Purpose: To illustrate that rotational inertia (moment of inertia) depends not only on the mass of an object but also on the mass distribution relative to the axis of rotation.

A Plexiglas tube equipped with weights that can be located anywhere between the center of the tube and the two ends. Thumbscrews hold the weights in place.

With the weights at either the center or the ends, rotate the tube back and forth about an axis perpendicular to the tube. Move the weights to the other extreme position and compare the torque required.

Even though the difference probably will be obvious to the class as the instructor rotates the tube, it perhaps will be more convincing to let a student do the rotating, or maybe it could be handed around for several students to try.

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