Mechanics of Tennis

Sports Mechanics Of Tennis
The hitting and subsequent motion of a tennis ball in playing a forehand topspin
Abstract
The forehand topspin is one of the primary techniques that is utilised in modern day tennis. It has been used to enhance a player’s overall forehand skills that result in the maximising of a players groundstroke power output. This report will analyse the motions the tennis player and tennis ball undergo, the forces acting on the player and the ball and lastly, the force transformation from the player to the ball. By examining the physical properties of this process, this report will attempt to describe the motions, forces and energy transformations that are present throughout the initial stance, the swing and contact and also, the forces acting on the ball after it is hit. This study will provide tennis players with information that could be used to optimise their overall forehand topspin technique which ultimately increases speed and accuracy.

Introduction
The forehand topspin is normally executed during a baseline rally and approach shots. It is also applied in passing shots. For most professional players, the topspin forehand is their main shot of choice in today’s high paced game. A forehand topspin is the best of both worlds, because a player can hit the tennis ball with maximum power and topspin while still being able to keep the ball in play.
The physics involved within the forehand topspin examines the motions involved from the generation of power from the human body and racquet which is then transferred to the ball in order to apply an optimum amount of power and a forward rotation on the tennis ball. Also, air resistance and gravity on the ball after the impact off the tennis racquet to the opposing opponent eventually results in a decrease of speed and rotation.
This technique is considered one of the most effective forehand groundstroke used in today 's style of tennis. The forehand topspin aims to maximise the ball 's speed whilst travelling in the air and also after it lands on the court due to the forward rotation of the ball.

The Initial Stance
The initial stance of the forehand topspin is very important because of the generation of power. Elliot and Wood (1983) suggested that power or force in tennis is generated by a sequence of movements carried out by the body. These sequences involve the right footwork technique where the legs are bent and the feet are pushing against the ground. As a result, the ground exerts force that propels the player upwards or forward as a reaction. This force then is transferred towards the upper body generating some biomechanical energy. From this, we can see that the role of the legs during the initial stance of the topspin forehand is of utmost importance as it is the initiation of power. The generation of power is also increased through the involvement of the hips, trunk, shoulder, elbow and wrist action. The synchronization of all these bodily movements is vital to maximize power with the proper technique.

Diagram 1: This diagram illustrates the forces acting on the player during the initial stance. The player 's legs exert force towards the ground and as a reaction, the ground exerts force back to the player which the player is able to generate towards the upper body in order to maximise power.

The Swing and Contact
The swing and contact between the racquet and the ball during the forehand topspin is very important as they are both masses that collide with each other. During this collision, they exert force against each other which results in the propulsion of the ball (Brody, Cross and Lindsey, 2002). During the swing and contact, gravitational force should always be considered as it is always present.

Diagram 2: This diagram illustrates the swing from the initial stance, the contact of the racquet and ball and the follow through.

The Forces Acting On The Ball
There are two stages that this report shall look at in regards to the stages that the tennis ball undergoes. This section focuses on the forces acting on the ball after the initial contact from the racquet and the forces acting on the ball when it hits the ground. By closely looking at the ball after the contact phase, it has now become a projectile because it is travelling through the air without any means of self-propulsion. Since it is a projectile, the only acting force is gravity accompanied by air resistance. Once the tennis ball comes into contact with the ground, the ball 's velocity decreases due to the friction caused by the ball hitting the ground.

Diagram 3: This diagram illustrates the forces acting on the ball after it has collided with the racquet. The tennis ball undergoes a decrease in velocity and height due to gravity. Diagram 4: This diagram illustrates the contact between the ball and the ground. It shows the ball 's shape slightly deformed due to the absorption of force, the spin direction, friction force and direction of the ball.

Measurement
Measurements of each stage of the forehand topspin process are important in order to evaluate the performance of the tennis player. As a result, this allows the player to evaluate his technique and make improvements. By using different types of measuring methods that look into force, velocity and energy, it provides the bowler with useful information about each phase of the forehand topspin action.

Multi-flash photography is a useful tool in providing frame-by-frame images which will show the entire forehand topspin process and provide measurements which will assist in portraying the relevant motions.

The use of a camera with video capability will provide a detailed analysis of the entire forehand topspin process. This video clip can be used with a program called video point. Video point is a program which enables you to plot all types of measurements such as acceleration, velocity etc. This is a very detailed way of analysing the bowling process.

Energy Transformations
The forehand topspin involves numerous energy transformations throughout all the stages in order to maximise velocity. The initial stance generates kinetic energy from the reaction force from the ground by the feet pushing off. It is then transferred towards the upper body. This kinetic energy is then channelled to the arms and then on to the tennis racquet. Heat is also generated during this process. The collision of the tennis racquet and the ball causes elastic potential energy and the elasticity of the strings store heat energy. Kinetic energy is then transferred to the ball and it is then propelled to the other side of the court. The amount of force applied throughout the initial stance, the swing and contact generated is of utmost importance as it affects the vertical/horizontal velocity of the tennis ball.

Diagram 5: Energy Transformations
Initial Stance The Swing and Contact Ball
Heat
Heat
Heat
Heat

Kinetic Energy
Kinetic Energy
Elastic Potential Energy
Elastic Potential Energy
Kinetic Energy
Kinetic Energy

Heat
Heat

In conclusion, the forehand topspin can be maximised with the proper technique and knowledge of the physics behind it. By looking at the forces and energy transformations of the initial stance, the swing and contact and the forces on the ball provides tennis players or coaches useful information that can assist in creating optimum performance.

References
Brody, H., R. & Lindsey, C. (2002). The Physics and Technology of Tennis. California: Racquet Tech Publishing.
Cross, R. (2004, May 11). Personal Communication.
Elliot, B. & Wood, G. (1983). The Biomechanics of the Foot-up and Foot-back Tennis Service Techniques. The Australian Journal of Sport Sciences, 3(2), 3-6.

References: Brody, H., R. & Lindsey, C. (2002). The Physics and Technology of Tennis. California: Racquet Tech Publishing. Cross, R. (2004, May 11). Personal Communication. Elliot, B. & Wood, G. (1983). The Biomechanics of the Foot-up and Foot-back Tennis Service Techniques. The Australian Journal of Sport Sciences, 3(2), 3-6.