Understanding the Application of the Parallel-Axis Theorem

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SUMMARY

The discussion centers on the application of the Parallel-Axis Theorem in calculating the moment of inertia for a solid sphere rotating about an external axis. The correct formula for the moment of inertia is confirmed as I = (2/5)MR^2 + M*D^2, where D represents the distance from the center of mass to the new axis of rotation. It is established that the theorem applies regardless of whether the axis of rotation is inside or outside the body. This clarification aids in accurately determining the moment of inertia for various rotational scenarios.

PREREQUISITES
  • Understanding of moment of inertia and its calculation
  • Familiarity with the Parallel-Axis Theorem
  • Basic knowledge of rotational dynamics
  • Concept of center of mass in rigid bodies
NEXT STEPS
  • Study the derivation of the Parallel-Axis Theorem in detail
  • Explore applications of moment of inertia in engineering contexts
  • Learn about the impact of different shapes on moment of inertia calculations
  • Investigate the relationship between torque, angular acceleration, and moment of inertia
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Students of physics, mechanical engineers, and anyone interested in understanding rotational motion and dynamics.

Niles
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Homework Statement


If I have a solid sphere (I = (2/5)MR^2) and it rotates around a point on an axis that is 5m away (it has radius 0.1m) - is the moment of inertia then: I = (2/5)MR^2 + M*(4.9m)^2?

My question is - does the parallel-axis only work when we are moving the axis of rotation around "inside" the body or also outside it?
 
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It works inside or outside. I'd say that I = (2/5)MR^2 + M*D^2, where D is the distance from the center of mass to the desired axis.
 
Of course, my bad - but thanks again. You have helped me very much.
 

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