There are so many ball sports in the Olympics, why is it the fastest?

Did you watch the Paris Olympics?

Ball games are the highlight of the Olympic Games.

Have you ever thought about this while watching the game?

In so many ball sports

Which ball has the fastest speed?

Which ball flies the farthest?

This is the "king" of ball speed?

All ball sports involve hitting a ball with your hands, feet, bat or racket, and the differences in size, shape and weight of the ball give them different speeds and trajectories.

So the question is, among these ball sports, which ball is the fastest? Is it the exciting football, the sweat-inducing tennis, or the table tennis that is so fast that you can't see the trajectory?

The answer is actually - badminton, which looks the least like a ball!

The fastest badminton record officially recognized by Guinness World Records comes from Danish player Kolding. On January 10, 2017, at the Indian Super Badminton League, Kolding smashed a ball at a speed of 426 km/h (about 118 m/s) in an official match. What does this mean? The highest speed of the badminton in this record is faster than the maximum operating speed of the "Fuxing" EMU train (400 km/h).

Image source: Physics of ball sports

The maximum speed of various ball sports

Why can badminton fly so fast? The reason is not complicated. It is mainly because badminton is relatively light (weighing only 5 grams) and the racket is long enough (no more than 680mm).

Image source: Annu. Rev. Fluid Mech

Basic parameters of various balls such as size, weight and speed

The movement of a ball in the air is often only affected by air resistance and gravity, and its speed generally only gradually decreases (except for basketballs). To achieve the fastest movement speed, the ball needs to achieve the maximum acceleration at the moment it leaves the athlete's contact . Compared with tennis, football and other balls, badminton is very light, so the same force on it will produce a greater acceleration.

Image source: Physics of ball sports

Golf and badminton swings

The most "flying" ball - golf

Golf ball is the ball that flies the farthest , and a single shot can move more than 200 meters. A standard golf course usually has 18 holes, with a total length of 6,002 to 6,400 meters and an area of ​​50 to 75 hectares (1 hectare = 10,000 square meters). The actual size depends on the terrain of the course.

Not only that, golf has also gone beyond the earth and become the first interstellar ball sport. On February 6, 1971, Alan Shepard, an astronaut on the Apollo 14 mission, swung a club and played golf on the moon, making him the first and only person in history to have played golf on the moon.

Image source: NASA astronaut Allen playing golf on the moon

There is a surprising phenomenon about golf balls: the smoother the golf ball, the farther it flies.

We all think that a sphere is the most perfect shape. The smoother the surface, the less friction there is between the sphere and the atmosphere during flight. With the same amount of force, it should fly farther. However, this is not the case with golf balls.

Image source: "50 Years of Golf" The evolution of golf

In the book "The Wonderful Science of Fluid Motion" written by Professor Mao Genhai, there is such a data: under the same conditions, the resistance of a golf ball covered with dimples during flight is only half of that of a smooth ball, and the flight distance is 5 times that of a smooth ball. When an object moves in a fluid, the resistance caused by the pressure difference between the front and the back is called "form drag". Modern nuclear submarines use a "water drop shape" to reduce form drag.

Image source: Science Popularization China

As shown in the figure above, the vertical plate at the top has the largest shape resistance because the "low-pressure area" behind it is the largest. The low-pressure area of ​​the second sphere is reduced until the water drop shape at the bottom, which has the smallest shape resistance. Through fluid mechanics experiments, people have found that the smooth ball has a smaller low-pressure area than the ball covered with dimples. The countless dimples on the ball can keep the air close to the surface of the sphere, which allows the smooth airflow to extend along the surface of the sphere to a further position before separation occurs.

Image courtesy of aerospace engineer Jeffrey A. Scott

The most popular ball sport - football

Whether in terms of influence, number of participants or popularity of events, football is undoubtedly the world's number one sport. However, since we are talking about the issue of ball speed and body resistance today, let's also take a look at the impact of football stitching on the trajectory of the ball.

The Jabulani football is a new football designed for the 2010 World Cup finals in South Africa. It is also the most criticized football in recent World Cups. When it was first released, the manufacturer advertised that it only used 8 pieces of skin to complete the football, which perfectly covered the inner liner. It is the roundest football in history.

However, this ball is a "nightmare" for goalkeepers. Aerodynamicist Dr. Mehta proposed that "the size of the roughness determines the optimal critical speed for the 'butterfly ball effect' to occur."

Butterfly ball trajectory

The butterfly ball refers to a ball that has almost no rotation when flying in the air, which makes its flight trajectory unpredictable and difficult for the goalkeeper to judge. The principle of the butterfly ball is that there are seams on the surface of the ball. During the flight, when the airflow passes through the seams, more turbulence is generated. Due to the asymmetry between the left and right, the turbulence increases the deflection force on the side of the ball. The wake swings left and right, and the flight is erratic, like a fluttering butterfly.

Conventional footballs are usually made of 32 pieces of spherical surface stitched together by seams . The total length and depth of the seams determine the smoothness of the football. The more seams, the rougher it is. Conventional footballs generally produce the maximum "butterfly ball effect" at a speed of 48 kilometers per hour.

The Celebration football, due to its very short total seam length, became the smoothest football at the time. After aerodynamic tests, people found that the Celebration football would produce the maximum butterfly ball effect when the ball speed was 80 to 88 kilometers per hour, and a speed of around 80 kilometers per hour was exactly the typical ball speed for shooting and free kicks.