LogFAQs > #896711796

Gravity is always going to act on the center of mass, yes.

"Radius vector" probably isn't the standard name. The standard way to write torque though is as the cross product of F and r (both vectors), where F represents the force vector, and r is a displacement vector which points from the point of rotation to the point at which the force is acting. Taking the vector jargon out of that the scalar form is going to just be F*r*sin(theta), where F=mg and r=length/2.

(Again, the reason r=length/2 is because gravity is acting at the middle (center of mass) of te rod, and the pivot point is the end of the rod.)
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