Students must label the forces they draw in their force diagrams on the back side of the assignment, but the amount of labeling can be decided by the teacher. Some labels such as FN for the normal force and Fg for gravity are typical, but there are variations such as N for the normal force or W for the weight of the object, which is the force of gravity acting on the object. The important thing is that the students and teacher agree on a set of standard force labels so that they can communicate clearly with each other.
Some teachers require students to use “agent-object” notation or “on what by what” notation that describes what object the force acts on and what other object applies that force. The answer key shows this extra notation. The level of detail depends on what the students are ready for and what they need.