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).
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).
"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.
Jeff - "In your mind"
Thank you for letting me know what I had in my mind. I had no idea.
It still doesn't justify the statement that you made and I quoted. I included the movement of the left shoulder in my statement. You've still omitted the ever changing distance between the left shoulder and the clubhead.
If you're choosing to speak specifically about the Start Down, that's one small part. The "more circular" statement was vague at best, and it's still lacking.
I am puzzled when you state that the clubhead arc is likely to be less circular than the hand arc because of the following problem - the everchanging distance between the left shoulder and the clubhead.
I suspect that you don't spend much time studying golf swings using a swing analyser program and that you don't plot the clubhead arc and hand arc to see what is really happening.
The clubhead arc is amazingly circular in reality, compared to the hand arc.
Here is a strobe photograph showing the clubhead and hand arcs.
Note that the clubhead arc is much more circular than the hand arc.
Here is a composite photograph of Aaron Baddeley' swing.
Note how circular the clubhead's path is in space -despite a varying distance from the clubhead to the left shoulder.
I have previously posted photos of the hand arc of Tiger Woods, which shows an U-shaped hand arc.
Here is Sergio Garcia's hand arc.
Even when taking into account the camera perspective distortion problem (due the camera not being perpendicular to the plane of the clubshaft and the plane of the hand motion), it should be readily apparent that the clubhead arc of a good golfer is more rounded than the hand arc.
I suspect that you don't spend much time studying golf swings using a swing analyser program and that you don't plot the clubhead arc and hand arc to see what is really happening.
Yeah, and I'm sure you never looked at an x-ray during your residency.
I've only given about 13,000 video lessons in the last ten years. I hope I can learn how to use the software before I start getting really busy.
Hybrid Mode
