Defining the Forces of the Golf Swing
Your feet generate forces when they push against the ground. These forces act to propel your body and create motion. Two types of forces are important to the golf swing: normal forces and shear forces. Normal forces are illustrated in the linear components of the swing, and shear forces are illustrated in the rotational components of the swing.
Normal forces are applied by the feet downward or perpendicular to the ground. Weight is transferred to the back foot during the backswing and to the front foot during the downswing. When weight is shifted to one foot, the amount of force supplied by the foot increases while the normal force applied by the other foot decreases. This action defines the linear component of the movement. The linear movement of the body during the golf swing is very important because it is from this movement that the body develops momentum that enhances the rotational speed and power of the hips.
Shear force is applied by the feet along the surface of, or parallel to, the ground. Through the swing, shear forces are being applied by both feet. These shear forces create torque that turns the hips around the axis of the trunk. This defines the rotational component of the lower body movement. The rotational component can be related most directly to the ultimate club head speed attained in the swing.
When faults occur in lower body mechanics, the effect on the golf swing is analogous to cracks in the foundation of a house. When a stable base is lost, swing efficiency erodes. The most common fault in lower body mechanics is sliding. When a golfer slides, the interaction between the linear and rotational components breaks down, weight transfer is diminished, and rotation is lost.