Let's review the three main parts of this movement. You can follow physics, but I do not recommend trying this triple-double in your garden.
If you want to do Any type of flippingyou must be in the field for a while. Otherwise, you are only a human who rolls on the floor. This can be fun, but it's not really tumbling.
Once a human leaves the ground, he essentially remains only a force acting on him: the gravitational force. It is a pulling force that depends on the local gravitational field (g = 9.8 Newtons per kilogram) and the mass of the human (or any object). This constant downward force causes a person to accelerate down. But because the force and the acceleration depend on the mass, this one cancels. All objects falling freely on the Earth's surface have the same acceleration of -9.8 m / s2.
Rhett Allain, an associate professor of physics at Southeastern Louisiana University, writes on physics for WIRED.
The other advantage of the gravitational force is that it acts only in the vertical direction. This means that there is no net effort in the horizontal direction. Without a net force, there is no gear change. Once in the air, Simone's center of gravity will move at a constant speed, with the same horizontal speed she ran before the jump.
But in the vertical direction, it rises upwards with a certain vertical speed. This speed decreases as it goes up to reach zero at the highest point of the jump. At this point, she begins to descend and increase her speed until she returns to the ground.
As this motion has a constant acceleration, we can model it with what is called a "kinematic equation". It's a relationship between position, speed and time and it looks like this.
For this tumbling pass, we know Simone 's starting and finishing positions – they are identical, so let' s just say that they are zero. Now, if I know the total time, I can find its initial upward speed. Watching the video (and using Video Analysis Tracker), I get a total time in the air of 1.18 seconds. Yes, it seems longer than that – but it's an awesome time. This gives a launch speed of 5.78 meters per second (about 13 mph).
And if it increased this launch speed to 7 m / s? This would give him a suspension time of 1.43 seconds. Yes, it's still super short. The key here is that it is very difficult to be in the air for a long time. If you want to do some twists in the airyou need to focus on rotating faster than keeping in the air longer. Jumping is difficult.
To be clear on the terminology – a rocker is a rotation of a human around an axis that runs through your hips. Here is an animation I did for an old ticket (yes, it is created in Python with GlowScript).
The rotation is represented by the red arrow that points along the axis of rotation. It's a flip.
The key here is to rotate your body all around this axis in the air. If you do not do a full rotation, bad things happen. Fortunately for Simone Biles, she has a length ahead in the stunning appearance of this tumbling movement. It is already spinning before the jump starts. Before the triple-double, it starts with a fairly high rotation rate of about 11.8 radians per second (1.9 rotations per second).
Once in the air, she accelerates slightly to about 12.2 rad / s by folding her arms and legs. In the absence of external torque, it will have a constant angular momentum. The angular momentum is a measure of the rotation of an object that takes into account both the speed of rotation and the distribution of the mass. As part of its mass approaches the axis of rotation, the influence of mass on kinetic moment decreases. To maintain the kinetic moment, the rotational speed must increase. That's why a "fallback" is easier than a layout (where the body stays upright).
The last element of this triple-double is the triple twist. A twist is a rotation of the human body around an axis that goes from head to toe. Here is an animation.
But note that there is a big difference between the twist and the flip-flop in Simone's gym movement. She was already turning around her hips before leaving the ground – but she was not turning already. She had to add that twist to the last part of that pass. There are two ways to twist in the air.
The first way is called a torque twist. The couple is the rotational equivalent of a force. When a force changes the moment of an object, the torque changes the angular momentum. However, you can not apply torque when you are in the air – you must do it while you are still in contact with the ground. If you push forward with one foot and back with the other foot, you will exercise a couple. This couple will result in your twisting motion once you leave the ground. It's simple You can try it yourself.
Alas, a torque twist will only take you that far. The second option is a torsion of the angular momentum. Once in the air, a person can change position. This change of position will result in unsymmetrical mass distribution and produce an astonishing result. Even if the angular momentum remains constant, the angular velocity (the direction of rotation) will change. If both the angular velocity (red arrow) and kinetic moment (yellow arrow) are represented by arrows, this twist would look like this.
Note that the angular momentum is constant – as it should be, because there is no torque in the air. But exactly how do you do that? Note that in the air Simone moves one arm up and one arm down? This changes its mass distribution and starts the twist. Remember – she makes three turns. Is it crazy? Yes, it's a hard blow. Simone does it anyway.
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