Finding moment of inertia for a hemisphere

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Homework Help Overview

The problem involves finding the moment of inertia for a hollow hemisphere about the x-axis, given specific parameters such as radius and areal density. The context is rooted in the study of rotational dynamics and properties of geometric shapes.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the moment of inertia for a complete spherical shell and consider how this might relate to the hollow hemisphere. Questions arise about whether the moment of inertia for the hemisphere would simply be half that of the complete sphere.

Discussion Status

The discussion is active, with participants exploring different interpretations of how the moment of inertia behaves when transitioning from a full sphere to a hemisphere. Some guidance has been provided regarding the relationship between the moments of inertia of the whole and half spheres, though no consensus has been reached.

Contextual Notes

Participants are working with the assumption that the hollow hemisphere's moment of inertia can be derived from known properties of the complete sphere, while also questioning the implications of cutting the sphere along different axes.

dinospamoni
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Homework Statement



A thin walled hollow sphere of radius 16 cm is sliced in half. What is the moment of inertia of this hollow hemisphere about the x-axis if the areal density is 90 g/cm2?

Homework Equations



No idea

The Attempt at a Solution



I've had no luck with this. I've already found the outward facing area of the sphere and the z component of the center of mass, if that help.

Really anything that could set me on the right track would be awesome
 

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Would it help to think about what the answer would be for a complete spherical shell?
 
For a complete spherical shell, it would be the same in all directions.

So for half a shell, would it be half of what it would if it were a whole sphere? I feel like that's too easy
 
dinospamoni said:
For a complete spherical shell, it would be the same in all directions.

So for half a shell, would it be half of what it would if it were a whole sphere? I feel like that's too easy

Now and then, a problem is much easier than it seems. Each half would have the same MI about this axis, and the MI of the whole sphere would be the sum of the two.
 
Does this mean MI_z=2*MI_x?
 
No, it would be the same. Whether you cut the sphere in half along the axis of rotation or perpendicular to it, you produce two halves with the same MI about the axis, so each half must have half the MI of the whole sphere.
 
Ah I see now. Thanks a ton!
 

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