Are these remarks consistent with the physics of how the ball moves through the air? Are they even consistent with each other? If the ball is moving anywhere near the speeds seen in a typical professional match, this drag force is greater than the force of gravity.
It can be described by this formula: where. This equalizing effect is only magnified by slow conditions in which the drag force is stronger. Just like a slow court surface, slow dense air helps defensive players who play with less power by minimizing the advantage wielded by bigger-hitting opponents.
Unlike the drag coefficient, which is fairly constant over the range of speeds tennis balls travel, the lift coefficient varies, roughly in proportion to the spin coefficient. In this diagram, based on photographs taken in a wind tunnel where streams of smoke were injected into the air, the blue areas represent layers of air moving around the ball:.
Instead, its flow becomes turbulent , tumbling chaotically like churning water in the wake of a speedboat, and leaves a low-pressure area behind the ball. The difference in pressure between the front and back sides of the ball is the main contributor to the drag force. This causes the airflow to become turbulent earlier on that side, shifting the low pressure wake toward that side as well.
On the other side of the ball, the airflow stays smooth longer, allowing it to follow some of the curve on the back surface of the ball. In the case of the topspin shown in the diagram, the net effect is to deflect the air upwards as it flows around the ball, and the reaction force pushes the ball downward.
