WHAT IS THE PURPOSE OF BACKSPIN?
The only forces acting on the ball after it leaves the players hand is the force due to the acceleration of gravity and angular momentum (L), backspin on the basketball.
Fg = mball(g)
L = Iw
Backspin is not placed on a basketball to change its path in the air because the air resistance on the ball is so small that air resistance is negligible so backspin could not physically affect the path of the ball. Instead backspin is placed on the ball so that when the ball comes into contact with the rim the ball will bounce off the rim softer than without spin. This happens because when the spinning ball rubs against the rim there is an opposing frictional force that transfers the energy due to friction into heat. Therefore the ball will have less energy after it hits the rim than before making the rebound of the ball softer. Once the ball hits the rim the backspin on the ball switches direction and the ball bounces off at a lower angle creating a better chance for the ball to go in.