Before the lesson begins, draw your own flip book as a sequence of images on index cards. Fifteen to 20 cards should be enough to give you sufficient thickness for a steady flip. For explanation's sake, the animation you make will be a ball bouncing up and down. To animate the ball, you draw a circle at the top of your first card, the same circle slightly lower on the next card, and so on until you have drawn a circle at the bottom of a card; at that point, continue drawing circles on the subsequent cards, only going upward. Remember to order the cards so that the beginning of the animation is at the bottom of the stack and progresses upward from there.
Pull out the bottom card of your flip book to show the children and ask them what they see. Regardless of their answer, tell them it's a ball. Then ask them if they know how to make the ball in the picture bounce. Place the card back at the bottom of the stack, hold it in place by the side and flip it for the students to see the animation of the ball bouncing.
Explain to the kids that the human eye can't track the pictures by themselves when they're moving too quickly. As a result, the brain makes a shortcut and runs the images together. The shortcut can come out as the illusion of motion if the still images are drawn in sequence. Explain that sequence means each drawing is a little bit different from the one before it and approaches a goal. In the case of the bouncing ball, it goes down, down, down, then up, up, up.
Give each child a stack of blank index cards and a pencil, and tell them they get to make their own flip books. Suggest that they try to reproduce the bouncing ball, but give them free rein to draw anything they like. Stand by to answer any questions they might have, and guide them on how to track their drawings on each card.