If the application is directly through the projectile’s center of gravity, only linear motion results from the force. As the projecting force is moved farther from the center of gravity, rotary motion of the object increases at the expense of linear motion. If the force is below the object’s center of gravity, backspin results. If the force is above the object’s center of gravity, topspin results. The striking of the ball above or below it’s center of gravity which can intern result in topspin or backspin which can change the direction of the ball when it hits the court and also in the air.
The force of gravity on a object starts to diminish it’s vertical velocity as soon as contact is broken. The factors that determine how soon gravity will cause the object to descend are weight, amount of force driving it upward, and the effect of air resistance on the object.
The relationship of speed and air resistance is that as speed increases air resistance plays a more significant role. Objects that are less dense and streamlined are influenced less by air resistance, and the less surface area an object presents, the less will be the effect of air resistance on the object. The tennis ball being somewhat small, round, hollow, and fuzzy, makes it less dense, more streamlined, and it presents less surface area. This all intern makes the tennis ball a pretty streamlined.
The optimal angle for maximum distance when the beginning and end points are at the same level is 45 degrees. The effects of a less than optimal angle results in little distance. The effect of a greater then optimal angle can also result in little distance.
When starting points are above or below ending points, reduce angle to get maximum distance. Since the greatest angle for projection is 45 degrees, the tennis serve is struck downward as close to 45 degrees as possible.
The relationship of the angle of incidence to the angle of reflection is equal. This means that the angle at which the object approaches a surface is equal to the angle at which it leaves that surface. The factors that could change this would be irregular shapes of the two colliding surfaces, the force resulting from elasticity of the object, and the spin of the object both during and after contact. If all else is constant , the angle the tennis ball hits the ground is the angle it will project of the ground. Also in tennis spin will effect the angle.
A highly elastic object will quickly spring back to its original shape after being compressed. The compression of the tennis ball is somewhat moderate but there is also what is called a high compression ball on the market. The elasticity is really high because the ball is made out of rubber, which has a good restitution. The greatest rebound results from a moderately compressed ball with high elasticity. For tennis, a stiff racket and loose strings will produce the greatest elasticity of the ball because the racket if loose does not have great restitution as well as the strings do. Also the ball is highly compressed and has a lot of elasticity to it, to help propel it fast.
An object propelled without spin tends to waver because of air resistance against the object’s irregular surface. A small amount of spin on an object produces a stabilizing effect which tends to hold it on its line of flight. Increased spin will tend to cause the object to curve in the same direction as the spin because of unequal air pressure cause by the spinning. During the serve or contact with the ball spin is added to the ball to throw the opponent off guard. The effect of the spin is to make the opponent change direction very quickly.
To cause an object to spin in the desired direction, the striking implement should be drawn across the object in the direction of the desired spin. Topspin is caused by an implement striking forward-upward. Backspin is produced when the strike is made forward-downward. In the serve topspin is added to draw the ball out or make it jump up. Backspin is added to make the ball fall short, so to make the opponent run to the net.
Topspin causes a lower angle of rebound, a longer bounce, and more roll. Backspin causes a higher angle of rebound, a shorter bounce, and less roll. In the serve these spins are used to throw the opponent off guard and to make them make a quick decision and mess up.
The effects on a vertical surface are different than on a horizontal surface. Topspin causes a higher rebound , backspin causes a lower rebound, right spin causes a rebound to the left, and left spin causes a rebound to the right. Tennis serve does not happen on a vertical surface at all.
The serve is the most important part of tennis, it starts the game and sets the tone for the match. Many of the professionals today have mastered most of theses principles, and these principles can be seen by just watching a match by a valid tennis player.
Biomechanics
The Tennis Serve
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