Make a Zoetrope for 4th of July

What is a zoetrope?

A zeotrope is a spinning toy that is similar to a flip book in that the quick flashing of pictures makesthe viewer think they are seeing an animation.

Some zoetropes, like the one imaged here, are hand driven. That is, the viewer uses a crank to turn the zoetrope and see the image animation.

Our zoetrope will spin like a top, allowing us to spin the zoetrope and then view it.

Why does a zoetrope look animated?

The set of images that a zoetrope provide end up looking animated to us, why?

There are two things – the persistence of vision, and the phi phenomenom – that come into play when our eyes view more than 10 frames per second (fps). Under 10fps and we just see individual images.

Above 10fps and our brain will start doing extra work to make it look animated, although it will seem jerky until you hit about 24fps, which is the frame rate that motion pictures are shot at.

As you increase the frame rate you also increase the fluidity of the animation you are watching as demonstrated below.

The persistence of vision

The persistence of vision refers to an optical illusion where discrete images (like those singular images you drew), blend into a single image that our brain perceives as motion. We continue to see an image after it is no longer there – an easily recognizable example of this is the flash on a camera. We see the flash long after the light from the camera bulb is no longer on. As images are flashed at our eyes we don’t see the black space between images, allowing a fluid experience.

The phi phenomenon

The phi phenomenon is when a set of images are created to give the illusion of movement. For example, a series of dots progressing to the left would be viewed as a dot moving left when viewed at a high enough frame rate.

In this way the phi phenomenon allows us to perceive the motion, while the persistence of vision allows us to see that motion fluidly, and not in a stop-motion jerky manner.

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