The Physics of the Golf Swing - PowerPoint Presentation

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The Physics of the Golf SwingSlide2

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.Slide3

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 ball.Slide4
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Force Summation

Purpose

Principles

QuestionsSlide8

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.Slide9

Principles

Principle 1

Use as many body parts that relate to the movement as possible.Slide10

Principles

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 last. Slide11

Principles

Principle 3

Muscle need to be used and accelerated with the correct timing.Slide12

Principles

Principle 4

All the muscles used must go through their greatest range of motion to achieve maximum momentum. Slide13

Summary

The 4 principles of force summation are:

More muscles

Correct sequencing

Correct timing

Greatest range of motionThese 4 principles all help to generate maximum force.Slide14

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.Slide15

Major Muscles Use in Force SummationSlide16
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Golf swing using the priciples

of Force Summation

Write a paragraph talking about force summation in golf using, movement terms, key muscle names

etcSlide18

Newton’s laws

Understanding the physics of the golf swing starts with understanding and applying Newton’s three laws of motion

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.Slide19
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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.  Slide22

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.   Slide23

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 effortless.Slide24

Ernie Els

linksSlide25

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.Slide26

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.Slide27

Centirpedal/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.  Slide28

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!Slide29

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LEVERS IN GOLFSlide32

GOLF CLASS 3 LEVER

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.Slide33

Golf Swing Class 3 LeverSlide34

Projectile MotionSlide35

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.Slide36

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.Slide37

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 landing.Slide38

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?Slide39
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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.Slide41
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Conservation of Momentum

Momentum: mass of an object times its velocity

The 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. Slide43

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.Slide44

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.Slide45

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