A simple experiment is described where the tip of a metal ruler is used to strike a 50 g mass. Since
the ruler is very flexible, the impact duration is much longer than usual, giving the impression
that the ruler simply pushes the mass forward at low speed over a long distance. The tip of the
ruler remains in contact with the mass throughout the impact. However, the impact is best described
as a long duration collision with a coefficient of restitution (COR) greater than zero, despite the
fact that the relative speed during and at the end of the collision is zero. If the mass rests on a
table and if the ruler strikes the table before striking the mass, then the ruler bends and stores
elastic energy. The result is a superelastic collision where the COR is greater than unity.