The physics settings for a 3D object affects how it behaves in simulation. The mass of the object is the physics setting available to edit.
To edit the mass:
If the Materials tab is not already open, on the Resources tabs, click Materials.
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On the Materials tab, click the 3D object. Details of the object are displayed in the Context view.
In the Context view, click Physics. The Edit Mass dialog box is displayed.
Type in the required mass and click OK.