When learning the chapter of "circle", it is difficult for students to understand the concept because of the complex relationship among chord, arc, central angle and chord distance. The author made 1 teaching aid from discarded instant noodle barrels and thumbtacks, and named it "circular dynamic demonstrator". Manufacturing method: the bottom of one flour bucket faces upwards, the side of the other flour bucket is cut into strips with scissors to make two central angles, two chords and the center distance between the two chords, and the circular surface at the bottom is cut into two circular arcs and colored; Then fix it in the center of the bottom of the flour barrel with a thumbtack, which is also a rotating shaft. When demonstrating, as long as the rotating shaft rotates one of the two groups of quantities from the initial position (non-coincidence) to coincidence, we can draw a conclusion through observation: in the same circle or the same circle, when the two central angles are equal, the distances between chords, arcs and chords are equal, and the dynamic demonstration is intuitive and vivid, which can stimulate students' interest in learning and improve students' learning efficiency.