If you take a ball on the end of a string. Then just swing it around you. Feel what your hand is doing as the ball is swinging in a circle. It is constantly putting force on the rope to keep the ball swinging in a circle. If your arm goes the same direction the ball goes it slows the ball down. The same thing happens in your swing. Watch a hammer thrower. As the hammer comes around into the throw area the body pushes back away from the hammer to accelerate it. The same is true in a golf swing.