LARGE-DIAMETER TENNIS BALL

Abstract: A tennis ball has a diameter about 5% to about 13% greater than the diameter of a standard tennis ball. The ball has about the same weight, and the thickness of the core of the ball is less than that of a standard ball. The rebound and coefficient of restitution of the ball are equal to or better than the rebound and coefficient of restitution of a standard ball.

Description: LARGE-DIAMETER TENNIS BALI; Background This invention relates to tennis balls, and, more particularly, to a tennis ball which plays slower than a standard tennis ball. Tennis has been a popular sport for decades. However, the popularity of tennis peaked during the 1970's, and the number of participants in the sport has declined since that time. One of the primary reasons why many tennis players decrease or discontinue their participation in the sport is the real or perceived difficulty of the sport or the real or perceived low level of skill of the player. Many people feel that a substantial amount of playing time is required to reach and maintain a certain level of skill in tennis, and some people who do not have the time or the commitment to achieve that level simply stop playing the game. Some attempts have been made to make the game of tennis easier. For example, in about 1976 Spalding introduced a tennis ball called the "Australian." This ball was described as a slower playing ball than a standard tennis ball which resulted in longer rallies and a more enjoyable game of tennis. The slower play resulted from lower air pressure and coefficient of restitution compared to a standard ball. However, this ball never became popular, and it is believed that this was because the ball lacked liveliness and therefore felt heavy and dead on the racket. Pressureless tennis balls, which typically play slower than standard tennis balls, have suffered from the same drawbacks. as the Australian ball. The Tretorn pressureless ball, has improved rebound height. However, this ball still lacks liveliness at high impact speeds, thereby resulting in a heavy, dead feel on the racket. Summary of the Invention This invention provides a new tennis ball which plays slower than a standard tennis ball yet which is more lively than a standard ball. The diameter of the ball is about 3% to about 11% larger than the diameter of a standard ball so that the ball moves through the air more slowly than a standard ball and has increased visibility. Since the new ball is slower than a standard ball, the new ball is more likely to fall inbounds when hit with a greater force or when hit over the net at a greater height. The slower ball is also easier to reach by the player. Accordingly, the new ball is more forgiving, provides more margin for error, requires less skill, and provides longer rallies than a standard ball. Even though the new ball is slower, the new ball has increased liv ness as measured by rebound and coefficient of restitution. Although the ball is larger than a standard ball, it weighs the same because the core is thinner. The ball therefore feels light and lively on the racket. Description of the Drawing The invention will be explained in conjunction with an illustrative embodiment shown in the accompanying drawing, in which - Fig. 1 is an illustration, partially broken away of a tennis ball formed in accordance with the invention; Fig. 2 is an illustration of the flight paths of various sized tennis balls which are hit from the baseline at the same angle and velocity; Figs. 3 and 4 are illustrations similar to Fig. 2 of various sized tennis balls which are hit at lower velocities; Fig. 5 is an illustration of the eight paths of various sized tennis balls which are hit from the baseline at the same velocity but different angles; and Figs. 6 and 7 are illustrations similar to Fig. 5 of various sized tennis balls which are hit at lower velocities. Description of Specific Embodiment A tennis ball 10 is comprised of a core 11 formed of rubber or other elastomeric material and a felt cover 12. The core is molded in the conventional manner, but, as will be explained in detail hereinafter, the diameter and thickness of the core are different than the diameter and thickness of a standard tennis ball core. The felt cover 12 is formed from light weight woven felt. The weight of the felt is 14 ounces per square yard compared to 22 ounces per square yard for woven felt which is conventionally used. The thickness of the cover is about 0.094 inch, compared to about 0.120 inch for a standard ball. Standard tennis balls conform to the following specifications of the United States Tennis Association for size, weight, and rebound: "The ball shall have a uniform outer surface and shall be white or yellow in color. If there are any seams they shall be stitchless. The ball shall be more than two and half inches (6.35cm) and less than two and five-eighths inches (6.67cm) in diameter, and more than two ounces (56.7 grams) and less than two and one-sixteenth ounces (58.5 grams) in weight. The ball shall have a bound of more than 53 inches (135cm) and less than 58 inches (147cm) when-dropped 100 inches (254cm) upon a concrete base. The ball shall have a forward deformation of more than .220 of an inch (.56cm) and less than .290 of an inch (.74cm) and a return deformation of more than .350 of an inch (.89cm) and less than .425 of an inch (1.08cm) at 18 lbs. (8.165 kg) load. The two defor mation figures shall be the averages of three individual readings along three axes of the ball and no two individual readings shall differ by more than .030 of an inch (.08cm) in each case. All tests for bound, size and deformation shall be made in accordance with I.L.T.F. regulations." I have found that a ball which has an outside diameter between about 3% to about 11% larger than the outside diameter of a standard tennis ball will play slower than a standard ball and that the larger ball will have surprisingly good liveliness and rebound if the weight of the ball is kept at the standard weight by reducing the thickness of the core. Heretofore, tennis balls which played slower than standard tennis balls had unsatisfactory rebound and felt heavy on the racket. However, balls formed in accordance with my invention have even better rebound and coefficient of restitution than standard balls. My ball therefore feels light and lively on the racket. The foregoing chart compares the physical characteristics of a standard tennis ball and balls formed in accordance with my invention and also of balls which are about 1% and about 15% larger than standard: Thidmess Outside Thickness of Felt Diameter of Core Cover Weight Rebound (inches) (inches) (inches) (grams) ( (inches) Standard ball (Wilson T1001) 2.621 0.132 0.120 56.9 54.6 1.2% larger ball 2.652 0.122 0.094 55.6 57.4 2.6% larger ball 2.689 0.118 0.094 55.7 57.5 4.6% larger ball 2.741 0.113 0.094 54.1 57.5 8.0% larger ball 2.830 0.106 0.094 54.7 58.2 11.2% larger ball 2.915 0.100 0.094 55.7 57.6 15.0% larger ball 3.013 0.094 0.094 58.6 57.7 The coefficient of restitution (COR) of the foregoing balls was measured and compared at various impact speeds: vs. vs. 70 feet standard 100 feet standard per second ball per second ball Standard ball (Wilson T1001) 0.616 0.522 1.2% larger ball 0.651 +.035 0.550 +0.028 2.6% larger ball* 0.655 +.039 0.556 +0.034 4.6% larger ball 0.661 +.045 0.564 +0.042 8.0% larger ball 0.668 +.052 0.576 +0.054 11.2% larger ball 0.675 +.059 0.577 +0.055 15.0% larger ball 0.679 +.063 0.583 +0.061 (*Extrapolated.) The larger balls surprisingly exhibited better coefficient of restitution as the impact speed increased. However, the increase is not linear, and the optimum increase is obtained at about a 4.68 increase in size. The change in COR at 70 feet per second from the standard ball to the 4.6% larger ball is +0.45, but the change from the 4.6% ball to the 15% ball is only +0.18. The observed increase of COR with ball size is believed to be caused by a number of factors: 1. The thinner walls of the larger balls may dissipate less energy, since they experience less strain for a given amount of bending. 2. As a ball gets larger with thinner walls, it becomes more like an air spring and less like a rubber spring. Air, of course, has much less damping effect than rubber. 3. The time duration of the impact has been shown to be greater for ther larger balls. This means that the deflection rate, and thus the energy dissipation, may be lower. The deflection of the various balls was: Deflection (inches) Standard ball (Wilson T1001) 0.231 1.2% larger ball 0.233 2.6% larger ball 0.247 4.6% larger ball 0.266 8.0% larger ball 0.287 11.2% larger ball 0.318 15.0% larger ball 0.323 Defelction, which relates to less playability and heavier feel as it increases, is also not linearly related to size. The change in deflection from the standard ball to the 4.6% ball was +0.35 and from the 4.6% ball to the 15% ball was +0.57. Fig. 2 is a computer simulation of the flight paths of various sized balls which are launched by a tennis ball cannon at the same velocity and launch angle. Controlled data on actual launches is difficult to obtain because the tennis ball cannon launches different sized balls slightly differently and launches a particular sized ball inconsistently and because of the uncontrollable variables of spin, wind, etc. However, the accuracy of the computer simulation was verified by an actual launch with each size of ball. In Fig. 2 the standard tennis ball is launched from one baseline of a tennis court at a velocity of 117 feet per second at an angle which will enable the ball to fall on the other baseline 78 feet away. The launch angle in Fig. 2 is 5.30 . It will be seen that as the balls get larger, they do not travel as far and are more likely to fall inside the baseline. Figs. 3 and 4 are similar to Fig. 2. However, the launch speed and angle in Fig. 3 is 96 feet per second and 9.20, respectively, and the launch speed and angle in Fig. 4 is 76 feet per second and 16.90. Fig. 5 is a computer simulation of the flight paths of various sized balls which are launched from nne baseline at the same velocity and at an angle which will enable the ball to hit the other baseline. It will be seen that as the balls get larger, they can be hit over the net at a greater height and still land inbounds. Thus, the margin c error increases as the size of the ball increases. The launch speed in Fig. 5 was 96 feet per second. Figs. 6 and 7 are similar to Fig. 5 but the launch speed was 76 feet per second and 66 feet per second, respectively. Play testing was used to determine the acceptable range of the larger ball. Testing by tennis players under actual playing conditions is important because the acceptability of tennis equipment depends to a large extent on "feel" and "perceived" performance rather than on predicted performance. The play testing indicated that balls which were 1.2% larger than a standard ball did not exhibit significantly different playing characteristics than a standard ball. A ball which was 4.6% larger was noticeably slower than a standard ball, and the players felt that they were more accurate and were able to hit with more control with the larger ball, that rallies lasted longer, and that they had more time to set up for the ball. These same characteristics were also exhibited by balls which were 8.0% and 11.2% larger than a standard ball, although the 11.2% ball felt heavy to some players. On the other hand, a ball which was 15% larger than a standard ball was not satisfactory. The 15% ball was perceived as too slow and too heavy, and players felt that they could not hit the ball with sufficient power. Further, the 15% ball is affected more by spin, and this ball curved excessively when the players imparted spin to the ball. It is believed that the spin of a ball is proportional to the moment of inertia of the ball. The moment of inertia I of a spherical shell is: I = 2/3 MR2 where M is the mass and R is the outside radius. As the radius increases, the moment of inertia increases = with the square of the radius. Accordingly, the 15% larger ball curves excessively when spin is imparted to the ball. Accordingly, players are able to obtain increased accuracy and longer rallies with balls within the range of 2.6% to 11.2% larger than a standard ball. The 4.6% and 8.0% balls were superior to the 11.2% ball, and the optimum performance was obtained with the 4.6% ball. While in the foregoing specification a detailed description of specific embodiments of the invention was set forth for the purpose of illustration, it will be understood that many of the details herein given may be varied considerably by those skilled in the art without departing from the spirit and scope of the invention.

Claims: I CLAIM: 1. A tennis ball comprising an elastomeric core and a felt cover attached to the outside surface of the core, the outside diameter of the ball being within the range of about 2.689 to about 2.915 inches. 2. The tennis ball of claim 1 in which the weight of the ball is about 54 to about 58.5 grams. 3. The tennis ball of claim 1 in which the thickness of the core is within the range of about 0.118 to about 0.100 inch. 4. The tennis ball of claim 1 in which the thickness of the felt cover is about 0.094 inch. 5. The tennis ball of claim 1 in which the weight of the felt cover is about 14 ounces per square yard. 6. The tennis ball of claim 1 in which the coefficient of restitution of the ball is about 0.651 to about 0.675 at 70 feet per second. 7. The tennis ball of claim 1 in which the outside diameter of the ball is within the range of about 2.689 to about 2.830 inches. 8. The tennis ball of claim 1 in which the outside diameter of the ball is within the range of about 2.741 to about 2.830 inches. 9. The tennis ball of claim 1 in which the outside diameter of the ball is about 2.741 inches. 10. A tennis ball comprising an elastomeric core and a felt cover attached to the outside surface of the core, the outside diameter of the ball being within the range of about 2.689 to about 2.915 inches, the weight of the ball being about 54 to about 58.5 grams, and the thickness of the core being within the range of about 0.118 to about 0.100 inch. 11. The tennis ball of claim 10 .'.r which the ti=ncss of the felt cover is about 0.094 inch. 12. The tennis ball of claim 10 in which the weight of the felt cover is about 14 ounces per square yard. 13. The tennis ball of claim 10 in which the coefficient of restitution of the ball is about 0.651 to about 0.675 at 70 feet per second. 14. The tennis ball of claim 10 in which the outside diameter of the ball is within the range of about 2.689 to about 2.830 inches and the thickness of the core is within the range of about 0.118 to about 0.106 inch. 15. The tennis ball of claim 10 in which the outside diameter of the ball is within the range of about 2.741 to about 2.830 inches and the thickness of the core is within the range of about 0.113 to about 0.106 inch. 16. The tennis ball of claim 10 in which the outside diameter of the ball is about 2.741 inches and the thickness of the core is about 0.113 inch.

Inventors: CLAIRE, BRIAN
Applicants: WILSON SPORTING GOODS COMPANY
Application year: 1985
Main classification: A63B39
IPC codes: A63B39, A63B43