# Lateral inversion up-left and down-right confusion

1. Dec 2, 2012

### rishch

Hi :)

So I'm learning about lateral inversion in plane mirrors and it's a bit confusing. I think of it like this:-

Suppose you had a clone of your self who is standing next to you and facing the same direction. He walks a few steps forward and then turns to face you. When he turns to face you he does this by turning 180 which effectively switches left to right and right to left but the head and foot do not exchange positions. However if you think of a mirror it's turning to face you WITHOUT switching left to right so it appears inverted. It would be like putting paint on your body and then hugging the mirror.

But suppose you turn 90 degrees (maybe you can lie down on a table) and look in a mirror you're still laterally inverted but it's up-down inversion relative to the first case. And while you were lying down on the table, if a friend were to come and stand next to you he would also be laterally inverted. It's like the mirror is doing both at the same time. How?

And there's a question in my textbook "can you think how a single plane mirror can reverse up-down, up-left and down-right?" I'm not sure what up-left and down-right means.

2. Dec 2, 2012

3. Dec 2, 2012

### rishch

Yes the last video is exactly what I was thinking. We're actually switching front to back but the brain interprets this as rotation. I guess that's because in real life you can't switch front to back. I also think that it's because we have a vertical line of symmetry.

4. Dec 2, 2012

### rishch

Oh and I just wanted to ask what aperture is of a mirror is? Is it area or length or what?

5. Dec 2, 2012

the diameter

Dave

6. Dec 2, 2012

### rishch

So would it be the length of the arc or the length of the line joining the two end points of the mirror?