"Though a force, or a resulting sum of forces, may be centripetal, there is not an actual "Centripetal Force" that would appear on an FBD. Since an FBD is a diagram of physical forces at work upon a body, and a centripetal force is not the reaction of some physical object upon another, it would not be proper to show it. You might have a tension force, a weight force, a normal force, electric forces, magnetic forces, or any number of reactions, but actually labeling any of them "centripetal" would be unconventional".
-Yahoo
