Torque ( "Rotational Force" )
Remember, torque is a vector. When we write
r and F are vectors and their "cross product" or "vector product" is also a vector! We determine the direction of the "cross product" or "vector product" by yet another version of the "right hand rule".
Draw a vector r from the axis of rotation to the location of the force F.
To evaluate a cross product such as we must redraw the vectors r and F so they begin at a common origin:
Now rotate the first vector, r, into the second vector, F, using the fingers of your right hand (!). The new vector, tau , now points in the direction of your thumb!
The order is important in a "cross product" or a "vector product".
C = A x B
D = B x A
C = - D
A x B = - B x A
The "cross product" or "vector product" does not commute!
(c) 2002, Doug Davis; all rights reserved
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