Mass Moments of Inertia ReadOUT

[SolidCreative]

I am having trouble understanding why there are 3 values for I (inertia). For example, Ix (0.022,1.000,0.344)

Is there any good sites that fully explain the mass properities readout?

What is the value for I for the following part with in the following link?

http://i17.tinypic.com/67y9yxj.jpg

thanks a million,

Matthew

 

[pdybeck]

Matthew,

These are the axes of rotational inertia. Your rotational inertia of a mass will vary depending upon what your axis of revoultion is. The 3 values given are for your rotations about x, y, and z axes according to your global coordinates. Consider a long shaft that is modeled along the z-axis. The rotational inertia should be much less about the z-axis than it would be about the x and y axes. This is due to the fundmanetal relationship of inertia = MR^2 (where r is the distance from each piece of matter to the axis of revolution). Essentially what SolidWorks/Cosmos does is calculate this value based on the geometry at hand. You could do the same by hand using an integral over the length of your geometry (not recommended as it is lengthy and describing the equation is often difficult for geometry that is anything but simple). You would have to do this 3 times, 1 for each axis of revolution you may want to consider. SolidWorks/Cosmos does this for you and gives the results with respect to the 3 different axes. You want to make sure that your axis of revolution coincides with the axes that these values are calculated on, otherwise you would have to adjust using the parallel axis theorem, or create your geometry on a more convenient coordinate system.

http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html

http://hyperphysics.phy-astr.gsu.edu/hbase/mi2.html

http://en.wikipedia.org/wiki/Rotational_inertia

Pete