From: fortunati.luigi@gmail.com   
      
   Luigi Fortunati il 17/04/2025 04:40:06 ha scritto:   
   > The spring AB is a body.   
   >   
   > If I exert the force F on the end A, the spring accelerates according=20   
   > to Newton's second law F=3Dma and contracts with respect to its length =   
   at=20   
   > rest.   
   >   
   > Why is there this contraction if there is no opposing force on the=20   
   > other side of the spring?   
   >   
   > Or perhaps, there is an opposing force?   
   >   
   > Luigi Fortunati   
   >   
   > [[Mod. note -- There are two possibilities:   
   >   
   > If the spring is *massless* (obviously this is an idealization, but it'=   
   s   
   > a useful case for conceptual purposes), then the spring doesn't contrac=   
   t   
   > (it just accelerates as a rigid body), since as you notes thereis no   
   > opposing force on the other side of the spring.   
   >   
   > If the spring has *nonzero mass*, then the inertia of the various parts   
   > of the spring provides the opposing force.  To work this out in detail   
   > we'd need to write out equations of motion (Newton's 2nd law + Hooke's =   
   law)   
   > for the individual parts of the spring, then solve these equations.   
   > -- jt]]   
      
   Against whom is this opposing force of the spring with mass directed?   
      
   Is it directed only against me who am pushing it or is it also directed=20   
   against the spring itself?   
      
   If it is directed *only* against me, why does the spring compress?   
      
   Luigi.   
      
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