The figure to the left shows a simulation of two "cars". The Green block is a simple piece of wood. On each of the blocks are two wheels. The wheels are shown as yellow dough-nut shaped objects. Each wheel is free to spin about its axis.

The white plane is a flat surface that is slightly inclined. When the "cars" are released, they will begin moving toward the bottom right corner of the figure. One car has its wheels forward, the other has wheels in the rear.

One of them will "flip" around. Either they will both end wheels forward or both wheels in back.

Which will it be? Wheels forward or wheels back? Why?