Our Research Project - Ball/Court Interaction

Ball/Court Interaction
(Page 14)

Ball/Court Interaction
Ball Velocity Before and After the Bounce

The velocity charts were very, very interesting! Below we've summarized the differences in velocity reduction after the bounce for the "slow" (red clay, green clay and hard courts), versus the "fast" (grass court). The "slow" average is the average of those 3 courts. By looking at the individual averages for flat, low topspin, etc. farther down the page below you see how consistent these velocity reductions were.

How did these velocity reductions correlate to the earlier ball speed work from the Sybase Open? Overall, the velocities in our study were somewhat slower than those recorded at the Sybase - but definitely similar results. Going back to data on the backhand return of the serve for Sampras, the average velocity pre-bounce was 32 miles/hour, the average velocity post-bounce was 21 miles/hour or a reduction of 34%. We see similar numbers in our results here. (Spin rate was fairly impossible to obtain from the Sybase footage - the ball was just a tiny speck.)

Keep in mind that a low velocity reduction means that the velocity out remained close to the value of the velocity in. Compare the flat average reduction to the topspin reductions. As we add more topspin, the balls velocity out is not reduced as much. You can see the numbers drop from low topspin to heavy topspin.

Compare the medium underspin and heavy underspin to the flat and topspin balls. Medium underspin in our study reduced the ball's velocity the most.

But look at the reductions for the grass court in the first chart! The results show the following: grass courts reduce the velocity of the ball more than the other courts. How can this be? Grass is supposed to be the "fast" court!!! Note also that in all cases the grass court velocity in was higher or equal to the other court/ball's velocity in. So what does "fast" mean!

Spin Type Average Velocity
Reduction for "Slow" Courts
Red, Green, Hard: Average Velocity
Reduction for "Fast" Court
Grass:

Flat 38.4 49.0
Low Topspin 31.8 43.0
Medium Topspin 25.0 35.5
Heavy Topspin 15.0 27.5
Medium Underspin 46.8 50.5
Heavy Underspin 42.6 52.0

Flat

Court: Ball: Velocity Before
Bounce (MPH): Velocity After
Bounce (MPH): Velocity
Reduction

Green Clay Wilson US Open 33 20 39%
Green Clay Wilson Clay 34 21 38%
Red Clay Wilson US Open 29 18 38%
Red Clay Roland Garros 31 19 39%
Hard US Open 32 20 38%
Grass US Open 35 18 49%
Grass Wimbledon 35 18 49%

Low Topspin

Court: Ball: Velocity Before
Bounce (MPH): Velocity After
Bounce (MPH): Velocity
Reduction

Green Clay Wilson US Open 34 23 32%
Green Clay Wilson Clay 33 23 30%
Red Clay Wilson US Open 31 21 32%
Red Clay Roland Garros 32 21 34%
Hard US Open 35 24 31%
Grass US Open 38 21 45%
Grass Wimbledon 37 22 41%

Medium Topspin

Court: Ball: Velocity Before
Bounce (MPH): Velocity After
Bounce (MPH): Velocity
Reduction

Green Clay Wilson US Open -NA- -NA- -NA-
Green Clay Wilson Clay 36 27 25%
Red Clay Wilson US Open 35 26 26%
Red Clay Roland Garros -NA- -NA- -NA-
Hard US Open 37 28 24%
Grass US Open 39 24 38%
Grass Wimbledon 39 26 33%

Heavy Topspin

Court: Ball: Velocity Before
Bounce (MPH): Velocity After
Bounce (MPH): Velocity
Reduction

Green Clay Wilson US Open 37 31 16%
Green Clay Wilson Clay 37 32 14%
Red Clay Wilson US Open 36 30 17%
Red Clay Roland Garros 35 29 17%
Hard US Open 35 31 11%
Grass US Open 39 28 28%
Grass Wimbledon 41 30 27%

Medium Underspin

Court: Ball: Velocity Before
Bounce (MPH): Velocity After
Bounce (MPH): Velocity
Reduction

Green Clay Wilson US Open 32 17 47%
Green Clay Wilson Clay 31 16 48%
Red Clay Wilson US Open 31 17 45%
Red Clay Roland Garros 28 15 46%
Hard US Open 29 15 48%
Grass US Open 36 18 50%
Grass Wimbledon 35 17 51%

Heavy Underspin

Court: Ball: Velocity Before
Bounce (MPH): Velocity After
Bounce (MPH): Velocity
Reduction

Green Clay Wilson US Open 23 13 43%
Green Clay Wilson Clay 33 19 42%
Red Clay Wilson US Open 31 18 42%
Red Clay Roland Garros 30 17 43%
Hard US Open 28 16 43%
Grass US Open 33 16 52%
Grass Wimbledon 33 16 52%

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