This Week's Experiment - #305 Floating Finger
This week's experiment came from my niece, Lauren. She demonstrated some of
the things she has been doing in science class. This is one that we did as
kids, just for fun. Now I see the science side of it as well. To try it,
you will need:
your fingers
your eyes
This is a really simple one that shows some of how our eyes work. Start by
pretending to be a mosquito. By that I mean to stick out your finger as if
you are pointing at something. Put your hand to the end of your nose where
your finger will stick out, like the long, thin snout of a mosquito. You
can even hum a bit if you want to complete the image. While you are doing
that, look at your finger. Yes, I know that it is not easy to look at it
when it is that close, but that is part of the experiment.
What do you see? Two fingers! One on the right side of your nose and one
on the left. Each finger you see is transparent, so although you can see
the finger, you can also see through it. Why do you see this? It is
because your eyes are seeing your finger from two different angles. You can
see this better by closing one eye. Suddenly, one of the transparent
fingers will disappear. The other becomes solid. Your brain is only
getting one image, so things look normal. Now open both eyes and the two
transparent fingers are back. Close the other eye. Again, you now see
only one finger and again it is solid, but it is on the other side. With
both eyes open, on the left side, one eye sees a finger, but the other sees
whatever is behind the finger. The same thing happens on the right side, in
reverse. As your brain puts the two images together, you see two
transparent fingers instead of one solid one.
Now for the fun part of the experiment. Stop playing mosquito. (You can
still hum if you want.) This time, you will need both hands. With your
right hand, stick out your index finger, just as if you were pointing at
something. Hold your hand on the right side of your face with your finger
pointing to the left, so that the end of your finger is about three inches in
front of your right eye. What do you see? A transparent finger, right?
Keep that finger in place and do the same thing with your left hand in front
of your left eye. Now you should see two transparent fingers, one in front
of each eye.
Here is where things really get interesting. Slowly move your fingers
toward each other. As the two transparent fingers cross, you will see
something strange. Suddenly, you will see a solid, double ended finger
floating between the two transparent fingers! What is going on?
Your finger looks transparent because one eye is seeing the finger and the
other is seeing what is in the room behind the finger. Your brain puts the
two images together, and you see a transparent finger. When the two images
cross, you get a different result. One eye sees your right finger. The
other eye sees your left finger, in the same place. Neither eye can see
what is in the room behind the fingers, so the floating finger looks solid as
your brain combines the two images. Keep moving your fingers together until
they touch. Now, you should see two solid fingers, with a solid, double
ended finger between them. Your brain, combining the two different images,
has come up with a very strange combination, which as a child, I found very
funny. It probably says something about my level of thinking that I still
do. Have a great week!
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
|
