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Question about gravity and forces acted upon

  1. Jun 21, 2017 #1
    1. The problem statement, all variables and given/known data


    My professor said that since gravity pushes down any object on earth, the objects themselves push up against earth. Intuitively this is difficult too grasp, can anyone give an example or anything to help me out. Thank you
     
    Last edited by a moderator: Jun 21, 2017
  2. jcsd
  3. Jun 21, 2017 #2
    This is Netwons's Third Law, two object exert force on each other in equal magnitudes but in opposite directions.
    http://hyperphysics.phy-astr.gsu.edu/hbase/Newt.html
    So try to think this way and consider their masses and due to force their accelerations.You ll see that it makes sense.
     
  4. Jun 22, 2017 #3
    I figure it would be a bit clearer if said as: "earth's gravity pulls down any object and if the object is stopped from falling because it is resting on the surface, or something else supported by the surface, that's what is pushing up against the object, with an equal and opposite force. Although perhaps he also meant, a bit counter-intuitively, that looking up from the object's point of view, since the pull of gravity goes both ways, the gravity of the object is also pulling the earth down. In any case, I'd make a case for there being a bit of ambiguity there.
     
  5. Jun 23, 2017 #4

    haruspex

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    That might be a bit confusing. I guess you mean "down" from the point of view of the object's gravitational field, i.e. up towards the object in terms of normal up and down.
     
  6. Jun 23, 2017 #5
    Yes, that's what I was saying. Just speculating if there were even some unlikely ambiguity in the original statement.
     
  7. Jun 25, 2017 #6
    Thank you everyone!
     
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