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What happen if the normal reaction force is less than zero ?

  1. Jul 1, 2015 #1
    1. The problem statement, all variables and given/known data
    why the object will fall of when the normal reaction force is less than zero ? P/s : the normal reaction force is in downward direction...
    How if if the normal reaction force is less than zero ? the normal reaction is in upward direction ?

    2. Relevant equations


    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Jul 1, 2015 #2

    andrevdh

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    The track can only push the object away, not pull it towards it.
     
  4. Jul 1, 2015 #3
    I still don't understand why when the normal reaction force is less than zero , the object will lose contact with the track ?
     
  5. Jul 1, 2015 #4

    andrevdh

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    N is the normal reaction force from the track.
    If the object is not pushing against the track
    then it lost contact with it!
    Which means it is falling.
    So if N is upwards, or negative, which is impossible
    since it cannot pull the object towards it, then the object
    is falling. In the limiting case where it as the ppoint of leaving the
    track N = 0. At this point it is "floating" and wants to leave the track
    or at the point of falling since the only force on it is gravity or its weight.
     
  6. Jul 1, 2015 #5
    If the object is pushing against the track ,the object will surely losing contact with the track right , the object would fall of ?
     
  7. Jul 1, 2015 #6

    andrevdh

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    No, if the object is pushing against the track then it means it is supported by the track.
    Just like if you stand on the floor you push against it and it supports you with the normal force.
     
  8. Jul 1, 2015 #7
    Ok, I think I can understand it....
     
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