Examples of Parabolas

When a ball is thrown into the air, its path is the parabola shown in Figure 5.4.4, with the highest point at the vertex.

Figure 5.4.4

Telescope mirrors and radar antennae are in the shape of parabolas. This is done because all light rays coming from the direction of the axis will be reflected to a single point, the focus (see Figure 5.4.5). For the same reason, reflectors for searchlights and automobile headlights are shaped like parabolas, with the light at the focus.

Figure 5.4.5

A parabola with a vertical axis (and horizontal directrix) is called a vertical parabola. The vertex of a vertical parabola is either the highest or lowest point, because it is the point closest to the directrix.

Example 1