A person asked this question of me recently and it generated some discussion amongst the people in the room (many of whom had a limited background in physics). The original question went something like this: suppose that a ball is initially at rest in a wagon and the wagon is given a horizontal pull (so that the ball appears to roll to the back of the wagon). The wagon is then brought to an abrupt stop. Does the ball continue to roll backward relative to the wagon because that is the way the ball was spinning? After some discussion the question was modified to be more like this: Suppose that there is a ball which rests on an infinite horizontal plane. The plane is pulled horizontally so that it reaches a high speed with respect to its initial rest state and then the plane is brought abruptly to rest. What is the behavior of the ball a) as seen from the initial rest frame and b) as seen from the frame of the plane? To avoid a rather lengthy first post I'll avoid writing my answer to the question for now, but I'm interested to see some responses. Kinda funny that this question is almost identical to Feynman's story of asking his father about the behavior of a ball in a wagon!