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I have 2 point masses $m_1$ and $m_2$ connected via a massless rigid rod to a center. $m_1$ is at the distance $r_1$ from the center and $m_2$ is at the distance $r_2$ from the center. How would i calculate the moment of inertia of the system?

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  • $\begingroup$ Are you looking for the MMOI about the rod center, or the center of mass? The former is going to be larger than the latter. $\endgroup$ – ja72 Jan 15 '16 at 5:32
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It is the sum of the point mass moments of inertia

$$I=\sum_i m_ir_i^2 =m_1r_1^2+m_2r_2^2+...$$

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  • $\begingroup$ This is the MMOI about the rod center, and not the center of mass. Of course the OP wasn't clear where the MMOI should be measured. $\endgroup$ – ja72 Jan 15 '16 at 5:06
  • $\begingroup$ I assume he put the axle at the middle of the rod, because the given distances are "from the center". $\endgroup$ – redivider Jan 15 '16 at 5:13

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