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[FAQ]

FAQ: Why is the mass moment of inertia reported in units of (length)^5 ?

By default, Discovery SpaceClaim does not assign a material to a new model.  The lack of a material assignment also means there is no value specified for density, which makes it impossible to display the result using the typical units for the mass moment of inertia:

 

The mass moment of inertia for a body can be calculated using the general equation

where

is the material density, is the distance from any given point within the body to the axis of revolution, and  is the total volume of the body in units of length cubed.

After integrating this general equation, we are left with the following terms and corresponding SI units, for example:

 

 

However, without an assigned density, the terms cannot be canceled and thus the result of the calculation is displayed as  .

Users may also notice that the Mass Properties tool reports the Center of Volume of a part until a density is specified, at which point the label in the results changes to Center of Mass.