The notations most commonly used on force diagrams to show forces acting on an object include F(G), F(N), F(T), and F(fr). F(G) is the force of gravity or weight. F(N) is normal, or surface, force. F(T) is the force of tension, and F(fr) is the force of friction. The other answers - F(P), F(Z), F(F), and F(D) - are irrelevant or inapplicable to the notations on a diagram about force.
