Science Water Experiment for Kids Creates Invisibility Illusion

Magicians often use basic scientific principles of light and optics to fool the eye and make people believe they can make things disappear or turn invisible. The following elementary science experiment shows how simple light refraction and reflection can cause small objects to apparently vanish.

Educational Materials

  • 1 clear glass or plastic jar with an opaque lid (an empty peanut butter jar or jam jar would be ideal)
  • 1 stamp (or some other flat object, like a sticker) small enough to fit completely under the jar
  • A container of water

Classroom Science Experiment/Kids Magic Trick

  1. Place the stamp on a table. Allow the kids to view the stamp from the side (not from the top down).
  2. Now place the jar over the stamp/sticker, making sure to keep the lid on the jar. The kids should still be able to see the stamp/sticker from an angle.
  3. Lift the jar off of the stamp, unscrew the lid, and fill the jar with water. Put the jar back on the stamp/sticker.
  4. Kids will find that the stamp, which they could clearly see through the jar before, has now apparently vanished!

Light Reflection Science Facts

We see objects when light reflects off of them, allowing our eyes and brain to process an image of the object. When light passes from water to air, however, the light bends (or refracts) because it travels through water at a slower speed than through air. This refraction can create distorted or displaced images of the actual objects.

 

In the experiment above, light refraction caused the stamp to appear higher near the water’s surface. Because the jar was covered by a lid, however, the audience could not see the reflected image of the stamp, creating the optical illusion that the stamp had vanished. If the kids were able to come closer to the jar and view it from the top down, they would be able to see a distorted image of the stamp through the water.

Discussion Questions

Magic shows aside, can you think of places where light refraction occurs naturally? What kind of optical illusions might it cause? (Consider ponds or lakes where fish can appear to be in different places thanks to light refraction – and consider how this might make it difficult for fishermen, bears, or birds to catch fish).

If this science experiment were done with a different type of jar (glass, plastic, differently shaped etc.)? (If possible, let kids try this experiment/magic trick several times using different jars and various types of objects – such as coins or colored paper – that they can try to make disappear).

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