You can make a rigid body from any geometry in your scene. A rigid body can be a single object, or it can comprise several objects grouped together, known as a . If you designate an object whose geometry changes over time as a rigid body, the simulation uses its geometry at the start frame.
reactor lets you assign the physical properties that each body will have in the simulation, such as mass, friction, and whether the body can collide with other rigid bodies. You can specify a proxy geometry for a rigid body, which allows reactor to treat the rigid body as an easier-to-simulate shape for the purpose of the simulation. You can also specify how your rigid body should be displayed when previewing the simulation.