When it comes to mirrors we all have many questions, like…
Why do words appear backward in a mirror?
Why letters are inverted in the mirror?
Why do mirrors flip horizontally but not vertically?
A lot of people seem to ask this question when they wear a T-shirt in front of a mirror. Why are the letters on the T-shirt reversed in the mirror, while your head appears right side up? Why does a mirror only reverse things in the horizontal dimension?
For example, when you hold up a sign saying “damn” in the mirror”, it flips reads a backward “nmad”, but the letters are still the right way up.
Mirror image is a tricky thing, but it’s pretty clear when you look at words in a reflection, that mirrors flip things horizontally rather than vertically.
So here’s what science has to say:
Mirrors don’t reverse things left to right. Mirrors don’t actually reverse anything. It’s you who is doing the flipping.
Think about how a mirror works. Photons — particles of light — stream toward the smooth pane of glass and bounce off it. The image of everything in front of the mirror is reflected backward, retracing the path it traveled to get there.
Nothing is switching left to right or up-down. Instead, it’s being inverted front to back.
In a contemplative whiteboard animation, Minute Physics explains the manner in which a mirror reflects the image in front of it, which will help you to understand better.