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Moment of Inertia Challenge

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Submitted by Rich on Sun, 11/10/2019 - 17:58

The Moment of Inertia Challenge

Determinig the moment of inertia about the center of mass mathematically of an object with complex geometry is not an easy task.  Consider, for example, the empty 3D filament reel shown in Figure 1, an empty 1-kg Polymaker Polylite PLA reel.  With its holes and intricate axle design, the best way to determine the moment-of-inertia about its center of mass is via a laboratory experiment.  Voyager (or PocketLab One) is mounted to the reel for data collection.  

Empty 3D filament reel with PocketLab Voyager attached
Figure 1 - Empty 3D filament reel with PocketLab Voyager attached

There are many experimental setups by which this can be accomplished.  Your challenge is to determine the moment of inertia about the center of mass using the PocketLab app, Voyager, and the setup shown in Figure 2.  You may also use a ruler and a weighing scale.  A roughly 2-meter length of adding machine tape is taped to and wound around the axle of an empty 3D filament reel.  The reel is released from rest and allowed to fall to the floor, during which PocketLab records the necessary data.

Moment of inertia lab setup
Figure 2 - Moment of inertia lab setup

For clarification, the short 4-second slow motion video below shows a typical run.  OK!  You're on your own.  Figure out the physics theory, work on the fine details for the experiment, and state any assumptions you are making.  Remember your goal is to determine the moment of inertia of the empty 3D filament real about its center of mass.  Good luck! 

Another Similar Experiment

The Physics of a Falling and Unrolling TP Roll

Snapshot of the moment of inertia challenge movie
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