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6J11.u1 - Pulfrich Pendulum

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​6J11.u1 - Pulfrich Pendulum

Preview
SelectSelected
Title6J11.u1 - Pulfrich Pendulum
Objective

Demonstrate an optical illusion.​

StatusAvailable
Assembly Instructions

Instructions
Mount the bright orange mass on the overhead suspension and swing it in a plane parallel to the long dimension of the lecture bench. If you view the pendulum with an approximately 50% filter over one eye, with both eyes open. Green filter works best, but blue, red, or neutral gray work somewhat.   The weight appears to move in a large oval with the sense of motion changing as you switch to the other eye. The string also appears to stretch when seen from above (i.e., from the back rows of the lecture hall), but this is harder to observe. There are enough filters so every one in the class can see the effect. ​

Setup Time15
Operation Time
Preview Time5
Operation Instructions

Start the orange mass swinging and have the students cover one eye while both eyes are open.  They should observe the apparent path of travel be an oval even though the actual path is linear.​

ExportableNo
Demo on DimeNo
PIRA 200No
Export Instructions (if different)
HazardsNone
Analysis/Information

Intense signals travel faster on optic nerves than weaker signals.  Thus the eye with attenuation sees the object at an earlier position.  With the right eye covered, the apparent path is counter-clockwise from above.  The time difference is approximately 2-3 milliseconds.  For further details see J.T. Enright, Science 168, 464, 1970​

Category6 Optics
Subcategory6J - The Eye
Keywordsmiscellaneous optics
Construction Information
 
Equipment TitleUse SHIFT+ENTER to open the menu (new window).
  
QuantityUse SHIFT+ENTER to open the menu (new window).
  
pendulum bob orange round 3.5 inches with eye hook
1
steel cable - hung from catwalk
1
50% filter - red, blue, green, neutral gray