Cardboard tubes, tin can, Nutella jar, Tylenol box, yogurt containers, old windshield wipers, coffee cup... What do these recyclables have to do with gravity?
After much tweaking and taping and re-taping and chasing the ball down the stairs (our issue with gravity) and getting the ball back from the cat (it's her toy afterall), we have finally achieved success with our experiment.
Serena declared that she's going to duplicate this on every wall in the house. Better eat more Nutella, fast.
Resource: Bill Nye the Science Guy DVD - "Gravity"