The possessed pendulum: a profound illusion
People sometimes mistakenly assume that magic tricks are supernatural events caused by spiritual forces, simply because they seem so real. Magic tricks are not created by any supernatural means, but rather through some clever scientific methods. This series of articles introduces some magic tricks that you can easily learn and perform using readily available items around your home. The science, cause and effect of each trick will be explained.
Materials you will need
a rope about three feet (1 meter) long
a heavy object to act as a pendulum (a small ball works well)
dark glasses that you can cut in half or a dark lens that you can hold up to your eye.
method
Tie the string to the heavy object, if you are using a ball, wrap the string around the ball several times to hold the ball securely. Hang the pendulum in front of a blank wall. It should rock slowly from side to side.
Distribute glasses or sunglasses to your audience. Ask them to watch the movement of the pendulum with both eyes open, and ask someone to describe the path of the pendulum.
Then have someone hold a dark lens in front of your right eye, keeping both eyes open. Again ask them to describe the motion of the pendulum. She will appear to be swinging in a clockwise oval path.
Now have everyone change the lens to the left eye. The pendulum will appear to change its direction of rotation. It will appear to be swinging in an oval path counterclockwise.
illusion explained
The brightness of an image affects how light-sensitive cells in the retina respond. A very bright light causes the nerves to fire a fraction of a second sooner than a dimmer light. Both eyes are looking at a moving object, but one eye is covered by a darker lens, so it will see the object less brightly than the naked eye. The nerves in the retina of the uncovered eye will send their message to the brain before the covered eye, thus producing an illusion of depth. You will see the pendulum swing in a circular path instead of just swinging back and forth. When you switch the lens to the other eye, the movement pattern is reversed.
This is great entertainment for a party. Perform some of these tricks that I am describing in this series for a fun-filled party with your family and friends where you will not only entertain but you and your friends will learn the scientific principles that make these tricks possible.
