Faster Than the Eye
Can See
PURPOSE
Demonstrate the phenomenon
of "vision persistence."
PERFORMING THE EXPERIMENT
-
Using a marking pen, draw a picture of a bird, monkey,
or lion in the center of one circular gummed label.
-
Use a different colored marking pen to draw a picture
of a cage appropriate for the animal in the center of another circular
gummed label. (Other suggestions would be pictures of a fish on one
label, water on the other; an airplane on one label, blue sky on the other.)
-
Stick one picture on one side of a plastic disc,
making sure that the holes in the disc are at the sides of your picture.
-
Stick the other picture on the opposite side of the
plastic disc, making sure that the top of the second picture is opposite
the bottom of the first picture and vice versa and the holes in the disc
are at the sides of your picture. Each picture will then be right-side
up as the disc spins.
-
Cut two pieces of heavy thread of equal length
- 45-60 cm long. Thread one length of thread through a hole
on one side of the plastic disc, then through the hole next to it and tie
a knot in the length of thread. Repeat with the other length of thread
through the holes on the opposite side of the disc.
-
Place one loop of string on one index finger and
the other loop of string on your other index finger. Whirl the disc
so the string loops twist very tightly.
-
Slowly pull your hands apart, causing the thread
to untwist and the disc to spin. As the disc spins, you should see
your bird, monkey, or other animal inside the cage.
-
You may take home what you have made.
EXPLANATION
The rods and cones in our eyes
maintain a picture of what we are looking at for a brief time following
the actual view of that picture. In this experiment the rods and
cones maintain the picture long enough for the arrival of the next image.
This is called vision persistence and enables us to view a film and see
movement, even though the film is composed of a series of still pictures.
EQUIPMENT NEEDED
1-1/2" plastic disk (poker
chip) which has 4 holes drilled through it - two 1/4" apart near one edge
of the disc and the other two 1/4 " apart near the opposite edge of the
disc; heavy (button) thread; white gummed labels - 1" diameter; thin-line
marking pens.
REFERENCE
Modified from Robert W. Wood,
Physics
for Kids, 49 Easy Experiments with Optics, Tab Books, Blue Ridge Summit,
PA, 1990, page 42.
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