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Mirror and letters

  1. Feb 18, 2013 #1
    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.
     
  2. jcsd
  3. Feb 18, 2013 #2

    Dale

    Staff: Mentor

    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.
     
  4. Feb 18, 2013 #3

    jbriggs444

    User Avatar
    Science Advisor

    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.
     
  5. Feb 18, 2013 #4
    From the man himself:

     
    Last edited by a moderator: Sep 25, 2014
  6. Feb 18, 2013 #5

    jtbell

    User Avatar

    Staff: Mentor

    We had a thread about this not too long ago:

    https://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". :smile:
     
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