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Confusing Conceptual Question on Newton's Laws of Motion

  1. Apr 16, 2012 #1
    This conceptual question really got me thinking but I'm not sure how I would explain it:

    Your friend has been studying physics. She tells you that because of Newton's Third Law, she exerts a force on the Earth opposite to the force that it exerts on her. this worries her a lot because she thinks that total force from all of the six billion people on the Earth will eventually push it out of orbit. Is she right - could this happen? Explain your answer using physics principle.

    Many thanks.
  2. jcsd
  3. Apr 16, 2012 #2
    What do you think?
  4. Apr 17, 2012 #3


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    Gravity is symmetric in that the attraction the Earth exerts on you equals the attraction you exert on the Earth. And just as the pushback you get from the ground balances the gravitational attraction on you, the pushback your feet give to the ground balances your gravitational attraction on it.
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