To avoid this, she could open up into a layout position fractionally before landing to slow down her rotation before she makes contact with the ground. Biles chooses the middle option (pike) – in the video below you can see how she even “over rotates” this vault in competition and needs to take a big step back after landing. Conversely, the tucked position would produce the smallest moment of inertia and highest rotational speed. In the layout position, moment of inertia is highest and the speed of rotation will be at its lowest. These three positions illustrate the concept of moment of inertia, which represents the resistance of an object to rotation. “Piking” means that she bends at the hips and keeps her knees straight, as opposed to a “layout” (extended hips and knees), or “tucked” (flexed hips and knees) position. In Simone Biles’ latest ground-breaking vault, she performs 2.5 somersaults (starting from her hands on the vault table and landing on her feet) in a piked position. So, the direction and speed at which the gymnast leaves the vault table will determine how high and how far they travel, and ultimately how much time they will have in the air to complete the twists and somersaults. In a vault, the take-off height will always be higher than the landing height, and there is not a lot that the gymnast can do to manipulate this variable – they will always want to be fully extended at the point of take-off and at initial contact with the ground. The first vaults to be performed consisted of jumping, placing hands on the table and swinging feet around the side to a landing. This trajectory is determined by three factors: (i) how high the centre of mass is at take-off compared to landing, (ii) the angle of projection of the centre of mass, and (iii) speed of the centre of mass at take-off. When vault was revitalized by the Father of Gymnastics in the late 18th century, it lost its neck and became much more rounded and symmetrical allowing for a wide variety of vaults to be performed. Even though the movement of the limbs can alter the direction and speed of rotation of the body (more on that in the next section), the trajectory (flight path) of the athlete’s centre of mass is fixed once they are in flight. The vault only gives gymnasts one shot to execute their skill. Air resistance on the body of a gymnast in a competition hall is almost zero, so gravity is really the only force that can change the motion of the gymnast once they take-off from the vault table and it pulls them downwards towards the Earth. The only forces that act on an object (including a human body) in flight are gravity and air resistance.
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