Every tiny part of an object is affected by gravity (see gravity), which can be approximately regarded as a system of forces intersecting the earth's center. Because the size of an object is much smaller than that of radius of the earth, the gravitational force acting on a general object can be approximately regarded as a parallel force system, and the total weight of the object is the resultant force of these gravitational forces.
Everything on the earth is affected by the gravity of the earth. If an object is divided into countless parts, the gravity of all these tiny parts will form a spatial intersection force system (the intersection point is in the center of the earth). Because the size of the object is much smaller than the radius of the earth, it can be approximately considered that this force system is a spatial parallel force system, and the resultant force G of this parallel force system is the gravity of the object.
Determination of center of gravity:
The position of the center of gravity of an object with uniform mass distribution is only related to the shape of the object. For objects with regular shapes, the center of gravity is at the geometric center, for example, the center of a uniform thin straight rod is at the midpoint of the rod, the center of a uniform sphere is at the center of the sphere, and the center of gravity of a uniform cylinder is at the midpoint of the shaft. The center of gravity of irregular objects can be determined by hanging method.
For objects with uneven mass distribution, the position of the center of gravity is not only related to the shape of the object, but also related to the mass distribution inside the object. The center of gravity of the truck changes with the change of loading capacity and loading position, and the center of gravity of the crane changes with the weight and height of the hoisted object.
Above content reference: Baidu Encyclopedia-Center of gravity