External spin factors

3.1 Determinant factors that influence spin

The determining factors, which influence the ball spin are divided into: (a) external factors and (b) internal factors.

3.1.1 External factors

The main external factors are the following:

a) The mass distribution of the ball and its surface properties. The largest part of the total ball mass is on its surface while its inside is empty. A table tennis ball has a19mm (0.7in) radius, 0.4mm (0.01in) thickness, and 2.5gr (0.09oz) weight. If it is replaced with another ball of the same radius but with a solid inside such as a golf ball, its kinetic energy from the stroke could not be converted into spin.

b) The type of the table surface and the floor. These two elements influence the amount of spin and speed of the ball.

c) The speed glue used prior the match.

d) The air resistance. Air decreases the amount of spin. Its action is proportional to the ball speed and the type of spin.

e) The racket and the interaction of the ball with the rubber surface. The rubber material and the sponge influence the amount of spin onthe ball. The offensive rubbers, which are characterized for their ability to give more spin on the ball, satisfy at least two conditions:

• The amount of produced spin is proportional to the amount of friction between rubber and ball during the stroke.
• The kinetic energy, which is produced during the impact of the ball on the racket is converted into spin and speed in direct proportion to the thickness of the sponge and the softness of the rubber.