I got some new toys last week and was excited to use them today. We got eight new “rotational inertia demonstrators” and I plan to use them a bunch for both AP physics 1 and AP physics C. Today the students in AP physics 1 determined the effect that the distribution of mass on a heavy pulley has on its angular acceleration. The four rods on the heavy pulley have masses that can be moved along the rods to change their distance from the axis of rotation. The students used the same hanging mass for each trial, moved the masses on the heavy pulley for each trial, and measured the time it took for the hanging mass to reach the table top after it was released. After they calculated acceleration of the hanging mass and angular acceleration of the pulley they made graphs of angular acceleration vs. radius of the adjustable masses. They got really nice inverse function curves and I look forward to using the results to introduce moment of inertia next week.

After the students learn the math involved they will be asked to graph their data so the slope of the graph is equal to the mass of the adjustable masses. I tried it myself last week and it came out pretty well with less than 10% error.