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  • Re: Newton's Third Law and Inertia

    From Mikko@21:1/5 to Luigi Fortunati on Sun Apr 6 11:50:11 2025
    On 2025-04-05 20:31:24 +0000, Luigi Fortunati said:

    Newton's third law says that if body A exerts a force on body B, body B reacts with an equal and opposite force against body A.

    Newton, speaking of inertia, says: "A body exerts this force [inertia]
    only, when another force, impressed upon it, endeavors to change its condition".

    It seems that he is talking about exactly the same forces.

    If not, what differences are there between the two?

    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.

    --
    Mikko

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  • From Mikko@21:1/5 to Luigi Fortunati on Tue Apr 8 11:27:48 2025
    On 2025-04-07 12:26:37 +0000, Luigi Fortunati said:

    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

    That does not make sense. In the midern language the word "force" has
    a wide variety of different meanings. It had most of these meanings
    already in 1729 when Motte translated Principia in English. However,
    one important meaning is newer: a quantity in physics. As Newton did
    not define the term before its use in the definition of "vis insita"
    it must be intepreted according to its meaning in ordinary English of
    the year 1729, or one must interprete the original Latin text according
    to the common Latin meanings of the year 1726 when the 3rd edition of
    Principia was published.

    --
    Mikko

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