  When a falling ball chain strikes a surface, a tension is created that pulls
the chain downward. This causes a downward acceleration that is larger than
free-fall, which has been observed by recent experiments. Here a theoretical
description of this surprising phenomenon is developed. The equation of motion
for the falling chain is derived, and then solved for a general form of the
tension. the size of the tension needed to produce the observed motion is
relatively small and is explained here as coming from the rotation of a link
just above where the chain collides with the surface. This simple model is used
to calculate the size of the tension in terms of physically measurable
quantities: the length and width of link, the maximum bending angle at a
junction, the inclination angle of the surface, and the coefficients of
friction and restitution between the chain and the surface. The model's
predictions agree with the results of current experiments. New experiments are
proposed that can test the model.
