INERTIAL AND VIBRATIONAL CHARACTERISTICS OF PADDLE RACKETS, AND THE RELATION TO FREQUENT IMPACT AREAS

  • Aldo J. Viollaz
  • Aluísio O.V. Avila
  • N. Gomes Borges Jun.
  • José C. Pio da Fonseca
Keywords: paddle racket, restitution, inertia, vibrations, impact areas

Abstract

The first aim of this paper was the determination of the inertial and vibrational characteristic of paddle rackets, locating the center of percussion (CP), and the node of the fundamental mode of vibration (NVL). A second aim was the location of the frequent impact areas on the racket face to contrast these areas with the CP and NVL. The inertial characteristics of the rackets were determined using the classic pendulum method. The oscillation periods were measured with a precision of 0.001s using a high-speed video camera (180 Hz), given a standard error equal to 1 mm for the location of the CP. Accelerometer techniques were used to determine the natural frequency of the rackets with an error of 2 Hz and to locate the NVL with a precision of 1 mm. A field study was done with advanced paddle players to locate the areas of the racket face that they use for the different type of shots; this was done using rackets sensitized with carbon paper. The average location of the CP of 20 paddle rackets was mm 115 = CP l from the top of the racket, with a standard deviation of mm 3 = CP s indicating a small variability in the position of the CP among the different rackets. The average location of the NVL for these same rackets were mm 109 @ NV l with mm 4 = NV s , so the average distance between the CP and the NVL is only 6 mm, and therefore the locations of these points are not critical for the performance of the paddle rackets. The results of the field study show that advanced paddle players use different areas of the racket face for the drive, smash and volleys shots, mm 128 = d l , mm 83 = s l and mm 146 = v l being their average location, respectively, with standard errors of mm 22 = d s mm 14 = v s mm 11 = s s . A t-test was used to determine whether the differences among the locations are statistically significant, the results being 6 , 2 - = t and 014 , 0 = p between drive and volley ; 4 , 11 - = t and 11 10 . 2 , 1 - = p between volley and smash and 2 , 6 - = t and 6 10 . 4 , 1 - = p between drive and smash. These results indicate the existence of statistically significant differences between the impact locations used in the different type of shots. The paddle rackets have CP and NVL locations between 100 and 120 mm from the top of the racket, so that impacts in this region do not transfer much vibration and force to the player's arm. The impacts between this region and the CM of the racket have a high apparent coefficient of restitution (ACOR), as has been shown in another paper. Impacts near the top of the racket (as in the smash) have lower ACORs and lack the advantages of the CP and the NVL, transferring more vibration and force to the player's arm.