The purpose and design of the clubs within your set and how they influence the golf ball differently. Every club, including the putter, is designed to hit below the equator of the ball. Naturally, the putter nearest the equator, down to the most lofted wedge, nearest the South Pole. That collision inspires launch, spin, distance, etc. The golf club travels on a circular and rotational path so the ball can travel on a straight flight, clubface and path explanation and why the ball might curve and vary trajectory.