Last night I was waiting in line at the supermarket when I saw a 2-liter bottle of Pepsi sitting on the second section of the conveyor belt – the part that’s runs slightly downhill, after the scanner. The bottle was rotating on axis as the conveyor belt moved under it (a sight I’ve seen many times), and slowly it rolled to the source end of the conveyor belt – uphill.
I figured out after a few minutes that it wasn’t violating the law of conservation of energy, as there was a power source connected (the motor and, before that, the power station’s generator). But what the hell mechanism was enabling the bottle to roll uphill? (I asked the checkout
clerk, and her helpful explanation was, “Yeah, they do that sometimes.”)
Without having access to the exact setup, I can only guess. The bottle was resting on two things - the moving conveyor belt, and the stationary piece of steel at its end. The conveyor belt has more friction, so it causes the bottle to roll, therefore the bottle is trying to roll up the piece of steel that it’s also resting on. The force due to friction that the steel is putting on the side of the bottle is enough to overcome the force of gravity pulling it down the slope.
I just noticed that you said it started out on the lower end of the belt, and then travelled uphill. I’ll modify my guess to be that part of the bottle was hanging off the side of the belt, and making contact with the table surface. The moving belt caused the bottle to roll, so the end of the bottle was trying to grip the table top, and that was enough force to overcome gravity.