The Variable Inertia demonstrates an abstract concept in an easy-to-understand manner. It consists of two semi-clear plastic discs with the same mass and diameter. The discs are hollow inside with molded compartments. The 19mm steel balls can be placed inside the discs in a variety of configurations. Based on the location of the steel balls, the distribution of the mass will change, and the discs will become either "center heavy" or "rim heavy." How does changing the position of the mass affect the speed at which they roll? The semi-transparent discs will allow your student to see where the mass has been placed inside the discs. After conducting the experiment, the student will be able to relate the position of the mass to the outcome of the experiment.