Idea

Every conic posseses its optical property. Parabola reflects every beam parallel to the parabola’s symmetry axis to pass through its focus. 

Components

• fixed base with mirror vertical wall in form of parabola (horizontal cross section),
• carrier that moves along line perpendicular to the parabola axis,
• source of thin beam adjusted to the carrier, e. g. laser pointer,
• some small thing as a target to be located at the focus: a ball, cube, toy. 

Operation

A visitor is suggested to hold a simple experiment. At first determine the focus. It is easy to be seen since the beam has slight slope downwards and it its trajectory is visible on the base. Due to continuous movement of the carrier the focus is easy to notice.

The second step is to pose the target and verify the solution or demonstrate it to the companion.

Advantage

of this physical_ex is in its exceeding of merely demonstration of optical property. Playing parabolic billiards (commonly presented in math museums) you can only check that balls get into the marked focus. This exhibit allows visitor to find the focus.