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Can Science Improve Your Tennis Game?
The aim of this project was to investigate if a set of scientifically supported
statements could be drawn to improve a player’s tennis game.
Theoretical studies as well as a series of experiments were carried out,
aiming to discover how specific tennis racquet features along with
environmental conditions and court surfaces influence a tennis ball in
motion.
Hypothesis
The presence of a shock absorber will have no significant impact on the
rebound speed of the ball after impact. However, the frequency of the
sound produced from the impact should be lowered as a direct result of
the presence of shock absorbers.
Method
Using a ball machine, tennis balls were fired at a clamped racquet (see
Figure 1 below) and the movement of the ball was filmed with a high-
speed camera to measure the horizontal speed of the ball before and
after impact. The frequency of the string vibrations were recorded using a
computer software called ‘Pratt’ and then played back through a sound
analysis software ‘picometer’ to analyse the highest intensity frequencies.
The experiment was repeated with two types of shock absorbers.
Results
Looking at Graph 1, all the results were very close together – the
maximum difference in the percentage return was only 1.10%. Similarly,
no clear correlation was seen with the frequency results. For example, the
maximum variation was merely 1.5 SD away from the mean.
Conclusion
As expected, the data demonstrated that the presence of a shock
absorber had no effect on the rebound speed of the ball. In terms of the
frequency readings, shock absorbers had little impact on the frequency of
string vibrations, so much so that within the accuracy of the experiment, it
was impossible to record any variations in the frequency.
Hypothesis
Lowering string tension increases the power of the racquet.
Method
The same experimental setup was used as The Effect of Shock Absorbers
on Ball Speed and Sound. The experiment was then repeated with varying
string tensions for three different racquet models.
Results
For the Babolat Aero Pro Drive and the Wilson Ultra Pro High Beam
Series, the results showed a clear trend where the percentage return
increased as string tension decreased. For example, the Wilson racquet
showed a 1.3% increase in % return when the string tension was
deceased from 342N to 307N (df = 9, P < 0.05). On the contrary, the
Babolat Pure Drive results showed no relationship. However, this result
was discarded due to high variation. Table 1 below summaries the results.
Apart from the experimental results, the theoretical predictions that were
made as part of this study supported the hypothesis.
Conclusion
Conclusively, both the experimental results and the theoretical predictions
confirmed that lowering string tension does indeed increase the power of
the racquet.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Racquet 1 Racquet 2 Racquet 3 Racquet 4
Freq
ue
ncy
/kH
z
Graph 1: Frequency of String Vibrations with Various Shock Absorbers
None Babolat Head
70
72
74
76
78
80
82
84
17 22 27 32
He
igh
t (c
m)
Temperature (°C)
Graph 3: Changes in Ball Rebound Height with Temperature
Introduction
The Effect of String Tension on Racquet
Power
The Effect of Shock Absorbers on Ball
Speed and Sound
Hypothesis
A higher temperature results in a higher bounce of the ball upon impact
with the racquet. The reasoning behind this is that higher temperatures
cause an increased pressure inside the tennis ball and a lower string
tension of the racquet.
Method
Tennis balls were kept at two different temperatures – room temperature,
and the temperature of a standard fridge (4°C). Balls at a known
temperature were dropped from a height of 1m onto a clamped racquet
10 times each, and the motion of the rebound was filmed using a high-
speed camera. The recording allowed for the calculation of the maximum
height reached by the bounced ball, and the experimental results were
analysed.
Results
Overall, the results supported the hypothesis, which predicted that tennis
balls would bounce higher in greater temperatures as shown in Graph 3.
The linear trend showed that a 1°C rise in temperature caused a 0.64cm
increase in bounce height.
Conclusion
It was concluded that a higher temperature does indeed result in a higher
bounce of the ball upon impact with the racquet.
The Effect of Environmental
Temperature on Tennis Ball Bounce
Hypothesis
Increasing the mass of a racquet increases the power because the heavier
the racquet, the more kinetic energy the ball gains after impact.
Method
The experiment consisted of suspending a beam between two ladders and
swinging a racquet into a freely suspended tennis ball while recording the
impact with a high-speed camera. The maximum ball height after impact
was then measured by analysing the videos. The experiment was
repeated with varying racquet masses for two different racquet models.
Results
As Graph 2 shows on the right, the two sets of results contradict each
other. The Babolat Roddick Jnr showed a linear relationship of 0.20cm
increase in maximum ball height per 1g increase in the mass of the
racquet. However, this relationship was not observed with the Wilson High
Beam Series.
Conclusion
Due to the highly contradictory results, it was concluded that the
hypothesis could neither be confirmed or denied, implying the experiment
needed improved accuracy.
The Effect of Racquet Mass on Power
Hypothesis
Low friction surfaces (grass, hard) will be the fastest surfaces and cause less
spin than high friction surfaces (clay). Hard surfaces (hard court, clay) will
cause a higher ball bounce than softer surfaces (grass). A wetter surface will
decrease the bounce.
Method
Speed of Ball: A ball machine fired tennis balls onto the surface and a high-
speed camera measured the horizontal speed of the ball before and after the
bounce. The percentage return was calculated.
Spin of Ball: A ball was released 1.5m along a wooden plank slanted at an
angle of 50° and a high-speed camera measured the number of ball
revolutions per minute after the bounce.
Height of Bounce: A ball was dropped vertically from a height of 1.5m and
the height of the bounce was measured using a high-speed camera in both
dry and wet conditions.
Results
There was a 7.89% increase in ball speed from the lowest friction surfaces
(hard) to the highest friction surface (clay). Therefore, the results support the
hypothesis. Clay was the slowest as expected and it produced the highest
RPM as expected. This was followed by hard, artificial grass then grass in
decreasing order of RPM. Hard, more responsive surfaces (hard, clay)
resulted in a higher bounces than the less firm surface (grass). Additionally,
dampness reduced the responsiveness of the court as was predicted by the
hypothesis.
Conclusion
• Grass is a high speed, less-responsive surface. It favours offensive players
and the use of backspin shots, (e.g. slice).
• Hard is a high-speed, more-responsive surface. It favours offensive players
and the use of topspin.
• Clay is a low-speed, more-responsive surface that enhances ball spin. It
favours defensive players and the use of topspin.
• Artificial grass is a medium-speed, medium-responsive surface. It does not
favour a certain style of play and thus can be recommended as a standard
surface, perhaps for new tennis players.
The Effect of Court Surface on Ball Speed,
Spin and Ball Bounce
Rob Bower & Rod Cross (2004). ‘String tension effects on tennis ball rebound
speed and accuracy during playing conditions.’
Rod Cross (2006). ‘Dynamic properties of tennis balls.’
Simon Goodwill (2005) ‘Does higher string tension give more control and
spin?’
Jeff Cooper. ‘A closer look at string tension.’
Troy C. Romana (2014). ‘Tennis Shock Absorbers: Bad Vibes?’
Wonderoplolis.org (2014). ‘Does Temperature Affect the Bounce of a Ball?’
TutorVista.com. ‘Reynolds Number Formula’
Chris Woodford Explainthatstuff.com (2014). ‘Aerodynamics: an introduction’
References
Racquet String Tension (N) % Return (mean ± SD)
Wilson Ultra Pro High
Beam Series307 73.3 ± 0.9
342 72.3 ± 0.5
Babolat Pure Drive 258 73.0 ± 1.3
300 72.5 ± 1.5
Babolat Aero Pro Drive 249 74.1 ± 0.9
282 72.2 ± 0.8
1.5m
Clamp
Ball Machine
Speed Camera
Reference Points
3m
Racquet
Ball
Important Definition
0
20
40
60
80
100
120
140
160
180
200
0 50 100 150 200 250 300 350
He
igh
t In
crea
se o
f Te
nn
is B
all
Added Mass to Racquet (g)
Graph 2: Relationship Between Added Mass to Racquet and Increased Ball Height
Wilson High Beam Series Babolat Rodick Jnr
Figure 1: The racquet clamp used in the shock
absorber and string tension experiments
Figure 2: A diagram of the experimental setup for
the shock absorber and string tension experiments
Table 1: A table showing the string tension (N), the mean and the SD of percentage return of the three different
racquet models that were tested
Samir C | Sam C | Alex H-D | Sechan Y | Jaehyeon K
The Perse School, Cambridge, United Kingdom
Figure 3: Different types of court surfaces tested: top left – grass; top right – artificial grass; bottom left – clay;
bottom right - hard
% Return = Rebound Speed / Incoming Speed x 100
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