Originally Posted by Chas Tennis
The article below on the kick serve says that the serve bounces so high because it hits the court at a large angle. Since the ball curves more it will travel a longer path. How would serve trajectory based on sound measurements affect the velocity calculation compared to a flat serve?
Rod Cross, the kick serve in "TW University" link above
For comparisons, the standard measurement has become the radar measurement after hitting the ball.
This is exactly the reason they measure this way. Trajectories and various spins vastly alter simpler radar methods. As a simple example using a hand-held radar, if you have a car traveling around a curve, the only point that you should measure the car's velocity (as speed and velocity are not the same) is when it as close to dead-on ahead of you (assuming you're standing in the track and somehow will not be killed by a speeding race car). If you measure it at any other time during the curve, the reading you will get is of its velocity which is going to be lower than its speed (what you really want to know). Put simply: how fast it is going around a bend is not the same as how fast it is approaching your fixed measurement point. The latter is slower. Since a serve can travel in a severe arc, measurements right off the stringbed (in the car example, when you're staring right at the headlights and take the reading) are the most accurate measure.