The straight line with the diameter of the semicircle is called the axis of rotation, and the rotating body formed by the semicircle rotating once is called the sphere, which is called the sphere for short. The center of the semicircle is called the center of the sphere. The radius of a semicircle is called the radius of a ball.

The diameter of a semicircle is called the diameter of a ball. Representation of the ball: represented by letters representing the center of the ball.

Type of ball

There are many kinds of balls, and their names include: football, handball, basketball, volleyball, badminton, tennis, golf, ice hockey, baseball, softball, rattan ball, shuttlecock, table tennis, billiards, cricket, squash, croquet, rugby, hockey, water polo, polo, bowling, fitness ball and gateball.

1, badminton. Badminton is mainly played by the combination of hands and badminton. Large amount of exercise, suitable for indoor or windless outdoor.

2. Table tennis. Table tennis is China's national game, which emphasizes the tacit cooperation between the hand and the racket and the adaptability of the eyes to the ball.

3. Basketball. Playing basketball well depends on the team ability of a group of people rather than individuals. Playing basketball well can also exercise our quality in all aspects. This is a wonderful ball game.

4. volleyball. Playing volleyball depends on gestures and movements. To play volleyball well, you must practice kung fu in place.

5. tennis. The amount of tennis exercise is also very large, and the decomposition exercise is a big step.

6.bowling. This kind of ball game is easy to build personal confidence and exercise our arm strength, which is very good.