>>>>   
   >>>> According to Newton, yes.   
   >>>> According to Einstein, no.   
   >>>   
   >>> So, according to your mumbling guru - (the second   
   >>> derivative of  position in time) of an Earth   
   >>> satellite - is 0. Right, poor trash?   
   >>>   
   >>   
   >> According to elementary math:   
   >> The second derivative of the position of the satellite   
   >> in the non-rotating Earth centred frame of reference (ECI)   
   >> is a vector which is pointing towards the centre of the Earth   
   >> with magnitude v²/r, where v is the satellite's orbital speed   
   >> and r is the radius of the orbit.   
      
   I will elaborate on this (there may be lurkers):   
   In NM accelerations is not generally the second derivative of   
   the position, it is the derivative of the velocity.   
      
   That is because the position function P(t,x,y,z) is frame   
   dependent. So the function P(t,x,y,z) will be different   
   in different inertial frames.   
   The velocity is also frame dependent, but the derivative   
   of the velocity is the same in all frames.   
      
   >   
   > So, is it 0 or isn't it 0 according to   
   > your moronic religion?   
      
   Why are you asking questions which are answered in the post   
   you are responding to?   
   >>   
   >> According to Newton this is the centripetal acceleration   
   >> of the satellite, a = v²/r.   
      
   In this case, the position function _in the ECI frame_ is   
   a circle, and its derivative is a velocity vector with   
   constant magnitude and direction perpendicular to the position   
   function, as explained above.   
      
   >>   
   >> But according to Einstein the proper acceleration of the satellite   
   >> is a = F/m where m is the mass of the satellite and F is the force   
   >> acting on it. Since no force is acting on an object in free-fall,   
   >> the proper acceleration of the satellite is zero.   
   >   
   >   
   > If dv/dt is not 0 (or is it?) and "proper acceleration"   
   > of relativistic idiots is 0 - i guess acceleration   
   > is no longer dv/dt for relativistic idiots. Is it?   
      
   No, it isn't dv/dt.   
      
   I will elaborate.   
   In SR/GR "proper acceleration" is the acceleration measured   
   in the rest frame. So there is no velocity to derivate,   
   and the proper acceleration is as explained above.   
      
   In GR, the acceleration is what an accelerometer shows.   
   An accelerometer in free-fall  will show zero acceleration,   
   an accelerometer on the ground will show 9.81 m/s² acceleration   
   upwards.   
      
   Do you think the accelerometer shows this because GR says so,   
   or do you think it has something to do with laws of nature?   
      
   >   
   > Well, since a mumbling idiot postulated that   
   > shark must eat grass, because that's what   
   > "Laws of Nature" are - no wonder that a sheep   
   > became a "shark".   
   >   
      
   Yes, I know.   
   You understand nothing, and can't respond   
   with anything but nonsense.   
   --   
   Paul   
      
   https://paulba.no/   
      
   --- SoupGate-Win32 v1.05   
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