Angle of Impact or Release
The Angle of Impact/Release refers to the angle the bag impacts the board or the angle of your arm is at in relation to the ground.
Video of the path of a bag from release to impact
From the angle of impact/release, we can provide a value that can be used to calculate a perceived speed. If your arm is parallel to the ground or the bag impacts the board at a very shallow angle, we can give that a value closer to 1. Alternatively, if your arm is nearly vertical or the bag impacts the board perpendicularly, that would be a value closer to 10.
Any value that is closer to 1 has more horizontal momentum. This means it will take a greater distance to stop or is faster. Values closer to 10 has more vertical momentum, take a greater distance to stop, or is slower.
These values are derived from the direction of the momentum of the bag. If a bag is coming in at a low angle, most of the momentum is in a horizontal direction and allows it to be transferred up the board. Whereas, when a bag impacts the board at a high angle, the momentum is vertical and goes down to the surface of the board.
Think of this as trying to skip a rock across the water. The flatter and more parallel you throw the rock, the more skips you will get because the momentum is parallel to the surface. If you throw that rock up so it hits close to 90 degrees to the surface of the water, the momentum is vertical and won't skip.