Hogan's hips

[grahler]

f=ma force is mass x acceleration

centripetal acceleration is the force used by accelerating your body mass upwards during the downswing

when you swing a yo yo for example in a circle what force makes it swing faster?

your hand pulls the string towards the center of the circle=centripetal acceleration.

If your body's center of gravity is in the center of your swing arc (or close to it) moving your body up while swinging down applies centripetal force and thus acceleration to the club.

The difficulty is that the club is swinging in a large arc-the direction to most efficiently use centripetal force changes as the club moves.

stand up asyou swing down is not very efficient.

I believe Hogan sequenced his lowerbody/core so well that he was ableto use centripetal acceleration to his advantage.

Another point-most swings I have seen Hogan do-his forst move in transition (triggered byhisleft knee breaking in)
was powered by gravity-try getting to top of backswing position with a firm right leg-slightly lift your left foot what happens-you will begin to fall left. The Hogan transition.

Look at Hogan's left leg hip and left shoulder and observe the direction of travel.
I would guess under close examination the motions are apllying centripetal force in an efficient manner.
Remember the yoyo and watch the angle of theleft arm I see centripetal force being applied very efficiently.

f=ma

Iwould bet most good golfers of which I am not one shift their cog forward and down slightly and by about halfway down and through they are pressing down with front foot and rotating the left shoulder around and up in avery efficient application of force towards the center of their arc.

Comments?

[grahler]

I apologize if my post seemed off topic or not applicable.
How about another try at Hogan's hips the OP topic.
Seems like one way to get to left side is to break in left knee during centered turn('falling down' onto left leg)
and another way is kinda S&T ish straighten right knee and tilt.
One way (the first) utilizes gravity and the other way uses a push from the right side.
I would be interested to hear opinions on which Hogan used and also what people prefer.
I have spent a lot of time this year working on my pivot and I wouldloveto hear further discussion on what folks think is the optimal way to pivot.
Should one push up onto the left leg or fall down onto it and push up during the downswing???
Thoughts?

[TeeAce]

[quote name='grahler' timestamp='1285471853' post='2714210']
I apologize if my post seemed off topic or not applicable.
How about another try at Hogan's hips the OP topic.
Seems like one way to get to left side is to break in left knee during centered turn('falling down' onto left leg)
and another way is kinda S&T ish straighten right knee and tilt.
One way (the first) utilizes gravity and the other way uses a push from the right side.
I would be interested to hear opinions on which Hogan used and also what people prefer.
I have spent a lot of time this year working on my pivot and I wouldloveto hear further discussion on what folks think is the optimal way to pivot.
Should one push up onto the left leg or fall down onto it and push up during the downswing???
Thoughts?
[/quote]

Push away from the target with left and push to the target with right.

Golf swing seems to be upright arc only to confuse us. Arms and has their own role but it's mainly that they can't do anything else what we can see. The player should focus only to the rotation looked from bird eye view.

[Matt1960]

[quote name='TeeAce' timestamp='1285507664' post='2714514']
[quote name='grahler' timestamp='1285471853' post='2714210']
I apologize if my post seemed off topic or not applicable.
How about another try at Hogan's hips the OP topic.
Seems like one way to get to left side is to break in left knee during centered turn('falling down' onto left leg)
and another way is kinda S&T ish straighten right knee and tilt.
One way (the first) utilizes gravity and the other way uses a push from the right side.
I would be interested to hear opinions on which Hogan used and also what people prefer.
I have spent a lot of time this year working on my pivot and I wouldloveto hear further discussion on what folks think is the optimal way to pivot.
Should one push up onto the left leg or fall down onto it and push up during the downswing???
Thoughts?
[/quote]

Push away from the target with left and push to the target with right.

Golf swing seems to be upright arc only to confuse us. Arms and has their own role but it's mainly that they can't do anything else what we can see. The player should focus only to the rotation looked from bird eye view.



[/quote]

I can stand on either just my left leg or just my right leg and rotate my hips to the left without too much problem. I can also do it on both legs either feeling a pulling action or a pushing action, or both.
All of these seem to perform the correct action, which is the most important I think.
In other words I have not got a clue which is right.

TeeAce,
Would pushing from the left, away from target straighten the left leg prematurely?

[grahler]

The thing that gets me is this-in a normal setup the legs are spread apart-in order to post on the left foot and spin in a Hoganesque action seems like the left hip must come forward to be directly over the left foot. In some videos it looks to me like Hogan just kind of froze his right leg while turning back with a steady head-if you look carefully it looks like a large part of his shift forward is caused not by consciously straightening his right leg but by breaking in his left knee(sort of falling and then catching himself-veryinstinctual)
I am trying to figure out ift his is a good technique or a correct interpretation of Hogan.

[TeeAce]

[quote name='grahler' timestamp='1285557074' post='2715589']
The thing that gets me is this-in a normal setup the legs are spread apart-in order to post on the left foot and spin in a Hoganesque action seems like the left hip must come forward to be directly over the left foot. In some videos it looks to me like Hogan just kind of froze his right leg while turning back with a steady head-if you look carefully it looks like a large part of his shift forward is caused not by consciously straightening his right leg but by breaking in his left knee(sort of falling and then catching himself-veryinstinctual)
I am trying to figure out ift his is a good technique or a correct interpretation of Hogan.
[/quote]

Just think about how Your body acts when You jump. What do You do first? Flex, then jump, because thats how muscles work. So i f You want to have powerful action on Your left leg, flex&jump

[grahler]

The problem is ideally a swing IMO should have a controlled powerful action. I played competitive tennis through college-you tell me to leap-I am gonna be off the ground!
My idea of an ideal Hoganesque action requires precision and repeatability.
Hogan never appears to jump at the ball...

[Dariusz J.]

[quote name='grahler' timestamp='1285639544' post='2717255']
The problem is ideally a swing IMO should have a controlled powerful action. I played competitive tennis through college-you tell me to leap-I am gonna be off the ground!
My idea of an ideal Hoganesque action requires precision and repeatability.
Hogan never appears to jump at the ball...
[/quote]

Yes, because IMHO Hogan benefitted more from horizontally acting forces (e.g. torgues) than from vertically acting ones (flexion/extension). His lead foot stayed firmly on the ground all the time after he replaced it during transition. No sign of jumping action.

Cheers

[eightiron]

[quote name='Dariusz J.' timestamp='1285659042' post='2717576']
[quote name='grahler' timestamp='1285639544' post='2717255']
The problem is ideally a swing IMO should have a controlled powerful action. I played competitive tennis through college-you tell me to leap-I am gonna be off the ground!
My idea of an ideal Hoganesque action requires precision and repeatability.
Hogan never appears to jump at the ball...
[/quote]

Yes, because IMHO Hogan benefitted more from horizontally acting forces (e.g. torgues) than from vertically acting ones (flexion/extension). His lead foot stayed firmly on the ground all the time after he replaced it during transition. No sign of jumping action.

Cheers
[/quote]


Well, this makes no sense at all , since Hogan would then look like an over-rotated twist top . The irony is that on one post you claim hogan moves his hips and shoulders on a 45 deg angle up and back and yet he has no flexion and extension
Well how does he just rotate in flexion and not move his head from release point ?
How does Hogan take a divot with a 3 wood ?
Why does Hogans head move forward and down and increase his 1st tilt ( increasing flexion / left side bend ) in transition / early downswing ?

[Dariusz J.]

Indeed, it doesn't make sense if one reads only what one wants like you already did. Flexion and extension must and are always present in a golf swing motion (where have I said that they aren't ???). The point is that some concepts base their kinetics on them a lot - vide e.g. S&T, while Hogan's motion did not so much because he was utilizing hard body structure torques a lot. He simply did not need to jump hard at impact. Moreover, observing players who often jump off their shoes I can't see much torques in lower limb joints - classic qui pro quo situation, IMO.

Cheers

[eightiron]

Dariusz you must some new information on stack and tilt cause I thought they tuck the butt and extend the upper thorasic, have no idea what you are talking about with the jump out of the ground................this may be a point that might be empasized to a chop that stays in flexion , but not something that would be mentioned to someone that already gets out of the ground
Thats what i see when all the hogan swingers do all this rotation only stuff , over-rotated in flexion ............it ain't Hogan, he may have felt he did ,but had the other stuff going on .......so where are you without the other stuff, for a biomechanics minded person , you sure dodged the hard questions

[Dariusz J.]

Eight, as far as my knowledge about S&T swing is concerned, tucking the butt and extending lumbar/thoracic spine is a typical jumper's move. The fact is that they do not literally jump off their shoes but use the ground in a more vertically oriented way (again, like a jumper do - pushing off the ground) and less horizontally oriented forces (shear ones used to create torques), that was vividly present in Hogan's swing motion.
It's not to say that Hogan did not use extension to help in his kinetics, in fact he used a lot, but it was neither the most important source of power for him nor aything that helped him in automating his motion.

Cheers

[SwingNV]

Hogan definitely used ground forces, but not by pushing off the ground. I think Hogan's terrific extension is a result of him trying NOT to extend, but rather pull himself into the ground. That way, he contains maximum energy for the strike. If you consciously push up, you expend all your energy at that moment. If you only use torques, then you will remain in flexion too long as 8Iron stated. But If you try and pull yourself down into the ground, inevitably you will extend at the perfect moment, due to the fact that you have an object flying over 100mph trying to pull away from you.

You know, a player can purposely lower himself into the ground by using his hamstrings and calves. In fact, if you reread the chapter on Stance and Posture in 5 Lessons, you will find that's how Hogan describes establishing your posture. Don't bend from the hips, bend from the thighs down. He states, "this a purposeful movement." He didn't say unlock your knees and let gravity lower you. Purposely lower yourself. How would you do that, and which muscles do you use? Hogan also states when you are in the correct posture, you should feel more live tension below your knees than above. If I simply unlock my knees to bend, I feel no live tension. If I try and do any foot screwing, I feel more tension in my thighs and hardly any in my calves. If i purposely lower myself using my hamstrings and calves, i get tremendous live tension from my knees down.

There is a reason Hogan stated in bold something like, ABOVE ALL ELSE, A PLAYERS KNEES MUST BE PROPERLY FLEXED.

[eightiron]

[quote name='Dariusz J.' timestamp='1285684860' post='2717931']
Eight, as far as my knowledge about S&T swing is concerned, tucking the butt and extending lumbar/thoracic spine is a typical jumper's move. The fact is that they do not literally jump off their shoes but use the ground in a more vertically oriented way (again, like a jumper do - pushing off the ground) and less horizontally oriented forces (shear ones used to create torques), that was vividly present in Hogan's swing motion.
It's not to say that Hogan did not use extension to help in his kinetics, in fact he used a lot, but it was neither the most important source of power for him nor aything that helped him in automating his motion.

Cheers
[/quote]


Dariusz where are you getting your information on shear forces? Chris Welch , a biomedical engineer , did a video on this and his concept of shear forces are that they have / are a byproduct which includes a huge vertical component / downward pressure into the ground

[Dariusz J.]

Eight, Newtonian physics. I try to say my own words so forgive me if I forgot something or used improper English. Shear force is a force acting parallelly or at an angle different to 90* to another material while a "normal" stress is acting perpendicularly to it - and, therefore creating unevenly allocated pressures/stresses that cause torques. Saying in layman terms, the friction must be larger so that the shear forces can be applied - say, when you stand on an ice, you can easily jump but rather you won't preset your knee joint because of a too small friction.

Cheers

[eightiron]

[quote name='Dariusz J.' timestamp='1285707963' post='2718579']
Eight, Newtonian physics. I try to say my own words so forgive me if I forgot something or used improper English. Shear force is a force acting parallelly or at an angle different to 90* to another material while a "normal" stress is acting perpendicularly to it - and, therefore creating unevenly allocated pressures/stresses that cause torques. Saying in layman terms, the friction must be larger so that the shear forces can be applied - say, when you stand on an ice, you can easily jump but rather you won't preset your knee joint because of a too small friction.

Cheers
[/quote]

Seems like the biomedical engineer has a different take on the subject, the gist of what he showed was the vertical / perpendicular force or normal force going into the ground produced the byproduct shear force, which in turn sped up the rotation of the hips.... so i'm deriving from this that flexing into the ground increases the normal forces producing more shear forces

[Dariusz J.]

[quote name='eightiron' timestamp='1285711825' post='2718683']Seems like the biomedical engineer has a different take on the subject, the gist of what he showed was the vertical / perpendicular force or normal force going into the ground produced the byproduct shear force, which in turn sped up the rotation of the hips.... so i'm deriving from this that flexing into the ground increases the normal forces producing more shear forces
[/quote]

Well, I do not know what he had on his mind. Here is the quote of English language definition as simple as I could find:
"Shear force - external force that acts parallel to a plane, unlike compressive force and tensile force which act perpendicularly."

Now, as said before, vertically oriented forces (compressive/tensile) are present in a jumper's motion where there are no torques involved provided there is no additional horizontally oriented element involved. And this horizontally oriented elemnent is totally dependent on a sufficient amount of friction present.

Perhaps it would be easier for everyone to understand and to use exactly the notions [b]vertically and horizontally oriented forces[/b] and to remember that the first ones occur while flexion/extension occurs while assiociating the latter with torques and friction involved.

Cheers

[grahler]

Can anyone show a video of Hogan that shows he was jumping at the ball?


I cannot imagine true control coming from a jumping action.



Rotation is more easily controlled. IMO Darius has insight into Hogan.

[TeeAce]

[quote name='grahler' timestamp='1285813612' post='2720895']
Can anyone show a video of Hogan that shows he was jumping at the ball?


I cannot imagine true control coming from a jumping action

Rotation is more easily controlled. IMO Darius has insight into Hogan.

[/quote]

One can jump in so many ways. Maybe I don't know the right term in english, but at least I have never meant anything that acts up. It's possible to jump up, back, ahead or both sides. I totally agree with Dariusz in this. But its not black and white. There is no one direction of the force, rather it's a mixture of directions and even changes during the downswing.

[Dariusz J.]

[quote name='grahler' timestamp='1285813612' post='2720895']
Can anyone show a video of Hogan that shows he was jumping at the ball?
I cannot imagine true control coming from a jumping action.
[b]Rotation is more easily controlled[/b]. IMO Darius has insight into Hogan.
[/quote]

Exactly. Neither Hogan nor Moe nor Trevino nor Knudsen - the best and most consistent ballstrikers never jumped off their shoes. Of course, not without a cause, as you noticed.
BTW, according to my studies - that's why my SPC concept depicting the best macroscale model for consistentcy, repeatability and partial automating of the motion ballstriking for a human is based on horizontally oriented forces.
Most probably, the model would be totally different if my researches concerned long driving.

Cheers


[quote name='TeeAce' timestamp='1285824580' post='2721141']
One can jump in so many ways. Maybe I don't know the right term in english, but at least I have never meant anything that acts up. It's possible to jump up, back, ahead or both sides. I totally agree with Dariusz in this. But its not black and white. There is no one direction of the force, rather it's a mixture of directions and even changes during the downswing.
[/quote]

Good post. Indeed, the vectors would rather never show 100% horizontal or 100% vertical orientation. Although horizontally oriented forces are more important for consistency there are surely vertically oriented forces as well in each possible golf swing motion.
What is interesting, however, is that torques that occur in legs (ankle/knee joints, partially hip joints) "guide" horizontally oriented forces more to the ground (because those joints are located outside the main body) somehow making the vertically oriented forces less evident and, hence not allowing to disturb the fluency of the kinetic chain release (no jump at impact). It is an indirect but very good explanation why the stance cannot be too narrow if we want horizontally oriented forces to prevail in the motion.

Cheers

[eightiron]

[quote name='grahler' timestamp='1285813612' post='2720895']
Can anyone show a video of Hogan that shows he was jumping at the ball?


I cannot imagine true control coming from a jumping action.



Rotation is more easily controlled. IMO Darius has insight into Hogan.




[/quote]

well i guess than the proof would be in the pudding as in his golfswing!! Dariusz does your automatic rotation shear forces swing look like this?

[Dariusz J.]

First, again (!) I never said there are no vertically oriented forces in Hogan's motion. Contrary to that, I even underlined that they must be present in every good swing. The difference between motions with more vertically oriented forces vs. motions with more horizontally oriented (and vice versa) is fluid, but often visible.
Secondly, this pic shows his late follow through, not impact. Instead, show me single impact pic when he has jumped off the ground or was looking as he is just about to jump at impact.

Cheers

[eightiron]

[quote name='Dariusz J.' timestamp='1285847963' post='2721316']
First, again (!) I never said there are no vertically oriented forces in Hogan's motion. Contrary to that, I even underlined that they must be present in every good swing. The difference between motions with more vertically oriented forces vs. motions with more horizontally oriented (and vice versa) is fluid, but often visible.
Secondly, this pic shows his late follow through, not impact. Instead, show me single impact pic when he has jumped off the ground or was looking as he is just about to jump at impact.

Cheers
[/quote]

Nobody said he jumped off the ground , your explanation of shear forces is just nothing like what real experts state on the subject. You just don't get it that if you load your left wrist and increase tilt into the ball ( flexion ) , there has to " out of the ground" happening as well as rotation

[Matt1960]

So, if we are saying there are non vertical forces going on along with some vertical forces. Can these all be measured somehow?
Machines like sam balance lab will accurately measure dynamic forces, but is this just vertical forces?
How can shear forces be measured too?

[12 piece bucket]

[quote name='eightiron' timestamp='1285678828' post='2717762']
Dariusz you must some new information on stack and tilt cause I thought they tuck the butt and extend the upper thorasic, have no idea what you are talking about with the jump out of the ground................this may be a point that might be empasized to a chop that stays in flexion , but not something that would be mentioned to someone that already gets out of the ground
Thats what i see when all the hogan swingers do all this rotation only stuff , over-rotated in flexion ...........[b].it ain't Hogan, he may have felt he did ,but had the other stuff going on[/b] .......so where are you without the other stuff, for a biomechanics minded person , you sure dodged the hard questions
[/quote]

Agreed . . . . funny when you see him doing those super slow mo practice swings . . . he doesn't extend anything like he did in the real deal.

[Dariusz J.]

[quote name='eightiron' timestamp='1285848528' post='2721323']
Nobody said he jumped off the ground , your explanation of shear forces is just nothing like what real experts state on the subject. You just don't get it that if you load your left wrist and increase tilt into the ball ( flexion ) , there has to " out of the ground" happening as well as rotation
[/quote]

No, exactly it is you who don't get it, my friend. I have even copied and bring the definition of the shear force up your nose and you still are wandering around the main topic so that something different is more valid.
You're a master of changing/adding new subjects to the discussion when you lack arguments though.
For the last time - where I said that there is no vertically oriented forces in a golf swing motion. Where ???

Cheers

[grahler]

I think the picture shown being so late into followthrough shows Hogan in a midpoint of catching himself to retain his balance. Late in the followthrough with club and arms in front moving fast there has to be another force resisting else he will fall over.
Early Michelle Wie would be a good example of what I mean by jumping at the ball-she was developing velocity in a diff way than Hogan.
The Wie motion is the squat both knees flexing more and then jumping when she comes down.
Hogan's head lowers a bit during backswing but I do not think I have seen him squat-usually I have seen his left knee break in andhis hips travel forward slightly this is what makes his headcomedown abit.
He used his core in a truly unique way...genius.

[eightiron]

[quote name='Dariusz J.' timestamp='1285860448' post='2721588']
[quote name='eightiron' timestamp='1285848528' post='2721323']
Nobody said he jumped off the ground , your explanation of shear forces is just nothing like what real experts state on the subject. You just don't get it that if you load your left wrist and increase tilt into the ball ( flexion ) , there has to " out of the ground" happening as well as rotation
[/quote]

No, exactly it is you who don't get it, my friend. I have even copied and bring the definition of the shear force up your nose and you still are wandering around the main topic so that something different is more valid.
You're a master of changing/adding new subjects to the discussion when you lack arguments though.
For the last time - where I said that there is no vertically oriented forces in a golf swing motion. Where ???

Cheers
[/quote]


Never changed the subject , just pointed you in the correct direction , not sure about lacking arguements , I asked you a few questions related to this topic a few posts back and you didn't answer one of them

Here is what a real expert said on the subject of ground forces

[b]"the downward force or normal force is important in creating friction or a connection to the ground which is crucial to creating shear force[/b]... the more shear force created the more potential rotational speed at the pelvis (pitchers create a huge amount of shear because of their stride forward down the incline of the mound and hence have incredible pelvic speed compared to a golfer)"

The same expert had an opinion on what created the stride forward / or lateral motion in the golfswing and as you can read from above it wasn't from shear forces

[hoganfan924]

[quote name='eightiron' timestamp='1285887096' post='2722286']
[quote name='Dariusz J.' timestamp='1285860448' post='2721588']
[quote name='eightiron' timestamp='1285848528' post='2721323']
Nobody said he jumped off the ground , your explanation of shear forces is just nothing like what real experts state on the subject. You just don't get it that if you load your left wrist and increase tilt into the ball ( flexion ) , there has to " out of the ground" happening as well as rotation
[/quote]

No, exactly it is you who don't get it, my friend. I have even copied and bring the definition of the shear force up your nose and you still are wandering around the main topic so that something different is more valid.
You're a master of changing/adding new subjects to the discussion when you lack arguments though.
For the last time - where I said that there is no vertically oriented forces in a golf swing motion. Where ???

Cheers
[/quote]


Never changed the subject , just pointed you in the correct direction , not sure about lacking arguements , I asked you a few questions related to this topic a few posts back and you didn't answer one of them

Here is what a real expert said on the subject of ground forces

[b]"the downward force or normal force is important in creating friction or a connection to the ground which is crucial to creating shear force[/b]... the more shear force created the more potential rotational speed at the pelvis (pitchers create a huge amount of shear because of their stride forward down the incline of the mound and hence have incredible pelvic speed compared to a golfer)"

The same expert had an opinion on what created the stride forward / or lateral motion in the golfswing and as you can read from above it wasn't from shear forces
[/quote]

For anyone with even a modicum of knowledge of physics, this is really stating the obvious. Maximum friction force between the shoe and turf = mu x normal force. The shear force cannot exceed the friction force or your foot will slip. mu is the coefficient of friction (in this case between the shoe and turf, which should be a little greater than 1 with a spiked shoe). All that means is that you must have normal force (in a static condition this would be your weight) in order to create a shear force. In the dynamics of a golf swing where the golfer loads up into the left leg in the downswing, the normal force could be significantly greater than the weight due to the accelerations involved (the old F=MA).

Now some golfers may use a "squat and straighten" move with the left leg to help power the movement of the pelvis (and creating more normal force, like Tiger's old "snap the left knee"), and you can clearly see in many of them that their left heels come off the ground, while others use more core rotation with the left (and right) foot providing the ground reaction force (shear force) to "couterbalance" their core muscle power moving the pelvis. I believe that all decent golfer use both, some just use one more than the other. Stack and Tilters are more the "jumpers" as they clearly advocate "crushing the can and jumping up through impact," while Hogan IMO, was more core rotation, as he clearly maintains a very flat and stable left foot through impact and also maintains a considerably bent left knee at impact. He does, however, straighten the right leg and this also provides some force into the pelvis to keep it rotating. Maybe this is why Hogan liked that extra spike in his shoes, as he attemped to create high shear forces without "jumping." He needed maximum mu.

I don't think you and Darius are really saying anything very different from each other. You guys just like to argue. lol

[Dariusz J.]

[quote name='Matt1960' timestamp='1285850160' post='2721350']
So, if we are saying there are non vertical forces going on along with some vertical forces. Can these all be measured somehow?
Machines like sam balance lab will accurately measure dynamic forces, but is this just vertical forces?
How can shear forces be measured too?
[/quote]

Good point. I think it can be done through analyzing the resolution of pressures of both feet. The more the pressure is spreaded evenly on the sole the less amount of horizontally oriented forces are present. But this is just pure guess of mine.

Cheers

[quote name='eightiron' timestamp='1285887096' post='2722286']
Never changed the subject , just pointed you in the correct direction , not sure about lacking arguements , I asked you a few questions related to this topic a few posts back and you didn't answer one of them

Here is what a real expert said on the subject of ground forces

[b]"the downward force or normal force is important in creating friction or a connection to the ground which is crucial to creating shear force[/b]... the more shear force created the more potential rotational speed at the pelvis (pitchers create a huge amount of shear because of their stride forward down the incline of the mound and hence have incredible pelvic speed compared to a golfer)"

The same expert had an opinion on what created the stride forward / or lateral motion in the golfswing and as you can read from above it wasn't from shear forces
[/quote]

Eight, I have already responded to this in earlier posts. I said I don't know what your expert had on his mind when formulating these words - the more as you said it is just a part taken out of wider context.
Shear forces enhance all horizontally oriented forces both linear as well as rotational ones. IMO, one can't say that lateral motion is not dependent on shear forces while rotational one is fully dependent on them. It would be an absurd, especially taking into account human's anatomy.

Cheers

[quote name='hoganfan924' timestamp='1285900636' post='2722581']
For anyone with even a modicum of knowledge of physics, this is really stating the obvious. Maximum friction force between the shoe and turf = mu x normal force. The shear force cannot exceed the friction force or your foot will slip. mu is the coefficient of friction (in this case between the shoe and turf, which should be a little greater than 1 with a spiked shoe). All that means is that you must have normal force (in a static condition this would be your weight) in order to create a shear force. In the dynamics of a golf swing where the golfer loads up into the left leg in the downswing, the normal force could be significantly greater than the weight due to the accelerations involved (the old F=MA).

Now some golfers may use a "squat and straighten" move with the left leg to help power the movement of the pelvis (and creating more normal force, like Tiger's old "snap the left knee"), and you can clearly see in many of them that their left heels come off the ground, while others use more core rotation with the left (and right) foot providing the ground reaction force (shear force) to "couterbalance" their core muscle power moving the pelvis. I believe that all decent golfer use both, some just use one more than the other. Stack and Tilters are more the "jumpers" as they clearly advocate "crushing the can and jumping up through impact," while Hogan IMO, was more core rotation, as he clearly maintains a very flat and stable left foot through impact and also maintains a considerably bent left knee at impact. He does, however, straighten the right leg and this also provides some force into the pelvis to keep it rotating. Maybe this is why Hogan liked that extra spike in his shoes, as he attemped to create high shear forces without "jumping." He needed maximum mu.

I don't think you and Darius are really saying anything very different from each other. You guys just like to argue. lol
[/quote]

A very good post, HF. I appreciate your contribution he since it all is being explained in good English now and, therefore, much clearer for everyone.

Cheers