Calculating Moment of Inertia for Combined Shapes

  • Thread starter Hayden Leete
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In summary, the conversation discusses how to calculate the moment of inertia of a complex shape made of multiple planes. It is suggested to find the moment of inertia of each individual piece and then add them together using the parallel axis theorem. The axis of choice is the blue center of mass and research was done to understand this concept.
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Hayden Leete
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https://scontent-syd1-1.xx.fbcdn.net/hphotos-xfl1/v/t34.0-12/13015003_664975026975127_933044449_n.png?oh=0259712996d9a6dde812f6d8886f56b9&oe=5715CA95
So, it's straight forward enough to calculate the moment of inertia of basic planes with evenly distributed mass, but if I were to say glue the red and green plane together, how would I find the moment of inertia of the blue shape?
 
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  • #2
Hayden Leete said:
how would I find the moment of inertia of the blue shape?
About what axis?

You can find the moment of inertia of each piece about the axis of choice, then just add them. (You'll need the parallel axis theorem.)
 
  • #3
Doc Al said:
About what axis?

You can find the moment of inertia of each piece about the axis of choice, then just add them. (You'll need the parallel axis theorem.)

probably should have specified, the z axis, or the axis perpendicular to the plane. the axis of choice is the blue COM, and I don't know how to find the moment of inertia of each shape except with central axes (I don't know much in the world of rotational inertia)
 
  • #4
actually you know what, through more googling and researching stuffs, I've figured it out. I've been trying to find somewhere to explain this to me for a while now, but I didn't know exactly what to search for until your reply, so thanks for that :biggrin:
 

What is rotational inertia?

Rotational inertia, also known as moment of inertia, is a physical property of an object that describes its resistance to change in rotational motion.

How is rotational inertia calculated?

The rotational inertia of an object is calculated by multiplying the mass of the object by the square of its distance from the axis of rotation.

What is the purpose of combining rotational inertias?

Combining rotational inertias is important when dealing with complex systems that involve multiple rotating objects. It allows us to calculate the overall rotational inertia of the system and predict its behavior.

What is the difference between rotational and translational inertia?

Rotational inertia deals with the resistance to change in rotational motion, while translational inertia deals with the resistance to change in linear motion.

What factors affect the rotational inertia of an object?

The rotational inertia of an object is affected by its mass, shape, and the distance of its mass from the axis of rotation. The distribution of mass within the object also plays a role in determining its rotational inertia.

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