Tennis , Golf , and Loose Gravel: Insight from Easy Mathematical Models

Wimbledon watchers and tennis players cannot fail to be aware of the importance of the service. Players like Tanner are noted for the high speed of their service, whilst the fate of a championship often depends on which player manages to get the larger proportion of his or her first service into play. Why is it so difficult to get a service in when the region in which the ball is permitted to land is a rectangle 21 feet long by 13 1/2 feet wide? Why does a server who fails to get the first service in usually reduce the speed of the second attempt? Can we arrive at a better understanding of the situation?