Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Clive Chambners on 15/07/2008 10:00:47

Title: Why does a mirror reverse right and left but not top and bottom?
Post by: Clive Chambners on 15/07/2008 10:00:47
Clive Chambners asked the Naked Scientists:
Dear Drs

I briefly heard Drs Rhod & Karl recently talking about mirrors reflecting left to right but not up & down, this got me thinking and I came up with this explanation which I hope makes some sense.
Imagine the object being viewed as a projector of an image which on its way to you hits the back of a screen which you are viewing from the front.

You see a correct image.

If you now walk around the side of the screen and view the back of it, as if the screen were a mirror reflecting the image back to you, you will see the traditional mirror image of the object, ie just reversed left to right.

If you had chosen to fly over the screen and down the other side, head first, you would have seen the image just revered top to bottom!

So it depends on your movement as to which way the image is reversed.


Clive Chambers

What do you think?
Title: Re: Why does a mirror reverse right and left but not top and bottom?
Post by: lyner on 15/07/2008 11:10:38
Actually, although we call it 'lateral inversion', there is NO reversal. In the image we see, the top bits stay at the top and your left bits are on (your) left, etc.. However, if someone were standing beside the mirror, facing you, it would be THEIR left which would be towards YOUR right. They would be the ones who have switched because they would have rotated (about a vertical axis) to face you, whereas your image hasn't. They could, just / almost as easily, have stood on their head in order to face you - although it is not likely- and then their left would be on your left side.

Words written on the chest of the real person will read correctly because that's what we have learned to read but words written on your own chest will not be recognised on your image because you never learned to read that way.
Essentially, what has changed in a mirror image is the Rotational relationship between 'up' and 'left', etc. - a clock, in a mirror, appears to be going Anticlockwise.