Four rods are included: The first set (taken from the demonstration B1-17: CENTER OF MASS - STICKS) includes a uniform wooden rod and a second rod with a weight at one end. The second set are two rods with the same mass, one weighted at the center and one weighted at both ends.
The student is asked to determine the difference between the rods. The difference between the first set is readily apparent, but determining the difference between the second set requires some experimenting. One way to "feel" the difference between the two latter rods is to hold each at the center and rotate your wrist back and forth. The large moment of inertia of the rod with weighted ends makes rotation of your wrist rather difficult compared with the rod weighted at the center.