Making Optical Illusion Spinners

Doug Schamel and John Lahr showing Fairbanks grade school children how to make optical illusion spinners from CD-ROM disks donated by local radio stations. This is a technique that Ronald Bonnsetter of the University of Nebraska developed and demonstrated at the September, 1997, POLARIS teacher's conference in Anchorage, Alaska.

Making CD-spinners was just one of many activities available for families during the October opening of the Science Exploratorium Center set up in Denali Elementary school by Doug Schamel and Debbie Rockney.

For this project, first get a bunch of unneeded CD's from local radio stations. They toss out lots of demo CD's. Some of the lyrics are in poor taste, so I microwave the CD's for a few seconds to eliminate any possibility of actually listening to them.

Then, holding a penny with pliers, heat it in a propane flame for a few seconds and force it into the center hole of the CD so that the plane of the penny is orthogonal to the plane of the CD. Alternatively, set the penny on the burner of an electric stove set to medium heat for a few seconds.  Then grab it with pliers and press it into the CD's center hole.  The plastic of the CD melts and then sticks to the penny as soon as it cools. This is now a well balanced disk that will spin for a long time on a hard smooth surface.

Here is a gif image of the spiral design.  The spiral and Benham's disk designs are available in PDF format and in MS-Word97 format.   They are also posted on the Exploratorium's web site (spiral design and Benham's disk design).  Print out copies reduced so that they will just fit on a 4.75-inch diameter CD. With a short slit in the center that fits over the penny, these patterns can be easily spun.  The Benham's disk generates colors.   If you fix your eyes for a minute or so on the spinning spiral pattern that appears to shrink and then look a something else, such as someone's head, it will appear to be expanding.

More things to do with CD's

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