J. Nat. Scien. & Math. Res. Vol. 2 No.1 (2016) 85-90, 85 Copyright @2016, JNSMR, ISSN: 2460-4453 Available online at http://journal.walisongo.ac.id/index.php/jnsmr Effect of the Pull and Diameter String of Badminton Racket Based on Coeffisient of Restitution Value Ivan Setia Arianto 1, , Nuri 2 and Agus Yulianto 3 1 SMP Islam Al Azhar 29 Semarang, Central Java, Indonesia 2 SMK Tunas Harapan Pati, Central Java, Indonesia 3 Physic Department, Faculty of Mathematics and Natural Sciences, Semarang State University, Indonesia Corresponding author: ivankovic90@hotmail.com Recived: 02 March 2016, Revised: 20 April 2016 Accepted: 25 May 2016. Abstracts Racket and strings is an important factor in the badminton sport. The aim of this study to analyze the pull and the diameter racket string based on restitution coefficient of shuttlecock. The variation of pull was measured used racket Vinlux Miotex Power 007. Six variation of racket string are (22, 23, 24, 25, 26, and 27) lbs. The diameter of the strings has kept constant of 0.66 mm. The other variable is the diameter variation of the strings are (0.62, 0.64, 0.66, 0.68, and 0.70) mm, respectively and the pull of the strings are kept constant of 24 lbs. Based on the result, the increasing of the pull was decreased the COR value, from 0.541 to 0.374 for 22 lbs to 27 lbs, respectively. Furthermore, the similar trend for the diameter variation with the pull variation, the COR value was decreases with the increasing of the diameter, from 0.529 to 0.447 for (0.62 to 0.70) mm. We can conclude, the increases of the pull and diameter variation was decresed COR value of shuttlecock. ©2016 JNSMR UIN Walisongo. All rights reserved. Key words: String; Racket; Coefisien of restitution. 1. Introduction Badminton is one of the most popular sports in Indonesia. Generally, badminton sport can in Indonesia has become a mainstay for achievement with frequent title. Many world class achievement and the Olympic badminton athletes who achieved so that the name of Indonesia in the international world of sports. Racket and strings like two sides of a coin that can not be separated. Both are important factors for a game of badminton. Racket superior useless if using strings ugly as easily break off and reflections shuttlecock irregular [1]. Otherwise if you choose a racket carelessly will affect the strength of the strings hold [2]. Racket with greater weight will generate higher ball velocity in the smash than the weight of the racket which is lighter. It was