The Poincare group, the group of transformations of the plane which preserve the Minkowski distance between points, is derived as compositions of suitably defined reflections in straight lines. It is shown that any such transformations must be one of four types. (Author/JN)

Presents a problem to determine conditions under which two identical masses, constrained to move along two perpendicular wires, would collide when positioned on the wires and released with no initial velocity. Offers a solution that utilizes the position of the center of mass and a computer simulation of the phenomenon. (MDH)

An incident light ray parallel to the optical axis of a parabolic mirror will be reflected at the focal point and vice versa. Presents a mathematical proof that uses calculus, algebra, and geometry to prove this reflective property. (MDH)