Algodoo

The motor drags a special image back and forth behind a segmented mask, which gives the illusion of motion. You can drag either the image or the mask and get the same result. This particular mask and image has a gap to mask ratio of six to one. That is, the gap between any two mask segments is one sixth the width of each mask segment.

I made the image by using the CSG function to chop a ball into multiple slices, and then I cloned it five times for a total of six segmented balls. Each ball in the sequence has been shifted by six gap widths. When properly arranged, it gives the illusion of motion. You can also make spinners, walking animals, and other animated scenes.

You can learn about this type of illusion, and even learn how to make your own images by Googling "Lenticular Image". In the real world, this type of image uses a special sheet of clear plastic that has one surface covered with long, skinny lenses. Some children's cards are made this way that give the illusion of a moving image when rocked back and forth while viewing the image.