How does a mirror work?

You stand in front of a mirror and wave. The person in the mirror waves back at exactly the same moment. How does the mirror know what you look like?

Mirrors bounce light

To see anything, your eyes need light. Light leaves the sun or a lamp, lands on your face, and bounces off in all directions. Some of it flies into the room.

A mirror has a very smooth, shiny back hiding behind the glass. When light hits something rough, it scatters everywhere in a messy way. But when light hits a mirror, it bounces off neatly, like a ball rolling straight back off a flat wall.

A neat copy of you

Because the bounce is so tidy, the light from your face travels to the mirror and comes straight back to your eyes. Nothing gets jumbled up. So you see a clear picture — a reflection — that looks just like you.

There is one funny thing: the reflection is flipped. Lift your right hand, and your mirror-self lifts the hand on the other side!

Smooth is the secret

A still pond can act like a mirror too, because the water is smooth and flat. Stir the water and the picture breaks into wobbly pieces. Smoothness is the magic that keeps a reflection clear.

Wonder fact: Light is super speedy. Your reflection bounces back so fast that you could never catch the mirror being even a tiny bit late!