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Am I right to conclude this about mass?

  1. May 24, 2009 #1
    When a force applies on a freely moving mass, it opposes the motion, to oppose the motion there should be a force. So we can conclude that if a mass is made to move, it applies a force on the force that applies on it
    If any moving mass is set to motion, without collapsing itself (or breaking), it can be said that the normal reaction given by the mass is equal to the force that applies on it.
  2. jcsd
  3. May 24, 2009 #2


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    Gold Member

    Yes, exactly Newton's Third Law.
  4. May 25, 2009 #3
    You are saying a force on a mass exists if and only if there is an acceleration (in your terms, if "it opposes the motion"). This is Newton's First Law.

    It doesn't make sense to "apply a force on a force". Instead, we should say "apply a force to an object causing that force". As Pengwuino said, this is Newton's third law. I wouldn't say we can "conclude" this is true just because what you said before was true, though.
  5. May 26, 2009 #4
    Ok...thanks a lot people!
  6. May 26, 2009 #5
    Force without motion does no work. A mass M on a table has a downward force Mg, and the table has an equal opposing upward force -Mg, so the two forces balance , and no work is done.
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