striking movements and the position of the striking part of the body determine the
need for observing certain requirements and taking adequate measures to limit the
traumatic effect. These include several physiologically-therapeutic and some purely
engineering measures and further technical study of the physical and mechanical
processes involved in the course of the play, investigation of the vibration processes
being one of the most essential ones as well as improving the sport equipment for the
game [19].
7. Theoretical grounds of alternative phase models.
In general, the stages involved for the accomplishment of this operation can
briefly be formulated as follows:
1. Shooting stage
2. Flying stage
3. Tennis racket loading stage
The first and the third stage of the operation are basically involved with the
collision phenomenon [19]. Therefore, we shall need to present here the assumptions
we use to study the above-mentioned phenomenon along with some elements from
7.1.1 Impact force and collision definition
Experience has shown that there are some phenomena, when the speed of
material objects points vary unevenly for a very short time interval. Phenomena where
the speed of points from a given mechanical system varies by a finite value within a
very short period of time are referred to as collision. The collision phenomenon leads
results in the occurrence of very strong forces of finite impulses. As a proof of this
statement let us examine a material particle subjected to collision. Then, according to
the theorem of impulses [19] we could express:
Where v and v0 is the speed after and before the collision, F is the impact force;
S is the impact impulse and τ is the duration of the collision. The left-hand side of this
