Find Moment of Inertia Around CoM: Summation Formula & Point Mass

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SUMMARY

The discussion focuses on calculating the moment of inertia (MOI) around the center of mass (CoM) when the axis of rotation is not aligned with the CoM. The parallel axis theorem is employed to transfer the MOI from the CoM to the desired axis of rotation. The user provides a detailed integral setup for a uniform density rectangular area, resulting in a simplified formula for the MOI. The final expression derived is M [ (L_x^2)/3 - 2(L_x)(r_x) + 3r_x^2 + (L_y^2)/3 - 2(L_y)(r_y) + 3r_y^2], which reflects the contributions of the dimensions and shifts from the CoM.

PREREQUISITES
  • Understanding of moment of inertia and its significance in rotational dynamics
  • Familiarity with the parallel axis theorem
  • Knowledge of double integrals and their application in physics
  • Concept of uniform density in the context of area moments
NEXT STEPS
  • Study the application of the parallel axis theorem in various geometries
  • Learn about calculating moments of inertia for different shapes, such as cylinders and spheres
  • Explore advanced integration techniques for complex shapes in physics
  • Investigate the implications of moment of inertia in dynamic systems and stability analysis
USEFUL FOR

Students and professionals in physics and engineering, particularly those focused on mechanics, structural analysis, and dynamics, will benefit from this discussion.

genericpumpkin
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How do I find the moment of inertia around the CoM of an object when the axis of rotation is not through the CoM?

When Are summation formula used in equations and what exactly constitutes a point mass? regarding moments of inertia?
 
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Use the parallel axis theorem to transfer the MOI from the c.o.m. to the axis of rotation.
 
I took the concept of a parallel axis shift and didn't require it to be parallel.

DoubleIntegral from -r_y to(L_y-r_y) and -r_x to (L_x - r_x) of ((x-r_x)^2+(y-r_y)^2)dm
For dm I used Mdxdy/(L_x)(L_y)

Clarifying, x and y are my variables, L_x is the x length of my object, and L_y is the length in the y direction. r_x and r_y are the distances or "shifts" of my axis from the center of mass in the x and y directions respectively.

Here's what I got (after quite a bit of simplification)

M [ (L_x^2)/3 - 2(L_x)(r_x) +3r_x^2 + (L_y^2)/3 - 2(L_y)(r_y) + 3r_y^2]

Anyone care to check my work? Or at least my initial setup? I didn't really get as much out of moments as I could've in my mechanics class, so I took this opportunity to brush up on them.
Btw I'm integrating a uniform density rectangular area moment. I hope you followed that lol
 

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