physics platformer.

hi, im making a platformer, using physics, where youve gotta control a little ball and get it to the end of the level.. simple.

my problem is that i want the ball to be able to roll up certain walls and across ceilings and stuff but cant for the life of me figure out how to do this..

anyone know how i can do this?

you might be able to use set the ball to have both physic and platform and have the wall or ceiling call in what the new math in the physic and platform behavior Acceleration, gravity but that just my guess?