In: Physics
Find the moment of inertia of a circular disk of radius R and
mass M that rotates on an axis passing through its center. [Answer:
½ MR2]
Step 1: Pictorial representation: Sketch a neat picture to
represent the situation.
Step 2: Physical representation: 1) Cut the disk into many small
rings as it has the circular symmetry. 2) Set up your coordinate
system and choose its origin at the pivot point (or the axle
location) for convenience. Then choose a not-special piece as a
representative of those small masses dm:
Step 3: Determine the moment of inertia of this representative
small mass and evaluate the integral for the total moment of
inertia:
Step 4: Use the parallel-axis theorem to determine the moment of
inertia of the disk around an axis located at the edge of the disk.
Then compare the two moments of inertia and explain how the results
make sense to you.