You can mute a collision so that all obstacles, or just certain ones, do not take part in the dynamics calculations.
To mute a collision
Open the Simulate Rigid Bodies compound’s property editor and select the option that you want:
• Select Mute to mute the simulation for all rigid bodies connected to the Simulate Rigid Bodies node.
• Select Collide to have all rigid bodies connected to the Simulate Rigid Bodies node participate in the collision; deselect this option it to prevent them all from participating.
• For each individual connected Obstacle, select Active to have it participate in the collision, or deselect it to prevent it from participating.
Autodesk Softimage v.7.5