Epic moves! How difficult is the 4A challenged by Yuzuru Hanyu? 4.5 turns in one second...

Expert of this article: Guo Guangxing, engineer in the energy field

Reviewer of this article: Fu Qiang, member of the China Writers Association, Beijing Writers Association, and Beijing Science Writers Association, senior engineer, PhD of the School of Physics, Peking University

On the morning of February 10, the men's singles figure skating free skating event of the Beijing Winter Olympics was held at the Beijing Capital Gymnasium.

This match is likely to be one that attracts much attention.

Having won the championship in this event in the past two Winter Olympics, Yuzuru Hanyu challenged the most difficult 4A move in figure skating at this Winter Olympics.

But unfortunately, he fell on the ice in the first two moves. He finally got 188.06 points and a total score of 283.21.

What is this action that is considered to challenge the limits of human beings? Let's learn about it now.

Exploring the physics of "ballet on ice"

Why can figure skaters perform difficult movements such as jumps and spins on the ice?

Figure skating combines beauty and dynamism, and is known as "ballet on ice". Athletes have to perform a series of movements on the ice, including jumping and spinning.

During the rotation process, they often control the position and posture of their arms, because angular momentum is conserved during rotation, and if they open their arms, the moment of inertia will increase and the rotation speed will decrease. Conversely, the rotation speed will increase.

The principle of the rotation does not seem complicated, but the jumping action is quite challenging. When the athlete takes off, he needs to pay attention to the direction of the force, and apply a diagonal downward force when pushing the ice surface, so that he leaves the ice surface and does oblique throwing motion. This force also provides the initial velocity of the oblique throwing motion, as well as the torque that forms the angular momentum of the athlete's rotation.

However, if the athlete enters the suspended phase (the body is in mid-air), the external force torque is zero (gravity acts on the center of mass), and the angular momentum cannot be changed. At this time, they often change their posture to reduce the moment of inertia and increase the angular velocity of rotation, such as flattening their arms and gathering their hands above their heads.

How difficult is the 4A that Yuzuru Hanyu challenges?

The professional name for 4A is "Axel Quadruple Jump", which is recognized as the most difficult move in figure skating and was first performed by Norwegian skater Axel Paulsen in 1882.

4A seems to have one more jump than 3A, but it actually has four and a half turns, and this one and a half turns makes the highest point of 4A increase by a full 17 centimeters, and the landing point also increases by more than 1 meter. In order to prepare these necessary conditions, athletes must increase their speed by 10% before taking off.

In addition, the A jump is a forward leap. Before turning, the athlete's center of gravity is inevitably on the outside of the ice skates. If you are not careful, the ice skates are very likely to slip sideways, which is very dangerous.

Yuzuru Hanyu successfully completed 4A for the first time in the open training match before the Beijing Winter Olympics trials, but it was difficult to control it easily. In the training for the Beijing Winter Olympics, he tried 4A several times, but failed. In the free skate, Yuzuru Hanyu made a mistake in the first jump of 4A and fell to the ground.

The physics of snow acrobatics

Gu Ailing participates in freestyle skiing and has won the women's freestyle skiing big air championship.

Unlike other skiing events, freestyle skiers can choose to try more types of moves. Typical and more difficult moves include somersaults and spins.

When the athlete starts walking along the snow, he has a constant angular momentum. But when he is in the air, his body curls up to reduce the moment of inertia and obtain a greater rotation speed, thus ensuring more turns and completing more difficult movements. When he is about to land, in order to ensure a smooth landing, he needs to spread his arms, increase the moment of inertia and reduce the speed of the flip.

Therefore, the position and posture of a skier's arms during a flip is important. The athlete's body interacts with the oncoming airflow, and the right posture can significantly reduce air resistance during the competition phase.

In addition, equipment also affects air resistance. The resistance generated by additional equipment such as jackets and helmets accounts for about 8% of the total resistance. The area of ​​the jacket is much larger than that of the helmet, so it is more important to design it to reduce drag. It is also important to choose the right fabric according to the athlete's movement speed, because knitted and woven fabrics have different surface morphologies and different performance characteristics in aerodynamics.

The application of physical skills in "Chess on Ice"

Curling is a unique ice and snow sport that focuses more on the strategy of "deployment of troops" and is known as "chess on ice".

First of all, the curling track itself is not flat. It is concave in the middle and slightly raised on both sides, forming a U-shaped slide. The curling track is sprayed with water droplets many times to make its surface as uneven as pebbles. From the moment the curling stone leaves the pitcher, the tiny friction between it and the ice surface is the only influence that changes its trajectory.

Brushing the ice can remove small amounts of dirt and debris from the path, scrub frost that has formed on the ice surface, and most importantly, melt small amounts of ice. Ice melts into water under the action of pressure and friction. This thin layer of water acts like a lubricant, making the friction on the ice surface very small. Brushing the ice can not only make the curling stone slide further, but also adjust its forward trajectory.

Second, the thrower gently flicks the handle of the stone before releasing it, causing it to spin on itself. If it spins counterclockwise, it bends slightly to the left as it moves forward, and if it spins clockwise, it deflects to the right.

Friction is opposite to the direction of motion, so the spinning curling stone will not only experience backward friction, but also friction in the opposite direction of rotation. For example, a curling stone spinning clockwise will experience leftward friction on the front half and rightward friction on the back half.

The Winter Olympics are still in full swing

I wish the Winter Olympic athletes great success

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