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  • The spring

    From Luigi Fortunati@fortunati.luigi@gmail.com to sci.physics.research on Thu Apr 17 09:40:06 2025
    From Newsgroup: sci.physics.research

    The spring AB is a body.

    If I exert the force F on the end A, the spring accelerates according
    to Newton's second law F=ma and contracts with respect to its length at
    rest.

    Why is there this contraction if there is no opposing force on the
    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 contract
    (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]]
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  • From Luigi Fortunati@fortunati.luigi@gmail.com to sci.physics.research on Sat Apr 19 23:53:40 2025
    From Newsgroup: sci.physics.research

    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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