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How are our hands chiral?

  1. Jan 29, 2012 #1
    How are our hands chiral??

    How are human hands chiral at all. Put them in the praying position and they are superimposable!
    "The left hand is a non-superposable mirror image of the right hand; no matter how the two hands are oriented, it is impossible for all the major features of both hands to coincide" says wikipedia.
    Some of my teachers and friends say you cannot rotate them like that but clearly we can orient them in any way we want so in the praying posiiton when palm faces palm hands are superimposed
    I dont understand this at all - why are hands referred to as chiral at all?
  2. jcsd
  3. Jan 29, 2012 #2
    Re: How are our hands chiral??

    Hi jd12345,

    I think you're misunderstanding the word "superimposable". This means that the outlines of the hands should be able to match up exactly-- i.e. one hand can occupy exactly the same space as the other hand. One way to see this is to think of a left-handed glove. This glove delineates a region of space that the left hand can occupy, but the right hand cannot. No matter how we rotate a disembodied right hand, it will never fit snugly into a left-handed glove. Because it can't occupy the same region of space as the left, it is not superimposable with the left.

    In the praying position, one face of each hand is indeed matching up along the same outline, but the whole hands are not. So this does not demonstrate superimposability.
  4. Jan 29, 2012 #3


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    Re: How are our hands chiral??

    Make your left-hand curl one direction (let's define that as clockwise) and give a thumbs up. In order for your right hand to curl clockwise, it must give a thumbs down.
  5. Jan 30, 2012 #4
    Re: How are our hands chiral??

    got it , thank you
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