Michael Berry wrote a paper called Regular and Irregular Motion. He determined the predictability of the path of a struck billiards ball. The path after the first impact is easy to determine with basic geometry. The second path is a bit harder, but still relatively easy. By the 9th impact Berry determined that the gravitational pull of a person standing next to the table had enough of an influence on the ball path that it was necessary to be included in the calculations.
important conderation for long term projections.
