Both the parabola and the catenary are curves that can be seen in everyday life—or rather, only parts of them, since both extend to infinity.
The first, the parabola, appears in the perspective view of a circle seen from within—for example, the tiers of seats in a circular theater—or, in some cases, in the patch of light cast on a wall by a lampshade or flashlight. It can also be seen in the shape of water jets and the paths of fireworks. Finally, it is the first mathematical curve that students in tenth grade (French seconde) draw when they study the graph of the squaring function.
The cone of light from a flashlight aimed at a wall at the right angle traces a parabola.
