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Homework Help: Newton’s Third Law Question

  1. Jul 22, 2011 #1
    I was just wondering if, according to Newton’s Third Law, every action force has an equal reaction force that acts in the opposite direction, why do these forces not just cancel each other out, resulting in no net force and therefore no motion?
  2. jcsd
  3. Jul 22, 2011 #2
    Because the two forces act on two different objects, not on the same object. For example, an object on the ground has the force of gravity acting downward, and the norrmal force acting upward. There is also the gravitational force of the object on the earth as well, but this is the force on the earth, not the object

    These result in 0 net force on the object. But that same object in the air only has the force of gravity acting upon it, resulting in change in velocity.
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