Hi S
I think we discussed this same issue on the Ben Allen post ?
newtongolfinstitute.proboards.com/thread/677/ben-allen-jnr-papers?page=2Our exchange of comments are below but I did discuss Ben Allen's 'physics proof' with Dave Tutelman on the 26th Jan 2019 (a copy of my question to DT, his exchange with Ben Allen , and his final conclusions are shown further below).
DG
PS. It seems that stalling the hands does not create a burst of speed by limiting the radius of the swing to the wrist joints, but an acute change in hand path can create an increase in clubhead speed. Further, the quicker the hand speed while conducting this acute change in hand path can also increase the clubhead speed. The feasibility of doing this 'move' would be dependent on a real golfers biomechanical capabilities.
Hope this assists.
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Hi DG,
As I don't want to infringe and copy here Dr. Allen's work, first read "Functional Swing Deconstruction Nicklaus - Part 2, page 9, to understand his argument about "free roll" having a shorter circular radius than a swing something short of free roll.
The formula for centripetal force has radius as a variable and, given a certain velocity, the shorter the radius the greater the centripetal force.
Dr. Allen's definition of roll is (in the purest sense), during final release, the act of aligning the club from parallel to the target line to perpendicular to the target line. (Axial rotation of the shaft has nothing to do with how the club "rolls" and has nothing to do with centripetal acceleration even though there is axial rotation of the shaft during release.)
In a nutshell, Dr. Allen's argument is that anything less than free roll (completion of the release of the club when the butt of the grip is as stationary as possible) involves requiring 1) a stronger left hand grip and 2) greater body rotation by impact to accomplish that portion of free roll that is absent during roll of the club. He argues that the stronger left hand grip prevents the clubhead from prematurely "passing" the hands from a face-on view perspective. (Free roll encourages the clubhead to pass the hands.) He argues that the resultant more open body position by impact results in a greater radius over which the club can roll and thus centripetally accelerate, which reduces the potential centripetal acceleration. As a result, he argues that the resultant inefficiency requires greater and greater physical effort to achieve the clubhead speed absent such inefficiencies.
To put this all in perspective, Dr. Allen would believe that the modern tour pro builds the "centrifugal inefficiency" into his swing to avoid inconsistency in the timing of free roll.
I have no way of measuring the difference in radius of roll between Nicklaus and J.B. Holmes. However, I intuitively believe that if the modern swing does have a built in centrifugal inefficiency, it can't possibly result in any meaningful inefficiency during release.
S
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Post by dubiousgolfer on Oct 3, 2019 at 4:38pm
So lets look at an example of reduced radius (increased centripetal acceleration) of a rotating object, say the hands of a spinning ice-skater.
This is mentioned on Tutelmans website:
Ice skater analogy of the golf swing
The most important picture to keep in mind is the transfer of energy with unfolding.
Think of this as the reverse of the ice skater effect. The ice skater initially has the arms extended and works to move them as fast as possible. The skater then pulls the arms in close to the body. This causes the body speed up so that the skater spins fast. It is important to note that the hands actually slow down in this process, but we only watch the body. The body is spinning faster, true. But, because the hands' radius of rotation is shorter than before, the velocity of the hands is lower than before.
In the golf swing, the opposite occurs. The golfer initially holds the club close to the body using wrist cock, and works very hard to build up the kinetic energy in the body and arms. The golfer then allows the club to swing away from the body, so the body and arms slow down and the club speeds up. I emphasise the term “allows”, because it can be an entirely passive process; the golfer does not have to make the club swing out – it happens naturally.
In summary...
The ice skater:
First builds speed in arms,
then folds the arms close to the body,
to speed up the body
The golfer:
First builds speed in body,
then unfolds the club from the body,
to speed up the club.
However, if Ben Allen is really promoting a sudden change in hand path to increase clubhead speed , then that would make sense to me . When I look at Vardon's swing it looks like his hands 'turn the corner' and he releasing the club using the physics as explained by D'Alembert's principle . He looks like he is flipping through impact because he's stalled his pivot and left arm. I personally cannot see how purposely stalling the left arm will increase clubhead speed. But if those hickory shafts had lagging bend into impact , then I suppose Vardon could have used some active right wrist extension to flexion happening at or through impact to increase CHS.
DG
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Hi DG,
All good except that instead of "stall left arm and pivot," it's likely just the pivot that Vardon stalls. I think that continuing to pull to left arm is counterproductive in terms of wanting to allow the clubhead to "flee outward." The pivot is going to decelerate anyway; it's just a matter of when.
As a side note, Dr. Allen contends that intense arm speed during the acceleration phase is incompatible with a "hand pause" necessary for maximum centrifugal acceleration during final release. I don't think that this is even worth pondering when trying to build an efficient, elite swing.
S
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MY QUESTION TO DAVE TUTELMAN:Wondering if Ben Allen Jnr's reasoning about decreasing the radius of the golf swing in the late downswing by delaying left arm angular rotation (around the left shoulder socket) while incorporating a 'rolling hand/wrist tactic' (like Harry Vardon) can create a burst of clubhead speed.
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DAVE TUTELMANS REPLY TO ME PLUS HIS DISCUSSION WITH BEN ALLEN:
I'm afraid Ben Allen's article is flawed from the get-go. The physics/math goes off the rails early in the paper. When I got onto Academia.edu and downloaded the paper, I got a note from Ben requesting feedback. Here are the notes I sent him as feedback, just in case you want to know what is wrong with Ben's analysis
__________________________
13 hours
BA
Ben Allen Jr
your thoughts - especially critical ones - would be appreciated
thanks
_________________________
2 hours
DT
Dave Tutelman
Ben, I'm looking at "Reengineering 11: centripetal acceleration in the golf swing." I don't see any date of your authorship nor upload. It would help the context if I knew it -- but of course it's hardly essential to understand the material.
Thanks,
DaveT
___________________________
1 hour
DT
Dave Tutelman
Ben, I'm about three scrolls into the paper. It is entirely likely I'll agree with your conclusion, once I have verified that it matches some wording in the intro that I didn't quite understand. But the math/physics justification has a big problem already.
Your very first vector diagram does not work! The reason is that you are adding an acceleration vector and a velocity vector. You can only add ANYTHING (vectors or scalars) if they have the same units. But here they don't:
wg is a momentum, which is proportional to velocity. (mv)
cf is a force, which is proportional to acceleration (ma)
So wg could have units of gram-meters/sec
And cf could have units of gram-meters/sec^2
That is a serious outage!
So they are not the same units, and cannot be added. Any conclusion you draw from adding a velocity and an acceleration is going to be flawed.
I'll keep plodding on for a while and see what develops.
DaveT
_________________________
1 hour
DT
Dave Tutelman
"Note that forcing the club head to travel a circular path is the action that accelerates the club head – not an active input of energy via a positive energy input to drive angular acceleration by a move the golfer makes."
Ben, we're in big trouble here! The centripetal force on the clubhead, which is what you show as cf, does not increase clubhead speed at all!
You seem to be taking the approach that the hands are still and the club's angular velocity is the whole story with both clubhead speed and the dynamics of the situation (forces). Not so. Even at impact, the hands have 15-20% of the speed that the clubhead does. And hand kinematics during this lower downswing is a very important key. No, the hands are not applying a torque couple to the club; you are correct there. But if the hands were not moving, just pulling the clubhead straight in along the shaft, you would get no increase of clubhead speed at all during this part of the swing.
I'm going to drop out here, because this is really far from what biomechanics has as the principles of the swing. There are some disputes among biomechanists, but this argument is far from the area of universal agreement.
Sorry to disappoint, but that appears to be what is what.
__________________________
DAVE TUTELMAN CONCLUSIONSo I conclude that Ben really doesn't have a basis for saying what he does. Is his conclusion therefore false? Maybe so, maybe not. But his argument for that conclusion has no merit at all.