The document discusses free-body diagrams and calculating net force. It provides 11 examples of diagrams with forces acting on an object, and in each case the net force is equal to the sum of the horizontal and vertical forces. For example, in one case there are forces of 120 N and 100 N acting, so the net force is 120 - 100 = 20 N. In another, forces of 30 N and 80 N give a net force of 30 - 80 = -50 N. The document uses free-body diagrams to illustrate calculating net force from individual forces.