How we did it:
- glass cup (3) - smooth sides
- food coloring
Fill each of the three cups with water. Use food coloring to dye one cup red, another blue, and the last yellow.
Now arrange the cups in a triangle shape with the yellow cup in front. You might imagine that where the blue and yellow cup overlaps you would see green. Conversely, where the red and yellow cups overlap one might expect to see orange. However, the colors are switched!
If you arrange the cups a different way, do the colors still flip?
What is going on?
What you are seeing is a beautiful example of refraction - the bending of light as it passes through two different materials. When viewed from the side, a glass of water acts like a magnifying glass, bending any light that passes through it towards the center of the glass. Light rays from the blue and red glasses pass through the yellow glass and are bent towards the center, sending the familiar combinations of green (yellow + blue) and orange (yellow + red) to opposite sides when the light finally reaches your eyes.
This trick depends on the distances between the glasses and your own viewing distance. What happens if you move closer to the glasses? What happens when you move the yellow glass further from the red and blue glasses?
You can also play with refraction by drawing an arrow on a piece of paper and holding the arrow behind a glass of water. At some distances, the arrow will point in its original direction, but at other distances, the arrow will flip!