Why is the surface of golf not smooth like table tennis, but bumpy? Surface like golf ball can make the air turbulent around the ball, avoid the eddy current behind the ball and cause the ball to slow down. When golf balls fly fast, symmetrical whirlpools are formed behind the balls. After the fluid molecules near the balls walk along the balls for a period, they leave the sphere. This phenomenon is also known as boundary layer separation. Behind the golf ball is a whirlpool with a small central pressure, while the pressure in front of the ball is relatively high. Because of this pressure difference, the ball is subjected to a relatively large resistance. Generally speaking, the faster the ball flies, the earlier the boundary layer separates, the larger the eddy area behind the ball, and the greater the drag caused by the pressure difference. Because of the early separation of the boundary layer, the pressure difference resistance between the front and back of the smooth sphere is very large, and the flight distance is greatly shortened. When the golf ball has small pits, there are some small eddies near the pits when flying. Because of the attraction of these small eddies, the fluid molecules near the golf ball surface are attracted by the eddies, and the separation points of the boundary layer are pushed back a lot. At this time, the large eddy area formed behind the golf ball is much smaller than that formed by the smooth ball, which greatly reduces the drag caused by the pressure difference between front and back. In addition, small pits also affect the lift of golf balls. A spinning ball with a rough surface will deflect the airflow like an airplane wing to generate lift. The spin of the ball can make the air pressure below the ball higher than that above it. This imbalance can generate upward thrust.