Parts are assembly components that are included in the motion simulation and represent a rigid body whose motion is to be simulated.
You can designate a part as a moving part or as a stationary (grounded) part. A moving part has six degrees of freedom, while a grounded part has none. A ground part has a symbol attached to show that it has been grounded. Joints are added between parts to constrain how the parts can move relative to one another. Joints remove degrees of freedom from the parts to which they are attached.
You can also rigidly connect a part to another part using a fixed joint.
In COSMOSMotion, a moving part can be a single rigid part or a rigid subassembly. The term rigid body means that the individual components that make up the rigid body are rigidly attached to each other: during animation, they move together as they move with respect to other rigid bodies.
If a subassembly is set to flexible in SolidWorks, all the underlying parts are displayed at the top level of the Assembly Components branch of the IntelliMotion Browser and can be used as individual rigid bodies. The constraints between these part are automatically mapped into COSMOSMotion.
The ground rigid body is unique. It is, by definition, at absolute rest. All mechanisms have a ground rigid body. It serves as the reference frame for the remaining rigid bodies. All moving rigid bodies in your mechanism move with respect to ground. More than one geometric entity can be grouped on the grounded rigid body, but only one rigid body can be specified as ground.
In SolidWorks, any component that is fixed in your assembly is automatically attached to ground when you begin a new mechanism and map the assembly constraints. The component name is listed as part of Ground in the mechanism feature tree. When you have an open mechanism, you can also attach a component to ground by using a fixed constraint. However, the component does not appear in the Ground list in the mechanism feature tree.
By default, mass properties are automatically obtained from the solids in your assembly. You can override the mass properties with custom values.
Mass properties are important in COSMOSMotion because inertial loads affect reaction loads in joints that could be used as inputs for structural analyses.