There are various types of objects in TDW that are non-physics objects, meaning that they won't interact with PhysX or Flex. Usually, these objects are used in purely visual simulations or for debugging.
Non-physics objects have been added into TDW in a relatively piecemeal fashion. Some are are technically objects in the TDW sense, meaning that they will respond to non-physics object commands. Other non-physics objects use entirely different backend code. For example, position markers are not objects in the TDW sense and will only respond to position marker commands.
Next: Position markers