From: mikko.levanto@iki.fi   
      
   On 2025-06-04 23:27:28 +0000, Luigi Fortunati said:   
      
   > Mikko il 01/06/2025 20:06:05 ha scritto:   
   >> On 2025-06-01 08:10:52 +0000, Luigi Fortunati said:   
   >>   
   >>> Is the equality between action and reaction based exclusively on the   
   >>> third law formulated by Newton and considered so obvious that it never   
   >>> needed any experiment to confirm it, or has some experiment actually   
   >>> been carried out?   
   >>   
   >> Newton based the low on experiments performed before he wrote the   
   >> Principia. Later experiments have not found any deviation from the   
   >> law.   
   >   
   > What are these experiments on which Newton based his third law and what   
   > are the subsequent ones?   
      
   The primary topic of Newton's Pricipia is celestial mechanics. Newton's   
   laws reproduce Kepler's laws in the two body problem. They also reproduce   
   the observed deviations from Kepler's laws, most important of which is   
   the deviation in Saturn's orbit near the conjunction with Jupiter.   
      
   Observed collisions had not shown any deviation from Newton's laws.   
   However, the observations were not as accurate as the observations   
   of the planets.   
      
   >> The equality of action and reaction can be inferred from the law of   
   >> conservation of momentum, which is also confirmed by all experiment.   
   >   
   > I aborted 27 answers before giving birth to this one, the substance was   
   > always the same but one was too verbose, the other with too many   
   > numbers and too many equations, the other too complicated and so on.   
   >   
   > I also wanted to do this one again from scratch but I said "enough   
   > now!".   
   >   
   > Well then, it is absolutely true that the conservation of momentum is   
   > confirmed by all experiments but it is not at all true that from it one   
   > can deduce the equality between action and reaction.   
      
   The equality of action and reaction means that the sum of all forces   
   in an isolated system (i.e., one with no external interactions) is   
   zero.   
      
   The conservation of momentum means that the sum of momenta in an isolated   
   system is constant in time. The time derivative of a momentum is a force.   
   The time derivative of the sum of the momenta on an isloated system is   
   zero so the sum of the forces is zero. For a two body system this means   
   that the sum of the action force and the reaction force is zero, i.e.,   
   the forces are equal in magnitude and opposite in direction.   
      
   --   
   Mikko   
      
   --- SoupGate-Win32 v1.05   
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