A cross-sectional shape of each of dimples 8 of a golf ball 2 is a wave-like curve. The wave-like curve has two first curves 14, two second curves 16, two third curves 18, and one fourth curve 20. Each first curve 14 and each third curve 18 are upwardly convex. Each second curve 16 and the fourth curve 20 are downwardly convex. Each first curve 14 is connoted to a land 10 at an edge (Ed). Each second curve 16 is connected to the first curve 14 at a first inflexion point 22. Each third curve 18 is connected to the second curve 16 at a second inflexion point 24. The fourth curve 20 is connected to the third curves 18 at third inflexion points 26. In the wave-like curve, the upwardly convex curves 14 and 18 and the downwardly convex curves 16 and 20 are alternately arranged.

[0004] 2. Description of the Related Art

[0005] Golf balls have a large number of dimples on the surface thereof. The dimples disturb the air flow around the golf ball during flight to cause turbulent flow separation. By causing the turbulent flow separation, separation points of the air from the golf ball shift backwards leading to a reduction of drag. The turbulent flow separation promotes the displacement between the separation point on the upper side and the separation point on the lower side of the golf ball, which results from the backspin, thereby enhancing the lift force that acts upon the golf ball. The reduction of drag and the enhancement of lift force are referred to as a "dimple effect". Excellent dimples efficiently disturb the airflow. The excellent dimples produce a long flight distance.

[0006] There have been various proposals for the shapes of dimples. U.S. Pat. No. 7,250,012 discloses a golf ball that has dimples each having an annular tubular portion. U.S. Pat. No. 7,503,857 discloses a golf ball that has dimples each having formed therein a raised region.

[0007] The greatest interest to golf players concerning golf balls is flight distance. In light of flight performance, there is room for improvement in the shapes of dimples. An object of the present invention is to provide a golf ball having excellent flight performance.

SUMMARY OF THE INVENTION

[0008] A golf ball according to the present invention has a large number of dimples on a surface thereof. Each dimple has a curved surface. A cross-sectional shape of the curved surface is a wave-like curve in which a plurality of upwardly convex portions and a plurality of downwardly convex portions are alternately arranged.

[0009] The golf ball according to the present invention has excellent flight performance. The detailed reason has not been identified, but it is inferred that this is because separation of air from the dimple surface in the dimple is prevented and separated air re-contacts the dimple surface in the dimple.