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Homework Help: Newton third law

  1. Nov 3, 2008 #1

    True or False:
    - According to newton third law, the algebraic sum of the forces in the system is equal to zero.

    I think the answer is FALSE because, the third law of newton says that F1 = - F2

    and the " - " is for the direction, so that F1 = F2 in the quantity ==> F1 + F2 [tex]\neq [/tex] 0
  2. jcsd
  3. Nov 3, 2008 #2
    Well, from what i understand from Newton's third law is, any force will have a counter force of the same magnitude in the opposite direction. So, if u add both, it would be zero.. however, i am not sure that is what they are asking..
  4. Nov 3, 2008 #3
    The answer is true.
    If F1 = - F2, the two forces are equal but one is negative
    For example,
    1+ -1 = 0
    At least that is what I think
  5. Dec 9, 2008 #4
    i think its false ,,,
    because each force is acting on seperate body,,
    so we can not find the the algebraic sum of the forces ,,

  6. Dec 9, 2008 #5

    D H

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    Staff Emeritus
    Science Advisor

    This question is impossible to answer without further information on what "the system" means. We have a template that specifically asks for 1. The problem statement, all variables and given/known data. You should have followed the template, UNknown.

    Sure you can. Just add them vectorially. This is a very important concept. The (vectorial) sum of all internal forces must be zero in an isolated system.
  7. Dec 9, 2008 #6
    thank you for the correction ,,,
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