What is animation?

Think about how animations work
in a flip-book, or cartoons on TV, or a movie reel.
What do these animation technologies have in common?
They create the illusion of motion by rapidly transitioning
a single frame that you are viewing to other frames
within a pre-defined sequence.

Suppose you want to create your own Flutter animation
without using the animations library.
Start with the simplest case possible:
Your goal is to animate a ball
so that it repeatedly bounces up and down.
The following example demonstrates a first attempt
using a naive approach.
Can you spot the lines of code that create the effect?

Example: bouncing ball (starter code 1)