Post by dubiousgolfer on Sept 1, 2020 12:12:34 GMT -5
I have been mulling over DT's email reply below and its very difficult to visualise what's happening in a golf swing.
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I understand why you are confused. Your diagram gets it right, as do Q&A
#1 and #2. But it is counterintuitive. Why? Well, it you apply the
couple at MHP-A you FEEL a very different resistance than if you apply
it at the CoM.
So what is the difference between "spin" (couple at CoM) and "orbital"
(couple at MHP-A, the handle or grip of the club)? Great question. But
in order to answer it, we need to disabuse ourselves of the idea of
"orbital" motion of the club when the couple is applied at MHP-A. It is
still pure spin.
So what would create the orbital motion, if a couple at MHP-A does not?
Another great question. Let's look more closely.
If we want an orbital motion, we want the club to spin about the hands,
not about its CoM. BUT... that requires the CoM to move. Let's impose on
this a great truth of Newton's Laws: the laws of forces and torques act
on the CoM. You know that! You just created a diagram and a pair of Q&A
that affirm that truth.
But there is a consequence when we try for orbital motion. For the club
to orbit around the hands, the CoM has to move. In order to achieve an
angular acceleration of A radians/sec/Sec, the CoM has to achieve a
linear acceleration L of R*A (where R is the radius, the distance from
MHP-A to CoM). That linear acceleration requires a force to produce it.
And the only thing in the diagram putting force on the club is the
hands. So the hands are not just applying a couple for orbital motion;
the are applying a couple PLUS an extra force from the hands.
Don't believe it? Grab a club and extend it and your arms horizontally.
Now waggle the club back and forth. Get the following feelings:
(1) FEEL: Let the hands, arms, and shoulders be as "soft" as possible,
JUST applying the turning couple. NOTICE: the softer you leave the
hands/arms/shoulders, the more the hands move in opposition to the
motion of the clubhead. In fact, the closer the center of rotation moves
toward the CoM.
(2) FEEL: Put enough firmness into the hands so the hands are still and
the movement is the CoM orbiting the hands. NOTICE: the other rotational
forces you feel: shoulders, hips, maybe even legs. All these are to pump
a lateral (linear) force into the hands to MOVE the CoM in addition to
rotating it.
--------------------------------------
According to DT it's the linear force that is required to move the COM (ie. which I assume is basically via the pivot and shoulder girdle muscles) and dragging it around in a curved path. If we add a separate 'spin' factor to the club by some 'moment of a couple' , then the clubhead and grip handle will be angularly accelerated around the COM, but how much will it contribute to the 'net' clubhead speed by impact.
The COM of my driver is about 10 inches above the bottom edge of the clubhead so I was wondering how much clubhead speed would be generated if the club was twirled around its COM . The club would have to move from horizontal at P4 to vertical by P7 and that means a rotation of approx 270 degrees in the 0.25 secs it takes on average to perform the downswing.
The distance covered by the clubface in 0.25 secs (only by spinning alone around its COM) would be the arc length of a circle (10 inch radius) with a subtended angle of 270 degrees.
Circumference of a 10 inch circle (ie. 0.25 metres) = 2 Pi * r = 1.57 m
360 degrees is equivalent to 1.57m
1degree is equivalent to 1.57/360
270 degrees is equivalent to (1.57/360) * 270 = 1.18 m
So if the clubhead has moved 1.18m in 0.25 secs
0.25 secs is equivalent to 1.18 m
1 sec is equivalent to 1.18 /0.25 = 4.72 m/s which is 10.5 mph
This is the average speed if the club started from P4 at 10.5 mph and stayed constant for 0.25 secs until P7. Therefore I can imagine that it could be significantly higher at P7 if it started from 0 mph at P4.
So it does seem that allowing the clubhead to spin freely around the COM while its also being accelerated by the linear force can create a significant increase in clubhead speed (if your hands/wrists are frictionless enough to allow the handle to spin). The timing for allowing the spin to happen seems paramount to either prevent the wrists uncocking too early or too late before impact. Also , to prevent the clubhead from uncocking/flipping the left wrist too early means having to move the hands (ie. linear force direction) quick enough in a curved path to not let the increasingly accelerated COM catch up and align itself with the linear force.
In fact , around P6 , the COM of the club is moving so fast that the hands/wrists cannot be moved quick enough in a curved direction to stop the COM aligning itself with the linear force (causing early uncocking of the wrists and probable flipping in the late downswing before impact) so one needs to prevent too much spin by applying the PP1 force on the handle . This actually causes the COM to start moving around the 'mid-hand-point' but is it detrimental to clubhead speed compared to 'spin' by impact?
I don't know the answer yet but will investigate further.
DG
----------------------------------------------------------
I understand why you are confused. Your diagram gets it right, as do Q&A
#1 and #2. But it is counterintuitive. Why? Well, it you apply the
couple at MHP-A you FEEL a very different resistance than if you apply
it at the CoM.
So what is the difference between "spin" (couple at CoM) and "orbital"
(couple at MHP-A, the handle or grip of the club)? Great question. But
in order to answer it, we need to disabuse ourselves of the idea of
"orbital" motion of the club when the couple is applied at MHP-A. It is
still pure spin.
So what would create the orbital motion, if a couple at MHP-A does not?
Another great question. Let's look more closely.
If we want an orbital motion, we want the club to spin about the hands,
not about its CoM. BUT... that requires the CoM to move. Let's impose on
this a great truth of Newton's Laws: the laws of forces and torques act
on the CoM. You know that! You just created a diagram and a pair of Q&A
that affirm that truth.
But there is a consequence when we try for orbital motion. For the club
to orbit around the hands, the CoM has to move. In order to achieve an
angular acceleration of A radians/sec/Sec, the CoM has to achieve a
linear acceleration L of R*A (where R is the radius, the distance from
MHP-A to CoM). That linear acceleration requires a force to produce it.
And the only thing in the diagram putting force on the club is the
hands. So the hands are not just applying a couple for orbital motion;
the are applying a couple PLUS an extra force from the hands.
Don't believe it? Grab a club and extend it and your arms horizontally.
Now waggle the club back and forth. Get the following feelings:
(1) FEEL: Let the hands, arms, and shoulders be as "soft" as possible,
JUST applying the turning couple. NOTICE: the softer you leave the
hands/arms/shoulders, the more the hands move in opposition to the
motion of the clubhead. In fact, the closer the center of rotation moves
toward the CoM.
(2) FEEL: Put enough firmness into the hands so the hands are still and
the movement is the CoM orbiting the hands. NOTICE: the other rotational
forces you feel: shoulders, hips, maybe even legs. All these are to pump
a lateral (linear) force into the hands to MOVE the CoM in addition to
rotating it.
--------------------------------------
According to DT it's the linear force that is required to move the COM (ie. which I assume is basically via the pivot and shoulder girdle muscles) and dragging it around in a curved path. If we add a separate 'spin' factor to the club by some 'moment of a couple' , then the clubhead and grip handle will be angularly accelerated around the COM, but how much will it contribute to the 'net' clubhead speed by impact.
The COM of my driver is about 10 inches above the bottom edge of the clubhead so I was wondering how much clubhead speed would be generated if the club was twirled around its COM . The club would have to move from horizontal at P4 to vertical by P7 and that means a rotation of approx 270 degrees in the 0.25 secs it takes on average to perform the downswing.
The distance covered by the clubface in 0.25 secs (only by spinning alone around its COM) would be the arc length of a circle (10 inch radius) with a subtended angle of 270 degrees.
Circumference of a 10 inch circle (ie. 0.25 metres) = 2 Pi * r = 1.57 m
360 degrees is equivalent to 1.57m
1degree is equivalent to 1.57/360
270 degrees is equivalent to (1.57/360) * 270 = 1.18 m
So if the clubhead has moved 1.18m in 0.25 secs
0.25 secs is equivalent to 1.18 m
1 sec is equivalent to 1.18 /0.25 = 4.72 m/s which is 10.5 mph
This is the average speed if the club started from P4 at 10.5 mph and stayed constant for 0.25 secs until P7. Therefore I can imagine that it could be significantly higher at P7 if it started from 0 mph at P4.
So it does seem that allowing the clubhead to spin freely around the COM while its also being accelerated by the linear force can create a significant increase in clubhead speed (if your hands/wrists are frictionless enough to allow the handle to spin). The timing for allowing the spin to happen seems paramount to either prevent the wrists uncocking too early or too late before impact. Also , to prevent the clubhead from uncocking/flipping the left wrist too early means having to move the hands (ie. linear force direction) quick enough in a curved path to not let the increasingly accelerated COM catch up and align itself with the linear force.
In fact , around P6 , the COM of the club is moving so fast that the hands/wrists cannot be moved quick enough in a curved direction to stop the COM aligning itself with the linear force (causing early uncocking of the wrists and probable flipping in the late downswing before impact) so one needs to prevent too much spin by applying the PP1 force on the handle . This actually causes the COM to start moving around the 'mid-hand-point' but is it detrimental to clubhead speed compared to 'spin' by impact?
I don't know the answer yet but will investigate further.
DG