Mass Properties - Inertia

[RamblinWreck06]

I'm trying to use SW to help me confirm a calculation I've done by hand. I have an equilateral tetrahedron (4-sided solid, all sides equilateral triangles) and I'm trying to calculate its moment of inertia about one of its edges. I've put a coordinate system in the center of one of the edges on the base and selected it in the mass properties box. I assume that Ixx will be my moment of inertia along the edge as long as my x-direction is defined along that edge. Am I correct? What do Ixy, Ixz, Iyx, etc tell me?

Thanks,

 

[abrewmaster]

Solidworks calculates the moments of inertia taken at the center of mass and also the moments of inertia at the center of the coordinate system. Depending on which one you're looking at, probably the center of the coordinate system in your case, the Ixy, Ixz, Iyz ones are basically telling you how off center your part is from the axis. If you had a cube for example but you made the origin of the coordinate system at one of the corners you would get the moment of inertia taken at the center of mass to be 0 for all the Ixy, Ixz, Iyz parts but for the moment of inertia taken at the origin you might get different values.

 

[SnTMan]

I'm confused by a simple execrise. SW reports Moments of Inertia in units of weight*length^2. Commonly used moment of intetia (second area moment) is in units of length^4. What's up?

Regards,

Mike

 

[abrewmaster]

I'm confused by a simple execrise. SW reports Moments of Inertia in units of weight*length^2. Commonly used moment of intetia (second area moment) is in units of length^4. What's up?

One is mass moment of inertia and the other is geometrical moment of inertia.

 

[SnTMan]

Ah, yes, had forgotten about all that. So if I need the second area moment, can I get it from SW, or do I have to go to ACAD?

RamblinWreck06, my apologies for hi-jacking your thread.

Regards,

Mike

 

[abrewmaster]

Ah, yes, had forgotten about all that. So if I need the second area moment, can I get it from SW, or do I have to go to ACAD?

You should be able to go to Section Properties next to Mass Properties and then select the face/plane that you want the properties for.

 

[SnTMan]

abrewmaster, thank you

RamblinWreck06, hope my digression has answered some of your questions.