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In this activity, students take advantage of persistence of vision with a simple apparatus that turns a series of static images into motion.

In a stroboscope, slits open and close in front of your eye as the disc rotates. Each time a slit opens, you glimpse the scene on the far side of the disk. Each open-slit image lingers in your eye and brain long enough to merge with the next image.

This phenomenon, called "persistence of vision", will give your brain the illusion that motion is taking place.


  • Understand that visual information is processed in the brain.


  • Per student:
    large mirror for students to view their stroboscopes in motion
    Stroboscope template (printed or glued on light cardboard)
    pencil with eraser at one end

Key Questions

  • What do you see in the mirror?
  • Why does it seem that the image is moving?

What To Do

  1. Cut out the stroboscope template. Don’t forget to cut out the slits around the edge!
  2. Poke a pin through the middle of the circle then fix the disk to the pencil by poking the pin into the eraser.
  3. Spin the template and look through the slits at the back towards a mirror.


  • On the reverse side of the stroboscope you have cut out, create your own changing image using either dots (to represent a ball dropping), or your own drawing. Start off with something simple and then see if you can make it even more challenging!