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Which law of motion accounts for seatbelts

  1. Feb 5, 2016 #1
    1. The problem statement, all variables and
    given/known data

    What would the best choice be:Newton's Law 1 or 2 or 3. Wearing a seatbelt and when it stops.
    2. Relevant equations

    3. The attempt at a solution
    I thought the best choice would be 3 because for every action there's a reaction. I don't know any responses that fit to Newton's Law 1. I don't think it's Law 1 because objects tend to stay in motion/rest unless acted by external force, and there was an unbalanced force that caused change - or does it also imply that if an unbalance force is exerted it fits Newton's Law 1? The seat belt causes an external force and Law 1 states that the net force would be 0

    One more question why would this be Newton's 1st law?
    "a frog leaping upward off his lily pad is pulled downward by gravity and lands on another lily pad instead of contiuing on in a straight line"
    I'm confused about if an object were to stop would it be considered Newton's 1st law
    Last edited: Feb 5, 2016
  2. jcsd
  3. Feb 5, 2016 #2


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    First answer this: why do you wear a seatbelt?
  4. Feb 5, 2016 #3
    In your analysis, I don't see any consideration of Newton's 2nd law. Is your body decelerating? Is the seat belt exerting a force on your body? Have you drawn a free body diagram of your body during the time the seat belt force is acting on it?
  5. Feb 5, 2016 #4
    The seat belt exerts a force to stop the person from going forward.

    If there is an acceleration/deceleration does it mean that it isn't Newton's 1st law?
  6. Feb 5, 2016 #5


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    So, you get into your car, you fasten your seat belt and the seat belt "stops you going forward"? Really? Is that why you wear a seat belt? It's not why I wear one!
  7. Feb 5, 2016 #6


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    What's wrong with going forward?
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