I don't like the statement that "the FCW is what the makes the pen move." It might make the student think that the forces on the aircraft are unbalanced in a constant speed glide.
The aircraft is moving because it's moving, and Newton's first law says it's going to keep on moving unless a force acts to change its motion. Yes, there is a component of weight in the direction of the aircraft's motion, but that force is exactly balanced by drag and the component of lift acting in the opposite direction.