  A theoretical analysis about the influence of the Hertz elastic contact on a
three body chain collision is presented. In spite of the elastic character of
the collision, the final velocity of each particle depends on the particular
interaction between them. A system involving two elastic spheres falling
together one in top of the other under the action of gravity, and colliding
with an horizontal hard wall is studied in detail. The effect of the Hertz
contact interaction can be easily put in evidence for some particular
situations.
