The first vortex dilates and moves slower, while the second contracts and shoots through the first; after which the motion is reversed periodically, as if in a game of leap-frog.
With system changes you would update these in a " leap frog " manner.
You may also want to check out Leap Frog which offers a slew of resources for students in all stages learning to read.
Companies like Leap Frog and Fisher Price offer electronic toys that are tough enough for preschoolers to enjoy.
Original Leap Frog systems encouraged kids to learn phonics, and other basic preschool skills.
