Which cube has a larger moment of inertia?

In summary, the conversation discusses the moment of inertia of two cubes and which one has a larger value. The speaker suggests that the cube on the right may have a larger moment of inertia due to its rotation not being through the principal axes. They also mention the parallel axis theorem, which states that the moment of inertia about an arbitrary axis is equal to the moment of inertia about a parallel axis passing through the center of mass plus the moment of inertia of the body about the arbitrary axis, taken as if all of the mass of the body were at the center of mass. However, the other person points out that the parallel axis theorem may not apply in this case since both cubes have their axis passing through the center of mass. The conversation ends with
  • #1
Cosmossos
100
0
To which of the two cubes has a larger moment of inertia?
attachment.php?attachmentid=23012&d=1263306125.jpg


I think it's the right one because We know that the minimal moment of inertia is throw the principal axes that goes throw the center of mass. in the right one , the rotation isn't throw the principal axes . there is also the following theorem :

The moment of inertia about an arbitrary axis is equal to the
moment of inertia about a parallel axis passing through the
center of mass plus the moment of inertia of the body about
the arbitrary axis, taken as if all of the mass M of the body
were at the center of mass.

Am I wrong?
 
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  • #2
If I'm reading your diagram correctly, the parallel axis theorem wouldn't apply since in both cases, the axis passes through the center of mass of the cube. But if the moment of inertia is always minimized around a principal axis, that would be a valid reason for arguing that the one on the right is greater.

Personally, I might try to work it out by integration to really convince myself.
 

1. What is moment of inertia?

Moment of inertia is a measure of an object's resistance to changes in its rotational motion. It is a physical property that depends on the mass distribution of the object and the axis of rotation.

2. How is moment of inertia calculated for a cube?

The moment of inertia for a cube can be calculated using the formula I = (1/6) * m * a^2, where m is the mass of the cube and a is the length of one side.

3. What is the significance of moment of inertia for a cube?

Moment of inertia plays a crucial role in understanding the rotational behavior of a cube. It determines how easily the cube can be rotated around different axes and affects its stability and angular acceleration.

4. How does the moment of inertia change for a cube with a different mass or size?

The moment of inertia for a cube is directly proportional to its mass and the square of its size. This means that a cube with a larger mass or size will have a greater moment of inertia, making it more difficult to rotate.

5. Can the moment of inertia of a cube be changed?

Yes, the moment of inertia of a cube can be changed by altering its mass distribution or changing the axis of rotation. For example, a cube will have a different moment of inertia if it is rotated about one of its corners instead of its center.

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