Two-piece golf ball

Abstract

A golf ball 2 includes a core 4 and a cover 6 . A value V calculated by the following mathematical formula is equal to or less than 1080 Hz. V =NF(2)2−2/3*NF(2)1 In the mathematical formula, NF(2)1 represents a secondary natural frequency of the core 4 , and NF(2)2 represents a secondary natural frequency of the golf ball 2 . A difference (H1s−H1o) between a Shore C hardness H1s at a surface of the core 4 and a Shore C hardness H1o at a central point of the core 4 is equal to or greater than 10. An amount of compressive deformation Df1 of the core 4 is equal to or greater than 4.1 mm.

What is claimed is: 
     
         1 . A two-piece golf ball including a core and a cover positioned outside the core, wherein
 a value V calculated by the following mathematical formula is equal to or less than 1080 Hz,
     V =NF(2)2−2/3*NF(2)1,
 
   
       wherein NF(2)1 represents a secondary natural frequency of the core, and NF(2)2 represents a secondary natural frequency of the golf ball. 
     
     
         2 . The two-piece golf ball according to  claim 1 , wherein a difference (H1s−H1o) between a Shore C hardness H1s at a surface of the core and a Shore C hardness H1o at a central point of the core is equal to or greater than 10. 
     
     
         3 . The two-piece golf ball according to  claim 1 , wherein the value V is equal to or less than 1040 Hz. 
     
     
         4 . The two-piece golf ball according to  claim 3 , wherein the value V is equal to or less than 1000 Hz. 
     
     
         5 . The two-piece golf ball according to  claim 1 , wherein an amount of compressive deformation Df1 of the core is equal to or greater than 4.1 mm. 
     
     
         6 . The two-piece golf ball according to  claim 1 , wherein an amount of compressive deformation Df2 of the two-piece golf ball is equal to or greater than 3.5 mm. 
     
     
         7 . The two-piece golf ball according to  claim 1 , wherein a thickness T2 of the cover is equal to or greater than 0.80 mm but equal to or less than 2.00 mm. 
     
     
         8 . The two-piece golf ball according to  claim 1 , wherein a Shore D hardness H2 of the cover is equal to or greater than 50 but equal to or less than 65.