Welcome to the the Physics Clas blog!! I hope you’re all doing great!!

In this episode, I simply wanted to reacquaint us with Rotational Inertia or the “Moment” of Inertia (I). So I go though the bird/insect scenario again and I review the frisbee problem because many were absent and I didn’t go over it with the second group. Now, the video came out good except it shrinks a little when you put in in iMovie so the top couple lines are chopped on the problems but I read them out loud. So please forgive me as I navigate the precise placement. I hope you find it fun (there’s an outtake right at the beginning) and if you could comment on the sponsor of the episode (there’s a little commercial in there somewhere) that would be great!!

So, after I review Moment of Inertia, I talk about how how we can use the principle of the Conservation of Energy for an extended object that is rotating as its center of mass is moving through space. In such a situation, it turns out that we can write the extended object’s Total Kinetic Energy (K) as the sum of its Rotational Kinetic Energy (Kr) and its Translational Kinetic Energy (Kt). Specifically, the movement of the CoM and the rotation around the CoM!

Here are the two questions I would like you to have a go with!

(1) Three beads with masses m1<m2<m3 are each placed on a rod at distances of La<Lb<Lc from the axis of rotation of the rod with a rotational inertia of Irod (meaning the rod itself has a rotational inertia that is part of the total). Express the smallest rotational inertia of the system in terms of Irod and the masses and locations of the beads.

(2) A potter’s flywheel is a circular concrete slab, 6.5 cm thick, with a mass of 60.0 kg and a diameter or 35.0 cm. The disk rotates about an axis that passes through its center, perpendicular to its surface. Calculate the speed of the slab about its center if it’s Rotational KE is 15.0 J. The (I) for a disk is 1/2mr^2.

Thanks so much everyone!!! Y’all are simply amazing!!