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I Newton´s second law: Force definition? (Philosophy matter).

  1. Nov 16, 2017 #1
    Hi people!

    A may be philosophical question, in fact my doubt comes from epistemology class:

    Newton´s second law is a definition of force based on 2 previously defined things: momentum and time or is a relation found by Newton between 3 previously defined things: force; momentum and time?

  2. jcsd
  3. Nov 16, 2017 #2


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    Staff: Mentor

    As I see it, Newton's first law defines force as quantity which is necessary, in the sense of a cause, to change the movement of a body. Newton's second law states, that the change of movement is proportional to the force and of the same direction. So a body and its movement are the two quantities, which are previously defined. We identify body with mass (and volume) in this context and it is simply matter, which might be the philosophical part of it, because it refers to something material. Also movement is taken from real life experiences but is better measurable than body as the ratio between change of location in a period of time. Therefore from an epistemological point of view, we need matter, location and time. For a physicist time is what a clock measures, location what can be pointed at, and matter as mentioned above, something with mass and volume. These are measurable quantities for physicists, and subject to existential questions for philosophers. In this sense Newton used very fundamental concepts which are experienced in every day life to deduce the concept of force.
  4. Nov 16, 2017 #3
    The three laws of motion are Newton's definition of force. This definition was required to avoid confusions with other concepts of force (e.g. from Aristoteles).
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