Sybase Open Ball Speed (Page 2)

The team found that the maximum speed recorded by the radar guns on the serve corresponded very closely with the computer program analysis. For the 23 first serves for which the team had radar gun readings, the average speed was 117mph. For the same 23 serves, the average maximum speed calculated by our software program was 121mph, a difference of about 3.5%.

What the spectators saw on the radar guns was probably extremely accurate, but what about what they couldn't see? The results of the analysis were clear--the ball slows down dramatically after the hit in pro tennis, both on the serve, and on all the other shots. By the time the ball had bounced on the court, every Sampras shot had lost roughly 50% of its initial speed. By the time the opponent returned the ball, or it crossed the baseline out of play for a winner, this number could reach as high as 60%.

What did that mean in terms of the individual shots, starting with Sampras's most famous shot--his first serve? In total 29 first serves (including the 23 with matching radar gun numbers) were analyzed. The program showed that the average maximum speed of these serves was 120mph.

Before the serves bounced in the service box, this average speed was down to 87mph. The air resistance, i.e., the drag as the ball traveled through the air, had already reduced the ball speed by over 30mph.

But the bounce of the ball on the court--an event that lasts only around .004 of a second--reduced the speed even more. Sampras's first serves went from an average of 87mph just before the bounce to an average of 62mph after the bounce. This was a loss of another 25mph in a tiny fraction of a second.

Taken together then the air resistance during the flight of the ball and friction of the bounce on the court reduced the average speed from 120mph to just over 60mph -- about half the initial velocity.

As the ball traveled up off the court toward the player it continued to loss even more speed. At the point the player hit the return, or the ball passed the baseline in the case of an ace, Sampras's serves lost an average of another 8mph, or about another 13% of the speed the ball was traveling after the bounce. For the returner, this means that a Pete Sampras serve that began traveling toward him at 120mph was actually going only about 55mph, less than half or about 45% of the initial speed at the time of the return.

So the answer to the question "does the ball speed up after the bounce" was a definite - NO!

Sampras'1st Serve:

Number of Serves	Location	Max MPH After Hit	Pre-Bounce MPH	Post Bounce MPH	End MPH
4	Deuce DTM	127 MPH	89 MPH	67 MPH	58 MPH
7	Deuce Wide	113 MPH	81 MPH	57 MPH	50 MPH
13	Ad DTM	123 MPH	90 MPH	63 MPH	55 MPH
5	Ad Wide	117 MPH	86 MPH	60 MPH	53 MPH
Average	---	120 MPH	87 MPH	62 MPH	54 MPH
Speed Change	---	---	-33 MPH	-25 MPH	-8 MPH
% Speed Change	---	---	-27%	-29%	-13%
Cumulative Speed Change	---	---	-27%	-48%	-55%