Friday, August 13, 2010

The Two Of You

"The world is full of obvious things which nobody by any chance ever observes." So said Sherlock Holmes in "The Hound of the Baskervilles".

   One of those 'obvious thing's' found in everyone’s world is a flat mirror. There's probably one hanging on your living room wall and for sure there is at least one where you shave or comb your hair.
   Ask your kids or grand kids to stand in front of a mirror and tell you what they see. They will see a lot of things like their own image, objects in the room, their hair is uncombed, etc., but they will not observe that their image appears to be behind the mirror
   Ask them to touch the nose of their mirror image. In trying to comply with your request, they should observe that instead of the finger touching the nose, it touches the surface of the mirror!
   When looking into a flat, plane mirror, there is the real you, in front of the mirror, and then there is a virtual you, an image of you (cleverly called mirror image), as seen in the mirror! The two are not exactly identical.
   To observe a difference between the two images, ask the kids to look into a mirror, close their right eye, and observe which eye the mirror image closes. It comes as a shock to most that the mirror image closes its left eye!
   The word AMBULANCE is often painted in its reversed form,

on the front of the vehicle. A driver, looking into the rear-view mirror, sees


and correctly identifies the vehicle as an emergency vehicle and pulls to the side of the road. 

   To demonstrate, I've printed a page with the word AMBULANCE reversed on the page (I have graphics software that reverses text). When viewed in a plane mirror, the mirror left-right reverses the word so that it reads correctly, just as you would see it spelled correctly in your rear-view mirror.

  Besides the left-right reversal, there are several interesting mathematical and scientific relationships to be discovered exploring mirror reflection. Here's a good question to ask. Since a plane mirror reverses left and right, why doesn't the mirror reverse up and down?
   In the next mirror post, I will explore the relationship between the distance an object is in front of a mirror, and the distance the image appears to be behind the mirror. I know several ways to demonstrate this relationship so I'll start with the simplest and most intuitive method.