When you stop to think about all the physics involved in your golf swing, it blows your mind. From gravity, to shaft flex, to action-reaction, physics is constantly involved in the game. Let's start at the begining of the golf swing. The ball remains at rest initially because of Newton's first law. Since there is no unbalanced force on the ball, it remains at rest.
Gravity causes the ball to tend to move down, but the ground provides a balancing force on it.
Now to the swing. As you start your swing, you slowly begin to move the club away from the ball. The motion that you create becomes circular. As the backswing motion is completed and the downswing begins, there is flex in the shaft of the club. This accelerates the clubhead as it is brought through the plane of the ball.