Pivot center

[Yoda]

Yoda - I think that this debate is getting unnecessarily complicated and unproductive.

Jeff . . . this praise . . . coming from you . . . I'm not worthy. But thanks anyway . . . you've made my day!

I think of it this way.

The orbiting ball receives all its energy via the string. The source of the energy is the hand moving in a circular manner. The energy travels outwards from the hand to the orbiting ball- along the string. That energy is required to perform two roles - i) keep the ball moving at a constant speed and ii) keep the ball moving in a circle at its constant surface speed.

When a orbiting object travels at a constant speed it may not need much energy to keep it moving at a constant speed (if there is little frictional resistance to its movement in space), but it requires constant energy input to constantly change direction (in order to move in a circular path). In other words, although the orbiting ball is traveling at a constant surface speed, it needs a constant source of energy to centripetally accelerate (accelerate towards its center of rotation). That energy comes from the hands and it is transmitted via the connecting string.

If you understand that viewpoint - then door 1 is correct.

Door 1

Behind Door #1:

"The CP pull is exerted by the hands and the pull is along the length of the string . . . "".

Buzzer Sound: EEEEEEEEEEEEEEEEEEEENNNNNNNNNNNNNNNHHHHH!!!!

Sorry, Jeff. Door #1 is not the correct answer. It never has been the correct answer, and it never will be the correct answer, despite your heroic attempts to obsolete every physics text ever written. Simply put, the axis of rotation is not the centripetal force. Try again . . .

However, one can look at this orbiting ball scenario from a different perspective, and look at the scenario from the orbiting ball's perspective. Then door 2 applies.

Door 2

Behind Door #2:

"The string transmits the CP pulling force from the ball to the hands (inwards pull towards the center)."

The ball experiences a centripetal force that pulls it towards its center of rotation. The pull is in the direction of centripetal acceleration. The ball doesn't know where the CP force is coming from - it only knows that it is being pulled by the string, and it happily thinks that the string is providing a CP force that keeps it a state of constant centripetal acceleration.

However, ultimately the centripetal force that keeps the orbiting ball traveling in a circle is derived from the orbiting hand's movement in space, and the energy must travel from the hands to the ball - travels outwards along the string. Some of that energy makes the ball move, and some of that energy supplies a centripetal force that conceptually travels back down the string and keeps the orbiting ball from flying into space. I find it meaningless to think of the string providing that CP force - because the string doesn't really create energy. It only allows part of the energy created by the orbiting hands to be translated into a CP force that pulls the orbiting ball towards the center.

Buzzer Sound: EEEEEEEEEEEEEEEEEEEENNNNNNNNNNNNNNNHHHHH!!!!

Sorry, Jeff. Door #2 is not the correct answer. The string doesn't transmit the centripetal force -- as you continue to maintain and would have us believe -- the string is the force! Try again . . .

I actually try to avoid using the terms "centripetal" and "centrifugal" in my thinking about the golf swing. It gets way too semantic and too complicated. The idea of a centrifugal force is merely a conceptual idea used to see the CP force as being balanced by an equal and opposite force. Many people state that it not really a force - because it cannot exist alone. I am sympathetic to the idea that it is not useful to conjure up the idea of a CF working in the opposite direction to a CP force.

I much prefer to think in terms of vectors of movement and force, and not use the terms CP force or CF force if I can avoid the terms. That's why I like nmgolfers explanation of the release phenomenon.

See - http://perfectgolfswingreview.net/Ne...%20Science.htm

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Sorry, Jeff. Attempting to divert the argument is poor tactics and just plain bad manners. Besides, the usual smoke and mirrors won't work here. Try again . . .

When I think of the golf swing, I never think of a rotational center.

Bad idea.

I simply see different body parts moving in 3-D space, and I simply think of the forces that move those body parts and their vector of movement. I think the same way with respect to the golf club. The golf club is only moved by pull-forces or push-forces exerted at grip level.

Yes, I can see how such a simple approach might work. After all, this whole centripetal-centrifugal thing is way too complicated. Especially when we're confronted with the truths taught in Physics 101. Best that we redefine the way the world works, right Jeff?

[Jeff]

mb6606

You sent me a link to this video of Jason Zuback's swing which has a number of slow mo sections.

I made the following series of images of his downswing



First of all, regarding the clubshaft. I see this problem of double images frequently - even when examining slow mo videos. This makes it difficult to know what is real versus camera distortion. Image 4 shows two images - one of the images has forwards shaft lean. Image 5 shows double images at impact with the shaft bent back in the one image, which would be expected post-impact.

I therefore do not know whether Jamie Sadlowski's forwardly bent shaft post-impact is "real" (possibly due to using a more flexible shaft) or due to camera distortion.

Secondly, look at Jason's swing. He has a centralised pivot action, and he reverse pivots slightly with a large hip turn (like Sam Snead) by the end-backswing - image 1. Note how he then has to reverse his spine tilt in the downswing so that he acquires a rightwards tilt-secondary axis tilt in the early downswing - image 3. I don't think that it is a biomechnaically efficient action. Note how he loses his clubhead lag angle - image 3. I think that it is due to the fact that he has to throw his upper torso and therefore arms backwards (away from the target) at the start of the downswing to reverse the spine tilt. The reversal of hand movement (going backwards away from the target) predisposes to an early release.

Here is another example of that phenomenon in an excellent golfer.



In the first swing, he reverse pivots slightly. Note his loss of clubhead lag angle. In his second swing I think he has a better pivot action with a reverse-K look, and a much better retention of his clubhead lag angle in the early downswing.

That's why I prefer Jamie's swing over Jason's swing. Jamie has a traditional swing with a reverse-K look at the end of his backswing, and he retains his clubhead lag angle well into the downswing.

Jeff.

[Jeff]

Yoda - I have been deciding whether to respond to your last post. Your tone is demeaning and ill-conducive to an ongoing debate. Why can't you simply state your disagreements without pontificatiing, and implying that you are the final arbiter of the "truth"?

I don't think that you understand my perspective.

I will rephrase it.

The hand's movement is the source of energy that gets the ball to move in space. The string transmits that energy to the ball by means of a continuously taut string - any hand movement in a circular manner causes the ball to move in a circular manner (at the same rpm but along a wider circle of greater radius). The energy imparted to the ball gets the ball to perform two actions - i) acquire a surface speed of a finite value; and ii) centripetally accelerate - which merely represents a constant change in direction so that the ball follows a circular path.

The string is continously taut. That is necessary to counteract the tendency of the ball to fly away (due to centrifugal forces). Therefore, you are correct to state that the taut string represents the centripetal pull towards the center to counteract the tendency of the ball to fly away in a straight line direction at a tangent to the circle. However, the centripetal pull is not created by the string - the string is merely reactive to the dynamic situation of an orbiting ball that has acquired enough energy to fly away unless the string remains taut and provides a centripetal pull towards the center.

My personal perspective is focused on the following facts.

1) The source of energy for the orbiting ball is the continuous movement of the hand in a circular motion.
2) The hand constantly pulls the orbiting ball via a taut string - so that the orbiting ball revolves at the same rpm as the hand.
3) The ball acquires motional energy from the hand via the taut string, and this energy includes a centrifugal tendency which requires an equal counteracting centripetal pull by the taut string to ensure that the orbiting ball moves in a circular orbit.
4) It is true that the taut string is a constant reflection of the centripetal pull towards the center. However, the string doesn't independently create that centripetal force. The centripetal force only becomes necessarily operant because the ball has acquired motional energy from the motion of the hand that would cause it to fly off into space unless there was a centripetal pull from the taut string to counteract/equalize that centrifugal tendency.

Jeff.

[Yoda]

Yoda - I have been deciding whether to respond to your last post. Your tone is demeaning and ill-conducive to an ongoing debate. Why can't you simply state your disagreements without pontificatiing, and implying that you are the final arbiter of the "truth"?

I don't think that you understand my perspective.

Yes, Jeff, I suppose my post was a bit much. But, you know what? For some reason, you inspire that in me!

Oh, and I completely understand your perspective on centripetal force, both from the 'hand's' point of view (Door #1) and the 'ball's' point of view (Door #2). Goodness knows you've spent enough time educating me. And your writings do indicate that you understand the essence of the forces involved. Yet, you then totally deep-end and restate to your own end basic laws of physics that have been accepted since the time Isaac Newton wrote his Philosophiæ Naturalis Principia Mathematica (1687). You put up a lot of good stuff, Jeff, but man, you make it difficult to sit idly by as you reinvent concepts that have served mankind well for centuries.

To me, that's arrogance.

And when I see it, I call it.

Then again, that's why I've created this Golf By Jeff Forum and given you domain. Here you can pick things apart to your heart's content and enjoy relative freedom from my comment. But, it's also why I've put a 'caveat emptor' sign at the front door and stated that your presence here does not imply endorsement of your opinions by LBG.

[Jeff]

Yoda - you stated-: "Then again, that's why I've created this Golf By Jeff Forum and given you domain. Here you can pick things apart to your heart's content and enjoy relative freedom from my comment. But, it's also why I've put a 'caveat emptor' sign at the front door and stated that your presence here does not imply endorsement of your opinions by LBG."

I have no problem with that "caveat emptor" sign at the front door. That does not insult me. That simply warns people to be very skeptical of my expressed opinions.

Also, when you state-: "Get your facts right, Jeff, and you'll have no beef from me. Otherwise, I suggest getting fitted for a flak jacket."

That doesn't bother me. You, or anybody else, is free to criticise me as much as they want.

However, I resent the following series of statements-: "Yet, you then totally deep-end and restate to your own end basic laws of physics that have been accepted since the time Isaac Newton wrote his Philosophiæ Naturalis Principia Mathematica (1687). You put up a lot of good stuff, Jeff, but man, you make it difficult to sit idly by as you reinvent concepts that have served mankind well for centuries. --- To me, that's arrogance."

I am obviously not attempting to reinvent Newtonian laws. I may be misunderstanding them, or misrepresenting them - but I am not arrogantly reinventing them. You know that! Also, if I am so obviously wrong, why didn't you bother to show me my errors by means of an explanatory logical argument?

Going back to the orbiting ball example.

Consider this diagram.



The ball is orbiting on the outer circle at a constant speed. The hand is moving along the inner circle. A taut string connects the hand to the orbiting ball.

At ball position X, the hand is slightly ahead of the ball when it is at position A. That means that the hand is pulling the orbiting ball via the taut string. The source of energy in the system is the hand-in-motion.

If the ball moves to position Y, then two forms of energy are required - i) energy to move the ball at a constant speed; ii) energy to move the ball in a circular direction (represented by the red arrows) and that represents energy to provide centripetal acceleration. Where does the energy come from? There is only one rational answer - it comes from the orbiting hand that moves from position A to position B. The taut string is simply an inert "connection" between the hand and the orbiting ball, and it allows hand motion to provide the energy to the orbiting ball, which then i) moves the orbiting ball at a constant speed and ii) it provides the energy to centripetally accelerate the ball so that it continues to move along a circular path. The string is not the source of any energy, or the source of a centripetal force.

If you disagree with my opinion, and you have the "facts", then please provide a counterargument.

Here is composite photo of Tiger Woods and Jamie Sadlowski.



The yellow dotted line shows the direction Tiger's hands and central clubshaft are pointing at when the club moves in the late downswing to impact. They are in a straight line relationship with a straight line drawn through the clubhead's sweetspot - the red dotted line. That makes biomechanical sense. Look at where Jamie Sadlowski's hands are pointing (yellow dotted line). They are not pointing at the clubhead's sweetspot. How does one explain that fact? Either we are dealing with an additional "force" (or factor) that has caused the clubhead and peripheral end of the clubshaft to be deflected forward (relative to the hand position), or we are dealing with a camera artifact. If you disagree with my opinion, and you know the "facts" then please provide a counterargument.

Jeff.

[Bigwill]

Yoda - you stated-: "Then again, that's why I've created this Golf By Jeff Forum and given you domain. Here you can pick things apart to your heart's content and enjoy relative freedom from my comment. But, it's also why I've put a 'caveat emptor' sign at the front door and stated that your presence here does not imply endorsement of your opinions by LBG."

I have no problem with that "caveat emptor" sign at the front door. That does not insult me. That simply warns people to be very skeptical of my expressed opinions.

Also, when you state-: "Get your facts right, Jeff, and you'll have no beef from me. Otherwise, I suggest getting fitted for a flak jacket."

That doesn't bother me. You, or anybody else, is free to criticise me as much as they want.

However, I resent the following series of statements-: "Yet, you then totally deep-end and restate to your own end basic laws of physics that have been accepted since the time Isaac Newton wrote his Philosophiæ Naturalis Principia Mathematica (1687). You put up a lot of good stuff, Jeff, but man, you make it difficult to sit idly by as you reinvent concepts that have served mankind well for centuries. --- To me, that's arrogance."

I am obviously not attempting to reinvent Newtonian laws. I may be misunderstanding them, or misrepresenting them - but I am not arrogantly reinventing them. You know that! Also, if I am so obviously wrong, why didn't you bother to show me my errors by means of an explanatory logical argument?

Going back to the orbiting ball example.

Consider this diagram.



The ball is orbiting on the outer circle at a constant speed. The hand is moving along the inner circle. A taut string connects the hand to the orbiting ball.

At ball position X, the hand is slightly ahead of the ball when it is at position A. That means that the hand is pulling the orbiting ball via the taut string. The source of energy in the system is the hand-in-motion.

If the ball moves to position Y, then two forms of energy are required - i) energy to move the ball at a constant speed; ii) energy to move the ball in a circular direction (represented by the red arrows) and that represents energy to provide centripetal acceleration. Where does the energy come from? There is only one rational answer - it comes from the orbiting hand that moves from position A to position B. The taut string is simply an inert "connection" between the hand and the orbiting ball, and it allows hand motion to provide the energy to the orbiting ball, which then i) moves the orbiting ball at a constant speed and ii) it provides the energy to centripetally accelerate the ball so that it continues to move along a circular path. The string is not the source of any energy, or the source of a centripetal force.

If you disagree with my opinion, and you have the "facts", then please provide a counterargument.

Here is composite photo of Tiger Woods and Jamie Sadlowski.



The yellow dotted line shows the direction Tiger's hands and central clubshaft are pointing at when the club moves in the late downswing to impact. They are in a straight line relationship with a straight line drawn through the clubhead's sweetspot - the red dotted line. That makes biomechanical sense. Look at where Jamie Sadlowski's hands are pointing (yellow dotted line). They are not pointing at the clubhead's sweetspot. How does one explain that fact? Either we are dealing with an additional "force" (or factor) that has caused the clubhead and peripheral end of the clubshaft to be deflected forward (relative to the hand position), or we are dealing with a camera artifact. If you disagree with my opinion, and you know the "facts" then please provide a counterargument.

Jeff.

Jeff, based on video I've seen, including the one I posted for you, I really don't believe that this photo is an accurate representation of the shaft's position during this interval, but rather is a "camera artifact". I have a really hard time believing that he could make any kind of consistent contact with a shaft that deflects that much, when he's swinging at 145 to 150 mph. His shaft likely looks more like Tiger's.

[Jeff]

Bigwill

I am very sympathetic to your opinion that it is a camera artifact. The degree of shaft deflection appears "too large" to be mechanically possible. The only other explanation that makes sense to me is that he is deliberately choosing a very flexible shaft in order to get additional "kick". I will remain open-minded about this possibility, although I increasingly suspect that your "camera artifact" opinion may be correct.

Jeff.

[Yoda]

Yoda - you stated-: "Then again, that's why I've created this Golf By Jeff Forum and given you domain. Here you can pick things apart to your heart's content and enjoy relative freedom from my comment . . ."

However, I resent the following series of statements-: "Yet, you then totally deep-end and restate to your own end basic laws of physics that have been accepted since the time Isaac Newton wrote his Philosophiæ Naturalis Principia Mathematica (1687). You put up a lot of good stuff, Jeff, but man, you make it difficult to sit idly by as you reinvent concepts that have served mankind well for centuries. --- To me, that's arrogance."

I am obviously not attempting to reinvent Newtonian laws. I may be misunderstanding them, or misrepresenting them - but I am not arrogantly reinventing them. You know that! Also, if I am so obviously wrong, why didn't you bother to show me my errors by means of an explanatory logical argument?
[Bold emphasis by Yoda.]

Jeff,

The facts in my posts #154 and #157 presented my argument (without, BTW, wearing out my readers). I'm done on this one. Per my advance notice above, I have entered the "enjoy relative freedom from my comment" phase. Enjoy!



Meanwhile, for old times sake, there are at least two pieces of unfinished business on the table that I would appreciate your cleaning up:

From my post #129:

Jeff,

BTW, you state that you see in my photos a "phenomenon that [you] have seen many times previously. Before release, the clubshaft is bent backwards and after release the clubshaft is bent forward." Question: How do you explain "The Snake" (Photo #4 in my post #127 above), where "after release", the Shaft simultaneously is bent both backwards and forwards?



Please include the photo in your reply, and for the visually-challenged among us, please trace the Shaft with a yellow line. Thanks!

And from my post #150:

Jeff,

Assume a tethered ball in orbit around an axis. Does the tether (and its tension) serve as the centripetal force of that action? If not, what does? If so, how does that differ from the concept of the clubhead tethered to its center (left shoulder) by the left arm and clubshaft?

Thank you for your attention.

[Jeff]

Yodas Luke

You wrote with respect to Yoda-: "he is the judge and the jury."

That is correct. However, my affection for Yoda, and my presence on this website, is predicated on the belief that Yoda will be a wise and fair judge and that he will not be prejudiced to such a degree that he would censor a forum member's sincere opinions. As long as Yoda adheres to that high standard, I have no reason to seek another golf website, like the one run by the "Italian Stallion" who will not tolerate anyone questioning his "high priest" wisdom.

You also stated that as a Senior Instructor, you have the responsibility for this site's contents and that you also have the right to criticise my posts. That is correct. I have forthrightly stated that I eagerly seek insightful criticism that will strenuously test the legitimacy of my opinions regarding the golf swing. The only way that I can know whether my ideas are solid is to test them for their falsifiability factor in an open forum. If my ideas can be easily falsified, then I obviously need to modify them to make them more "true".

My only objection to criticism is when it is targeted at me in an ad hominem way, and where the tone of the posts is very demeaning/belittling. I may be stupid and often wrong, but I am sincerely trying to seek the "truth". I may appear arrogant and bombastic when I argue passionately for the "truth" of my personal opinions, but I do not indulge in ad hominem attacks. If you look at the contents of my posts, they are very targeted at arguing about the issues - even if you think that my arguments are wrong-headed. If forum members thinks that my arguments are illogical, they simply have to provide a counterargument that demonstrates my lack of insight. They don't have to add supplementary belittling remarks.

I did presume that you regarded my posts as verbal defecation, which is the chief reason why I became sufficiently invoked to respond to your posts. I accept your "corrective" explanation, and I am willing to move on without harboring any grudges. I don't know you personally, and I have every reason to believe that you are a very nice person, who I would very much like to meet someday.

Jeff.

[Jeff]

Yodas Luke

You wrote-: "Might I suggest another golf website where pontificating and verbal defecation are the modi operandi?"

Yoda has kindly provided me with this forum where I can freely express my opinions (even if they represent in your mind "verbal defecation"). You are not obliged to visit this forum. Yoda has already stated that he has posted a "caveat emptor" sign in front of this forum. What excuse do you have for entering this forum and then complaining about the "quality" of my posts.

By the way, why do you have to have the psychological need to pontificate about an obvious typo error?

Jeff.