query: What is a tennis ball made out of?
passage: Tennis ball
Tennis balls are filled with air and are surfaced by a uniform felt-covered rubber compound. The felt delays flow separation in the boundary layer which reduces aerodynamic drag and gives the ball better flight properties.[3][4] Often the balls will have a number on them in addition to the brand name. This helps distinguish one set of balls from another of the same brand on an adjacent court.[5]
passage: Basketball (ball)
A basketball is a spherical ball used in basketball games. Basketballs typically range in size from very small promotional items only a few inches in diameter to extra large balls nearly a foot in diameter used in training exercises. For example, a youth basketball could be 27 inches (69cm) in circumference, while a National Collegiate Athletic Association (NCAA) men's ball would be a maximum of 30 inches (76cm) and an NCAA women's ball would be a maximum of 29 inches (74cm). The standard for a basketball in the National Basketball Association (NBA) is 29.5 inches (75cm) in circumference and for the Women's National Basketball Association (WNBA), a maximum circumference of 29 inches (74cm). High school and junior leagues normally use NCAA, NBA or WNBA sized balls.[1][2]