Question 6: A baseball moves past an observer from left to right spinning counter clock-wise. In which direction it tends to deflect?
When the ball moves past the observer from left to right and spinning in anti-clockwise direction in a horizontal plane. The air can be considered moving opposite to the direction of motion of the ball.
Now, toward the observer, the direction of the spin of the ball is opposite to the direction of the motion of the air. Therefore, the speed of air decreases. On the other side of the ball, i-e, away from the observer, the direction of the spin of the ball is along the direction of the air. Therefore, speed of the air increases.
The Bernoulli’s Principle is
According to this principle, an increased speed of air means decreased pressure and vice versa. Therefore, the pressure on the ball on the side toward the observer is more than the pressure on the side away from the observer. So the ball will deflect away from the observer.