A mirror flips left and right, but not up and down • Hacker News Board

Re: A mirror flips left and right, but not up and down

#81

Post by dasil003 » Fri, Jul 22, 2011, 5:01 PM UTC

dasil003 wrote: post #63

jws wrote: post #17

Earlier quoted context omitted.

The little players on a foosball table probably think mirrors flip up and down, since that is their normal method of turning around.

Is that true or does their mind explode because they see a figure that can only exist wearing the other color shirt?

Whoever downvoted me is an idiot.

The effect of left/right "flipping" is because we are left/right symmetrical and so we can imagine ourselves being the person in the mirror by turning that way. For up-down flipping to happen we have to be top-bottom symmetrical to even begin to think about it, although it might not be that simple since gravity continues to differntiate those directions.

Re: A mirror flips left and right, but not up and down

#82

Post by losvedir » Fri, Jul 22, 2011, 7:18 PM UTC

JonnieCache wrote: post #77

losvedir wrote: post #40

To go along with fun mirror-things to think about, how about this one: Stand in front of a mirror. Note the lowest point on your body that you can see in the reflection, whether it's your waist or thighs, or whatever. Now, no matter how close you get to the mirror or how far you step back, that will always be the lowest point on your body in the reflection. (e.g., you'll never be able to see your toes, if you couldn'…

LIES! I just tried this, the visible portion increased by about a 50cm when I stepped back about 3m. I guess this is because my big mirror isn't exactly flat to the wall. Come to think of it, it isn't even completely flat.

Ha, good point. I neglected to include that the mirror must be flat....

I'm glad you tried it, though! My friend told me this and I just didn't believe it until I tried it for myself.

Re: A mirror flips left and right, but not up and down

#83

Post by martincmartin » Fri, Jul 22, 2011, 7:19 PM UTC

BenoitEssiambre wrote: post #65

martincmartin wrote: post #27

Mirrors don't flip left and right, or up and down. They flip front and back.

This is the first part of the answer. The second part is that, since we define the left and right on an object relatively to its front and back, flipping the front and back also swaps how left and right are defined. There is no confusion with top and bottom as they are not defined relative to front and back.

Absolutely true.

Re: A mirror flips left and right, but not up and down

#84

Post by 7rurl » Fri, Jul 22, 2011, 7:44 PM UTC

daimyoyo wrote: post #34

I think a more interesting question is how the rear view mirror works. What I mean is how does a perfectly clear image become slightly dimmer when you adjust the angle of the mirror? I've seen that since I was a child but I've never understood why it works.(I never got past calc based physics in college so if the answer is obvious I apologize.)

The bright reflection is the reflection off the silver backing of the glass in the mirror (i.e. the normal mirror reflection). The dim reflection is the reflection off the surface of the glass (the same as the reflection you see of yourself when you look at a window when it is dark outside and bright inside).

Flipping the "switch" on the mirror simple changes the angle of the mirror by the exact amount needed to reflect the light from your rear window into your eye off either the silver surface or the glass surface.