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This chapter is from the book

Invisible Glass

See how you can make a bottle invisible!

Step By Step

Supplies

  • smooth, transparent drinking glass (not colored)

  • 2 or 3 tubes of glycerin (100 ml, found at pharmacies)

  • empty bottle of Tabasco, or other narrow transparent glass bottle, very clean and dry, with a screw-on top

  • PVC pipe

  • piece of paneling

  • superglue

Fill up the bottle with glycerin and screw the lid on tightly. Fill about one-third of the glass with glycerin. Slowly place the bottle in the glass. A part of the bottle will be submerged. What happens to this part? Why? What will happen if you place the bottle with glycerin in a clear glass with a third of its volume filled with water?

Optional

Use the PVC pipe, superglued onto the piece of paneling, as a holder for the glass. This will keep the glycerin from spilling over.

Fun Facts

Everyone knows that placing a knife in a glass of water makes it look bent. Of course, the knife out of the water isn't bent. Check it out for yourself. The light that comes from each part of the knife reaches you at the shortest time possible. (Light is most efficient!) In water, the speed of light is less than in air or in outer space. (You can also express it in terms of the refraction index, which is the ratio of the speed of light in the outer space and the speed of light in a transparent medium, like water and glass.) So, light is better off if it takes a shorter path in water, where it is slower (has a higher refraction index), and a longer path in air (has a refraction index of approximately 1), where it is faster. If light did not bend when it comes out of the water, its path in water would be longer and in air it would be shorter, so on the whole, the light would take more time to reach you. It then "prefers" to bend. This shows that light "sees" water and air as different media. What can you say now about the glycerin and glass? Do they look different for light? (Are their refraction indexes different or the same?)

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