The Physics of the Golf Swing

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Transcript The Physics of the Golf Swing

The Physics of the
Golf Swing
Understanding the Golf Swing
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.
Balance and Stability
In order to maximise distance in a golf drive, balance and
stability are crucial components. A golfers ideal set up is
to stand with their legs shoulder width apart, knees
slightly bent, with the line of gravity within the golfers
base of support and the core muscles activated (Hume,
Keogh, & Reid, 2005).
Diagram of a golfer with feet shoulder with apart, knees
slightly bent and line of gravity within base of support.
The larger the area of base of support the more stable the
golfer is; however if it becomes too large it can restrict
movement (Blazevich, 2010). Therefore, shoulder width
apart is the optimal width as it allows for a stable base,
whilst still allowing the fluent and complex movement of
the golf swing. Similarly, bending the knees improves
balance and stability, as the body’s centre of mass is
closer to the base of support (Goehl, 2002). This allows
for improved stability as the body is well balanced.
Finally, by activating core muscles the body is kept rigid
rather than wobbly, further improving the golfers stability
(Hume, Keogh, & Reid, 2005). A stable set up allows the
golfer to generate more force and club head velocity with
his upper body whilst maintaining balance, in order to
exert maximum force and consequent distance on the
Force Summation
What is Force Summation?
It is the combination of forces produced by different
parts of the human body.
It’s purpose is to achieve maximum force/acceleration
and apply it to an object or the human body.
Principle 1
Use as many body parts that relate to the movement
as possible.
Principle 2
Body parts should move in a sequence with the bigger
muscles (e.g lower body and trunk) leading the action.
The smaller muscles closer to the object should be used
Principle 3
Muscle need to be used and accelerated with the
correct timing.
Principle 4
All the muscles used must go through their greatest
range of motion to achieve maximum momentum.
The 4 principles of force summation
More muscles
Correct sequencing
Correct timing
Greatest range of motion
These 4 principles all help to generate
maximum force.
Stability and Balance
It is important that all of these actions are performed
over a stable base.
This allows maximum force/acceleration to be applied
to the object.
Major Muscles Use in Force
Golf swing using the priciples
of Force Summation
Write a paragraph talking about force summation in golf
using, movement terms, key muscle names etc
Newton’s laws
Understanding the physics of the golf swing starts with
understanding and applying Newton’s three laws of
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.
Circular Motion
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.
Circular Motion
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.
Ernie Els Golf Swing
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
Ernie Els links
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.
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.
The best way to refine the action is practice!
For your arm, leg or any body part to move the appropriate muscles and bones must
work together as a series of levers. A lever comprises of three components 
Fulcrum or pivot - the point about which the lever rotates
Load - the force applied by the lever system
Effort - the force applied by the user of the lever system
The way in which a lever will operate is dependent on the type of lever.
Classification of Levers
Class 1 - The fulcrum lies between the effort and the load
Class 2 - The fulcrum is at one end, the effort at the other end and the load lies
between the effort and the fulcrum
Class 3 - The fulcrum is at one end, the load at the other end and the effort lies
between the load and the fulcrum
Class 1 Lever
Class 2 Lever
Class 3 Lever
Class 3 is the most common class of lever to be found in the human body.
Class 3 lever: This is where the fulcrum is at one end of the
lever, the load is at the other end, and the effort is in between.
These levers involve using a large effort to move a small load a
long distance.
An example is a person playing golf (see Diagram 6).
- In this case the golf club plus the person's arms is the lever,
- the golfer's shoulder is the fulcrum,
- the force being applied to the golf club by the golfer's hands - is the effort,
- and the load is the weight of the golf ball.
Other examples of Class 3 levers include:
using a cricket bat, a tennis racquet or a hockey stick to hit a
ball using a fishing rod to cast a fishing line.
Golf Swing Class 3 Lever
Projectile Motion
Many sports involve the throwing of a ball or other object. This powerpoint
discusses the basics of projectile motion, and for ease of understanding, we
will consider that there is no air resistance. The influence of air resistance,
friction, spin, and air flow around the object is discussed later.
Any projectile thrown, such as a ball, can be considered to have a vertical
and horizontal velocity component, as shown in this diagram
(blue=horizontal velocity component, red=vertical velocity component).
Throughout the path of the projectile, change occurs only in the vertical
direction due to the influence of gravity, while the horizontal component of
the velocity will not change. (This is not quite true, there will be a very
small slowdown in the horizontal direction due to air resistance).
The vertical velocity of the projectile gets smaller on the upward path until it
reaches the top of the parabola. At the top of the parabola, the vertical
component of the velocity is zero. After that point, the vertical component
changes direction and the magnitude increases in the downward direction and
the vertical distance traveled during each subsequent time interval increases.
Angle Of Release
For an object released at ground level, for any given release velocity, the
maximum distance is achieved using an angle of approximately 45 degrees.
However, as most implements in sport are released at a height above the
ground, say from about shoulder height, the optimum angle at release is
somewhat less than 45 degrees.
In golf we manipulate the angle of release by choosing a different club choice.
At times we don’t want to maximize the distance that we hit the ball. For
example approach shots at the green, getting out of a bunker etc. We are
looking for more ‘loft’ and for theball to remain stationary and not ‘run’ on
Height Of Release.
The height of release affects the trajectory of the projectile and, for a given
speed of release and angle of release, the horizontal displacement increases as
the height of release increases.
In golf we manipulate this using a tee to hit our first shot on a hole.
How can you manipulate the trajectory of your shot with the tee?
Why would you want to do this?
Moment of inertia
What is Moment of Inertia?
MOI is a term used in physics to measure the stability of an object
and how resistant it is to being twisted. The higher the MOI the
more resistant an object is to being twisted. In golf it is effectively
a measure of the forgiveness of the club at impact
Why is it important for the performance of golf clubs?
MOI is important in golf club design because most golfers do not hit
the ball in the centre of the clubface all the time. On off-centre
hits the club head is forced to rotate away from the target
resulting in a loss of directional control and ball speed.
A high MOI means that the club is more stable and therefore more
resistant to twisting, which translates to more ball speed and a
straighter shot. So for the average golfer a high MOI is beneficial as
it will lead to consistently straighter and longer shots from off
centre strikes.
Conservation of Momentum
Momentum: mass of an object times its velocity
 he Conservation of Momentum states that the total momentum before
the impact/action is equal to the total momentum after the
impact/action. The collision demonstrates conservation of momentum
because momentum of club transfers into momentum of the ball. The total
momentum of the two objects before the impact is equal to the total
momentum of the two objects after the impact. This collision causes the
ball to gain momentum because the club pushes on it causing the ball to
travel whereas the club loses momentum because the ball pushes back.
Before a collision, both the ball and club each have a certain momentum,
but with impact each have a change in momentum. The ultimate reaction
in the collision is that the momentum of the collision is conserved because
of the high speed of the ball after the collision (gaining) and the slowing
down of the club head during the collision (losing). Lastly, the collision is
not elastic because kinetic energy was lost during the collision when the
ball flattened and rolls up club face due to friction.
Coefficient of Restitution
The coefficient of restitution is a number which indicates how much
kinetic energy (energy of motion) remains after a collision of two objects.
If the coefficient is high (very close to 1.00) it means that very little kinetic
energy was lost during the collision. If the coefficient is low (close to zero)
it suggests that a large fraction of the kinetic energy was converted into
heat or was otherwise absorbed through deformation.
COR is actually a measurement of the energy transfer in a collision of
two objects. It can be expressed in a number between 0 and 1. For
example, when the USGA put a COR limit of 0.830 on driver faces, that
meant no driver would be deemed to be conforming to the rules if more
than 83% of the energy in the collision of the driver head with a golf
ball were transferred from the head to the ball.
Actually, higher COR faces work like this. In the collision of the clubface and
the ball, there is always some energy lost. This is because the face flexes
inward and the ball is compressed against the face. Both actions result in a
loss of energy. Of the two, the ball loses by far the most energy when a shot
is hit because it can squash as much as 30% of its diameter against the face
of the driver. In a normal shot hit with an old thick face stainless steel metal
wood, scientists estimate that 80% of the energy loss in such an impact
came from the ball while the balance of 20% came from the clubhead.
The idea of a higher COR face design, whether done for a driver or any other
clubhead, is to allow the face to flex inward a little more so that the ball is not
compressed as much against the face. When that happens, the face loses a
tiny bit more energy because of its increase in face flexing. But the ball then
loses a lot less energy than before because it is compressed so much less
because of the slight increase in face flexing.
The net result? The ball takes off at a higher velocity and flies farther for the
same clubhead speed and same loft angle on the clubface. Hence high
COR means more distance regardless of your clubhead speed.