Center of gravity
Center of gravity of a diver
Author:
Title 4
Learning objectives :
This experience allows students to understand the concept of center of gravity and its behavior during a complex movement. It develops the capacity for precise observation and understanding of the fundamental laws of mechanics.
Concepts covered
Center of gravity/center of mass, Parabolic motion, Gravity forces, Projectile trajectory, Barycenter
What students will do :
The student uses the FizziQ Kinematic Analysis module to study the movement of a diver based on a video from the library. After calibrating the scale, he must identify and point on each image the position of the athlete's center of gravity, a point which can be located outside the body depending on the posture. By exporting this data to the experiment notebook, the student observes the shape of the trajectory and verifies that it corresponds to a parabola.
What is required :
Smartphone or tablet with the FizziQ application, “Diving” video from the FizziQ library
Scientific background :
The center of gravity is the point of application of the resultant forces of gravity acting on a body. For an object subject only to gravity, this point follows a parabolic trajectory described by the equations of uniformly accelerated motion: x(t) = x₀ + v₀ₓt and y(t) = y₀ + v₀ᵧt - ½gt², where g is the acceleration of gravity (9.81 m/s²). In the case of an articulated body like a diver, the center of gravity corresponds to the weighted barycenter of the masses of the different parts of the body. Its relative position is not fixed and can be located outside the physical body, depending on the posture adopted. For example, when the diver curls or stretches, their center of gravity shifts relative to their anatomy, but the overall trajectory of that point remains invariably parabolic. The interest of this experience lies in the confrontation between visual intuition (complex rotational movement) and physical rigor (simple parabolic trajectory of the center of gravity).