Serving is undoubtedly the most important part of modern tennis. The faster you serve, the better. However, if you break it down to the most basic scientific considerations, the speeds that top players can reach when they serve a serve are theoretically impossible.
How do they do this? Isaac Newton, ping-pong, and a bit of cheating (from a physical perspective) are the answers.
It Seems Impossible To Serve Fast
If the ball is hit from more than 2.6 metres above ground, it will not clear the net or land in the service area. This equation states that gravity doesn’t have enough time to drag a high speed ball inside the service area.
Even if the racket and player could reach almost three metres together, there would only be a 13 cm margin of error. This is only true if you are able to serve above the lowest portion of the net.
If you are not well over six feet (6’3), it is virtually impossible to serve super fast – from a physical standpoint. Even so, even the shortest players can serve over 180 kilometers per hour with remarkable accuracy.
How Is This Serve Possible?
Answer is simple: Players impart topspin to the ball. Isaac Newton observed this phenomenon and described it at least partially in 1672. However, HG Magnus (German physicist) is the one who most commonly describes top-spin. The ball will spin forwards if the racket is placed over the ball’s top during the serve. The ball will also spin when the air around it is spinning.
This layer of air is called the boundary layer by physicists and forms around all moving objects (a train, car, or truck passing will feel it). The ball presses against the oncoming wind, and the air above it collides with the oncoming. This air is deflected upwards and slowed down.
Air travelling under the ball meets air traveling in the opposite direction. It is then drag behind and then up. Newton’s third law states that every action has an opposite reaction. If air is drawn up behind the ball, the ball must respond by moving downwards.
The topspin tactic is often use by top-level players to great effect on the second serve. A top-level player will serve with a fast racket head speed to increase their topspin.
The ball will travel slower if the racket speed is reduce and the ball has more spin. The ball will still drop quickly to the ground, but the higher topspin gives you more room for error.
Beyond Brute Force
Muscle power is also important in the delivery of heat-infused food, but not as much as you might imagine. Our muscles are incredible motors. They produce the amazing forces that allow us to lift heavy items, climb mountains, and move around.
It has long known and experimentally proven 80 years ago that muscles don’t have the ability to produce much force if they are shortening very quickly. Theoretically, it is impossible to travel at high speeds using muscle power alone. We humans have to cheat a little. You may have noticed that top tennis players throw their rackets at the ball when serving, as you can see from this video.
To throw like a football player, their body must move in front of their arm. The upper arm must move before the lower, the lower arms before the hand, and both the hand and fingers must move before the arm. The wrist snaps inward. When the legs are already extend and the upper arms have stopped moving forward, the racket moves faster.
Throw-Like Movement Transfers Serves
This throw-like movement transfers a lot of energy from the shoulders and legs to the hands. Because the hand and forearm are still moving at end of serve, much of the energy from the body is transfer to them during the serving process. The entire arm or body is smaller than the hand. It has lots of energy and moves very quickly.
The difference in time between the movements of the upper and lower bodies also allows elastic tissues like tendons to store energy. These tissues quickly recoil in the serve later in the arm when it snaps forwards. They release the stored energy at speeds that are faster than muscle contractions.
This throw-like movement, rather than brute force, causes the hand to move faster than our muscles can handle. To serve at your best, your racket must thrown in a manner that the ball projects at high speed. Add some spin. It’s just simple physics.