Speedy Birdie—The Fastest Projectile in Sport

It is part of human nature to wonder about the extent of our capabilities. Sport has always been considered the best way to test and expand upon our physical abilities. China has had organized sports since at least 2000 B.C. Ancient Egypt had competitive swimming, javelin throwing, high jump and wrestling contests. There is also evidence that polo and jousting were invented in Ancient Persia. The world-famous Olympic Games were established in Ancient Greece in a small village called Olympia.

The achievements by great athletes are always recognized: the fastest human to run 100 meters or 200 meters (both Usain Bolt), or the longest jump ever achieved (8.95 m by Mike Powell). However, the objects that these great athletes use to achieve their records also need to be appreciated. 

What is the fastest projectile in sport? Is it the baseball, the hockey puck, the tennis ball? The obvious answer might seem like the golf ball, where a weighted titanium club head is striking a plastic ball, sending it flying hundreds of yards. According to Guinness World Records, the fastest golf drive is a 349.38 km/h (217.09 mph) by Ryan Winther. Surprisingly, in terms of speed, the golf ball only comes in a distant second. 

The fastest recorded birdie hit during a competitive game is 426 km/h (264 mph) by the Danish player Mads Pieler Kolding. As a comparison with other racket sports, the fastest serve in squash is 281 km/h (175 mph), tennis’ fastest serve is 263 km/h (163 mph), and table tennis has a world-record shot speed of 116 km/h (72 mph).

So, what is it that makes the birdie fly so fast?

Of course, the speed of a birdie can only be determined if there is a way to measure it. Enter Hawk-Eye, the Sony-owned computer vision system. It is used in several sports such as cricket, tennis, soccer, badminton, rugby and volleyball. It functions through several high-performance cameras that track the ball from multiple angles. The video from these cameras is triangulated and combined to create a three-dimensional representation of the ball’s trajectory. In badminton, it is used to help officiate line calls and service faults, as well as to measure the speed of the birdie.

Unlike other sports, where the projectiles are designed to reduce drag and increase speed, the birdie has distinctive flight characteristics. Birdies are made from 16 carefully selected goose or duck feathers planted into a head made of the bark from a cork tree—which in total weigh only about five grams. Aerodynamically, this makes it a high-drag projectile that decelerates. With its symmetrical cone-shaped feather skirt, it is designed to be stable in flight, thus giving players more control over shots and helping to ensure that the high speeds do not make it unmanageable.

The birdie’s center of mass is about 3 cm in front of its center of pressure (similar to center of mass, the center of pressure can be thought of as the point where all the pressure forces, from the racket and the air, can be considered to have a single point of application). The different centers of mass and pressure cause the birdie to exhibit its unique stabilizing aerodynamic torque and its characteristic flip upon impact.

Plastic birdies are also available, but professional players prefer the feathered version because they can be hit at higher speeds, minimizing the opponent’s reaction time.

The swing of the racket in badminton must be able to generate enough momentum to overcome drag and impart power to the birdie. Consequently, rackets, which are designed to be thin and light, are generally made of graphite, carbon fiber, aluminum or titanium. The racket heads are also designed to be small to further reduce drag. 

During a stroke, the inertial forces generated from the high accelerations cause the racket to bend at its moment of inertia. As the racket is swung forward, it bends backward and snaps back, returning to its original shape as impact occurs. Though minor, this deformation imparts additional velocity to the birdie upon impact.

Another factor to consider is the racket’s center of gravity. The racket head is heavier as the center of gravity is closer to the head, leading to more of the racket’s mass concentrating on the birdie and transferring even more kinetic energy to it, resulting in faster smashes.

Since the birdie impact takes place in the racket’s string bed, it is important to analyze the tension in the rackets as well. A racket’s string tension across its face is important because it affects the control of the birdie and how much energy can be transmitted to it. This can be quantified using Hook’s law, F = kx (where “F” is the force transmitted, “k” is the stiffness of the string that depends on the string material and the original length of the string, and “x” is the length of the string elongated). With a high-tension string, the length of string to cover the racket will be shorter, which decreases its original length and enlarges the “k” value. As a result, the racket will have a stiffer string bed, in which case the birdie will almost instantaneously bounce off the racket as no elastic energy is stored in the string. However, with a higher tension, the sweet spot will be smaller.

Conversely, a lower tension string will lead to a looser string bed and therefore a larger sweet spot area. When the birdie hits a racket’s string bed, there is more elasticity in the swing, and the birdie will travel farther and at a higher speed. If a racket with low-tension strings were to be used to hit a smash with the same amount of power, it will go faster and harder than with a racket using high-tension strings. The elasticity and flexibility of the strings help increase the speed of the shot, but at the cost of control because this extra bounce factor is harder to account for. Therefore, a higher tension across the strings results in faster and quicker control in the shots, while a low tension across the strings results in a bouncier shot with more elasticity to help in velocity but with less control.

Without a doubt, the most powerful shot in badminton is the smash, as evidenced by the fact that the world record was achieved with a forehand smash. To maximize the speed of the smash, various parts of the body need to work in sync to generate and deliver power into the shot. The energy starts from the player’s foot and transfers to the waist, shoulder, arm, forearm, wrist, racket head and finally to the birdie.

Potential energy is concentrated in the right leg and transmitted through the leg upwards. The arm is held back to maximize the distance the wrist travels before the racket hits the birdie. Energy is transmitted to the hip and the player’s body weight shifts to the left foot. The arm is swung as quickly as possible and the wrist is flexed to further amplify the linear speed of the racket. Energy is transmitted from the hip to the wrist as the body weight is completely transferred on to the left foot.

For maximum energy transfer, the chest faces perpendicular to the location where the birdie comes from to achieve maximum torque. When the birdie arrives and the smash is initiated, the player’s shoulder joint acts as a pivot point, followed by the elbow, which also acts as a pivot point. The forearm is stretched so that the whole arm is straightened and the palm faces forward. Finally, the wrist is snapped forward to make the birdie travel downward. All these movements contribute to the final velocity of the racket head, with the energy transferring from the player’s leg to the waist, and then to the shoulder, arm, forearm, wrist, racket head, and ultimately to the birdie.

There are also different “speeds” of birdies, which in badminton terminology refers to how far it will travel when struck with standard force. The farther the birdie goes, the faster it is considered. Because of weight differences and other factors, birdies come in varying speeds. This is because different playing conditions can have a varying effect on birdie speed, so a different birdie “speed” is chosen based on the prevalent conditions. The higher the altitude, the faster the birdie will travel due to lower air density as compared to sea level. Additionally, birdies travel faster in warmer weather, because a higher temperature results in a reduction in air density. Moreover, as badminton is played indoors, a more humid environment can slow down the birdie.

So, there you have it. The fastest-moving object in sport is by a long distance the badminton birdie. The many factors affecting its speed include the design of the birdie itself, racket design, racket string tension, body positioning and atmospheric conditions. If there are still any doubts about badminton being the fastest sport in the world, the video below should help assuage them.