The COR is then found from the ratio of rebound height to drop height. The power spot is found at the point where the coefficient of restitution COR is at its maximum. The sweet spots are influenced by the racket material and design, as well as the tension of the strings.
Manufacturers often design rackets so that the sweet spots are in certain locations, for example at the centre of the racket. This is suitable for most players, but for professionals the situation is more complex, as there can be more than one sweet spot. The latest development in the evolution of the tennis racket has been the inclusion of smart materials in the handle that are capable of reducing frame vibration.
The materials used, called piezoelectric ceramics, generate an electric charge when they are under a mechanical force or stress , and, inversely, produce a mechanical force or displacement when an electric charge is applied. When used in tennis rackets, the piezoelectric ceramics convert mechanical vibrations into electrical energy, which, in combination with a microchip, converts that electrical energy back into a mechanical force that stiffens the racket frame and reduces vibration.
The majority of players don't like vibrations, as they often result in a loss of control, fatigue of the player and an unsatisfactory feeling when the ball is hit. It is important, however, that not all vibration is eliminated as this is provides feedback to the player about the quality of their tennis shot. The Head sporting goods company have led the way with these new style tennis rackets and players such as Andre Agassi and Sebastien Grosjean have already used them in tournaments.
There are, however, some disadvantages to the dramatic developments in sporting equipment we described in this article. Over the years the style of tennis has changed considerably and many spectators have been complaining that the pace of the game and, more specifically, the pace of the serve, are making tennis boring to watch. This is particularly true of fast surfaces like the grass courts used at Wimbledon where the pace of a game is significantly quicker than those seen on slower clay surfaces.
Let's compare a serve of mph approximate average 1st serve speed of men's serve at Wimbledon and one of mph the current record for the fastest men's serve , both travelling approximately For the purpose of this comparison, the calculation assumes that the ball loses no speed during its trajectory and bounce. In reality the ball will slow and therefore increase the time for the receiver to react.
The speed of mph is equivalent to Therefore it takes the ball travelling at that speed The same calculation for the speed of mph gives 0. Thus, an increase of 40mph reduces the amount of time a player has to react to a serve by 0.
This may not sound like a lot, but in such a fast paced game fractions of a second can really count. When a serve comes to the receiver at increasingly higher speeds, their reaction time will gradually diminish until a physical limit is reached an athletes reaction time to an external stimulus is about 0. The International Tennis Federation ITF , keen to "preserve the nature of the game", have approved three different kinds of ball, a slow one to be used on fast court surfaces, a fast one to be used on slow court surfaces and a medium for the in-between case.
It is hoped that the slower balls make the game easier to learn, more fun to play and more stimulating to watch. This article first appeared in Physics Review , a magazine for A level physics students. It is reproduced here with kind permission. Professor Claire Davis is a chartered engineer and works in the School of Metallurgy and Materials at the University of Birmingham, where she teaches materials science, metallurgy and sports science and materials technology students.
Her research interests are focused on microstructure-property relationships in metals. Elizabeth Swinbank is a physicist who, following a PhD at Cambridge, has taught at both school and university level. She is a Fellow in Science Education at the University of York where she is involved in a variety of science curriculum initiatives.
Her current interests include directing the Salters Horners Advanced Physics project, developing resources for the new Extended Project qualification and chairing the editorial board of Physics Review magazine. This and other texts I have read concentrate on the elasticity of the racquet.
As a tennis player and civil engineer my experience strongly suggests that the string tension and modulus of elasticity are just if not more important. Many players use different string type in the longitudinal as opposed to the cross strings while others use different tensions. My inclination is to attempt to share the impact force of the ball equally between the longitudinal and cross strings by using the one string type and a higher tension in the longitudinal strings.
Composite rackets are also tested for stiffness. Inspectors weigh both types of racket, usually before and after stringing, to make sure they meet specifications. They also check the balance, as this is extremely important to how well the racket plays. It should not be too heavy at the head or in the handle, but balance close to the mid-point though some models are designed to be deliberately head-heavy.
The grommet holes are inspected. If these are not smooth or even, string tension is affected, and strings may break against rough edges. The finishing details are also subjected to visual inspection. The butt cap should fit snugly, and the printing on the frame and strings should be even and clear. The grip should be wound smoothly, and there should be no nicks or scratches.
Some rackets may be play-tested, especially if it is a new design. The science of tennis rackets is surprisingly complex—not the manufacturing process but the physics of string and frame vibration as the ball connects with the racket. Rackets are now being designed by laboratory scientists who use mathematics to calculate the effects of weight, size, and material changes.
Since the rules governing acceptable rackets are very broad, innovators have a lot of leeway. New rackets are also being made with computer-aided design CAD and computer-aided manufacturing CAM , which allows precise calculation of material rigidity and center of gravity.
As such advanced science is being lavished on the tennis racket, doubtless new models with eccentric features will continue to be developed. The trend today is toward lighter, bigger rackets, and these are viable because of advanced materials engineering. Brody, Howard. Fisher, Marshall Jon. Gelberg, Nadine J. Sparrow, David. What are tennis racquets made of? Racquet frames were made of wood until the s. Now, they're made of graphite, fibreglass and other man-made materials.
It means racquets are a lot lighter - but just as strong. Tennis legend Bjorn Borg won 11 Grand Slam titles in the s and 80s using a wooden racquet. In he made a comeback wanting to prove his old-fashioned wooden racquet was still good enough. But he was blown away by little-known Jordi Arresse using a modern graphite racquet. When big hitter Mark Philippoussis compared the speed of his serves using wood and graphite racquets, they were found to be almost the same.
The difference was that the graphite racquet was far more accurate. Talk tennis on our messageboards. Common grip materials include rubber, leather or synthetic polymer materials such as neoprene. Synthetic grips can have a textured or patterned surface, which helps improve friction. Nylon is one of the most common materials used to make tennis racket strings.
Depending on their chemical composition, nylon strings can be soft or firm. Strings made with a nylon-core offer a good level of performance and durability and are less expensive than other types of materials. Another string material option is polyester.
A polyester string offers less power but more spin and tends to have a stiffer feel than nylon. Polyester strings can be combined with nylon-core strings to create a durable string bed with a softer feel. The most playable string is natural gut, which is made from animal intestines.
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