if something moves through something else then that something will collide with that something else
gathering_things_together is moving_into. separated_thing is divided_thing. separated_thing is not divided_thing. change is when_one_thing_becomes_another_thing. gathering_things_together is not moving_into. spreading_stuff_onto_surface is spreading. change is not when_one_thing_becomes_another_thing. spreading_stuff_onto_surface is not spreading.