A pencil is on a sheet of paper that is being pulled along a table top. As the paper is pulled faster, the pencil begins to roll. Does it roll forward or backward?
The first movie in this series, pencil1.mov, shows the motion before the paper accelerates. Use it to make a prediction about the direction that the pencil will roll. Carefully define what you mean by "backward" and "forward"! Use the second movie, pencil2.mov, to see if your prediction is correct. Observe carefully! Were your definitions complete enough? You can use video analysis to measure the velocities of the paper and pencil.