On the way up:
The velocity vector starts out with some magnitude when it leaves my hand. It shrinks and shrinks and shrinks as the object rises, losing 9.8 m/s of speed every second, and becoming zero at the top of the arc. The vector points straight up all the way.
At the top:
The vector instantly snaps around, stops pointing up, and starts pointing down.
On the way down:
The vector grows and grows and grows as the object falls, gaining 9.8 m/s of speed every second. Just as it reaches the speed with which it left the hand, it plops back into the hand. The vector points straight down all the way.
