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