The acceleration due to gravity on Earth is 9.8 m/s per second.
That means that an object out in the open gains 9.8 m/s of speed
downward, or loses 9.8 m/s of speed upward, every second.
The ball starts out with 12 m/s of speed upward. It loses 9.8 m/s
of speed upward every second. After (12 / 9.8) = 1.22 seconds,
it has run out of upward speed, and begins moving downward.
