I want to draw a graph for a ball thrown directly up in the air. I know that when I throw the ball up in the air the acceleration will be constant. So if I draw a graph with the accelation as function of time, I would get a horizontal line. I have read that the line should be drawn below zero at the y-axis, but why? And it cuts the y-axis at -g, what is the explanation to that? Why do I need to look at the acceleration as g? Thank you.