9 We’re doing the math here with the ball traveling as the crow flies, for simplicity. Please do not write in with corrections. If you want to factor in the serve’s bounce and so compute the total distance traveled by the ball as the sum of an oblique triangle’s^* two shorter legs, then by all means go ahead—you’ll end up with between two and five additional hundredths of a second, which is not significant.

^* (The slower a tennis court’s surface, the closer to a right triangle you’re going to have. On fast grass, the bounce’s angle is always oblique.)