Part 2: Spin/ Magnus Effect
In tennis, another physics concept used is the Magnus Effect. This causes the ball to rotate, which is called spin. The more spin on the ball, the further it will go after it bounces on the other side of the court. The spinning ball causes drag forces on the bottom and top of the ball to be unequal. When a tennis ball has backspin on it, the drag of the ball at the bottom is greater than the drag on top of the ball because the velocity of the bottom of the ball is in the same direction as the ball is headed. This means that the ball has a greater magnitude velocity relative to the air around it and the rest of the ball, which means a greater drag force. Like the drag at the bottom of the ball, the drag at the top of the ball is reduced due to the top of the ball having a lower velocity to the air around it than the rest of the ball. Both of these forces can be thought of as exerting an unequal pressure on the ball with the greater drag responding to the greater pressure. The resulting pressure difference then causes a net force on the ball in the direction of the low pressure. When there is backspin, it results in an upward force on the ball, and when there is top spin, it results in downward force on the ball.