The importance of ground forces in the downswing

[DOCW3]

I try to read your posts with special care because of their technical content but also because they encourage participation. What caught my attention originally was the qualifying “if so desired.” Similarly, your most recent post seems to introduce a different way of characterizing swings based on vertical knee motion. If this is correct, I would want to know more.

DOCW3,

Asking intelligent questions is the gateway to knowledge. But they have to be formulated.

The maximum shear torque is determined by the static friction. If the static friction threshold is exceeded one has kinetic friction which is much smaller.

There are two very different ways to increase the static friction threshold depending on what type of golf swing is being performed.

An obvious ways is to have some knee flex from the top and trying to undo it. This increases the vertical ground reaction force and hence the static friction force.

But it can also, paradoxically, be obtained just doing the opposite thing. Raising body slightly in the back swing and lowering it in the down swing.

As the body decelerates, as it has to eventually, there will be an increasing vertical ground reaction force and ensuing greater static friction.

Two different mechanisms at work. In the first case leg muscles directly creating forces and in the other creating potential energy in back swing and conversion into inertial force.

Also two different types of golf swings, one where one feels like getting away from mother earth, the other more like trying to get closer.

 

[mandrin]

I try to read your posts with special care because of their technical content but also because they encourage participation. What caught my attention originally was the qualifying “if so desired.” Similarly, your most recent post seems to introduce a different way of characterizing swings based on vertical knee motion. If this is correct, I would want to know more.

DOCW3,

Sorry, I missed your post as the thread surprisingly quick slipped into the archives. Out of sight out of heart.

The matter of ground forces is really only important for a golfer who swings at quite respectable speeds and as usual looks for more.

Tiger seems to do both vertical actions I mentioned. Going down first vertically from the top, actually quite a bit, and then through impact raises his center of mass.

This is not quite so easy as it requires two subsequent motions in opposing directions in only a very short time span.

The first vertical downward motion can be considered a true power move as it sets everything into motion without causing an outward torque acting on the club.

This would indeed be the case if the first motion would involve only rotation as will occur in a golf swing being primarily rotational in nature.

The vertical motion, either up or down, is controlled by the knee flex. I don't think much attention is given in golf instruction to this vertical motion, especially the down ward motion.

The snappy upward motion is getting more attention as this is something one can more readily notice on TV being done by tour pros and long distance pros.

The upward motion is nowadays referred to as parametric acceleration since Miura's paper on the subject. It is governed by the same physics involved in a playground swing.

 

[natep]

Tiger actually increases his hip flexion as he lowers. He may be also flexing from the knees, but it's not the only thing responsible for the lowering.

 

[lia41985]

The upward motion is nowadays referred to as parametric acceleration since Miura's paper on the subject. It is governed by the same physics involved in a playground swing.

I know you're compared it to a swing but I've thought about it as a teeter totter--am I misunderstanding you?:
<iframe title="YouTube video player" width="480" height="390" src="http://www.youtube.com/embed/3MmYoUjg-3E" frameborder="0" allowfullscreen></iframe>

 

[mandrin]

I know you're compared it to a swing but I've thought about it as a teeter totter--am I misunderstanding you?:

<iframe title="YouTube video player" width="480" height="390" src="http://www.youtube.com/embed/3MmYoUjg-3E" frameborder="0" allowfullscreen></iframe>

lia41985,

The teeter totter is energized by sequential pushing relative to the ground.

With a playground swing there is no contact with the ground and internal motion/rotation is used to energize the swing motion.

Two very different mechanisms at work.

Some time back (2006) I posted about the playground swing and the similarity with the golfer's upward motion through impact.

Golf swing and playground swing

Golf swing & playground

I did some Googling and found an excellent article with interesting video clips.

Pumping of a Swing

You have now all that is required to be an expert on parametric acceleration in golf.

 

[lia41985]

The teeter totter is energized by sequential pushing relative to the ground.

Mandrin,
Would you say that a golf swing is also energized by sequential pushing relative to the ground? I ask because this is one way in which I've visualized the golf swing:

I've been asked a couple of times around the forum by what it means to step on the back foot to start the backswing. This, of course, is not my idea. But I thought this might help in visualizing:
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In that thread, another poster took it further:

mmm...being a former skateboarder (and one who could ollie much better than this youtube kid), i might give this a whirl. ollie to start, nollie (lead foot ollie) into the transition. i always thought there was a big similarity between golf and skating. the "compression into the ground" is the exact same as pumping to gain speed on ramps, and balance and rhythm are of paramount importance.

The way I'm seeing it, ground reaction forces are important to start the backswing with the step on the back foot, on the run up and sit in the forward swing in which the "weight shifts" to the forward foot, and then in the jump ("brisk, upward" motion of the lead leg) going into the through swing. What's your view? Thanks again for the great thought and insight.

 

[mandrin]

Mandrin,
Would you say that a golf swing is also energized by sequential pushing relative to the ground? I ask because this is one way in which I've visualized the golf swing:

In that thread, another poster took it further:

The way I'm seeing it, ground reaction forces are important to start the backswing with the step on the back foot, on the run up and sit in the forward swing in which the "weight shifts" to the forward foot, and then in the jump ("brisk, upward" motion of the lead leg) going into the through swing. What's your view? Thanks again for the great thought and insight.

lia41985,

Imagine a big spike going through the center of each foot anchoring them solidly to the earth. No need for invoking any ground force. Whatever might be the violence of the motion executed by the golfer there is no need to worry, the feet remain perfectly in place.

Now relax a bit this painful anchoring and imagine efficient friction by adequate spiking of some sort between the shoes and the earth. Only for very violent motion and improper technique will be there be a problem of slippage.

What am trying to convey is the notion that often one makes a big deal of ground force but one does not have to worry about them that much. Juts as gravity it is there. Normally one's weight and golf shoes will do the job.

Mathematically, ground forces have to be invoked, but the golfer, when swinging, probably better forget about the notion of ground forces, as perhaps some magic sort of available energy which he has not yet learned to harness.

Also parametric acceleration is really not a very big source for additional clubhead speed. Just experiment for yourself and swing using a swing speed device and compare swinging with and without the 'vertical jump' through impact.

The exact dynamics of pushing with the two feet, together or sequentially, each with its particular angle relative to the vertical, and the possible lateral force and torque generated this way, in addition to the torque each leg can generate, is a rather complicated mix.

 

[dbl]

Strangely enough, in the March Golf Digest, Leadbetter has a small article with "new research" and the role of ground reaction forces. :O

 

[lia41985]

The exact dynamics of pushing with the two feet, together or sequentially, each with its particular angle relative to the vertical, and the possible lateral force and torque generated this way, in addition to the torque each leg can generate, is a rather complicated mix.

Thanks for the explanation, mandrin. This particular part made me think of Bubba Watson. Check out his right foot action--he's got the jump and you can see the angle of the foot changing throughout the swing to accommodate his huge turn back and his snappy swing through:
<iframe title="YouTube video player" width="640" height="390" src="http://www.youtube.com/embed/blcEltknGD0" frameborder="0" allowfullscreen></iframe>
You can also see this phenomenon in Jack Nickalus:
<iframe title="YouTube video player" width="480" height="390" src="http://www.youtube.com/embed/5ocMJecgW2w" frameborder="0" allowfullscreen></iframe>

 

[mandrin]

Strangely enough, in the March Golf Digest, Leadbetter has a small article with "new research" and the role of ground reaction forces. :O

dbl,

Leadbetter's article in March Golf Digest is typical of what I sense in these type of articles about ground forces and leverage. Suggesting there is something new to incorporate in one's swing. However ground forces are always present like gravity. Can't escape them.

''Get More Distance Out Of The Ground''

Subtle subliminal suggestion that there is some useful entity, independent of the action of a golfer, which the poor amateur has yet not discovered. There is nothing in the ground, only the sweat dripping off the golfer, using his muscles.

''My work with biomechanics researcher Jean-Jacques Rivet has proved that most amateurs don't push into the ground effectively to create leverage in their swings. And leverage leads to power.''

Pushing is relative to some support. Where is the support from above which allows the golfer to push into the ground? The apparent feeling of pushing is due to either 1) mental focus / increased awareness, 2) dynamic internal action.

''With the use of J.J.'s data, we've found three spots in the average golfer's swing where a lack of leverage is most evident: the takeaway, halfway back and the transition.''

There is no need for thinking in terms of ground force / leverage in the take away and half way back. A bit more during transition. Ground force / leverage is really only playing an important role in the down swing when the swing is at full throttle.

''Ground force in the takeaway:
Pro:25% of body weight
Amateur:70% of body weight''

As written it has no meaning, ill-defined.

''Most amateurs tend to lose leverage early in the backswing by raising their bodies, which lightens the force they apply to the ground. The pros do the opposite and apply even more force, giving them a much more stable base to coil the upper body.''

That is really funny indeed. Simply raising your bodies and you loose weight. Should be commercialized as a new revolutionary diet. Yet whilst amateurs seemingly get lighter and the pros heavier, an amateur has nevertheless 70 % of bodyweight and a pro only 25 % of bodyweight.


Anyhow the whole article is typical for many golf instruction articles. Desperate need to continuously come up with something new to feed the insatiable golf magazines year after year with something which does not look too much being old stuff rehashed. The article typically suggests in a vague round about way that ground forces are very important and that amateurs are typically missing the boat. There is a quality implied for ground forces which they don't possess. But I must admit it will quite likely greatly impress the average amateur, sounding all so scientific.

 

[dbl]

Mandrin, I totally agree that ground forces are "just there." But I assumed, from that article, that from the measured differences between pros and hackers that the pros were doing some runup and jump (etc) steps...but maybe it was just not explained. Now that you point out that 2 of the 3 points they mentioned are in the backswing....well never mind!

 

[art]

I am a 'newbie' to this very informative golf blog, and to get a good start, want to thank Brian, Mandrin, and all of you that respond and communicate your experiences and knowledge to the rest of us seeking golf truth.

This first, (but clearly will not be my last input) has been motivated by reflecting on 'Mandrins' recent, and thought provoking note, posted 1-22-2011, " Analysis of conservation of angular momentum using model including ground reaction force".

It certainly is interesting to better understand how the angular momenta at various locations, ie. between m1 and the earth, etc.,affect the ground reaction forces. Thanks.

But, could/would you 'Mandrin' PLEASE DRIVE the 4 torsional springs/dampers with representative golfer values, and present the effect of various combination's of these torques/angular momenta on m4 and especially a representation of club angular velocity ???

 

[Brian Manzella]

I am a 'newbie' to this very informative golf blog, and to get a good start, want to thank Brian, Mandrin, and all of you that respond and communicate your experiences and knowledge to the rest of us seeking golf truth.

This first, (but clearly will not be my last input) has been motivated by reflecting on 'Mandrins' recent, and thought provoking note, posted 1-22-2011, " Analysis of conservation of angular momentum using model including ground reaction force".

It certainly is interesting to better understand how the angular momenta at various locations, ie. between m1 and the earth, etc.,affect the ground reaction forces. Thanks.

But, could/would you 'Mandrin' PLEASE DRIVE the 4 torsional springs/dampers with representative golfer values, and present the effect of various combination's of these torques/angular momenta on m4 and especially a representation of club angular velocity ???

I like to see that as well, Art.

 

[MikeD2]

Good grab, Lia. I also thought of Watson's swing along with the Queen of "brisk upward motion", Laura Davies.