Calculating moments of intertia

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Homework Help Overview

The discussion revolves around calculating the moments of inertia for particles with respect to different axes of rotation. The context includes specific particle positions and the application of relevant formulas in physics.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of the moment of inertia formula, with some suggesting the use of integration while others argue for a simpler approach for point masses. Questions arise regarding the calculations for multiple particles and the validity of the results obtained.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the moment of inertia calculations. Some guidance has been offered regarding the assumptions made in the calculations, but no consensus has been reached on the correct approach or final answers.

Contextual Notes

Participants are working under the constraints of homework rules, which may limit the information they can share or the methods they can use. There is also a focus on ensuring the correct application of formulas and units in the context of point masses.

Linus Pauling
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1. Find the moment of inertia I_x of particle a with respect to the x-axis (that is, if the x-axis is the axis of rotation), the moment of inertia I_y of particle a with respect to the y axis, and the moment of inertia I_z of particle a with respect to the z axis (the axis that passes through the origin perpendicular to both the x and y axes).

Particle a is located at x=3r, y=r, z=o



2. I = Integral(x^2 + y^2)



3. I_x = 1/3 * mr^3
I_y = 3mr^3
I_z = 10/3 * mr^3
 
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Surely the formula is I = m*r^2 ?
so I_x = mr^2.
No integration needed when you have a point charge. The particle is a distance r from the x-axis. Your r^3 answers don't even have the right units.
 
Ah, ok thanks. Now I am supposed to consider a second particle, b, located at x=r and y=-4r, and calculate the total moment of inertia for the two particles of this system, with the y-axis as the axis of rotation.

Why 10mr^2 not the answer? I obtain this my summing I_ya + I_yb = 9mr^2 + mr^2
 
This is is driving me crazy :cry:
 
10mr^2 looks good to me, assuming the two particles have the same mass.
 

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