The parabola, a geometric shape that can be defined as the locus of points equidistant from an axis called the directrix and a point called the focus.
Parabolas
crop up everywhere in nature and in things we make. If you kick a ball
or throw a stone up at an angle into the air, the trajectory or path
traced out is in the shape of a parabola. Similarly for a jet of water
or projectile from a gun. Satellite dishes, radio and optical
telescopes, flashlights and car headlamps all have parabolic reflectors
because of a useful property of the shape: Rays from the focus of the
parabola hitting the reflector are "bounced" outwards in a parallel beam
(in the case of a light, heat, microwave or sound source) and vice
versa for incoming parallel rays so they're focused on a detector (for a
satellite dish or telescope).
Graphic created with Geogebra (GIF export resolution is a bit low and limited to 400 pixels wide, hence the fuzziness, so I have to figure out if it's possible to increase this)