The Definition of a Moment

Consider a force located a distance from the origin of a rectangular coordinate system (Fig. 1); is measured in the plane of the force and the point , perpendicular to the line of action of . The moment of about the point , or about the axis through normal to the plane of and , is defined as the vector , whose magnitude is , whose direction is the line , normal to the plane of and , and whose sense is the direction of advance of a right-handed screw rotated by the force . This rule for sense may also be stated by saying that if one looks in the direction of , will appear to turn clockwise around .