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An object moving in pure rotation about an axle can be described in two different but equivalent ways. 1.) The
- The object is only rotating, but the moment of inertia about the fixed axle must be found using the parallel axis theorem.
- The object is rotating about the center of mass and its center of mass is translating.
To see why these descriptions are equivalent, consider how we would find the angular momentum and energy of a bar pivoted at one end.
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