Super technical video - In-Plane Couple and Moment of Force During the Golf Swing

[nevets88]

Haven't finished watching this yet, but if anyone can explain this in layman's terms and what the takeaways are, that would be awesome.

Quote

This video describes the results from a 3D inverse dynamics analysis of the golf swing. The impulse-momentum framework is applied and how the contribution from the couple and the net force influence the overall torque applied to the club by the golfer are explained.

 

 

[DaveP043]

This takes me back to my first or second year of engineering school, engineering mechanics class.  In essence, a couple is a pair of forces, acting in exactly opposite directions but not at the same location.  The result on the object, in this case the golf club, is that it would rotate, but not translate (move).  A Force, applied any direction other than directly through the Center of Gravity, causes the object to translate as well as to rotate.  The total rotational impulse, the torque, is the sum of the effect of the couple plus the effect of the force multiplied by the distance between the force's direction and the CG.  If you think of the grip of the hands as a single point of attachment, the "force plus couple" is the simplest way of expressing the action of the hands on the club at any time.  Your hands are forcing the club to move (or stop moving) as well as to rotate (or stop rotating).  

As far as any takeaways, for me there's nothing in my 5-minute review of a 15 minutes video that makes me change the way I think about the golf swing.

[saevel25]

35 minutes ago, DaveP043 said:

This takes me back to my first or second year of engineering school, engineering mechanics class.

I try to forget that class. Kinematics and Dynamics were not a good class for me

Though it's interesting that the moment when the couple hits zero in the downswing is near the same point that the hands reach their max speed and start to slow down. It's that point the club starts it's transition to want to overtake the hands.

I agree there really isn't anything new here. It just describes a good kinematic sequence in more physics terms.

 

[Etzwane]

 

DaveP043 gave the correct physics explanations. In golf terms and looking only at in plane forces as in the video: a force applied to handle transverse to the shaft will cause the handle to mode but also the club to rotate. Wrist cocking will cause the club to rotate around the hands (not the center of mass so it's a combination of rotation around the center of mass and movement of the COM).

In the backswing, if one has very loose wrists (no torque) and start the backswing (force on the handle) the club will rotate and give the "scottish lag". It is necessary to add torque to maintain the club in synch with the arms. No very interesting so far.

The same applies at the transition: the force on the handle tends to increase the club head lag while the wrist might have reach their maximum deviation and tend to uncock. The same effect continues in the downswing up to the moment the force aligns to the shaft (around p6 for these good players, when the hands path is roughly horizontal), then the force on shaft helps release the lag.... and even more when the hands move up again (I guess that's the "idea" behind the "Manzella jump").

The interplay between force and torque in the downswing and the timing of one overtaking the other brings back to my mind the TGM concept of the delivery path of the power package (in a simplfied manner, path of the hands): its form would affect how and when the force acts on the club.

 

 

Edited March 14, 2016 by Etzwane

[DaveP043]

10 minutes ago, Etzwane said:

DaveP043 gave the correct physics explanations.

Its nice to know that I've retained a tiny bit of that long-ago education!  Its not like we actually use this stuff in everyday engineering or construction.  But I still say that for me and my own golf its little more than an interesting exercise.  They've used the physical characteristics of the club, and the motion of the club, to calculate the forces that were required to produce that motion.  

[natureboy]

5 hours ago, Etzwane said:

In the backswing, if one has very loose wrists (no torque) and start the backswing (force on the handle) the club will rotate and give the "scottish lag". It is necessary to add torque to maintain the club in synch with the arms. No very interesting so far.

Do you mean a 'caddy drag' takeaway? I haven't come across the 'Scottish Lag' term before?

 

Maybe the intended lesson from the video is to swing very 'flat' and jump like Bubba / Lexi?

Edited March 14, 2016 by natureboy

[Etzwane]

12 hours ago, natureboy said:

Do you mean a 'caddy drag' takeaway? I haven't come across the 'Scottish Lag' term before?

 

Maybe the intended lesson from the video is to swing very 'flat' and jump like Bubba / Lexi?

Yes, 'caddy drag' takeaway is it (looks like the denomination depends on which side of the  pond one is).

[iacas]

The first video in the "series" (of two) is of course:

 

[Mr. Desmond]

This is why I pay an instructor ... I have clients who are engineers, it's like watching paint dry to listen to most of them. They do not understand how lawyers think ... on the line between black and white  --- and that's a good thing.

Enjoy.

[ghalfaire]

I like the last comment "I hope this clears that up".   Reminds me of my sophomore year and the study of Dynamic Systems where the Prof often said "that's pretty simple isn't it (it often wasn't).  I once had a professor in Thermodynamics who ask on a test "explain entropy as if you were talking to your mother".  (I know this is sexist but it was the late sixties.)  Anyway the point was that you need consider the audience when you write if you expect to inform the audience of anything useful, e.g. one should write to express not impress.  My advice to nevets88 is to not worry about the video and as it is clearly not intended for the average golfer and probably nothing useful in it for the player even if you took the dynamic systems class.  

[iacas]

 

[natureboy]

On 3/14/2016 at 9:07 AM, nevets88 said:

Haven't finished watching this yet, but if anyone can explain this in layman's terms and what the takeaways are, that would be awesome.

My rough takeaway from all three would be:

1. This way of modeling the golf swing is able to translate externally measured accelerations (change in velocity over time) of the club into an accurate measurement of force (torque) that is being applied by a golfer throughout the swing. In other words the model lets you deduce from club head movement how much muscular force a golfer is applying as well as when in the swing it's being applied.

2. Most of the muscular torque is applied around the change of direction of the club when the club is moving very slowly.

3. It's very hard to apply much effective torque when the clubhead is moving its fastest around impact (it largely freewheels).

4. At the top of an efficient full swing there is a trail hand torque that acts in opposition (a couple) to that of the lead arm / hand and is actually slightly greater than the lead arm / hand torque. This net force resists the expected automatic release of the shaft from the torque delivered by the lead arm / hand (and the couple) and helps preserve lag. Or in other words a little extra 'push' (or resistance in some form) from the trail arm / hand through the grip opposes the 'pull' from the lead arm / hand and helps create 'natural' lag in a dynamic way (as opposed to active 'holding of angles' with wrist muscles). He does not discuss what actions / movements cause this only that it must be happening due to the motion of the club's center of mass (up away from the ground) after the change of direction.

• IMO the force is caused by the trail arm 'elbow move'. As the trail elbow 'drives in' (trail humerus adduction w/ external rotation) the trail hand is directed upwards into the club handle in a direction partially opposing the lead arm / hand torque.
• Or this observation about the torques could be somewhat validating the Nicklaus' 'feel' of "You can't release the club too soon (as long as you move into your left side and swing the club from inside the target line)" implying some trail arm extension muscular effort (force - not the trail arm actually extending & straightening)  early in the downswing might help maintain lag.

Edited March 26, 2016 by natureboy

[natureboy]

One thing I would add to what I wrote above is that the deduced torques being quite low around impact might make one think there is less effort on the part of the 'efficient swing' golfer. However, Sasho clearly employs a Bubba Watson / Lexi Thompson 'jump' that involves a lot of effort / muscular force to apply some extra / late pull (parametric acceleration) on the shaft from the rising lead shoulder pulling on the lead arm / hand.

I think what is going on is that late in the downswing the angular velocity of the club plus the reduced angle between the lead arm and club shaft makes it harder to effectively apply torque. That doesn't mean it isn't valuable to try because the effort can help reduce or delay the onset of a negative torque (drag on the handle) that can reduce clubhead speed (as occurred in one of the example pro swings). Avoiding a 'trail side' drag on the shaft may be why Couples and Singh have often been shown with their trail hand gripping driver very loosely or off the shaft past impact.

 

Edited March 26, 2016 by natureboy

[Lihu]

I'm really amazed how much weight he shifted that close to the transition.

[Mike Boatright]

On 3/14/2016 at 6:07 AM, nevets88 said:

This video describes the results from a 3D inverse dynamics analysis of the golf swing. The impulse-momentum framework is applied and how the contribution from the couple and the net force influence the overall torque applied to the club by the golfer are explained.

Beats me seems mostly irrelevant kinda like explaining the science of jumping how the force gets stored in your legs and the jumping motion x the force of gravity results in your total height. Kinda interesting I guess beyond me actually.

[natureboy]

An unorthodox swing to be sure, but the 'trail elbow move' is there likely contributing to preservation of lag per Dr. Sasho's point about trail arm force.

It's almost like a more extreme version of Nicklaus. More upright lead arm at the top matched by more 'flying' right elbow. He has the head backing out / stand up move like Nicklaus too, but more pronounced.

[natureboy]

May be of interest to others: difference in the forces profile of the 'example swing' and that of a 'multiple major winner' (2nd image).

While the 'multiple Major winner' swing actually went slightly negative in torque before impact on 'that swing' (slight drop in clubhead speed), the onset of the positive torque was significantly earlier than the first swing (more total torque applied?); and the rise / fall in the torque leading up to impact looks much smoother overall, while there are some 'hiccups' and a more cliff-like drop in the first example.

[Buckeyebowman]

On 3/16/2016 at 9:03 AM, Mr. Desmond said:

This is why I pay an instructor ... I have clients who are engineers, it's like watching paint dry to listen to most of them. They do not understand how lawyers think ... on the line between black and white  --- and that's a good thing.

Enjoy.

I agree! These are people who are way too smart for their own, or our, good, who seek to "explain" the golf swing in terms that are inexplicable to the average golfer!

Just teach me how to swing the damn golf club in a way that makes the ball go where I want it to! Sheesh!