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General direction of torque

  1. Oct 26, 2012 #1
    My book defines the general formula for torque as:

    n.(r×F), where . means dot product, n is a unit vector along the line about which you are taking the torque, F is the force acting at some point, and r is the vector from the line to the point at which the force acts. So I know that when the line about which you are taking the torque is perpendicular to r, then the torque is defined as r×F, so it has a direction perpendicular to r and F.

    However, what would be the direction of the torque if n is not perpendicular to r? n.(r×F) does not reveal the direction since it is just a scalar. Would the direction still be just r×F in this general case?
  2. jcsd
  3. Oct 26, 2012 #2
    nvm i think i just answered my question....if you just consider the torque about each axis then its obvious that the direction of the torque is just the direction of r×F
  4. Oct 27, 2012 #3


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    Science Advisor
    Homework Helper

    Hi Aziza! :smile:

    Yes, what your book defines as the torque about an axis is really the component of the torque along that axis. :wink:
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