Instructor notes for PHYS141 moments of inertia lab.
Whether or not this lab runs is semi-dependent on whether or not the students have seen moments of inertia in lecture. As designed it assumes knowledge of the basics and the lab is an exercise in figuring out how to apply the theory to the problem.
Students are given an IoLab device and two hoops which can be combined as shown.
The object of the lab is to determine the moment of inertia of the IoLab. To first order it can be treated as a rectangular object, but the IoLab does not have a uniform mass density through out it's body. So by measuring the total moment of inertia of the device plus hoops, and the hoops separately, one can determine the actual moment of inertia of the IoLab about it's long axis. This value can then be compared to the first order estimate.
Students are asked to figure out two different ways of measuring the moment of inertia of the apparatus as it rolls down an inclined plane. For one method they are asked to analyze the problem using kinematics, force diagrams, etc. For the other method they are expected to analyze it using conservation of energy. For each method students are expected to determine what physical parameters need to be measured, for which there exist corresponding sensors in the IoLab device itself. They then construct and execute an experiment for each method. This provides them with two independent measurements of the moment of inertia of the system which they can compare for consistency. Then they can extract the moment of inertia of the IoLab assuming that they can simply calculate it for the two hoops.