Mirror and letters

Numeriprimi

Hello.
I have got basic question for you. Can you explain it simply?

Why are the letters in a mirror overturned on left-right and not upside-down?

Thanks. And sorry for my bad English.

DaleSpam

They are not turned left-right. The left-most letter is still on the left and the right-most letter is still on the right.

When a person turns to face you the left-most letter is on the right and the right-most letter is on the left.

Mirrors do not switch left-right nor do they switch up-down. When people face you they do switch left-right but not up-down. That is why mirrors seem strange left-right but not up-down. They are strange because they do not do a turn that we are used to seeing people do.

jbriggs444

A mirror reverses front and back (*). This means that the three-dimensional symmetry of an image in the mirror has been reversed; a mirror image of a right hand looks like a left hand and vice versa.

A front-to-back reversal is identical to a left-to-right reversal coupled with a 180 degree rotation. Either interpretation is valid. As Dale points out, the interpretation that feels natural is a left-to-right reversal with a 180 degree rotation.

(*) Where "front" and "back" are referenced against the plane of the mirror.

mickybob

From the man himself:

http://www.youtube.com/watch?v=msN87y-iEx0

jtbell

We had a thread about this not too long ago:

http://www.physicsforums.com/showthread.php?t=647426

Take a look at the picture attached to post #8, and then re-consider whether the letters are really "overturned on left-right".