Rotatin'

B Block took time to focus on the problem solving aspect of rotational equilibrium. Objects can exist in rotational equilibrium, translational equilibrium, neither or both, depending on the specific circumstances. The problems we are looking at have objects in both forms of equilibrium and we are assessing the forces at work. Remember to use both conditions for equilibrium as tools (F_net = 0 and τ_net = 0) and choose rotational axes wisely. A force applied directly to the axis of rotation does not produce torque and that can help reduce the number of variables in a problem. Over the next couple of days, we'll be working on your rotational dynamics lab and I can help you with any individual issues working these problems during lab time.

C Block worked on a lab dealing with torque and balance. When we speak of balance, we are usually talking about an object being in rotational equilibrium and for that to occur, the sum of all torques on the object must be zero. For each mass you placed on your suspended meter stick, you used the weight and lever-arm distance to calculate its individual torque and with a thought about direction, demonstrated that the clockwise torque in your system balanced the counterclockwise torque. The post-lab problems deal with torque and balance and we'll go over those tomorrow before looking at the concepts of center of mass and moment of inertial.

E Block finished the data analysis for their rotational dynamics lab and folks should think carefully about the write-up hints I put on the board. With the disks, how did torque affect angular acceleration and why was the acceleration different between the single disk and the two disks stacked? Why was the slope of the line for your masses on a rod as large a value as it was? Why did the different positions of the masses on the rod affect the slopes of the lines? We'll start going over these ideas in class tomorrow, so pay attention and use those discussions to help script your synopsis.

F Block discussed the idea of center of mass and moment of inertia. We looked at some demonstrations that showed how the ease of rotation was affected by an object's mass distribution and how moment of inertia, torque and angular acceleration played together through the formula τ_net = Iα. We'll delve more deeply into that relationship in the next section when we really focus on the role moment of inertia plays in other aspects of rotational motion.