286 Rotation of a Rigid Object About a Fixed AxisQ10.12The moment of inertia depends on the distribution of mass with respect to a given axis. If the axis ischanged, then each bit of mass that makes up the object is a different distance from the axis. Inexample 10.6 in the text, the moment of inertia of a uniform rigid rod about an axis perpendicular tothe rod and passing through the center of mass is derived. If you spin a pencil back and forth aboutthis axis, you will get a feeling for its stubbornness against changing rotation. Now change the axisabout which you rotate it by spinning it back and forth about the axis that goes down the middle ofthe graphite. Easier, isn’t it? The moment of inertia about the graphite is much smaller, as the massof the pencil is concentrated near this axis.Q10.13Compared to an axis through the center of mass, any other parallel axis will have larger averagesquared distance from the axis to the particles of which the object is composed.
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