Moment of inertia of disk about off centre axis

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SUMMARY

The moment of inertia of a uniform disk of mass m and radius r about an axis normal to the disk, through a point x from the center, can be calculated using the parallel axis theorem. The density ρ is used in the integral I=ρ∫r^2 dA, which requires proper limits for r in polar coordinates. The angle θ ranges from 0 to 2π, while the maximum value of r varies based on the geometry of the disk. The correct formulation involves expressing the distance D in terms of polar coordinates and integrating over the entire disk.

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  • Understanding of moment of inertia concepts
  • Familiarity with polar coordinates
  • Knowledge of the parallel axis theorem
  • Basic integration techniques in calculus
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  • Study the application of the parallel axis theorem in rotational dynamics
  • Learn how to set limits for integrals in polar coordinates
  • Explore the derivation of moment of inertia for various shapes
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Lucy Yeats
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Homework Statement



Find the moment of inertia of a uniform disk of mass m and radius r about an axis normal to the disk, through a point x from the centre.

Homework Equations





The Attempt at a Solution



Let ρ be the density. I=ρ∫r^2 dA=ρ∫∫r^3 dr dθ in polar coordinates.
However I don't know what the limits of r should be. θ is between 0 and 2 pi, but r max varies, so I'm confused.
 
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use parallel axis theorem
 
Lucy Yeats said:

The Attempt at a Solution



Let ρ be the density. I=ρ∫r^2 dA=ρ∫∫r^3 dr dθ in polar coordinates.
However I don't know what the limits of r should be. θ is between 0 and 2 pi, but r max varies, so I'm confused.

Your integral is not correct.
The contribution to the moment of inertia of a mass element, at distance D from the axis, is D2dm. Write up D in terms of r and φ (the polar coordinates. ) You have to integrate for the whole disk.

ehild
 

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