8.1 Collecting information
From various sources [5], [6], [8], discussions and contacts with specialists and
players we were able to identify and select the initial data needed to develop the task.
These include the following:
- Ball flying speed throughout the game. Among some of the best players this
speed can reach up to 210 – 215 km/h and this is one of the most important
parameters for our purpose here.
- Racket length – up to 27 inches;
- Centre of gravity and location with respect to the length. From this point of
view rackets are “heavy head” and “light-head” ones;
- Operating area of the string – 500 to 700 cm2;
- String thickness - string diameter 1.25 to 1.75 mm. String positioning is
important to the load on the string and the tension forces occurring in it and it could be
either uniformly or ununiformly positioned;
- Hardness of the string area of the racket. This is very significant and strongly
affects the value of vibrations occurring in the head, rim and handle of the racket;
- Hardness of the body of the racket. This is the degree of yielding (tendency
for elastic deformation) of the body of the racket. Important factors for this parameter
are the design, materials and manufacturing process. For professional rackets this
varies from 50kg to 75 kg.
This quality is proportional to the dynamic inertia, manageability and control and
inversely proportional to the length, head size and power.
The dynamic inertia is of significant importance for the high quality tennis
rackets. Such rackets are made lighter to ensure better ball control and manageability
and at the same time give higher acceleration to the ball when striking it due to their
improved dynamic inertia. This involves the use of new materials: titanium, carbon,
etc. strings. This parameter usually varies between 290 and 360 [4].
The Power characteristic is important to the loading scheme. It characterises the
relation between the energy acquired from the ball and the energy available in the
racket during the strike. The aim is to provide maximum ball acceleration with
minimum effort of the hand. In professional rackets this characteristic varies within 25
and 80. The power is directly proportional to the length, head size, balance (centre of
