The magician covers a box with a silk scarf. Slowly, she raises the box into the air. While holding the covered box, she suddenly flicks her wrist. The scarf goes limp and the box disappears. How did she do it? We’re not telling, but we do have a magical activity that also produces a phantom shape in thin air.
Things Required:
Sheer nylon stocking
Plastic grocery bag
Smooth wall
Directions:
With one hand, hold the top of the stocking against a flat wall. Use the other hand to stroke the stocking in one direction with the plastic grocery bag. As you stroke the nylon material, smooth it against the surface of the wall.
After several strokes, release the stocking. What happens to the material? How is this similar to sticking balloons to a wall? How is it different?
Now gently grasp the top of the stocking and move it away from the wall. Make sure it does not touch anything (including yourself). Hold out the stocking. What happens to its shape? Can you explain your observation?
This Is What Happens:
As the plastic bag moves over the nylon, it picks up negative charges. This produces a stocking with a net positive charge. This charged stocking acts like the negatively charged balloon and induces an opposite charge in the nearby wall. The negative and positive charges attract and the stocking clings to the wall. When the stocking is pulled from the wall, it still retains its net positive charge. These charges, which are distributed throughout the stocking material, push away from one another. This causes the stocking to “expand” and take on the shape of the leg it was manufactured in.
