Momentum Powered Uphill Roller!? Help!! Basically, I need to make a rubber-band powered device that will roll up a hill. The hill is very very shallow, and 3 meters long. I CANNOT simply use something that utilizes a center of gravity (i.e. the double cone roller). Right now I have 2 liter bottle, with a hook in one end. The hook is mounted to the bottle in a way that it DOES NOT spin. A rubber band goes from this hook inside the bottle to a weight in the center of the bottle. The weight has a rod attached to it, that goes straight through the center of the cap. This rod and weight CAN spin and it does. But, when I test it on just a flat surface, the bottle just jumps a little and settles, not rolling at all. Another way of showing my design is like this: (----O-----)--I The parenthesis being the cap and bottom of the bottle. The zero is the weight. The dotted line on the left is a rubber band, mounted to the bottle on a non-rotating hook. The dotted line on the right is a rod that goes all the way through the bottle, and has a small handle at the end for twisting up the rubber band. The question is, how can I fix this to make it move, and eventually to roll up a hill??