Different coordinated center of mass and center of gravity?

3D Design Volume Model
1

With SolidWorks 2024:

When measuring " Mass Properties" on an assembly, the coordinates of the center of gravity are obtained, and if the " Create Center of Mass function" checkbox is selected, the center of mass point is created after closing the " Mass Properties" measurement.

If I measure the coordinates of the center of mass and compare it to the values of the coordinates of the center of gravity obtained during the measurement in " Mass Properties"; I get different coordinates.

Why do we have different coordinates for the center of gravity and the center of mass?

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Hello @Marc_JIMENEZ and welcome.

Simply because the center of mass and the center of gravity are not the same thing.

I refer you to this article:

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I was going to say it :wink:

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Why doesn't SolidWorks provide a function to create the center of gravity?

During the measurement of " mass properties" we obtain the center of gravity, yet we do not make any parameterization for the gravitational field (direction, value, etc.), so what is this calculation based on?

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You are wrong, or rather Solidworks is deceiving you, when you do the calculation " Mass Property" it is the center of mass that is dimensioned.
image

As for the notion of " Center of Gravity ", it is more a question of a bad translation / mechanical convention (see misnomer).

Edit: I don't see the connection with the Center of Symmetry function... Working on a perfect sphere?

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The center of gravity is defined by the gravitational field. This gravitational field is linked to mass, of course, but the center of mass can be off-center with respect to the center of gravity. See article pointed out by @Sylk

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Indeed, when we click on <Replace Mass Properties> the XYZ coordinates correspond to the coordinates of the center of gravity.
==> misuse of language or vagueness

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And in English, what does it say? I say this because I've seen so many screwed-up translations made in France by badgers who don't understand what they're translating.
In movies typically. Translating " 10% of the speed of light " as " 10% of a light-year " in a Transformers... When we translate units of speed by units of distance, we hit rock bottom... Long live France.

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sorry, I made a mistake when I wrote... I meant center of gravity (and not symmetry...)

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In English, it says " center of mass " and " center of gravity ". DS likes to cultivate ambiguity or even imprecision, it grows well in their kingdom :european_castle:

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centre de masse vs centre de gravité

Here is a screenshot to explain my problem...
In blue the coordinates of the center of mass, and in red the center of gravity.

(sorry I have to hide the 3D preview)

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I have to check on my side but it seems to me that:
The coordinates of the center of mass are relative to the origin of the assembly
As for the coordinates of what Solidworks call center of gravity is relative to the center of the bounding box.
Unless it's just a problem of reconstruction...

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The good news is that the values are different, which tends to prove that they are indeed 2 distinct things, even in SW.

What is more ambiguous is that the moment of inertia concerns the center of mass but that it is followed by the values of the CoG...

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After some tests, it appears that the difference in coordinates between the two " centers " is due to the reconstruction.
The center of " gravity " requires reconstruction.
Whereas the center of mass seems to be recalculated with each change.
=> Solidworks 2022

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That's @Maclane our big winner of the day I think.
SW only manages centers of mass (because we never talk about gravity in SW unless we go into simulation).
So the name center of gravity in mass properties is wrong: it's a center of mass.
It's the intern in charge of the translation who screwed up: it's OK in English:

image
image695×648 85.5 KB

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Oh thank you @froussel in the end I was right...

CQFD :triumph:

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