Golf Swing Dynamics

The dynamics of the golf swing is important to every golfer's game. To hit a golf ball, the golfer swings a club while standing at the side of a motionless ball positioned on the ground. Such a swing involves angular motion. In physics, angular motion is defined as the movement of a body about a fixed point, or axis. Speed, velocity, acceleration, momentum, mass, torque, kinetic energy, and centripetal force, are some of the concepts involved in the golf swing. For instance, the twisting motion of the swing produces torque (rotating motion) on the club. This force changes with the angular velocity (rate of rotation) of the club, which causes additional rotation to take place.

Since most club heads weigh approximately the same, the head's velocity at the impact point is an important concept for hitting a golf ball long distances. The faster the head is swung, the greater the amount of kinetic energy—which is proportional to the head's mass times its velocity squared—that will be transferred from the head to the ball. This energy transfer results directly in a faster ball speed off the golf tee.

The swing involves the rotation of the human body in order to accelerate the club head so that it will collide with the ball. The right-handed golfer stands to the side of the ball with the left shoulder and hip pointing in the flight direction. The club is gripped with the right hand below the left hand. The hips and knees are slightly bent, and the arms hang off the shoulders.

In physical terms, the swing can be viewed as two levers: one lever consisting of the combined efforts of the shoulder, arms, and hands rotating about an axis through the upper chest and a second lever consisting of the club rotating about an axis through the golfer's hands. With this in mind, the swing consists of four parts: backswing, downswing, impact, and follow-through.

The backswing (or upswing) is a coordinated backward movement of the club and the golfer's hands and a rotation of the golfer's trunk. The golfer's weight shifts to the right, while the pelvis and shoulders are turned, the arms lifted, and the elbows and wrists bent. At the completion of the backswing, the hands are above the right shoulder, with the club pointing approximately in the direction of ball flight.

The downswing assures that, when arriving at the impact point, the club head is moving at maximum speed and in the required direction and the clubface is moving in that identical direction. The downswing begins with forward movement of the hips, which occurs just before the club head reaches the zenith of the backswing. The hip's forward motion rotates the upper body and moves both levers through the beginning of the downswing. The relative positions of the shoulders, arms, hands, and golf club are fixed. When the left arm becomes horizontal, the hands continue their path through a circular arc at constant speed while the club head's speed increases rapidly as the angle between the club shaft and left arm straightens. At the end of the down-swing, the right elbow is brought down and close to the body's right side. During the final moments, the wrists are rolled through approximately 90° so the back of the left hand and the clubface are brought around perpendicular to that direction.

At this time, the forces on the golfer's hand resolve into two components: the radial force (centripetal force) that acts toward the axis that the shoulders-arms-hands lever rotates (which restricts the motion of the handgrip to a circular arc), and the tangential force that acts in a direction parallel to the path followed by the handgrip (which helps to accelerate the club).

The critical features of the swing at the moment of impact are the position of the club head, the orientation of the clubface, and the velocity at which they are moving. Generally, the club face is at a 90° angle to the required direction; the club head's center of gravity is directly behind the ball's center; and the club head is moving forward with maximum speed.

The follow-through consists of a continued rotation to the left. At the end, the golfer's weight has shifted almost completely to the left foot, the body is turned entirely to the left, and the hands are above the left shoulder with the golf club positioned over the player's back.

The golf club acquires its energy from three sources: the golfer's torque acting on the arms as they move through the downswing's arc; the potential energy of the arms and club at the top of the back-swing (which turns to kinetic energy as the arms and club drop down during the swing); and the work done by the golfer during the shifting of the axis of the swing.

see also Golf; Golf ball construction and flight dynamics; Golf: Psychology of the swing.