How can a mirror help you see behind you?

Picture yourself in the back seat of a car. The grown-up who drives sits in front and faces the road. Up by the front window hangs a small mirror.

The driver glances up at that mirror, and there you are, waving! Touch a mirror at home, and feel how cool and smooth the glass is. So how can a mirror help you see behind you?

It all starts with light. Light from the sun shines into the car and lands on you. Then it bounces off your face and your waving hand.

Some of that bouncing light flies toward the small mirror. Light always zooms in a straight line. That is how it gets from you to the glass.

A mirror is glass with a thin, shiny coat of metal on its back. The glass and that coat are both very, very smooth. So where do you think the light goes when it hits the mirror?

The light bounces off the mirror, like a ball bounces off a wall. Because the mirror is so smooth, the light stays in neat order and keeps your shape. Now it flies toward the driver's eyes.

The light lands in the driver's eyes. The driver sees a picture of you inside the mirror. That picture is called a reflection, which means the picture a mirror bounces back to you.

The driver never has to turn around. The light from the back seat turned a corner at the mirror. So the reflection shows the driver what is behind.

A hand mirror works the same way for you. When you hold it near your face and tip it a little, light from behind you bounces off it into your eyes. Then the mirror shows you the room at your back.

Light from behind you bounces off the mirror into your eyes. That reflection shows you what is behind you.

Back in the car, the driver glances up at the small mirror once more. There you are again, still waving from the back seat.