We started today by investigating moment of inertia. I gave each group two metersticks of about the same mass (the range of masses of the metersticks in my room was large: 95 grams!) and 2000 grams of masses. I then challenged them to make two sets of objects with the same mass and same center of mass but wildly different moments of inertia. Oh, and the mass can't be anywhere in the 45 cm-55 cm range on the meterstick because that's where we'd put our hands to rotate the sticks horizontally back and forth to get a sense of its rotational inertia around the 50-cm mark. They came up with a few different solutions. We tried them all and found the biggest difference in rotational inertia came from the biggest difference in the distance from the pivot point.
Then we took off all the masses from the meterstick with the large moment of inertia. They now had their meter stick with two 500-gram masses pretty close to the center of the meterstick. Using the units of the moment of inertia as a hint, I asked them to guess where they could put much smaller masses on the other meterstick so the two metersticks would have the same center of mass and same rotational inertia around the 50-cm mark but different masses. A picture of one of their solutions is above.
We then worked on a few problems with unbalanced torque. Then I took a page out of Kelly O'Shea's book (again) and used Tic-Tacs to show that sometimes they bounce higher after hitting the table when they're spinning. We talked about how there must be rotational energy.