Force Diagram

The two names are not interchangeable in AP Physics, and the CED keeps them apart on purpose. Both appear as separate bullets on the appendix list of representations used in the course, and Topic 5.3 explains why.

EK 5.3.B.1 states that torques can be described using force diagrams, and EK 5.3.B.1.i adds that they are similar to free-body diagrams and are used to analyze the torques exerted on a rigid system. EK 5.3.B.1.ii carries the distinction: like free-body diagrams, force diagrams represent the relative magnitude and direction of the forces exerted on a rigid system, and force diagrams also depict the location at which those forces are exerted relative to the axis of rotation.

Location is the whole difference. A free-body diagram treats its subject as an object with no size, so EK 2.2.B.3 has every arrow originating from a single dot standing for the center of mass. That is fine for translation, where only the vector sum matters. It is useless for rotation, because $\tau = rF_\perp$ depends on $r$, the distance from the axis to the point of application, and a dot has no $r$.

So the diagram follows the model. Asking how fast the wheel's center moves, draw a free-body diagram. Asking whether the wheel starts spinning, draw a force diagram and put each arrow where the force is really exerted.

The drawing routine transfers over: same forces, same two-object test for whether an arrow is real. Work through it in how to draw a free-body diagram, then apply the geometry in how to calculate torque.