What if I say that the mirror doesn't flip left and right? You've heard it right the mirror doesn't do the flipping. As the above answers say the mirror shows what is right infront of it. It's you(we humans) who think it is flipping.
Let me get this in detail
Before we begin tell me ,
'What makes you think that the mirror flips your left and right?' Or may be
'what image do you think the mirror flips?'
The second question is a follow up question of the first one.
To answer these questions you need a camera not just an ordinary camera an imaginary,invisible camera { i.e i(camera) i,as in x+iy not in iPhone pun intended}
Now take a picture of yourself (No, not a selfie)with that camera at a distance x and at height of your eye from ground. What do you see? you will see a picture of 'beautiful you' in that picture with your left and right unswapped
Now place a mirror(big one) facing you at a distance x/2 from you while you are standing still ( now you know why I said,no selfie)
Now take a picture of the mirror with the cam at your eye (I know it's practically not possible but trust me this 'i' can do anything) what do you see? You will see the same 'you' as beautiful as you were in the first pic but with your left and right swapped
Now you see that the image is a flipped left and right. (I guess you can answer the second question now) Now, your question is why didn't the camera flip the up and down, right? I'm getting there.
It's because of you.It's because you did something when you were taking the second pic. You must be thinking 'what did I do? I barely moved'
After you inserted the mirror when I asked you take the second pic, how did you bring the cam from x to you and make it face the mirror?
You brought the cam to you with its lens still facing you and turned the camera around by 180 ° towards the mirror about the vertical axis (bringing it to you and turning need not be in the same order) that's why the image is looking flipped left-right.
Had you turned the camera 180 degrees about the horizontal axis we would have seen a vertically inverted image.
I hope you understand what turning about horizontal axis means.
When you turn the camera by 180° about horizontal the camera will face the mirror and the camera will be upside down
Remember:
turning about vertical
Turning about horizontal
You took it for granted that your the camera has to be turned that way only because it doesn't make any sense taking pics with upside down camera. It like looking at the world with legs up and head down. Yes nobody looks at it that way but that that's what makes the difference.
- To avoid confusion take another pic with camera facing the mirror and the camera is upside down. I.e turned 180° degrees about horizontal.
What do you see now? If you look at the pic in the camera. It's again 'you',beautiful as ever but your are upside down, it's not just you it's the whole world that is upside down (caution:Normal digital cameras sometimes correct the orientation for you using gravity sensor and may show upright image of you)