How to Calculate the Moment of Inertia of Rods
An object's moment of inertia depends on its shape. An ice skater spinning in place can change his or her angular velocity by compressing into a rod-like shape, thereby changing their moment of inertia. A single solid rod can have different moments of inertia depending on how it is spinning. If the ends are equidistant from the axis of rotation, its moment of inertia will be less than the same rod rotating with one end as the axis of rotation.
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Instructions
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Measure the weight of the rod using a scale. Keep it from rolling around while you are taking the measurement. Use the metric scale and measure in kilograms.
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Measure the length of the rod. Keep your measurement in meters to avoid conversions later.
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Determine the axis of rotation of the rod. It can be anywhere from the end of the rod to the exact midpoint. Measure the length from the axis of rotation to the end of the rod farthest from the axis.
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Multiply the mass by the square of the length between the axis and the end of the rod. Then multiply this product by 1/12 if the rod is rotating about its center point, 7/48 if the axis is located at 1/4 the length of the rod, or 1/3 if the rod is rotating about one of the end points. Inertia is measured in kg*m^2.
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References
- Photo Credit Figure Skates image by Alaskajade from Fotolia.com
