# 29.2 Moment of Inertia of a Rod | Summary and Q&A

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June 2, 2017
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29.2 Moment of Inertia of a Rod

## TL;DR

Learn how to calculate the moment of inertia of a rigid rod by breaking down the key terms and setting up the integral.

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### Q: How is the moment of inertia of a rigid rod calculated?

The moment of inertia of a rigid rod can be calculated by integrating the product of the mass element (dm) and the distance (r) from the axis of rotation squared, using the formula Icm = ∫ dm * r^2.

### Q: What does the integration variable represent in the moment of inertia calculation?

The integration variable, represented by x in this context, represents the distance of the mass element (dm) from the chosen axis of rotation. It is used to divide the rod into small elements for the integral summation.

### Q: How is the mass element (dm) expressed in terms of the integration variable (x)?

The mass element (dm) is expressed in terms of the differential length (dx) using the formula dm = (mass per unit length) * dx. This formula takes into account the assumption of uniform density of the rod.

### Q: What does the integral in the moment of inertia calculation represent?

The integral in the moment of inertia calculation sums up the contributions of all the small mass elements (dm) in the rod. It is obtained by dividing the rod into small elements and adding up their individual contributions.

## Summary & Key Takeaways

• The moment of inertia of a continuous body, such as a rigid rod, can be calculated by integrating the product of the mass element and the distance from the axis of rotation squared.

• Key terms in the moment of inertia calculation include the integration variable, the mass element (dm), and the distance (r) from the point of calculation to the axis of rotation.

• To set up the integral, a coordinate system is selected with the origin placed at the center of mass, and an arbitrary mass element (dm) and integration variable (x) are chosen.