Step-by-step tutorial
Step 1
Gather your materials.
Step 2
Cut a 4 inch diameter circle out of cardboard.
Step 3
Glue a white paper circle over the cardboard.
Step 4
Divide the circle into 7 equal sections.
Step 5
Color each section in a different rainbow color.
Step 6
Poke a pencil through the center of the circle.
Step 7
Spin the circle as fast as you can in the jar and watch as the colors blend.
Learn more
This colorful blending effect happens because of a phenomenon called "persistence of vision". When light reflects off an object, your brain holds onto that image for about a fraction of a second after the object moves. When you spin the disc rapidly, your eyes can't process each separate color wedge as it passes by. Instead, the images of all seven rainbow colors overlap on your retina, tricking your brain into blending the wavelengths together to appear as a single white or greyish-white light.
