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I Why do we have Newton's first law

  1. May 31, 2017 #1
    Hey guy!
    I know how Newton's first law said but i cant understand why.
    So can you pleas help and tell me why.
    Thank you!
     
  2. jcsd
  3. May 31, 2017 #2

    fresh_42

    Staff: Mentor

    What do you accept as an answer? Newton's first law says, if nothing happens, then everything stays as it is. Shouldn't it be far more questionable, if this was not the case?
     
  4. May 31, 2017 #3
    Why is if nothing happens, then everything stays as it is
     
  5. May 31, 2017 #4

    russ_watters

    User Avatar

    Staff: Mentor

    I don't think science can answer a "why" question, but I don't think I'd want to live in a universe where things happened for no reason!
     
  6. May 31, 2017 #5

    fresh_42

    Staff: Mentor

    Isn't this your daily experience? There is no answer as to "why" questions. Therefore I asked you on which basis you would accept an answer. You have to define first, what is acceptable and what is not. I assume it wouldn't satisfy you if I said: "Because it's how universe is built." So what to use instead as common basis?
    Have a look:

     
  7. May 31, 2017 #6

    jbriggs444

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    Science Advisor

    A pre-Newtonian idea might be that in the absence of external influences, all objects come to rest. Newton's first law says that this is not so. If you look closely, when something comes to rest it is the result of the action of an external force. Remove that force and the object keeps moving.
     
    Last edited: May 31, 2017
  8. May 31, 2017 #7
    As fresh_42 said: "Therefore I asked you on which basis you would accept an answer."

    I think i want a simple but not too simple answer like: "Because it's how universe is built."

    And the video you show me, it was verry useful. Thank!
     
  9. Jun 1, 2017 #8
    Well, most of the "why?" questions sooner or later will end up with that answer...
     
  10. Jun 1, 2017 #9
    Ha! Nice one!
     
  11. Jun 1, 2017 #10

    fresh_42

    Staff: Mentor

    A less "final" answer could be: It is due to observations and the way we describe things like action or motion, or in general the change of states. And every time something changes as @jbriggs444 has mentioned, there can be observed a force: friction, air resistance or a direct push. Removing these forces leads to a static system (in the sense that differentiating along time equals zero). So Newton's laws are careful observations expressed in the physical, resp. mathematical language we use to describe observations.

    Why do we have it? Because that's what scientists do, they observe and try to find a pattern. It might well be that he wasn't the first one to observe these laws, but it happened that the constellation of historic era (at the end of renaissance and the beginning of the age of enlightenment), global context (Europe), human cultural development (Latin as language of science, long enough after Gutenberg) as well as the personal situation of Newton (royal astrologist) allowed him to observe it and write it down and be read by others of his time.
     
  12. Jun 1, 2017 #11
    You picked out the first law only does that mean you understand the second law? If so you can imagine the first law as a special case of the second law:

    When the resultant force (F) is zero the acceleration (a) must be zero. If the object is not accelerating it must be at rest or moving with a constant velocity (moving in a straight line and at steady speed).
     
  13. Jun 1, 2017 #12
    I've been watching The Mechanical Universe lately, and have found it really good. Maybe this episode will interest you.



    It has a lot of historical context that explains where the first law of Newton comes from.
     
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