Q:

# How do you calculate the moment of inertia of a rod?

A:

Calculating the moment of inertia for a rod requires you to know the mass, length and location of the rotational axis. An estimation may be required with regards to the position of this axis.

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1. Measure the mass of the rod

Measure the mass of the rod on a scale. Take the measurement using a unit from the metric system, preferably kilograms.

2. Measure the length of the rod

Measure the length of the rod from one end to the other. To maintain consistency in units, continue to use the metric system.

3. Determine the location of the axis of rotation

Locate the axis of rotation, and observe its position relative to the rod. You likely need to estimate this position as being at the center, end or one-fourth of the way down the rod.

4. Select the suitable equation

Based on the position of the rotational axis, determine the most suitable equation to use. If the axis is located at an end, use the equation I = (1/3)ML^2, where M is the mass and L is the length. If the axis is located at the center of the rod, use the equation I = (1/12)ML^2. If the axis is located a fourth of the way down the rod, use the equation I = (7/48)ML^2.

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