H OLY COW--

Why is there a hole in your hand?

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What is Needed

 

• A long wrapping paper or mailing tube
• Your hand

 

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What to Do

 

Get a long wrapping paper or mailing tube. With your right hand hold the tube directly in front of your face so you can look through the tube with one eye. Place your left hand palm up, against the side of the tube at a distance of about 10 to 20 inches from your face. Now look through the tube at some distant object. Behold! You will find you see a big, clean hole right in the middle of your hand.

 

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What is Happening?

 

In many ways your eye resembles a camera. Both have lenses that form images. Both have an adjustment at the front for letting in more light, or less. Both have some way of registering the image on the back. In the camera the lights and darks of the image are registered on film. Your eye registers the image by numerous nerves on the retina. Each nerve is like a long electric wire with one end on the retina and the other end deep inside the brain.

 

When the sensitive end of a nerve on the retina is struck by light, a kind of electric current travels to a certain spot on the brain. Your brain receives thousands of such electric messages from the many nerves on the retina. Each image on the retina forms a different pattern of such electric messages. Your brain puts together the pattern to recognize the objects outside.

 

Continued on back

 

This experiment shows that a different image is observed in each eye. This occurs because each eye is in a slightly different place. Your brain puts together the slightly different images in each eye to form a single impression. You can now see why a hole in your hand was observed when you looked through a tube. The eye that looked through the tube did not see the hand. The eye that saw the hand did not see the round end of the tube. When your brain put together both at the two images together you saw both together at the same time. Thus the hole and the hand appeared in the same place, and you saw a “hole” in your hand.

 

 

                                                                       

Purdue University Department of Physics Physics on the Road Hands-On