A common example of a screw is the wrench associated with a force acting on a rigid body. Let P be the point of application of the force F and let P be the vector locating this point in a fixed frame. The wrench W = (F, P × F) is a screw. The resultant force and moment obtained from all the forces F i, i = 1,..., n, acting on a rigid body is simply the sum of the individual wrenches W i, that is