Most golfers believe that their ball will not fly as well in warm humid air as in dry air. But humid air is less dense than dry air at the same temperature. The distance any projectile travels, including a golf ball, is determined by gravity and friction.
Gravity is the force that pulls all objects toward the center of the earth.
It exerts a downward force on the golf ball as soon as it is launched, a force that eventually brings it back to the ground. When the density of air is zero, such as in a vacuum, there is no friction. In this case, it is easy to compute precisely how long the golf ball remains airborne. The ball will follow a parabolic path as it fights gravity going up, and gives way to gravity on its return to the ground. We need only consider the vertical and horizontal velocity of the ball once it is hit to determine the distance the ball will travel along a parabolic path.