Torque ( "Rotational Force" )
Remember, torque is a vector. When we write
or
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".
D = B x A
C = - D
A x B = - B x A
The "cross product" or "vector product" does not commute!
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