At 11:25 on the morning of July 26th, at the women’s skateboarding finals of the Tokyo Olympics Street Event, Chinese player Zeng Wenhui represented China in this new event and finished the competition with a total score of sixth. At the age of 16, she is not only the first person to appear in the Olympic skateboarding event in Chinese history, but also the first person to enter the Olympic skateboarding finals in Chinese history.
Let us also look forward to Zhang Xin, who will represent China in the women’s skateboard bowling event on August 4.
Yesterday, skateboarding was the first show in the Olympics. As a senior skateboarder (two years since I bought the board, it’s still the same as the new one) , I watched the whole journey.
Although it is not good to skate, the editor of physics in skateboard can still talk about it.
1. Olympic Games and Skateboarding
Skateboarding is one of the most widely known extreme sports. There are many theories about its origin, but it is generally believed that it began on the West Coast of the United States in the 1940s. How simple was the skateboard at that time, it was to fix several metal wheels on a wooden board. In the 1950s, clay composites replaced metal wheels. But the wheels of these two boards at that time were too hard, and the bones could be shattered every time you slipped . So the skateboard fell into decline for a while. However, in the 1970s, the emergence of polyurethane wheels made skateboarding popular all over the world.
From the invention of the skateboard to the present, the material of the board body has also used fiberglass, aluminum and plastic. But compared to hard maple, which is a strong and flexible wood, it is difficult for this non-wood material to strike a balance between flexibility and strength. On the contrary, the wooden board does this. A bridge is connected under the board, and the bridge is connected with two wheels. The bridge squeezes the PU gasket in it to absorb the impact or make the steering of the skateboard.
The structure of skateboards Source: expression.edu
Since the 1980s, skateboarding has been more of a street sport. However, in 2016, the International Olympic Committee officially announced that skateboarding has entered the Olympic Games and will produce 4 gold medals at the 2020 Games. Our country will also send two female players , Zhang Xin and Zeng Wenhui.
Of course, there are many kinds of skateboards, and different skateboards have different ways of playing, as well as longboard, fishboard, freestyle skateboard and so on. The skateboarding event selected for the Olympics is the double tilt skateboard.
There are two events in the competition, namely street -male and female and park (or bowl pool) -male and female. The venue of the street competition is on a street-like route with handles and seats, using these props to complete the action. Probably because the facilities on the road were not old enough, I jumped up with a board to polish it. The venue for the park game is in a “bowl”. Athletes will complete the designed route here and demonstrate technical movements while the “bowl mouth” is in the air.
Map of Tokyo Olympic Park Games ©California Skateparks
Map of Tokyo Olympic Street Games ©California Skateparks
Second, the physical principles in skateboarding
The principle of the upper board and the lower board is the same. First put your dominant foot on the board, and accelerate or decelerate yourself by pushing the ground or rubbing against the ground with the other foot.
First , let’s talk about carving . When the skater is sliding in a curve, every time the direction changes, the skater needs to step on the turning side of the board forcefully, so that the inner and outer wheels are in concentric circles with different radii. The difference between the inner and outer wheels completes the steering of the skateboard.
Turn to the front and rear skateboard posture
At the same time, if the speed is relatively fast, it is necessary to tilt the body so that the combined force of gravity and supporting force provides centripetal force . This way it won’t be thrown out on the board. However, it should be noted that the principle of steering here does not conform to the Ackerman steering geometry in car steering, because the axial direction of the inner and outer wheels of the skateboard is always the same straight line.
In fact, these are the most basics for learning skateboarding. After learning the basic movements, you must learn technical movements. Otherwise, your conscience will not hurt as a skateboarder (Xiaobian: It won’t hurt) .
Let me talk about a very simple technical action-Hippie Jump. The athlete takes off vertically on the board, maintains the same horizontal speed as the board, and makes an upward throw motion relative to the board. But relative to the ground, the horizontal velocity is the oblique throwing motion of the board.
Athlete’s trajectory source: real-world-physics-problems.com
After crossing the obstacle, it can fall on the skateboard just below the obstacle when falling. The essence of the action is to not have a little forward or backward force when taking off , otherwise it will not fall on the board after crossing the obstacle. At the same time, the jump must be high enough and fast enough, otherwise it will be over obstacles.
The most basic movement of skateboarding, ollie, can be said to dissuade many young comrades who have not yet started skateboarding.
The trajectory of the two wheels when making ollie Source: wired.com
Moreover, ollie is the core of almost all high-level technical movements. If ollie is not well practiced, there is no way to practice higher-level technical movements. This is a technique that allows the skater to jump into the air with the board. This technique can be used to overcome some obstacles. The whole process is as follows: First, athletes will lower their center of gravity, which makes them jump higher. When taking off, the difference from Hippie Jump is that the order of closing the legs is different. It can also be seen from the picture above that the time for the two wheels to leave the ground is also different.
After taking off, first retract the front foot first, and the head of the skateboard is tilted due to leverage. If the back foot is retracted in time, it can give the board the feeling of hitting the bottom of the board and popping up.
Blue represents ground support, black represents gravity, and red represents the force that athletes give to the skateboard. Source: real-world-physics-problems.com
Then the forefoot slides towards the board head and tilts (for better control of the board surface) , so that the forefoot can “grab” the board head with a rough surface. At this time, the force on the board head in the air can be decomposed into parallel to the board. Face forward, and two forces perpendicular to the plate face downward (as in step 3) . These two forces are sufficient to control the trajectory of the board in the air. Because the force perpendicular to the surface of the board exerts a torque on the skateboard in the air, the tail of the board should also be lifted. And the force parallel to the board surface can “drag” the skateboard in the air, and control the skateboard to fall to the right position under one’s feet.
After the tail is raised, the rear foot is actually the same as the front foot. The force applied to the skateboard will also be broken down into two forces, parallel to the back of the board and perpendicular to the down of the board. At this time, the two forces parallel to the board surface can control the skateboard to fall in a suitable position under one’s feet. The following is a schematic diagram of the force that the skateboard receives at different moments of ollie.
The force that the skateboard always receives when doing ollie Source: wired.com
This is also a basic technical action that requires the principle of conservation of angular momentum. Need to add the skateboard clockwise/counterclockwise rotation 180° on the basis of ollie (regular foot rotation counterclockwise, goofy foot rotation clockwise) .
The whole person obeys the conservation of angular momentum, and because there is no torque produced, it is impossible to complete the overall rotation in the air. How to rotate 180°? In fact, they maintain the conservation of momentum by rotating the upper and lower body in opposite directions to ensure the 180° rotation of the skateboard.
Moreover, opening your hands in the air can increase the value of H1, thereby increasing the H2 of the lower body, which makes it easier to turn the lower body. After landing, in order to restore the dislocation of the upper body, it is only necessary to use the torque given by the friction of the ground at this time to restore the upper body.
3. Sliding in the bowl
In the park game, in order to be able to have a high enough speed on the side of the bowl, so as to have enough time for aerial technical maneuvers. Players will adjust the height of the center of gravity to ensure the speed at the highest point.
This process can also be explained by the conservation of angular momentum. If the athlete’s take-off process at the mouth of the bowl is analogous to a pendulum with a fixed point o and a retractable length, this process can be analyzed. Just adjust to take a half-squatting posture before rushing to the “bowl mouth” and increase the distance of oG as shown in the figure, so that the moment of inertia can be increased. Get up when you rush out of the bowl, reduce the oG distance, reduce the moment of inertia, and conserve the angular momentum. It is possible to obtain a speed higher than the original center of gravity when the “bowl mouth” is released.
Fourth, the safety of skateboarding
I see many skateboarders doing technical moves when they are fast, and I will inevitably sweat for them. But as long as you master the correct fall posture, you will ensure the smallest possible injury. By observing the falling postures of the athletes in the Olympic games, it is very obvious that people generally use a forward-rolling method to protect themselves and reduce the momentum in the horizontal direction by rolling.
Instead of sliding friction with rolling friction, it’s wonderful~ So, to learn skateboarding, you have to learn to fall. Otherwise, if it slides out horizontally due to inertia, it will cause greater damage to the human body. But don’t roll up on purpose.
There are also skateboarders who often jump from a high platform. After they come down, they will be the same as those who are okay. If someone really jumps from such a high place at such a fast speed, even if they roll, something will definitely happen. Do skateboarders really have iron bodies?
The answer is of course not. From the technical action we just mentioned-Hippie Jump, we can know that in this process, the athlete only experiences an approximate throw-up motion relative to the skateboard. At the last landing, there is a gap between the athlete and the board. The force is almost only in the vertical direction. As long as we humans can accept such a high drop height, then this action can be completed. Moreover, the wheels of the skateboard have the elasticity of the board surface, which can also alleviate this impact to a certain extent.
However, if the skateboard is separated from the foot and cannot be rolled in a timely manner, it is very likely to cause fractures, sprains and other consequences. Because at the moment of landing, the ground has not only upward support for the person, but also horizontal friction. The combined force of the two must exceed the support. The effect of this instant impact on the person’s ankle is very huge. So every time I see athletes fall, I worry about them.
I hope that every athlete can show off his demeanor in the competition, play his own level, and more importantly, pay attention to safety!
This article comes from WeChat public account : Institute of Physics, Chinese Academy of Sciences (ID: cas-iop) , author: Kun
Posted by:CoinYuppie，Reprinted with attribution to:https://coinyuppie.com/guide-to-spectating-skateboarding-games-if-you-dont-know-how-to-play/
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