In the fall 2006, the National Basketball Association (NBA) started using basketballs made with synthetic, or manmade material instead of leather. They made the switch because they wanted every basketball they use to feel and bounce the same.
However, some players complained right away that the new balls bounced differently and were actually harder to control than leather ones. Dallas Mavericks owner Mark Cuban asked for help the Department of Physics at the University of Texas. The scientists investigated friction that affects the ability of a player to hold onto a ball. "The greater the friction, the better it will stick to his hand", explains Horwitz, one of the physicists who worked on the project.
Tests on both wet and dry balls showed that while the plastic ball was easier to grip when dry, it had less friction and became much harder to hold onto when wet. That's because sweating stays on the surface of the synthetic balls but gets absorbed into the leather balls—an important detail for sweaty athletes.
In January, the NBA went back to use the traditional leather balls. They aren't perfect, but for now, that's just the way the ball bounces.
The NBA started using synthetic basketballs instead of leather ones because ______.
A.NBA players had used the leather balls for too long a time
B.NBA officials wanted a switch with which to start a reform
C.they emphasized that synthetic materials are manmade
D.they wanted every basketball to feel and bounce the same
第5题
A.为实现安全阀的在线校验,可在安全阀与压力表间装设爆破片装置。
B.安全泄放装置必须直接装在压力容器上。
C.压力容器的安全阀不能可靠工作时,应装设爆破片装置,或采用爆破片装置与安全阀装置组合的结构
第7题
A.安全润开启压力等于压力容器的俊计压力
B.安全阀开启压力低于压力容器的设计压力
C.安全阀开启压力等于爆破片装置的标定爆破压力
D.安全阀开启压力略高于爆破片装置的标定爆破压力
为了保护您的账号安全,请在“上学吧”公众号进行验证,点击“官网服务”-“账号验证”后输入验证码“”完成验证,验证成功后方可继续查看答案!