- #1
carllacan
- 274
- 3
Homework Statement
Calculate the moment of inertia of a cube which rotates along an axis along its diagonal.
Homework Equations
Moment of inertia definition: [itex]I = \int \rho (\vec{r}) \vec{r} ^2 dV[/itex]
Angular velocity vector; [itex]\vec{\omega}=\omega (\frac{1}{\sqrt{3}}, \frac{1}{\sqrt{3}}, \frac{1}{\sqrt{3}})[/itex]
The Attempt at a Solution
My biggest problem is on finding the position vector for the volume element. My try at it goes like this:
[itex]
\vec{r} = \vec{p}- \vec{p}·\vec{\omega} \frac{\vec{\omega}}{\omega}
[/itex]
Where [itex]\vec{p}[/itex] is the point of interest. With this we calculate the difference between the point's vector and a vector with the direction of [itex]\vec{\omega}[/itex] and magnitude equal to that of the component of [itex]\vec{p}[/itex] along [itex]\vec{\omega}[/itex]. This should be the shortest vector from the axis of rotation to the point. Am I right?
I think, however, that there is an easier way to solve this. Isn't there any shortcut similar to the Steiner Theorem, only for rotates axes?
Thank you.