Tennis stars are being served and volleyed to fuel a new and unique experiment
PROFESSIONAL tennis players gracing the courts at Wimbledon may be rich and famous but they are also unwitting guinea-pigs in a new experiment in which the laws of physics - and especially aerodynamics - are being put to use to bring about certain changes.
The past 10 years have seen the
emergence of the 'power game'. Tennis
rackets have become upto 20 per cent
sturdier as manufacturers use stiff
graphite fibres and make them large-
headed. The players themselves have
become taller and stronger; most of the
top 10 men being over 183 cms (6 ft).
The result is that the service speed has
risen, so that on Centre Court they typically average 100 mph. But, the tennis
balls remain the same. Since the above
factors cannot be altered, all that tournament organisers can do
is slowing down the balls
to make the game more
thrilling.
Two factors are crucial
in deciding the speed at
which the ball travels: the
resilience of the rubber (to
which the internal pressure contributes) and its
effective cross-section,
which affects the ball's air
resistance.
Attempts were made
this year at Wimbledon to
use balls which were pressurised at two per cent
below the norm. However
due to the hot weather the
balls heated up very fast
reaching the same speed
as normal balls within a
couple of rallies.
Geoff Thwates of GT
Technology, Cambridge,
recently ran a series of
computer simulations of
the effect of pressure
reduction on tennis balls.
He found that while a ball
rebounds about five per
cent less when bouncing on a hard surface," the velocity of the ball off the
racket is only decreased by one per cent
for the same pressure reduction".
Therefore it is the velocity of the ball off
the server's racket which really matters
and that which needs to be altered if the
player's opponent is to be given an
increased chance of
returning a service.
Thwaites also warned that
softer balls will skid further "and may cause more
difficulty with line calls".
Organisers of the
French open, held in
Paris, tried a similar
experiment but by incorporating smaller balls.
Their object was to speed
up the game rather than slow it down:
their floor surface, of crushed brick, is
one of the slowest in the world, while
Wimbledon's is the fastest.
The Wimbledon balls use the same
rubber as those in the French Open, but
at a lower pressure, which means that
when a racket hits the ball, it 'gives'
more. But when the rubber - and consequently
the gas inside the ball
heats up, the pressure rises
again.
To increase the cross-section would mean that
the ball slows down quicker as it volleys through the
air." To really have an
effect, you would have to
look for a 10 per cent
reduction in the speed
of the balls," says
Robert Haines, a technical consultant to the
International Tennis Federation who has worked
for the ball manufacturer
Dunlop - Slazenger for the
past 30 years. "You would
have to make the ball's
cross-section about 20 per
cent bigger. To get a 10
per cent reduction by lowering the pressure, you'd
get a pretty squashy ball. It
would be unsatisfactory
to the players", Haines
adds. Thwates's computer
studies had also yielded
the same results. It seems
from these results that
little can be done with
the ball to change the
game.
Meanwhile, professional tennis players could
probably resign themselves-to their fate as the
best-paid and most
glamorous scientific guinea-pigs in the world.
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