From: fortunati.luigi@gmail.com   
      
   Mikko il 06/04/2025 13:50:11 ha scritto:   
   > Newton's language and the language of Motte's translation are archaic.   
   > Current language is cleared but it was developed much later.   
   >   
   > Inertia is not a force. It is a phenomenon. Force is a number or vector   
   > that quantifies an interaction.   
      
   Newton, with his archaic language, when he wrote "force" meant force   
   and, explaining inertia, he repeats it nine times (I have highlighted   
   them below):   
   "The vis insita, or innate *force* of matter, is a power of resisting,   
   by which every body, as much as it lies, endeavors to persevere in its   
   present state, whether it be of rest, or of moving uniformly forward in   
   a right line. This *force* is proportional to the body whose *force* it   
   is; and differs nothing from the inactivity of the mass, but in our   
   manner of conceiving it. A body, from the inactivity of matter, is not   
   without difficulty put out of its state of rest or motion. Upon which   
   account, this vis insita, may, by a most significant name, be called   
   vis inertiae, or *force* of inactivity. But a body exerts this *force*   
   only, when another *force*, impressed upon it, endeavors to change its   
   condition; and the exercise of this *force* may be considered both as   
   resistance and impulse; it is resistance, in so far as the body, for   
   maintaining its present state, withstands the *force* impressed; it is   
   impulse, in so far as the body, by not easily giving way to the   
   impressed *force* of another, endeavors, to change the state of that   
   another. Resistance is usually ascribed to bodies at rest, and impulse   
   to those in motion; but motion and rest, as commonly conceived, are   
   only relatively distinguished; nor are these bodies always truly at   
   rest, which commonly are taken to be so".   
      
   Was Newton wrong to talk about force? Was he wrong to say that inertia   
   is a force?   
      
   First of all, he doesn't say that inertia is *always* a force but it is   
   "*only* when another *force*, impressed on a body, endeavors to change   
   its condition".   
      
   I point out that this is the exact definition of the third law and he   
   explains it even better in the following when he writes that: inertia   
   "is resistance, in so far as the body, for maintaining its present   
   state, withstands the *force* impressed; it is impulse, in so far as   
   the body, by not easily giving way to the impressed *force* of another,   
   endeavors, to change the state of that another".   
      
   Here there is the inertia of both bodies that act and react   
   reciprocally.   
      
   So, the inertia of the two bodies A and B that are approaching is NOT   
   force but becomes force (as Newton says) *only* when body A tries to   
   change the condition of body B and body B tries to change the condition   
   of body A!   
      
   That is, inertia becomes force *only* when the two bodies come into   
   contact and not before or after.   
      
   Only during.   
      
   Luigi Fortunati   
      
   --- SoupGate-DOS v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)