Oakeedokee wrote:
If a mirror reverses an image left to right, why doesn't it reverse it top to bottom?
That's a really good question, and my go to whenever any one says "does anyone have any questions" after a presentation etc. just to see their response. I think it's one that Feynman used to ask his first year students (the other one being - if the sky is blue because blue has a shorter wavelength than red so is refracted more, why isn't it violet which has the shortest wavelength?), not to see if they knew the answer but to see their thought process when trying to tackle it.
This one's a little tricky to try and explain without drawing diagrams, but I'll give it a go.
The trick isn't to think about mirrors in terms of left and right, but in terms of absolute directions (e.g. East and West). Imagine there's a mirror in front of you which is due North. Stuff on your East is still to the East in the mirror. That hasn't changed. What has changed is the direction you're looking at it from (effectively, at least).
If there's an object to the North East of you (still between you and the mirror), when you look at it, you're seeing the light rays bouncing off the object and heading South. When looking at it in the mirror, the light rays bouncing off the object are heading North (before being reflected at you), i.e. you're looking at it from opposite direction. It's still to your East, but because left and right are relative directions, it's moved from your right to your left. Which makes sense as you're looking at it from the other direction.
If you hold up a clock, you'll see three is on the right (East). If you hold that still but walk around to the other side so you're looking at the back of it, the three is still on the East, but now it's on your left. That's essentially what you're doing when you're looking at a mirror - looking at the other side of things, which means that although absolute directions haven't changed, the relative directions have.
Sorry that's a bit of a convulted way of explaining things, but hope that's helped.