matt kluck
New
Excellent
Good one, Jon!!
MK
Good one, Jon!!
MK
The importance of ground forces in the downswing
- Thread starter James Marshall (Hogan1953)
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mandrin
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I mention in my post to cnadon that normal forces determine the friction forces and that it can be increased increasing one's dynamic weight through some brisk upward motion.
DOCW3 asks himself the question should this statement be questioned.
Jon then sort of repeats what I had posted before.
Subsequently Matt congratulates Jon with his excellent post.
I can't help finding this sequence kind of funny.
Jon Hardesty
New
Mandrin,
My apologies for being redundant.
My apologies for being redundant.
matt kluck
New
Mandrin,
Mine for not reading the entire post.
MK
Mine for not reading the entire post.
MK
Jon Hardesty
New
Mandrin,
In using the ground reaction forces as an external force for the angular momentum, would it be correct to say that the more energy that can be created by the grf the more you have to be redistributed in the wrist to club connection?
In using the ground reaction forces as an external force for the angular momentum, would it be correct to say that the more energy that can be created by the grf the more you have to be redistributed in the wrist to club connection?
mandrin
New
Jon,
Yes, correct, the more there is generated proximally the more there is potentially available peripherally.
But a very important additional element has to be equally considered – proper timing/sequencing.
Strong inexperienced male golfers can likely produce plenty of input momentum but its is usually spoiled and miss-timed and not very effective at impact.
Jon Hardesty
New
Great info Mandrin...Thanks!
mandrin
New
wulsy,
Intuitively I think to feel what you are after. With ground reaction forces there is a funny mix of it being thought of as both a reaction but also as being an action, and that is kind of confusing. But always keep in mind that it is the golfer doing all the sweating, mother earth is just stoically resisting. The primary cause for all torques is the golfer.
In a sense, as you mentioned, one can consider the ground reaction force to allow the various golfer produced torques to be effective. Without a ground reaction force these torques would not be able to produce some kind of effective golf swing motion. But when analyzing it scientifically, using a free body diagram, the ground reaction forces appears immediately also as the basic input action force/torque.
Initially the golfer produces torques between various body parts. From Newton's third law we know that for every action force there is always an equal and opposite reaction force. If we, through the feet and legs, start twisting the lower body, there has to be an equal and opposite ground reaction torque from Newton's 3d law. But if the ground reaction force is initially a reaction force it subsequently acts nevertheless as an action force with regard to the golfer.
Thanks again mandrin,
Could it be that there is "repeated two way traffic" between the body torques and the GRFs during the swing which makes it difficult to differentiate between action and reaction forces? Could a reaction force actually be used to produce another force which could be regarded as "reaction-reaction" force and so on, thus producing an accumulation effect?
Could it be that there is "repeated two way traffic" between the body torques and the GRFs during the swing which makes it difficult to differentiate between action and reaction forces? Could a reaction force actually be used to produce another force which could be regarded as "reaction-reaction" force and so on, thus producing an accumulation effect?
Taking this a bit further, the input momentum generated, even if timed correctly, can still be spoiled with miss-timed kinematic sequencing of the peripheral parts(improper kinetic chain sequencing).
Mandrin:
Regarding how you generate torque between the first "subsystem" and the ground: If you take a standard backswing where the majority of the foot pressure is in your right foot...is the torque generated by transfering some weight back to the left foot and then applying horizontal force in both feet to create a couple / torque OR is it more realistic to think of it as having the weight on right foot at transition and creating torque primarily in the right leg using horizontal forces between two pressure points (ball and heel of foot) to create a torque in the "right leg post"?
Also: If you generate net torque during transition with torque between the ground the first subsystem (legs/hips)...what is the significance of losing (or greatly reducing) the the connection to the ground at somepoint before contact? For example, could a golfer generate a bunch of "external torque" during transition and then jump off the ground in the downswing and have no ground contact during impact?
Thanks for your contributions.
Regarding how you generate torque between the first "subsystem" and the ground: If you take a standard backswing where the majority of the foot pressure is in your right foot...is the torque generated by transfering some weight back to the left foot and then applying horizontal force in both feet to create a couple / torque OR is it more realistic to think of it as having the weight on right foot at transition and creating torque primarily in the right leg using horizontal forces between two pressure points (ball and heel of foot) to create a torque in the "right leg post"?
Also: If you generate net torque during transition with torque between the ground the first subsystem (legs/hips)...what is the significance of losing (or greatly reducing) the the connection to the ground at somepoint before contact? For example, could a golfer generate a bunch of "external torque" during transition and then jump off the ground in the downswing and have no ground contact during impact?
Thanks for your contributions.
mandrin
New
wulsy,
There is no Alice in Wonderland Through the Looking Glass Magic. The intrinsic nature of force nevertheless has been a mystery for a very long time and still is, so if you are feeling uneasy about forces, you are not alone, many great scientists through history felt the same way.
What is considered an action or a reaction force also depends on the way we look at it. This is defined by the free body diagram. In a given multibody system I can decide how I divide the system in sub-systems. All forces acting on a particular chosen subsystem are taken to be external forces, hence cause/action forces.
The largest force in a golf swing occurs at the wrist joints. Taking the golfer as one system this force is considered to be an internal reaction force. Yet when analyzing the motion of the club separately this same force is considered to be an external action force.
Similarly I can take the golfer and earth as one system. Then the forces at the interface (feet) are simply internal reaction forces. But when I take the earth and the golfer separately than there is an external action force exerted on the earth and an equal and opposite external action force acting on the golfer.
mandrin
New
spktho,
Yes, quit true. Even if I meant to include kinematic sequencing, the notion of timing is perhaps not the most appropriate to convey this idea.
mandrin
New
Vintner,
These are rather specific questions more for someone versed in biomechanics and having done force plates measurement and being up to date on the literature in this field. I can only simply relate to my own very limited experiments using either lead leg, or both legs as platform for a golf swing. I can generate similar clubhead speeds. This tells me that many options are open to a golfer and that the obvious logical choice of a stable platform of two feet is perhaps optimum but that alternatives are not for away. Moreover it shows me that quite different ways exists, using different leverage and various muscle groups, to obtain adequate driving torque. But likely there is an optimum biomechanical approach when one is seeking peak performance.
Vintner,
Looking at a tennis serve motion, one might be enticed to think that perhaps the same is possible for a golfer. It would however be quite something to see a golfer swinging full out with a driver making no contact with the earth at impact.
But measurements done with the small stature Japanese golfer, Hidemichi Tanaka, in a biomechanics lab, conclusively showed that the ground reaction force actually peaked at impact and reached the impressive magnitude of 184 percent of his body weight. One have indeed some golfer's make a brisk upward vertical move, standing up on their toes through impact. This might appear as if they are better off being of the ground with both feet, like occurs in a tennis serving motion. However the contrary is true as the expert golfer is actually trying, during this time, to actually increase the ground reaction force, by jumping up, snapping his knee(s) straight.
This particular action is now known with the fancy name of parametric acceleration since Miura's paper got more wide spread known in golf. But it was known before as shortening the swing radius. Laura Davies is a good example of an old timer knowing this feat instinctively. I posted on this before, quite a while back, comparing it to the action of a playground swing action.
The paradox is that the only way a golfer can try to reduce interaction with the earth is not by jumping up and away from the earth but rather by getting quickly closer to the earth, by letting himself 'fall' to the earth.
There is a basic difference between a golf stroke and a tennis serving motion. In the latter everything moves in the same direction whereas in a golf down swing jumping up involves motions in opposite directions.Excellent, thank you Mandrin. I always enjoy your posts on this and various forums. I asked about leaving the ground because I occasionally spin out with my hips on poor swings and I feel like I have very little connection to the ground. I was wondering if the poor results were from an inability to generate torque (i.e. my spinout was internal and not contributing to my angular momentum) or just from poor impact alignments in that circumstance. I appreciate the response.
Interesting stuff mandrin.
The science kind of shows that that crazy great feeling of total synergy in a golf swing is like a great piece of music or a beautiful verse - there's no one formula for producing it and each time it happens it was actually unique and not a reproduction.
That's important for those teaching and just goes to show that methods and models can be no more than a guide to the golf-blind.
The science kind of shows that that crazy great feeling of total synergy in a golf swing is like a great piece of music or a beautiful verse - there's no one formula for producing it and each time it happens it was actually unique and not a reproduction.
That's important for those teaching and just goes to show that methods and models can be no more than a guide to the golf-blind.
mandrin
New
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.
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