Proving moment of inertia of hollow sphere with y^2+x^2=R^2 method

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SUMMARY

The moment of inertia of a thin-walled hollow sphere can be derived using the equation I = ∫ r² dm, where dm represents a differential mass element. To compute dm, one can express it in terms of the area of a ring and the sphere's density. The integration should be performed from y = -R to y = +R, utilizing the equation y² + x² = R² to define the geometry of the sphere. This approach avoids multivariable integrals while allowing for trigonometric substitution as needed.

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  • Understanding of single-variable calculus
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  • Basic knowledge of moment of inertia concepts
  • Ability to perform trigonometric substitutions
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parsa418
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Could anyone prove the moment of inertia of a thin walled hollow sphere using the y^2 + x^2 = r^2. I have only studied up to single variable calculus. I can take regular integrals but not multivariable integrals. I don't want to use the angle method or any polar coordinate systems except in the part where I might use it for trigonometric substitution to evaluate the integral.
Thanks
 
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parsa418 said:
Could anyone prove the moment of inertia of a thin walled hollow sphere using the y^2 + x^2 = r^2. I have only studied up to single variable calculus. I can take regular integrals but not multivariable integrals. I don't want to use the angle method or any polar coordinate systems except in the part where I might use it for trigonometric substitution to evaluate the integral.
Thanks
You are missing a z^2 there for the third dimension.

The moment of inertia is simply:

I = \int r^2dm

Let dm be a slice of the sphere of thickness dy. Can you express dm in terms of area of that ring and density? Then integrate from y = -R to +R

AM
 

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