From: tjroberts137@sbcglobal.net   
      
   On 7/7/18 8:35 PM, Ed Lake wrote:   
   > [... much silliness omitted] A stone dropped from a moving train cannot drop   
   > straight down because inertia will cause it to move with the train until   
   > gravity stops it.   
      
   You repeatedly omit important information in your descriptions. Here you   
   omitted   
   WHO is doing the observing. To the train observer, the stone DOES drop straight   
   down [#]; to the embankment observer it does not. BOTH are correct (in that   
   this   
   is indeed what they observe). BOTH are consistent with the laws of physics (how   
   could they not???).   
      
   	(And, of course, "gravity" does not stop it, the floor of   
   	 the train stops its fall.)   
      
   	[#] Ignoring the distance the train moves during the fall   
   	compared to the radius of the earth; I also omit many details.   
      
   > The observation that the stone fell straight down was "incorrect" because it   
   > was inconsistent with the laws of physics.   
      
   Not true (ignoring your OUTRAGEOUS AND UNUSUAL meaning of "incorrect"). The   
   train observer's observation that the stone fell straight down is fully   
   consistent with the laws of physics. You clearly do not know what those laws   
   ACTUALLY are.   
      
   	Hint: If an observation is inconsistent with the "laws of   
   	physics", then those "laws" MUST BE WRONG. After all, that   
   	is what science is.   
      
   Here are two different DESCRIPTIONS of a single fall of the stone, by two   
   observers using two different inertial frames and Newtonian mechanics; they   
   apply THE SAME law of physics (F=ma). Both begin when the stone is dropped [#]:   
      
   Embankment observer: The force of gravity F points straight down, and I apply   
   F=ma to the stone with mass m; the initial condition is the stone's initial   
   velocity in the train's forward direction relative to my embankment frame, and   
   the trajectory is a parabolic fall relative to my embankment frame (constant   
   horizontal velocity, accelerating downward).   
      
   Train observer: The force of gravity F points straight down, and I apply F=ma   
   to   
   the stone with mass m; the initial condition is the stone's initial velocity of   
   zero relative to my train frame, and the trajectory is a fall straight down   
   relative to my train frame (zero horizontal velocity, accelerating downward).   
      
   	Newton's second law, F=ma, is a differential equation that   
   	can be solved for the position of an object in terms of an   
   	inertial frame's coordinates. Applying this equation requires   
   	initial conditions, which must of course be expressed in terms   
   	of the frame used. It applies to ANY inertial frame within the   
   	domain of Newtonian mechanics (e.g. NOT to Einstein's thought   
   	experiments).   
      
   [This has wandered very far from Einstein's thought experiments, and it is   
   useless to continue until you improve the precision of your thinking and   
   writing, and also learn some very basic physics. Goodbye.]   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)