OK.....I'm not disagreeing with you....I just want to know why it's traveling on this curve? And....how does it do this (law?) if we've set up our bow with the arrow level? I'd like to understand this.
THE LAW OF GRAVITY!
We set our bow up to ensure that the arrow is perpendicular to the string, the only way to accurately do that is to use bubble levels. Thats it.
When we shoot at things far away we have to aim slightly up to conteract gravity.
So I think you've got it. We set up level, aim at a target 20 yrds away which makes the arrow at a3 degree angle of relative to level (for illustrative purposes), because we raise the arrow rest up w/ the sight to aim, and the nock stays in the same place.
Then we release the arrow travels up and passes through the sight line because when it leaves the bow it has some forces from the bow pushing it up. When gravity overtakes the forces fromthe bow the arrow begins to fall. And we hope it intersects the line of sight at the target.
Think of throwing a ball straight up, its going to come down, eventually all the force we put in the ball is overtaken by gravitational forces.