Understanding the Golf Swing
The Physical and Mental Dynamics of the Golf Swing
By O'Tar T. Norwood
Handicap: Best 14 - Current 18
There are two reasons that there is no discussion of physics in golf instruction, golf commentary or golf magazines. First, the mere mention of physics causes the average person to completely lose interest. Second, most if not all of golf professionals and low handicappers are born with a natural swing and have never struggled with its fundamental difficulties. As a result they tend to emphasize the mechanics of the swing instead of the underlying physics. Understanding the physics and the principals of circular motion are essential for learning a swing for a person born without one.
Understanding the physics of the golf swing starts with understanding and applying Newton’s three laws of motion (See footnote below). 1) We know according to Newton’s first law that a golf ball will just sit on a tee held there by gravity and the ground until it is hit by another force. 2) We know that according to Newton’s second law that the harder we hit the ball the further it will go. 3) We know that according to Newton’s third law that for every action there is an equal and opposite reaction.
These laws are pretty straight forward and easy to understand as long as the object is traveling in a straight line but when that object makes a turn and begins to form a circle other forces come into play, namely, the forces of circular motion. Any point on a curved path can be extended to become a full circle. The two main forces of circular motion are centrifugal force (away from center) which everyone has heard of and centripetal force (towards the center) which most people have never heard of. Remember that the club head is traveling in a circle around your body.
Although we are largely unaware of it we deal with circular motion
constantly during life. In fact, all animals that move deal with it
instinctively. Every time we move in any direction other than a straight
line we compensate for it in one way or another. When we walk, run, drive,
and make a turn we are dealing with it. It is an intregal part of all
sports, throwing, swinging a bat or golf club, diving, swimming, flying, and
all track and field sports.
The key to harnessing the effortless power of the golf swing is controlling centrifugal force and that is done by pulling (increasing centripetal force) on the club head which in turn increases centrifugal force. The more you pull, the more you increase centrifugal force and the faster the club head travels. That is why golfers like Ernie Els appear to be swinging so easily yet generate so much power (club head speed). They are pulling on the club. You can’t really see a “pull” like you can see a “hit.” This is why a good swing appears to be so effortless.
Put another way, think of the club head as making a circle around the body, and then think of what happens when you forcefully shorten the radius of a circle (pull). The club head moves faster! Newton’s third law.
1) Newton's three laws of motion: (1) a body remains in a state of rest or uniform motion unless acted on by an external force; (2) change in motion is proportional to and in the same direction as the application force; (3) to every action there is an equal and opposite reaction.
Tiger at impact illustrating Newton's third law. Force against counter force, upper body against lower body. Weight on left stiff leg (left side), hips pointed forward, head and shoulders pulling back against hips, weight on left foot and centrifugal force of club.
|From Golf Digest||
CP=Centripetal Force CF=Centrifugal Force
The golf swing is simply a winding up of the body and then a very forceful unwinding. The wind up is not difficult, simply twist the body to the right and get the weight on right (back) foot with club over shoulder.
The unwinding is the problem. It starts with initiating weight shift to left foot and unwinding body from the bottom to the top. As the unwinding proceeds the club is naturally pulled down creating centrifugal force. When arms are at about horizontal level with wrists still cocked, the power begins! This power is created by pulling (centripetal force) on the club causing wrists to uncock and club head to speed up dramatically. The harder the pull the faster the club head speed. This is the key to the golf swing.
The neurocircuitry of the brain and nervous system is incapable of sending individual messages to each muscle groups in the instant it takes to complete the golf swing. The brain is set up to work in patterns and concepts so the best way for it to understand the swing is to compare it to another activity it already naturally understands or already can do.
Activities Related to the Golf Swing
What do all these activities have in common? They involve the principles of circular motion. The most important of these principles are centripetal force, towards the center and centrifugal force, away from center. Thinking of it another way would be force against counter force. Then think of the golf swing as the club head traveling in a circle around your body and then think of what happens to a body traveling in a circle when the radius of that circle is forcefully shortened. The object moves faster. Again, this is the key to understanding the golf swing.
The Universe and all of it's spinning planets, stars and moons are governed by the laws of circular motion and the delicate balance between centripetal force (gravity) and centrifugal force.
Spinning ice skater
What happens when a spinning ice skater with her arms extended and one leg extended pulls in her arms and the leg? She spins faster.
Twirling a ball on a string
Probably the best example and easiest to reproduce is twirling an object on a string in a circle. Ideally a tennis ball with a 3 or 4 feet string attached to it. If the tennis ball is swung vertically in a clockwise direction (if right handed) it gives you the feeling of the golf swing. You will notice that the harder you pull on the string faster the ball moves. To more closely imitate the golf swing try to pull or slightly jerk the string just prior to the ball reaching the bottom of the circle.
Swinging in a swing
Gravity is the main force in swinging in a swing. Weight shift enforces it. Remember when you learned to swing in a swing. If the swing is not moving no matter what you do nothing happens. But once you get the swing started remember at the height of the swing going back, you lean back, pull on the ropes with your hands and have your feet tucked under the seat. Then you lean back even harder on the ropes and force your feet forward. This forces the swing down with the aid of gravity. Then you continue to pull and lean back with your feet pushed forward until you reach the top of the arc on the other side. Gravity pulls you back and you repeat the process each time going higher. Your upper body and head move against the direction of the swing and lower body. This shifting of weight remember, was called “pumping.” This action is instinctive in most people even children. You can place a child in a swing for the first time and after the child gets going you will note the child is naturally shifting his weight and “pumping.” In effect the child is increasing and decreasing the radius of the circle by shifting his weight, thus shortening and lengthening the radius of the circle.
Standing up in a swing is easier to understand. At the top of the arc, knees are bent and are straightened forcefully during decent to the bottom of the arc. This in effect pushes weight towards the center of the circle in turn shortening the radius of the circle.
Throwing a Ball
Compare the way a typical boy throws a ball and the way a typical girl throws a ball. Apologies to girls who throw “like a boy.” When a boy throws a ball he rears back, cocks his arm, raises his left foot (if he is right handed) and then initiates the throw by thrusting his lower body forward, uncoiling his hips and throwing his right arm and hand forward and then snapping his wrists at the end of the throw. The other key movement is that he snaps his head and shoulders back against the forward movement of his arm and hand. The head and shoulders snap back causing the wrists and hand to snap forward.
When a girl throws a ball you know she is not doing it right but at first you are not sure what’s wrong. Actually she does everything wrong. There is no hip turn, no body coil, no rearing back of the upper body and her head and shoulders move forward with the throw thus providing no counter force to the forward thrust of the arm and wrist, so there is no wrist snap. This can be compared to the golf swing in that high handicappers tend to look more like a girl throwing a ball and the low handicappers or professionals look more like a boy throwing a ball. In each case you know something is wrong but you are not quite sure what it is. The main factor that makes the difference is the absence or presence of counter force.
Cracking a whip
We have all cracked a whip or have tried to crack a whip. The principle is the same as snapping a towel. The point is to jerk back on the whip just before the whip reaches its full length thus snapping the tip and creating a noise. This jerking back represents centripetal force. Transferring this principle to the golf swing involves pulling on the club during the down swing to increase the velocity of the club head. In this case the club head would be compared to the tip of the whip. To appreciate how important this is, think of this. The tip of the whip breaks the sound barrier! The sound barrier is 740 mph! In golf we are only trying to reach about 100 mph.
Swinging the putter with two fingers
This is a mini, slow motion reproduction of the golf swing and illustrates very clearly how increased counter force (centripetal force) causes increased club head speed.
Hold a putter between the
index finger and thumb and swing it gently. To swing the putter higher
you actually pull the putter up and back
at the bottom against the
direction of the putter head at the bottom of the arc of the swing. If
you actually almost jerk up
at the bottom of the arc it swings much
Another way to demonstrate this phenomenon or feeling is by leaning over at the waist and allowing your left arm (if you are right handed) to be entirely relaxed and hang loosely down like a pendulum (the arm must be entirely relaxed and dangle). Start swinging your arm with the movement of your shoulder and turning of your hips. Then just when your arm almost reaches the bottom of the arc jerk your body up a little bit and you will notice your arm swings very high.
Allowing your left heel to rise with the swing of the arm and then slamming it to the ground can even better demonstrate it. This raising your heel and stepping forward with your left foot in baseball is called “posting.” In golf, it is not a clear-cut forward step; it is a weight shift, and is called “getting to your left side.”
The purest examples of circular motion in sports are the classic Greek discus throw and hammer throw. The goal in coaching these two sports is to get the athlete to think of their arms as a mere rope or limp connection to the discus or hammer. This forces them to concentrate entirely on turning in a circle using the powerful muscles of trunk and legs. This same relaxation is important to some extent in the golf swing. The arms should be used to guide the club but not used for power.
You can see the pull (centripetal force).
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