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Homework Help: If there's a book resting a a table, (newton's third law concept)

  1. Apr 19, 2009 #1
    1. The problem statement, all variables and given/known data
    would you say that "the two forces exerted on the book ar ethe normal force directed up and the weight of the book directed down. These are equal and opposite to one another. By newton's third law they are a third law force pair, so the normal force is always equal to the weight of the book."

    3. The attempt at a solution

    I said disagree, since the normal force is exerted by the table, not the book, and the rest of the concept seems right.


  2. jcsd
  3. Apr 19, 2009 #2
    You are correct to disagree. What if the table were inclined? Would the normal force on the book equal the weight mg?
    Last edited: Apr 19, 2009
  4. Apr 19, 2009 #3
    "They are a third law force pair"
    They're not...
    both forces exerted on the same body, the reaction force of mg(aka weight) is the force the body exerts on Earth.
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