Facing a Half-Day

Today was the last full day of the week and it was a busy one...

B Block began their rotational motion lab. Data was collected that allowed students to measure angular acceleration for a variety of torques and that information will be plotted to assess the object's moment of inertia. For the rod with weights, we'll also take a look at how changing the spacing of the weights affects the moment of inertia, though from our previous discussions, you should have a pretty good idea as to the outcome. Tomorrow is set aside for graphing and analyzing your data - don't forget to get the rod data from the other groups!

C Block engaged in a discussion of center of mass and moment on inertia, two very important concepts for rotational motion. An object's center of mass is the point around which the object will naturally rotate when acted on only by gravity. It is also the balance point, and if your center of mass moves beyond your base of support - consider yourself toppled. We'll expand on these ideas tomorrow, along with our lab work on torque and balance.

E Block took a look at torque, center of mass and moment of inertia. Torque and moment of inertia are critical in providing a framework around which to evaluate and explain your experimental results from your rotational dynamics lab, so I hoped good attention was paid by all attendees. Remember that your lab is not due until next Tuesday or Wednesday, so don't kill yourself trying to get it written up over the break. But, do start thinking about how the increasing torques affected angular acceleration for each trial, how increasing mass for your discs affected angular acceleration (when subject to the same torque) and how using a different shape played into the game. For your rod, it approximates point masses acting away from the axis of rotation, so you should have some idea of how its moment of inertia should compare with comparably massed discs. Also, how did changing the mass spacing affect the moment of inertia? Did the pattern make sense? If now, explain what might have happened to give unexpected results.

F Block worked on rotational equilibrium - where objects are subject to a net torque of 0. Whether you are not rotating or rotating at constant angular speed, you are in rotational equilibrium - angular acceleration is noted when you are subject to net torque. Objects can exist in translational or rotational equilibrium, both at the same time or neither, depending on the situation. We looked at some problems to see how to use these two conditions of equilibrium to analyze forces in a system. We'll go over them on Monday when we return and see how folks feel about moving on to angular momentum.

If I don't see you tomorrow - have a great Thanksgiving!