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Net external torque

  1. Aug 27, 2015 #1
    My textbook says any torques associated with the internal forces acting in a system of particles are zero and therefore net external torque = total angular momentum/ time

    First of all, what is net external torque? Is it just net torque? Is there a thing called internal torque?
    Second, why is any torques associated with the internal forces acting in a system of particles are zero?

    Thanks!
     
  2. jcsd
  3. Aug 27, 2015 #2
    The torque due to forces exerted by objects outside of the system boundary.

    Yes. Due to forces exerted by objects inside the system boundary.

    This is a consequence of Newton's third law because all action-reaction pairs are equal and opposite. The derivation is straightforward and similar to that of the total internal momentum of a system being zero.

    Edit: for clarity
     
  4. Aug 27, 2015 #3
    Thank you!
     
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