Thanks, yes. I think you are all saying the same thing. The ruler is not acting to drive the large wheel, it is a force pushing the bottom wheels. It's a good effect though. When you first see it, it seems incredible.
I don't think John and I are saying quite the same thing. My picture/feel does not require even a slight angle in the ruler - just friction between the upper wheel and the ruler as it is moved. I am merely trying to provide an intuitive, especially a kinesthetic, feel, as a context for rpenner's equations of motion.
Then I agree with John in one sense..... The force is not on the upper wheel but the lower wheel. And you in another....... It does not matter how far the ruler moves I'm sure I would agree with rpenner as well, but his analysis was beyond my level of understanding. ( That's not a criticism ) I don't think that anyone so far has agreed with the conclusions of the Youtube poster. Except myself initially, and I have changed my mind.
I too regard the intuitive picture of the lower wheel being pushed - I picture an armature of little imaginary sticks tracing the path from the ruler to the ground through the lower wheel - as key. But I think a perfectly horizontal motion of the ruler, no angle, will produce the motion of the wheels pictured. I'm not sure what you meant by "how far the ruler moves".
Just that the ruler is acting as a force. It does not interact with the top wheel. It doesn't matter how much it moves in relation to it, just how much energy it supplies to the whole system. I thought that that was what you meant. I think that the model does show that a force on a body in one direction can result in the motion of that body in the opposite direction. What do you think?
