A sphere is surrounded by a surface, which is called a sphere.

A ball is a rotating body formed by taking a straight line with a semicircle diameter as the rotation axis and the semicircle surface rotates once, which is also called a sphere. The surface of a ball is a curved surface, called a sphere, and the center of the ball is called the center of the ball.

Extended data:

Cut a ball with a plane, the cross section is round. The cross section of the ball has the following characteristics:

(1) The straight line connecting the center of the sphere and the center of the section is perpendicular to the section.

(2) The distance d from the center of the sphere to the cross section has the following relations with the radius r of the center of the sphere and the radius r of the cross section: r? =R？ d？

(3) A circle whose sphere is cut by a plane passing through the center of the sphere is called a great circle, and a circle cut by a section not passing through the center of the sphere is called a small circle.

(4) On the sphere, the length of the shortest connecting line between two points is the length of a bad arc between these two points, which we call the spherical distance between two points.

References:

Baidu encyclopedia-ball