Prof. Dr. Intisar Kazim Abdul Karim, a lecturer from the Individual Games Branch at the College of Physical Education and Sports Sciences for Women has delivered a scientific lecture for the students of the undergraduate studies entitled (How the point of effect of force works to determine the shape of the trajectory: the amount and direction of projectile rotation).
She has referred during her speech to the cases of changing the trajectory of the projectile’s movement according to the point of impact of the force, especially, when the effect of the force passes in the center of mass of the ball, the movement that occurs as a result of the effect of that force is linear and its direction is forward, but when the effect of the force passes at any point outside the center of mass of the ball, it results in a rotational movement that is in the forward or backward direction, so determining the direction of rotation is depending on the place or point of contact of the ball with the surface of the racket, where such blows are called a spiral or a rotational blow. Also Dr. Intisar Kazim recommended the need for the professors and coaches of racket, tennis and badminton, as well as other ball games such as volleyball, to know the purpose of linking the point of action of the force with the target of the blow, and the point of impact of the force and its magnitude in determining the speed.