In the demonstration a sponge basically sticks to the wall of a rotating cylinder. What force is directed toward the center of the circle in this case?

1. Static friction (9/36) (25%)
2. Kinetic friction (0/36) (0%)
3. Normal force (25/36) (69%)
4. Tension (0/36) (0%)
5. None of the above, it's a centripetal force (0/36) (0%)
6. None of the above, there is no force directed toward the center (2/36) (6%)