This spinning top offers an interesting surprise. When spun, the black and white pattern changes colors. Experiment with this simple toy under a variety of lighting conditions to discover different results. Although there are theories about this bit of visual trickery, no one is quite certain why it works. The toy came about in 1894 when C.E. Benham created a black and white top that, when spun, revealed different colors.
Make a Benham Disk
- Cut a 4” or 5” diameter circle from a piece of paper. (Use a compass or trace a compact disk.)
- Fold the circle in half.
- Color one half black.
- Divide the other half into four equal sections.
- With a pencil, lightly draw twelve arcs from the center toward the outside (use a compass to do this, if possible).
- In one section, color over three of the pencil lines so they are black. In each section, trace over three of the lines in black. Avoid coloring parts of the same arc in different sections. An example of a pattern is to color the first three arcs in section one; the next three arcs in section two; arcs seven, eight, and nine in section three; and the outer three arcs in the fourth sections. Erase the pencil lines.
- Cut a same size circle out of cardstock or lightweight cardboard (like from a cereal box).
- Glue the patterned paper onto the cardboard disk with a glue stick.
- Poke a hole in the center of the disk with a pushpin. Remove the pin and push a toothpick in place. Add a dab of glue to the underside around the toothpick to hold it in place. (Option, attach the disk with a pin to a pencil eraser. The pencil may not spin like a top. Rub the pencil between the palms and watch the moving disk.)
Experimenting With Optical Illusions
- Spin the disk at various speeds.
- Spin the disk clockwise and counterclockwise. The arcs will seem to close up and form six rings. At a slow speed, spinning clockwise, the outer rings look blue and the inner rings look red. Spin the top counterclockwise and the colors reverse!
- Try spinning the disk in sunlight, incandescent, and fluorescent lighting.
- Change the pattern from the one described above. Observe the results.
- Change the color of the paper disk.
Explaining This Visual Trickery
The arcs seem to close up into circles because the eye continues to see the arc for a short time after it disappears. The red and blue colors appear because the white side of the disk is visible for an instant before being interrupted by the black side of the disk.
The entire color spectrum is present in white light. However, the human eye records the colors for different lengths of time. The eye sees part of the color spectrum – blue, the shortest rays, and red, the longest rays when the disk spins.
The Benham disk allows children to experiment with this simple optical illusion. Change the pattern on disk, alter the speed the top is spun, and try spinning the disk in different lighting conditions.
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