pingpong , which is also called table tennis, is the national ball sport in China. pingpong ball is round and very small , only about three or four centimeters in diameter. it is also very light , normally made of plastics.
american football, also called rugby, is popular game among americans. rugby is oval-shaped, and much bigger than pingpong balls. and it is made of normally leather, so much heavier than a pingpong ball
basketball, which is the biggest of the three, is also round. it is about 20centimeters in diameter.