I agree 100% with what you state about the circle of an ellipse.
I drew those yellow lines because so many people think that the clubhead swingarc is circular, and they also believe that the body's swing center is the center of that circular clubhead arc.
You wrote-: "The centripetal force always points in the direction normal (perpendicular) to the path at any instant towards the instantaneous center of curvature. That location would rarely if ever be a golfer's body part (left shoulder... spine etc....) Its a location in space determined solely by the path of the object."
Exactly! That's the point that I have been making all this time.
You also wrote-: "Also... as the words "centripetal force requirement" imply, its something that is required to keep an object rotating but not something that does work (force through distance = work) or stores energy."
I think that centripetal force must do some work if it changes the direction of movement of an object (traveling at a constant speed) from a straight line path to a circular path. Force is surely needed to centripetally accelerate the object so that it moves more centrally (towards that instantaneous center of curvacture) while it is traveling at a constant speed.
I agree that CP force cannot store energy - the CP energy is in constant use if the object continues to travel along a circular path (if it is constantly being centripetally accelerated).
You wrote-: "Measuring a radius of a circle from an oblique camera angle can give you an invalid reading. Any measurement of the hand of a clock should be taken when facing the clock."
That's perfectly correct. I am presuming that all readers understand that all my photographs are only representative - that they are 2-D images of 3-D motions, and that there will be perspective distortion due to an imperfect camera angle relative to the relevant clubshaft/hand plane. However, I do not believe that the fundamental principles that I am attempting to demonstrate are incorrect - because of these camera angle problems. For example, the clubhead arc of Tiger Woods driver swing (from the Nike commercial) is obviously distorted because the camera angle is face-on - while the clubead arc motion is on the inclined plane. However, it remains a "fact" that the radius of the clubhead arc (relative to the swing center) is very different at different time points during the downswing and followthrough, and that the swing center cannot be conceived to be the dead-center of a circle of the clubhead arc's rotational arc motion in space. The same "fact" applies to Tiger's hand arc photo - it is only representative because the camera angle is not perpendicular to the hand arc's circular arc of motion in space.
Jeff.
The picture on the cover of Search for the Perfect Swing is a good series of time-elapsed photos. The picture's also found in Chapter 3, with explanations. It's a worthwhile read.
When you wrote: "The hand arc is not as circular as the clubhead path."
I don't know how you can arrive at such a conclusion, with or without faulty camera angles.
Let's make the geometry simple, if anyone else is going to learn anything. And, we'll consider the center of the circle the left shoulder, since it's the top of the radius. Let's call the left shoulder "A". We'll call the hands "B" and the clubhead "C".
Scenario #1, Hands:
If the distance between "A" and "B" remains somewhat constant (Extensor Action), "B" should inscribe a circle on a piece of paper, like a compass. If we complicate it by letting "A" move (like the golf stroke), the circle becomes somewhat elliptical.
Scenario #2, Clubhead:
If we measure the distance between "A" and "C", we have to consider the cocking and uncocking of the left wrist (shortening and lengthening of the radius).
I agree 100% with what you state about the circle of an ellipse.
I drew those yellow lines because so many people think that the clubhead swingarc is circular, and they also believe that the body's swing center is the center of that circular clubhead arc.
Well it ain't circular and the center of curvature probably isn't static or loctated at that particular location so to me those lines are meaningless. We'll never all agree on the whys and wherefores of the golf swing and that's ok.
Originally Posted by Jeff
You wrote-: "The centripetal force always points in the direction normal (perpendicular) to the path at any instant towards the instantaneous center of curvature. That location would rarely if ever be a golfer's body part (left shoulder... spine etc....) Its a location in space determined solely by the path of the object."
Exactly! That's the point that I have been making all this time.
Oh... we agree then. The centripetal component of the shaft axial load is always directed at the instantaneous center of curvature.
Originally Posted by Jeff
You also wrote-: "Also... as the words "centripetal force requirement" imply, its something that is required to keep an object rotating but not something that does work (force through distance = work) or stores energy."
I think that centripetal force must do some work if it changes the direction of movement of an object (traveling at a constant speed) from a straight line path to a circular path. Force is surely needed to centripetally accelerate the object so that it moves more centrally (towards that instantaneous center of curvacture) while it is traveling at a constant speed.
Nope.... sometimes forces do no work and when the don't do work they can't contribute power (or store energy)
Lets step back.
Work is Force X Distance (has units of energy)
Power is Work / time
So for a force to do work it must move the mass through a distance otherwise no work is done. Lets say you tie a rope to you car bumper and you try to roll your car down the driveway but you forgot you left the parking brake on. YOU try like hell generating a big tension force in the rope but the car doesn't budge. How much work did you do? Your body and mucles may think you did alot but the answer is none.
You release the parking brake and try again. You put 100 lbf tention on the rope and roll the car 20 feet before collapsing of exhaustion. How much work did you do? 100*20 = 200 ft-lbs of work
Now lets say your wife was timing you and she watch you struggle for 20 seconds before bursting in to laughter when you collaped. How much power did you put out?
I agree that CP force cannot store energy - the CP energy is in constant use if the object continues to travel along a circular path (if it is constantly being centripetally accelerated).
Jeff.
See above ... the CP (acceleration) which becomes a force when we multiply by the mass (of the clubhead) does no work. It uses NO energy. Its merely that component of the force in the shaft that is required to keep the clubhead rotating. The CP force neither creates nor stores nor destroys energy. Its what needed to facilitate the motion ... a kinematic requirement ...
Now...
This is where it gets confusing and interesting... If said golfer supplys more force in the centripetal direction than is needed to maintain the rotation then the club head mass will begin move towards the center of rotation (zeta dot is non-zero in the equation shown) and consequently theta double dot (angluar acceleration) increases compensurately:
Better golfers can inject an extra bit of energy (excess force in the centripetal direction) which translates directly into angular acceleration (theta double dot) which translates directly to increased club head speed. This is that parametric acceleration I keep harping about lately. Its why Jaime and Boomboom and little Alexis Thomson are all pulling up at the last second.
"Let's make the geometry simple, if anyone else is going to learn anything. And, we'll consider the center of the circle the left shoulder, since it's the top of the radius. Let's call the left shoulder "A". We'll call the hands "B" and the clubhead "C".
Scenario #1, Hands:
If the distance between "A" and "B" remains somewhat constant (Extensor Action), "B" should inscribe a circle on a piece of paper, like a compass. If we complicate it by letting "A" move (like the golf stroke), the circle becomes somewhat elliptical."
In your mind, the hand arc's 3-D movement in space should be dominated by the movement of B in a circular rotational arc around the axis point of A, which theoretically should produce a circular hand arc. However, you are minimizing the importance of the independent movement of A as significantly affecting the shape of the hand arc - when you write "somewhat elliptical". The reality is that the independent movement of A dominates the early downswing.
In the early downswing, the pelvis shift movement pulls the power package assembly intact all the way down to waist level - without significant separation of the left arm from the chest wall (PA#4 remains loaded). That means that there is no rotational movement of B around the axis point of A, and most of the hand movement in space is due to the movement of the left shoulder socket (A).
You can see that phenomenon is Ben Hogan's swing here.
Look at how much Hogan's hands move down in the early downswing - without any rotational movement of B around the axis point of A as a result of the release of PA#4. The loaded/intact left arm flying wedge's relationship to the left shoulder socket remains unchanged until the hands reach waist level, and it is only then that PA#4 releases allowing B to rotate around the axis point of A in a circular fashion.
The same phenomenon can see in this bird's eye view series of images.
Note that the left arm-shoulder angle remains roughly the same during the early downswing (I incorrectly placed the apex of that wedge in image 1 which makes the angle look wider) - until the hands get down to waist level.
That means that the first part of the hand arc (in the early downswing) essentially doesn't involve any rotational movement of B around the axis point of A (due to the release of pA#4), and is mainly due to the independent movement of A. That's why the hand arc is generally U-shaped, and not circular.
Jeff.
Last edited by Jeff : 12-23-2008 at 11:56 PM.
Reason: added clarifying comments
"Let's make the geometry simple, if anyone else is going to learn anything. And, we'll consider the center of the circle the left shoulder, since it's the top of the radius. Let's call the left shoulder "A". We'll call the hands "B" and the clubhead "C".
Scenario #1, Hands:
If the distance between "A" and "B" remains somewhat constant (Extensor Action), "B" should inscribe a circle on a piece of paper, like a compass. If we complicate it by letting "A" move (like the golf stroke), the circle becomes somewhat elliptical."
In your mind, the hand arc's 3-D movement in space should be dominated by the movement of B in a circular rotational arc around the axis point of A, which theoretically should produce a circular hand arc. However, you are minimizing the importance of the independent movement of A as significantly affecting the shape of the hand arc - when you write "somewhat elliptical". The reality is that the independent movement of A dominates the early downswing.
In the early downswing, the pelvis shift movement pulls the power package assembly intact all the way down to waist level - without significant separation of the left arm from the chest wall (PA#4 remains loaded). That means that there is no rotational movement of B around the axis point of A, and most of the hand movement in space is due to the movement of the left shoulder socket (A).
You can see that phenomenon is Ben Hogan's swing here.
Look at how much Hogan's hands move down in the early downswing - without any rotational movement of B around the axis point of A as a result of the release of PA#4. The loaded/intact left arm flying wedge's relationship to the left shoulder socket remains unchanged until the hands reach waist level, and it is only then that PA#4 releases allowing B to rotate around the axis point of A in a circular fashion.
The same phenomenon can see in this bird's eye view series of images.
Note that the left arm-shoulder angle remains roughly the same during the early downswing (I incorrectly placed the apex of that wedge in image 1 which makes the angle look wider) - until the hands get down to waist level.
That means that the first part of the hand arc (in the early downswing) essentially doesn't involve any rotational movement of B around the axis point of A (due to the release of pA#4), and is mainly due to the independent movement of A. That's why the hand arc is generally U-shaped, and not circular.
Jeff.
Wow!
Un-huh . . .
And Amen!
For the rest of us:
Except as effected by Wristcock for Power considerations, the Hands and Clubhead ideally move in concentric circles. This is Rhythm (2-0; 6-B-3-0; and The Glossary / Rhythm / Wristcock).
But - what's the point of a back swing at all if there's no energy storage related to the golf stroke? Why not just move the club forward from address?
(Rethorical quesion: Of course energy is stored through the down swing. You increase the mv2 all the way to the ball.)
Well no... energy is not stored (or conserved). The golf swing is not very efficient. We do the backswind to establish "potential" energy ....a small amount of gravitational rho*g*h and a whole lot of musclar-skeletal "P.E.". The backswing is like putting "fuel" in the muscular-skeletal engine.
At the top of the backswing our "kinetic linkage" is displaced to one end of its "range of motion" and our muscles are outstreched and ready to contract.
Once the downswing begins muscles fire, the linkage begins moving and eventually some 22% (Nesbit) of that potential energy gets converted into Kinetic energy (1/2 m V^2) concentrated at the head of the club. None of it really ever gets stored (for long) or in a benificial way (i.e. club shaft bend doesn't help us). Like Wishon I believe "shaft kick" is a myth.
Now setting all of this aside.....
It is quite possible in the "optimal" (if there is such a thing) golf swing there is a point on the golfer's body that remains steady (motionless). I have no problem with people calling that a swing center or what ever as long as they realize is highly unlikely that this spot is where "centripetal force" gets directed for anything other than an instant and probably then just by coincidence.
Yoda - you wrote-: "Except as effected by Wristcock for Power considerations, the Hands and Clubhead ideally move in concentric circles. This is Rhythm!"
Un-huh! Especially in 10-23-A.
Thanks for sharing your opinion,
Now, I can go back to regular (I mean "reality") programming.
Yoda - you wrote-: "Except as effected by Wristcock for Power considerations, the Hands and Clubhead ideally move in concentric circles. This is Rhythm!"
Un-huh! Especially in 10-23-A.
Thanks for sharing your opinion,
Now, I can go back to regular (I mean "reality") programming.
Jeff.
Got it, Jeff.
Leave aside the fact that each of the Delivery Paths (10-23-A/B/C/D/E) have their separate identity from Rhythm . . .
Let your world continue to unfold as you see fit.
Thrill a minute on Spaceship Jeff!
P.S. And, hey, I like that flak jacket . . . It's you!
The different hand delivery paths get their separate identity from rhythm --- the rhythm between the i) torso rotational movement (including secondary axis tilt variations) and ii) the left arm rotational movement at the level of the left shoulder socket (including variations in left arm/hand plane shift during the left arm's rotational movement). Varying rhythm produces variably-shaped hand arc paths, and some of those hand arc paths are not perfectly circular in nature.
Linear Mode
