Simulating rigid body interactions in modo is easily handled with
recoil, a fully integrated dynamics simulation plug-in for modo 501
developed by Eric Soulvie.
Utilizing the popular open-source Bullet Physics engine, recoil
simplifies the setup and execution of complex physical simulations by
combining robust collision detection with a variety of constraints,
forces, and controls. By simply tagging any mesh item to be dynamic,
it is ready to respond to forces like gravity or collisions from other
objects in your modo scene. The recoil plug-in lets you quickly create
incredibly complex animations of interacting objects that would be
almost impossible to simulate manually. It is also useful for
"stacking" up objects so that they rest against each other (see
gumball image below).