Golf ball

Abstract

A golf ball ( 1 ) comprises a core ( 3 ) and a cover ( 5 ). The core ( 3 ) has a six-layer structure having first to sixth layers ( 7, 9, 11, 13, 15, 17 ). An inner layer of the core 3 has a low modulus of elasticity. To the contrary, an outer layer of the core ( 3 ) has a high modulus of elasticity. If time series data on force in a z direction which is applied to a load cell provided on a back face of a collision plate inclined by 22 degrees with respect to a horizontal direction when the golf ball ( 1 ) impacts with the collision plate at a speed of 35 m/s in a vertical upward direction are represented by Fn(t), time series data on force in an x direction are represented by Ft(t) and a time taken after a start of the impact before the Fn(t) is first changed from a positive number to zero is represented by T 1 and a time taken after the start of the impact before the Ft(t) is first changed from a positive number to a negative number is represented by T 2 , a value of (T 1 /T 2 ) is 1.85 to 2.10. The golf ball ( 1 ) has a great launch angle and generates a low back spin rate.

What is claimed is:  
     
         1 . A golf ball in which if a direction of a counterclockwise rotation by 22 degrees with respect to a vertical upward direction is set to a z direction, a direction of a counterclockwise rotation by 22 degrees with respect to a horizontal right direction is set to an x direction, time series data on force in the z direction which is applied to a load cell provided on a back face of a collision plate having a surface extended in the x direction when the golf ball impacts with the collision plate at a speed of 35 m/s in the vertical upward direction are represented by Fn(t), time series data on force in the x direction are represented by Ft(t), a time taken after a start of the impact before the Fn(t) is first changed from a positive number to zero is represented by T 1  and a time taken after the start of the impact before the Ft(t) is first changed from a positive number to a negative number is represented by T 2 , a value of (T 1 /T 2 ) is 1.85 to 2.10.  
     
     
         2 . The golf ball according to  claim 1 , wherein the value of (T 1 /T 2 ) is 1.95 to 2.10.  
     
     
         3 . The golf ball according to  claim 1 , wherein the value of (T 1 /T 2 ) is 2.00 to 2.09.