objects colliding can cause changes to those objects
colliding_with_obstacle is colliding. colliding is barrier_situation_physical_force. colliding is irreflexive_action. colliding is not barrier_situation_physical_force. colliding is event. colliding is not event. colliding_with_obstacle is not colliding. object_displacement_event is change_of_location. colliding is change_of_location. colliding is not change_of_location.