The moment of inertia of a rod that is rotating off the end of the rod.

[Lewis Edmunds]

Is there a formula for the moment of inertia? A thin, uniform density rod is rotating about an axis that is off the end of the rod, so it looks a bit like this:

------- |
(------- is the rod and | is the axis of rotation, so the rod is rotating out of the plane of your screen)

I just have a problem about an ice skater spinning and moving their arms, and I'm not sure how to work out the moment of inertia of the arms. The problem says to model them as two rod-like arms that are attached to the the outside of the torso (modelled as a cylinder)

 

[Doc Al]

Do you know the moment of inertia of a rod about its center of mass? If so, use the parallel axis theorem to find the moment of inertia about the axis that you need.

 

[OldEngr63]

If you don't know the parallel axis theorem, you can find the MMOI directly by integration.