Retrograde Motion Illusion for an Electric Fan

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This Demonstration shows the rotation of an electric fan in slow motion—by about a factor of 10—for computer display compatibility. The fan rotates clockwise. A conventional incandescent light source is somewhat stroboscopic, due to the 60-cycle alternating current powering it.
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Contributed by: S. M. Blinder (March 2011)
Open content licensed under CC BY-NC-SA
Snapshots
Details
Snapshot 1: At relatively low RPM, see clockwise rotation.
Snapshot 2: Speeding up rotation, get retrograde illusion.
Permanent Citation
"Retrograde Motion Illusion for an Electric Fan"
http://demonstrations.wolfram.com/RetrogradeMotionIllusionForAnElectricFan/
Wolfram Demonstrations Project
Published: March 7 2011