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Homework Help: Action/reaction on superposed masses

  1. Oct 27, 2005 #1
    If two masses are superposed one on the other and my hand is holding supporting them, the force that is applied on the system is equivalent to their weight. So the reaction of those two masses toward my hand is also equivalent to their combined weight. If mass 1 is on my hand, and mass 2 on mass 1, mass 1 transfers an amount of force to mass 2, which is equivalent to its weight. By action reaction this weight also applies on mass 1. Why is it that the reaction of mass 2 is directly transfered to my hand trought mass 1 and not acting directly on it?
  2. jcsd
  3. Oct 28, 2005 #2


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    It's not. The reaction is indirect.
    Mass2 is directly suppported by mass1, which is directly supported by your hand.
    Your hand must supply the reaction that supports both masses, otherwise they will fall to the ground. This reaction acts directly on mass1 since that is the object that your hand is in contact with.
    Mass1 must then supply (directly) a reaction upon mass2, where it is in contact with it, and so prevent mass2 from falling through mass1 !
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