HOWTO make a penny disappear by changing the speed of light


21 Responses to “HOWTO make a penny disappear by changing the speed of light”

  1. PhosPhorious says:

    Fucking pennies!  How do they work?

  2. Yuna Meal says:

    I would have said this is about reflection.

  3. wrwetzel says:

    Read about “Total Internal Reflection”:

    It is the same effect that makes some of the surface of a swimming pool look like a mirror when viewed from under water. If the water is completely still you can see up and out through a disk directly overhead. The rest of the surface looks like a mirror, reflecting the image of the walls of the pool.


  4. Gemma says:

    Cory, in your first sentence, change “wet” to “dry”. He shows the illusion fails if the penny is wetted.

  5. Ehlyah says:

    And this person is qualified to teach physics? This is basic stuff.

  6. C.J. Hayes says:

    I would’ve used a different analogy.  “Imagine the penny is there, but you can’t see it! Light is involved!”

  7. ian jones says:

    A physics TEACHER not understanding this is like an English teacher being bamboozled by The Cat in The Hat.

  8. The Ouroborus says:

    This guy sounds incredibly bored.

  9. Brian Koss says:

    If he is a science teacher, he should have an explanation for this phenomena.  It’s simple refraction, people.  Nothing of value here, move along.

  10. ryuchi says:

    Well, it’s like putting the pennie on the other side of a mirror–you can’t see it. Then u put it infront of the mirror–u see it. Then you put water–you RUIN the condition to produce a mirror-effect: two types of dencities–Air & Glass/water/

    Glass and water are similar (in fact glass is liquid that “spills” slow in time) so when u make the pennie wet and stick it to the “mirror surface” you provide the same densitiy from both sides of the mirror (water) which ruins the mirror effect (needs two far different densities: air & water/glass) blabla

    my two pennies anyways

    • flosofl says:

      (in fact glass is liquid that “spills” slow in time)

      I wish people would stop spreading this. Glass is NOT a liquid. It is an amorphous solid.

      From List of common misconceptions

      Glass is not a high-viscosity liquid at room temperature: it is an amorphous solid, although it does have some chemical properties normally associated with liquids. Panes of stained glass windows often have thicker glass at the bottom than at the top, and this has been cited as an example of the slow flow of glass over centuries. However, this unevenness is due to the window manufacturing processes used in earlier eras, which produced glass panes that were unevenly thick at the time of their installation. Normally the thick end of glass would be installed at the bottom of the frame, but it is also common to find old windows where the thicker end has been installed to the sides or the top

      It’s almost as bad as the “We only use 10% of our brain” canard.

      EDIT: added wiki link and quote

  11. Gabriel Meister says:

    Cory — well played, good sir, with your sneaky link to SR Delany’s wonderful autobiographical work.  More folks should read it, it’s beautiful.

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