Endless belt and release physics

[Jeff]

Mike

You don't have to apologize for being blunt. I encourage all forum members to attack my arguments rigorously without restraint, because I believe so strongly in the Popperian falsification principle. My ideas/opinions are only valid to the extent that they cannot be falsified, and I don't know if they can be falsified if people don't vigorously challenge my opinions.

When I stated that my knowledge of physics-terms could be inexact, then it doesn't mean that I am knowingly using those "terms" imprecisely. My understanding of the term "angular acceleration" is totally compatible with the Wikipedia definition. However, I believe that angular acceleration doesn't always refer to a point-object moving around a "fixed" point in a circular motion, but it can also apply to a linear structure (eg. clubshaft) moving around a fulcrum hinge point (eg. hands) which is itself in motion. In nm golfer's mathematical explanation, he is referring to the clubshaft when he talks about angular acceleration, and not solely the clubhead. When I stated that one can see the clubhead progressively moving a greater distance per unit time during the release phase, and that this represents angular acceleration, I really meant that the clubhead is a "marker" for the rate of angular acceleration of the clubshaft, which means that the grip end of the club must be experiencing the same degree of angular acceleration as the clubhead end (because they are both simply point-locations on the same clubshaft).

I therefore don't understand your comment-: "For example in regards to the Bobby Jones photo the end of the clubshaft and the clubhead are picking up angular acceleration but the grip end of the shaft is not picking up angular acceleration."

You also made the following statement-: ""As it's the linear speed of the clubhead that is the real intent of the release and the clubhead can be picking up clubhead linear speed with an extension of the swing radius and at the same time have no increase in the angular acceleration of the clubhead."

I cannot understand your opinion - from the perspective of nm golfer's mathematical explanation of the release phenomenon. You seem to be implying that the clubhead (which is merely a point-location on the clubshaft) can pick up linear speed due to an extension of the swing radius without any angular acceleration of the clubshaft. When you refer to "swing radius" I presume that you are talking about the distance between the left shoulder socket and the clubhead. If my understanding is correct, then I think that you may have your logical argument back-to-front. The swing radius can only increase (in the presence of a left arm of constant length) if the 90 degree angle between the left arm and clubshaft changes toward a 180 degree situation (left arm and clubshaft become more in-line). That happens as a result of the release phenomenon - which is due to the clubshaft acquiring angular acceleration during the release phase. If one accepts my reasoning, then this other statement of yours doesn't make sense - "For example you could have a situation where you have angular deceleration yet with an extension of the radius an increase in the linear speed of the clubhead." How can the swing radius be increasing if angular acceleration of the clubshaft is decreasing.

It is true that we are mainly interested in the linear speed of the clubhead at impact, but I think that the linear speed of the clubhead is derived to a large extent from the fact that the clubshaft is angularly accelerated during the release phenomenon.

Jeff.

[dkerby]

Jeff & BerntR, Seems to me that you guys are sticking with
the premiss that the left shoulder is offset to the center of
rotation. This is true, in most cases, with the shift and turn
concept. With the Hogan move, that V.J. Present, the left
shoulder is already even or ahead of the ball at the top of
the swing so that Hogan could have a left shoulder impact
circle center. On pg. 83 of "The Final Missing Piece" V.J.
says: "Review sequences of Hogan's sing in figure 43. From
this vantage point, the white spot above his right hip pocket
actually moves backsward or away from the target at the
start of his downswing. If the hips had moved forward to
start the downswing, this white spot would also move
forward or at least stay in the same position'. The pictures also
indicate that the left was at the ball at the top of the swing.

With shift and turn in the downsing, I can see many of your
points. But using V.J. and Hogans pictures from V.J.'s book to illustrate
what happens in a shift and turn method can certainly be confusing.
V.J. pointed out that his book not a method. It is an explanation of one Man's method.

[Mike O]

Mike

You don't have to apologize for being blunt. I encourage all forum members to attack my arguments rigorously without restraint, because I believe so strongly in the Popperian falsification principle. My ideas/opinions are only valid to the extent that they cannot be falsified, and I don't know if they can be falsified if people don't vigorously challenge my opinions.

When I stated that my knowledge of physics-terms could be inexact, then it doesn't mean that I am knowingly using those "terms" imprecisely. My understanding of the term "angular acceleration" is totally compatible with the Wikipedia definition. However, I believe that angular acceleration doesn't always refer to a point-object moving around a "fixed" point in a circular motion, but it can also apply to a linear structure (eg. clubshaft) moving around a fulcrum hinge point (eg. hands) which is itself in motion. In nm golfer's mathematical explanation, he is referring to the clubshaft when he talks about angular acceleration, and not solely the clubhead. When I stated that one can see the clubhead progressively moving a greater distance per unit time during the release phase, and that this represents angular acceleration, I really meant that the clubhead is a "marker" for the rate of angular acceleration of the clubshaft, which means that the grip end of the club must be experiencing the same degree of angular acceleration as the clubhead end (because they are both simply point-locations on the same clubshaft).

I therefore don't understand your comment-: "For example in regards to the Bobby Jones photo the end of the clubshaft and the clubhead are picking up angular acceleration but the grip end of the shaft is not picking up angular acceleration."
Jeff.

The way that I measured angular acceleration was to measure the distance between each clubhead (during release) on the Bobby Jones sequence via a paper and pencil on my computer screen. I concluded that there was angular acceleration of the clubhead i.e. the distances between each clubhead was increasing during release but no angular acceleration of the hands or grip end of the club i.e. when I measured the distance between them there was no increase in distance.

Now, if the grip was the center of rotation and the shaft was rotating around the grip end- then in that simple experiment- the whole shaft or any portion of the shaft would have the same angular acceleration. However, in the golf swing with #2 and #3 accumulators releasing and various other mechanical features happening simultaneously- you don't have or don't have to have a situation where both ends of the club have the same angular acceleration. Said another way- in a single center rotating system all points of rotation will have the same angular acceleration. However, in a multiple center(s) rotating system- not all of the points in rotation have to have the same angular acceleration. And the golf swing is a multiple center rotating system.

[Jeff]

Bernt

I, unfortunately, cannot understand your physics explanation or its applicability to the release phenomenon.

To start with my understanding-problem.

Issue 1:

Consider your diagram, which could be thought of as a shaft that is hinge-centered in the center of the circle, and rotating in a circular motion.

You talk of a tangential acceleration and a radial acceleration. You state that tangential acceleration applies to the direction that the clubhead (which is merely the peripheral end of that centrally-hinged shaft) is moving at any moment in time. I can understand that point and the "correct" applicability of your directional-arrow labelled aT (which is at a 90 degree tangent to the radius of the circle). I cannot understand your term "radial acceleration" as you have drawn the first arrow AR as being directed towards the center of the circle (along the longitudinal axis of the shaft). I can think of that "centrally-directed" force" as being a centripetal force, but not a radially-accelerated force. I can also think of the term "radial acceleration" as being representative of the angular acceleration of the shaft as its rotates around its central hinge-axis point. I particularly cannot understand your use of the two aR arrows drawn at a tangent to the circle at the 9 o'clock and 3 o'clock position - what do those aR arrows (drawn at a 90 degree tangent-angle to the circle) represent?

Issue 2:

I still cannot understand your concept of a swing center. Are you referring to the upper swing center of the body?

Here is an image showing the movement of Tiger Woods left shoulder socket and upper swing center during his downswing.



In image 1, the green dot shows the position of the left shoulder socket at different time-points during the downswing, while the red line is a straight line drawn from the left shoulder socket to the clubhead. One can see how the left shoulder socket moves in space during the evolution of the downswing.

In image 2, the green dot is drawn at the upper swing center (midway point between the two shoulder sockets as seen in a frontal-view). The red line is a straight line drawn between the clubhead and the upper swing center. One can see that the upper swing center stays very centralised during the downswing.

So, in conclusion (using my concept of an upper swing center), the left shoulder socket's sequential movement in space during the downswing has no relationship to the stable movement of the upper swing center (which remains very centralised during the downswing).

Issue 3:

You state that tangential acceleration and radial acceleration forces are applied to the clubhead via the hands. I don't understand this point at all. I can understand the concept of the terms "tangential/radial" as being applicable to the circular motion of the left arm around a "fixed" point (left shoulder socket). However, in a "real life" golf swing, the left shoulder socket is constantly moving in space during the downswing, and therefore the final speed/direction of movement of the hands during the downswing is the end-product of two interlinked movements - i) the speed of rotation of the left arm at the shoulder socket, and ii) the rate/direction of curvilinear movement of the left shoulder socket in space. The beauty of nm golfer's "release phenomenon" explanation is that he doesn't need to know what moves the hands. He simply states that movement of the hands has two components - i) a constantly-variable direction of movement; and ii) a constantly-variable speed of movement; and that these two variables produce angular acceleration of the clubshaft because the COG of the clubshaft is not in-line with the constantly-varibale directional movement of the hands. nm golfer doesn't have to use the terms "tangential" or "radial" in his explanation of the "release phenomenon", and his explanation makes sense whether the hands travel in a circular, or elliptical, or C-shaped/J-shaped curvilinear manner.


Jeff.

[Jeff]

Mike - you state that you can think of the clubhead having angular acceleration, but you don't equally think that the clubshaft can have angular acceleration because you presumably perceive that the grip end of the club is not simply rotating around a"fixed" point in space.

The problem for me regarding your statements relates to the question as to where is the locus of the central point of the "imaginary circle" that allows you to describe the clubhead's movements in terms of having angular acceleration, while you are not willing to accept the idea that other parts of the clubshaft also have angular acceleration? You seem to be willing to entertain the idea of an "imaginary" central locus for the clubhead's movement, but you are unwilling to apply that same conceptual idea to any other point on the clubshaft eg. grip end.

By the way, I think that even if the left hand is moving at a constant speed during the release phenomenon, it doesn't mean that the grip end of the clubshaft has to travel at the same speed as the hands - because the left wrist is uncocking during the release phenomenon.

In nm golfer's explanation, the central hinge-point locus for the clubshaft's rotary movement is always at the hands - even though the hands have a constantly-variable directional movement and constantly-variable speed of movement. At each fractional moment in time, the clubshaft can develop angular acceleration with respect to its radial movement around the "instantaneous" hand-axis hinge point. In other words, the clubshaft has a circular motion around a constantly moving central locus hinge-point at all time-points during the downswing (even during the release of power accumulator #2) and all points on the clubshaft have the same degree of angular acceleration because the shaft is a rigid structure, but the clubhead's motion (or grip end's motion) relative to "any" locus point on the body is not circular, and cannot therefore be precisely described in terms of "angular acceleration".

Jeff.

[Jeff]

Bernt

I am sorry that I didn't explain that when I produced Tiger's photo showing the "release phenomenon", that I didn't accurately time-sequence the clubshaft placement events. I only wanted to produce an illustrative photo showing many clubshaft time-points, but I didn't attempt to make sure that the "time" between each clubshaft point was perfectly time-equalised.

Jeff.

[Mike O]

Mike - you state that you can think of the clubhead having angular acceleration, but you don't equally think that the clubshaft can have angular acceleration because you presumably perceive that the grip end of the club is not simply rotating around a"fixed" point in space.

The problem for me regarding your statements relates to the question as to where is the locus of the central point of the "imaginary circle" that allows you to describe the clubhead's movements in terms of having angular acceleration, while you are not willing to accept the idea that other parts of the clubshaft also have angular acceleration? You seem to be willing to entertain the idea of an "imaginary" central locus for the clubhead's movement, but you are unwilling to apply that same conceptual idea to any other point on the clubshaft eg. grip end.

By the way, I think that even if the left hand is moving at a constant speed during the release phenomenon, it doesn't mean that the grip end of the clubshaft has to travel at the same speed as the hands - because the left wrist is uncocking during the release phenomenon.

In nm golfer's explanation, the central hinge-point locus for the clubshaft's rotary movement is always at the hands - even though the hands have a constantly-variable directional movement and constantly-variable speed of movement. At each fractional moment in time, the clubshaft can develop angular acceleration with respect to its radial movement around the "instantaneous" hand-axis hinge point. In other words, the clubshaft has a circular motion around a constantly moving central locus hinge-point at all time-points during the downswing (even during the release of power accumulator #2) and all points on the clubshaft have the same degree of angular acceleration because the shaft is a rigid structure, but the clubhead's motion (or grip end's motion) relative to "any" locus point on the body is not circular, and cannot therefore be precisely described in terms of "angular acceleration".

Jeff.

Jeff,
First, I'm only referencing your posts - in that- I took a cursory look at nm's stuff and wasn't interested in trying to figure out what he or she was saying. I don't think that should cause us a problem.

I think you misquoted or mis-understood me in your first paragraph above.
The center of the hands would be combination of the "top of the spine" and the left shoulder moving centers. The clubhead would have centers at those two places plus accumulators #2 and #3.

However, I did describe how I made the measurements of the clubhead and the grip end of the club. Why don't you make the measurements of the grip end and tell me what you come up with in regards to the angular acceleration?

[Jeff]

Mike

When you refer to an "imaginary point" located "somewhere" between the left shoulder and upper spine as being the "center" of an "imaginary circle" circumscribed by the hands, then I can basically understand your conceptual idea in a certain way. What you are apparently doing is simply taking the hand arc movement => then you are perceiving it as being a circular arc (even though the arc doesn't have a perfectly circular shape) => then you are trying to locate its "central locus point" with respect to the golfer's body ("central locus point" being "equivalent" to the central axis point of the circle that represents the hand circle).

So, for example, here is a diagram showing the movements of the hands, and clubshaft, and clubhead in a low handicap golfer.



Point X is the center of the circle for both the hand arc and the clubhead arc, and one can conceptually think of the angular acceleration of the hands and/or clubhead with reference to that central "X" point (which is conceptually located "somewhere" in the golfer's body).

However, that doesn't help us understand the release phenomenon, because the clubshaft is released (and not the clubhead) with respect to the hands and the clubshaft in that diagram is not rotating in a circular fashion around point X. Therefore, one cannot conceive of the clubshaft having angular acceleration with respect to point "X".

nmgolfer gets around this problem by using the double pendulum swing model.



The double pendulum swing model involves a central arm ( represented by the golfer's conjoined two arms) and a peripheral arm (clubshaft) connected together at a peripheral hinge point. nm golfer's mathematical explanation attempts to explain the release phenomenon occurring at the peripheral hinge point using the following assumptions - i) that the hinge joint is passive and therefore the forces causing the clubshaft's release is passive (not directly related to any active hand unhinging action); ii) and that the clubshaft's movement in space can only be affected by movement of the peripheral hinge point (hands) in space - without having to be concerned about the underlying body forces that cause the hands to move (body forces that torque the central arm). Regarding nm golfer's explanation, the clubshaft can be angularly accelerated at the peripheral hinge point, which serves as the "center" for the angular rotation of the clubshaft around the peripheral hinge point (hands). In other words, the clubshaft rotates around a central point (hands) and therefore the grip end of the club must (by definition) angularly-rotate at the same rpm speed as the clubhead end of the club because the clubshaft is a rigid structure rotating around a central hinge point (although the clubhead end obviously has a faster curvilinear speed than the grip end). In nm golfer's explanation, what's the source of power that allows the clubshaft to develop angular acceleration? It is derived from the fact that the peripheral hinge point (hands) constantly move about in space, and the hand movement has both a directional quality and a velocity quality. The movement of the hands (peripheral hinge point) causes the club to develop angular acceleration, because the movement of the hands is at an angle to the COG of the clubshaft. The clubshaft therefore rotates in a circle relative to the hands, and the angular rpm acceleration of every part of the clubshaft (grip end and clubhead end) must be the same. nm golfer's explanation explains how the club develops angular acceleration with respect to the hands, and how the club releases with respect to the hands. nm golfer's explanation doesn't have to concern itself with "imaginary" locus points - point X in the first diagram.

Jeff.

[BerntR]

Mike



Jeff.

I like this illustration.

But imo it is not entirely complete.

A third circle around the neck, tangenting the shoulders are missing. The golf swing is basically three-lever system: The left shoulder spinning around the neck, the left arm spinning around the left shoulder. And the club spinning around the left arm.

The Torque around the neck is required as long as we wish to accelerate the club. And the quality and quantity of this is THE determining factor for clubhead speed. But in addition, torque is reqired for the shoulder/arm joint (extensior action or a driving right side). And torque is also required for the arm/club joint - early in the down swing.

[Jeff]

Bernt

I can understand why you would envision the need for what you call a "three lever" system to represent a body-driven/pivot-driven golf swing where the third lever can be conceived to be a "lever" between the central torque generator and the left arm at the left shoulder socket hinge point. However, whether you mentally envision a three-lever system (equivalent to a body-generated/pivot-driven dowswing action), or a two-lever system (equivalent to a pure arm swinger - ala Leslie King's or Peter Croker's teaching philospophy), the basic physics of the release phenomenon is going to be the same - dependent on the direction of movement/speed of movement of the most peripheral hinge point (at the hands) during the downswing as it relates to the COG of the club. The clubshaft has no idea what is driving the hands to move in a certain direction at a certain speed, and it only responds to the direction/speed of the pulling force at the most peripheral hinge point - a hinge point between the left arm (at the left hand) and the clubshaft. The clubshaft is unaware if there is another hinge point in the golfer's swing system - a central hinge point that must exist in a three lever system.

Jeff.