When I spin a ping pong ball on the table, it rolls forward in the opposite direction of the spin, and then eventually changes direction and rolls backward.
Here's a video demonstrating the effect.
Why does that happen?
Answer
One way to explain it that makes sense to me is that the backwards spin on the ball is a force pushing the ball toward you. The one time applied force of your finger that creates the backward spin also pushes the ball forward, but the backspin stays almost constant. At the moment you spin the ball, the forward force is greater then that of the backspin, so the ball moves away. After time zero, the backspin is the only force acting horizontally (you aren't still touching the ball, so there is no applied force) and so the ball slows, then returns because of a negative acceleration.
If you were to graph this motion as Position (away from you) vs Time, you would get a graph that looks similar to the motion of a ball thrown upwards and pulled back by gravity.
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